1. Complement system Xiaojian Wang IMMUNOLOGY
Institute of immunology, ZJU

2. Complement
Introduction
Activation of the Complement System 
Regulation of complement activation
Biologic function of complement system

3. Jules Bodet ( ),
Discoverer of complement
Nobel prize in 1919

4. complement
19世纪末，继抗毒素之后，又限快发现了免疫溶菌现象。Pfeiffer（1894）用新鲜免疫血清在豚鼠体内观察到对霍乱弧菌的溶菌现象。Bordet发现如将新鲜免疫血清加热60℃30分钟可丧失溶能力。他认为在新鲜免疫血清内存在二种不同物质与溶菌作用有关。一种对热稳定的物质称为溶菌素即抗体，有特异性，另一种对热不稳定的物质，可存在于正常血清中，为非特异性成分，称之为补体

5. Introduction complement Complement (C)
Complement System 
补体是由30余种补体固有成分、补体受体和细胞膜补体调节蛋白的多分子系统，故称为补体系统（complement system）。

6. Introduction Components of C system 1. Innate C components
complement
Introduction
Components of C system 
1. Innate C components
2. Regulatory Proteins
3. Complement receptor

7. Introduction Components of C system 1. innate components
complement
Introduction
Components of C system  
1. innate components
classical pathway:C1q,C1r,C1s,C4, C3,C2
Alternative pathway:B,D,P,C3
MBL pathway:MBL,MASP
terminal pathway:C5,C6,C7,C8,C9
MASP: MBL 相关丝氨酸蛋白酶

8. Introduction 2. regulatory proteins C1-INH, C4-BP, I factor, H factor
complement
Introduction
2. regulatory proteins
C1-INH, C4-BP, I factor, H factor
S protein,Sp40/40,
decay-accelerating factor (DAF)
3. complement receptor
CR1—CR5,C3aR,C4aR,C5aR
Inhibit help

9. Introduction nomenclature : C--complement C1,C2,C3,C5 B,D,H,I,P factor
C4B,DAF
a--small fragment C2a,C3a
b--large fragment C2b,C3b,C5b
¯--activated(enzyme) C1
i--inactivated iC3b

10. The properties of Complement glycoprotein:  globulin
Labile to heat: The activity of C is destroyed
(inactivated) by heating serum at 56℃ for 30 minutes .
C produced cells : Hepatocytes and Macrophages
Belongs acute phase protein
zymogen to protease: number of complement
proteins are zymogens that can be activated by
proteolytic cleavage
占总蛋白的5%-6% RT 很快失活， 10度内保持3-4天

11. Activation of the C System
complement
Activation of the C System
Pathways of complement activation:
triggered-enzyme cascade
1. Classical pathway
2. Alternative pathway
3. MBL pathway MBL:mannose-binding lectin

12. Classical pathway complement 1. C1 activation by Ag-Ab complex
2. C4 and C2 activation
generation C3 convertase
3. C3 activation (generation of C5 convertase)
4. Generation of C5 convertase marks the end of the classical pathway

13. Three steps：Classical pathway
1. Recognition ( C1 activation )
involved：C1q, C1r, C1s
Ag + Ab→IC→bind C1q→C1r→C1s→C1
2. Activation
involved：C4, C2 and C3
(1) C4 and C2 activation, generation of C3 convertase
(2) C3 activation (generation of C5 convertase)
3. Attack (terminal pathway)
involved：C5,C6,C7,C8,C9
the membrane attack complex(MAC):C5b6789
the MAC causes lysis of cells

14. Recognition ( C1 activation )
complement
Recognition ( C1 activation )
Activator: Ag-Ab complex /IC
Combinding CH2 of IgG or CH3 of IgM
One of IgM molecule or two molecules
of IgG are needed.
IgM>IgG3>IgG1>IgG2
Soluble antibody can’t activate complement

17. complement
classical pathway
C1 molecule

18. Activation
The components involved:
C4,C2 and C3
(1)C4 and C C3 convertase
(2)C4,C2,C C5 convertase

19. Classical Pathway Generation of C3-convertaseb
Ca++
C1r
C1s
C1q C4

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

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

22. complement

23. complement

24. Attack (terminal pathway) involved：C5,C6,C7,C8,C9
the membrane attack complex(MAC):C5b6789
the MAC causes lysis of cells
C5b67 暴露膜结合部位

25. complement
Terminal pathway(MAC)

26. complement
Terminal pathway

28. Alternative pathway Activators： LPS(endotoxin),
certain complex polysaccharides,
IgA and IgG4
旁路途径 ，替代激活途径， 不依赖于抗体， 而由微生物或外源异物直接激活C3。
进化过程中， 最早出现的补体活化途径。

31. Alternative pathway complement factor B and factor D involved
It is rather different from the MBL and classical pathway.
1. no C1,C4 and C2 involved
factor B and factor D involved
2. the presence of suitable activator
surfaces,such as bacterial and
fungal cell walls.
3. C3b: from the classical pathway;
spontaneous produced C3b

32. Characters of alternative pathway
1. it can recognize “self” and “non-self”
2. the amplification loop

33. Mannan-binding lectin pathway
Activators：MBL (similar to C1q, hexamer)
MBL recognizes certain carbohydrates expressed on the surface of microorganisms ↓
MBL activate two MBL-associated serine proteases
--- MASP and MASP-2
↓ ↓
cleaves C cleaves C4,C2 to generate
activate the alternative the C3 convertase (C4b2a)
pathway directly

37. Regulation of complement activation
1.Self-regulation
C4b2b C3bBb C4b C3b C5b
2.Control proteins
Classical pathway: C1INH C4bp
I MCP DAF (C3b和Bb)
Alternative pathway:H I CR1 DAF
MCP Properdin
Formation of MAC: C8bp CD59(MIRL)
MCP: 膜辅蛋白
MIRL: 膜反应性溶解抑制物

38. Regulation of complement activation

39. Regulation of complement activation

40. Regulation of complement activation

41. Regulation of complement activation

43. Biologic function of complement system
1. mediates anti-infection immunity
(1) Lysis of cell or microorganisms
(2) opsonization
(3) inflammation

44. complement mediated the lysis of cells

45. function:enhance phagocytosis
complement
opsonization
opsonin:C3b,C4b,iC3b
cell:phagocyte
receptor:CR1,CR3,CR4
function:enhance phagocytosis

47. symptoms: redness, swelling,
complement
(3) inflammatory response
symptoms: redness, swelling,
heat and pain
inflammation mediators:
C5a,C3a,C4a ( anaphylatoxins)
C5a (chemotaxis)

48. Biologic function of complement system

49. 2. Complement maintains homeostasis
1) clearance of IC
C3b
2) elimination of apoptosis cells
C1q,C3b,iC3b

51. 3. Complement mediates adaptive immunity
1) Induction of immune response
2) Proliferation and differentiation
of immune cells c3d
3) Effective stage of immune response
4) Immune memory
4. Interaction with other enzyme system

52. Summary
Review the differences between the three pathways of complement in terms of how they are activated.
Why the complement do not attack autologous cells?

53. Thanks!