PubAnnotation

Id	Subject	Object	Predicate	Lexical cue
T1	0-20	Sentence	denotes	A 21st Century Evil:
T2	21-66	Sentence	denotes	Immunopathology and New Therapies of COVID-19
T3	68-76	Sentence	denotes	Abstract
T4	77-204	Sentence	denotes	Coronavirus Disease 2019 (COVID-19) has been classified as a global threat, affecting millions of people and killing thousands.
T5	205-321	Sentence	denotes	It is caused by the SARS-CoV-2 virus, which emerged at the end of 2019 in Wuhan, China, quickly spreading worldwide.
T6	322-521	Sentence	denotes	COVID-19 is a disease with symptoms that range from fever and breathing difficulty to acute respiratory distress and death, critically affecting older patients and people with previous comorbidities.
T7	522-683	Sentence	denotes	SARS-CoV-2 uses the angiotensin-converting enzyme 2 (ACE2) receptor and mainly spreads through the respiratory tract, which it then uses to reach several organs.
T8	684-1020	Sentence	denotes	The immune system of infected patients has been demonstrated to suffer important alterations, such as lymphopenia, exhausted lymphocytes, excessive amounts of inflammatory monocytes and macrophages, especially in the lungs, and cytokine storms, which may contribute to its severity and difficulty of establishing an effective treatment.
T9	1021-1218	Sentence	denotes	Even though no specific treatment is currently available, several studies have been investigating potential therapeutic strategies, including the use of previously approved drugs and immunotherapy.
T10	1219-1497	Sentence	denotes	In this context, this review addresses the interaction between SARS-CoV-2 and the patient’s host immune system during infection, in addition to discussing the main immunopathological mechanisms involved in the development of the disease and potential new therapeutic approaches.
T11	1499-1511	Sentence	denotes	Introduction
T12	1512-1808	Sentence	denotes	The ongoing outbreak of Coronavirus Disease 2019 (COVID-19) has been classified as a threat of international concern and a public health emergency, having affected almost 30 million people and killed more than 900,000 around the world so far, according to the World Health Organization (WHO) (1).
T13	1809-2053	Sentence	denotes	The etiologic agent of this pandemic is Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the third coronavirus to have emerged as a public health issue and to cause an outbreak in the human population over the past two decades (2).
T14	2054-2238	Sentence	denotes	This is the nomenclature referred to in this paper (3), which is derived from its similarity to the SARS-CoV virus that caused the outbreak in 2003, which is now known as “SARS-CoV-1”.
T15	2239-2396	Sentence	denotes	Coronaviruses belong to a group of single-stranded RNA viruses and are regarded as one of the main types of viruses that affect the human respiratory system.
T16	2397-2603	Sentence	denotes	SARS-CoV-2 is the seventh coronavirus known to have infected humans; SARS-CoV-1, MERS-CoV, and SARS-CoV-2 can cause serious illness, whereas HKU1, NL63, OC43, and 229E are associated with mild symptoms (4).
T17	2604-2731	Sentence	denotes	SARS-CoV-2 emerged at the end of 2019 in Wuhan, China, with reports of infection in humans and quickly spread around the world.
T18	2732-3030	Sentence	denotes	The virus causes COVID-19, which consists of a spectrum of clinical syndromes, ranging from fever and breathing difficulty to acute respiratory distress and death, critically affecting older patients and people with comorbidities, including heart disease, diabetes, and other health conditions (5).
T19	3031-3305	Sentence	denotes	SARS-CoV-2 infection can be subdivided into the following three general phases: the spread of the virus in the body – known as viremia –; the acute phase with the appearance of clinical signs; and the stage of convalescence, which progresses either to recovery or death (6).
T20	3306-3500	Sentence	denotes	The pathological mechanism, so far unraveled, has proposed the role of the host’s angiotensin-converting enzyme 2 (ACE2) and its affinity with viral receptors, especially the glycoprotein spike.
T21	3501-3648	Sentence	denotes	The high affinity between these molecules facilitates viral dissemination in the body and allows the infectious condition to be established (7, 8).
T22	3649-4002	Sentence	denotes	The immune systems of infected patients have demonstrated important changes, such as lower effector T cells, loss of the antiviral capacity of CD8+ T lymphocytes and natural killer cells (NK), and the excessive release of inflammatory mediators, which may contribute to the disease severity and difficulty in establishing an effective treatment (9, 10).
T23	4003-4305	Sentence	denotes	This is a highly transmissible virus, whose contagion usually occurs through droplets released by infected individuals when they cough, sneeze, or talk, directly contaminating other people by reaching mucous membranes on the face or contaminating the environment, later acting as a transmission source.
T24	4306-4475	Sentence	denotes	Until now, we have relied on quarantine, social isolation, and infection-control measures to prevent disease spread, as well as supportive care for infected individuals.
T25	4476-4597	Sentence	denotes	A specific antiviral agent to treat the infected individuals and decrease viral transmission (11, 12) is yet to be found.
T26	4598-4823	Sentence	denotes	Several research groups around the world have been working on possible therapeutic strategies against SARS-CoV-2 by applying commercially available drugs, hoping to accelerate the discovery of an effective treatment (13, 14).
T27	4824-5039	Sentence	denotes	Since many studies are made available online on a daily basis, both in journals and in preprint servers, for this review we used only studies already published and peer-reviewed in order to avoid biased information.
T28	5040-5224	Sentence	denotes	In this scenario, understanding the virus dynamics and host response is essential to formulate strategies for antiviral treatment, vaccination, and epidemiological control of COVID-19.
T29	5225-5456	Sentence	denotes	Thus, our goal is to review SARS-CoV-2’s interaction with the patient’s host immune system during infection and discuss the main immunopathological mechanisms involved in COVID-19, as well as potential new therapeutical approaches.
T30	5458-5470	Sentence	denotes	Coronavirus:
T31	5471-5482	Sentence	denotes	An Overview
T32	5483-5678	Sentence	denotes	Coronaviruses (CoVs) consist of a group of enveloped, non-segmented, positive-sense single-stranded RNA viruses from the order Nidovirales, family Coronaviridae, and subfamily Orthocoronavirinae.
T33	5679-5849	Sentence	denotes	Coronaviruses have the largest genome of all RNA viruses, encoding viral proteins involved in transcribing viral RNA, replication, structure, and accessory proteins (15).
T34	5850-6133	Sentence	denotes	The virus has four main proteins – spike, envelope, membrane, and nucleocapsid (S, E, M, and N, respectively) – important for the virus to enter and replicate in the host cell (16), also representing the main molecules used for diagnosis, antiviral treatment, and potential vaccines.
T35	6134-6249	Sentence	denotes	According to antigenic and genetic criteria, CoVs are classified into three groups: α-CoVs, β-CoVs and γ-CoVs (17).
T36	6250-6417	Sentence	denotes	Coronaviruses of human infection (hCoVs) are detected in both α-CoVs (hCoV-229E and NL63) and β-CoVs (MERS-CoV, hCoV-OC43, hCoV-HKU1, SARS-CoV-1, and SARS-CoV-2) (18).
T37	6418-6621	Sentence	denotes	In addition to infecting humans, α-CoVs and β-CoVs can infect several species of mammals, including bats and pigs, while γ-CoVs infects birds, wild cats, pigs, and some species of marine mammals (19–22).
T38	6622-6772	Sentence	denotes	CoVs have a high potential of jumping between species and their genome is characterized by high-frequency recombination and a high mutation rate (23).
T39	6773-7002	Sentence	denotes	hCoVs are responsible for the common cold and other respiratory pathologies with different degrees of severity, especially in babies, the elderly, and immunocompromised patients, characterized by human-to-human transmission (24).
T40	7003-7235	Sentence	denotes	Coronavirus severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) (25–27) are caused by human β-CoVs and represent a serious illness with a case-fatality ratio of 9 - 10% and 35%, respectively (8, 28).
T41	7236-7493	Sentence	denotes	In contrast, according to data provided by the WHO, COVID-19 caused by SARS-CoV-2 shows an estimated lethality of ~5% of reported cases (data reported until July 2020) (29), reaching rates of up to 15% among elderly patients and patients with comorbidities.
T42	7494-7694	Sentence	denotes	Despite the lower case-fatality rate, the high viral transmissibility of SARS-CoV-2 generates an overall number of cases that far outweighs SARS or MERS for spreading more easily among people (5, 28).
T43	7695-7870	Sentence	denotes	The first report of a COVID-19 case in Wuhan, China, occurred in December 2019, and in February the WHO declared the matter a public health emergency of international concern.
T44	7871-8047	Sentence	denotes	Until now (September 2020), reports of COVID-19 account for almost 30 million cases and more than 900 thousand deaths in more than 220 countries, territories, or areas (1, 29).
T45	8048-8218	Sentence	denotes	Imperial College, UK (30) proposed a mathematical model whose prospects indicate 7 billion infections and 40 million deaths in 2020 in the absence of mitigation measures.
T46	8219-8619	Sentence	denotes	Both SARS-CoV and MERS-CoV were initially believed to have resulted from a zoonotic spread from a bat population (31). α-CoVs and β-CoVs are believed to have evolved over thousands of years, restricted to bats and intermediate mammalian hosts (civet cats for SARS-CoV-1 and dromedary camels for MERS-CoV), which probably contributed to the zoonotic transmission of the new coronavirus to humans (32).
T47	8620-8805	Sentence	denotes	Regarding SARS-CoV-2 transmission, several works have demonstrated that coronaviruses found in pangolins (Manis javanica) and SARS-CoV-2 share a genomic similarity of approximately 91%.
T48	8806-9017	Sentence	denotes	The presence of the virus in samples of pulmonary fibrosis in pangolins found around the COVID-19 outbreak suggests that these animals were the hosts responsible for spreading the virus among humans (4, 21, 33).
T49	9018-9244	Sentence	denotes	In contrast, some researchers claim that SARS-CoV-2 did not come directly from pangolins since, despite their similarity, the viruses found in these animals do not have the essential tools needed to infect human cells (4, 34).
T50	9245-9439	Sentence	denotes	Thus, the possibility of other animals, such as ferrets and snakes, acting as intermediate hosts for SARS-CoV-2 and being responsible for zoonotic transmission is still under consideration (35).
T51	9440-9659	Sentence	denotes	Since SARS-CoV-2 genomes’ information is still scarce and genomes of other coronaviruses closely related to this virus have limited availability (36), the evolutionary origin of SARS-CoV-2 is yet to be fully understood.
T52	9660-9851	Sentence	denotes	So far, it is known that, compared with other β-CoVs, SARS-CoV-2 shows 50, 79, and 88 - 96% of genome similarity with MERS-CoV, SARS-CoV-1, and the bat SARS-like virus, respectively (37, 38).
T53	9852-10054	Sentence	denotes	The genomic changes of SARS-CoV-2 appear in both non-structural and structural proteins – notably in proteins S, M, and N – affecting viral multiplication, encapsulation, tropism, and transmission (39).
T54	10055-10584	Sentence	denotes	Two important characteristics were described in the genome of SARS-CoV-2 that lead to alterations in the S protein: (i) receptor-binding domain (RBD), which is the most variable part of the viral genome, appears to be optimized for binding to the human ACE2 receptor, and (ii) presence of a polybasic (furin) cleavage site at the S1 and S2 boundary, via the insertion of twelve nucleotides, which allows effective cleavage by furin and other proteases and has a role in determining viral tropism, infectivity, and host range (4).
T55	10585-10669	Sentence	denotes	Such genomic changes also affected the recognition of these viruses by immune cells.
T56	10670-10898	Sentence	denotes	Baruah and Bose (40) demonstrated that Sars-CoV-2 has specific regions for B cell and cytotoxic T cell glycoproteins recognition, which does not coincide with those found in bat-derived CoV, SARS-CoV-1, or MERS-CoV ( Figure 1 ).
T57	10899-11055	Sentence	denotes	Such distinguished interaction of cells and viruses can promote unusual immunomodulation or immune responses that contribute to the severity of the disease.
T58	11056-11150	Sentence	denotes	All aspects of immunomodulation and immune evasion will be discussed in the subsequent topics.
T59	11151-11214	Sentence	denotes	Figure 1 Genetic evolution of SARS-CoV-2 and its consequences.
T60	11215-11422	Sentence	denotes	Compared with other β-CoVs, SARS-CoV-2 has similarities of 50, 79, and 88 - 96% to MERS-CoV, SARS-CoV-1, and bat SARS-like-CoV genome, respectively, with 91% similarity with SARS-like CoV found in pangolins.
T61	11423-11684	Sentence	denotes	The virus resulted from mutations that caused changes in important proteins for its virulence; notably, the spike, matrix, envelope, and nucleocapsid proteins caused alterations in host cell interactions, which culminated in a new aggressive disease (COVID-19).
T62	11685-11746	Sentence	denotes	RBD (receptor binding domain), S1 (subunit 1) S2 (subunit 2).
T63	11748-11774	Sentence	denotes	Pathogenesis of SARS-CoV-2
T64	11776-11803	Sentence	denotes	Viral Entry and Replication
T65	11804-11901	Sentence	denotes	A virus starts its infection by binding viral particles to the host’s surface cellular receptors.
T66	11902-12036	Sentence	denotes	The recognition of cellular receptors is the first step towards viral entry into host cells, in addition to determining their tropism.
T67	12037-12255	Sentence	denotes	The ability to engage receptors and the affinity of binding can define the efficiency of a virus when infecting an organism, while the amount of these receptors present in cells can indicate the intensity of infection.
T68	12256-12473	Sentence	denotes	Viruses that have a high capacity to bind to more conserved receptors are more likely to migrate between different species, which may also reflect the susceptibility of hosts and increase viral pathogenicity (40, 41).
T69	12474-12634	Sentence	denotes	As well as the other β-CoVs, the SARS-CoV-2 genome has a long open reading frame (ORF) 1ab region, followed by regions that encode S, E, M, and N proteins (42).
T70	12635-12751	Sentence	denotes	Homotrimers of S proteins are present on the viral surface and are responsible for attaching to host receptors (43).
T71	12752-12878	Sentence	denotes	The E protein plays a role in the assembly and release of the virus, in addition to being involved in viral pathogenesis (44).
T72	12879-13017	Sentence	denotes	The M protein has three transmembrane domains and shapes the virions, promotes membrane curvature, and binds to the nucleocapsid (45, 46).
T73	13018-13243	Sentence	denotes	Lastly, the N protein contains two domains that can bind to the RNA virus and is also an antagonist of interferon (IFN) and a virally-encoded repressor of RNA interference, which appears to benefit viral replication (47, 48).
T74	13244-13402	Sentence	denotes	The S protein of SARS-CoV-2 plays an important role in determining tropism for being able to activate receptors in host cells and induce the invasion process.
T75	13403-13555	Sentence	denotes	This protein is cleaved by proteases into the S1 and S2 subunits, which are responsible for receptor recognition and membrane fusion, respectively (39).
T76	13556-13914	Sentence	denotes	Several articles have experimentally demonstrated that the RDB in the S protein, especially in the S1 region, binds to the peptidase domain (PD) of the ACE2 receptor, which is part of the renin-angiotensin-aldosterone system, an enzyme present in the plasma membrane mainly of pulmonary, endothelial, cardiac, renal, and intestinal cells (7, 22, 38, 49, 50).
T77	13915-14068	Sentence	denotes	The S2 subunit is known to contain the fusion peptide, in which it is inserted into the host cell membrane to trigger the fusogenic reaction (7, 51, 52).
T78	14069-14207	Sentence	denotes	The interaction of the S glycoprotein with the CD26 receptor and CD209L (39, 53, 54) is also suggested, however, its role remains unclear.
T79	14208-14453	Sentence	denotes	The binding of the virus to the ACE2 receptor causes stabilization of the RBD in the standing-up state and triggers conformational changes in the S complex, resulting in the release of the S1 subunit and activation of S2 fusogenic activity (55).
T80	14454-14616	Sentence	denotes	The S2 subunit contains an N-terminal fusion peptide (FP), heptad repeat 1 (HR1), heptad repeat 2 (HR2), a transmembrane region (TM), and a cytoplasmic tail (CT).
T81	14617-14889	Sentence	denotes	During the fusion process, the FP portion is exposed and inserts into the membrane of the target cell, leading to a modification in S2, then the HR1 and HR2 come together to form a six-helical bundle (6-HR) structure, which allows the fusion between the membranes (55–57).
T82	14890-15031	Sentence	denotes	Therefore, CoVs need to elicit exogenous proteases to perform modifications of their binding receptors necessary for the connection to occur.
T83	15032-15260	Sentence	denotes	SARS-CoV-2 has its own furin-like proteases, which play a role in these changes, providing it with an evolutionary advantage in relation to other coronaviruses and improving the process of cell infection and viral dissemination.
T84	15261-15386	Sentence	denotes	Concerning exogenous proteins, SARS-CoV-2 can also use host proteins to prepare its S glycoprotein for receptor binding (49).
T85	15387-15601	Sentence	denotes	Hoffman et al. (7) demonstrated in vitro that strains of the virus isolated from COVID-19 patients can use both the host protease transmembrane serine protease 2 (TMPRSS2) and cathepsins B/L to prime the S protein.
T86	15602-15801	Sentence	denotes	The entry mechanism of CoVs in host cells depends on the strain and species considered, as well as tissue and cell-type specificities (receptor/protease availability and local microenvironment) (58).
T87	15802-15996	Sentence	denotes	After binding to a target host cell via interactions with cellular receptors, viral entry of CoVs can occur in two manners: (i) the endosomal pathway and (ii) the non-endosomal pathway (59, 60).
T88	15997-16231	Sentence	denotes	The endosomal pathway is facilitated by low pH and pH-dependent endosomal cysteine protease cathepsins, helping to overcome the energetically unfavorable membrane fusion reaction and facilitating endosomal cell entry of CoVs (61, 62).
T89	16232-16349	Sentence	denotes	The non-endosomal pathway is dependent on TMPRSS2, which allows the activation of the S protein for viral entry (63).
T90	16350-16619	Sentence	denotes	Once the viral genome is inside the host cell cytoplasm, translation of viral RNA produces RNA-dependent RNA polymerase (RdRp), which uses viral RNA as a template to generate virus-specific mRNAs (subgenomic mRNAs) from subgenomic negative-strand intermediates (64–66).
T91	16620-16723	Sentence	denotes	Translation of subgenomic mRNAs leads to the production of structural and nonstructural viral proteins.
T92	16724-16935	Sentence	denotes	Thus, after their formation, structural proteins are inserted into the membrane of the endoplasmic reticulum or Golgi, and viral particles germinate into the endoplasmic reticulum-Golgi intermediate compartment.
T93	16936-17053	Sentence	denotes	Finally, the vesicles containing the virus particles fuse with the plasma membrane to release the virus (65, 67, 68).
T94	17054-17124	Sentence	denotes	Another possible mechanism for CoV entry may occur through antibodies.
T95	17125-17487	Sentence	denotes	During the binding of the virus-antibody complex, simultaneous binding of viral proteins to antigen-binding fragment (Fab) regions of immunoglobulin G (IgG) and of the fragment crystallizable (Fc) portion of the antibody to Fc gamma receptors (FcγRs) that are expressed by immune cells occurs, promoting viral entry without the use of the ACE2 receptor (69, 70).
T96	17488-17765	Sentence	denotes	However, the presence of viral RNA in the endosomes signals via the Toll-like 3 (TLR3), TLR7, or TLR8 receptor, activating the host cell to release pro-inflammatory cytokines that lead to exacerbated tissue damage, a phenomenon called antibody-dependent enhancement (ADE) (71).
T97	17766-18047	Sentence	denotes	Such a mechanism for SARS‐CoV‐2 is not yet fully understood, but previous coronavirus infections or SARS‐CoV‐2 convalescent patients with different SARS‐CoV‐2 strains could promote ADE, as experimentally shown for antibodies against the MERS‐CoV or SARS‐CoV-1 spike S protein (72).
T98	18048-18271	Sentence	denotes	Several studies have shown that sera administration induced increased SARS-CoV-1 viral entry into cells that express the Fc receptor, and serum-dependent SARS-CoV-1 entry does not pass through the endosome pathway (73, 74).
T99	18272-18553	Sentence	denotes	This mechanism was characterized by Yip et al. (75) and Wang et al. (76), who revealed that the anti-Spike protein antibodies were in fact responsible for the infection of immune cells, and the enhancement of the infection can be improved by increasing the dilutions of antibodies.
T100	18554-18794	Sentence	denotes	In relation to MERS-CoV, a similar mechanism has been demonstrated, since neutralizing monoclonal antibodies (nAb) are able to bind to the spike-S surface protein, allowing conformational changes and being subject to proteolytic activation.
T101	18795-18937	Sentence	denotes	Meanwhile, nAb binds to the cell surface IgG Fc receptor, guiding viral entry through canonical pathways dependent on the viral receptor (77).
T102	18938-19219	Sentence	denotes	Recent studies with COVID-19 patients reported that there was a strong IgG antibody response against the nucleocapsid protein and a delay in eliminating the virus, leading to an increase in the severity of the infection and contributing to the hypothesis of ADE of SARS-CoV-2 (78).
T103	19220-19463	Sentence	denotes	In view of this, the geographic discrepancy in pathogenesis can be explained, since individuals who have experienced previous exposure to coronaviruses are experiencing the effects of ADE due to the heterogeneity of the antigenic epitope (79).
T104	19464-19642	Sentence	denotes	In addition, the potential of human antibodies for vaccination will depend on whether antibodies play a role in disease progression or in protecting against viral infection (70).
T105	19643-19903	Sentence	denotes	As an evasion mechanism, CoVs use a glycan conformational shield to prevent the recognition of the virus by the immune system, and, for this reason, S glycoproteins are found in trimers form and require structural alterations to engage with cellular receptors.
T106	19904-20142	Sentence	denotes	In most of the hCoVs described, these S trimers are found in a naturally closed conformation, however, this mechanism also causes a delay in the process of cell infection due to the need for major changes in the glycoprotein conformation.
T107	20143-20403	Sentence	denotes	It was described that, in SARS-CoV-2, the S trimers seem to exist in a partially open state, which prevents recognition by the immune system, but accelerates the initiation of conformational changes in the receptor and the processes of binding and fusion (49).
T108	20405-20426	Sentence	denotes	Pathogenic Mechanisms
T109	20427-20581	Sentence	denotes	Considering the similarity between SARS-CoV-1 and SARS-CoV-2, it is likely that their biochemical interactions and pathogenesis are also similar (80, 81).
T110	20582-20737	Sentence	denotes	Once SARS-CoV-2 was reported to use ACE2 to enter host cells, it is suggested that the virus may target a cell spectrum similar to SARS-CoV-1 (38, 82, 83).
T111	20738-20926	Sentence	denotes	SARS-CoV-1 is known to mainly infect macrophages and pneumocytes in the lungs, as well as other extrapulmonary tissues that express ACE2, which can also be expected for SARS-CoV-2 (82–84).
T112	20927-21206	Sentence	denotes	However, the affinity of SARS-CoV-2 to ACE2 is 10–20-fold higher than that of SARS-CoV-1, which could explain its higher transmissibility and demonstrate that it can bind more efficiently to host cells, having a robust infection in ACE2+ cells in the upper respiratory tract (7).
T113	21207-21445	Sentence	denotes	ACE2 is an enzyme belonging to the renin-angiotensin system, located on the cell surface of type II alveolar epithelial cells in the lungs and cells of other tissues, and plays a crucial role in controlling vasoactive effects in the body.
T114	21446-21598	Sentence	denotes	Despite their similarities, ACE and ACE2 have different substrate specificities with distinct functionalities that perform opposite actions in the body.
T115	21599-21794	Sentence	denotes	In brief, ACE cleaves angiotensin I to generate angiotensin II, the peptide that binds and activates angiotensin type 1 receptor (AT1R) to constrict blood vessels, thereby raising blood pressure.
T116	21795-21978	Sentence	denotes	In contrast, ACE2 inactivates angiotensin II (Ang-II) while generating angiotensin 1-7 (Ang-1-7), a potent heptapeptide that acts in vasodilation and attenuation of inflammation (85).
T117	21979-22247	Sentence	denotes	Therefore, considering that SARS-CoV-2 uses ACE2 to enter cells, the main hypothesis of pulmonary pathology is that the increased activity of ACE (Ang-II) over ACE2 (Ang-1-7) may cause acute lung injury since the binding of the S protein to ACE2 leads to its blockage.
T118	22248-22475	Sentence	denotes	Thus, the suppression of ACE2 occurs due to the increased internalization and release of ACE2 from the cell surface, which leads to a decrease in tissue ACE2 and the generation of Ang-1-7, and consequently higher Ang-II levels.
T119	22476-22687	Sentence	denotes	Because of this, as shown in an experimental SARS-CoV-1 model, this process can drive an Ang II-AT1R-mediated inflammatory response in the lungs and potentially induce direct parenchymal injury (67, 80, 86, 87).
T120	22688-22981	Sentence	denotes	Another hypothesis states that SARS-CoV-2 infection blocks ACE2 function when binding to host cells, inhibiting its role of cleaving bradykinin and, as a consequence, bradykinin accumulates in the lung, promoting pulmonary edemas due to vasodilator activity and consequent respiratory failure.
T121	22982-23161	Sentence	denotes	The increased bradykinin activation in the pulmonary endothelium can also induce neutrophil migration, enhancing tissue damage caused by the respiratory burst of these cells (88).
T122	23162-23279	Sentence	denotes	ACE2 is also highly expressed and co-expressed with TMPRSS2 in nasal epithelial cells, chalices, and hair cells (89).
T123	23280-23628	Sentence	denotes	This finding is in accordance with the high detection of viral RNA in the upper airways present in nasal swabs and throats of both symptomatic and asymptomatic patients, demonstrating that the nasal epithelium is an important site for the infection to initiate and can represent an essential reservoir for viral dissemination and transmission (38).
T124	23629-23918	Sentence	denotes	Although the virus mainly affects the lungs, there are reports that SARS-CoV-2 also has organotropism, accompanied by dysfunction, in multiple organs, including the kidneys, liver, heart, and brain, which can influence the course of the disease and possibly worsen pre-existing conditions.
T125	23919-24100	Sentence	denotes	It has been reported that ACE2, TMPRSS2, and cathepsin L can be expressed on glial cells and neurons, cardiomyocytes, liver cells, bile duct cells, and renal tubular cells (90, 91).
T126	24101-24341	Sentence	denotes	Evidence indicates that SARS-CoV-2 “neuroinvasion” can establish a direct entry along the olfactory nerve, mainly through the nasal olfactory epithelium, which expresses ACE2 and TMPRSS2, allowing access to the central nervous system (CNS).
T127	24342-24656	Sentence	denotes	The spread of the virus through the hematogenous or transsynaptic pathway has also been widely discussed, however, it is known that the different levels of neurotropism and neurovirulence in patients with COVID-19 can be explained by a combination of viral factors and their interaction with the host (41, 92, 93).
T128	24657-24902	Sentence	denotes	Regarding the evolution of infected individuals, aging, comorbidities, and weakening of the immune system are factors that generally cause the infection to intensify at the acute phase, leading to the manifestation of more severe conditions (6).
T129	24903-25146	Sentence	denotes	Thus, according to epidemiological studies, it is known that patients with chronic conditions, such as hypertension, diabetes, and chronic obstructive pulmonary disease (COPD), are more likely to develop a critical form of the disease (94–96).
T130	25147-25346	Sentence	denotes	The risk of applying medication commonly used in hypertension treatments to COVID-19 patients (97, 98) has raised different hypotheses over the issue of invoking a higher expression of ACE2 (99–101).
T131	25347-25823	Sentence	denotes	A systematic review assessing the clinical outcomes for SARS-CoV-2-infected individuals regarding treatment using angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin receptor blockers (ARBs) concluded that these types of drugs have no deleterious effects and should continue to be used in COVID-19 patients (102), reinforcing the recommendations of several medical societies, including the American Heart Association (103) and European Society of Cardiology (104).
T132	25824-26017	Sentence	denotes	Respiratory diseases, such as COPD and asthma, cause a reduced lung function and greater susceptibility to lung inflammation, and are expected to show a potentially critical course of COVID-19.
T133	26018-26386	Sentence	denotes	COPD patients are already considered more susceptible to the development of pneumonia based on the clinical characteristics exhibited, such as lung structural damage, alterations in local/systemic inflammatory response, impaired host immunity, microbiome imbalance, persistent mucus production, and the presence of potentially pathogenic bacteria in the airways (105).
T134	26387-26527	Sentence	denotes	Additionally, in the scenario of COVID-19, smokers and individuals with COPD have shown to have increased airway expressions of ACE-2 (106).
T135	26528-26795	Sentence	denotes	It is still worth mentioning that patients who have this type of disorder often use corticosteroid immune-suppressing drugs, whose effect of reducing the immunity to respiratory infections may represent another contributing factor to a higher risk of infection (107).
T136	26797-26830	Sentence	denotes	Clinical and Radiological Changes
T137	26831-27070	Sentence	denotes	Most COVID-19 patients exhibit mild to moderate symptoms, but approximately 15% progress to critical pneumonia and 5% eventually develop acute respiratory distress syndrome (ARDS), septic shock, multiple organ failure, and death (26, 108).
T138	27071-27230	Sentence	denotes	Once the infection is installed, the spectrum of clinical presentations has been reported to range from asymptomatic infection to critical respiratory failure.
T139	27231-27327	Sentence	denotes	According to the severity of symptoms, patients can be classified as mild, severe, and critical.
T140	27328-27578	Sentence	denotes	In general, the most commonly reported symptoms are fever, cough, myalgia, fatigue, pneumonia, dyspnea, as well as the loss of smell and taste, whereas less common reported symptoms include headache, diarrhea, hemoptysis, and a runny nose (108, 109).
T141	27579-27743	Sentence	denotes	Most critically ill patients present progressive respiratory failure due to alveolar damage caused by hyper inflammation, which can result in lethal pneumonia (26).
T142	27744-27973	Sentence	denotes	A retrospective study conducted by Liu et al. (110) demonstrated that older patients with SARS-CoV-2 showed higher pneumonia severity index scores and had a higher chance of multiple lobe involvement compared with young patients.
T143	27974-28078	Sentence	denotes	Elderly adults are more susceptible to SARS-CoV-2 and have a high risk of morbidity and mortality (111).
T144	28079-28229	Sentence	denotes	This can be explained by factors such as physiological changes and multiple age-related comorbidities, in addition to associated polymedication (112).
T145	28230-28388	Sentence	denotes	Regarding the potential involvement of COVID-19 in the CNS, studies have investigated the neurological changes developed throughout the course of the disease.
T146	28389-28532	Sentence	denotes	Nonspecific symptoms (dizziness, headache, and seizure) and specific symptoms (loss of smell or taste and stroke) were described (91, 113–115).
T147	28533-28667	Sentence	denotes	Epidemiological studies have reported that some patients infected with SARS‐CoV‐2 did report headaches (8%), nausea, or vomiting (1%).
T148	28668-28887	Sentence	denotes	A more recent study investigating 214 COVID‐19 patients found that about 88% of critically ill patients displayed neurologic manifestations, including acute cerebrovascular diseases and impaired consciousness (26, 116).
T149	28888-29122	Sentence	denotes	Among patients diagnosed with SARS-CoV-2, it has been reported that renal dysfunction is characterized by high levels of blood urea nitrogen, creatinine, uric acid, and D-dimer, associated with proteinuria and hematuria (90, 117–119).
T150	29123-29276	Sentence	denotes	Recent studies have reported an incidence between 3-9% of acute kidney injury in COVID-19 patients, demonstrating renal abnormalities (94, 96, 111, 120).
T151	29277-29573	Sentence	denotes	Cardiovascular complications are also associated with COVID-19 infection, including myocardial injury, myocarditis, acute myocardial infarction, heart failure, dysrhythmias, and venous thromboembolic events, being significant contributors to the mortality associated with this disease (121, 122).
T152	29574-29970	Sentence	denotes	Several studies found that CoVs can also affect other body regions, such as the gastrointestinal tract and ocular tissues (123, 124); some of them specifically investigated changes in the gastrointestinal tract and identified the presence of SARS-CoV-2 RNA in samples of anal/rectal swabs and feces of infected patients, establishing that the virus could be transmitted orally or fecally as well.
T153	29971-30319	Sentence	denotes	Additionally, symptoms such as diarrhea, vomiting, and intestinal pain (125) have also been reported for SARS-CoV-2-positive patients, which can be associated with the expression of ACE2 in gastrointestinal epithelial cells, present especially in the small and large intestines, contributing to viral infection and replication in these cells (126).
T154	30320-30500	Sentence	denotes	Regarding ocular tissues, some studies have also identified the manifestation of conjunctivitis in patients with COVID-19 (<1%) (96), however, it is an underestimated number (127).
T155	30501-30822	Sentence	denotes	Currently, it is still unclear how SARS-CoV-2 can cause conjunctivitis, but theories include: (i) conjunctiva can be a direct inoculation site for the virus, (ii) the virus can reach the upper respiratory tract through the nasolacrimal duct, or (iii) infection can occur via hematogenous through the lacrimal gland (123).
T156	30823-31046	Sentence	denotes	Histologically, biopsy samples of lungs reveal evident desquamation and hyaline membrane formation of pneumocytes, in addition to bilateral diffused alveolar damages along with cellular fibromyxoid exudate, indicating ARDS.
T157	31047-31237	Sentence	denotes	In addition, the cytopathic effects found include multinucleated syncytial cells, increased atypical pneumocytes, and the presence of inflammatory infiltrates of mononuclear cells (26, 108).
T158	31238-31373	Sentence	denotes	More recently, reports on COVID-19 have included the occurrence of coagulation abnormalities in most critically ill patients (128–131).
T159	31374-31598	Sentence	denotes	Tang et al. (132) reported the occurrence of disseminated intravascular coagulation in 71.4% of non-surviving COVID-19 patients and in only 0.6% of surviving patients, suggesting a high frequency in severe COVID-19 patients.
T160	31599-31829	Sentence	denotes	Autopsies performed on patients with COVID-19 also demonstrated small fibrinous thrombi in pulmonary arterioles with endothelial tumefaction, the presence of megakaryocytes, and indications of coagulation cascade activation (133).
T161	31830-32275	Sentence	denotes	Although it is important to consider the direct procoagulant properties of SARS-CoV-2, the combination of immobility, systemic inflammation, platelet activation, endothelial dysfunction, and stasis of blood flow can lead to thrombotic complications that mimic systemic coagulopathies associated with severe infections, such as sepsis-induced coagulopathy (SIC), disseminated intravascular coagulation (DIC), and thrombotic microangiopathy (130).
T162	32276-32568	Sentence	denotes	However, COVID-19 has some distinct features that may establish a new category of coagulopathy, denominated COVID-19 associated coagulopathy (CAC), whose main markers are higher D-dimer concentration and fibrinogen levels, a relatively lower platelet count, and longer prothrombin time (129).
T163	32569-32643	Sentence	denotes	In COVID-19 patients, CAC has been associated with higher mortality (131).
T164	32644-32975	Sentence	denotes	Chest computed tomography (CT) in patients with COVID-19 has commonly demonstrated multifocal “ground-glass” opacity (GGO) in the lungs, which can occur concurrently with consolidation in posterior and peripheral areas, suggesting a pneumonia pattern in the organization of lung injury and indicating disease progression (134–136).
T165	32976-33217	Sentence	denotes	Another important manifestation found through chest CTs is reticular pattern formation with interlobular septal thickening, which might be associated with interstitial lymphocyte infiltration and determine the disease course (108, 137, 138).
T166	33218-33691	Sentence	denotes	CT has highlighted many other alterations, including the “crazy-paving” pattern, which may result from the alveolar edema and interstitial inflammation in acute lung injury, and air bronchogram with a pattern of air-filled (low-attenuation) bronchi, but with gelatinous mucus and several airway changes, such as bronchiectasis and bronchial wall thickening resulting from the destruction of bronchial wall structure, proliferation of fibrous tissue, and fibrosis (137–140).
T167	33693-33727	Sentence	denotes	Immune Response Against SARS-CoV-2
T168	33729-33743	Sentence	denotes	Cytokine Storm
T169	33744-34119	Sentence	denotes	Antiviral immune response is usually coordinated by IFN-type cytokines that activate cells and intensify the response against these invading agents, triggered by the recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs), such as toll-like receptors (TLR), fundamental for pathogen recognition and activation of innate immunity.
T170	34120-34270	Sentence	denotes	Type 7 of TLR (TLR7) – expressed on the surface of endosomes predominantly in the lungs, placenta, and spleen – might play a central role in COVID-19.
