Transcript Complement
Complement functions • Host benefit: – – – – – – opsonization to enhance phagocytosis phagocyte attraction and activation lysis of bacteria and infected cells regulation of antibody responses clearance of immune complexes clearance of apoptotic cells • Host detriment: – Inflammation, anaphylaxis Proteins of the complement system (nomenclature) • C1(qrs), C2, C3, C4, C5, C6, C7, C8, C9 • factors B, D, H and I, properdin (P) • mannose binding lectin (MBL), MBL associated serine proteases (MASP-1 MASP-2) • C1 inhibitor (C1-INH, serpin), C4-binding protein (C4-BP), decay accelerating factor (DAF), Complement receptor 1 (CR1), proteinS (vitronectin) Pathways of complement activation CLASSICAL PATHWAY antibody dependent LECTIN PATHWAY ALTERNATIVE PATHWAY antibody independent Activation of C3 and generation of C5 convertase activation of C5 LYTIC ATTACK PATHWAY Components of the Classical Pathway C3 C1 complex C4 Classical Pathway Generation of C3-convertase Classical Pathway Generation of C3-convertase _____ C4b2a is C3 convertase C4b Classical Pathway Generation of C5-convertase ________ C4b2a3b is C5 convertase; it leads into the Membrane Attack Pathway C4b C3b Lytic pathway Generation of C5 convertase leads to the activation of the Lytic pathway Components of the lytic pathway C7 C6 C 9 Lytic pathway C5-activation b C4b C3b Lytic pathway assembly of the lytic complex C6 C7 b Lytic pathway: insertion of lytic complex into cell membrane C6 C7 CC C C C9 9 9 9C 9C C C9 9 9 9 b Biological Activities of Classical Pathway Components Component Biological Activity C2b Prokinin; cleaved by plasmin to yield kinin, which results in edema C3a Anaphylotoxin; can activate basophils and mast cells to degranulate resulting in increased vascular permeability and contraction of smooth muscle cells, which may lead to anaphylaxis C3b Opsonin Activation of phagocytic cells C4a Anaphylaotoxin C4b Opsonin 13 Components of the alternative pathway C3 Spontaneous C3 activation Generation of C3 convertase C3 i b C3b C3iBb complex has a very short half life C3-activation the amplification loop If spontaneously-generated C3b is not degraded C3b b C3 b C3-activation the amplification loop C3 b b C3b C3b C3b C3-activation the amplification loop C3b C3b C3b C3b C3-activation the amplification loop C3b C3b C3b C5-convertase of the two pathways C5-convertase of the Classical and lectin Pathways C3b C4b C5-convertase of the Alternative Pathway C3b C3b Biological effects of C5a Biological properties of C-activation products Product Biological Effects Regulation C3b (opsonin) opsonization; phagocyte activation factors H & I C4a as C3, but less (anaphylatoxin) potent (C3-INA) C4b (opsonin) C4-BP, factor I opsonization; phagocytosis Biological properties of C-activation products Product Biological Effects Regulation C5a (chemotactic factor) anaphylactic as C3, but much more potent; attracts & activates PMN causes neutrophil aggregation, stimulation of oxidative metabolism and leukotriene release carboxypeptidase-B (C3-INA) C5b67 chemotaxis, attaches to other membranes protein-S