PubAnnotation

Id	Subject	Object	Predicate	Lexical cue
T11	0-12	Sentence	denotes	Introduction
T12	13-309	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	310-554	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	555-739	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	740-897	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	898-1104	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	1105-1232	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	1233-1531	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	1532-1806	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	1807-2001	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	2002-2149	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	2150-2503	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	2504-2806	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	2807-2976	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	2977-3098	Sentence	denotes	A specific antiviral agent to treat the infected individuals and decrease viral transmission (11, 12) is yet to be found.
T26	3099-3324	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	3325-3540	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	3541-3725	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	3726-3957	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	3959-3971	Sentence	denotes	Coronavirus:
T31	3972-3983	Sentence	denotes	An Overview
T32	3984-4179	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	4180-4350	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	4351-4634	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	4635-4750	Sentence	denotes	According to antigenic and genetic criteria, CoVs are classified into three groups: α-CoVs, β-CoVs and γ-CoVs (17).
T36	4751-4918	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	4919-5122	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	5123-5273	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	5274-5503	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	5504-5736	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	5737-5994	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	5995-6195	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	6196-6371	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	6372-6548	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	6549-6719	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	6720-7120	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	7121-7306	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	7307-7518	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	7519-7745	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	7746-7940	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	7941-8160	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	8161-8352	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	8353-8555	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	8556-9085	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	9086-9170	Sentence	denotes	Such genomic changes also affected the recognition of these viruses by immune cells.
T56	9171-9399	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	9400-9556	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	9557-9651	Sentence	denotes	All aspects of immunomodulation and immune evasion will be discussed in the subsequent topics.
T59	9652-9715	Sentence	denotes	Figure 1 Genetic evolution of SARS-CoV-2 and its consequences.
T60	9716-9923	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	9924-10185	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	10186-10247	Sentence	denotes	RBD (receptor binding domain), S1 (subunit 1) S2 (subunit 2).
T63	10249-10275	Sentence	denotes	Pathogenesis of SARS-CoV-2
T64	10277-10304	Sentence	denotes	Viral Entry and Replication
T65	10305-10402	Sentence	denotes	A virus starts its infection by binding viral particles to the host’s surface cellular receptors.
T66	10403-10537	Sentence	denotes	The recognition of cellular receptors is the first step towards viral entry into host cells, in addition to determining their tropism.
T67	10538-10756	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	10757-10974	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	10975-11135	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	11136-11252	Sentence	denotes	Homotrimers of S proteins are present on the viral surface and are responsible for attaching to host receptors (43).
T71	11253-11379	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	11380-11518	Sentence	denotes	The M protein has three transmembrane domains and shapes the virions, promotes membrane curvature, and binds to the nucleocapsid (45, 46).
T73	11519-11744	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	11745-11903	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	11904-12056	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	12057-12415	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	12416-12569	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	12570-12708	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	12709-12954	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	12955-13117	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	13118-13390	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	13391-13532	Sentence	denotes	Therefore, CoVs need to elicit exogenous proteases to perform modifications of their binding receptors necessary for the connection to occur.
T83	13533-13761	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	13762-13887	Sentence	denotes	Concerning exogenous proteins, SARS-CoV-2 can also use host proteins to prepare its S glycoprotein for receptor binding (49).
T85	13888-14102	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	14103-14302	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	14303-14497	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	14498-14732	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	14733-14850	Sentence	denotes	The non-endosomal pathway is dependent on TMPRSS2, which allows the activation of the S protein for viral entry (63).
T90	14851-15120	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	15121-15224	Sentence	denotes	Translation of subgenomic mRNAs leads to the production of structural and nonstructural viral proteins.
T92	15225-15436	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	15437-15554	Sentence	denotes	Finally, the vesicles containing the virus particles fuse with the plasma membrane to release the virus (65, 67, 68).
T94	15555-15625	Sentence	denotes	Another possible mechanism for CoV entry may occur through antibodies.
T95	15626-15988	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	15989-16266	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	16267-16548	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	16549-16772	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	16773-17054	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	17055-17295	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	17296-17438	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	17439-17720	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	17721-17964	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	17965-18143	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	18144-18404	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	18405-18643	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	18644-18904	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	18906-18927	Sentence	denotes	Pathogenic Mechanisms
T109	18928-19082	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	19083-19238	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	19239-19427	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	19428-19707	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	19708-19946	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	19947-20099	Sentence	denotes	Despite their similarities, ACE and ACE2 have different substrate specificities with distinct functionalities that perform opposite actions in the body.
T115	20100-20295	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	20296-20479	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	20480-20748	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	20749-20976	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	20977-21188	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	21189-21482	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	21483-21662	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	21663-21780	Sentence	denotes	ACE2 is also highly expressed and co-expressed with TMPRSS2 in nasal epithelial cells, chalices, and hair cells (89).
T123	21781-22129	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	22130-22419	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	22420-22601	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	22602-22842	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	22843-23157	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	23158-23403	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	23404-23647	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	23648-23847	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	23848-24324	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	24325-24518	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	24519-24887	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	24888-25028	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	25029-25296	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	25298-25331	Sentence	denotes	Clinical and Radiological Changes
T137	25332-25571	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	25572-25731	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	25732-25828	Sentence	denotes	According to the severity of symptoms, patients can be classified as mild, severe, and critical.