T171	34271-34483	Sentence	denotes	This receptor has been reported to quickly recognize single-stranded SARS-CoV-1 RNA, inducing the production of pro-inflammatory cytokines such as TNF-α, IL-6, and IL-12 in plasmacytoid dendritic cells (141–143).
T172	34484-34640	Sentence	denotes	The recognition of SARS-CoV-2 RNA by TLR7 can mediate the release of cytokines in response to the virus, a context in which IL-6 may play an important role.
T173	34641-34889	Sentence	denotes	It has been well described that IL-6 is a pleiotropic cytokine with distinct functions in different contexts in the immune system, being fundamental for the formation of follicular T helper lymphocytes and the generation of long-lived plasma cells.
T174	34890-35228	Sentence	denotes	However, this cytokine can also inhibit the activity of CD8+ cytotoxic lymphocytes by inducing the expression of PD1 in these cells, in addition to inhibiting suppressors of cytokine signaling 3 (SOCS3), an important protein responsible for controlling cytokine production, leading to an excessive release of inflammatory mediators (144).
T175	35229-35552	Sentence	denotes	The pathophysiology of COVID-19 is yet to be fully elucidated and several gaps still need to be filled, however, several studies have shown an increase in cytokines, notably pro-inflammatory, in the serum of infected patients, which has been associated with hyper inflammation and the lung injury particular to the disease.
T176	35553-35838	Sentence	denotes	The main cytokines described include TNF-α, IFN-γ, IL-1β, IL-1Ra, IL-2R, IL-6, IL-7, IL-8, IL-9, IL-10, basic FGF, G-CSF, GM-CSF, IP-10, MCP-1, MIP-1a, PD6F, and VEGF, in addition to an increase in other inflammation biomarkers, such as C-reactive protein, ferritin, and procalcitonin.
T177	35839-35965	Sentence	denotes	However, mediators related to the complement system, such as C3 and C4, did not present any difference in healthy individuals.
T178	35966-36320	Sentence	denotes	Furthermore, even higher levels of these mediators were found in patients of critical COVID-19 cases, suggesting that the severity of the disease may be associated with this huge amount of inflammatory mediators, called cytokine storm, which overloads the immune system with information, preventing the establishment of an effective immune response (26).
T179	36321-36782	Sentence	denotes	For example, a study published by Valle et al. showed that COVID-19 patients have higher levels of IL-6, IL-8, and TNF-alpha than healthy individuals on hospital admission; moreover, when they stratified the population by low versus high cytokine levels and applied a risk competition model, it was found that each cytokine is an independent predictive factor of the patients’ overall survival and is significantly associated with worse clinical outcomes (145).
T180	36783-36995	Sentence	denotes	On the other hand, in theory, a type I IFN-mediated response activates the JAK-STAT signaling pathway that should be able to suppress viral replication and prevent the virus from spreading early in the infection.
T181	36996-37121	Sentence	denotes	This is probably what occurs in asymptomatic individuals who can establish an effective response against SARS-CoV-2 (9, 141).
T182	37122-37296	Sentence	denotes	However, in several viruses, viral proteins can modulate the production of this type of IFN, impairing the generation of an effective antiviral response (141, 143, 146, 147).
T183	37297-37618	Sentence	denotes	Li et al. (148) conducted an in vitro experiment that revealed a strong capacity of ORF6, ORF8, and nucleocapsid proteins of SARS-CoV-2 to inhibit IFN-β and NF-κB activity, in addition to genes containing interferon-stimulated response elements (ISREs), suggesting that the virus has an important IFN antagonist activity.
T184	37619-37845	Sentence	denotes	By monitoring the production of type I IFN in SARS-CoV-2-positive patients, Trouillet-Assant et al. (149) found a peak in IFN-α2 production between 8 and 10 days after the onset of symptoms, in general, which reduces overtime.
T185	37846-38025	Sentence	denotes	However, as many as one critically ill patient in five was unable to produce any amount of type I IFN and had a higher viral load, respiratory failure, and worse clinical outcome.
T186	38026-38267	Sentence	denotes	Nonetheless, Zhou et al. (150) conducted a study that demonstrated that SARS-CoV-2 infection induced a markedly elevated expression of IFN-related inflammatory genes, which appears to decrease over time in mild cases, but not in severe ones.
T187	38268-38384	Sentence	denotes	Additionally, Major et al. (151) described the role of types I and III of IFN in lung repair during viral infection.
T188	38385-38606	Sentence	denotes	The production of IFN-α/β and IFN-λ in C57BL/6 mice was detected immediately at the early stage of influenza virus infection and decreased over time, having reached undetectable levels at the onset of epithelial recovery.
T189	38607-38854	Sentence	denotes	Interestingly, the treatment with IFN-α, β, or λ during the recovery phase reduced the proliferation type II alveolar epithelial cells by activation of IFN-induced p53, aggravating lung injury, disease severity, and susceptibility to coinfections.
T190	38855-39012	Sentence	denotes	Therefore, time and duration of IFN are critical factors for viral infection response and should be thoroughly considered as a COVID-19 therapeutic strategy.
T191	39013-39301	Sentence	denotes	Similarly, an experimental study conducted with MERS patients indicated that type I IFN has protective activity against this infection and the blockade of its signaling resulted in delayed virus clearance, enhanced neutrophil infiltration, and impaired MERS-CoV–specific T cell responses.
T192	39302-39390	Sentence	denotes	Additionally, early treatment using this type of IFN prevented fatal infections in mice.
T193	39391-39784	Sentence	denotes	However, the late treatment did not cure the animals and failed to effectively inhibit virus replication, increased infiltration, and activation of monocytes, macrophages, and neutrophils in the lungs, in addition to having enhanced proinflammatory cytokine expression, which led to fatal pneumonia, indicating that type I IFN plays a central role at the very beginning of the infection (152).
T194	39785-39947	Sentence	denotes	Therefore, using IFN in SARS-CoV-2 treatment seems to be beneficial at the early infection stage, especially for patients unable to produce this type of response.
T195	39948-40127	Sentence	denotes	Furthermore, as the disease progresses, the use of inflammatory cytokine blockers for patients who fail at regulating their production over time could represent a better strategy.
T196	40128-40401	Sentence	denotes	COVID-19 patients also have high levels of production of anti-inflammatory cytokines, such as IL-10, perhaps as a way of compensating for the exacerbated inflammatory response, which can lead to a picture of immune dissonance and anergy towards the infection (26, 153–155).
T197	40402-40630	Sentence	denotes	It is fundamental to perform further studies that elucidate the mechanisms of the immune response and the balance between pro-inflammatory and anti-inflammatory response patterns to understand the immunopathogenesis of COVID-19.
T198	40631-40750	Sentence	denotes	IL-7 is a pleiotropic cytokine that plays an essential role in the differentiation and clonal expansion of lymphocytes.
T199	40751-41077	Sentence	denotes	Chi et al. (156) described the production of IL-7 in COVID-19 patients; when compared to healthy controls, both asymptomatic and symptomatic individuals in the acute phase show an increase in the levels of this cytokine, however convalescent individuals return to the basal state equal to that observed in healthy individuals.
T200	41078-41232	Sentence	denotes	When symptomatic individuals were stratified according to the severity of the disease, those with moderate to severe conditions had higher levels of IL-7.
T201	41233-41499	Sentence	denotes	In addition, SARS-CoV-2-specific T cells from the peripheral blood of convalescent individuals of COVID-19 show high expressions of CD127, a receptor necessary for homeostatic cell proliferation triggered by IL-7, which may be related to the recovery observed (157).
T202	41500-41651	Sentence	denotes	Patients with a severe COVID-19 condition, on the other hand, have an increased IL-7 production, but contradictorily they also have severe lymphopenia.
T203	41652-41856	Sentence	denotes	Thus, we speculate that the deficiency in the expression of CD127 might occur in severely ill patients, which culminates in the deficiency of cell proliferation induced by IL-7 and consequent lymphopenia.
T204	41857-41981	Sentence	denotes	However, studies that seek to evaluate the expression profile of IL-7 and CD127 in COVID-19 patients need to be carried out.
T205	41982-42097	Sentence	denotes	In addition, the use of IL-7 as a treatment for COVID-19 patients has been evaluated and will be discussed further.
T206	42098-42231	Sentence	denotes	Several pro-inflammatory cytokines have been described in COVID-19 patients and are associated with the disease’s immunopathogenesis.
T207	42232-42323	Sentence	denotes	Among them, IL-1β and TNF-α stand out for playing a central role in this context (26, 156).
T208	42324-42718	Sentence	denotes	The respiratory failure characteristic of SARS-CoV-2 infection, especially in individuals who develop the most severe forms of the disease, occurs independently of infection or viral replication in the epithelial bronchial cells and probably occurs due to exacerbated inflammatory dysregulation, resulting from activation of the NLRP3 inflammasome pathway and consequent release of IL-1β (158).
T209	42719-43001	Sentence	denotes	However, although several articles have shown an increase in IL-1β production in COVID-19 patients and early treatment with IL-1 receptor blockers has helped prevent respiratory failure (159), its exact role in the immunopathogenesis of the disease has not yet been fully described.
T210	43002-43075	Sentence	denotes	Cytokine storms may have great relevance in the pathogenesis of COVID-19.
T211	43076-43196	Sentence	denotes	The induction of inflammatory mediators can induce cell damage, especially in lung tissues, causing respiratory failure.
T212	43197-43429	Sentence	denotes	In addition, several of these mediators have potent vasodilator activity, which at the local level can cause pulmonary edemas, while at the systemic level leads to septic shock, worsening the clinical condition of these individuals.
T213	43430-43746	Sentence	denotes	Similarly, several studies have shown that viral infections can induce cytokine storms, or take advantage of it, to establish infection and escape from the immune system, intensifying pathological phenomena such as those observed in sepsis, in addition to increasing the mortality rate of this population (160, 161).
T214	43747-44044	Sentence	denotes	Despite the absence of direct evidence of the role of cytokines and chemokines in lung injury, initial studies have shown that the increase in these pro-inflammatory mediators is associated with lung injury in patients with COVID-19 and has a central role in the pathogenesis of the disease (153).
T215	44045-44278	Sentence	denotes	The balance of the innate immune response is essential at the beginning of the infection, while its imbalance can culminate in excessive inflammation, which hinders the establishment of an effective immune response against the virus.
T216	44279-44599	Sentence	denotes	Therefore, using hemoperfusion can be an important tool to treat severe COVID-19 patients who developed cytokine storms, as well as other treatments focusing on controlling and reducing hyper inflammation using specific blockers or monoclonal antibodies directed against the mediator or to antagonize its receptor (144).
T217	44601-44623	Sentence	denotes	Innate Immune Response
T218	44624-44805	Sentence	denotes	The innate immune system is the first line of defense against pathogens through the activation of PRR in macrophages, neutrophils, and dendritic cells by the interaction with PAMPs.
T219	44806-45026	Sentence	denotes	An effective innate immune response against viruses like SARS-CoV-2 is essential not only to initiate the response but also to structure the basis for the production of a robust and more specific adaptive response (162).
T220	45027-45158	Sentence	denotes	Changes in this process, commonly observed in viral infections, can cause an immune imbalance and susceptibility of the host (163).
T221	45159-45328	Sentence	denotes	Patients who develop severe COVID-19 exhibited a marked increase in neutrophil and reduced lymphocytes counts compared with patients with mild signs of the disease (10).
T222	45329-45553	Sentence	denotes	A general increase in the number of circulating neutrophils and the reduction of lymphocytes enhance the neutrophil/lymphocyte ratio, which has been used as a predictor of the infection severity and development of pneumonia.
T223	45554-45701	Sentence	denotes	In addition to being a predictor of a worse prognosis, an increase in this ratio also indicates a serious immune imbalance in these patients (153).
T224	45702-45983	Sentence	denotes	In addition to having high levels of cell-free DNA, myeloperoxidase-DNA, and citrullinated histone H3 – important markers of neutrophil extracellular traps (NETs) –, the serum of COVID-19-positive patients was able to strongly trigger NETosis in healthy neutrophils in vitro (164).
T225	45984-46273	Sentence	denotes	Despite representing important strategies to eliminate pathogens by neutrophils, NETs damage healthy tissue and induce inflammation (165), in addition to featuring a variety of oxidizing agents and being involved in several vascular diseases, as well as pathogen-induced acute lung injury.
T226	46274-46523	Sentence	denotes	The release of NETs by neutrophils can be triggered by several factors, such as virus-damaged epithelial cells, activated platelets, activated endothelial cells, and inflammatory cytokines, such as IL-1β, IL-8, and G-CSF, among others (95, 166–169).
T227	46524-46664	Sentence	denotes	In this context, it is fundamental to conduct studies assessing the role of neutrophils and NETs to better understand COVID-19 pathogenesis.
T228	46665-46840	Sentence	denotes	Concerning monocytes, COVID-19 patients have shown an abundant circulation of CD14+ CD16+ cells, with a sharper increase in patients who developed severe respiratory syndrome.
T229	46841-47036	Sentence	denotes	This subtype of monocytes can over-secrete TNF-α, IL-1β, and IL-6 and expand quickly in systemic infections, implying that they must play an important role in the rapid defense against pathogens.
T230	47037-47171	Sentence	denotes	Controversially, these cells are the main producers of IL-10, which makes their exact function in immune responses elusive (170, 171).
T231	47172-47388	Sentence	denotes	Additionally, Dutertre et al. (172) demonstrated that CD14+ CD16+ monocytes are responsible for TNF overproduction in HIV infections and might be considered the major actor in immune hyperactivation in disease (172).
T232	47389-47557	Sentence	denotes	A study assessing bronchoalveolar lavage of SARS-CoV-2-positive individuals found an abundance of monocytes-derived inflammatory macrophages in critically ill patients.
T233	47558-47777	Sentence	denotes	In addition, the authors observed through single-cell analysis that these macrophages can contribute to local inflammation by recruiting inflammatory monocytes and neutrophils through CCR1 and CXCR2 chemokine receptors.
T234	47778-47940	Sentence	denotes	However, in patients who presented a moderate form of the disease, macrophages produced chemo-attractants for the recruitment of T cells, such as CXCR3 and CXCR6.
T235	47941-48063	Sentence	denotes	Such a difference in response might be the key to understanding the pathogenesis of respiratory failure in COVID-19 (173).
T236	48064-48323	Sentence	denotes	Furthermore, critically ill patients have also manifested rapid proliferation of another subpopulation of monocytes characterized by GM-CSF+ IL-6+, which may be related to inflammatory risk and impairment of the lungs when migrating in large quantities (170).
T237	48324-48573	Sentence	denotes	GM-CSF has been described as an active part of the pathogenesis of autoimmune and inflammatory diseases, mainly in the involvement of myeloid cells, such as monocytes, which can initiate tissue damage in a dependent manner on this marker (174, 175).
T238	48574-48985	Sentence	denotes	In addition, high levels of mediators, such as IL-6, TNF-, and IL-10, found in these patients are likely to have been produced by these monocytes and to be highly involved in cytokine storm and pathogenesis of SARS-CoV-2, since as the disease progresses these mediators reduce, which is correlated to the restoration of the immune function of CD4+ and CD8+ T lymphocytes, which is further discussed later (154).
T239	48986-49187	Sentence	denotes	Critical COVID-19 patients have shown excessive activation of circulating HLA-DR- monocytes, which has been associated with the onset of respiratory failure, suggesting its role as a predictive factor.
T240	49188-49391	Sentence	denotes	The lack of expression of HLA-DR in monocytes may indicate a modulatory capacity of the virus, which prevents the antigen presentation and hampers the formation of an adaptive immune response (176, 177).
T241	49392-49614	Sentence	denotes	During an in vitro experiment, Yang et al. (178) found that, despite being permissive to infection by SARS-CoV-2, human monocyte-derived macrophages and dendritic cells are not able to effectively produce viral replicates.
T242	49615-49735	Sentence	denotes	Despite their central role in pathogenesis, this may indicate that these cells are not important reservoirs for viruses.
T243	49736-49976	Sentence	denotes	In addition, neither of the cell types developed a response based on type II IFN, but macrophages had lower production of type I and III IFN than the control, indicating that the virus can inhibit a response mediated by these types of IFNs.
T244	49977-50109	Sentence	denotes	Additionally, macrophages were able to trigger an exacerbated inflammatory response with higher TNF-α, IL-8, IP10, MIP1α, and IL-1β.
T245	50110-50261	Sentence	denotes	Dendritic cells had not been reported to show such inflammatory phenomenon, which is due to the ability of SARS-CoV-2 to inhibit STAT1 phosphorylation.
T246	50262-50498	Sentence	denotes	Such important attenuation of dendritic cell response caused by the virus may have important implications for humans to develop effective immunity, therefore, further studies should seek to better elucidate such a relevant relationship.
T247	50499-50911	Sentence	denotes	Similarly, in the presence of IFN-α and GM-CSF, circulating monocytes should quickly differentiate into monocyte-derived dendritic cells (mDC), which are important antigen-presenting cells capable of phagocyting viruses and initiating the adaptive immune response process, as well as activating CD4+ T cells, generating immune memory in the process, and refining the body’s defense against infections (179, 180).
T248	50912-51063	Sentence	denotes	The number of mDCs has not increased in patients infected with SARS-CoV-2 compared with healthy controls, even in the most severe cases of the disease.
T249	51064-51327	Sentence	denotes	Interestingly, the levels of GM-CSF in the serum of these patients are highly elevated, which should lead these cells to increase, demonstrating that the virus may have a mechanism to control the production of IFN-α and consequent differentiation of mDCs (9, 26).
T250	51328-51533	Sentence	denotes	In the same way, individuals infected and not infected with SARS-CoV-2 have similar levels of IL-12, an important cytokine produced by mDC that is involved in the differentiation of naïve T cells (9, 181).
T251	51534-51738	Sentence	denotes	Thus, we hypothesize that the lack of mDC generation and consequent inability of the infected individual to produce IL-12 may be among the main factors of innate immunity-related pathogenesis of COVID-19.
T252	51739-51990	Sentence	denotes	As further discussed, the increase in naïve T cells, reduced cell functionality of CD4+, CD8+, and natural killers (NK), and delay in the appearance of humoral response found in these patients indicates a failure in the generation and function of mDC.
T253	51991-52099	Sentence	denotes	Therefore, it is urgent to carry out studies aimed at analyzing the effect of SARS-CoV-2 on dendritic cells.
T254	52101-52115	Sentence	denotes	T Helper Cells
T255	52116-52234	Sentence	denotes	Establishing and maintaining immune response and memory generation against viruses depends on the activity of T cells.
T256	52235-52372	Sentence	denotes	These lymphocytes originate from bone marrow progenitor cells and migrate to the thymus for maturation, selection, and peripheral export.
T257	52373-52651	Sentence	denotes	Peripheral T cells are subdivided into groups that include naïve T cells, which are capable of responding to new antigens, memory T cells derived from previous antigen activations and maintain long-term immunity, and regulatory T cells that coordinate the immune response (163).
T258	52652-53012	Sentence	denotes	The immune response begins when naïve T cells encounter antigens and co-stimulatory molecules presented by antigen-presenting cells, such as dendritic cells that phagocytize the virus, resulting in the production of IL-2, proliferation, and differentiation of effector T cells, which migrate to various sites to promote the elimination of pathogens (163, 182).
T259	53013-53203	Sentence	denotes	Inflammatory factors induced by viruses can trigger a storm of mediators that cause changes in the differentiation and activation of T cells, disturbing the homeostasis of the immune system.
T260	53204-53423	Sentence	denotes	In patients with COVID-19, the overall percentage of T lymphocytes is generally reduced, especially CD4+ CD3+ T lymphocytes, which have an activation phenotype, a reduction much more pronounced in severely ill patients.
T261	53424-53585	Sentence	denotes	Furthermore, a higher percentage of CD4+ CD45RA+ naïve cells and lower CD4+ CD3+ CD45RO+ memory T cells were also found in COVID-19 patients (10, 153, 183, 184).
T262	53586-53732	Sentence	denotes	Polyfunctional CD4+ T cells are characterized by the expression of activation markers as well as their capacity to produce IFN-γ, IL-2, and TNF-α.
T263	53733-53877	Sentence	denotes	These cells have been linked to an excellent response against viral infections and during the development of immunity by vaccination (185, 186).
T264	53878-54245	Sentence	denotes	Even though COVID-19 patients have shown an increase in the expression of molecules related to T CD4+ activation, such as CD69, CD38, and CD44, molecules related to their function, such as intracellular IFN-γ, IL-2, and TNF-α, are reduced, especially in individuals with a more severe stage of the disease (9, 170), indicating an impairment of polyfunctional T cells.
T265	54246-54448	Sentence	denotes	Li et al. (187) demonstrated that patients infected with SARS-CoV-1 had elevated levels of polyfunctional CD4+ T cells, especially those in a severe condition but who progressed to clinical improvement.
T266	54449-54700	Sentence	denotes	In contrast, critically ill patients with SARS-CoV-2 demonstrated a drastic reduction of this cell subtype, which may indicate that this virus has developed its own mechanisms to control cellular responses, thus differing from other coronaviruses (9).
T267	54701-54935	Sentence	denotes	Similarly, Chen et al. (154) demonstrated that CD4+ T lymphocytes from COVID-19 patients showed increased expressions of T cell immunoglobulin-3 (Tim-3), a type I transmembrane protein that acts as a negative regulator of Th1 pattern.
T268	54936-55138	Sentence	denotes	CD4+ cells showed low expression of this marker at the early phase of infection, having progressively increased over time, indicating that the exhaustion of these cells occurs as the disease progresses.
T269	55139-55511	Sentence	denotes	Many studies with SARS-CoV-2 positive patients have described the generation of these exhausted pathological lymphocytes that exacerbate the inflammatory response at the early stage of infection, initiating a cytokine storm, followed by cell exhaustion and loss of functionality, a phenomenon that has appeared mainly in more severe cases of the disease (9, 10, 170, 188).
T270	55512-55650	Sentence	denotes	The vast majority of studies to date show impairment of proliferation, maturation, and response of T cells, especially in sicker patients.
T271	55651-55972	Sentence	denotes	This may indicate that SARS-CoV-2, similarly to other viral infections, can interfere with the function of CD4+ cells at the very beginning of the infection, causing excessive release of inflammatory mediators and exhaustion of the response capacity of these cells over time, reducing the host’s antiviral immunity (189).
T272	55973-56409	Sentence	denotes	What seems to happen in COVID-19 is that the total lymphocyte count is reduced in these patients and, among the remaining T cells, the highest percentage is from naïve CD4+ T lymphocytes, while the activated subpopulations, although few, present a phenotype with excess and reduced markers related to activation and function, respectively, indicating that, despite overactivation, these cells fail to exercise effective immune activity.
T273	56410-56518	Sentence	denotes	Another important point is the reduction of regulatory T cells CD4+ CD25+ Foxp3+ verified in these patients.
T274	56519-56782	Sentence	denotes	These cells have a fundamental role in the negative regulation of inflammation, control of cell proliferation, and the effector function of several cells, which probably has contributed to the excessive inflammation observed in critically ill patients (153, 190).
T275	56783-57050	Sentence	denotes	It has been described that regulatory T cells play a central role in mitigating the immune response in several viral infections (191); reducing the number of these cells in patients with COVID-19 can lead to loss of regulatory functions and consequent cytokine storm.
T276	57051-57435	Sentence	denotes	It has been described in several studies that COVID-19 patients have a reduced number of circulating Treg cells, which may be due to the increase in soluble IL-2 receptors (IL-2R or CD25) that potentially scavenges IL-2, reducing their bioavailability for binding to CD25 on the cell surface, thus preventing the induction of the clonal expansion signal of Treg cells (153, 192, 193).
T277	57437-57452	Sentence	denotes	Cytotoxic Cells
T278	57453-57551	Sentence	denotes	T lymphocytes CD8+ and NK are essential to control viral infections due to their cytotoxic effect.
T279	57552-57751	Sentence	denotes	These cells become activated after recognizing antigens attached to molecules of MHC-I presented by infected cells, which usually leads to the death of the infected cell by effector mechanisms (163).
T280	57752-57938	Sentence	denotes	Kamiya et al. (194) demonstrated that SARS-CoV-2 infection in humans dramatically reduces the total CD8+ and NK cell count, especially in patients who have developed more severe disease.
T281	57939-58404	Sentence	denotes	The inhibition of these cells was characterized by an increase in the expression of NK inhibitory receptor CD94/NK group 2 member A (NKG2A), a type C lectin receptor of cytotoxic cells that acts as a potent suppressor when binding to minimally polymorphic MHC-I that present peptide sequences of other MHC-I molecules, inducing an inhibitory signal through two receptors with tyrosine-based inhibition motifs that suppress cytokine secretion and cytotoxic activity.
T282	58405-58626	Sentence	denotes	In patients who recovered from COVID-19, CD8+ and NK cell counts and the reduction in NKG2A expression were restored, suggesting that the inhibition of these cells is a result of SARS-CoV-2-mediated immunomodulation (10).
T283	58627-58810	Sentence	denotes	Corroborating these data, it has been reported that other viral infections also manage to increase the expression of NKG2A in NK cells as a way to escape from the immune system (195).
T284	58811-59165	Sentence	denotes	SARS-CoV-2 studies involving CD8+ T cells have shown exhaustion of the effector capacity of these cells over time by the reduction of granzyme B, perforins, and lysosome-associated membrane protein 1, also known as LAMP-1 or CD107a, described as a marker of cytotoxic cells’ degranulation and an important parameter to assess the activity of these cells.
T285	59166-59329	Sentence	denotes	CD8+ T cells from COVID-19 patients have a very marked activation phenotype with an increase in CD69, CD38, CD137, and CD44, especially in critically ill patients.
T286	59330-59553	Sentence	denotes	However, despite presenting an increase in these activation molecules, these cells also have enhanced cell exhaustion proteins, such as PD1, Tim3, CTLA-4, and TIGIT, especially in more critically ill patients (9, 154, 170).
T287	59554-59790	Sentence	denotes	TIGIT receptor, present in T and NK cells, can bind to dendritic cell CD155 receptors and induce an increased expression of IL-10 and reduce IL-12, in addition to inhibiting T cell activation and blocking cytotoxicity of NK cells (196).
T288	59791-59932	Sentence	denotes	The use of specific blockers for these receptors, such as anti-PD1 and anti-TIGIT, has helped in the recovery of the function of these cells.
T289	59933-60134	Sentence	denotes	Therefore, it is logical to assume that specific NKG2A blockers could be an important tool to assist in the treatment of SARS-CoV-2 infections, restoring the functionality of cytotoxic cells (10, 195).
T290	60135-60617	Sentence	denotes	Together, these data described the increase in activation markers and cellular exhaustion, in addition to the reduction in functionality markers indicating that, like CD4+ T lymphocytes, these cells were probably hyperactivated right at the beginning of the infection, collaborating with the generation of a cytokine storm, until they became exhausted and lost their functional capacity, causing reduction of antigen-specific response and loss of its antiviral effects ( Figure 2 ).
T291	60618-60663	Sentence	denotes	Figure 2 Immune response in COVID-19 stages.
T292	60664-60722	Sentence	denotes	SARS-CoV-2 infection is divided into three general phases.
T293	60723-60978	Sentence	denotes	In the first one, called viremia, the virus spreads through the body and there is excessive activation of immune cells with exacerbated production of inflammatory mediators, such as IFN-γ, IL-2, and TNF-α, triggering cytokine storms and immune impairment.
T294	60979-61283	Sentence	denotes	The second (acute) phase, characterized by the appearance of COVID-19 symptoms, presents a profile of immune cells still hyperactivated, but with the presence of cell exhaustion markers, such as Tim3, PD1, TIGIT, and NKG2A, in addition to losing the functional capacity of producign IFN, IL-2, and TNF-α.
T295	61284-61556	Sentence	denotes	In this period there is still the appearance of CD14+ CD16+ hyperinflammatory monocytes, with a high production capacity of TNF-α, IL-1β, and IL-6, which will migrate to the lungs, contributing to the pathogenesis of respiratory failure and maintaining the cytokine storm.
T296	61557-61699	Sentence	denotes	The lethargic state of the immune system in the early stages of infection may be related to the delay in the generation of a humoral response.
T297	61700-61830	Sentence	denotes	In the third, or convalescence, phase, the individual can evolve in two opposite directions, recovery or clinical worsening/death.
T298	61831-61958	Sentence	denotes	In recovery, cells of lymphoid origin recover their effector function and lose markers of exhaustion, while IgG levels improve.
T299	61959-62054	Sentence	denotes	On the other hand, in patients with clinical worsening, this status of immune anergy continues.
T300	62056-62072	Sentence	denotes	Humoral Response
T301	62073-62209	Sentence	denotes	Detecting a humoral response against SARS-CoV-2 has been the focus of attention to developing faster and more accurate diagnostic tools.
T302	62210-62480	Sentence	denotes	A study assessing the presence of IgA, IgM, and IgG against SARS-CoV-2 in infected patients found that IgA levels begin to rise in the first seven days after the onset of symptoms and continue increasing until it stabilizes near the 14th day after the onset of symptoms.
T303	62481-62709	Sentence	denotes	Additionally, IgM production appears as early as IgA, the antibody titration in the first seven days after the onset of symptoms was very low, starting to increase only from the eighth day, reaching a plateau after the 14th day.
T304	62710-62873	Sentence	denotes	The average time of appearance of specific IgG against SARS-CoV-2 starts 14 days after the appearance of symptoms and grows exponentially until the 21st day (197).
T305	62874-63038	Sentence	denotes	These data corroborate the disease stages proposed by Lin et al. (6) (presented in the introduction), and the changes in the immune response present in the disease.
T306	63039-63215	Sentence	denotes	The early appearance of IgA results from the first contact of the virus with the individual’s mucosa at the moment of contagion and continues to increase until the acute phase.
T307	63216-63788	Sentence	denotes	Despite viremia and symptom onset, IgM levels only begin to rise from the eighth day after symptom onset, indicating anergy in the immune response during this period, perhaps caused by dysfunction in antigen-presenting cells, such as dendritic cells, and also by reducing the amount of activated T helper cells, which play a central role in triggering the immunity acquired by the activation and clonal expansion of B lymphocytes, in addition to the formation of germinal centers and generation of plasma cells that produce high affinity and avidity antibodies (198, 199).
T308	63789-63987	Sentence	denotes	The appearance of IgG near the third stage of the disease may be related to the clinical evolution of patients and those who fail to establish an efficient immune response might be at risk of death.
T309	63988-64132	Sentence	denotes	Interestingly, Guo et al. (197) found that approximately 22% of COVID-19 patients confirmed by RTq-PCR did not present detectable levels of IgM.
T310	64133-64332	Sentence	denotes	Most of these individuals were tested in the first seven days after the onset of symptoms, therefore the lack of IgM can be justified by the delay in generating a humoral response against SARS-CoV-2.
T311	64333-64467	Sentence	denotes	However, some critically ill patients followed for a longer period remained negative for IgM even 22 days after the onset of symptoms.
T312	64468-64710	Sentence	denotes	As for IgG levels, some patients took 30 to 40 days after the appearance of symptoms to show some detectable level of IgG, suggesting a possible failure in the production of antibodies that may have contributed to the severity of the disease.
T313	64711-64983	Sentence	denotes	It is possible that the generation of antibodies in more advanced stages of COVID-19 does not benefit the recovery process since most pathological mechanisms at this stage might be more related to the excess of inflammatory mediators than the presence of the virus itself.
T314	64984-65306	Sentence	denotes	In recovered patients, the magnitude of the production of neutralizing antibodies (nAb) against SARS-CoV-2 is positively correlated with the severity of the disease; while asymptomatic individuals have little or no capacity to produce nAb, individuals who recovered from severe cases of COVID-19 had robust nAb production.
T315	65307-65511	Sentence	denotes	Also, these severe recovered patients showed an increase in B cell receptor (BCR) rearrangement, which may demonstrate that the effective production of nAb requires enhanced and prolonged BCR stimulation.
T316	65512-65716	Sentence	denotes	Asymptomatic or mild symptomatic patients may possibly mount robust SARS-CoV-2 specific CD8 + T cell responses, which can provide protection by directly eliminating the target cells infected by the virus.
T317	65717-65841	Sentence	denotes	However, due to the lack of immunity provided by nAb, these individuals might suffer from SARS-CoV-2 reinfection (200, 201).
T318	65842-66255	Sentence	denotes	In the same way, Zhang et al. (202) also demonstrated that patients who recovered from severe COVID-19 have high levels of BCR clonal expansion and B cell activation, indicating a more robust humoral response than patients with mild disease, thus asymptomatic individuals or those with mild COVID-19 probably have different cell and humoral responses than individuals who developed the severe form of the disease.
T319	66256-66426	Sentence	denotes	In an article published by Chen et al, the serum of 26 patients who recovered from COVID-19 were analyzed for the production of IgG anti-SARS-CoV-2 S1 protein antibodies.
T320	66427-66639	Sentence	denotes	It was found that, despite the majority of patients presenting high IgG titers, only three individuals had antibodies that effectively neutralized the binding of the viral glycoprotein to the human ACE2 receptor.
T321	66640-66894	Sentence	denotes	In addition, the authors successfully managed to clone two different neutralizing antibodies from these patients with the ability to inhibit virus-cell binding, opening up the potential for using them as a possible source of treatment for COVID-19 (203).
T322	66895-67033	Sentence	denotes	In theory, the production of specific neutralizing antibodies against SARS-CoV-2 should be able to combat the virus and reduce viral load.
T323	67034-67190	Sentence	denotes	The production of immune memory verified in the blood of recovered patients has also been used to treat COVID-19 patients, as we will discuss further (204).
T324	67192-67210	Sentence	denotes	COVID-19 Treatment
T325	67211-67356	Sentence	denotes	To date, no effective vaccines or therapeutic antiviral agents have been approved for the treatment of COVID-19 or any other human CoV infection.
T326	67357-67424	Sentence	denotes	The main approach to disease management focuses on supportive care.
T327	67425-67690	Sentence	denotes	To contain the viral transmission and disease, rapid public health interventions using immune cell-based therapies, antibodies, antivirals, new drugs, or vaccine strategies have focused on reducing mortality, virus spread, and mitigating potential future outbreaks.
T328	67691-67978	Sentence	denotes	In this context, we conducted a survey of the main SARS-CoV-2 drugs/treatments following three criteria: peer-reviewed published scientific literature, with clinical trials that are underway, and that display a broad spectrum of action in the face of various viral and parasitic disease.
T329	67979-68093	Sentence	denotes	The researched data (until September 2020) for ongoing and completed trials were searched in “clinicaltrials.gov”.
T330	68095-68113	Sentence	denotes	Enhancing Immunity
T331	68114-68296	Sentence	denotes	As exposed in the previous topics, currently there are no proven treatments for SARS-CoV-2 infections, thus, much has been discussed about the maintenance of a healthy immune system.
T332	68297-68475	Sentence	denotes	In this sense, the use of vitamins and other essential components for the proper functioning of the immune response can be an important approach in times of risk like this (205).
