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Complement receptor

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Complement receptor
SymbolComplement receptor

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

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.[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.[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 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
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

Deficits in complement receptor expression can cause disease.[6] Mutations in complement receptors which alter receptor function can also increase risk of certain diseases.[1]

See also


External links

Template:Pattern recognition receptors


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