Complement receptor
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| Name = Complement receptor
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A complement receptor is a membrane-bound receptor belonging to the complement system, which is part of the innate immune system. Complement receptors bind effector protein fragments that are produced in response to antigen-antibody complexes or damage-associated molecules.{{cite journal | vauthors = Holers VM | title = Complement and its receptors: new insights into human disease | journal = Annual Review of Immunology | volume = 32 | pages = 433–59 | date = 29 January 2014 | pmid = 24499275 | doi = 10.1146/annurev-immunol-032713-120154 | doi-access = free }} Complement receptor activation contributes to the regulation of inflammation, leukocyte extravasation, and phagocytosis; it also contributes to the adaptive immune response.{{cite journal|title=Complement Receptors |vauthors=Verschoor A, Kemper C, Köhl J |journal=eLS |date = 15 September 2017 |pages=1–17 |doi=10.1002/9780470015902.a0000512.pub3 |isbn=9780470015902 }}{{cite journal | vauthors = Carroll MC | title = Complement and humoral immunity | journal = Vaccine | volume = 26 | issue = Suppl 8 | pages = I28-33 | date = December 2008 | pmid = 19388161 | pmc = 4018718 | doi = 10.1016/j.vaccine.2008.11.022 }} Different complement receptors can participate in either the classical complement pathway, the alternative complement pathway, or both.{{cite book|url=https://www.ncbi.nlm.nih.gov/books/NBK27100|chapter=The complement system and innate immunity| vauthors = Janeway Jr CA, Travers P, Walport M, Shlomchik MJ |year=2001|edition=5th|title=Immunobiology: The Immune System in Health and Disease|publisher=Garland Science|access-date=2020-06-17|location=New York }}
Expression and function
White blood cells, particularly monocytes and macrophages, express complement receptors on their surface. All four complement receptors can bind to fragments of complement component 3 or complement component 4 coated on pathogen surface, but the receptors trigger different downstream activities. Complement receptor (CR) 1, 3, and 4 function as opsonins which stimulate phagocytosis, whereas CR2 is expressed only on B cells as a co-receptor.
Red blood cells (RBCs) also express CR1, which enables RBCs to carry complement-bound antigen-antibody complexes to the liver and spleen for degradation.{{cite book | first = Peter | last = Parham | name-list-style = vanc |title=The Immune System | year = 2005 |edition=2nd|publisher=Garland Science|isbn=9780815340935}}
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! CR # | Name | Molecular weight (Da, approx.) | Ligand | CD | Major cell types{{ref|A|a}} | Major activities |
| CR1 | Complement receptor 1 | 190,000–250,000
|C3b, C4b, iC3b | CD35 | B, E, FDC, Mac, M0, PMN
| Immune complex transport (E); phagocytosis (PMN, Mac); immune adhesion (E); cofactor and decay-acceleration; secondary Epstein-Barr virus receptor | ||
| CR2 | Complement receptor 2 | 145,000
|C3d, iC3b, C3dg, Epstein-Barr virus | CD21 | B, FDC
| B cell coactivator, primary Epstein-Barr virus receptor, CD23 receptor | ||
| CR3 | Macrophage-1 antigen or "integrin αMβ2" | 170,000 α chain + common 95,000 β chain
|iC3b | CD11b+CD18 | FDC, Mac, M0, PMN
| Leukocyte adherence, phagocytosis of iC3b-bound particles | ||
| CR4 | Integrin alphaXbeta2 or "p150,95" | 150,000 α chain + common 95,000 β chain
|iC3b | CD11c+CD18 | D, Mac, M0, PMN
| Leukocyte adhesion | ||
| C3AR1 | C3a receptor | 75,000
|C3a | – | Endo, MC, Pha
| Cell activation | ||
| C5AR1 | C5a receptor | 50,000
| C5a | CD88 | Endo, MC, Pha
| Cell activation, immune polarization, chemotaxis | ||
| C5AR2
|36,000 |C5a | – | |Chemotaxis |
:a.{{note|a}}B: B cell. E: erythrocyte. Endo: endothelial cell. D: dendritic cell. FDC: follicular dendritic cell. Mac: macrophage. MC: mast cell. M0: monocyte. Pha: phagocyte. PMN: polymorphonuclear leukocyte.
Clinical significance
{{Main | Complement system#Role in disease | Classical complement pathway#Clinical significance | Alternative complement pathway#Role in disease}}
Deficits in complement receptor expression can cause disease.{{cite web | vauthors = Schwartz RA, Thomas I |url=http://emedicine.medscape.com/article/1051238-overview |title=Complement Receptor Deficiency: eMedicine Dermatology |website=Medscape |access-date=2010-12-07}} Mutations in complement receptors which alter receptor function can also increase risk of certain diseases.
See also
References
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External links
- {{MeshName|Complement+receptors}}
{{Complement system}}
{{Pattern recognition receptors}}