T140	25829-26079	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	26080-26244	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	26245-26474	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	26475-26579	Sentence	denotes	Elderly adults are more susceptible to SARS-CoV-2 and have a high risk of morbidity and mortality (111).
T144	26580-26730	Sentence	denotes	This can be explained by factors such as physiological changes and multiple age-related comorbidities, in addition to associated polymedication (112).
T145	26731-26889	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	26890-27033	Sentence	denotes	Nonspecific symptoms (dizziness, headache, and seizure) and specific symptoms (loss of smell or taste and stroke) were described (91, 113–115).
T147	27034-27168	Sentence	denotes	Epidemiological studies have reported that some patients infected with SARS‐CoV‐2 did report headaches (8%), nausea, or vomiting (1%).
T148	27169-27388	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	27389-27623	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	27624-27777	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	27778-28074	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	28075-28471	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	28472-28820	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	28821-29001	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	29002-29323	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	29324-29547	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	29548-29738	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	29739-29874	Sentence	denotes	More recently, reports on COVID-19 have included the occurrence of coagulation abnormalities in most critically ill patients (128–131).
T159	29875-30099	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	30100-30330	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	30331-30776	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	30777-31069	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	31070-31144	Sentence	denotes	In COVID-19 patients, CAC has been associated with higher mortality (131).
T164	31145-31476	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	31477-31718	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	31719-32192	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	32194-32228	Sentence	denotes	Immune Response Against SARS-CoV-2
T168	32230-32244	Sentence	denotes	Cytokine Storm
T169	32245-32620	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	32621-32771	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	32772-32984	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	32985-33141	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	33142-33390	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	33391-33729	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	33730-34053	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	34054-34339	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	34340-34466	Sentence	denotes	However, mediators related to the complement system, such as C3 and C4, did not present any difference in healthy individuals.
T178	34467-34821	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	34822-35283	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	35284-35496	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	35497-35622	Sentence	denotes	This is probably what occurs in asymptomatic individuals who can establish an effective response against SARS-CoV-2 (9, 141).
T182	35623-35797	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	35798-36119	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	36120-36346	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	36347-36526	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	36527-36768	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	36769-36885	Sentence	denotes	Additionally, Major et al. (151) described the role of types I and III of IFN in lung repair during viral infection.
T188	36886-37107	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	37108-37355	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	37356-37513	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	37514-37802	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	37803-37891	Sentence	denotes	Additionally, early treatment using this type of IFN prevented fatal infections in mice.
T193	37892-38285	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	38286-38448	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	38449-38628	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	38629-38902	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	38903-39131	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	39132-39251	Sentence	denotes	IL-7 is a pleiotropic cytokine that plays an essential role in the differentiation and clonal expansion of lymphocytes.
T199	39252-39578	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	39579-39733	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	39734-40000	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	40001-40152	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	40153-40357	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	40358-40482	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	40483-40598	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	40599-40732	Sentence	denotes	Several pro-inflammatory cytokines have been described in COVID-19 patients and are associated with the disease’s immunopathogenesis.
T207	40733-40824	Sentence	denotes	Among them, IL-1β and TNF-α stand out for playing a central role in this context (26, 156).
T208	40825-41219	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	41220-41502	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	41503-41576	Sentence	denotes	Cytokine storms may have great relevance in the pathogenesis of COVID-19.
T211	41577-41697	Sentence	denotes	The induction of inflammatory mediators can induce cell damage, especially in lung tissues, causing respiratory failure.
T212	41698-41930	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	41931-42247	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	42248-42545	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	42546-42779	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	42780-43100	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	43102-43124	Sentence	denotes	Innate Immune Response
T218	43125-43306	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	43307-43527	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	43528-43659	Sentence	denotes	Changes in this process, commonly observed in viral infections, can cause an immune imbalance and susceptibility of the host (163).
T221	43660-43829	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	43830-44054	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	44055-44202	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	44203-44484	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	44485-44774	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	44775-45024	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	45025-45165	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	45166-45341	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	45342-45537	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	45538-45672	Sentence	denotes	Controversially, these cells are the main producers of IL-10, which makes their exact function in immune responses elusive (170, 171).
T231	45673-45889	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	45890-46058	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	46059-46278	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	46279-46441	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	46442-46564	Sentence	denotes	Such a difference in response might be the key to understanding the pathogenesis of respiratory failure in COVID-19 (173).
T236	46565-46824	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	46825-47074	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	47075-47486	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	47487-47688	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	47689-47892	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	47893-48115	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	48116-48236	Sentence	denotes	Despite their central role in pathogenesis, this may indicate that these cells are not important reservoirs for viruses.
T243	48237-48477	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	48478-48610	Sentence	denotes	Additionally, macrophages were able to trigger an exacerbated inflammatory response with higher TNF-α, IL-8, IP10, MIP1α, and IL-1β.
T245	48611-48762	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	48763-48999	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	49000-49412	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	49413-49564	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	49565-49828	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	49829-50034	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	50035-50239	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	50240-50491	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	50492-50600	Sentence	denotes	Therefore, it is urgent to carry out studies aimed at analyzing the effect of SARS-CoV-2 on dendritic cells.
T254	50602-50616	Sentence	denotes	T Helper Cells
T255	50617-50735	Sentence	denotes	Establishing and maintaining immune response and memory generation against viruses depends on the activity of T cells.
T256	50736-50873	Sentence	denotes	These lymphocytes originate from bone marrow progenitor cells and migrate to the thymus for maturation, selection, and peripheral export.
