Table 2 Complement receptors Protein Specificity Structure Cell type(s) Key features Cell surface proteins CRI C3b,C4b, 4 allotypes: Erythrocytes,eosinophils,monocytes, Member of RCA family iC3b,C3c 160 kD: macrophages,neutrophils,B and some Accelerates dissociation of CP and AP C3 convertases I lymp ar podocytes,follicula ctor for factor 250 kDa cells CR2 140 kDa B cells,T cells,follicular dendritic cells CR3 iC3b,C3dg 170 kDa a chain Polymorphonuclear cells,monocytes,natural Member of the leucocyte-integrin family 95 kDa B chain killer cells,some B and T lymphocytes in phagocytosis of C3b-coated neutrophi s,cytotoxicity of cells bearing activated complement CR4 iC3b 150 kDa a chain Monocytes,macrophages,NK and ADCC Functions in cell adhesion 150,95) 95 kDa B chain effector lymphocytes,neutrophils C3aR C3a.C4a 95 kDa Mast cells,neutrophils,basophils,monocytes, Depending on cell type,functions include chemotaxis,chemokinesis T lymphocytes,eosinophils f网 CSaR C5a 43 kDa Neutrophils,eosinophils,monocytes, Depending on cell type,functions include directed chemotaxis.cell adhesion and aggregation,release of granular enzymes and histamine vas lial cells Augments the humoral and cellular responses C3eR C3dk.C3e Not characterized Neutrophils.monocytes Lysosomal enzyme release.leucocytosis DAF C3b Bb 75kDa Erythrocytes.all leucocytes.platelets Accelerates decay of CP and AP C3 convertases C4b 2a MCP C3b,iC3b. 45-70kD2 C4b cells,epithelial cells,mesenchymal cells Does not accelerate decay of C3 convertases CD59 C8,C9 18-20kDE Inhibits MAC on host cell Undefined C3(B chain) Neutrophils,eosinophils Eosinophil cvtotoxicity inhibitor Inhibitor of neutrophil adherence -dependent cellular cytotoxicity;NK,natural killer;DAF,decay-accelerating factor. Table 2 Complement receptors CP, classical pathway; AP, alternative pathway; RCA, regulators of complement activation; ADCC, antibody-dependent cellular cytotoxicity; NK, natural killer; DAF, decay-accelerating factor; MCP, membrane cofactor protein. Protein Specificity Structure Cell type(s) Key features Cell surface proteins CR1 C3b, C4b, iC3b, C3c 4 allotypes: 160 kDa 190 kDa 220 kDa 250 kDa Erythrocytes, eosinophils, monocytes, macrophages, neutrophils, B and some T lymphocytes, glomerular podocytes, follicular dendritic cells, mast cells, polymorphonuclear cells Member of RCA family Accelerates dissociation of CP and AP C3 convertases Cofactor for factor I Helps to process immune complexes Involved in phagocytosis CR2 iC3b, C3dg, EBV gp350 140 kDa B cells, T cells, follicular dendritic cells Member of RCA family Plays a role in immunoregulation CR3 iC3b, C3dg 170 kDa α chain 95 kDa β chain Polymorphonuclear cells, monocytes, natural killer cells, some B and T lymphocytes Member of the leucocyte–integrin family Involved in phagocytosis of iC3b-coated particles, adhesion of neutrophils, cytotoxicity of cells bearing activated complement components CR4 (p150, 95) iC3b 150 kDa α chain 95 kDa β chain Monocytes, macrophages, NK and ADCC effector lymphocytes, neutrophils Functions in cell adhesion C3aR C3a, C4a 95 kDa Mast cells, neutrophils, basophils, monocytes, T lymphocytes, eosinophils Depending on cell type, functions include chemotaxis, chemokinesis, cell aggregation and adhesion, release of lysosomal contents, may play a role in immunoregulation C5aR C5a 43 kDa Neutrophils, eosinophils, monocytes, macrophages, liver parenchymal cells, lung vascular smooth muscle and endothelial cells, bronchial and alveolar epithelial cells, astrocytes Depending on cell type, functions include directed chemotaxis, cell adhesion and aggregation, release of granular enzymes and histamine Augments the humoral and cellular responses C3eR C3dk, C3e Not characterized Neutrophils, monocytes Lysosomal enzyme release, leucocytosis DAF C3b,Bb, C4b,2a 75 kDa Erythrocytes, all leucocytes, platelets Accelerates decay of CP and AP C3 convertases MCP C3b, iC3b, C4b 45–70 kDa Neutrophils, monocytes, platelets, reticulocytes, most lymphocytes, granulocytes, endothelial cells, epithelial cells, mesenchymal cells Member of RCA family Cofactor for factor I Does not accelerate decay of C3 convertases CD59 C8, C9 18–20 kDa Inhibits MAC on host cells Undefined C3 (β chain) Neutrophils, eosinophils Eosinophil cytotoxicity inhibitor Inhibitor of neutrophil adherence Complement 8 ENCYCLOPEDIA OF LIFE SCIENCES / & 2001 Nature Publishing Group / www.els.net