Table 1-continued Conce Protein Structure (ug mL-) Cellular sources Key function C4bp 460-540kDa 250 Hepatocytes,mononuclear phagocytes Cofactor for factor I.Accelerates the decay of 70 kDa o chain CP C3 convertase CLOP 45 kDa B chair EDIA OF Lectin pathway MBL(192-582kDa) Dimer to hexamer.Subunit 1-4 Binds to mannans of microorganisms contains (x3)32 kDa chain activating the lectin pathway MASPI(83 kDa) Monomer 6 Cleaves C2,C4(?).C3 MASP2 (83 kDa) Monomer 6 Cleaves C2.C4 Late components C5 110 kDa a chain Hepatocytes,mononuclear phagocytes, Initiates the assembly of MAC 75 kDa B chain T/B lymphocytes,fibroblasts,epithelial cells,astrocytes C6 120 kDa Hepatocytes,neutrophils,astrocytes Participates in the formation of MAC C7 105 kDa 55 Participates in the formation of MAC C8 64 kDa achain 80 Hepatocytes,pneumocytes,astrocytes Participates in the formation of MAC 64 kDa B chain 22 kDa ychain C9 71 kDa Hepatocytes,astrocytes,fibroblasts, Participates in the formation of MAC macrophages,monocytes,platelets CP,classical pathway,AP,alt MBL,mannose-binding lectin,MASP,MBI -associated serine protease ComplementCP, classical pathway; AP, alternative pathway; MAC, membrane attack complex; MBL, mannose-binding lectin; MASP, MBL-associated serine protease. C4bp 460 –540 kDa 70 kDa α chain 45 kDa β chain 250 Hepatocytes, mononuclear phagocytes Cofactor for factor I. Accelerates the decay of CP C3 convertase Lectin pathway MBL (192 –582 kDa) Dimer to hexamer. Subunit contains ( ×3) 32 kDa chain 1–4 Binds to mannans of microorganisms, activating the lectin pathway MASP1 (83 kDa) Monomer 6 Cleaves C2, C4 (?), C3 MASP2 (83 kDa) Monomer 6 Cleaves C2, C4 Late components C5 110 kDa α chain 75 kDa β chain 75 Hepatocytes, mononuclear phagocytes, T/B lymphocytes, fibroblasts, epithelial cells, astrocytes Initiates the assembly of MAC C6 120 kDa 45 Hepatocytes, neutrophils, astrocytes Participates in the formation of MAC C7 105 kDa 55 Hepatocytes, mononuclear phagocytes, fibroblasts, astrocytes Participates in the formation of MAC C8 64 kDa α chain 64 kDa β chain 22 kDa γ chain 80 Hepatocytes, pneumocytes, astrocytes Participates in the formation of MAC C9 71 kDa 60 Hepatocytes, astrocytes, fibroblasts, macrophages, monocytes, platelets Participates in the formation of MAC Protein Structure Concentration (µg mL–1) Cellular sources Key function Table 1 – continued Complement 5 ENCYCLOPEDIA OF LIFE SCIENCES / & 2001 Nature Publishing Group / www.els.net