T257	50874-51152	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	51153-51513	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	51514-51704	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	51705-51924	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	51925-52086	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	52087-52233	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	52234-52378	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	52379-52746	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	52747-52949	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	52950-53201	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	53202-53436	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	53437-53639	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	53640-54012	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	54013-54151	Sentence	denotes	The vast majority of studies to date show impairment of proliferation, maturation, and response of T cells, especially in sicker patients.
T271	54152-54473	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	54474-54910	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	54911-55019	Sentence	denotes	Another important point is the reduction of regulatory T cells CD4+ CD25+ Foxp3+ verified in these patients.
T274	55020-55283	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	55284-55551	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	55552-55936	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	55938-55953	Sentence	denotes	Cytotoxic Cells
T278	55954-56052	Sentence	denotes	T lymphocytes CD8+ and NK are essential to control viral infections due to their cytotoxic effect.
T279	56053-56252	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	56253-56439	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	56440-56905	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	56906-57127	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	57128-57311	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	57312-57666	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	57667-57830	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	57831-58054	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	58055-58291	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	58292-58433	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	58434-58635	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	58636-59118	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	59119-59164	Sentence	denotes	Figure 2 Immune response in COVID-19 stages.
T292	59165-59223	Sentence	denotes	SARS-CoV-2 infection is divided into three general phases.
T293	59224-59479	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	59480-59784	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	59785-60057	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	60058-60200	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	60201-60331	Sentence	denotes	In the third, or convalescence, phase, the individual can evolve in two opposite directions, recovery or clinical worsening/death.
T298	60332-60459	Sentence	denotes	In recovery, cells of lymphoid origin recover their effector function and lose markers of exhaustion, while IgG levels improve.
T299	60460-60555	Sentence	denotes	On the other hand, in patients with clinical worsening, this status of immune anergy continues.
T300	60557-60573	Sentence	denotes	Humoral Response
T301	60574-60710	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	60711-60981	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	60982-61210	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	61211-61374	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	61375-61539	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	61540-61716	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	61717-62289	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	62290-62488	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	62489-62633	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	62634-62833	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	62834-62968	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	62969-63211	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	63212-63484	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	63485-63807	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	63808-64012	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	64013-64217	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	64218-64342	Sentence	denotes	However, due to the lack of immunity provided by nAb, these individuals might suffer from SARS-CoV-2 reinfection (200, 201).
T318	64343-64756	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	64757-64927	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	64928-65140	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	65141-65395	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	65396-65534	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	65535-65691	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	65693-65711	Sentence	denotes	COVID-19 Treatment
T325	65712-65857	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	65858-65925	Sentence	denotes	The main approach to disease management focuses on supportive care.
T327	65926-66191	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	66192-66479	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	66480-66594	Sentence	denotes	The researched data (until September 2020) for ongoing and completed trials were searched in “clinicaltrials.gov”.
T330	66596-66614	Sentence	denotes	Enhancing Immunity
T331	66615-66797	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	66798-66976	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	66977-67361	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	67362-67543	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	67544-67698	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	67699-67961	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	67962-68186	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	68187-68473	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	68474-68624	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	68625-68736	Sentence	denotes	As for vitamin E, it has been shown that its deficiency can impair cellular and humoral immune responses (214).
T341	68737-68919	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	68920-69228	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	69230-69243	Sentence	denotes	Immunotherapy
T344	69245-69267	Sentence	denotes	Antibody-Based therapy
T345	69268-69498	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	69499-69650	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	69651-69845	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	69846-70102	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	70103-70225	Sentence	denotes	Viral neutralization by nAbs is also an immunotherapeutic approach and directly recognizes epitopic regions of SARS-CoV-2.
T350	70226-70536	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	70537-70625	Sentence	denotes	The therapeutic use of mAbs has shown good outcomes, mainly due to its high specificity.
T352	70626-70800	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	70801-70938	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	70939-71157	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	71158-71262	Sentence	denotes	Thus, the combination of nAbs with different viral targets and sources could improve treatment efficacy.
T356	71263-71464	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	71465-71549	Sentence	denotes	Furthermore, some immunomodulatory mAbs have been tested in the context of COVID-19.
T358	71550-71889	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	71890-71942	Sentence	denotes	However, clinical observations remain controversial.
T360	71943-72248	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	72249-72474	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	72475-72677	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	72678-72777	Sentence	denotes	In general, data from analyses on the use of this type of mAbs remain inconclusive (243, 246, 247).
T364	72778-73052	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	73053-73194	Sentence	denotes	However, seeking to verify the effectiveness of using mAbs blocking inflammatory mediators, dozens of clinical trials are currently underway.
T366	73195-73604	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	73605-73803	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	73804-74017	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	74018-74437	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	74438-74576	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	74577-74706	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	74707-74913	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	74914-75134	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	75135-75216	Sentence	denotes	Further, 60% of the patients were discharged one month after the treatment (271).
T375	75217-75368	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	75369-75544	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	75545-75714	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	75715-76026	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	76027-76314	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	76315-76436	Sentence	denotes	Nonetheless, understanding the efficacy and safety of CP therapy relies on the completion of the ongoing clinical trials.
T381	76437-76723	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	76724-76901	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	76902-77172	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	77173-77378	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	77379-77727	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	77728-77912	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	77913-78083	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	78084-78258	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	78260-78285	Sentence	denotes	Immune Cell-Based Therapy