T333	68476-68860	Sentence	denotes	Several studies have shown that the use of supplements helps in enhancing the immune response and recovery from viral infections, as is the case with the use of vitamin A and D or selenium to improve the humoral immunity of individuals vaccinated against influenza virus (206, 207), or the use of zinc to improve the immune response of individuals infected with torquetenovirus (208).
T334	68861-69042	Sentence	denotes	Among vitamin supplements, vitamin D stands out for having an immunomodulatory effect on both adaptive and innate immune responses, helping in the development of B, T, and NK cells.
T335	69043-69197	Sentence	denotes	In addition, it has the ability to stimulate the production of antioxidant responses and microbicidal molecules such as defensins and cathelicidins (209).
T336	69198-69460	Sentence	denotes	The use of vitamin D has also been associated with the prevention of respiratory diseases associated with viral infections (210), and epidemiological data suggest that vitamin D deficiency increases the susceptibility to acute viral respiratory infections (211).
T337	69461-69685	Sentence	denotes	However, a study in the United Kingdom that evaluated plasmatic concentrations of vitamin D in samples from COVID-19 patients found no association between circulating vitamin D levels and the risk for disease severity (212).
T338	69686-69972	Sentence	denotes	The use of supplementation with other types of vitamins has also been described in viral infections; the use of vitamin C, for example, a potent antioxidant and an important enzyme cofactor, contributes to the development of the immune response, helping in the production of type I IFN.
T339	69973-70123	Sentence	denotes	However, a systematic review with meta-analysis found no evidence that the use of vitamin C has any effect in preventing common cold infections (213).
T340	70124-70235	Sentence	denotes	As for vitamin E, it has been shown that its deficiency can impair cellular and humoral immune responses (214).
T341	70236-70418	Sentence	denotes	However, the use of vitamin E has been associated with an increased risk of pneumonia and has shown no significant effect in preventing lower respiratory tract infections (215, 216).
T342	70419-70727	Sentence	denotes	In view of the controversial results, more than 50 ongoing clinical trials are seeking to clarify the role of vitamins, minerals, and other dietary supplementation in the prophylaxis and treatment of COVID-19, analyzing parameters such as the risk of infection, risk of hospitalization, and clinical outcome.
T343	70729-70742	Sentence	denotes	Immunotherapy
T344	70744-70766	Sentence	denotes	Antibody-Based therapy
T345	70767-70997	Sentence	denotes	Considered an efficient method for the clinical treatment of different infectious diseases, including MERS-CoV and SARS-CoV-1 (217), antibody-based immunotherapy has been studied as a potentially applicable tool to treat COVID-19.
T346	70998-71149	Sentence	denotes	The mechanisms involved with its effects against SARS-CoV-2 are related to preventing the virus from entering the host cells, blocking its replication.
T347	71150-71344	Sentence	denotes	The virus entry block was studied for acting both in the cell receptor ACE2 and directly on the virus (neutralizing antibodies [nAbs]), specifically in the S1 subunit of the S protein (218–220).
T348	71345-71601	Sentence	denotes	Regarding the blocking of ACE2 receptors, the application of some mechanisms stand out: the soluble version of ACE2 fused to an immunoglobulin Fc domain (ACE2-Fc), RDB domain attached to Fc (RDB-Fc), and receptor-targeted monoclonal antibodies (mAb) (221).
T349	71602-71724	Sentence	denotes	Viral neutralization by nAbs is also an immunotherapeutic approach and directly recognizes epitopic regions of SARS-CoV-2.
T350	71725-72035	Sentence	denotes	This effect can be achieved either directly through mAbs manufactured in laboratories or by using polyclonal antibodies (pAbs) (218). nAbs act directly on the virus, preventing its infectivity by activating several pathways, such as the complement system, cell cytotoxicity, and phagocytic clearance (222–224).
T351	72036-72124	Sentence	denotes	The therapeutic use of mAbs has shown good outcomes, mainly due to its high specificity.
T352	72125-72299	Sentence	denotes	Recently, several mAbs against viruses have been developed, including SARS-CoV-1 and MERS-CoV, in which the S protein is the major target described both in vitro and in vivo.
T353	72300-72437	Sentence	denotes	According to some studies, the specific nAbs against SARS-CoV-1 RBD in the S protein could effectively block SARS-CoV-2 entry (218, 225).
T354	72438-72656	Sentence	denotes	However, Wrapp et al. (226) tested several published SARS-CoV-1 RBD-specific nAbs and found that they do not have substantial binding to the S protein of SARS-CoV-2, suggesting that the cross-reactivity may be limited.
T355	72657-72761	Sentence	denotes	Thus, the combination of nAbs with different viral targets and sources could improve treatment efficacy.
T356	72762-72963	Sentence	denotes	In addition to experimental studies, to date, more than 10 clinical trials have aimed at testing human mAbs against SARS-Cov-2 (227–235), which could also represent an alternative, effective treatment.
T357	72964-73048	Sentence	denotes	Furthermore, some immunomodulatory mAbs have been tested in the context of COVID-19.
T358	73049-73388	Sentence	denotes	It is remarkable that until now most of the data published regarding the use of immunomodulatory mAbs derive from studies using either anti-IL-6 or anti-IL-6R, probably because using IL-6 blockers seems promising at controlling the cytokine storm associated with the development of ARDS in more aggressive patterns of SARS-CoV-2 infection.
T359	73389-73441	Sentence	denotes	However, clinical observations remain controversial.
T360	73442-73747	Sentence	denotes	Although some studies found considerable clinical improvements resulting from treatment with IL-6 blockers (236–239), others do not report any significant difference between the clinical features of groups treated with anti-IL6/IL-6R mAbs and their respective controls (without anti-IL-6/IL-6R) (240–243).
T361	73748-73973	Sentence	denotes	These controversial results can be explained by the pleiotropic function of IL-6, which also play an important anti-inflammatory role, questioning the use of IL-6 blockade to suppress inflammation-induced tissue damage (244).
T362	73974-74176	Sentence	denotes	Additionally, severe side effects have been associated with the use of IL-6 blockers, including enhanced hepatic enzymes, thrombocytopenia, severe bacterial and fungal infections, and sepsis (241, 245).
T363	74177-74276	Sentence	denotes	In general, data from analyses on the use of this type of mAbs remain inconclusive (243, 246, 247).
T364	74277-74551	Sentence	denotes	Recent findings are optimistic, but data validation by robust scientific evidence has been hampered by the small sample size in most case reports and studies on the use of mAbs blocking other immune mediators, such as IL-1β, GM-CSF, and complement protein C5 (238, 248–250).
T365	74552-74693	Sentence	denotes	However, seeking to verify the effectiveness of using mAbs blocking inflammatory mediators, dozens of clinical trials are currently underway.
T366	74694-75103	Sentence	denotes	Aiming at reducing the hyper inflammation found in the lungs of SARS-CoV-2-infected patients, different clinical studies are currently investigating the activities of mAbs anti-JAK, anti-GM-CSF, anti-GM-CSF receptor, anti-M-CSF receptor, anti-CD14, anti-IFNγ, anti-VEGF, anti-BKT, anti-CCR5, anti-IL-6, anti-IL-6 receptor, anti-TNFα, anti-IL1β, anti-IL1β receptor, and complement C5 inhibitor (220, 251, 252).
T367	75104-75302	Sentence	denotes	Similarly, ongoing clinical trials have sought to reverse the hyper-thrombotic state found in critically ill patients by using anti-P-selectin, anti-CTGF, and factor XIIa antagonist mAbs (253, 254).
T368	75303-75516	Sentence	denotes	Furthermore, to restore the exhausted T lymphocytes’ and NK cells’ immunity, other clinical studies applied anti-PD1 mAbs under the hypothesis of a stimulus of anti-viral response and prevention of ARDS (255–257).
T369	75517-75936	Sentence	denotes	More recently, the passive administration of pAbs has also been tested in COVID-19 patients (222–224, 258–267), also known as convalescent plasma (CP) or immune plasma, which is already used effectively and safely in the treatment of other severe acute respiratory syndrome infections of viral etiology, such as SARS, MERS, and H1N1, and offers only a short-term but rapid immunity to the susceptible individuals (268).
T370	75937-76075	Sentence	denotes	A strict criterion to select the CP donor states that the individual must show clinical recovery and test negative for the virus presence.
T371	76076-76205	Sentence	denotes	Thus, after being confirmed, a high titer of neutralizing antibodies against SARS-CoV-2 must be stored in blood banks (269, 270).
T372	76206-76412	Sentence	denotes	Some reviews related to patients who received transfusion with CP showed a reduction in viral load, improvement in clinical symptoms, better radiological findings, and improved survival (260, 261, 271–273).
T373	76413-76633	Sentence	denotes	In addition, after having received CP containing nAbs, COVID-19 patients had significant improvements from the beginning of treatment (until 22 days), presenting lower fever, decreased viral load, and higher nAbs levels.
T374	76634-76715	Sentence	denotes	Further, 60% of the patients were discharged one month after the treatment (271).
T375	76716-76867	Sentence	denotes	Better outcomes were found in early administration of CP (before SARS-CoV-2 seroconversion), preferably on day 5, for obtaining maximum efficacy (268).
T376	76868-77043	Sentence	denotes	More recently, Li et al. found no statistically significant clinical improvement or mortality reduction in a randomized clinical trial with CP-treated COVID-19 patients (274).
T377	77044-77213	Sentence	denotes	However, the authors reported that CP treatment is potentially beneficial to critically ill patients by suggesting a possible antiviral efficiency of high titer of nAbs.
T378	77214-77525	Sentence	denotes	Notably, there are clinical controversies, ethical issues, and potential risks associated with convalescent plasma therapy (275), such as the possibility of ADE development, exacerbating the disease severity, and causing a significant illness in future exposure to coronaviruses infection (268, 276, 277) (REF).
T379	77526-77813	Sentence	denotes	Divergences between studies may be caused by variations in the composition of CP, which is highly variable and includes a variety of blood-derived components, timing of CP administration, titer of the specific antibody in administered plasma, and presence of blood borne pathogens (268).
T380	77814-77935	Sentence	denotes	Nonetheless, understanding the efficacy and safety of CP therapy relies on the completion of the ongoing clinical trials.
T381	77936-78222	Sentence	denotes	Another therapeutic strategy using antibodies is intravenous immunoglobulin (IVIg) that contains polyclonal IgG isolated from healthy donors, which can be further enhanced by using IgG antibodies collected from recovered COVID-19 patients in the same geographical region as the patient.
T382	78223-78400	Sentence	denotes	Results have been mostly positive, although many of these therapies have not been formally evaluated through a randomized, double-blind, placebo-controlled clinical trial (278).
T383	78401-78671	Sentence	denotes	According to recent studies, IVIg can be used effectively in early stages of SARS-CoV-2 infection (before the initiation of systemic damage), reducing the use of mechanical ventilation, preventing the progression of pulmonary lesions, and promoting early recovery (268).
T384	78672-78877	Sentence	denotes	Also, cross-neutralization activity was shown against SARS-CoV-2 in commercial IVIg manufactured prior to the COVID-19 pandemic and are currently under evaluation as potential therapies for COVID-19 (279).
T385	78878-79226	Sentence	denotes	Thus, intravenous use of immunoglobulins can prove helpful in therapy against SARS-CoV-2, however, adjustments in the therapeutic regimen are necessary for all IVIg possibilities, as well as a complete understanding of the possible adverse effects, such as the risk of ADE (278, 279), that are being studied in more than 10 ongoing clinical trials.
T386	79227-79411	Sentence	denotes	Some works have shown that therapies focusing on the interaction between SARS-CoV-1 and the ACE2 receptor may be extended for use in SARS-CoV-2 patients as an immunotherapy tool (218).
T387	79412-79582	Sentence	denotes	However, other authors refute this idea based on the fact that recent studies showed limited cross-neutralization between SARS-CoV-1 antibodies and SARS-CoV-2 (280, 281).
T388	79583-79757	Sentence	denotes	Furthermore, it was shown that SARS-CoV-2 S protein binds ACE2 with a higher affinity than SARS-CoV-1, suggesting that such interaction differs between the two viruses (266).
T389	79759-79784	Sentence	denotes	Immune Cell-Based Therapy
T390	79785-79952	Sentence	denotes	In addition to antibody-based therapies, scientists have been studying immune cell-based therapies as a tool to combat COVID-19, focusing especially on NK and T cells.
T391	79953-80156	Sentence	denotes	The importance of NK cells as the first antiviral responders can be seen in patients with NK cell deficiency and immunocompromised individuals who have increased susceptibility to viral infections (282).
T392	80157-80412	Sentence	denotes	In this sense, Market et al. (282) gathered the main reports so far addressing potential therapies focusing on mediating NK cell activity to mitigate the immunopathological consequences of COVID-19, and consequently lighten the load on our health systems.
T393	80413-80517	Sentence	denotes	Some ongoing clinical trials have been studying the use of NK cell therapy through different approaches.
T394	80518-80770	Sentence	denotes	A randomized phase I/II trial studied the infusions of CYNK-001 cells, an allogeneic off-the-shelf cell therapy enriched for CD56+/CD3- NK cells expanded from human placental CD34+ cells in 86 hospitalized patients with moderate COVID-19 disease (283).
T395	80771-80904	Sentence	denotes	Another randomized phase I/II study explored the use of NKG2D-ACE2 CAR-NK cells with each common, severe, and critical type COVID-19.
T396	80905-81149	Sentence	denotes	The authors hypothesize that these cells target the S protein of SARS-CoV-2 and NKG2DL on the surface of infected cells with ACE2 and NKG2D, respectively, seeking out the elimination of SARS-CoV-2 virus particles and their infected cells (284).
T397	81150-81375	Sentence	denotes	The unregulated profile of the immune response in critically ill COVID-19 patients may be due to the reduction of Treg cells, which culminates in excessive release of inflammatory mediators and cytokine storms (153, 191–193).
T398	81376-81526	Sentence	denotes	Thus, the use of adoptive transfer of these cells as a measure of inflammatory control in critically ill patients is a promising therapeutic approach.
T399	81527-81882	Sentence	denotes	The infusion of autologous polyclonal Treg has already been used to treat inflammatory diseases, such as type 1 diabetes (285), however the use of autologous cells takes a long time, due to the period necessary for differentiation and clonal expansion, making this an unviable and costly method for infectious diseases, as is the case with COVID-19 (286).
T400	81883-82057	Sentence	denotes	A viable alternative is the use of allogeneic human leukocyte antigen-matched umbilical cord-derived Tregs (UBC-Treg) which can be widely expanded and used on a larger scale.
T401	82058-82311	Sentence	denotes	A recent case study used 1x108 administration of UBC-Treg in two patients with COVID-19 who had severe respiratory failure, and both demonstrated significant clinical improvement and reduced inflammatory markers four days after starting treatment (287).
T402	82312-82433	Sentence	denotes	There are currently two clinical trials underway that aim to infuse Treg cells in patients with severe COVID-19 and ARDS.
T403	82434-82618	Sentence	denotes	The first one is a multi-center, prospective, double-blinded, placebo-controlled phase 1 randomized clinical trial, which has 45 patients who will receive cryopreserved UBC-Treg (288).
T404	82619-82799	Sentence	denotes	The second one is a randomized, double-blind, placebo-controlled phase 2 study with 88 participants who will receive off-the-shelf allogeneic hybrid Treg/Th2 cells (RAPA-501-ALLO).
T405	82800-82927	Sentence	denotes	RAPA-501-ALLO cells will be generated from healthy donors, cryopreserved, banked, and made available for off-the-shelf therapy.
T406	82928-83158	Sentence	denotes	The cells are manipulated ex vivo to differentiate into two anti-inflammatory phenotypes simultaneously, generating hybrid Treg/Th2 cells, with the potential to reduce inflammation and mediate a protective effect on tissues (289).
T407	83159-83401	Sentence	denotes	In addition to therapeutic approaches using Treg cell infusion, another three clinical trials are underway with the aim of evaluating treatment using specific SARS-CoV-2 T cells isolated from individuals who recovered from COVID-19 (290–292).
T408	83402-83588	Sentence	denotes	The use of virus-specific T cells for off-the-shelf treatment has been used in several viral infections, such as cytomegalovirus, HHV6, adenoviruses, Ebola virus, and BK virus (293–296).
T409	83589-83907	Sentence	denotes	Although vaccination provides T cells-based virus-specific immunity, the path to its development is long, so the use of adoptive cell transfer techniques from healthy individuals who recovered from COVID-19 and developed an effective cell response is probably the fastest way to treat critically ill individuals (297).
T410	83908-84183	Sentence	denotes	Besides that, as mentioned before, asymptomatic or mild symptomatic patients may possibly mount robust SARS-CoV-2 specific CD8+ T cell responses (200, 201), therefore, the use of these individuals’ cells to treat critically ill patients with COVID-19 can be a promising tool.
T411	84184-84406	Sentence	denotes	The clinical use of IL-7 has been implemented in the treatment of cancer patients and infectious diseases, mainly with the objective of improving the immune response by stimulating the generation of lymphocytes (298, 299).
T412	84407-84717	Sentence	denotes	In addition, IL-7 administration has been reported to increase CD4 + and CD8 + T lymphocyte counts without inducing the production of pro-inflammatory mediators, making it a promising method of recovering immune function in patients with disorders related to cytokine storms, such as sepsis and COVID-19 (300).
T413	84718-84983	Sentence	denotes	In a case study conducted by Monneret et al. (301), compassionate administration of IL-7 to a patient with severe COVID-19 significantly improved total lymphocyte count and HLA-DR expression in circulating monocytes four days after administration of the first dose.
T414	84984-85078	Sentence	denotes	The patient also showed a significant improvement in lung involvement and negative viral load.
T415	85079-85451	Sentence	denotes	Another study conducted by Laterre et al. (302), who administered IL-7 to COVID-19 patients found that there was a significant improvement in the lymphocyte count after starting treatment, in addition, the patients did not show any change in TNF-α levels, IL-1β, and IL-12p70, which may indicate that IL-7 therapy may be safe for patients with severe inflammatory changes.
T416	85452-85592	Sentence	denotes	Thus, the use of IL-7-based immunotherapy can be an important tool to be used in future clinical trials in patients with severe lymphopenia.
T417	85593-85815	Sentence	denotes	Therefore, the data available to date do not ensure the success of immunotherapy applied in patients with COVID-19, thus, further studies specifically targeting SARS-CoV-2 should be performed to provide more specific data.
T418	85816-85898	Sentence	denotes	However, immunotherapy is effective and of immediate use, being of short duration.
T419	85899-86071	Sentence	denotes	This approach also presented limitations, such as the possibility of abnormal reactions and other serious risks, such as induction of severe acute lung injury or ADE (225).
T420	86072-86349	Sentence	denotes	Although we are living through a unique moment in science, with some mismatched information and novel, important discoveries being made every day, immunotherapy seems to be a possibly effective option to help patients until an effective, safe vaccine or treatment is developed.
T421	86351-86382	Sentence	denotes	Drug Options Against SARS-CoV-2
T422	86383-86543	Sentence	denotes	Although some drugs appear to be effective against SARS-CoV-2 and are able to improve COVID-19 symptoms, there is no specific antiviral compound for this virus.
T423	86544-86804	Sentence	denotes	In the face of such a global health emergency, several clinically used drugs are being reviewed and redirected to be tested in patients who have critical complications of COVID-19 in an attempt to eliminate the virus and modulate the patient’s immune response.
T424	86806-86816	Sentence	denotes	Antivirals
T425	86817-87064	Sentence	denotes	Due to the large amount of experimental and clinical studies assessing the effectiveness of antiviral therapy against SARS-CoV-2, we have seen the importance of this class of drugs in reducing the viral load peak at the beginning of the infection.
T426	87065-87295	Sentence	denotes	Evidence from laboratory, animal, and clinical studies demonstrate that the use of associated or isolated antivirals can delay the progression of lung lesions and decrease the possibility of respiratory transmission of SARS-CoV-2.
T427	87296-87452	Sentence	denotes	In this study, we selected the following most promising treatment options: lopinavir/ritonavir, arbidol, ribavirin, remdesivir, favipiravir, and type I IFN.
T428	87453-87844	Sentence	denotes	In the context of discovering new drugs, it is efficient to test the efficacy of existing antiviral drugs regarding the treatment of related viral infections. After the emergence of SARS in 2003, the screening of approved drugs identified an effective SARS-CoV-2 antiviral-drug candidate: the combination of the human immunodeficiency virus (HIV) protease inhibitors lopinavir and ritonavir.
T429	87845-88000	Sentence	denotes	However, lopinavir has insufficient oral bioavailability for significant therapeutic activity due to rapid catabolism by the cytochrome P450 enzyme system.
T430	88001-88213	Sentence	denotes	Thus, ritonavir is a cytochrome P450 and glycoproteins inhibitor, which increases the lopinavir plasma half-life, enhancing the pharmacokinetic and pharmacodynamic activities against the viral HIV-protease (303).
T431	88214-88524	Sentence	denotes	Chu et al. (304) described the possible mechanism of action of these drugs on SARS-CoV-1, suggesting that they act by inhibiting intracellular viral multiplication, preventing the action of the protease enzyme, which leads to the formation of an immature and less infectious virus with no ability to replicate.
T432	88525-88670	Sentence	denotes	Choy et al. (305) were successful at demonstrating the antiviral effect of lopinavir against SARS-CoV-2, but this was not the case for ritonavir.
T433	88671-88836	Sentence	denotes	In turn, Kang et al. (306) found a lower viral load in infected SARS-CoV-2 Vero cells treated with lopinavir/ritonavir in relation to the untreated infected control.
T434	88837-89114	Sentence	denotes	Although no consensus has been reached on its efficacy, dosage, or administration period, the literature includes some case reports, case series, and observational studies reporting a protective effect of the lopinavir/ritonavir combination in COVID-19 patients (110, 307–312).
T435	89115-89345	Sentence	denotes	Conversely, Cao et al. (313) conducted a controlled open‐label study with 199 hospitalized severe COVID‐19 patients randomly divided into two groups: a standard care group and a lopinavir/ritonavir treatment group (400 mg/100 mg).
T436	89346-89532	Sentence	denotes	No benefit was observed in the lopinavir/ritonavir treatment group, showing no significant results for faster clinical improvement, lower mortality, or decreased viral RNA detectability.
T437	89533-89739	Sentence	denotes	Although there are 85 clinical trials in progress testing lopinavir/ritonavir associated with other drugs on SARS-CoV-2 and/or COVID-19, WHO stopped the study of lopinavir/ritonavir in the Solidarity Trial.
T438	89740-89957	Sentence	denotes	Deng et al. (312) have studied the association of lopinavir/ritonavir with arbidol treatment and demonstrated a significant improvement in COVID-19 patients compared with a group treated only with lopinavir/ritonavir.
T439	89958-90092	Sentence	denotes	Arbidol (umifenovir) is a broad-spectrum antiviral and immunomodulatory compound used to treat influenza and many other viruses (314).
T440	90093-90398	Sentence	denotes	Analyses of molecular dynamics and structure-guided drug-binding have suggested an efficiency of arbidol at blocking or hampering the trimerization of the SARS-CoV-2 spike glycoprotein, in addition to inhibiting virus-cell interactions, which supports the potential use of arbidol to treat COVID-19 (315).
T441	90399-90635	Sentence	denotes	Chen et al. (316) demonstrated that arbidol therapy was able to shorten the course of the disease and promote clinical improvement, resulting in low fever and improvements in dry cough without side effects faster than the control group.
T442	90636-90767	Sentence	denotes	Zhu et al. (317) also demonstrated the effects of arbidol by retrospectively analyzing the clinical data from 50 COVID-19 patients.
T443	90768-91142	Sentence	denotes	The study demonstrated that the use of arbidol monotherapy, without association with other drugs, was more effective than the treatment with lopinavir/ritonavir, showing clinical improvement of the disease, presenting a total elimination of viral load over a shorter duration; in addition, no fever or ARDS were reported compared with those in the lopinavir/ritonavir group.
T444	91143-91357	Sentence	denotes	Ribavirin is another antiviral drug used in association with lopinavir/ritonavir to treat SARS-CoV-1 and was able to reduce viral load, risk of adverse clinical outcomes, ARDS, or death in SARS patients (304, 318).
T445	91358-91585	Sentence	denotes	Ribavirin has a broad antiviral spectrum as it is a nucleotide analog that competes for the active site of RdRp, a crucial enzyme in the life cycle of RNA viruses, inhibiting viral replication and transcription (221, 319, 320).
T446	91586-91792	Sentence	denotes	Elfiky (320) conducted an in silico study demonstrating that ribavirin and other antivirals such as sofosbuvir can strongly bind to coronavirus RdRp, preventing the transcription of new copies of viral RNA.
T447	91793-92003	Sentence	denotes	Only a few clinical studies have investigated the effect of ribavirin on COVID-19 patients, with the studies available generally focusing on the association of ribavirin and other therapeutic schemes (321–323).
T448	92004-92101	Sentence	denotes	Nevertheless, China’s government (324) has recommended the use of ribavirin in COVID-19 patients.
T449	92102-92193	Sentence	denotes	Remdesivir (RDV) is also among the several potential drugs tested for SARS-CoV-2 treatment.
T450	92194-92368	Sentence	denotes	Originally developed to treat Ebola virus infection, RDV is active against RNA viruses from different families, including Coronaviridae (e.g., SARS-CoV-1 and MERS-CoV) (325).
T451	92369-92446	Sentence	denotes	RDV showed an in vitro effective antiviral activity against SARS-CoV-2 (326).
T452	92447-92672	Sentence	denotes	Grein et al. (327) conducted a cohort study with 53 COVID-19 patients treated with RDV and found that 68% of them had improved oxygen-support class, whereas 57% of the patients receiving mechanical ventilation were extubated.
T453	92673-92823	Sentence	denotes	Overall mortality reached 13% over a median follow-up of 18 days, however, viral load data were not collected to confirm the antiviral effects of RDV.
T454	92824-93050	Sentence	denotes	The biggest issue with this study is that the authors did not include a group without RDV, which hampers the performance of comparative statistical analyses to prove whether the data found resulted from the treatment with RDV.
T455	93051-93281	Sentence	denotes	Another double-blind, randomized, placebo-controlled trial of intravenous RDV conducted in adults hospitalized with COVID-19 with evidence of lower respiratory tract involvement was performed in different parts of the world (328).
T456	93282-93502	Sentence	denotes	The study of Beigel and colleagues (328) enrolled 1,063 COVID19 pneumonia patients, 538 of whom were assigned to the treatment with RDV and 521 to a placebo, showed the effectiveness of RDV in treating COVID-19 patients.
T457	93503-93715	Sentence	denotes	The drug was superior to the placebo in reducing the recovery time in hospitalized COVID-19 patients and decreased the mortality rate in the RDV group, however, this result did not reach statistical significance.
T458	93716-93974	Sentence	denotes	Antionori et al. (329), analyzing patients with severe COVID-19 pneumonia in an intensive care unit (ICU) who were treated for 10 days with RDV, found that on the 28th day, 38.9% showed improvement, 16.7% were still on mechanical ventilation, and 44.4% died.
T459	93975-94155	Sentence	denotes	The data suggest that this treatment can benefit hospitalized patients who are not in the ICU, where the clinical result was better and adverse events are observed less frequently.
T460	94156-94374	Sentence	denotes	Alternatively, the randomized, double-blind, placebo-controlled, multicenter trial with 273 ill individuals performed by Wang et al. revealed that RDV intravenous administration was well-tolerated in COVID-19 patients.
T461	94375-94466	Sentence	denotes	However, the authors did not find any clinical improvement or significant antiviral effect.
T462	94467-94678	Sentence	denotes	Goldman et al. (330), in another phase 3 clinical trial on 397 patients with severe COVID-19 without mechanical ventilation support, also did not find differences between 5-day and 10-day courses of RDV therapy.
T463	94679-94886	Sentence	denotes	The RDV data currently available are still controversial, however, dozens of clinical studies are currently using this drug as an alternative treatment for COVID-19, possibly further elucidating its effects.
T464	94887-95063	Sentence	denotes	The efficiency of favipiravir, another anti-influenza RdRp inhibitor, has also been clinically assessed and was approved for COVID-19 treatment in China, March 2020 (331, 332).
T465	95064-95190	Sentence	denotes	An experimental study carried out with the VERO cell line showed that the drug has in vitro activity against SARS-CoV-2 (326).
T466	95191-95507	Sentence	denotes	Aiming at comparing the effects of favipiravir and lopinavir/ritonavir, Cai et al. (333) conducted an open, non-randomized, before-after controlled study with 80 patients and found that favipiravir favored viral clearance and improved chest CT, having caused fewer adverse effects than the lopinavir/ritonavir group.
T467	95508-95576	Sentence	denotes	Currently, 31 clinical trials using this medication are in progress.
T468	95577-95785	Sentence	denotes	Regarding antivirals, type I IFN is a group of cytokines comprising the α and β subtypes, among others, with an important role in antiviral immunity that interferes with viral replication, as discussed above.
T469	95786-96073	Sentence	denotes	Many studies have shown the protective effect of type I IFN associated with antiviral therapies for patients with SARS and MERS [reviewed by Sallard et al. (334)], which arouses the interest of the scientific community in type I IFN as a potential treatment against SARS-CoV-2 (334–337).
T470	96074-96226	Sentence	denotes	Despite their efficacy against SARS-CoV-2 (338, 339), the results of in vitro studies using IFN-α and -β to treat COVID-19 patients remain inconclusive.
T471	96227-96438	Sentence	denotes	Such uncertain nature of the results is associated with biases present in these studies, which include limited-size sample, heterogeneous experimental designs/clinical status, and the type of IFN isoform tested.
T472	96439-96633	Sentence	denotes	In addition, since COVID-19 treatments rarely involve monotherapy, it is difficult to assess whether the results derived from the tested IFN or the drugs used in combination (322, 323, 340–343).
T473	96634-96890	Sentence	denotes	It is also worth mentioning that, as discussed above, type I IFN appears to exacerbate inflammation in the progression to severe COVID-19; the timing of administration and subgroups targeted for treatment with type I IFN need to be considered with caution.
T474	96891-97247	Sentence	denotes	A recent retrospective multicenter cohort study of 446 Chinese patients with COVID-19 reported that among severe to critical COVID-19 patients, early administration (≤5 days after admission) of IFN-α2b decreased mortality in comparison with no admission of IFN-α2b, whereas no significant benefit was associated with IFN-α2b use in moderately ill patients.
T475	97248-97364	Sentence	denotes	However, late use of IFN-α2b increased mortality and delayed recovery of severe to critical COVID-19 patients (344).
T476	97365-97590	Sentence	denotes	Zhou et al. (341), investigated the isolated effect of IFN-α in a cohort study comparing 77 patients with moderate COVID-19 treated with nebulized IFN-α2b (5 mU b.i.d.), oral arbidol (200 mg t.i.d.), or a combination of both.
T477	97591-97872	Sentence	denotes	Although the study did not include a control group, the treatment with IFN-α2b, either containing arbidol or not, significantly reduced the duration of detectable virus in the upper respiratory tract and the circulating of inflammatory markers (IL-6 and C-reactive protein levels).
T478	97873-98202	Sentence	denotes	Still, in a retrospective multicenter cohort study with 141 mild COVID-19 patients by Xu et al. (342), the arbidol/IFN-α2b combination proved more effective in accelerating pneumonia recovery than IFN-α2b monotherapy, but this was not the case for viral clearance or reducing the length of hospital stay than IFN-α2b monotherapy.
T479	98203-98544	Sentence	denotes	Hung et al. (322) assessed the effect of IFN-β on COVID-19 patients and found that the triple combination of IFN-β1b, lopinavir/ritonavir, and ribavirin was safer and more effective than lopinavir/ritonavir alone at alleviating symptoms, shortening the duration of viral shedding and hospital stay in patients with mild to moderate COVID-19.
T480	98545-98674	Sentence	denotes	Similarly, an open randomized clinical trial was carried out by Danoudi-Monfared et al. (345), analyzing treatment with IFN-β-1a.
T481	98675-98915	Sentence	denotes	The IFN group of COVID-19 patients (n=42) received IFN β-1a in addition to the protocol medications (hydroxychloroquine plus lopinavir-ritonavir or atazanavir-ritonavir) while the control group (n=39) received only the protocol medications.
T482	98916-99043	Sentence	denotes	The IFN-β-1a-treated patients showed a significantly increased discharge rate on day 14 and decreased mortality within 28 days.
T483	99044-99152	Sentence	denotes	A better survival rate was also observed when patients received IFN- β-1a in the early stage of the disease.
T484	99153-99249	Sentence	denotes	The COVID-19 treatment guidelines of many countries already recommend the use of IFNs α/β (335).
T485	99250-99376	Sentence	denotes	Currently, all over the world, more than 20 clinical trials are using IFN-α and/or β alone or in association with other drugs.
T486	99378-99412	Sentence	denotes	Chloroquine and Hydroxychloroquine
T487	99413-99566	Sentence	denotes	Chloroquine and hydroxychloroquine have been used worldwide for more than 70 years, and they are part of the WHO model list of essential medicines (346).
T488	99567-99905	Sentence	denotes	They were synthesized specifically for the treatment and chemoprevention of malaria, but their immunomodulatory activity led these drugs to be used against autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, and other inflammatory rheumatic diseases; they also show broad-spectrum antiviral effects (347–349).
T489	99906-100092	Sentence	denotes	Regarding the chemical structure, hydroxychloroquine differs from chloroquine in the presence of a hydroxyl group at the end of the side chain: the N-ethyl substituent is β-hydroxylated.
T490	100093-100348	Sentence	denotes	Both drugs have similar pharmacokinetics, with rapid gastrointestinal absorption and renal elimination, but different clinical indications and toxic doses, in which hydroxychloroquine is less toxic and more clinically used in the malaria model (348, 350).
T491	100349-100477	Sentence	denotes	The action mechanism of these drugs has direct molecular effects on lysosomal activity, autophagy, and signaling pathways (347).
T492	100478-100676	Sentence	denotes	As antivirals, chloroquine is known to block SARS-CoV-1-infection by increasing endosomal pH required for virus entry, as well as interfering with the glycosylation of cellular receptors (351, 352).
T493	100677-100973	Sentence	denotes	The possible mechanism against SARS-CoV-2 is the inhibition of virus entry by altering the glycosylation of ACE2, reducing the binding efficiency between ACE2 in host cells and the S protein on the surface of the SARS-CoV-2, thus preventing the virus from binding to target cells (348, 351, 353).
T494	100974-101103	Sentence	denotes	In addition to a potent antiviral inhibition, the immunomodulatory activity of these drugs is well established in the literature.
T495	101104-101558	Sentence	denotes	Proposed effects of chloroquine on the immune system include increasing the export of soluble antigens into the cytosol of dendritic cells, the blocking of TLR7 and TLR9 signaling, thus reconstructing CD8+ cytotoxic viral response, and inhibiting and/or reducing the production of inflammatory cytokines like IL-1, IL-6, TNF, and IFN-α (347, 354–359), which has an important role in the immunopathogenesis of COVID-19, as previously reported in item 4.1.
T496	101559-101714	Sentence	denotes	In vitro studies on SARS-CoV-2 have demonstrated the low-dose action of these drugs, having found the lowest half-maximal effective concentrations (EC50s).
T497	101715-101821	Sentence	denotes	In addition, their association with azithromycin significantly inhibited viral replication (326, 360–362).
T498	101822-102074	Sentence	denotes	In humans, a study by Gao, Tian, and Yang (363) showed that patients treated with chloroquine phosphate had inhibited exacerbation of pneumonia, improving lung imaging findings, promoting a virus-negative conversion, and shortening the COVID-19 course.
T499	102075-102317	Sentence	denotes	The association of hydroxychloroquine with other drugs is also suggested, with emphasis on studies using azithromycin, a broad-spectrum macrolide antibiotic primarily used to treat respiratory, enteric, and genitourinary bacterial infections.
T500	102318-102467	Sentence	denotes	Despite not yet being approved for antiviral therapy, it has been studied in vitro and in clinical trials for activity against several viruses (364).

