Complement system 补体系统 IMMUNOLOGY Qingqing Wang Institute of Immunology Zhejiang University School of Medicine

Complement Contents 1. Introduction 2. Activation of the Complement System 3. Regulation of complement activation 4. Biological function of complement system

Jules Bodet ( ), 比利时科学家 Discoverer of Complement 1894 Bordet 发现绵羊抗霍乱血 清能够溶解霍乱弧菌，加热 56 ℃ 30 min 阻止其活性；加入新鲜非 免疫血清可恢复其活性。 百日咳杆菌 1919 Nobel Prize

Complement 补体（ Complement ）：新鲜血液中存在一种不耐热的成分，可 辅助特异性抗体介导的溶菌作用。

Introduction Complement (C) 补体  A group of serum proteins involved in the control of inflammation, the activation of phagocytes and the lytic attack on cell membranes.  This activity is destroyed (inactivated) by heating serum at 56  C for 30 minutes. Complement System consists of a large number of proteins which become enzymes after being activated. Complement

1. Activation proteins 2. Regulatory proteins 3. Complement receptor Complement I. Proteins of the Complement System

Activation Proteins Classical pathway: C1q, C1r, C1s, C4, C2 MBL pathway: MBL, MASP Alternative pathway: factor B, D Terminal pathway: C3, C5, C6, C7, C8, C9 Complement

Regulatory Proteins C1INH, C4bp, factor I, factor H S protein, membrane cofactor protein decay-accelerating factor (DAF) … Complement receptor CR1~CR5, C3aR, C2aR, C4aR… Complement

II. Complement catabolism Complement producing cells Liver hepatocytes Monocytes/Macrophages Epithelial cells Regulation of biosynthesis catabolism Complement

＊ 固有成分 按发现的先后分别命名为 C1(q 、 r 、 s) 、 C2 、 …C9 ； ＊ 其他成分 以英文大写字母表示，如 B 因子、 D 因子、 P 因子； ＊ 补体调节蛋白 多以其功能命名，如 C1 抑制物、 C4 结合蛋白、 促衰变因子等； ＊ 补体受体 多以其结合对象命名，如 C3aR 。 ＊ 补体活化后的裂解片段 以该成分的符号后面附加小写英文字母 表示。如 C3a 、 C3b 等；小片段用 a ，大片段用 b 。（人卫出版社 第 5 版） C2 特殊， C2a 为大片段， C2b 为小片段。 ＊ 具有酶活性的成分 在其符号上划 ¯ 横线表示。 ＊ 被灭活后的成分 其符号前加 i 。 Notation

Activation of the complement system 1. Classical pathway 2. MBL pathway MBL: mannan-binding lectin 3. Alternative pathway Complement

Classical pathway A suitable Ab bound to Ag, Ag-Ab complex IgM>IgG3>IgG1>IgG2 C1, C4, C2 and C3, Ca ++ and Mg ++ cations 1. C1 activation 2. C4 and C2 activation (generation of C3 convertase) 3. C3 activation (generation of C5 convertase) 4. Generation of C5 convertase marks the end of the classical pathway Complement

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Activators Activation of this pathway may occur via Ag- Ab complex (immune complex, IC) or by aggregated Ig. IgG (IgG1,IgG3) and IgM are most efficient in reacting with complement. Only one molecule of IgM is required, whereas at least two molecules of IgG are needed. Soluble antibody can’t activate complement Complement

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

Classical pathway Complement C1 molecule Ca ++

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Complement Classical pathway Ag-Ab complex C3 convertase C4b2a C5 convertase C4b2a3b C2b

Alternative pathway Activators ： bacterial lipopolysaccharides (endotoxin), certain complex polysaccharides normal: Circulating plasma C3 undergoes spontaneous hydrolysis of its thioester bond to form a conformationally altered species called C3(H 2 O). Once the thioester group has opened, C3(H 2 O) acts like C3b. C3 → C3a ↓ D C3b+B → C3bB → C3bBb (C3 convertase) → be dissociated ↑ - ↑ - I I/H abnormal: no factor I and H on the surface of bacterial C5 convertase :C3bBb3b or C3bnBb

Alternative pathway 1.It is rather different from the MBL and classical pathway. 2. no C1,C4 and C2 involved factor B and factor D involved 3. the presence of suitable activator surfaces,such as bacterial and fungal cell walls. 4. C3b: from the classical pathway; spontaneous produced C3b Complement