T390	78286-78453	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	78454-78657	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	78658-78913	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	78914-79018	Sentence	denotes	Some ongoing clinical trials have been studying the use of NK cell therapy through different approaches.
T394	79019-79271	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	79272-79405	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	79406-79650	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	79651-79876	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	79877-80027	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	80028-80383	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	80384-80558	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	80559-80812	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	80813-80934	Sentence	denotes	There are currently two clinical trials underway that aim to infuse Treg cells in patients with severe COVID-19 and ARDS.
T403	80935-81119	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	81120-81300	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	81301-81428	Sentence	denotes	RAPA-501-ALLO cells will be generated from healthy donors, cryopreserved, banked, and made available for off-the-shelf therapy.
T406	81429-81659	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	81660-81902	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	81903-82089	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	82090-82408	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	82409-82684	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	82685-82907	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	82908-83218	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	83219-83484	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	83485-83579	Sentence	denotes	The patient also showed a significant improvement in lung involvement and negative viral load.
T415	83580-83952	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	83953-84093	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	84094-84316	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	84317-84399	Sentence	denotes	However, immunotherapy is effective and of immediate use, being of short duration.
T419	84400-84572	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	84573-84850	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	84852-84883	Sentence	denotes	Drug Options Against SARS-CoV-2
T422	84884-85044	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	85045-85305	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	85307-85317	Sentence	denotes	Antivirals
T425	85318-85565	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	85566-85796	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	85797-85953	Sentence	denotes	In this study, we selected the following most promising treatment options: lopinavir/ritonavir, arbidol, ribavirin, remdesivir, favipiravir, and type I IFN.
T428	85954-86345	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	86346-86501	Sentence	denotes	However, lopinavir has insufficient oral bioavailability for significant therapeutic activity due to rapid catabolism by the cytochrome P450 enzyme system.
T430	86502-86714	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	86715-87025	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	87026-87171	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	87172-87337	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	87338-87615	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	87616-87846	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	87847-88033	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	88034-88240	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	88241-88458	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	88459-88593	Sentence	denotes	Arbidol (umifenovir) is a broad-spectrum antiviral and immunomodulatory compound used to treat influenza and many other viruses (314).
T440	88594-88899	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	88900-89136	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	89137-89268	Sentence	denotes	Zhu et al. (317) also demonstrated the effects of arbidol by retrospectively analyzing the clinical data from 50 COVID-19 patients.
T443	89269-89643	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	89644-89858	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	89859-90086	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	90087-90293	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	90294-90504	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	90505-90602	Sentence	denotes	Nevertheless, China’s government (324) has recommended the use of ribavirin in COVID-19 patients.
T449	90603-90694	Sentence	denotes	Remdesivir (RDV) is also among the several potential drugs tested for SARS-CoV-2 treatment.
T450	90695-90869	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	90870-90947	Sentence	denotes	RDV showed an in vitro effective antiviral activity against SARS-CoV-2 (326).
T452	90948-91173	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	91174-91324	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	91325-91551	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	91552-91782	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	91783-92003	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	92004-92216	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	92217-92475	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	92476-92656	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	92657-92875	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	92876-92967	Sentence	denotes	However, the authors did not find any clinical improvement or significant antiviral effect.
T462	92968-93179	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	93180-93387	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	93388-93564	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	93565-93691	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	93692-94008	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	94009-94077	Sentence	denotes	Currently, 31 clinical trials using this medication are in progress.
T468	94078-94286	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	94287-94574	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	94575-94727	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	94728-94939	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	94940-95134	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	95135-95391	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	95392-95748	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	95749-95865	Sentence	denotes	However, late use of IFN-α2b increased mortality and delayed recovery of severe to critical COVID-19 patients (344).
T476	95866-96091	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	96092-96373	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	96374-96703	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	96704-97045	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	97046-97175	Sentence	denotes	Similarly, an open randomized clinical trial was carried out by Danoudi-Monfared et al. (345), analyzing treatment with IFN-β-1a.
T481	97176-97416	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	97417-97544	Sentence	denotes	The IFN-β-1a-treated patients showed a significantly increased discharge rate on day 14 and decreased mortality within 28 days.
T483	97545-97653	Sentence	denotes	A better survival rate was also observed when patients received IFN- β-1a in the early stage of the disease.
T484	97654-97750	Sentence	denotes	The COVID-19 treatment guidelines of many countries already recommend the use of IFNs α/β (335).
T485	97751-97877	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	97879-97913	Sentence	denotes	Chloroquine and Hydroxychloroquine
T487	97914-98067	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	98068-98406	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	98407-98593	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	98594-98849	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	98850-98978	Sentence	denotes	The action mechanism of these drugs has direct molecular effects on lysosomal activity, autophagy, and signaling pathways (347).
T492	98979-99177	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	99178-99474	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	99475-99604	Sentence	denotes	In addition to a potent antiviral inhibition, the immunomodulatory activity of these drugs is well established in the literature.
T495	99605-100059	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	100060-100215	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	100216-100322	Sentence	denotes	In addition, their association with azithromycin significantly inhibited viral replication (326, 360–362).
T498	100323-100575	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	100576-100818	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	100819-100968	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	100969-101133	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	101134-101293	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	101294-101452	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	101453-101707	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	101708-101927	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	101928-102031	Sentence	denotes	Arshad et al. (367) performed a multicenter observational study, which included 2541 COVID-19 patients.
T507	102032-102227	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	102228-102447	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	102448-102653	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	102654-102945	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.