T1

0-20

Sentence

denotes

A 21st Century Evil:

T2

21-66

Sentence

denotes

Immunopathology and New Therapies of COVID-19

T3

68-76

Sentence

denotes

Abstract

T4

77-204

Sentence

denotes

Coronavirus Disease 2019 (COVID-19) has been classified as a global threat, affecting millions of people and killing thousands.

T5

205-321

Sentence

denotes

It is caused by the SARS-CoV-2 virus, which emerged at the end of 2019 in Wuhan, China, quickly spreading worldwide.

T6

322-521

Sentence

denotes

COVID-19 is a disease with symptoms that range from fever and breathing difficulty to acute respiratory distress and death, critically affecting older patients and people with previous comorbidities.

T7

522-683

Sentence

denotes

SARS-CoV-2 uses the angiotensin-converting enzyme 2 (ACE2) receptor and mainly spreads through the respiratory tract, which it then uses to reach several organs.

T8

684-1020

Sentence

denotes

The immune system of infected patients has been demonstrated to suffer important alterations, such as lymphopenia, exhausted lymphocytes, excessive amounts of inflammatory monocytes and macrophages, especially in the lungs, and cytokine storms, which may contribute to its severity and difficulty of establishing an effective treatment.

T9

1021-1218

Sentence

denotes

Even though no specific treatment is currently available, several studies have been investigating potential therapeutic strategies, including the use of previously approved drugs and immunotherapy.

T10

1219-1497

Sentence

denotes

In this context, this review addresses the interaction between SARS-CoV-2 and the patient’s host immune system during infection, in addition to discussing the main immunopathological mechanisms involved in the development of the disease and potential new therapeutic approaches.

T11

1499-1511

Sentence

denotes

Introduction

T12

1512-1808

Sentence

denotes

The ongoing outbreak of Coronavirus Disease 2019 (COVID-19) has been classified as a threat of international concern and a public health emergency, having affected almost 30 million people and killed more than 900,000 around the world so far, according to the World Health Organization (WHO) (1).

T13

1809-2053

Sentence

denotes

The etiologic agent of this pandemic is Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the third coronavirus to have emerged as a public health issue and to cause an outbreak in the human population over the past two decades (2).

T14

2054-2238

Sentence

denotes

This is the nomenclature referred to in this paper (3), which is derived from its similarity to the SARS-CoV virus that caused the outbreak in 2003, which is now known as “SARS-CoV-1”.

T15

2239-2396

Sentence

denotes

Coronaviruses belong to a group of single-stranded RNA viruses and are regarded as one of the main types of viruses that affect the human respiratory system.

T16

2397-2603

Sentence

denotes

SARS-CoV-2 is the seventh coronavirus known to have infected humans; SARS-CoV-1, MERS-CoV, and SARS-CoV-2 can cause serious illness, whereas HKU1, NL63, OC43, and 229E are associated with mild symptoms (4).

T17

2604-2731

Sentence

denotes

SARS-CoV-2 emerged at the end of 2019 in Wuhan, China, with reports of infection in humans and quickly spread around the world.

T18

2732-3030

Sentence

denotes

The virus causes COVID-19, which consists of a spectrum of clinical syndromes, ranging from fever and breathing difficulty to acute respiratory distress and death, critically affecting older patients and people with comorbidities, including heart disease, diabetes, and other health conditions (5).

T19

3031-3305

Sentence

denotes

SARS-CoV-2 infection can be subdivided into the following three general phases: the spread of the virus in the body – known as viremia –; the acute phase with the appearance of clinical signs; and the stage of convalescence, which progresses either to recovery or death (6).

T20

3306-3500

Sentence

denotes

The pathological mechanism, so far unraveled, has proposed the role of the host’s angiotensin-converting enzyme 2 (ACE2) and its affinity with viral receptors, especially the glycoprotein spike.

T21

3501-3648

Sentence

denotes

The high affinity between these molecules facilitates viral dissemination in the body and allows the infectious condition to be established (7, 8).

T22

3649-4002

Sentence

denotes

The immune systems of infected patients have demonstrated important changes, such as lower effector T cells, loss of the antiviral capacity of CD8+ T lymphocytes and natural killer cells (NK), and the excessive release of inflammatory mediators, which may contribute to the disease severity and difficulty in establishing an effective treatment (9, 10).

T23

4003-4305

Sentence

denotes

This is a highly transmissible virus, whose contagion usually occurs through droplets released by infected individuals when they cough, sneeze, or talk, directly contaminating other people by reaching mucous membranes on the face or contaminating the environment, later acting as a transmission source.

T24

4306-4475

Sentence

denotes

Until now, we have relied on quarantine, social isolation, and infection-control measures to prevent disease spread, as well as supportive care for infected individuals.

T25

4476-4597

Sentence

denotes

A specific antiviral agent to treat the infected individuals and decrease viral transmission (11, 12) is yet to be found.

T26

4598-4823

Sentence

denotes

Several research groups around the world have been working on possible therapeutic strategies against SARS-CoV-2 by applying commercially available drugs, hoping to accelerate the discovery of an effective treatment (13, 14).

T27

4824-5039

Sentence

denotes

Since many studies are made available online on a daily basis, both in journals and in preprint servers, for this review we used only studies already published and peer-reviewed in order to avoid biased information.

T28

5040-5224

Sentence

denotes

In this scenario, understanding the virus dynamics and host response is essential to formulate strategies for antiviral treatment, vaccination, and epidemiological control of COVID-19.

T29

5225-5456

Sentence

denotes

Thus, our goal is to review SARS-CoV-2’s interaction with the patient’s host immune system during infection and discuss the main immunopathological mechanisms involved in COVID-19, as well as potential new therapeutical approaches.

T30

5458-5470

Sentence

denotes

Coronavirus:

T31

5471-5482

Sentence

denotes

An Overview

T32

5483-5678

Sentence

denotes

Coronaviruses (CoVs) consist of a group of enveloped, non-segmented, positive-sense single-stranded RNA viruses from the order Nidovirales, family Coronaviridae, and subfamily Orthocoronavirinae.

T33

5679-5849

Sentence

denotes

Coronaviruses have the largest genome of all RNA viruses, encoding viral proteins involved in transcribing viral RNA, replication, structure, and accessory proteins (15).

T34

5850-6133

Sentence

denotes

The virus has four main proteins – spike, envelope, membrane, and nucleocapsid (S, E, M, and N, respectively) – important for the virus to enter and replicate in the host cell (16), also representing the main molecules used for diagnosis, antiviral treatment, and potential vaccines.

T35

6134-6249

Sentence

denotes

According to antigenic and genetic criteria, CoVs are classified into three groups: α-CoVs, β-CoVs and γ-CoVs (17).

T36

6250-6417

Sentence

denotes

Coronaviruses of human infection (hCoVs) are detected in both α-CoVs (hCoV-229E and NL63) and β-CoVs (MERS-CoV, hCoV-OC43, hCoV-HKU1, SARS-CoV-1, and SARS-CoV-2) (18).

T37

6418-6621

Sentence

denotes

In addition to infecting humans, α-CoVs and β-CoVs can infect several species of mammals, including bats and pigs, while γ-CoVs infects birds, wild cats, pigs, and some species of marine mammals (19–22).

T38

6622-6772

Sentence

denotes

CoVs have a high potential of jumping between species and their genome is characterized by high-frequency recombination and a high mutation rate (23).

T39

6773-7002

Sentence

denotes

hCoVs are responsible for the common cold and other respiratory pathologies with different degrees of severity, especially in babies, the elderly, and immunocompromised patients, characterized by human-to-human transmission (24).

T40

7003-7235

Sentence

denotes

Coronavirus severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) (25–27) are caused by human β-CoVs and represent a serious illness with a case-fatality ratio of 9 - 10% and 35%, respectively (8, 28).

T41

7236-7493

Sentence

denotes

In contrast, according to data provided by the WHO, COVID-19 caused by SARS-CoV-2 shows an estimated lethality of ~5% of reported cases (data reported until July 2020) (29), reaching rates of up to 15% among elderly patients and patients with comorbidities.

T42

7494-7694

Sentence

denotes

Despite the lower case-fatality rate, the high viral transmissibility of SARS-CoV-2 generates an overall number of cases that far outweighs SARS or MERS for spreading more easily among people (5, 28).

T43

7695-7870

Sentence

denotes

The first report of a COVID-19 case in Wuhan, China, occurred in December 2019, and in February the WHO declared the matter a public health emergency of international concern.

T44

7871-8047

Sentence

denotes

Until now (September 2020), reports of COVID-19 account for almost 30 million cases and more than 900 thousand deaths in more than 220 countries, territories, or areas (1, 29).

T45

8048-8218

Sentence

denotes

Imperial College, UK (30) proposed a mathematical model whose prospects indicate 7 billion infections and 40 million deaths in 2020 in the absence of mitigation measures.

T46

8219-8619

Sentence

denotes

Both SARS-CoV and MERS-CoV were initially believed to have resulted from a zoonotic spread from a bat population (31). α-CoVs and β-CoVs are believed to have evolved over thousands of years, restricted to bats and intermediate mammalian hosts (civet cats for SARS-CoV-1 and dromedary camels for MERS-CoV), which probably contributed to the zoonotic transmission of the new coronavirus to humans (32).

T47

8620-8805

Sentence

denotes

Regarding SARS-CoV-2 transmission, several works have demonstrated that coronaviruses found in pangolins (Manis javanica) and SARS-CoV-2 share a genomic similarity of approximately 91%.

T48

8806-9017

Sentence

denotes

The presence of the virus in samples of pulmonary fibrosis in pangolins found around the COVID-19 outbreak suggests that these animals were the hosts responsible for spreading the virus among humans (4, 21, 33).

T49

9018-9244

Sentence

denotes

In contrast, some researchers claim that SARS-CoV-2 did not come directly from pangolins since, despite their similarity, the viruses found in these animals do not have the essential tools needed to infect human cells (4, 34).