Alternative pathway Complement

Alternative pathway 1. It can recognize “self” and “non-self” 2. The amplification loop

MBL pathway Activators ： MBL (like C1q) MBL recognizes certain carbohydrates expressed on the surface of microorganisms. ↓ MBL activate two MBL-associated serine proteases MASP-1 and MASP-2. ↓ cleaves C3 cleaves C4 and C2 to activate the alternative generate the C3 convertase (C4b2a ) pathway directly

Activation of the Complement System MBL pathway When MBL binds to terminal mannose groups on bacterial carbohydrates, it activates MASP-1 and MASP-2, which go on to activate the classical pathway in an antibody-independent fashion. complement

MBL pathway Complement b a

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The Complement Pathways Lectin Pathway Classical Pathway Alternative Pathway C1q C4 C2 C3 C5 to C9 Lysis MBL C3 (H 2 O), C3b Factors D, B, Properdin MASP 1,2,3 C1r,C1s

Activation of the Complement System Terminal pathway:MAC(membrane attack complex) complement

Activation of the Complement System complement Terminal pathway

不同途径补体系统激活的比较 经典途径 MBL 途径旁路途径 免疫复合物病原体甘露糖残基 C1 、 C4 、 C2MASP 、 C4 、 C2 病原体表面 C3 、 B 、 D C3 转化酶 C5 转化酶 攻膜复合体

Regulation of complement activation 1.Self-regulation C4b2a C3bBb C4b C3b C5b 2.Control proteins classical pathway:C1INH C4bp I MCP DAF alternative pathway: H I CR1 DAF P formation of MAC: C8bp CD59 complement

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Regulation of complement activation complement

C1IHN 缺陷引起血管神经性水肿

Regulation of complement activation complement

Regulation of complement activation complement

Regulation of complement activation complement

Regulation of complement activation complement

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

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(1)complement mediated lysis of cells

溶菌溶细胞 补体的溶细胞作用

(2) opsonization opsonin: C3b, C4b, iC3b cell: phagocyte receptor: CR1, CR3, CR4 function: enhance phagocytosis complement

细菌 C3b 受体 吞噬细胞 补体的调理作用

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

肥大细胞 过敏介质 C5a C3a 补体的过敏毒素作用

C567C5a C3a 补体的趋化作用 中性粒细胞 单核 - 巨噬细胞 血管 组织

C1q—— 识别免疫复合物、识别病毒膜蛋白 C4a—— 过敏毒素 C4b—— 组成 C3 、 C5 转化酶、参与免疫粘附 C2b—— 组成 C3 、 C5 转化酶 C3a—— 过敏毒素、趋化因子 C3b—— 组成 C3 、 C5 转化酶、参与免疫粘附、调理作用 C5a—— 过敏毒素、趋化因子 C5b 、 C6 、 C7—— 趋化因子、组成攻膜复合体 C8 、 C9—— 组成攻膜复合体 Ba—— 参与免疫调节 Bb—— 组成 C3 、 C5 转化酶

2. Complement maintains homeostasis (1) clearance of IC (immune complex): C3b (2) elimination of apoptotic cells: C1q, C3b, iC3b

清除免疫复合物

3. Complement mediates adaptive immunity (1) Participates in the induction of immune response (CD19/CD21/CD81on B cells) (2) Participates in the proliferation and differentiation of immune cells (B cells) (3) Participates in the effector function of immune response (complement fixing Ab) (4) Participates in immune memory (through FDC) 4. Complement interacts with other enzyme systems

补体遗传缺陷可导致的疾病 缺陷蛋白 影 响 功 能 相 关 疾 病 C1 、 C2 、 C4 免疫复合物清除缺陷 SLE 、化脓性感染 补体传统激活途径活化缺陷 C3 免疫复合物清除及补体活化无能 SLE 、化脓性感染、肾小球肾炎 C1INH 炎性介质产生失控 遗传性血管水肿 DAF 、 CD59 补体对宿主细胞毒作用 阵发性夜间血红蛋白尿 CR3 外周血单核细胞黏附缺陷 感染（绿脓杆菌、假单胞菌等） H 因子 替代激活途径活化失控致低 C3 血症 SLE 、化脓性感染、肾小球肾炎

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