T11

0-12

Sentence

denotes

Introduction

T12

13-309

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

310-554

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

555-739

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

740-897

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

898-1104

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

1105-1232

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

1233-1531

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

1532-1806

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

1807-2001

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

2002-2149

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

2150-2503

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

2504-2806

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

2807-2976

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

2977-3098

Sentence

denotes

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

T26

3099-3324

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

3325-3540

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

3541-3725

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

3726-3957

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

3959-3971

Sentence

denotes

Coronavirus:

T31

3972-3983

Sentence

denotes

An Overview

T32

3984-4179

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

4180-4350

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

4351-4634

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

4635-4750

Sentence

denotes

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

T36

4751-4918

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

4919-5122

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

5123-5273

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

5274-5503

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

5504-5736

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

5737-5994

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

5995-6195

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

6196-6371

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

6372-6548

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

6549-6719

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

6720-7120

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

7121-7306

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

7307-7518

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

7519-7745

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

7746-7940

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

7941-8160

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

8161-8352

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

8353-8555

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

8556-9085

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

9086-9170

Sentence

denotes

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

T56

9171-9399

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

9400-9556

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

9557-9651

Sentence

denotes

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

T59

9652-9715

Sentence

denotes

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

T60

9716-9923

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

9924-10185

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

10186-10247

Sentence

denotes

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

T63

10249-10275

Sentence

denotes

Pathogenesis of SARS-CoV-2

T64

10277-10304

Sentence

denotes

Viral Entry and Replication

T65

10305-10402

Sentence

denotes

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

T66

10403-10537

Sentence

denotes

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

T67

10538-10756

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

10757-10974

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

10975-11135

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

11136-11252

Sentence

denotes

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

T71

11253-11379

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

11380-11518

Sentence

denotes

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

T73

11519-11744

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

11745-11903

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

11904-12056

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

12057-12415

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

12416-12569

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

12570-12708

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

12709-12954

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

12955-13117

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

13118-13390

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

13391-13532

Sentence

denotes

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

T83

13533-13761

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

13762-13887

Sentence

denotes

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

T85

13888-14102

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

14103-14302

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

14303-14497

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

14498-14732

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

14733-14850

Sentence

denotes

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

T90

14851-15120

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

15121-15224

Sentence

denotes

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

T92

15225-15436

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

15437-15554

Sentence

denotes

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

T94

15555-15625

Sentence

denotes

Another possible mechanism for CoV entry may occur through antibodies.