T50

9245-9439

Sentence

denotes

Thus, the possibility of other animals, such as ferrets and snakes, acting as intermediate hosts for SARS-CoV-2 and being responsible for zoonotic transmission is still under consideration (35).

T51

9440-9659

Sentence

denotes

Since SARS-CoV-2 genomes’ information is still scarce and genomes of other coronaviruses closely related to this virus have limited availability (36), the evolutionary origin of SARS-CoV-2 is yet to be fully understood.

T52

9660-9851

Sentence

denotes

So far, it is known that, compared with other β-CoVs, SARS-CoV-2 shows 50, 79, and 88 - 96% of genome similarity with MERS-CoV, SARS-CoV-1, and the bat SARS-like virus, respectively (37, 38).

T53

9852-10054

Sentence

denotes

The genomic changes of SARS-CoV-2 appear in both non-structural and structural proteins – notably in proteins S, M, and N – affecting viral multiplication, encapsulation, tropism, and transmission (39).

T54

10055-10584

Sentence

denotes

Two important characteristics were described in the genome of SARS-CoV-2 that lead to alterations in the S protein: (i) receptor-binding domain (RBD), which is the most variable part of the viral genome, appears to be optimized for binding to the human ACE2 receptor, and (ii) presence of a polybasic (furin) cleavage site at the S1 and S2 boundary, via the insertion of twelve nucleotides, which allows effective cleavage by furin and other proteases and has a role in determining viral tropism, infectivity, and host range (4).

T55

10585-10669

Sentence

denotes

Such genomic changes also affected the recognition of these viruses by immune cells.

T56

10670-10898

Sentence

denotes

Baruah and Bose (40) demonstrated that Sars-CoV-2 has specific regions for B cell and cytotoxic T cell glycoproteins recognition, which does not coincide with those found in bat-derived CoV, SARS-CoV-1, or MERS-CoV ( Figure 1 ).

T57

10899-11055

Sentence

denotes

Such distinguished interaction of cells and viruses can promote unusual immunomodulation or immune responses that contribute to the severity of the disease.

T58

11056-11150

Sentence

denotes

All aspects of immunomodulation and immune evasion will be discussed in the subsequent topics.

T59

11151-11214

Sentence

denotes

Figure 1 Genetic evolution of SARS-CoV-2 and its consequences.

T60

11215-11422

Sentence

denotes

Compared with other β-CoVs, SARS-CoV-2 has similarities of 50, 79, and 88 - 96% to MERS-CoV, SARS-CoV-1, and bat SARS-like-CoV genome, respectively, with 91% similarity with SARS-like CoV found in pangolins.

T61

11423-11684

Sentence

denotes

The virus resulted from mutations that caused changes in important proteins for its virulence; notably, the spike, matrix, envelope, and nucleocapsid proteins caused alterations in host cell interactions, which culminated in a new aggressive disease (COVID-19).

T62

11685-11746

Sentence

denotes

RBD (receptor binding domain), S1 (subunit 1) S2 (subunit 2).

T63

11748-11774

Sentence

denotes

Pathogenesis of SARS-CoV-2

T64

11776-11803

Sentence

denotes

Viral Entry and Replication

T65

11804-11901

Sentence

denotes

A virus starts its infection by binding viral particles to the host’s surface cellular receptors.

T66

11902-12036

Sentence

denotes

The recognition of cellular receptors is the first step towards viral entry into host cells, in addition to determining their tropism.

T67

12037-12255

Sentence

denotes

The ability to engage receptors and the affinity of binding can define the efficiency of a virus when infecting an organism, while the amount of these receptors present in cells can indicate the intensity of infection.

T68

12256-12473

Sentence

denotes

Viruses that have a high capacity to bind to more conserved receptors are more likely to migrate between different species, which may also reflect the susceptibility of hosts and increase viral pathogenicity (40, 41).

T69

12474-12634

Sentence

denotes

As well as the other β-CoVs, the SARS-CoV-2 genome has a long open reading frame (ORF) 1ab region, followed by regions that encode S, E, M, and N proteins (42).

T70

12635-12751

Sentence

denotes

Homotrimers of S proteins are present on the viral surface and are responsible for attaching to host receptors (43).

T71

12752-12878

Sentence

denotes

The E protein plays a role in the assembly and release of the virus, in addition to being involved in viral pathogenesis (44).

T72

12879-13017

Sentence

denotes

The M protein has three transmembrane domains and shapes the virions, promotes membrane curvature, and binds to the nucleocapsid (45, 46).

T73

13018-13243

Sentence

denotes

Lastly, the N protein contains two domains that can bind to the RNA virus and is also an antagonist of interferon (IFN) and a virally-encoded repressor of RNA interference, which appears to benefit viral replication (47, 48).

T74

13244-13402

Sentence

denotes

The S protein of SARS-CoV-2 plays an important role in determining tropism for being able to activate receptors in host cells and induce the invasion process.

T75

13403-13555

Sentence

denotes

This protein is cleaved by proteases into the S1 and S2 subunits, which are responsible for receptor recognition and membrane fusion, respectively (39).

T76

13556-13914

Sentence

denotes

Several articles have experimentally demonstrated that the RDB in the S protein, especially in the S1 region, binds to the peptidase domain (PD) of the ACE2 receptor, which is part of the renin-angiotensin-aldosterone system, an enzyme present in the plasma membrane mainly of pulmonary, endothelial, cardiac, renal, and intestinal cells (7, 22, 38, 49, 50).

T77

13915-14068

Sentence

denotes

The S2 subunit is known to contain the fusion peptide, in which it is inserted into the host cell membrane to trigger the fusogenic reaction (7, 51, 52).

T78

14069-14207

Sentence

denotes

The interaction of the S glycoprotein with the CD26 receptor and CD209L (39, 53, 54) is also suggested, however, its role remains unclear.

T79

14208-14453

Sentence

denotes

The binding of the virus to the ACE2 receptor causes stabilization of the RBD in the standing-up state and triggers conformational changes in the S complex, resulting in the release of the S1 subunit and activation of S2 fusogenic activity (55).

T80

14454-14616

Sentence

denotes

The S2 subunit contains an N-terminal fusion peptide (FP), heptad repeat 1 (HR1), heptad repeat 2 (HR2), a transmembrane region (TM), and a cytoplasmic tail (CT).

T81

14617-14889

Sentence

denotes

During the fusion process, the FP portion is exposed and inserts into the membrane of the target cell, leading to a modification in S2, then the HR1 and HR2 come together to form a six-helical bundle (6-HR) structure, which allows the fusion between the membranes (55–57).

T82

14890-15031

Sentence

denotes

Therefore, CoVs need to elicit exogenous proteases to perform modifications of their binding receptors necessary for the connection to occur.

T83

15032-15260

Sentence

denotes

SARS-CoV-2 has its own furin-like proteases, which play a role in these changes, providing it with an evolutionary advantage in relation to other coronaviruses and improving the process of cell infection and viral dissemination.

T84

15261-15386

Sentence

denotes

Concerning exogenous proteins, SARS-CoV-2 can also use host proteins to prepare its S glycoprotein for receptor binding (49).

T85

15387-15601

Sentence

denotes

Hoffman et al. (7) demonstrated in vitro that strains of the virus isolated from COVID-19 patients can use both the host protease transmembrane serine protease 2 (TMPRSS2) and cathepsins B/L to prime the S protein.

T86

15602-15801

Sentence

denotes

The entry mechanism of CoVs in host cells depends on the strain and species considered, as well as tissue and cell-type specificities (receptor/protease availability and local microenvironment) (58).

T87

15802-15996

Sentence

denotes

After binding to a target host cell via interactions with cellular receptors, viral entry of CoVs can occur in two manners: (i) the endosomal pathway and (ii) the non-endosomal pathway (59, 60).

T88

15997-16231

Sentence

denotes

The endosomal pathway is facilitated by low pH and pH-dependent endosomal cysteine protease cathepsins, helping to overcome the energetically unfavorable membrane fusion reaction and facilitating endosomal cell entry of CoVs (61, 62).

T89

16232-16349

Sentence

denotes

The non-endosomal pathway is dependent on TMPRSS2, which allows the activation of the S protein for viral entry (63).

T90

16350-16619

Sentence

denotes

Once the viral genome is inside the host cell cytoplasm, translation of viral RNA produces RNA-dependent RNA polymerase (RdRp), which uses viral RNA as a template to generate virus-specific mRNAs (subgenomic mRNAs) from subgenomic negative-strand intermediates (64–66).

T91

16620-16723

Sentence

denotes

Translation of subgenomic mRNAs leads to the production of structural and nonstructural viral proteins.

T92

16724-16935

Sentence

denotes

Thus, after their formation, structural proteins are inserted into the membrane of the endoplasmic reticulum or Golgi, and viral particles germinate into the endoplasmic reticulum-Golgi intermediate compartment.

T93

16936-17053

Sentence

denotes

Finally, the vesicles containing the virus particles fuse with the plasma membrane to release the virus (65, 67, 68).

T94

17054-17124

Sentence

denotes

Another possible mechanism for CoV entry may occur through antibodies.

T95

17125-17487

Sentence

denotes

During the binding of the virus-antibody complex, simultaneous binding of viral proteins to antigen-binding fragment (Fab) regions of immunoglobulin G (IgG) and of the fragment crystallizable (Fc) portion of the antibody to Fc gamma receptors (FcγRs) that are expressed by immune cells occurs, promoting viral entry without the use of the ACE2 receptor (69, 70).

T96

17488-17765

Sentence

denotes

However, the presence of viral RNA in the endosomes signals via the Toll-like 3 (TLR3), TLR7, or TLR8 receptor, activating the host cell to release pro-inflammatory cytokines that lead to exacerbated tissue damage, a phenomenon called antibody-dependent enhancement (ADE) (71).

T97

17766-18047

Sentence

denotes

Such a mechanism for SARS‐CoV‐2 is not yet fully understood, but previous coronavirus infections or SARS‐CoV‐2 convalescent patients with different SARS‐CoV‐2 strains could promote ADE, as experimentally shown for antibodies against the MERS‐CoV or SARS‐CoV-1 spike S protein (72).

T98

18048-18271

Sentence

denotes

Several studies have shown that sera administration induced increased SARS-CoV-1 viral entry into cells that express the Fc receptor, and serum-dependent SARS-CoV-1 entry does not pass through the endosome pathway (73, 74).

T99

18272-18553

Sentence

denotes

This mechanism was characterized by Yip et al. (75) and Wang et al. (76), who revealed that the anti-Spike protein antibodies were in fact responsible for the infection of immune cells, and the enhancement of the infection can be improved by increasing the dilutions of antibodies.

T100

18554-18794

Sentence

denotes

In relation to MERS-CoV, a similar mechanism has been demonstrated, since neutralizing monoclonal antibodies (nAb) are able to bind to the spike-S surface protein, allowing conformational changes and being subject to proteolytic activation.

T101

18795-18937

Sentence

denotes

Meanwhile, nAb binds to the cell surface IgG Fc receptor, guiding viral entry through canonical pathways dependent on the viral receptor (77).

T102

18938-19219

Sentence

denotes

Recent studies with COVID-19 patients reported that there was a strong IgG antibody response against the nucleocapsid protein and a delay in eliminating the virus, leading to an increase in the severity of the infection and contributing to the hypothesis of ADE of SARS-CoV-2 (78).

T103

19220-19463

Sentence

denotes

In view of this, the geographic discrepancy in pathogenesis can be explained, since individuals who have experienced previous exposure to coronaviruses are experiencing the effects of ADE due to the heterogeneity of the antigenic epitope (79).

T104

19464-19642

Sentence

denotes

In addition, the potential of human antibodies for vaccination will depend on whether antibodies play a role in disease progression or in protecting against viral infection (70).

T105

19643-19903

Sentence

denotes

As an evasion mechanism, CoVs use a glycan conformational shield to prevent the recognition of the virus by the immune system, and, for this reason, S glycoproteins are found in trimers form and require structural alterations to engage with cellular receptors.

T106

19904-20142

Sentence

denotes

In most of the hCoVs described, these S trimers are found in a naturally closed conformation, however, this mechanism also causes a delay in the process of cell infection due to the need for major changes in the glycoprotein conformation.

T107

20143-20403

Sentence

denotes

It was described that, in SARS-CoV-2, the S trimers seem to exist in a partially open state, which prevents recognition by the immune system, but accelerates the initiation of conformational changes in the receptor and the processes of binding and fusion (49).

T108

20405-20426

Sentence

denotes

Pathogenic Mechanisms

T109

20427-20581

Sentence

denotes

Considering the similarity between SARS-CoV-1 and SARS-CoV-2, it is likely that their biochemical interactions and pathogenesis are also similar (80, 81).

T110

20582-20737

Sentence

denotes

Once SARS-CoV-2 was reported to use ACE2 to enter host cells, it is suggested that the virus may target a cell spectrum similar to SARS-CoV-1 (38, 82, 83).

T111

20738-20926

Sentence

denotes

SARS-CoV-1 is known to mainly infect macrophages and pneumocytes in the lungs, as well as other extrapulmonary tissues that express ACE2, which can also be expected for SARS-CoV-2 (82–84).

T112

20927-21206

Sentence

denotes

However, the affinity of SARS-CoV-2 to ACE2 is 10–20-fold higher than that of SARS-CoV-1, which could explain its higher transmissibility and demonstrate that it can bind more efficiently to host cells, having a robust infection in ACE2+ cells in the upper respiratory tract (7).

T113

21207-21445

Sentence

denotes

ACE2 is an enzyme belonging to the renin-angiotensin system, located on the cell surface of type II alveolar epithelial cells in the lungs and cells of other tissues, and plays a crucial role in controlling vasoactive effects in the body.

T114

21446-21598

Sentence

denotes

Despite their similarities, ACE and ACE2 have different substrate specificities with distinct functionalities that perform opposite actions in the body.

T115

21599-21794

Sentence

denotes

In brief, ACE cleaves angiotensin I to generate angiotensin II, the peptide that binds and activates angiotensin type 1 receptor (AT1R) to constrict blood vessels, thereby raising blood pressure.

T116

21795-21978

Sentence

denotes

In contrast, ACE2 inactivates angiotensin II (Ang-II) while generating angiotensin 1-7 (Ang-1-7), a potent heptapeptide that acts in vasodilation and attenuation of inflammation (85).

T117

21979-22247

Sentence

denotes

Therefore, considering that SARS-CoV-2 uses ACE2 to enter cells, the main hypothesis of pulmonary pathology is that the increased activity of ACE (Ang-II) over ACE2 (Ang-1-7) may cause acute lung injury since the binding of the S protein to ACE2 leads to its blockage.

T118

22248-22475

Sentence

denotes

Thus, the suppression of ACE2 occurs due to the increased internalization and release of ACE2 from the cell surface, which leads to a decrease in tissue ACE2 and the generation of Ang-1-7, and consequently higher Ang-II levels.

T119

22476-22687

Sentence

denotes

Because of this, as shown in an experimental SARS-CoV-1 model, this process can drive an Ang II-AT1R-mediated inflammatory response in the lungs and potentially induce direct parenchymal injury (67, 80, 86, 87).

T120

22688-22981

Sentence

denotes

Another hypothesis states that SARS-CoV-2 infection blocks ACE2 function when binding to host cells, inhibiting its role of cleaving bradykinin and, as a consequence, bradykinin accumulates in the lung, promoting pulmonary edemas due to vasodilator activity and consequent respiratory failure.

T121

22982-23161

Sentence

denotes

The increased bradykinin activation in the pulmonary endothelium can also induce neutrophil migration, enhancing tissue damage caused by the respiratory burst of these cells (88).

T122

23162-23279

Sentence

denotes

ACE2 is also highly expressed and co-expressed with TMPRSS2 in nasal epithelial cells, chalices, and hair cells (89).

T123

23280-23628

Sentence

denotes

This finding is in accordance with the high detection of viral RNA in the upper airways present in nasal swabs and throats of both symptomatic and asymptomatic patients, demonstrating that the nasal epithelium is an important site for the infection to initiate and can represent an essential reservoir for viral dissemination and transmission (38).

T124

23629-23918

Sentence

denotes

Although the virus mainly affects the lungs, there are reports that SARS-CoV-2 also has organotropism, accompanied by dysfunction, in multiple organs, including the kidneys, liver, heart, and brain, which can influence the course of the disease and possibly worsen pre-existing conditions.

T125

23919-24100

Sentence

denotes

It has been reported that ACE2, TMPRSS2, and cathepsin L can be expressed on glial cells and neurons, cardiomyocytes, liver cells, bile duct cells, and renal tubular cells (90, 91).

T126

24101-24341

Sentence

denotes

Evidence indicates that SARS-CoV-2 “neuroinvasion” can establish a direct entry along the olfactory nerve, mainly through the nasal olfactory epithelium, which expresses ACE2 and TMPRSS2, allowing access to the central nervous system (CNS).

T127

24342-24656

Sentence

denotes

The spread of the virus through the hematogenous or transsynaptic pathway has also been widely discussed, however, it is known that the different levels of neurotropism and neurovirulence in patients with COVID-19 can be explained by a combination of viral factors and their interaction with the host (41, 92, 93).

T128

24657-24902

Sentence

denotes

Regarding the evolution of infected individuals, aging, comorbidities, and weakening of the immune system are factors that generally cause the infection to intensify at the acute phase, leading to the manifestation of more severe conditions (6).

T129

24903-25146

Sentence

denotes

Thus, according to epidemiological studies, it is known that patients with chronic conditions, such as hypertension, diabetes, and chronic obstructive pulmonary disease (COPD), are more likely to develop a critical form of the disease (94–96).

T130

25147-25346

Sentence

denotes

The risk of applying medication commonly used in hypertension treatments to COVID-19 patients (97, 98) has raised different hypotheses over the issue of invoking a higher expression of ACE2 (99–101).

T131

25347-25823

Sentence

denotes

A systematic review assessing the clinical outcomes for SARS-CoV-2-infected individuals regarding treatment using angiotensin-converting enzyme inhibitors (ACEIs) or angiotensin receptor blockers (ARBs) concluded that these types of drugs have no deleterious effects and should continue to be used in COVID-19 patients (102), reinforcing the recommendations of several medical societies, including the American Heart Association (103) and European Society of Cardiology (104).

T132

25824-26017

Sentence

denotes

Respiratory diseases, such as COPD and asthma, cause a reduced lung function and greater susceptibility to lung inflammation, and are expected to show a potentially critical course of COVID-19.

T133

26018-26386

Sentence

denotes

COPD patients are already considered more susceptible to the development of pneumonia based on the clinical characteristics exhibited, such as lung structural damage, alterations in local/systemic inflammatory response, impaired host immunity, microbiome imbalance, persistent mucus production, and the presence of potentially pathogenic bacteria in the airways (105).

T134

26387-26527

Sentence

denotes

Additionally, in the scenario of COVID-19, smokers and individuals with COPD have shown to have increased airway expressions of ACE-2 (106).

T135

26528-26795

Sentence

denotes

It is still worth mentioning that patients who have this type of disorder often use corticosteroid immune-suppressing drugs, whose effect of reducing the immunity to respiratory infections may represent another contributing factor to a higher risk of infection (107).

T136

26797-26830

Sentence

denotes

Clinical and Radiological Changes

T137

26831-27070

Sentence

denotes

Most COVID-19 patients exhibit mild to moderate symptoms, but approximately 15% progress to critical pneumonia and 5% eventually develop acute respiratory distress syndrome (ARDS), septic shock, multiple organ failure, and death (26, 108).

T138

27071-27230

Sentence

denotes

Once the infection is installed, the spectrum of clinical presentations has been reported to range from asymptomatic infection to critical respiratory failure.

T139

27231-27327

Sentence

denotes

According to the severity of symptoms, patients can be classified as mild, severe, and critical.

T140

27328-27578

Sentence

denotes

In general, the most commonly reported symptoms are fever, cough, myalgia, fatigue, pneumonia, dyspnea, as well as the loss of smell and taste, whereas less common reported symptoms include headache, diarrhea, hemoptysis, and a runny nose (108, 109).

T141

27579-27743

Sentence

denotes

Most critically ill patients present progressive respiratory failure due to alveolar damage caused by hyper inflammation, which can result in lethal pneumonia (26).

T142

27744-27973

Sentence

denotes

A retrospective study conducted by Liu et al. (110) demonstrated that older patients with SARS-CoV-2 showed higher pneumonia severity index scores and had a higher chance of multiple lobe involvement compared with young patients.

T143

27974-28078

Sentence

denotes

Elderly adults are more susceptible to SARS-CoV-2 and have a high risk of morbidity and mortality (111).

T144

28079-28229

Sentence

denotes

This can be explained by factors such as physiological changes and multiple age-related comorbidities, in addition to associated polymedication (112).

T145

28230-28388

Sentence

denotes

Regarding the potential involvement of COVID-19 in the CNS, studies have investigated the neurological changes developed throughout the course of the disease.

T146

28389-28532

Sentence

denotes

Nonspecific symptoms (dizziness, headache, and seizure) and specific symptoms (loss of smell or taste and stroke) were described (91, 113–115).

T147

28533-28667

Sentence

denotes

Epidemiological studies have reported that some patients infected with SARS‐CoV‐2 did report headaches (8%), nausea, or vomiting (1%).

T148

28668-28887

Sentence

denotes

A more recent study investigating 214 COVID‐19 patients found that about 88% of critically ill patients displayed neurologic manifestations, including acute cerebrovascular diseases and impaired consciousness (26, 116).

T149

28888-29122

Sentence

denotes

Among patients diagnosed with SARS-CoV-2, it has been reported that renal dysfunction is characterized by high levels of blood urea nitrogen, creatinine, uric acid, and D-dimer, associated with proteinuria and hematuria (90, 117–119).

T150

29123-29276

Sentence

denotes

Recent studies have reported an incidence between 3-9% of acute kidney injury in COVID-19 patients, demonstrating renal abnormalities (94, 96, 111, 120).

T151

29277-29573

Sentence

denotes

Cardiovascular complications are also associated with COVID-19 infection, including myocardial injury, myocarditis, acute myocardial infarction, heart failure, dysrhythmias, and venous thromboembolic events, being significant contributors to the mortality associated with this disease (121, 122).

T152

29574-29970

Sentence

denotes

Several studies found that CoVs can also affect other body regions, such as the gastrointestinal tract and ocular tissues (123, 124); some of them specifically investigated changes in the gastrointestinal tract and identified the presence of SARS-CoV-2 RNA in samples of anal/rectal swabs and feces of infected patients, establishing that the virus could be transmitted orally or fecally as well.

T153

29971-30319

Sentence

denotes

Additionally, symptoms such as diarrhea, vomiting, and intestinal pain (125) have also been reported for SARS-CoV-2-positive patients, which can be associated with the expression of ACE2 in gastrointestinal epithelial cells, present especially in the small and large intestines, contributing to viral infection and replication in these cells (126).

T154

30320-30500

Sentence

denotes

Regarding ocular tissues, some studies have also identified the manifestation of conjunctivitis in patients with COVID-19 (<1%) (96), however, it is an underestimated number (127).

T155

30501-30822

Sentence

denotes

Currently, it is still unclear how SARS-CoV-2 can cause conjunctivitis, but theories include: (i) conjunctiva can be a direct inoculation site for the virus, (ii) the virus can reach the upper respiratory tract through the nasolacrimal duct, or (iii) infection can occur via hematogenous through the lacrimal gland (123).

T156

30823-31046

Sentence

denotes

Histologically, biopsy samples of lungs reveal evident desquamation and hyaline membrane formation of pneumocytes, in addition to bilateral diffused alveolar damages along with cellular fibromyxoid exudate, indicating ARDS.

T157

31047-31237

Sentence

denotes

In addition, the cytopathic effects found include multinucleated syncytial cells, increased atypical pneumocytes, and the presence of inflammatory infiltrates of mononuclear cells (26, 108).

T158

31238-31373

Sentence

denotes

More recently, reports on COVID-19 have included the occurrence of coagulation abnormalities in most critically ill patients (128–131).

T159

31374-31598

Sentence

denotes

Tang et al. (132) reported the occurrence of disseminated intravascular coagulation in 71.4% of non-surviving COVID-19 patients and in only 0.6% of surviving patients, suggesting a high frequency in severe COVID-19 patients.

T160

31599-31829

Sentence

denotes

Autopsies performed on patients with COVID-19 also demonstrated small fibrinous thrombi in pulmonary arterioles with endothelial tumefaction, the presence of megakaryocytes, and indications of coagulation cascade activation (133).

T161

31830-32275

Sentence

denotes

Although it is important to consider the direct procoagulant properties of SARS-CoV-2, the combination of immobility, systemic inflammation, platelet activation, endothelial dysfunction, and stasis of blood flow can lead to thrombotic complications that mimic systemic coagulopathies associated with severe infections, such as sepsis-induced coagulopathy (SIC), disseminated intravascular coagulation (DIC), and thrombotic microangiopathy (130).

T162

32276-32568

Sentence

denotes

However, COVID-19 has some distinct features that may establish a new category of coagulopathy, denominated COVID-19 associated coagulopathy (CAC), whose main markers are higher D-dimer concentration and fibrinogen levels, a relatively lower platelet count, and longer prothrombin time (129).

T163

32569-32643

Sentence

denotes

In COVID-19 patients, CAC has been associated with higher mortality (131).

T164

32644-32975

Sentence

denotes

Chest computed tomography (CT) in patients with COVID-19 has commonly demonstrated multifocal “ground-glass” opacity (GGO) in the lungs, which can occur concurrently with consolidation in posterior and peripheral areas, suggesting a pneumonia pattern in the organization of lung injury and indicating disease progression (134–136).

T165

32976-33217

Sentence

denotes

Another important manifestation found through chest CTs is reticular pattern formation with interlobular septal thickening, which might be associated with interstitial lymphocyte infiltration and determine the disease course (108, 137, 138).

T166

33218-33691

Sentence

denotes

CT has highlighted many other alterations, including the “crazy-paving” pattern, which may result from the alveolar edema and interstitial inflammation in acute lung injury, and air bronchogram with a pattern of air-filled (low-attenuation) bronchi, but with gelatinous mucus and several airway changes, such as bronchiectasis and bronchial wall thickening resulting from the destruction of bronchial wall structure, proliferation of fibrous tissue, and fibrosis (137–140).

T167

33693-33727

Sentence

denotes

Immune Response Against SARS-CoV-2

T168

33729-33743

Sentence

denotes

Cytokine Storm

T169

33744-34119

Sentence

denotes

Antiviral immune response is usually coordinated by IFN-type cytokines that activate cells and intensify the response against these invading agents, triggered by the recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs), such as toll-like receptors (TLR), fundamental for pathogen recognition and activation of innate immunity.

T170

34120-34270

Sentence

denotes

Type 7 of TLR (TLR7) – expressed on the surface of endosomes predominantly in the lungs, placenta, and spleen – might play a central role in COVID-19.

T171

34271-34483

Sentence

denotes

This receptor has been reported to quickly recognize single-stranded SARS-CoV-1 RNA, inducing the production of pro-inflammatory cytokines such as TNF-α, IL-6, and IL-12 in plasmacytoid dendritic cells (141–143).

T172

34484-34640

Sentence

denotes

The recognition of SARS-CoV-2 RNA by TLR7 can mediate the release of cytokines in response to the virus, a context in which IL-6 may play an important role.

T173

34641-34889

Sentence

denotes

It has been well described that IL-6 is a pleiotropic cytokine with distinct functions in different contexts in the immune system, being fundamental for the formation of follicular T helper lymphocytes and the generation of long-lived plasma cells.

T174

34890-35228

Sentence

denotes

However, this cytokine can also inhibit the activity of CD8+ cytotoxic lymphocytes by inducing the expression of PD1 in these cells, in addition to inhibiting suppressors of cytokine signaling 3 (SOCS3), an important protein responsible for controlling cytokine production, leading to an excessive release of inflammatory mediators (144).

T175

35229-35552

Sentence

denotes

The pathophysiology of COVID-19 is yet to be fully elucidated and several gaps still need to be filled, however, several studies have shown an increase in cytokines, notably pro-inflammatory, in the serum of infected patients, which has been associated with hyper inflammation and the lung injury particular to the disease.

T176

35553-35838

Sentence

denotes

The main cytokines described include TNF-α, IFN-γ, IL-1β, IL-1Ra, IL-2R, IL-6, IL-7, IL-8, IL-9, IL-10, basic FGF, G-CSF, GM-CSF, IP-10, MCP-1, MIP-1a, PD6F, and VEGF, in addition to an increase in other inflammation biomarkers, such as C-reactive protein, ferritin, and procalcitonin.

T177

35839-35965

Sentence

denotes

However, mediators related to the complement system, such as C3 and C4, did not present any difference in healthy individuals.

T178

35966-36320

Sentence

denotes

Furthermore, even higher levels of these mediators were found in patients of critical COVID-19 cases, suggesting that the severity of the disease may be associated with this huge amount of inflammatory mediators, called cytokine storm, which overloads the immune system with information, preventing the establishment of an effective immune response (26).

T179

36321-36782

Sentence

denotes

For example, a study published by Valle et al. showed that COVID-19 patients have higher levels of IL-6, IL-8, and TNF-alpha than healthy individuals on hospital admission; moreover, when they stratified the population by low versus high cytokine levels and applied a risk competition model, it was found that each cytokine is an independent predictive factor of the patients’ overall survival and is significantly associated with worse clinical outcomes (145).

