Complement system Activation of immune system

Complement System

1. Innate Immunity Complement System

2. Complement: History Discovered in 1894 by Bordet It represents lytic activity of fresh serum Its lytic activity destroyed when heated at 56°C for 30 mins

3. The complement system The complement system refers to a series of more than 20 proteins, circulating in the blood and tissue fluids. Most of the proteins are normally inactive, but in response to the recognition of molecular components of microorganisms they become sequentially activated in an enzyme cascade. The activation of one protein enzymatically cleaves and activates the next protein in the cascade.

4. Complement Cascade The complement system (also called the complement cascade ) is a mechanism that complements other aspects of the immune response. Typically, the complement system acts as a part of the innate immune system, but it can work with the adaptive immune system if necessary.

5. complement is a complex network of plasma and membrane-associated serum proteins which can elicit highly efficient and tightly regulated inflammatory and cytolytic immune responses to infectious organisms(bacteria, viruses, parasites), tissue damaged by physical, chemical, or neoplastic insults, and other surfaces identified as ‘non-self’

6. Activation of complement leads to robust and efficient proteolytic cascades, which terminate in opsonization and lysis of the pathogen as well as in the generation of the classical inflammatory response through the production of potent pro-inflammatory molecules.

7. 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), Membrane 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), protein-S ( vitronectin )

8. C-activation : alteration of C proteins such that they interact with the next component C-inactivation : denaturation (usually by heat) of an early C-component resulting in loss of hemolytic activity C-fixation : utilization of C by Ag- Ab complexes Convertase /esterase : altered C-protein which acts as a proteolytic enzyme for another C-component Some Definitions

9. Activation product of complement proteins (nomenclature) When enzymatically cleaved, the larger moiety , binds to the activation complex or membrane and the smaller peptide is released in the microenvironment Letter “b” is usually added to the larger, membrane-binding, peptide and “a” to the smaller peptide ( e.g. , C3b/C3a, C4b/C4a, C5b/C5a), EXCEPT C2 (the larger, membrane-binding moiety is C2a; the smaller one is C2b) Activated component are usually over-lined: e.g. C1qrs

10. Activation of the complement System

11. Components of the Classical Pathway C4 C2 C3 C1 complex Ca ++ C1r C1s C1q

12. Ca ++ C1r C1s C1q C4 C4a b Classical Pathway Generation of C3-convertase

13. Classical Pathway Generation of C3-convertase C4b Mg ++ C4a Ca ++ C1r C1s C1q C2 C2b a C2 a _____ C4b2a is C3 convertase

14. Classical Pathway Generation of C5-convertase C4b Mg ++ C4a Ca ++ C1r C1s C1q C2b C2 a C3 C3a b ________ C4b2a3b is C5 convertase; it leads into the Membrane Attack Pathway

15. C 1 I nh C1qrs breakdown C1r C1s C1q C1r C1s

16. 16 Biological Activities of Classical Pathway Components Component Biological Activity C2b Prokinin; cleaved by plasmin to yield kinin, which results in edema C3a Anaphylatoxin ; 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 Anaphylatoxin C4b Opsonin

17. 17 Control of Classical Pathway Components Component Regulation All C1-inhibitor (C1-INH); dissociates C1r and C1s from C1q C3a C3a-inactivator (C3a-INA; Carboxypeptidase B) C3b Factors H and I; Factor H facilitates the degradation of C3b by Factor I C4a C3a-INH C4b C4 binding protein (C4-BP) and Factor I; C4-BP facilitates degradation of C4b by Factor I; C4-BP also prevents the association of C2a with C4b thus blocking formation of C3 convertase

18. Components of mannose-binding lectin pathway C4 MBL C2 MASP1 MASP2

19. Mannose-binding lectin pathway C4 MBL C4b C4a C4b C2 C2b C2a C2a _____ C4b2a is C3 convertase; it will lead to the generation of C5 convertase MASP1 MASP2

20. Alternative Pathway This pathway is activated by viruses, fungi, bacteria, parasites, cobra venom, immunoglobulin A, and polysaccharides and forms an important part of the defense mechanism independent of the immune response. Here, C3b binds to factor B that is cleaved by factor D to Bb. C3bBb complex then acts as the C3 convertase and generates more C3b through an amplification loop. Binding of factor H to C3b increases its inactivation by factor I. Properdin stabilizes it, preventing its inactivation by factors H and factor I.