T95

15626-15988

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

15989-16266

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

16267-16548

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

16549-16772

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

16773-17054

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

17055-17295

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

17296-17438

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

17439-17720

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

17721-17964

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

17965-18143

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

18144-18404

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

18405-18643

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

18644-18904

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

18906-18927

Sentence

denotes

Pathogenic Mechanisms

T109

18928-19082

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

19083-19238

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

19239-19427

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

19428-19707

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

19708-19946

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

19947-20099

Sentence

denotes

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

T115

20100-20295

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

20296-20479

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

20480-20748

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

20749-20976

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

20977-21188

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

21189-21482

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

21483-21662

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

21663-21780

Sentence

denotes

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

T123

21781-22129

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

22130-22419

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

22420-22601

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

22602-22842

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

22843-23157

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

23158-23403

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

23404-23647

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

23648-23847

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

23848-24324

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

24325-24518

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

24519-24887

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

24888-25028

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

25029-25296

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

25298-25331

Sentence

denotes

Clinical and Radiological Changes

T137

25332-25571

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

25572-25731

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

25732-25828

Sentence

denotes

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

T140

25829-26079

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

26080-26244

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

26245-26474

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

26475-26579

Sentence

denotes

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

T144

26580-26730

Sentence

denotes

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

T145

26731-26889

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

26890-27033

Sentence

denotes

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

T147

27034-27168

Sentence

denotes

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

T148

27169-27388

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

27389-27623

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

27624-27777

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

27778-28074

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

28075-28471

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

28472-28820

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

28821-29001

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

29002-29323

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

29324-29547

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

29548-29738

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

29739-29874

Sentence

denotes

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

T159

29875-30099

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

30100-30330

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

30331-30776

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

30777-31069

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

31070-31144

Sentence

denotes

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

T164

31145-31476

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

31477-31718

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

31719-32192

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

32194-32228

Sentence

denotes

Immune Response Against SARS-CoV-2

T168

32230-32244

Sentence

denotes

Cytokine Storm

T169

32245-32620

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

32621-32771

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

32772-32984

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

32985-33141

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

33142-33390

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

33391-33729

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

33730-34053

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

34054-34339

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

34340-34466

Sentence

denotes

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

T178

34467-34821

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

34822-35283

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

35284-35496

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

35497-35622

Sentence

denotes

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

T182

35623-35797

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

35798-36119

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

36120-36346

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

36347-36526

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

36527-36768

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

36769-36885

Sentence

denotes

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

T188

36886-37107

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

37108-37355

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

37356-37513

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

37514-37802

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

37803-37891

Sentence

denotes

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

T193

37892-38285

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

38286-38448

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

38449-38628

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

38629-38902

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

38903-39131

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

39132-39251

Sentence

denotes

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

T199

39252-39578

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

39579-39733

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

39734-40000

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

40001-40152

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

40153-40357

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

40358-40482

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

40483-40598

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

40599-40732

Sentence

denotes

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

T207

40733-40824

Sentence

denotes

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

T208

40825-41219

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

41220-41502

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

41503-41576

Sentence

denotes

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

T211

41577-41697

Sentence

denotes

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

T212

41698-41930

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

41931-42247

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

42248-42545

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

42546-42779

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

42780-43100

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

43102-43124

Sentence

denotes

Innate Immune Response

T218

43125-43306

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

43307-43527

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

43528-43659

Sentence

denotes

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

T221

43660-43829

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

43830-44054

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

44055-44202

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

44203-44484

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

44485-44774

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

44775-45024

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

45025-45165

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

45166-45341

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

45342-45537

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

45538-45672

Sentence

denotes

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

T231

45673-45889

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

45890-46058

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

46059-46278

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

46279-46441

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

46442-46564

Sentence

denotes

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

T236

46565-46824

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

46825-47074

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

47075-47486

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

47487-47688

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

47689-47892

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

47893-48115

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

48116-48236

Sentence

denotes

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

T243

48237-48477

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

48478-48610

Sentence

denotes

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

T245

48611-48762

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

48763-48999

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

49000-49412

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

49413-49564

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

49565-49828

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

49829-50034

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

50035-50239

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

50240-50491

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

50492-50600

Sentence

denotes

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

T254

50602-50616

Sentence

denotes

T Helper Cells

T255

50617-50735

Sentence

denotes

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

T256

50736-50873

Sentence

denotes

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

T257

50874-51152

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

51153-51513

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

51514-51704

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

51705-51924

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

51925-52086

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

52087-52233

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

52234-52378

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

52379-52746

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

52747-52949

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

52950-53201

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

53202-53436

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

53437-53639

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

53640-54012

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

54013-54151

Sentence

denotes

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

T271

54152-54473

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

54474-54910

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

54911-55019

Sentence

denotes

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

T274

55020-55283

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

55284-55551

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

55552-55936

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

55938-55953

Sentence

denotes

Cytotoxic Cells

T278

55954-56052

Sentence

denotes

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

T279

56053-56252

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

56253-56439

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

56440-56905

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

56906-57127

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

57128-57311

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

57312-57666

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

57667-57830

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

57831-58054

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

58055-58291

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

58292-58433

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

58434-58635

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

58636-59118

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

59119-59164

Sentence

denotes

Figure 2 Immune response in COVID-19 stages.