T180

36783-36995

Sentence

denotes

On the other hand, in theory, a type I IFN-mediated response activates the JAK-STAT signaling pathway that should be able to suppress viral replication and prevent the virus from spreading early in the infection.

T181

36996-37121

Sentence

denotes

This is probably what occurs in asymptomatic individuals who can establish an effective response against SARS-CoV-2 (9, 141).

T182

37122-37296

Sentence

denotes

However, in several viruses, viral proteins can modulate the production of this type of IFN, impairing the generation of an effective antiviral response (141, 143, 146, 147).

T183

37297-37618

Sentence

denotes

Li et al. (148) conducted an in vitro experiment that revealed a strong capacity of ORF6, ORF8, and nucleocapsid proteins of SARS-CoV-2 to inhibit IFN-β and NF-κB activity, in addition to genes containing interferon-stimulated response elements (ISREs), suggesting that the virus has an important IFN antagonist activity.

T184

37619-37845

Sentence

denotes

By monitoring the production of type I IFN in SARS-CoV-2-positive patients, Trouillet-Assant et al. (149) found a peak in IFN-α2 production between 8 and 10 days after the onset of symptoms, in general, which reduces overtime.

T185

37846-38025

Sentence

denotes

However, as many as one critically ill patient in five was unable to produce any amount of type I IFN and had a higher viral load, respiratory failure, and worse clinical outcome.

T186

38026-38267

Sentence

denotes

Nonetheless, Zhou et al. (150) conducted a study that demonstrated that SARS-CoV-2 infection induced a markedly elevated expression of IFN-related inflammatory genes, which appears to decrease over time in mild cases, but not in severe ones.

T187

38268-38384

Sentence

denotes

Additionally, Major et al. (151) described the role of types I and III of IFN in lung repair during viral infection.

T188

38385-38606

Sentence

denotes

The production of IFN-α/β and IFN-λ in C57BL/6 mice was detected immediately at the early stage of influenza virus infection and decreased over time, having reached undetectable levels at the onset of epithelial recovery.

T189

38607-38854

Sentence

denotes

Interestingly, the treatment with IFN-α, β, or λ during the recovery phase reduced the proliferation type II alveolar epithelial cells by activation of IFN-induced p53, aggravating lung injury, disease severity, and susceptibility to coinfections.

T190

38855-39012

Sentence

denotes

Therefore, time and duration of IFN are critical factors for viral infection response and should be thoroughly considered as a COVID-19 therapeutic strategy.

T191

39013-39301

Sentence

denotes

Similarly, an experimental study conducted with MERS patients indicated that type I IFN has protective activity against this infection and the blockade of its signaling resulted in delayed virus clearance, enhanced neutrophil infiltration, and impaired MERS-CoV–specific T cell responses.

T192

39302-39390

Sentence

denotes

Additionally, early treatment using this type of IFN prevented fatal infections in mice.

T193

39391-39784

Sentence

denotes

However, the late treatment did not cure the animals and failed to effectively inhibit virus replication, increased infiltration, and activation of monocytes, macrophages, and neutrophils in the lungs, in addition to having enhanced proinflammatory cytokine expression, which led to fatal pneumonia, indicating that type I IFN plays a central role at the very beginning of the infection (152).

T194

39785-39947

Sentence

denotes

Therefore, using IFN in SARS-CoV-2 treatment seems to be beneficial at the early infection stage, especially for patients unable to produce this type of response.

T195

39948-40127

Sentence

denotes

Furthermore, as the disease progresses, the use of inflammatory cytokine blockers for patients who fail at regulating their production over time could represent a better strategy.

T196

40128-40401

Sentence

denotes

COVID-19 patients also have high levels of production of anti-inflammatory cytokines, such as IL-10, perhaps as a way of compensating for the exacerbated inflammatory response, which can lead to a picture of immune dissonance and anergy towards the infection (26, 153–155).

T197

40402-40630

Sentence

denotes

It is fundamental to perform further studies that elucidate the mechanisms of the immune response and the balance between pro-inflammatory and anti-inflammatory response patterns to understand the immunopathogenesis of COVID-19.

T198

40631-40750

Sentence

denotes

IL-7 is a pleiotropic cytokine that plays an essential role in the differentiation and clonal expansion of lymphocytes.

T199

40751-41077

Sentence

denotes

Chi et al. (156) described the production of IL-7 in COVID-19 patients; when compared to healthy controls, both asymptomatic and symptomatic individuals in the acute phase show an increase in the levels of this cytokine, however convalescent individuals return to the basal state equal to that observed in healthy individuals.

T200

41078-41232

Sentence

denotes

When symptomatic individuals were stratified according to the severity of the disease, those with moderate to severe conditions had higher levels of IL-7.

T201

41233-41499

Sentence

denotes

In addition, SARS-CoV-2-specific T cells from the peripheral blood of convalescent individuals of COVID-19 show high expressions of CD127, a receptor necessary for homeostatic cell proliferation triggered by IL-7, which may be related to the recovery observed (157).

T202

41500-41651

Sentence

denotes

Patients with a severe COVID-19 condition, on the other hand, have an increased IL-7 production, but contradictorily they also have severe lymphopenia.

T203

41652-41856

Sentence

denotes

Thus, we speculate that the deficiency in the expression of CD127 might occur in severely ill patients, which culminates in the deficiency of cell proliferation induced by IL-7 and consequent lymphopenia.

T204

41857-41981

Sentence

denotes

However, studies that seek to evaluate the expression profile of IL-7 and CD127 in COVID-19 patients need to be carried out.

T205

41982-42097

Sentence

denotes

In addition, the use of IL-7 as a treatment for COVID-19 patients has been evaluated and will be discussed further.

T206

42098-42231

Sentence

denotes

Several pro-inflammatory cytokines have been described in COVID-19 patients and are associated with the disease’s immunopathogenesis.

T207

42232-42323

Sentence

denotes

Among them, IL-1β and TNF-α stand out for playing a central role in this context (26, 156).

T208

42324-42718

Sentence

denotes

The respiratory failure characteristic of SARS-CoV-2 infection, especially in individuals who develop the most severe forms of the disease, occurs independently of infection or viral replication in the epithelial bronchial cells and probably occurs due to exacerbated inflammatory dysregulation, resulting from activation of the NLRP3 inflammasome pathway and consequent release of IL-1β (158).

T209

42719-43001

Sentence

denotes

However, although several articles have shown an increase in IL-1β production in COVID-19 patients and early treatment with IL-1 receptor blockers has helped prevent respiratory failure (159), its exact role in the immunopathogenesis of the disease has not yet been fully described.

T210

43002-43075

Sentence

denotes

Cytokine storms may have great relevance in the pathogenesis of COVID-19.

T211

43076-43196

Sentence

denotes

The induction of inflammatory mediators can induce cell damage, especially in lung tissues, causing respiratory failure.

T212

43197-43429

Sentence

denotes

In addition, several of these mediators have potent vasodilator activity, which at the local level can cause pulmonary edemas, while at the systemic level leads to septic shock, worsening the clinical condition of these individuals.

T213

43430-43746

Sentence

denotes

Similarly, several studies have shown that viral infections can induce cytokine storms, or take advantage of it, to establish infection and escape from the immune system, intensifying pathological phenomena such as those observed in sepsis, in addition to increasing the mortality rate of this population (160, 161).

T214

43747-44044

Sentence

denotes

Despite the absence of direct evidence of the role of cytokines and chemokines in lung injury, initial studies have shown that the increase in these pro-inflammatory mediators is associated with lung injury in patients with COVID-19 and has a central role in the pathogenesis of the disease (153).

T215

44045-44278

Sentence

denotes

The balance of the innate immune response is essential at the beginning of the infection, while its imbalance can culminate in excessive inflammation, which hinders the establishment of an effective immune response against the virus.

T216

44279-44599

Sentence

denotes

Therefore, using hemoperfusion can be an important tool to treat severe COVID-19 patients who developed cytokine storms, as well as other treatments focusing on controlling and reducing hyper inflammation using specific blockers or monoclonal antibodies directed against the mediator or to antagonize its receptor (144).

T217

44601-44623

Sentence

denotes

Innate Immune Response

T218

44624-44805

Sentence

denotes

The innate immune system is the first line of defense against pathogens through the activation of PRR in macrophages, neutrophils, and dendritic cells by the interaction with PAMPs.

T219

44806-45026

Sentence

denotes

An effective innate immune response against viruses like SARS-CoV-2 is essential not only to initiate the response but also to structure the basis for the production of a robust and more specific adaptive response (162).

T220

45027-45158

Sentence

denotes

Changes in this process, commonly observed in viral infections, can cause an immune imbalance and susceptibility of the host (163).

T221

45159-45328

Sentence

denotes

Patients who develop severe COVID-19 exhibited a marked increase in neutrophil and reduced lymphocytes counts compared with patients with mild signs of the disease (10).

T222

45329-45553

Sentence

denotes

A general increase in the number of circulating neutrophils and the reduction of lymphocytes enhance the neutrophil/lymphocyte ratio, which has been used as a predictor of the infection severity and development of pneumonia.

T223

45554-45701

Sentence

denotes

In addition to being a predictor of a worse prognosis, an increase in this ratio also indicates a serious immune imbalance in these patients (153).

T224

45702-45983

Sentence

denotes

In addition to having high levels of cell-free DNA, myeloperoxidase-DNA, and citrullinated histone H3 – important markers of neutrophil extracellular traps (NETs) –, the serum of COVID-19-positive patients was able to strongly trigger NETosis in healthy neutrophils in vitro (164).

T225

45984-46273

Sentence

denotes

Despite representing important strategies to eliminate pathogens by neutrophils, NETs damage healthy tissue and induce inflammation (165), in addition to featuring a variety of oxidizing agents and being involved in several vascular diseases, as well as pathogen-induced acute lung injury.

T226

46274-46523

Sentence

denotes

The release of NETs by neutrophils can be triggered by several factors, such as virus-damaged epithelial cells, activated platelets, activated endothelial cells, and inflammatory cytokines, such as IL-1β, IL-8, and G-CSF, among others (95, 166–169).

T227

46524-46664

Sentence

denotes

In this context, it is fundamental to conduct studies assessing the role of neutrophils and NETs to better understand COVID-19 pathogenesis.

T228

46665-46840

Sentence

denotes

Concerning monocytes, COVID-19 patients have shown an abundant circulation of CD14+ CD16+ cells, with a sharper increase in patients who developed severe respiratory syndrome.

T229

46841-47036

Sentence

denotes

This subtype of monocytes can over-secrete TNF-α, IL-1β, and IL-6 and expand quickly in systemic infections, implying that they must play an important role in the rapid defense against pathogens.

T230

47037-47171

Sentence

denotes

Controversially, these cells are the main producers of IL-10, which makes their exact function in immune responses elusive (170, 171).

T231

47172-47388

Sentence

denotes

Additionally, Dutertre et al. (172) demonstrated that CD14+ CD16+ monocytes are responsible for TNF overproduction in HIV infections and might be considered the major actor in immune hyperactivation in disease (172).

T232

47389-47557

Sentence

denotes

A study assessing bronchoalveolar lavage of SARS-CoV-2-positive individuals found an abundance of monocytes-derived inflammatory macrophages in critically ill patients.

T233

47558-47777

Sentence

denotes

In addition, the authors observed through single-cell analysis that these macrophages can contribute to local inflammation by recruiting inflammatory monocytes and neutrophils through CCR1 and CXCR2 chemokine receptors.

T234

47778-47940

Sentence

denotes

However, in patients who presented a moderate form of the disease, macrophages produced chemo-attractants for the recruitment of T cells, such as CXCR3 and CXCR6.

T235

47941-48063

Sentence

denotes

Such a difference in response might be the key to understanding the pathogenesis of respiratory failure in COVID-19 (173).

T236

48064-48323

Sentence

denotes

Furthermore, critically ill patients have also manifested rapid proliferation of another subpopulation of monocytes characterized by GM-CSF+ IL-6+, which may be related to inflammatory risk and impairment of the lungs when migrating in large quantities (170).

T237

48324-48573

Sentence

denotes

GM-CSF has been described as an active part of the pathogenesis of autoimmune and inflammatory diseases, mainly in the involvement of myeloid cells, such as monocytes, which can initiate tissue damage in a dependent manner on this marker (174, 175).

T238

48574-48985

Sentence

denotes

In addition, high levels of mediators, such as IL-6, TNF-, and IL-10, found in these patients are likely to have been produced by these monocytes and to be highly involved in cytokine storm and pathogenesis of SARS-CoV-2, since as the disease progresses these mediators reduce, which is correlated to the restoration of the immune function of CD4+ and CD8+ T lymphocytes, which is further discussed later (154).

T239

48986-49187

Sentence

denotes

Critical COVID-19 patients have shown excessive activation of circulating HLA-DR- monocytes, which has been associated with the onset of respiratory failure, suggesting its role as a predictive factor.

T240

49188-49391

Sentence

denotes

The lack of expression of HLA-DR in monocytes may indicate a modulatory capacity of the virus, which prevents the antigen presentation and hampers the formation of an adaptive immune response (176, 177).

T241

49392-49614

Sentence

denotes

During an in vitro experiment, Yang et al. (178) found that, despite being permissive to infection by SARS-CoV-2, human monocyte-derived macrophages and dendritic cells are not able to effectively produce viral replicates.

T242

49615-49735

Sentence

denotes

Despite their central role in pathogenesis, this may indicate that these cells are not important reservoirs for viruses.

T243

49736-49976

Sentence

denotes

In addition, neither of the cell types developed a response based on type II IFN, but macrophages had lower production of type I and III IFN than the control, indicating that the virus can inhibit a response mediated by these types of IFNs.

T244

49977-50109

Sentence

denotes

Additionally, macrophages were able to trigger an exacerbated inflammatory response with higher TNF-α, IL-8, IP10, MIP1α, and IL-1β.

T245

50110-50261

Sentence

denotes

Dendritic cells had not been reported to show such inflammatory phenomenon, which is due to the ability of SARS-CoV-2 to inhibit STAT1 phosphorylation.

T246

50262-50498

Sentence

denotes

Such important attenuation of dendritic cell response caused by the virus may have important implications for humans to develop effective immunity, therefore, further studies should seek to better elucidate such a relevant relationship.

T247

50499-50911

Sentence

denotes

Similarly, in the presence of IFN-α and GM-CSF, circulating monocytes should quickly differentiate into monocyte-derived dendritic cells (mDC), which are important antigen-presenting cells capable of phagocyting viruses and initiating the adaptive immune response process, as well as activating CD4+ T cells, generating immune memory in the process, and refining the body’s defense against infections (179, 180).

T248

50912-51063

Sentence

denotes

The number of mDCs has not increased in patients infected with SARS-CoV-2 compared with healthy controls, even in the most severe cases of the disease.

T249

51064-51327

Sentence

denotes

Interestingly, the levels of GM-CSF in the serum of these patients are highly elevated, which should lead these cells to increase, demonstrating that the virus may have a mechanism to control the production of IFN-α and consequent differentiation of mDCs (9, 26).

T250

51328-51533

Sentence

denotes

In the same way, individuals infected and not infected with SARS-CoV-2 have similar levels of IL-12, an important cytokine produced by mDC that is involved in the differentiation of naïve T cells (9, 181).

T251

51534-51738

Sentence

denotes

Thus, we hypothesize that the lack of mDC generation and consequent inability of the infected individual to produce IL-12 may be among the main factors of innate immunity-related pathogenesis of COVID-19.

T252

51739-51990

Sentence

denotes

As further discussed, the increase in naïve T cells, reduced cell functionality of CD4+, CD8+, and natural killers (NK), and delay in the appearance of humoral response found in these patients indicates a failure in the generation and function of mDC.

T253

51991-52099

Sentence

denotes

Therefore, it is urgent to carry out studies aimed at analyzing the effect of SARS-CoV-2 on dendritic cells.

T254

52101-52115

Sentence

denotes

T Helper Cells

T255

52116-52234

Sentence

denotes

Establishing and maintaining immune response and memory generation against viruses depends on the activity of T cells.

T256

52235-52372

Sentence

denotes

These lymphocytes originate from bone marrow progenitor cells and migrate to the thymus for maturation, selection, and peripheral export.

T257

52373-52651

Sentence

denotes

Peripheral T cells are subdivided into groups that include naïve T cells, which are capable of responding to new antigens, memory T cells derived from previous antigen activations and maintain long-term immunity, and regulatory T cells that coordinate the immune response (163).

T258

52652-53012

Sentence

denotes

The immune response begins when naïve T cells encounter antigens and co-stimulatory molecules presented by antigen-presenting cells, such as dendritic cells that phagocytize the virus, resulting in the production of IL-2, proliferation, and differentiation of effector T cells, which migrate to various sites to promote the elimination of pathogens (163, 182).

T259

53013-53203

Sentence

denotes

Inflammatory factors induced by viruses can trigger a storm of mediators that cause changes in the differentiation and activation of T cells, disturbing the homeostasis of the immune system.

T260

53204-53423

Sentence

denotes

In patients with COVID-19, the overall percentage of T lymphocytes is generally reduced, especially CD4+ CD3+ T lymphocytes, which have an activation phenotype, a reduction much more pronounced in severely ill patients.

T261

53424-53585

Sentence

denotes

Furthermore, a higher percentage of CD4+ CD45RA+ naïve cells and lower CD4+ CD3+ CD45RO+ memory T cells were also found in COVID-19 patients (10, 153, 183, 184).

T262

53586-53732

Sentence

denotes

Polyfunctional CD4+ T cells are characterized by the expression of activation markers as well as their capacity to produce IFN-γ, IL-2, and TNF-α.

T263

53733-53877

Sentence

denotes

These cells have been linked to an excellent response against viral infections and during the development of immunity by vaccination (185, 186).

T264

53878-54245

Sentence

denotes

Even though COVID-19 patients have shown an increase in the expression of molecules related to T CD4+ activation, such as CD69, CD38, and CD44, molecules related to their function, such as intracellular IFN-γ, IL-2, and TNF-α, are reduced, especially in individuals with a more severe stage of the disease (9, 170), indicating an impairment of polyfunctional T cells.

T265

54246-54448

Sentence

denotes

Li et al. (187) demonstrated that patients infected with SARS-CoV-1 had elevated levels of polyfunctional CD4+ T cells, especially those in a severe condition but who progressed to clinical improvement.

T266

54449-54700

Sentence

denotes

In contrast, critically ill patients with SARS-CoV-2 demonstrated a drastic reduction of this cell subtype, which may indicate that this virus has developed its own mechanisms to control cellular responses, thus differing from other coronaviruses (9).

T267

54701-54935

Sentence

denotes

Similarly, Chen et al. (154) demonstrated that CD4+ T lymphocytes from COVID-19 patients showed increased expressions of T cell immunoglobulin-3 (Tim-3), a type I transmembrane protein that acts as a negative regulator of Th1 pattern.

T268

54936-55138

Sentence

denotes

CD4+ cells showed low expression of this marker at the early phase of infection, having progressively increased over time, indicating that the exhaustion of these cells occurs as the disease progresses.

T269

55139-55511

Sentence

denotes

Many studies with SARS-CoV-2 positive patients have described the generation of these exhausted pathological lymphocytes that exacerbate the inflammatory response at the early stage of infection, initiating a cytokine storm, followed by cell exhaustion and loss of functionality, a phenomenon that has appeared mainly in more severe cases of the disease (9, 10, 170, 188).

T270

55512-55650

Sentence

denotes

The vast majority of studies to date show impairment of proliferation, maturation, and response of T cells, especially in sicker patients.

T271

55651-55972

Sentence

denotes

This may indicate that SARS-CoV-2, similarly to other viral infections, can interfere with the function of CD4+ cells at the very beginning of the infection, causing excessive release of inflammatory mediators and exhaustion of the response capacity of these cells over time, reducing the host’s antiviral immunity (189).

T272

55973-56409

Sentence

denotes

What seems to happen in COVID-19 is that the total lymphocyte count is reduced in these patients and, among the remaining T cells, the highest percentage is from naïve CD4+ T lymphocytes, while the activated subpopulations, although few, present a phenotype with excess and reduced markers related to activation and function, respectively, indicating that, despite overactivation, these cells fail to exercise effective immune activity.

T273

56410-56518

Sentence

denotes

Another important point is the reduction of regulatory T cells CD4+ CD25+ Foxp3+ verified in these patients.

T274

56519-56782

Sentence

denotes

These cells have a fundamental role in the negative regulation of inflammation, control of cell proliferation, and the effector function of several cells, which probably has contributed to the excessive inflammation observed in critically ill patients (153, 190).

T275

56783-57050

Sentence

denotes

It has been described that regulatory T cells play a central role in mitigating the immune response in several viral infections (191); reducing the number of these cells in patients with COVID-19 can lead to loss of regulatory functions and consequent cytokine storm.

T276

57051-57435

Sentence

denotes

It has been described in several studies that COVID-19 patients have a reduced number of circulating Treg cells, which may be due to the increase in soluble IL-2 receptors (IL-2R or CD25) that potentially scavenges IL-2, reducing their bioavailability for binding to CD25 on the cell surface, thus preventing the induction of the clonal expansion signal of Treg cells (153, 192, 193).

T277

57437-57452

Sentence

denotes

Cytotoxic Cells

T278

57453-57551

Sentence

denotes

T lymphocytes CD8+ and NK are essential to control viral infections due to their cytotoxic effect.

T279

57552-57751

Sentence

denotes

These cells become activated after recognizing antigens attached to molecules of MHC-I presented by infected cells, which usually leads to the death of the infected cell by effector mechanisms (163).

T280

57752-57938

Sentence

denotes

Kamiya et al. (194) demonstrated that SARS-CoV-2 infection in humans dramatically reduces the total CD8+ and NK cell count, especially in patients who have developed more severe disease.

T281

57939-58404

Sentence

denotes

The inhibition of these cells was characterized by an increase in the expression of NK inhibitory receptor CD94/NK group 2 member A (NKG2A), a type C lectin receptor of cytotoxic cells that acts as a potent suppressor when binding to minimally polymorphic MHC-I that present peptide sequences of other MHC-I molecules, inducing an inhibitory signal through two receptors with tyrosine-based inhibition motifs that suppress cytokine secretion and cytotoxic activity.

T282

58405-58626

Sentence

denotes

In patients who recovered from COVID-19, CD8+ and NK cell counts and the reduction in NKG2A expression were restored, suggesting that the inhibition of these cells is a result of SARS-CoV-2-mediated immunomodulation (10).

T283

58627-58810

Sentence

denotes

Corroborating these data, it has been reported that other viral infections also manage to increase the expression of NKG2A in NK cells as a way to escape from the immune system (195).

T284

58811-59165

Sentence

denotes

SARS-CoV-2 studies involving CD8+ T cells have shown exhaustion of the effector capacity of these cells over time by the reduction of granzyme B, perforins, and lysosome-associated membrane protein 1, also known as LAMP-1 or CD107a, described as a marker of cytotoxic cells’ degranulation and an important parameter to assess the activity of these cells.

T285

59166-59329

Sentence

denotes

CD8+ T cells from COVID-19 patients have a very marked activation phenotype with an increase in CD69, CD38, CD137, and CD44, especially in critically ill patients.

T286

59330-59553

Sentence

denotes

However, despite presenting an increase in these activation molecules, these cells also have enhanced cell exhaustion proteins, such as PD1, Tim3, CTLA-4, and TIGIT, especially in more critically ill patients (9, 154, 170).

T287

59554-59790

Sentence

denotes

TIGIT receptor, present in T and NK cells, can bind to dendritic cell CD155 receptors and induce an increased expression of IL-10 and reduce IL-12, in addition to inhibiting T cell activation and blocking cytotoxicity of NK cells (196).

T288

59791-59932

Sentence

denotes

The use of specific blockers for these receptors, such as anti-PD1 and anti-TIGIT, has helped in the recovery of the function of these cells.

T289

59933-60134

Sentence

denotes

Therefore, it is logical to assume that specific NKG2A blockers could be an important tool to assist in the treatment of SARS-CoV-2 infections, restoring the functionality of cytotoxic cells (10, 195).

T290

60135-60617

Sentence

denotes

Together, these data described the increase in activation markers and cellular exhaustion, in addition to the reduction in functionality markers indicating that, like CD4+ T lymphocytes, these cells were probably hyperactivated right at the beginning of the infection, collaborating with the generation of a cytokine storm, until they became exhausted and lost their functional capacity, causing reduction of antigen-specific response and loss of its antiviral effects ( Figure 2 ).

T291

60618-60663

Sentence

denotes

Figure 2 Immune response in COVID-19 stages.

T292

60664-60722

Sentence

denotes

SARS-CoV-2 infection is divided into three general phases.

T293

60723-60978

Sentence

denotes

In the first one, called viremia, the virus spreads through the body and there is excessive activation of immune cells with exacerbated production of inflammatory mediators, such as IFN-γ, IL-2, and TNF-α, triggering cytokine storms and immune impairment.

T294

60979-61283

Sentence

denotes

The second (acute) phase, characterized by the appearance of COVID-19 symptoms, presents a profile of immune cells still hyperactivated, but with the presence of cell exhaustion markers, such as Tim3, PD1, TIGIT, and NKG2A, in addition to losing the functional capacity of producign IFN, IL-2, and TNF-α.

T295

61284-61556

Sentence

denotes

In this period there is still the appearance of CD14+ CD16+ hyperinflammatory monocytes, with a high production capacity of TNF-α, IL-1β, and IL-6, which will migrate to the lungs, contributing to the pathogenesis of respiratory failure and maintaining the cytokine storm.

T296

61557-61699

Sentence

denotes

The lethargic state of the immune system in the early stages of infection may be related to the delay in the generation of a humoral response.

T297

61700-61830

Sentence

denotes

In the third, or convalescence, phase, the individual can evolve in two opposite directions, recovery or clinical worsening/death.

T298

61831-61958

Sentence

denotes

In recovery, cells of lymphoid origin recover their effector function and lose markers of exhaustion, while IgG levels improve.

T299

61959-62054

Sentence

denotes

On the other hand, in patients with clinical worsening, this status of immune anergy continues.

T300

62056-62072

Sentence

denotes

Humoral Response

T301

62073-62209

Sentence

denotes

Detecting a humoral response against SARS-CoV-2 has been the focus of attention to developing faster and more accurate diagnostic tools.

T302

62210-62480

Sentence

denotes

A study assessing the presence of IgA, IgM, and IgG against SARS-CoV-2 in infected patients found that IgA levels begin to rise in the first seven days after the onset of symptoms and continue increasing until it stabilizes near the 14th day after the onset of symptoms.

T303

62481-62709

Sentence

denotes

Additionally, IgM production appears as early as IgA, the antibody titration in the first seven days after the onset of symptoms was very low, starting to increase only from the eighth day, reaching a plateau after the 14th day.

T304

62710-62873

Sentence

denotes

The average time of appearance of specific IgG against SARS-CoV-2 starts 14 days after the appearance of symptoms and grows exponentially until the 21st day (197).

T305

62874-63038

Sentence

denotes

These data corroborate the disease stages proposed by Lin et al. (6) (presented in the introduction), and the changes in the immune response present in the disease.

T306

63039-63215

Sentence

denotes

The early appearance of IgA results from the first contact of the virus with the individual’s mucosa at the moment of contagion and continues to increase until the acute phase.

T307

63216-63788

Sentence

denotes

Despite viremia and symptom onset, IgM levels only begin to rise from the eighth day after symptom onset, indicating anergy in the immune response during this period, perhaps caused by dysfunction in antigen-presenting cells, such as dendritic cells, and also by reducing the amount of activated T helper cells, which play a central role in triggering the immunity acquired by the activation and clonal expansion of B lymphocytes, in addition to the formation of germinal centers and generation of plasma cells that produce high affinity and avidity antibodies (198, 199).

T308

63789-63987

Sentence

denotes

The appearance of IgG near the third stage of the disease may be related to the clinical evolution of patients and those who fail to establish an efficient immune response might be at risk of death.

T309

63988-64132

Sentence

denotes

Interestingly, Guo et al. (197) found that approximately 22% of COVID-19 patients confirmed by RTq-PCR did not present detectable levels of IgM.

T310

64133-64332

Sentence

denotes

Most of these individuals were tested in the first seven days after the onset of symptoms, therefore the lack of IgM can be justified by the delay in generating a humoral response against SARS-CoV-2.

T311

64333-64467

Sentence

denotes

However, some critically ill patients followed for a longer period remained negative for IgM even 22 days after the onset of symptoms.

T312

64468-64710

Sentence

denotes

As for IgG levels, some patients took 30 to 40 days after the appearance of symptoms to show some detectable level of IgG, suggesting a possible failure in the production of antibodies that may have contributed to the severity of the disease.

T313

64711-64983

Sentence

denotes

It is possible that the generation of antibodies in more advanced stages of COVID-19 does not benefit the recovery process since most pathological mechanisms at this stage might be more related to the excess of inflammatory mediators than the presence of the virus itself.

T314

64984-65306

Sentence

denotes

In recovered patients, the magnitude of the production of neutralizing antibodies (nAb) against SARS-CoV-2 is positively correlated with the severity of the disease; while asymptomatic individuals have little or no capacity to produce nAb, individuals who recovered from severe cases of COVID-19 had robust nAb production.

