|Receptor||Ligand||CD number||Protein superfamily||Function|
|CR1||C3b||CD35||Regulators of complement
|Promotion of phagocytosis, immune complex (IC) clearance, processing of IC-bound C3b|
|CR2||C3dg (iC3b)||CD21||Regulators of complement activation||B-cell proliferation, alternative pathway activation|
|CR3||iC3b||CD11b/CD18||β2 integrin||reactive oxygen metabolites/nitric oxide (ROM/NO) synthesis, degranulation|
|CR4||iC3b||CD11c/CD18||β2 integrin||Phagocytosis, leucocyte migration|
|C3aR||C3a||-||G protein-coupled receptors||NO synthesis|
|C5aR||C5a; C5a-desarg||CD88||G protein-coupled receptors||Leucocyte chemoattraction, degranulation|
|cC1qR||C1q, MBL, SPA||-||-||Chemotaxis, promotion of phagocytosis, ROM|
|C1qRp||C1q, MBL, SPA||CD93||-||Synthesis, platelet aggregation, leucocyte migration|
|gC1qR||C1q||-||-||Regulation of B-cell activity|
Complement receptors are membrane proteins expressed on the surface of immune cells. They interact specifically with complement factors leading to the removal of antigen from the circulation.
In addition to promoting microorganism destruction by memebrane attack complex (MAC), the complement system exerts a wide-ranging influence on the activities of cells involved in the immune response. Thus, complement is instrumental in the direction of blood leucocytes to a site of inflammation; the induction of granule release and synthesis of cytotoxic oxygen- and nitrogen-containing compounds by leucocytes of the myeloid lineage; the promotion of particle phagocytosis by these cells; the clearance of soluble immune complexes (ICs) from the circulation; and the induction of a primary B-cell response to antigen. These effects are exerted through interaction of the activation products of complement factors C1, C3 or C5 with specific receptors on the responding cells. The receptors can be divided into three categories: (1) those recognizing the anaphylotoxic polypeptides, C3a, C5a and C5a-desarg, (2) those binding the active C3 fragment, C3b, and its degradation products, iC3b and C3dg, and (3) receptors for C1q and related collagenous lectins.
1. Leslie R G Q, et al. (2009). Complement receptors. eLS.
2. Brown E J. (1992). Complement receptors, adhesion, and phagocytosis. Infectious agents and disease, 1(2), 63.
3. Nielsen C H, et al. (1997). The roles of complement receptors type 1 (CR1, CD35) and type 3 (CR3, CD11b/CD18) in the regulation of the immune complex‐elicited respiratory burst of polymorphonuclear leukocytes in whole blood. European journal of immunology, 27(11), 2914-2919.
4. Ahearn J M, et al. (1989). Structure and function of the complement receptors, CR1 (CD35) and CR2 (CD21). Advances in immunology, 46, 183-21