Complement receptor (CR (with specific subtypes: CR1, CR2, CR3, CR4, C3a receptor [C3aR], C5a receptor 1 [C5aR1], C5a receptor 2 [C5aR2], and others))

A **complement receptor** is any one of several membrane-bound proteins that recognize fragments generated by activation of the complement system—a key part of innate immunity. These receptors are structurally diverse but functionally linked by their ability to bind products such as **C3b**, **iC3b**, **C4b**, **C3d**, **anaphylatoxins** (**C3a**, **C5a**), among others. The main human types include: | Name | Abbreviation | Ligands | Main Functions | |---|---|---|---| | Complement receptor 1 | CR1 / CD35 | C3b, iC3b, C4b | Immune complex clearance; regulation | | Complement receptor 2 | CR2 / CD21 | iC3b, C3dg, EBV gp350/220 protein | B cell activation; antibody production | | Complement receptor 3 | CR3 / Macrophage antigen 1 / CD11b+CD18 | iC3b | Phagocytosis; leukocyte adhesion | | Complement receptor 4 | CR4 / p150/95 / CD11c+CD18 | iC3b | Phagocytosis; leukocyte adhesion | | Complement component 5a Receptor (also called anaphylatoxin receptors) and others (CD88/CXCL16 etc.) | These molecules mediate critical processes including removal of pathogens via phagocytosis/opsonization, recruitment/migration/activation of leukocytes during inflammation/infection/tissue injury repair, bridging innate with adaptive immunity, and regulating homeostasis. Because “complement receptor” refers collectively to multiple distinct proteins rather than a single entity—and each has unique structure/function/disease relevance—it is important in structured data contexts to specify which subtype is meant.

Other names

Complement receptorsCRsCD35 (CR1)CD21 (CR2)CD11b/CD18 or Macrophage-1 antigen (CR3)CD11c/CD18 or p150,95 (CR4)C3AR1C5AR1/CD88

Antagonism/inhibition of ligand binding to block downstream inflammatory signaling. Modulation of immune cell activation by altering phagocytosis or chemotaxis.