T315

65307-65511

Sentence

denotes

Also, these severe recovered patients showed an increase in B cell receptor (BCR) rearrangement, which may demonstrate that the effective production of nAb requires enhanced and prolonged BCR stimulation.

T316

65512-65716

Sentence

denotes

Asymptomatic or mild symptomatic patients may possibly mount robust SARS-CoV-2 specific CD8 + T cell responses, which can provide protection by directly eliminating the target cells infected by the virus.

T317

65717-65841

Sentence

denotes

However, due to the lack of immunity provided by nAb, these individuals might suffer from SARS-CoV-2 reinfection (200, 201).

T318

65842-66255

Sentence

denotes

In the same way, Zhang et al. (202) also demonstrated that patients who recovered from severe COVID-19 have high levels of BCR clonal expansion and B cell activation, indicating a more robust humoral response than patients with mild disease, thus asymptomatic individuals or those with mild COVID-19 probably have different cell and humoral responses than individuals who developed the severe form of the disease.

T319

66256-66426

Sentence

denotes

In an article published by Chen et al, the serum of 26 patients who recovered from COVID-19 were analyzed for the production of IgG anti-SARS-CoV-2 S1 protein antibodies.

T320

66427-66639

Sentence

denotes

It was found that, despite the majority of patients presenting high IgG titers, only three individuals had antibodies that effectively neutralized the binding of the viral glycoprotein to the human ACE2 receptor.

T321

66640-66894

Sentence

denotes

In addition, the authors successfully managed to clone two different neutralizing antibodies from these patients with the ability to inhibit virus-cell binding, opening up the potential for using them as a possible source of treatment for COVID-19 (203).

T322

66895-67033

Sentence

denotes

In theory, the production of specific neutralizing antibodies against SARS-CoV-2 should be able to combat the virus and reduce viral load.

T323

67034-67190

Sentence

denotes

The production of immune memory verified in the blood of recovered patients has also been used to treat COVID-19 patients, as we will discuss further (204).

T324

67192-67210

Sentence

denotes

COVID-19 Treatment

T325

67211-67356

Sentence

denotes

To date, no effective vaccines or therapeutic antiviral agents have been approved for the treatment of COVID-19 or any other human CoV infection.

T326

67357-67424

Sentence

denotes

The main approach to disease management focuses on supportive care.

T327

67425-67690

Sentence

denotes

To contain the viral transmission and disease, rapid public health interventions using immune cell-based therapies, antibodies, antivirals, new drugs, or vaccine strategies have focused on reducing mortality, virus spread, and mitigating potential future outbreaks.

T328

67691-67978

Sentence

denotes

In this context, we conducted a survey of the main SARS-CoV-2 drugs/treatments following three criteria: peer-reviewed published scientific literature, with clinical trials that are underway, and that display a broad spectrum of action in the face of various viral and parasitic disease.

T329

67979-68093

Sentence

denotes

The researched data (until September 2020) for ongoing and completed trials were searched in “clinicaltrials.gov”.

T330

68095-68113

Sentence

denotes

Enhancing Immunity

T331

68114-68296

Sentence

denotes

As exposed in the previous topics, currently there are no proven treatments for SARS-CoV-2 infections, thus, much has been discussed about the maintenance of a healthy immune system.

T332

68297-68475

Sentence

denotes

In this sense, the use of vitamins and other essential components for the proper functioning of the immune response can be an important approach in times of risk like this (205).

T333

68476-68860

Sentence

denotes

Several studies have shown that the use of supplements helps in enhancing the immune response and recovery from viral infections, as is the case with the use of vitamin A and D or selenium to improve the humoral immunity of individuals vaccinated against influenza virus (206, 207), or the use of zinc to improve the immune response of individuals infected with torquetenovirus (208).

T334

68861-69042

Sentence

denotes

Among vitamin supplements, vitamin D stands out for having an immunomodulatory effect on both adaptive and innate immune responses, helping in the development of B, T, and NK cells.

T335

69043-69197

Sentence

denotes

In addition, it has the ability to stimulate the production of antioxidant responses and microbicidal molecules such as defensins and cathelicidins (209).

T336

69198-69460

Sentence

denotes

The use of vitamin D has also been associated with the prevention of respiratory diseases associated with viral infections (210), and epidemiological data suggest that vitamin D deficiency increases the susceptibility to acute viral respiratory infections (211).

T337

69461-69685

Sentence

denotes

However, a study in the United Kingdom that evaluated plasmatic concentrations of vitamin D in samples from COVID-19 patients found no association between circulating vitamin D levels and the risk for disease severity (212).

T338

69686-69972

Sentence

denotes

The use of supplementation with other types of vitamins has also been described in viral infections; the use of vitamin C, for example, a potent antioxidant and an important enzyme cofactor, contributes to the development of the immune response, helping in the production of type I IFN.

T339

69973-70123

Sentence

denotes

However, a systematic review with meta-analysis found no evidence that the use of vitamin C has any effect in preventing common cold infections (213).

T340

70124-70235

Sentence

denotes

As for vitamin E, it has been shown that its deficiency can impair cellular and humoral immune responses (214).

T341

70236-70418

Sentence

denotes

However, the use of vitamin E has been associated with an increased risk of pneumonia and has shown no significant effect in preventing lower respiratory tract infections (215, 216).

T342

70419-70727

Sentence

denotes

In view of the controversial results, more than 50 ongoing clinical trials are seeking to clarify the role of vitamins, minerals, and other dietary supplementation in the prophylaxis and treatment of COVID-19, analyzing parameters such as the risk of infection, risk of hospitalization, and clinical outcome.

T343

70729-70742

Sentence

denotes

Immunotherapy

T344

70744-70766

Sentence

denotes

Antibody-Based therapy

T345

70767-70997

Sentence

denotes

Considered an efficient method for the clinical treatment of different infectious diseases, including MERS-CoV and SARS-CoV-1 (217), antibody-based immunotherapy has been studied as a potentially applicable tool to treat COVID-19.

T346

70998-71149

Sentence

denotes

The mechanisms involved with its effects against SARS-CoV-2 are related to preventing the virus from entering the host cells, blocking its replication.

T347

71150-71344

Sentence

denotes

The virus entry block was studied for acting both in the cell receptor ACE2 and directly on the virus (neutralizing antibodies [nAbs]), specifically in the S1 subunit of the S protein (218–220).

T348

71345-71601

Sentence

denotes

Regarding the blocking of ACE2 receptors, the application of some mechanisms stand out: the soluble version of ACE2 fused to an immunoglobulin Fc domain (ACE2-Fc), RDB domain attached to Fc (RDB-Fc), and receptor-targeted monoclonal antibodies (mAb) (221).

T349

71602-71724

Sentence

denotes

Viral neutralization by nAbs is also an immunotherapeutic approach and directly recognizes epitopic regions of SARS-CoV-2.

T350

71725-72035

Sentence

denotes

This effect can be achieved either directly through mAbs manufactured in laboratories or by using polyclonal antibodies (pAbs) (218). nAbs act directly on the virus, preventing its infectivity by activating several pathways, such as the complement system, cell cytotoxicity, and phagocytic clearance (222–224).

T351

72036-72124

Sentence

denotes

The therapeutic use of mAbs has shown good outcomes, mainly due to its high specificity.

T352

72125-72299

Sentence

denotes

Recently, several mAbs against viruses have been developed, including SARS-CoV-1 and MERS-CoV, in which the S protein is the major target described both in vitro and in vivo.

T353

72300-72437

Sentence

denotes

According to some studies, the specific nAbs against SARS-CoV-1 RBD in the S protein could effectively block SARS-CoV-2 entry (218, 225).

T354

72438-72656

Sentence

denotes

However, Wrapp et al. (226) tested several published SARS-CoV-1 RBD-specific nAbs and found that they do not have substantial binding to the S protein of SARS-CoV-2, suggesting that the cross-reactivity may be limited.

T355

72657-72761

Sentence

denotes

Thus, the combination of nAbs with different viral targets and sources could improve treatment efficacy.

T356

72762-72963

Sentence

denotes

In addition to experimental studies, to date, more than 10 clinical trials have aimed at testing human mAbs against SARS-Cov-2 (227–235), which could also represent an alternative, effective treatment.

T357

72964-73048

Sentence

denotes

Furthermore, some immunomodulatory mAbs have been tested in the context of COVID-19.

T358

73049-73388

Sentence

denotes

It is remarkable that until now most of the data published regarding the use of immunomodulatory mAbs derive from studies using either anti-IL-6 or anti-IL-6R, probably because using IL-6 blockers seems promising at controlling the cytokine storm associated with the development of ARDS in more aggressive patterns of SARS-CoV-2 infection.

T359

73389-73441

Sentence

denotes

However, clinical observations remain controversial.

T360

73442-73747

Sentence

denotes

Although some studies found considerable clinical improvements resulting from treatment with IL-6 blockers (236–239), others do not report any significant difference between the clinical features of groups treated with anti-IL6/IL-6R mAbs and their respective controls (without anti-IL-6/IL-6R) (240–243).

T361

73748-73973

Sentence

denotes

These controversial results can be explained by the pleiotropic function of IL-6, which also play an important anti-inflammatory role, questioning the use of IL-6 blockade to suppress inflammation-induced tissue damage (244).

T362

73974-74176

Sentence

denotes

Additionally, severe side effects have been associated with the use of IL-6 blockers, including enhanced hepatic enzymes, thrombocytopenia, severe bacterial and fungal infections, and sepsis (241, 245).

T363

74177-74276

Sentence

denotes

In general, data from analyses on the use of this type of mAbs remain inconclusive (243, 246, 247).

T364

74277-74551

Sentence

denotes

Recent findings are optimistic, but data validation by robust scientific evidence has been hampered by the small sample size in most case reports and studies on the use of mAbs blocking other immune mediators, such as IL-1β, GM-CSF, and complement protein C5 (238, 248–250).

T365

74552-74693

Sentence

denotes

However, seeking to verify the effectiveness of using mAbs blocking inflammatory mediators, dozens of clinical trials are currently underway.

T366

74694-75103

Sentence

denotes

Aiming at reducing the hyper inflammation found in the lungs of SARS-CoV-2-infected patients, different clinical studies are currently investigating the activities of mAbs anti-JAK, anti-GM-CSF, anti-GM-CSF receptor, anti-M-CSF receptor, anti-CD14, anti-IFNγ, anti-VEGF, anti-BKT, anti-CCR5, anti-IL-6, anti-IL-6 receptor, anti-TNFα, anti-IL1β, anti-IL1β receptor, and complement C5 inhibitor (220, 251, 252).

T367

75104-75302

Sentence

denotes

Similarly, ongoing clinical trials have sought to reverse the hyper-thrombotic state found in critically ill patients by using anti-P-selectin, anti-CTGF, and factor XIIa antagonist mAbs (253, 254).

T368

75303-75516

Sentence

denotes

Furthermore, to restore the exhausted T lymphocytes’ and NK cells’ immunity, other clinical studies applied anti-PD1 mAbs under the hypothesis of a stimulus of anti-viral response and prevention of ARDS (255–257).

T369

75517-75936

Sentence

denotes

More recently, the passive administration of pAbs has also been tested in COVID-19 patients (222–224, 258–267), also known as convalescent plasma (CP) or immune plasma, which is already used effectively and safely in the treatment of other severe acute respiratory syndrome infections of viral etiology, such as SARS, MERS, and H1N1, and offers only a short-term but rapid immunity to the susceptible individuals (268).

T370

75937-76075

Sentence

denotes

A strict criterion to select the CP donor states that the individual must show clinical recovery and test negative for the virus presence.

T371

76076-76205

Sentence

denotes

Thus, after being confirmed, a high titer of neutralizing antibodies against SARS-CoV-2 must be stored in blood banks (269, 270).

T372

76206-76412

Sentence

denotes

Some reviews related to patients who received transfusion with CP showed a reduction in viral load, improvement in clinical symptoms, better radiological findings, and improved survival (260, 261, 271–273).

T373

76413-76633

Sentence

denotes

In addition, after having received CP containing nAbs, COVID-19 patients had significant improvements from the beginning of treatment (until 22 days), presenting lower fever, decreased viral load, and higher nAbs levels.

T374

76634-76715

Sentence

denotes

Further, 60% of the patients were discharged one month after the treatment (271).

T375

76716-76867

Sentence

denotes

Better outcomes were found in early administration of CP (before SARS-CoV-2 seroconversion), preferably on day 5, for obtaining maximum efficacy (268).

T376

76868-77043

Sentence

denotes

More recently, Li et al. found no statistically significant clinical improvement or mortality reduction in a randomized clinical trial with CP-treated COVID-19 patients (274).

T377

77044-77213

Sentence

denotes

However, the authors reported that CP treatment is potentially beneficial to critically ill patients by suggesting a possible antiviral efficiency of high titer of nAbs.

T378

77214-77525

Sentence

denotes

Notably, there are clinical controversies, ethical issues, and potential risks associated with convalescent plasma therapy (275), such as the possibility of ADE development, exacerbating the disease severity, and causing a significant illness in future exposure to coronaviruses infection (268, 276, 277) (REF).

T379

77526-77813

Sentence

denotes

Divergences between studies may be caused by variations in the composition of CP, which is highly variable and includes a variety of blood-derived components, timing of CP administration, titer of the specific antibody in administered plasma, and presence of blood borne pathogens (268).

T380

77814-77935

Sentence

denotes

Nonetheless, understanding the efficacy and safety of CP therapy relies on the completion of the ongoing clinical trials.

T381

77936-78222

Sentence

denotes

Another therapeutic strategy using antibodies is intravenous immunoglobulin (IVIg) that contains polyclonal IgG isolated from healthy donors, which can be further enhanced by using IgG antibodies collected from recovered COVID-19 patients in the same geographical region as the patient.

T382

78223-78400

Sentence

denotes

Results have been mostly positive, although many of these therapies have not been formally evaluated through a randomized, double-blind, placebo-controlled clinical trial (278).

T383

78401-78671

Sentence

denotes

According to recent studies, IVIg can be used effectively in early stages of SARS-CoV-2 infection (before the initiation of systemic damage), reducing the use of mechanical ventilation, preventing the progression of pulmonary lesions, and promoting early recovery (268).

T384

78672-78877

Sentence

denotes

Also, cross-neutralization activity was shown against SARS-CoV-2 in commercial IVIg manufactured prior to the COVID-19 pandemic and are currently under evaluation as potential therapies for COVID-19 (279).

T385

78878-79226

Sentence

denotes

Thus, intravenous use of immunoglobulins can prove helpful in therapy against SARS-CoV-2, however, adjustments in the therapeutic regimen are necessary for all IVIg possibilities, as well as a complete understanding of the possible adverse effects, such as the risk of ADE (278, 279), that are being studied in more than 10 ongoing clinical trials.

T386

79227-79411

Sentence

denotes

Some works have shown that therapies focusing on the interaction between SARS-CoV-1 and the ACE2 receptor may be extended for use in SARS-CoV-2 patients as an immunotherapy tool (218).

T387

79412-79582

Sentence

denotes

However, other authors refute this idea based on the fact that recent studies showed limited cross-neutralization between SARS-CoV-1 antibodies and SARS-CoV-2 (280, 281).

T388

79583-79757

Sentence

denotes

Furthermore, it was shown that SARS-CoV-2 S protein binds ACE2 with a higher affinity than SARS-CoV-1, suggesting that such interaction differs between the two viruses (266).

T389

79759-79784

Sentence

denotes

Immune Cell-Based Therapy

T390

79785-79952

Sentence

denotes

In addition to antibody-based therapies, scientists have been studying immune cell-based therapies as a tool to combat COVID-19, focusing especially on NK and T cells.

T391

79953-80156

Sentence

denotes

The importance of NK cells as the first antiviral responders can be seen in patients with NK cell deficiency and immunocompromised individuals who have increased susceptibility to viral infections (282).

T392

80157-80412

Sentence

denotes

In this sense, Market et al. (282) gathered the main reports so far addressing potential therapies focusing on mediating NK cell activity to mitigate the immunopathological consequences of COVID-19, and consequently lighten the load on our health systems.

T393

80413-80517

Sentence

denotes

Some ongoing clinical trials have been studying the use of NK cell therapy through different approaches.

T394

80518-80770

Sentence

denotes

A randomized phase I/II trial studied the infusions of CYNK-001 cells, an allogeneic off-the-shelf cell therapy enriched for CD56+/CD3- NK cells expanded from human placental CD34+ cells in 86 hospitalized patients with moderate COVID-19 disease (283).

T395

80771-80904

Sentence

denotes

Another randomized phase I/II study explored the use of NKG2D-ACE2 CAR-NK cells with each common, severe, and critical type COVID-19.

T396

80905-81149

Sentence

denotes

The authors hypothesize that these cells target the S protein of SARS-CoV-2 and NKG2DL on the surface of infected cells with ACE2 and NKG2D, respectively, seeking out the elimination of SARS-CoV-2 virus particles and their infected cells (284).

T397

81150-81375

Sentence

denotes

The unregulated profile of the immune response in critically ill COVID-19 patients may be due to the reduction of Treg cells, which culminates in excessive release of inflammatory mediators and cytokine storms (153, 191–193).

T398

81376-81526

Sentence

denotes

Thus, the use of adoptive transfer of these cells as a measure of inflammatory control in critically ill patients is a promising therapeutic approach.

T399

81527-81882

Sentence

denotes

The infusion of autologous polyclonal Treg has already been used to treat inflammatory diseases, such as type 1 diabetes (285), however the use of autologous cells takes a long time, due to the period necessary for differentiation and clonal expansion, making this an unviable and costly method for infectious diseases, as is the case with COVID-19 (286).

T400

81883-82057

Sentence

denotes

A viable alternative is the use of allogeneic human leukocyte antigen-matched umbilical cord-derived Tregs (UBC-Treg) which can be widely expanded and used on a larger scale.

T401

82058-82311

Sentence

denotes

A recent case study used 1x108 administration of UBC-Treg in two patients with COVID-19 who had severe respiratory failure, and both demonstrated significant clinical improvement and reduced inflammatory markers four days after starting treatment (287).

T402

82312-82433

Sentence

denotes

There are currently two clinical trials underway that aim to infuse Treg cells in patients with severe COVID-19 and ARDS.

T403

82434-82618

Sentence

denotes

The first one is a multi-center, prospective, double-blinded, placebo-controlled phase 1 randomized clinical trial, which has 45 patients who will receive cryopreserved UBC-Treg (288).

T404

82619-82799

Sentence

denotes

The second one is a randomized, double-blind, placebo-controlled phase 2 study with 88 participants who will receive off-the-shelf allogeneic hybrid Treg/Th2 cells (RAPA-501-ALLO).

T405

82800-82927

Sentence

denotes

RAPA-501-ALLO cells will be generated from healthy donors, cryopreserved, banked, and made available for off-the-shelf therapy.

T406

82928-83158

Sentence

denotes

The cells are manipulated ex vivo to differentiate into two anti-inflammatory phenotypes simultaneously, generating hybrid Treg/Th2 cells, with the potential to reduce inflammation and mediate a protective effect on tissues (289).

T407

83159-83401

Sentence

denotes

In addition to therapeutic approaches using Treg cell infusion, another three clinical trials are underway with the aim of evaluating treatment using specific SARS-CoV-2 T cells isolated from individuals who recovered from COVID-19 (290–292).

T408

83402-83588

Sentence

denotes

The use of virus-specific T cells for off-the-shelf treatment has been used in several viral infections, such as cytomegalovirus, HHV6, adenoviruses, Ebola virus, and BK virus (293–296).

T409

83589-83907

Sentence

denotes

Although vaccination provides T cells-based virus-specific immunity, the path to its development is long, so the use of adoptive cell transfer techniques from healthy individuals who recovered from COVID-19 and developed an effective cell response is probably the fastest way to treat critically ill individuals (297).

T410

83908-84183

Sentence

denotes

Besides that, as mentioned before, asymptomatic or mild symptomatic patients may possibly mount robust SARS-CoV-2 specific CD8+ T cell responses (200, 201), therefore, the use of these individuals’ cells to treat critically ill patients with COVID-19 can be a promising tool.

T411

84184-84406

Sentence

denotes

The clinical use of IL-7 has been implemented in the treatment of cancer patients and infectious diseases, mainly with the objective of improving the immune response by stimulating the generation of lymphocytes (298, 299).

T412

84407-84717

Sentence

denotes

In addition, IL-7 administration has been reported to increase CD4 + and CD8 + T lymphocyte counts without inducing the production of pro-inflammatory mediators, making it a promising method of recovering immune function in patients with disorders related to cytokine storms, such as sepsis and COVID-19 (300).

T413

84718-84983

Sentence

denotes

In a case study conducted by Monneret et al. (301), compassionate administration of IL-7 to a patient with severe COVID-19 significantly improved total lymphocyte count and HLA-DR expression in circulating monocytes four days after administration of the first dose.

T414

84984-85078

Sentence

denotes

The patient also showed a significant improvement in lung involvement and negative viral load.

T415

85079-85451

Sentence

denotes

Another study conducted by Laterre et al. (302), who administered IL-7 to COVID-19 patients found that there was a significant improvement in the lymphocyte count after starting treatment, in addition, the patients did not show any change in TNF-α levels, IL-1β, and IL-12p70, which may indicate that IL-7 therapy may be safe for patients with severe inflammatory changes.

T416

85452-85592

Sentence

denotes

Thus, the use of IL-7-based immunotherapy can be an important tool to be used in future clinical trials in patients with severe lymphopenia.

T417

85593-85815

Sentence

denotes

Therefore, the data available to date do not ensure the success of immunotherapy applied in patients with COVID-19, thus, further studies specifically targeting SARS-CoV-2 should be performed to provide more specific data.

T418

85816-85898

Sentence

denotes

However, immunotherapy is effective and of immediate use, being of short duration.

T419

85899-86071

Sentence

denotes

This approach also presented limitations, such as the possibility of abnormal reactions and other serious risks, such as induction of severe acute lung injury or ADE (225).

T420

86072-86349

Sentence

denotes

Although we are living through a unique moment in science, with some mismatched information and novel, important discoveries being made every day, immunotherapy seems to be a possibly effective option to help patients until an effective, safe vaccine or treatment is developed.

T421

86351-86382

Sentence

denotes

Drug Options Against SARS-CoV-2

T422

86383-86543

Sentence

denotes

Although some drugs appear to be effective against SARS-CoV-2 and are able to improve COVID-19 symptoms, there is no specific antiviral compound for this virus.

T423

86544-86804

Sentence

denotes

In the face of such a global health emergency, several clinically used drugs are being reviewed and redirected to be tested in patients who have critical complications of COVID-19 in an attempt to eliminate the virus and modulate the patient’s immune response.

T424

86806-86816

Sentence

denotes

Antivirals

T425

86817-87064

Sentence

denotes

Due to the large amount of experimental and clinical studies assessing the effectiveness of antiviral therapy against SARS-CoV-2, we have seen the importance of this class of drugs in reducing the viral load peak at the beginning of the infection.

T426

87065-87295

Sentence

denotes

Evidence from laboratory, animal, and clinical studies demonstrate that the use of associated or isolated antivirals can delay the progression of lung lesions and decrease the possibility of respiratory transmission of SARS-CoV-2.

T427

87296-87452

Sentence

denotes

In this study, we selected the following most promising treatment options: lopinavir/ritonavir, arbidol, ribavirin, remdesivir, favipiravir, and type I IFN.

T428

87453-87844

Sentence

denotes

In the context of discovering new drugs, it is efficient to test the efficacy of existing antiviral drugs regarding the treatment of related viral infections. After the emergence of SARS in 2003, the screening of approved drugs identified an effective SARS-CoV-2 antiviral-drug candidate: the combination of the human immunodeficiency virus (HIV) protease inhibitors lopinavir and ritonavir.

T429

87845-88000

Sentence

denotes

However, lopinavir has insufficient oral bioavailability for significant therapeutic activity due to rapid catabolism by the cytochrome P450 enzyme system.

T430

88001-88213

Sentence

denotes

Thus, ritonavir is a cytochrome P450 and glycoproteins inhibitor, which increases the lopinavir plasma half-life, enhancing the pharmacokinetic and pharmacodynamic activities against the viral HIV-protease (303).

T431

88214-88524

Sentence

denotes

Chu et al. (304) described the possible mechanism of action of these drugs on SARS-CoV-1, suggesting that they act by inhibiting intracellular viral multiplication, preventing the action of the protease enzyme, which leads to the formation of an immature and less infectious virus with no ability to replicate.

T432

88525-88670

Sentence

denotes

Choy et al. (305) were successful at demonstrating the antiviral effect of lopinavir against SARS-CoV-2, but this was not the case for ritonavir.

T433

88671-88836

Sentence

denotes

In turn, Kang et al. (306) found a lower viral load in infected SARS-CoV-2 Vero cells treated with lopinavir/ritonavir in relation to the untreated infected control.

T434

88837-89114

Sentence

denotes

Although no consensus has been reached on its efficacy, dosage, or administration period, the literature includes some case reports, case series, and observational studies reporting a protective effect of the lopinavir/ritonavir combination in COVID-19 patients (110, 307–312).

T435

89115-89345

Sentence

denotes

Conversely, Cao et al. (313) conducted a controlled open‐label study with 199 hospitalized severe COVID‐19 patients randomly divided into two groups: a standard care group and a lopinavir/ritonavir treatment group (400 mg/100 mg).

T436

89346-89532

Sentence

denotes

No benefit was observed in the lopinavir/ritonavir treatment group, showing no significant results for faster clinical improvement, lower mortality, or decreased viral RNA detectability.

T437

89533-89739

Sentence

denotes

Although there are 85 clinical trials in progress testing lopinavir/ritonavir associated with other drugs on SARS-CoV-2 and/or COVID-19, WHO stopped the study of lopinavir/ritonavir in the Solidarity Trial.

T438

89740-89957

Sentence

denotes

Deng et al. (312) have studied the association of lopinavir/ritonavir with arbidol treatment and demonstrated a significant improvement in COVID-19 patients compared with a group treated only with lopinavir/ritonavir.

T439

89958-90092

Sentence

denotes

Arbidol (umifenovir) is a broad-spectrum antiviral and immunomodulatory compound used to treat influenza and many other viruses (314).

T440

90093-90398

Sentence

denotes

Analyses of molecular dynamics and structure-guided drug-binding have suggested an efficiency of arbidol at blocking or hampering the trimerization of the SARS-CoV-2 spike glycoprotein, in addition to inhibiting virus-cell interactions, which supports the potential use of arbidol to treat COVID-19 (315).

T441

90399-90635

Sentence

denotes

Chen et al. (316) demonstrated that arbidol therapy was able to shorten the course of the disease and promote clinical improvement, resulting in low fever and improvements in dry cough without side effects faster than the control group.

T442

90636-90767

Sentence

denotes

Zhu et al. (317) also demonstrated the effects of arbidol by retrospectively analyzing the clinical data from 50 COVID-19 patients.

T443

90768-91142

Sentence

denotes

The study demonstrated that the use of arbidol monotherapy, without association with other drugs, was more effective than the treatment with lopinavir/ritonavir, showing clinical improvement of the disease, presenting a total elimination of viral load over a shorter duration; in addition, no fever or ARDS were reported compared with those in the lopinavir/ritonavir group.

T444

91143-91357

Sentence

denotes

Ribavirin is another antiviral drug used in association with lopinavir/ritonavir to treat SARS-CoV-1 and was able to reduce viral load, risk of adverse clinical outcomes, ARDS, or death in SARS patients (304, 318).

T445

91358-91585

Sentence

denotes

Ribavirin has a broad antiviral spectrum as it is a nucleotide analog that competes for the active site of RdRp, a crucial enzyme in the life cycle of RNA viruses, inhibiting viral replication and transcription (221, 319, 320).

T446

91586-91792

Sentence

denotes

Elfiky (320) conducted an in silico study demonstrating that ribavirin and other antivirals such as sofosbuvir can strongly bind to coronavirus RdRp, preventing the transcription of new copies of viral RNA.

T447

91793-92003

Sentence

denotes

Only a few clinical studies have investigated the effect of ribavirin on COVID-19 patients, with the studies available generally focusing on the association of ribavirin and other therapeutic schemes (321–323).

T448

92004-92101

Sentence

denotes

Nevertheless, China’s government (324) has recommended the use of ribavirin in COVID-19 patients.

T449

92102-92193

Sentence

denotes

Remdesivir (RDV) is also among the several potential drugs tested for SARS-CoV-2 treatment.

T450

92194-92368

Sentence

denotes

Originally developed to treat Ebola virus infection, RDV is active against RNA viruses from different families, including Coronaviridae (e.g., SARS-CoV-1 and MERS-CoV) (325).

T451

92369-92446

Sentence

denotes

RDV showed an in vitro effective antiviral activity against SARS-CoV-2 (326).

T452

92447-92672

Sentence

denotes

Grein et al. (327) conducted a cohort study with 53 COVID-19 patients treated with RDV and found that 68% of them had improved oxygen-support class, whereas 57% of the patients receiving mechanical ventilation were extubated.

T453

92673-92823

Sentence

denotes

Overall mortality reached 13% over a median follow-up of 18 days, however, viral load data were not collected to confirm the antiviral effects of RDV.

T454

92824-93050

Sentence

denotes

The biggest issue with this study is that the authors did not include a group without RDV, which hampers the performance of comparative statistical analyses to prove whether the data found resulted from the treatment with RDV.