T292

59165-59223

Sentence

denotes

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

T293

59224-59479

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

59480-59784

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

59785-60057

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

60058-60200

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

60201-60331

Sentence

denotes

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

T298

60332-60459

Sentence

denotes

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

T299

60460-60555

Sentence

denotes

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

T300

60557-60573

Sentence

denotes

Humoral Response

T301

60574-60710

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

60711-60981

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

60982-61210

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

61211-61374

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

61375-61539

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

61540-61716

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

61717-62289

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

62290-62488

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

62489-62633

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

62634-62833

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

62834-62968

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

62969-63211

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

63212-63484

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

63485-63807

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

63808-64012

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

64013-64217

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

64218-64342

Sentence

denotes

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

T318

64343-64756

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

64757-64927

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

64928-65140

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

65141-65395

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

65396-65534

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

65535-65691

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

65693-65711

Sentence

denotes

COVID-19 Treatment

T325

65712-65857

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

65858-65925

Sentence

denotes

The main approach to disease management focuses on supportive care.

T327

65926-66191

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

66192-66479

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

66480-66594

Sentence

denotes

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

T330

66596-66614

Sentence

denotes

Enhancing Immunity

T331

66615-66797

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

66798-66976

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

66977-67361

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

67362-67543

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

67544-67698

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

67699-67961

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

67962-68186

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

68187-68473

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

68474-68624

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

68625-68736

Sentence

denotes

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

T341

68737-68919

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

68920-69228

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

69230-69243

Sentence

denotes

Immunotherapy

T344

69245-69267

Sentence

denotes

Antibody-Based therapy

T345

69268-69498

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

69499-69650

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

69651-69845

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

69846-70102

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

70103-70225

Sentence

denotes

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

T350

70226-70536

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

70537-70625

Sentence

denotes

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

T352

70626-70800

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

70801-70938

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

70939-71157

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

71158-71262

Sentence

denotes

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

T356

71263-71464

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

71465-71549

Sentence

denotes

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

T358

71550-71889

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

71890-71942

Sentence

denotes

However, clinical observations remain controversial.