21. Components of the alternative pathway C3 B D P

22. Spontaneous C3 activation C3 H 2 O i B D Generation of C3 convertase C3iBb complex has a very short half life b C3 C3a b

23. B D b C3b If spontaneously-generated C3b is not degraded C3-activation the amplification loop C3 C3a b

24. C3a B D B b C3b C3 b C3-activation the amplification loop C3b C3a b

25. C3a C3a B b C3b C3b C3 B b B D b b C3a C3-activation the amplification loop C3b

26. C3a C3a B b C3b B b B b C3b C3a C3-activation the amplification loop C3b C3b

27. C3a C3a B b C3b B b B b C3a C3-activation the amplification loop C3b C3b

28. Control of spontaneous C3 activation via DAF C3b DAF prevents the binding of factor B to C3b B Autologous cell membrane DAF CR1

29. Control of spontaneous C3 activation via DAF DAF dislodges C3b-bound factor Bb B b b C3b Autologous cell membrane DAF CR1 B b

30. Autologous cell membrane C3b C3b B b H I iC3b Control of spontaneous C3 activation via CR1 B b I iC3b DAF CR1 DAF CR1

31. Degradation of spontaneously produced C3b C3b C3b iC3b iC3b I I C3dg C3dg C3c C3c

32. C3b stabilization and C5 activation C3b C3b finds an activator (protector) membrane C3 C3a b B D b P This is stable C5 convertase of the alternative pathway

33. C3b regulation on self and activator surfaces C3b

34. C5-convertase of the two pathways C3b B b C3b C5-convertase of the Alternative Pathway C4b C2a C3b C5-convertase of the Classical and lectin Pathways

35. Generation of C5 convertase leads to the activation of the Lytic pathway Lytic pathway

36. Components of the lytic pathway C6 C 9 C8 C7 C5

37. Lytic pathway C5-activation C3b C2 a C4b C5 b C5a

38. Lytic pathway assembly of the lytic complex C5 b C6 C7

39. Lytic pathway: insertion of lytic complex into cell membrane C5 b C6 C7 C8 C 9 C 9 C 9 C 9 C 9 C 9 C 9 C 9 C 9

40. Opsonization and phagocytosis complement bacterium C3b iC3b C4b OPSONIZATION Complement receptor BINDING PHAGOCYTOSIS Phagocytic cell

41. Neutrophil Neutrophil Activation Adhesion Neutrophil Neutrophil Chemotaxis Respiratory burst Monocyte Activation Cytokine production Mast cell Degranulation Vascular permeability Vascular wall transmigration Biological effects of C5a

42. Product Biological Effects Regulation Biological properties of C-activation products C2b (prokinin) edema C1-INH C3a (anaphylatoxin) mast cell degranulation; enhanced vascular permeability; anaphylaxis carboxy-peptidase- B (C3-INA)

43. Product Biological Effects Regulation Biological properties of C-activation products as C3, but less potent (C3-INA) C4a (anaphylatoxin) opsonization; phagocytosis C4b (opsonin) C4-BP, factor I C3b (opsonin) opsonization; phagocyte activation factors H & I

44. Product Biological Effects Regulation Biological properties of C-activation products anaphylactic as C3, but much more potent; attracts & activates PMN causes neutrophil aggregation, stimulation of oxidative metabolism and leukotriene release C5a (chemotactic factor) carboxy-peptidase-B (C3-INA) C5b67 protein-S chemotaxis, attaches to other membranes

45. 45 Complement Deficiencies and Disease Classical Pathway Pathway Component Disease Mechanism C1INH Hereditary Angioedema Overproduction of C2b (prokinin) C1, C2, C4 Predisposition to SLE Opsonization of immune complexes help keep them soluble, deficiency results in increased precipitation in tissues and inflammation

46. 46 Complement Deficiencies and Disease Lectin Pathway Pathway Component Disease Mechanism MBL Susceptibility to bacterial infections in infants or immunosuppressed Inability to initiate lectin pathway