PMC:7572937 / 2124-5409 JSONTXT

{"project":"MyTest","denotations":[{"id":"33082511-20303872-29997534","span":{"begin":611,"end":612},"obj":"20303872"},{"id":"33082511-19498085-29997535","span":{"begin":828,"end":829},"obj":"19498085"},{"id":"33082511-19498085-29997536","span":{"begin":1264,"end":1265},"obj":"19498085"},{"id":"33082511-19498085-29997537","span":{"begin":1535,"end":1536},"obj":"19498085"},{"id":"33082511-26174765-29997538","span":{"begin":1744,"end":1745},"obj":"26174765"},{"id":"33082511-27317359-29997539","span":{"begin":2033,"end":2034},"obj":"27317359"},{"id":"33082511-26174765-29997540","span":{"begin":2618,"end":2619},"obj":"26174765"},{"id":"33082511-19855405-29997541","span":{"begin":2620,"end":2621},"obj":"19855405"},{"id":"33082511-28153961-29997542","span":{"begin":2939,"end":2940},"obj":"28153961"},{"id":"33082511-28153961-29997543","span":{"begin":3156,"end":3157},"obj":"28153961"}],"namespaces":[{"prefix":"_base","uri":"https://www.uniprot.org/uniprot/testbase"},{"prefix":"UniProtKB","uri":"https://www.uniprot.org/uniprot/"},{"prefix":"uniprot","uri":"https://www.uniprot.org/uniprotkb/"}],"text":"Introduction\nPattern recognition receptors (PRRs) are mainly expressed in innate immune cells such as neutrophils, monocytes, and macrophages and induce immune responses to infection, injury, or stress by recognizing molecular patterns on antigens. Well-known PRRs include Toll-like receptors (TLRs), nucleotide-binding oligomerization domain-leucin rich repeat-containing receptors, retinoic acid-inducible gene 1-like receptors, and C-type lectin receptors, with TLRs being the most extensively studied among these receptors. Formyl peptide receptors (FPRs), which recognize formylated peptides, are also PRRs1. However, the characteristics of this receptor family are different from those of the other PRRs; FPRs recognize various endogenous molecules ranging from mitochondrial formylated peptides to lipid-derived mediators2.\nThere are three types of human FPRs (FPR1, FPR2, and FPR3) and eight types of murine FPRs (Fpr1, Fpr2, Fpr3 (Fpr-rs1), and Fpr-rs3 to 7). FPR1 was the first receptor discovered in the FPR family; this receptor detects formylated peptides with high affinity. FPR2 has lower affinity for bacterial formylated peptides than does FPR1 but has a wide range of ligands, such as amyloid peptides, antimicrobial peptides, and lipid mediators2. FPRs are highly expressed in innate immune cells such as neutrophils, monocytes, and macrophages. However, many reports have also demonstrated that nonhematopoietic cells, including epithelial cells, endothelial cells, neurons, and hepatocytes, express functional FPRs2.\nOur body maintains its homeostasis and protection from the external environment via different types of barriers. Skin and mucosal surfaces are the barriers separating the inside from the outside of the body3. The mucosal surfaces include the gastrointestinal (GI) tract, the respiratory tract, the oral cavity, the urogenital tract, and the eye. Tremendous amounts of commensal bacteria and pathogens exist in mucosal surfaces, and they come in direct contact with the harsh external environment4. To defend our body against external attacks, many immune cells are required in the surface region. As a result, in healthy adults, approximately 80% of immune cells are in the mucosal system5. Immune responses need to be restricted and regulated at the necessary sites to maintain homeostasis. Immune cells cooperate with other epithelial cells and stromal cells and compose an independent mucosal immune system. The mucosal immune system includes epithelial cells, macrophages, monocytes, neutrophils, B and T cells, innate lymphoid cells, dendritic cells, and natural killer cells3,6.\nThese various components in the mucosal system express PRRs that can recognize normal flora and pathogens. There have been many reports on the role of PRRs in the mucosal system. TLRs are the most extensively investigated PRRs in the mucosal system, and there are many reports on the function of TLRs in the GI tract7. TLRs are expressed in intestinal epithelial cells (IECs), and IECs show hyporesponsiveness to ligands of TLR2 and TLR4. Polymorphisms in TLR2 and TLR4 correlate with human inflammatory bowel disease (IBD) pathology7. This review summarizes recent reports on the understanding of the expression and function of FPRs in various mucosal surfaces."}