T455

93051-93281

Sentence

denotes

Another double-blind, randomized, placebo-controlled trial of intravenous RDV conducted in adults hospitalized with COVID-19 with evidence of lower respiratory tract involvement was performed in different parts of the world (328).

T456

93282-93502

Sentence

denotes

The study of Beigel and colleagues (328) enrolled 1,063 COVID19 pneumonia patients, 538 of whom were assigned to the treatment with RDV and 521 to a placebo, showed the effectiveness of RDV in treating COVID-19 patients.

T457

93503-93715

Sentence

denotes

The drug was superior to the placebo in reducing the recovery time in hospitalized COVID-19 patients and decreased the mortality rate in the RDV group, however, this result did not reach statistical significance.

T458

93716-93974

Sentence

denotes

Antionori et al. (329), analyzing patients with severe COVID-19 pneumonia in an intensive care unit (ICU) who were treated for 10 days with RDV, found that on the 28th day, 38.9% showed improvement, 16.7% were still on mechanical ventilation, and 44.4% died.

T459

93975-94155

Sentence

denotes

The data suggest that this treatment can benefit hospitalized patients who are not in the ICU, where the clinical result was better and adverse events are observed less frequently.

T460

94156-94374

Sentence

denotes

Alternatively, the randomized, double-blind, placebo-controlled, multicenter trial with 273 ill individuals performed by Wang et al. revealed that RDV intravenous administration was well-tolerated in COVID-19 patients.

T461

94375-94466

Sentence

denotes

However, the authors did not find any clinical improvement or significant antiviral effect.

T462

94467-94678

Sentence

denotes

Goldman et al. (330), in another phase 3 clinical trial on 397 patients with severe COVID-19 without mechanical ventilation support, also did not find differences between 5-day and 10-day courses of RDV therapy.

T463

94679-94886

Sentence

denotes

The RDV data currently available are still controversial, however, dozens of clinical studies are currently using this drug as an alternative treatment for COVID-19, possibly further elucidating its effects.

T464

94887-95063

Sentence

denotes

The efficiency of favipiravir, another anti-influenza RdRp inhibitor, has also been clinically assessed and was approved for COVID-19 treatment in China, March 2020 (331, 332).

T465

95064-95190

Sentence

denotes

An experimental study carried out with the VERO cell line showed that the drug has in vitro activity against SARS-CoV-2 (326).

T466

95191-95507

Sentence

denotes

Aiming at comparing the effects of favipiravir and lopinavir/ritonavir, Cai et al. (333) conducted an open, non-randomized, before-after controlled study with 80 patients and found that favipiravir favored viral clearance and improved chest CT, having caused fewer adverse effects than the lopinavir/ritonavir group.

T467

95508-95576

Sentence

denotes

Currently, 31 clinical trials using this medication are in progress.

T468

95577-95785

Sentence

denotes

Regarding antivirals, type I IFN is a group of cytokines comprising the α and β subtypes, among others, with an important role in antiviral immunity that interferes with viral replication, as discussed above.

T469

95786-96073

Sentence

denotes

Many studies have shown the protective effect of type I IFN associated with antiviral therapies for patients with SARS and MERS [reviewed by Sallard et al. (334)], which arouses the interest of the scientific community in type I IFN as a potential treatment against SARS-CoV-2 (334–337).

T470

96074-96226

Sentence

denotes

Despite their efficacy against SARS-CoV-2 (338, 339), the results of in vitro studies using IFN-α and -β to treat COVID-19 patients remain inconclusive.

T471

96227-96438

Sentence

denotes

Such uncertain nature of the results is associated with biases present in these studies, which include limited-size sample, heterogeneous experimental designs/clinical status, and the type of IFN isoform tested.

T472

96439-96633

Sentence

denotes

In addition, since COVID-19 treatments rarely involve monotherapy, it is difficult to assess whether the results derived from the tested IFN or the drugs used in combination (322, 323, 340–343).

T473

96634-96890

Sentence

denotes

It is also worth mentioning that, as discussed above, type I IFN appears to exacerbate inflammation in the progression to severe COVID-19; the timing of administration and subgroups targeted for treatment with type I IFN need to be considered with caution.

T474

96891-97247

Sentence

denotes

A recent retrospective multicenter cohort study of 446 Chinese patients with COVID-19 reported that among severe to critical COVID-19 patients, early administration (≤5 days after admission) of IFN-α2b decreased mortality in comparison with no admission of IFN-α2b, whereas no significant benefit was associated with IFN-α2b use in moderately ill patients.

T475

97248-97364

Sentence

denotes

However, late use of IFN-α2b increased mortality and delayed recovery of severe to critical COVID-19 patients (344).

T476

97365-97590

Sentence

denotes

Zhou et al. (341), investigated the isolated effect of IFN-α in a cohort study comparing 77 patients with moderate COVID-19 treated with nebulized IFN-α2b (5 mU b.i.d.), oral arbidol (200 mg t.i.d.), or a combination of both.

T477

97591-97872

Sentence

denotes

Although the study did not include a control group, the treatment with IFN-α2b, either containing arbidol or not, significantly reduced the duration of detectable virus in the upper respiratory tract and the circulating of inflammatory markers (IL-6 and C-reactive protein levels).

T478

97873-98202

Sentence

denotes

Still, in a retrospective multicenter cohort study with 141 mild COVID-19 patients by Xu et al. (342), the arbidol/IFN-α2b combination proved more effective in accelerating pneumonia recovery than IFN-α2b monotherapy, but this was not the case for viral clearance or reducing the length of hospital stay than IFN-α2b monotherapy.

T479

98203-98544

Sentence

denotes

Hung et al. (322) assessed the effect of IFN-β on COVID-19 patients and found that the triple combination of IFN-β1b, lopinavir/ritonavir, and ribavirin was safer and more effective than lopinavir/ritonavir alone at alleviating symptoms, shortening the duration of viral shedding and hospital stay in patients with mild to moderate COVID-19.

T480

98545-98674

Sentence

denotes

Similarly, an open randomized clinical trial was carried out by Danoudi-Monfared et al. (345), analyzing treatment with IFN-β-1a.

T481

98675-98915

Sentence

denotes

The IFN group of COVID-19 patients (n=42) received IFN β-1a in addition to the protocol medications (hydroxychloroquine plus lopinavir-ritonavir or atazanavir-ritonavir) while the control group (n=39) received only the protocol medications.

T482

98916-99043

Sentence

denotes

The IFN-β-1a-treated patients showed a significantly increased discharge rate on day 14 and decreased mortality within 28 days.

T483

99044-99152

Sentence

denotes

A better survival rate was also observed when patients received IFN- β-1a in the early stage of the disease.

T484

99153-99249

Sentence

denotes

The COVID-19 treatment guidelines of many countries already recommend the use of IFNs α/β (335).

T485

99250-99376

Sentence

denotes

Currently, all over the world, more than 20 clinical trials are using IFN-α and/or β alone or in association with other drugs.

T486

99378-99412

Sentence

denotes

Chloroquine and Hydroxychloroquine

T487

99413-99566

Sentence

denotes

Chloroquine and hydroxychloroquine have been used worldwide for more than 70 years, and they are part of the WHO model list of essential medicines (346).

T488

99567-99905

Sentence

denotes

They were synthesized specifically for the treatment and chemoprevention of malaria, but their immunomodulatory activity led these drugs to be used against autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, and other inflammatory rheumatic diseases; they also show broad-spectrum antiviral effects (347–349).

T489

99906-100092

Sentence

denotes

Regarding the chemical structure, hydroxychloroquine differs from chloroquine in the presence of a hydroxyl group at the end of the side chain: the N-ethyl substituent is β-hydroxylated.

T490

100093-100348

Sentence

denotes

Both drugs have similar pharmacokinetics, with rapid gastrointestinal absorption and renal elimination, but different clinical indications and toxic doses, in which hydroxychloroquine is less toxic and more clinically used in the malaria model (348, 350).

T491

100349-100477

Sentence

denotes

The action mechanism of these drugs has direct molecular effects on lysosomal activity, autophagy, and signaling pathways (347).

T492

100478-100676

Sentence

denotes

As antivirals, chloroquine is known to block SARS-CoV-1-infection by increasing endosomal pH required for virus entry, as well as interfering with the glycosylation of cellular receptors (351, 352).

T493

100677-100973

Sentence

denotes

The possible mechanism against SARS-CoV-2 is the inhibition of virus entry by altering the glycosylation of ACE2, reducing the binding efficiency between ACE2 in host cells and the S protein on the surface of the SARS-CoV-2, thus preventing the virus from binding to target cells (348, 351, 353).

T494

100974-101103

Sentence

denotes

In addition to a potent antiviral inhibition, the immunomodulatory activity of these drugs is well established in the literature.

T495

101104-101558

Sentence

denotes

Proposed effects of chloroquine on the immune system include increasing the export of soluble antigens into the cytosol of dendritic cells, the blocking of TLR7 and TLR9 signaling, thus reconstructing CD8+ cytotoxic viral response, and inhibiting and/or reducing the production of inflammatory cytokines like IL-1, IL-6, TNF, and IFN-α (347, 354–359), which has an important role in the immunopathogenesis of COVID-19, as previously reported in item 4.1.

T496

101559-101714

Sentence

denotes

In vitro studies on SARS-CoV-2 have demonstrated the low-dose action of these drugs, having found the lowest half-maximal effective concentrations (EC50s).

T497

101715-101821

Sentence

denotes

In addition, their association with azithromycin significantly inhibited viral replication (326, 360–362).

T498

101822-102074

Sentence

denotes

In humans, a study by Gao, Tian, and Yang (363) showed that patients treated with chloroquine phosphate had inhibited exacerbation of pneumonia, improving lung imaging findings, promoting a virus-negative conversion, and shortening the COVID-19 course.

T499

102075-102317

Sentence

denotes

The association of hydroxychloroquine with other drugs is also suggested, with emphasis on studies using azithromycin, a broad-spectrum macrolide antibiotic primarily used to treat respiratory, enteric, and genitourinary bacterial infections.

T500

102318-102467

Sentence

denotes

Despite not yet being approved for antiviral therapy, it has been studied in vitro and in clinical trials for activity against several viruses (364).

T501

102468-102632

Sentence

denotes

Gautret et al. (365) demonstrated the effectiveness of the hydroxychloroquine-azithromycin combination in a non-randomized clinical trial with 36 COVID-19 patients.

T502

102633-102792

Sentence

denotes

A 57.1% rate of cure was attributed to the patients treated with hydroxychloroquine, however, when combined with azithromycin, 100% of the patients were cured.

T503

102793-102951

Sentence

denotes

The authors suggested a synergistic effect of the drug combination since both were reported to have antiviral and immunomodulatory activity in the literature.

T504

102952-103206

Sentence

denotes

Gautret et al. (366) conducted another analysis to provide evidence of a beneficial effect of co-administration of hydroxychloroquine with azithromycin in a non-comparative and uncontrolled observational study with 80 mildly infected SARS-CoV-2 patients.

T505

103207-103426

Sentence

denotes

The hydroxychloroquine/azithromycin treatment showed that 81.3% of the patients had a favorable result with a rapid decrease in nasopharyngeal viral load at day 8 (93%), reducing the mean length of stay in the hospital.

T506

103427-103530

Sentence

denotes

Arshad et al. (367) performed a multicenter observational study, which included 2541 COVID-19 patients.

T507

103531-103726

Sentence

denotes

Patients were separated into four groups: untreated (n = 409), treated with hydroxychloroquine (n = 1202), the association of hydroxychloroquine and azithromycin, and azithromycin only (n = 147).

T508

103727-103946

Sentence

denotes

The authors suggested that the treatment with hydroxychloroquine alone and in combination with azithromycin was associated with a reduction in the hazard ratio for death when compared with receipt of neither medication.

T509

103947-104152

Sentence

denotes

However, a lot of controversy has been raised about these data, and many important limitations of this study were considered by several authors (368–373), threatening the validity of the reported findings.

T510

104153-104444

Sentence

denotes

Among these, there is the potential for immortal time bias and selection bias, the administration of corticosteroids in most patients treated with hydroxychloroquine than in other groups, and a disproportionately high share of patients with cardiovascular comorbidity in the untreated group.

T511

104445-104633

Sentence

denotes

Seeking to analyze the efficacy of early treatment using hydroxychloroquine and azithromycin, Million et al. (374) carried out a retrospective study with 1061 SARS-CoV-2 infected patients.

T512

104634-104796

Sentence

denotes

In the study, 91.7% of the patients reached good clinical results and virological cure within 10 days, while 4.3% had a poor outcome associated with advanced age.

T513

104797-104902

Sentence

denotes

However, it is worth mentioning that the study did not include a control group to establish a comparison.

T514

104903-105145

Sentence

denotes

To assess the use of hydroxychloroquine as a prophylactic measure, Boulware et al. (375) performed a randomized, double-blind trial in adults who had been exposed to individuals diagnosed with COVID-19, either in the home or work environment.

T515

105146-105241

Sentence

denotes

The authors found that postexposure prophylaxis did not prevent the development of the disease.

T516

105242-105485

Sentence

denotes

An important question that may be considered about chloroquine and its derivate is the numerous adverse effects reported, such as nausea, pruritus, headache, hypoglycemia, neuropsychiatric effects, and idiosyncratic hypersensitivity reactions.

T517

105486-105650

Sentence

denotes

In long-term treatments, effects such as retinopathy, vacuolar myopathy, neuropathy, restrictive cardiomyopathy, and cardiac conduction disorders are also reported.

T518

105651-105794

Sentence

denotes

Furthermore, its concomitant use with azithromycin may predispose patients to arrhythmias (213), which represents a major negative implication.

T519

105795-105940

Sentence

denotes

Huang et al. (376) conducted a randomized clinical trial with 22 patients in China to compare the effects of chloroquine and lopinavir/ritonavir.

T520

105941-106144

Sentence

denotes

Even though chloroquine led to some clinical improvement, half of the patients experienced adverse effects such as vomiting, abdominal pain, nausea, diarrhea, skin rashes, cough, and shortness of breath.

T521

106145-106484

Sentence

denotes

Satlin et al. (377), Magagnoli et al. (378), Rosenberg et al. (379), and Ip et al. (380) reported that treatment with hydroxychloroquine, azithromycin, or both were not associated with a survival benefit among patients and there were no significant differences in mortality for patients receiving hydroxychloroquine during hospitalization.

T522

106485-106697

Sentence

denotes

Similarly, Mahévas et al. (381) analyzed the efficacy of hydroxychloroquine in patients hospitalized with coronavirus pneumonia who needed oxygen but not intensive care, through a comparative observational study.

T523

106698-106765

Sentence

denotes

181 patients were analyzed, 84 of whom received hydroxychloroquine.

T524

106766-107036

Sentence

denotes

Data showed there was no effect on reducing admissions to intensive care or deaths on day 21 after hospital admission and the hydroxychloroquine treatment did not have any effect on survival without acute respiratory distress syndrome on day 21 after hospital admission.

T525

107037-107253

Sentence

denotes

Tang et al. (382) carried out a multicenter, open, randomized, and controlled clinical trial evaluating 150 patients admitted with confirmed mild to severe COVID-19; of these, 75 were treated with hydroxychloroquine.

T526

107254-107346

Sentence

denotes

The authors demonstrated that treatment does not contribute to the elimination of the virus.

T527

107347-107619

Sentence

denotes

Borba et al. (383) conducted a phase IIb, double-blind, randomized clinical trial comparing the effects of high doses (600 mg/twice daily for 10 days) and low doses (450 mg twice daily at day 1 and once daily for 4 days) of chloroquine in 81 and 40 patients, respectively.

T528

107620-107735

Sentence

denotes

The results did not evidence lower viral load in respiratory secretions, not even in combination with azithromycin.

T529

107736-107842

Sentence

denotes

The mortality rate for the high-dose group was over twice as high as the low-dose group (39.0% vs. 16.0%).

T530

107843-108068

Sentence

denotes

Additionally, some patients, mainly in the high-dose group, showed adverse effects, such as increased creatine phosphokinase (CK) and CK-MB, while the high-dosage group exhibited more corrected QT (QTc) interval prolongation.

T531

108069-108124

Sentence

denotes

Neither of the dosages was able to influence lethality.

T532

108125-108221

Sentence

denotes

The authors concluded that critically ill patients should not receive chloroquine at high doses.

T533

108222-108460

Sentence

denotes

In the meantime, a cohort study with 201 patients showed that the use of chloroquine or hydroxychloroquine combined with azithromycin generated a higher increase in QT prolongation than chloroquine or hydroxychloroquine monotherapy (384).

T534

108461-108658

Sentence

denotes

More recently, another large observational study involving 1376 cases of COVID-19 from New York found no significant association between the use of hydroxychloroquine and intubation or death (385).

T535

108659-108832

Sentence

denotes

Currently, chloroquine and hydroxychloroquine are the most largely studied compounds in the context of COVID-19 treatment, encompassing at least 320 ongoing clinical trials.

T536

108833-109033

Sentence

denotes

However, considering that more recent studies failed to prove any favorable effect of their use in COVID-19 patients, the WHO discontinued the study of hydroxychloroquine in the Solidarity Trial (13).

T537

109035-109050

Sentence

denotes

Antihelminthics

T538

109051-109341

Sentence

denotes

Amid the COVID-19 pandemic, the search for active molecules against the coronavirus should use advanced tools of computational biology and artificial intelligence for the recognition of drugs already approved and commercialized with potential effects on the replication of SARS-CoV-2 (386).

T539

109342-109621

Sentence

denotes

In this context, over the past few years, research has shown the antiviral potential in vitro, especially against RNA viruses, of Ivermectin, the best known and most widely used antiparasitic drug in human and veterinary medicine, with promising results against SARS-CoV-2 (387).

T540

109622-109855

Sentence

denotes

The model of Vero/hSLAM cells infected with a SARS-CoV-2 isolate showed the ivermectin antiviral effect in which 24h-ivermectin treatment reduced 93% of RNA viral load in the cell supernatant and 99.8% of the intracellular viral RNA.

T541

109856-110078

Sentence

denotes

The authors hypothesized that its probable mechanism of action occurs through the inhibition of nuclear import of importin-α/β1–mediated the IMPα/β1 heterodimer of viral proteins, as shown for other RNA viruses (387, 388).

T542

110079-110333

Sentence

denotes

Corroborating, Lehrer and Rheinstein (389) identified the ivermectin docking site between the region of leucine 91 of viral spike and the histidine 378 of the ACE2 receptor, which may interfere with the attachment of the spike to the human cell membrane.

T543

110334-110686

Sentence

denotes

Although the in vitro proliferation inhibition effect of Ivermectin against SARS-CoV-2 has been shown, there is no evidence that the IC50 of ~ 2 µM determined by Caly and colleagues can be achieved in the clinic where pharmacokinetics studies showed that even the maximum tested dosage of 1700 μg/kg presented only 0.28μM of plasma concentration (390).

T544

110687-110928

Sentence

denotes

According to Navarro et al. (391), no adverse effects of high doses of ivermectin have so far been demonstrated in clinical studies with patients, with only a few transient ocular events in those who experienced high doses (up to 400 μg/kg).

T545

110929-111174

Sentence

denotes

However, Duthaler et al. (392) demonstrated that the adverse effects of ivermectin in the body can vary according to the patient’s nutritional status, and the effects of high doses can be harmful, especially in patients with malnutrition levels.

T546

111175-111343

Sentence

denotes

The general consensus of the authors is that further studies are needed to evaluate the efficacy and safety of ivermectin administered in high doses against SARS-CoV-2.

T547

111344-111568

Sentence

denotes

Xu et al. (386) published a review article regarding niclosamide, an old anthelmintic used to treat tapeworm infections, showing promising antiviral activity against various viral infections, such as SARS-CoV-1 and MERS-CoV.

T548

111569-111674

Sentence

denotes

This drug has shown to act in vitro by enhancing autophagy and efficiently reducing MERS-CoV replication.

T549

111675-111870

Sentence

denotes

Originally developed as an antiprotozoal agent, nitazoxanide is another broad-spectrum antiviral agent that has been currently developed to treat influenza and other viral respiratory infections.

T550

111871-112056

Sentence

denotes

Nitazoxanide exhibited in vitro activity against MERS-CoV by inhibiting the expression of viral N protein, in addition to reducing the production of IL-6 in an in vivo model (393, 394).

T551

112057-112372

Sentence

denotes

Despite the lack of studies in the literature showing the effect of these anthelmintics on the COVID-19 model, clinical trials have currently included this type of antiviral agent in many countries; there are 37 clinical trials using ivermectin alone or associated with hydroxychloroquine, and 19 with nitazoxanide.

T552

112373-112475

Sentence

denotes

These studies are yet to be published and preliminary results are expected in the second half of 2020.

T553

112477-112491

Sentence

denotes

Anticoagulants

T554

112492-112661

Sentence

denotes

A high mortality risk in severe COVID-19 patients has been described, especially due to the development of disseminated intravascular coagulation and coagulopathy (395).

T555

112662-112840

Sentence

denotes

Patients with sepsis and disseminated intravascular coagulation may develop thromboembolic complications or microvascular clot deposition, contributing to multiple organ failure.

T556

112841-113123

Sentence

denotes

In patients with severe pneumonia, the activation of vascular endothelium, platelets, and leukocytes results in the unregulated generation of thrombin, both locally, in the lungs, and systemically, leading to fibrin deposition and subsequent tissue damage and microangiopathy (396).

T557

113124-113353

Sentence

denotes

In COVID-19 patients, severe pulmonary inflammation is believed to be associated with the regulation of pro-inflammatory cytokines, which can cause the dysfunction of endothelial cells and consequently higher thrombin production.

T558

113354-113446

Sentence

denotes

Therefore, the use of anticoagulant therapy could be beneficial for COVID-19 patients (397).

T559

113447-113707

Sentence

denotes

In a retrospective study with 449 patients with severe COVID-19, Tang et al. (395) observed a lower mortality rate in individuals treated with prophylactic heparin associated with coagulopathy compared with those who had not been treated with an anticoagulant.

T560

113708-113928

Sentence

denotes

The study associated the use of thrombosis prophylaxis with lower 28-day mortality in COVID-19 patients, but only for those presenting a high value of either sepsis-induced coagulopathy score (≥4) or D-dimer (≥3.0 mg/L).

T561

113929-114174

Sentence

denotes

Paranjpe et al. (398) carried out a large cohort analysis with 2773 COVID-19 patients in the United States, among which 28% received anticoagulant therapy, and also found an association of anticoagulant-based treatment with lower mortality risk.

T562

114175-114345

Sentence

denotes

The mortality rate in patients who required mechanical ventilation and received anticoagulant therapy was lower than those who had not been treated with an anticoagulant.

T563

114346-114570

Sentence

denotes

It is important to highlight that heparin has an anti-inflammatory effect that can bind to inflammatory cytokines, chemokines, and proinflammatory proteins, inhibiting neutrophil chemotaxis and leukocyte migration (399–401).

T564

114571-114778

Sentence

denotes

In the current COVID-19 context, there are over 60 ongoing clinical trials covering the use of thromboprophylaxis, which will certainly clarify the potential role of anticoagulants in patients with COVID-19.

T565

114780-114793

Sentence

denotes

Dexamethasone

T566

114794-115189

Sentence

denotes

Recent studies have demonstrated great interest in the role of corticosteroids to attenuate the pulmonary and systemic damage in COVID-19 patients because of their potent anti-inflammatory and antifibrotic properties, especially dexamethasone, a synthetic corticosteroid which is on the list of essential medicines of the World Health Organization and is readily available worldwide at low cost.

T567

115190-115320

Sentence

denotes

This drug acts as a broad-spectrum immunosuppressor and has greater activity in inflammatory and autoimmune conditions (402, 403).

T568

115321-115539

Sentence

denotes

Recently, the randomized RECOVERY study, conducted by the University of Oxford, declared dexamethasone as the world’s first treatment proven effective in reducing the risk of death among severely ill COVID-19 patients.

T569

115540-115654

Sentence

denotes

The trial accompanied a total of 2104 patients treated with dexamethasone and 4321 who received conventional care.

T570

115655-115906

Sentence

denotes

The dexamethasone group showed reduced 28-day mortality in COVID-19 patients receiving invasive mechanical ventilation or oxygen therapy without invasive mechanical ventilation, but not in patients who were not receiving any respiratory support (404).

T571

115907-116096

Sentence

denotes

Similar results were published by Tomazini et al. (405) in a Brazilian multicenter, randomized, open-label, clinical trial involving 299 adults with moderate or severe ARDS due to COVID-19.

T572

116097-116305

Sentence

denotes

The study showed that 144 patients who received dexamethasone treatment plus the standard treatment showed a significant increase in the number of days without mechanical ventilation during the first 28 days.

T573

116306-116643

Sentence

denotes

In the same way, Villar et al. (406) also published a multicenter randomized clinical trial and showed that early administration of dexamethasone in COVID-19 patients who had moderate and severe ARDS presented an increased average number of days without mechanical ventilation, as well as reduced mortality compared to the control group.

T574

116644-116757

Sentence

denotes

There are currently 29 clinical trials evaluating the therapeutic efficacy of dexamethasone in COVID-19 patients.

T575

116758-117053

Sentence

denotes

In the face of the huge amount of studies involving clinical trials to test drugs for SARS-CoV-2 and COVID-19 treatment, in addition to the different research methodologies and criteria addressed, on March 22, 2020 the WHO and partners launched the “SOLIDARITY”, an international clinical trial.

T576

117054-117238

Sentence

denotes

The purpose is to help find an effective treatment for COVID-19, seeking to establish consistent endpoints, control arms, and inclusion-exclusion criteria for this umbrella trial (13).

T577

117239-117457

Sentence

denotes

The SOLIDARITY trial includes hospitalized patients with COVID-19 from more than 90 countries around the world to compare treatment options with standard care and assess their relative effectiveness against SARS-CoV-2.

T578

117458-117623

Sentence

denotes

By enrolling patients from multiple countries, the SOLIDARITY trial aims at rapidly discovering if any of the drugs mitigate disease progression or improve survival.

T579

117624-117761

Sentence

denotes

According to the WHO director-general, the study will dramatically cut the time needed to generate robust evidence on how the drugs work.

T580

117762-117868

Sentence

denotes

Thus, the two most promising treatment options selected were Remdesivir or Lopinavir/Ritonavir with IFN-β.

T581

117869-117926

Sentence

denotes

Other drugs can be added based on emerging evidence (13).

T582

117928-117938

Sentence

denotes

Conclusion

T583

117939-118120

Sentence

denotes

In conclusion, this collection of works suggests that the genomic changes of SARS-CoV-2 are responsible for its higher transmissibility rate and severity in relation to other hCoVs.

T584

118121-118262

Sentence

denotes

Furthermore, the process of tropism and invasion of the virus is favored by its capacity of high-affinity bonding to the human ACE2 receptor.

T585

118263-118405

Sentence

denotes

Cytokines have a direct role in the immunopathogenesis of COVID-19 by inducing the hyper inflammation and lung injury peculiar to the disease.

T586

118406-118583

Sentence

denotes

Benefits of IFN-mediated response seem to occur only during early infection, and the failed control of its production over time might be related to the worsening of the disease.

T587

118584-118822

Sentence

denotes

Monocytes and macrophages have an important role in respiratory failure during COVID-19; several studies have reported that these cells migrate to the lungs, producing pro-inflammatory cytokines, like IL-6, and inducing epithelial damage.

T588

118823-119039

Sentence

denotes

Controversially, at later stages, COVID-19 patients present an impaired immune response due to exhausted phenotype and lower effector T cells, CD8+ T lymphocytes, and NK cells, culminating in antiviral immunity loss.

T589

119040-119306

Sentence

denotes

Theoretically, the production of specific antibodies against SARS-CoV-2 by the immune system should be able to combat the virus and reduce viral load, but in critically ill patients, it does not seem to occur effectively, contributing to the severity of the disease.

T590

119307-119606

Sentence

denotes

Unfortunately, no effective vaccines or therapeutic antiviral agents have been approved for the treatment of COVID-19 so far, but immunotherapy and some repositioned drugs originally used to treat inflammatory and coagulation disorders and viral and parasitic infections are ongoing clinical trials.

T591

119607-119809

Sentence

denotes

This is a unique moment in science and humanity, with some mismatched information, as well as novel, important discoveries being made every day, therefore, all information must be interpreted carefully.

T592

119810-119920

Sentence

denotes

Our review encompassed the most relevant articles in the area seeking to disseminate good-quality information.

T593

119922-119942

Sentence

denotes

Author Contributions

T594

119943-120011

Sentence

denotes

TS, FT-P, RS: study design, data collection, and manuscript writing.

T595

120012-120083

Sentence

denotes

MG, BB, MD, AR, AC, VC, and ES: data collection and manuscript writing.

T596

120084-120135

Sentence

denotes

IC, WP, and IC-C: text correction and organization.

T597

120136-120190

Sentence

denotes

MM-S: study design, text correction, and organization.

T598

120191-120265

Sentence

denotes

All authors contributed to the article and approved the submitted version.

T599

120266-120406

Sentence

denotes

The corresponding authors attest that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.

T600

120408-120428

Sentence

denotes

Conflict of Interest

T601

120429-120601

Sentence

denotes

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

T602

120603-120618

Sentence

denotes

Acknowledgments

T603

120619-120692

Sentence

denotes

We thank Ms. Ivy Gobetti for editing and correcting the English language.

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