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| Complement receptor | |
|---|---|
| Identifiers | |
| Symbol | Complement receptor |
| Membranome | 116 |
Acomplement receptor is a membrane-boundreceptor belonging to thecomplement system, which is part of theinnate immune system. Complement receptors bindeffectorprotein fragments that are produced in response to antigen-antibody complexes or damage-associated molecules.[1] Complement receptor activation contributes to the regulation ofinflammation,leukocyte extravasation, andphagocytosis; it also contributes to theadaptive immune response.[2][3] Different complement receptors can participate in either theclassical complement pathway, thealternative complement pathway, or both.[4]
White blood cells, particularlymonocytes andmacrophages,express complement receptors on their surface. All four complement receptors can bind to fragments ofcomplement component 3 orcomplement component 4 coated on pathogen surface, but the receptors trigger different downstream activities.[1] Complement receptor (CR) 1, 3, and 4 function asopsonins which stimulatephagocytosis, whereas CR2 is expressed only onB cells as aco-receptor.
Red blood cells (RBCs) also express CR1, which enables RBCs to carry complement-boundantigen-antibody complexes to theliver andspleen 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 |
| C5AR2 | C5a receptor 2 | 36,000 | C5a | – | Chemotaxis |
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]