{"project":"2_test","denotations":[{"id":"33082511-20303872-29997534","span":{"begin":611,"end":612},"obj":"20303872"},{"id":"33082511-19498085-29997535","span":{"begin":828,"end":829},"obj":"19498085"},{"id":"33082511-19498085-29997536","span":{"begin":1264,"end":1265},"obj":"19498085"},{"id":"33082511-19498085-29997537","span":{"begin":1535,"end":1536},"obj":"19498085"},{"id":"33082511-26174765-29997538","span":{"begin":1744,"end":1745},"obj":"26174765"},{"id":"33082511-27317359-29997539","span":{"begin":2033,"end":2034},"obj":"27317359"},{"id":"33082511-26174765-29997540","span":{"begin":2618,"end":2619},"obj":"26174765"},{"id":"33082511-19855405-29997541","span":{"begin":2620,"end":2621},"obj":"19855405"},{"id":"33082511-28153961-29997542","span":{"begin":2939,"end":2940},"obj":"28153961"},{"id":"33082511-28153961-29997543","span":{"begin":3156,"end":3157},"obj":"28153961"}],"text":"Introduction\nPattern recognition receptors (PRRs) are mainly expressed in innate immune cells such as neutrophils, monocytes, and macrophages and induce immune responses to infection, injury, or stress by recognizing molecular patterns on antigens. Well-known PRRs include Toll-like receptors (TLRs), nucleotide-binding oligomerization domain-leucin rich repeat-containing receptors, retinoic acid-inducible gene 1-like receptors, and C-type lectin receptors, with TLRs being the most extensively studied among these receptors. Formyl peptide receptors (FPRs), which recognize formylated peptides, are also PRRs1. However, the characteristics of this receptor family are different from those of the other PRRs; FPRs recognize various endogenous molecules ranging from mitochondrial formylated peptides to lipid-derived mediators2.\nThere are three types of human FPRs (FPR1, FPR2, and FPR3) and eight types of murine FPRs (Fpr1, Fpr2, Fpr3 (Fpr-rs1), and Fpr-rs3 to 7). FPR1 was the first receptor discovered in the FPR family; this receptor detects formylated peptides with high affinity. FPR2 has lower affinity for bacterial formylated peptides than does FPR1 but has a wide range of ligands, such as amyloid peptides, antimicrobial peptides, and lipid mediators2. FPRs are highly expressed in innate immune cells such as neutrophils, monocytes, and macrophages. However, many reports have also demonstrated that nonhematopoietic cells, including epithelial cells, endothelial cells, neurons, and hepatocytes, express functional FPRs2.\nOur body maintains its homeostasis and protection from the external environment via different types of barriers. Skin and mucosal surfaces are the barriers separating the inside from the outside of the body3. The mucosal surfaces include the gastrointestinal (GI) tract, the respiratory tract, the oral cavity, the urogenital tract, and the eye. Tremendous amounts of commensal bacteria and pathogens exist in mucosal surfaces, and they come in direct contact with the harsh external environment4. To defend our body against external attacks, many immune cells are required in the surface region. As a result, in healthy adults, approximately 80% of immune cells are in the mucosal system5. Immune responses need to be restricted and regulated at the necessary sites to maintain homeostasis. Immune cells cooperate with other epithelial cells and stromal cells and compose an independent mucosal immune system. The mucosal immune system includes epithelial cells, macrophages, monocytes, neutrophils, B and T cells, innate lymphoid cells, dendritic cells, and natural killer cells3,6.\nThese various components in the mucosal system express PRRs that can recognize normal flora and pathogens. There have been many reports on the role of PRRs in the mucosal system. TLRs are the most extensively investigated PRRs in the mucosal system, and there are many reports on the function of TLRs in the GI tract7. TLRs are expressed in intestinal epithelial cells (IECs), and IECs show hyporesponsiveness to ligands of TLR2 and TLR4. Polymorphisms in TLR2 and TLR4 correlate with human inflammatory bowel disease (IBD) pathology7. This review summarizes recent reports on the understanding of the expression and function of FPRs in various mucosal surfaces."}