The Complement System

2. The Complement System Janos Szebeni, MD, PhD. Nephrology Course lecture Sept 24, 2012

3. A rendszer lényege, történeti háttér • A vérben lévő 4 proteolitikus kaszkád egyike (koagulációs, kinin-kallikrein és fibrinolitikus rendszerek mellett) • ~50 glycoprotein, effektor és kontrol funkció • Plasmában oldott effector = 14 • Plasmában oldott control = 8 • Sejtmembránok felszinéhez kötött control = 13 • Plasmában oldott hasadási (aktivációs termék) = 10 • Sejtmembránok felszinéhez kötött (aktivációs termék) = 4 • 110 éve fedezték fel • Julet Bordet, 1895, Alexin • Mecsnyikov, Cytase • Paul Erlich, 1902, Complement

4. Immun Rendszer Specifikus (adaptive) Nem-specifikus (innate) Humoralis indukalt antitestek Humoralis természetes antitestek Cellularis PMN, NK sejtek, makrofagok Humoralis indukalt antitestek Cellularis Elkotelezett T sejtek Complement

5. Complement effektor fehérjék

6. Complement aktivációs termékek MW (kDa) MW (kDa) mg/mL

7. Complement Activation Pathways • Involves a “cascade” of successive components. • Enhances a small initiating signal. • Components are cleaved into activated fragments. • Fragments induce intense inflammatory responses to eliminate infectious agents.

8. Pathways of the complement activation • Distinct recognition events for each pathway • Classical - Antibodies, C-reactive protein • Lectin – Mannose-binding lectin (MBL) • Alternative – serum factors B, D, and P

9. A komplement rendszer regulációja Trends in Immunol., 23, 61, 2002

10. A C kaszkád

11. The Classical Pathway • Antigen-Antibody complexes are main activators of this pathway. • Activated by the formation of soluble Ag-Ab complexes or binding of Ab (IgM or IgG) to Ag on a target cell. • C-reactive protein binds to the surface of many bacteria and are also activators.

12. Component Protein ComplexC1

13. The C1 qrs complex

14. Classical Pathway

15. C4BP exclusively regulates the classical pathway

16. IgM Antibody

17. IgM and IgG moleculesBinding

18. C1q binds toIgM and IgG molecules

19. Activation Effectiveness • IgM is more effective at activating complement than IgG • C1q binds to the CH2 domain of Ig and requires at least two adjacent Fc regions • Activation of the Thiol-Ester bond and covalent attachment to antigen

20. The Lectin Pathway • Antibody-independent pathway • Activated by mannose-binding lectin to mannose residues on foreign surface • Binding activates MASP-1 and MASP-2 that cleave and activate C4 and C2 • Cleaved C4 and C2 generate C3 convertase • Converges with the classical pathway at activation of C3

21. Mannose-binding LectinPathway

22. The Alternative Pathway • Does not require Ag-Ab complex formation • Initiated by foreign cell surface proteins • Produces active C3 and C5 convertase • Active C3 is generated spontaneously • Host cells regulate the progression

23. Alternative Pathway

24. Factor H exclusively regulates the alternative pathway

25. C3 and C5 convertases of each pathway

26. Activation of C3 • Cleavage of C3 is a critical step in all three pathways. • C3 convertases split C3 into two fragments: C3a---smaller, fluid-phase anaphylatoxin C3b---larger, continues the sequential activation of successive components

27. Activities of activated C3 • C3a promotes inflammation • C3b fixation to surfaces leads to opsonization • C3b fixation leads to immune complex clearance • Generation of the C5 Convertase activity

28. Activation of C5 • Cleavage of C5 produces two fragments: C5a---released into the fluid phase, potent anaphylatoxin C5b---binds to the cell surface, nucleus for binding the terminal complement components

29. The Terminal Sequence • Terminal components of the complement cascade: C5b, C6, C7, C8, and C9 • Components are common to all pathways • Bind to each other and form a MAC • Results in cell lysis

30. Formation of the membrane attack complex (MAC)

31. Formation of MAC

32. Polymerized C9(poly-C9)

33. Poly-C9

34. Terminális Reakcióút Membrán attack complexképződés(C5b-9)

35. The “MAC” Attack(membrane lesion – side on view)

36. Complement pathway activators 1 • Classical pathway • IgM-containing immune complexes • IgG-containing immune complexes • Mannose-binding lectin(MBL) • C-reactive protein(CRP) • Serum amyloid P(SAP) • Myocardial damage products • Membranes of apoptotic cells • C4 nephritic factor (C4Nef) • Myelin

37. Complement pathway activators 2 • Alternative pathway • Tickover • Amplification from classical pathway C3b fixation • Repeating polysaccharides • Endotoxin • Virally infected cells(measles,influenza,Epstein-Barr virus) • IgA-containing immune complexes • Some Ig light Chains • C3 nephritic factor(C3Nef) • Cobra venom factor(CVF) • Zymosan(yeast cell wall) • Lectin pathway • Repeating simple sugars

38. Complement-fixing potential of antibodies • Classical pathway:IgM>IgG3>IgG1>IgG2>>IgG4 • IgA can activate the alternative pathway • IgE will activate complement only in unusual circumstances

39. Structural and functional homologs in activation pathways • C2 and factor B • C1q and mannose-binding lectin(MBL) • C1r/C1s and MASP-1/MASP-2 • C3/C4/C5 • C6/C7/C8/C9

40. Complement receptors • C1q receptor • Complement receptor 1(CR1) • Complement receptor 2(CR2) • Complement receptor 3(CR3) • Complement receptor 4(CR4) • C5a,C3a and C4a receptors

41. Fiziológas Funkciók • Infekcióesegyéb szövetkárositó hatásokelleni védekezés a gyulladásos válaszreakciógyorsitásával • Specifikusimmunválaszgyorsitása • Terhesség fenntartása • Szövet fejlödés, reparálás

42. Anaphylatoxinok és aktiválódó célsejtek 0.9 kDa C3a, C5a B sejt hizósejt granulocyta T sejt eosinofil monocyta basofil

43. Target Smooth muscle Mast cells Blood capillary wall Vascular endothelium Leukocytes Platelets Immune response Effect Contraction Histamine release Increase in vascular permeability Increased adhesiveness for leukocytes Adhesion,aggregation,chemotaxis,release of lysosomal enzymes,generation of oxygen radicals Aggregation,release of serotonin C3a:suppression C5a:enhancement Anaphylatoxins and disease

44. Complement regulatory proteins and primary locations Fluid phase • C1-INH • Factor I • Factor H • C4b-binding protein (C4-bp) • S protein(vitronectin) • SP-40,40(clusterin) • Carboxypeptidase • Cell membrane • Decay-accelerating factor(DAF,CD55) • Membrane cofactor protein(MCP,CD46) • CD59 • Membrane C3-proteinases • Matrix • Decorin

45. Inhibiting the classical pathway Why doesn’t complement attack our own tissues?

46. Biological Activities Of Complement • Production of Opsonins • Production of Anaphylatoxins • Lysis of Cells • Enhancing B Cell Response to Antigens • Controlling the Formation and Clearance of Immune Complexes • Removing Dead and Dying Cells • Responses to Viruses

48. Enhancing B Cell Responses to Antigens

49. Removal of Immune Complexes

50. Removal of Necrotic cells and Subcellular Membranes