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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-ref-ar14-1-0[1] Complement receptor activation contributes to the regulation of inflammation, leukocyte extravasation, and phagocytosis; it also contributes to the adaptive immune response.cite-ref-cr17-2-0[2]cite-ref-pmid19388161-3-0[3] Different complement receptors can participate in either the classical complement pathway, the alternative complement pathway, or both.cite-ref-janeway-2001-4-0[4]

• Expression and function

• Clinical significance

• See also

• References

• External links

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.cite-ref-ar14-1-1[1] 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-ref-5[5]

| CR # | Name | Molecular weight (Da, approx.) [ 1 ] | Ligand [ 4 ] | CD | Major cell types [ 4 ] a | Major activities [ 1 ] |

|---|---|---|---|---|---|---|

| 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 α M β 2 " | 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 | C5a receptor 2 | 36,000 | C5a | – | | Chemotaxis |

a.endnote-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.

Deficits in complement receptor expression can cause disease.cite-ref-emedicine-dermatology-6-0[6] Mutations in complement receptors which alter receptor function can also increase risk of certain diseases.cite-ref-ar14-1-4[1]

• Complement system

• Humoral immunity

• Immune system

cite-note-ar14-11. ↑ citerefholers2014Holers VM (29 January 2014). "Complement and its receptors: new insights into human disease". Annual Review of Immunology. 32: 433–59. doi:10.1146/annurev-immunol-032713-120154. PMID 24499275.

cite-note-cr17-22. ↑ citerefverschoorkemperk-hl2017Verschoor A, Kemper C, Köhl J (15 September 2017). "Complement Receptors". Encyclopedia of Life Sciences. pp. 1–17. doi:10.1002/9780470015902.a0000512.pub3. ISBN 9780470015902.

cite-note-pmid19388161-33. ↑ citerefcarroll2008Carroll MC (December 2008). "Complement and humoral immunity". Vaccine. 26 (Suppl 8): I28-33. doi:10.1016/j.vaccine.2008.11.022. PMC 4018718. PMID 19388161.

cite-note-janeway-2001-44. ↑ citerefjaneway-jrtraverswalportshlomchik2001Janeway Jr CA, Travers P, Walport M, Shlomchik MJ (2001). "The complement system and innate immunity". Immunobiology: The Immune System in Health and Disease (5th ed.). New York: Garland Science. Retrieved 17 June 2020.

cite-note-55. ↑ citerefparham2005Parham P (2005). The Immune System (2nd ed.). Garland Science. ISBN 9780815340935.

cite-note-emedicine-dermatology-66. ↑ citerefschwartzthomasSchwartz RA, Thomas I. "Complement Receptor Deficiency: eMedicine Dermatology". Medscape. Retrieved 7 December 2010.

• Complement+receptors at the U.S. National Library of Medicine Medical Subject Headings (MeSH)