T360

71943-72248

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

72249-72474

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

72475-72677

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

72678-72777

Sentence

denotes

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

T364

72778-73052

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

73053-73194

Sentence

denotes

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

T366

73195-73604

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

73605-73803

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

73804-74017

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

74018-74437

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

74438-74576

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

74577-74706

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

74707-74913

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

74914-75134

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

75135-75216

Sentence

denotes

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

T375

75217-75368

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

75369-75544

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

75545-75714

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

75715-76026

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

76027-76314

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

76315-76436

Sentence

denotes

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

T381

76437-76723

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

76724-76901

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

76902-77172

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

77173-77378

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

77379-77727

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

77728-77912

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

77913-78083

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

78084-78258

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

78260-78285

Sentence

denotes

Immune Cell-Based Therapy

T390

78286-78453

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

78454-78657

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

78658-78913

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

78914-79018

Sentence

denotes

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

T394

79019-79271

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

79272-79405

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

79406-79650

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

79651-79876

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

79877-80027

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

80028-80383

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

80384-80558

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

80559-80812

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

80813-80934

Sentence

denotes

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

T403

80935-81119

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

81120-81300

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

81301-81428

Sentence

denotes

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

T406

81429-81659

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

81660-81902

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

81903-82089

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

82090-82408

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

82409-82684

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

82685-82907

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

82908-83218

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

83219-83484

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

83485-83579

Sentence

denotes

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

T415

83580-83952

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

83953-84093

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

84094-84316

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

84317-84399

Sentence

denotes

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

T419

84400-84572

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

84573-84850

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

84852-84883

Sentence

denotes

Drug Options Against SARS-CoV-2

T422

84884-85044

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

85045-85305

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

85307-85317

Sentence

denotes

Antivirals

T425

85318-85565

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

85566-85796

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

85797-85953

Sentence

denotes

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

T428

85954-86345

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

86346-86501

Sentence

denotes

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

T430

86502-86714

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

86715-87025

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

87026-87171

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

87172-87337

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

87338-87615

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

87616-87846

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

87847-88033

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

88034-88240

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

88241-88458

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

88459-88593

Sentence

denotes

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

T440

88594-88899

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

88900-89136

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

89137-89268

Sentence

denotes

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

T443

89269-89643

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

89644-89858

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

89859-90086

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

90087-90293

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

90294-90504

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

90505-90602

Sentence

denotes

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

T449

90603-90694

Sentence

denotes

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

T450

90695-90869

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

90870-90947

Sentence

denotes

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

T452

90948-91173

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

91174-91324

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

91325-91551

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

91552-91782

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

91783-92003

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

92004-92216

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

92217-92475

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

92476-92656

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

92657-92875

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

92876-92967

Sentence

denotes

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

T462

92968-93179

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

93180-93387

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

93388-93564

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

93565-93691

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

93692-94008

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

94009-94077

Sentence

denotes

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

T468

94078-94286

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

94287-94574

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

94575-94727

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

94728-94939

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

94940-95134

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

95135-95391

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

95392-95748

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

95749-95865

Sentence

denotes

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

T476

95866-96091

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

96092-96373

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

96374-96703

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

96704-97045

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

97046-97175

Sentence

denotes

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

T481

97176-97416

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

97417-97544

Sentence

denotes

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

T483

97545-97653

Sentence

denotes

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

T484

97654-97750

Sentence

denotes

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

T485

97751-97877

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

97879-97913

Sentence

denotes

Chloroquine and Hydroxychloroquine

T487

97914-98067

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

98068-98406

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

98407-98593

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

98594-98849

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

98850-98978

Sentence

denotes

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

T492

98979-99177

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

99178-99474

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

99475-99604

Sentence

denotes

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

T495

99605-100059

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

100060-100215

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

100216-100322

Sentence

denotes

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

T498

100323-100575

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

100576-100818

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

100819-100968

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

100969-101133

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

101134-101293

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

101294-101452

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

101453-101707

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

101708-101927

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

101928-102031

Sentence

denotes

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

T507

102032-102227

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

102228-102447

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

102448-102653

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

102654-102945

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

102946-103134

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

103135-103297

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

103298-103403

Sentence

denotes

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

T514

103404-103646

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

103647-103742

Sentence

denotes

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

T516

103743-103986

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

103987-104151

Sentence

denotes

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

T518

104152-104295

Sentence

denotes

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

T519

104296-104441

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

104442-104645

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

104646-104985

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

104986-105198

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

105199-105266

Sentence

denotes

181 patients were analyzed, 84 of whom received hydroxychloroquine.

T524

105267-105537

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

105538-105754

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

105755-105847

Sentence

denotes

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

T527

105848-106120

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

106121-106236

Sentence

denotes

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

T529

106237-106343

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

106344-106569

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

106570-106625

Sentence

denotes

Neither of the dosages was able to influence lethality.

T532

106626-106722

Sentence

denotes

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

T533

106723-106961

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

106962-107159

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

107160-107333

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

107334-107534

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

107536-107551

Sentence

denotes

Antihelminthics

T538

107552-107842

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

107843-108122

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

108123-108356

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

108357-108579

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

108580-108834

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

108835-109187

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

109188-109429

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

109430-109675

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

109676-109844

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

109845-110069

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

110070-110175

Sentence

denotes

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

T549

110176-110371

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

110372-110557

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

110558-110873

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

110874-110976

Sentence

denotes

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

T553

110978-110992

Sentence

denotes

Anticoagulants

T554

110993-111162

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

111163-111341

Sentence

denotes

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

T556

111342-111624

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

111625-111854

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

111855-111947

Sentence

denotes

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

T559

111948-112208

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

112209-112429

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

112430-112675

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

112676-112846

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

112847-113071

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

113072-113279

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

113281-113294

Sentence

denotes

Dexamethasone

T566

113295-113690

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

113691-113821

Sentence

denotes

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

T568

113822-114040

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

114041-114155

Sentence

denotes

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

T570

114156-114407

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

114408-114597

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

114598-114806

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

114807-115144

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

115145-115258

Sentence

denotes

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

T575

115259-115554

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

115555-115739

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

115740-115958

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

115959-116124

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

116125-116262

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

116263-116369

Sentence

denotes

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

T581

116370-116427

Sentence

denotes

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

T582

116429-116439

Sentence

denotes

Conclusion

T583

116440-116621

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

116622-116763

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

116764-116906

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

116907-117084

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

117085-117323

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

117324-117540

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

117541-117807

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

117808-118107

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

118108-118310

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

118311-118421

Sentence

denotes

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

T593

118423-118443

Sentence

denotes

Author Contributions

T594

118444-118512

Sentence

denotes

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

T595

118513-118584

Sentence

denotes

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

T596

118585-118636

Sentence

denotes

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

T597

118637-118691

Sentence

denotes

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

T598

118692-118766

Sentence

denotes

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

T599

118767-118907

Sentence

denotes

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

T600

118909-118929

Sentence

denotes

Conflict of Interest

T601

118930-119102

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.

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