第第3章章 补体系统补体系统 (complement,C) 第第1节节 概述概述 概念概念：：补体系统补体系统—是存在与人和脊椎动物是存在与人和脊椎动物血清、组织液中和细胞表面的一组经活化血清、组织液中和细胞表面的一组经活化后具有酶活性的糖蛋白后具有酶活性的糖蛋白 分分 类类补体的固有成份：补体的固有成份：C1～～C9 、、B、、D、、MBL…补体调节成分：补体调节成分：C1抑制物、抑制物、I因子、因子、H因子因子 …补体受体：补体受体： CR1~5、、C3aR、、C5aR… 补体的基本特性补体的基本特性 1））连锁反应性连锁反应性:2）放大性：）放大性： C1q、、C3转化酶转化酶3）不稳定性）不稳定性: 56 C 30min4））作用的双重性：作用的双重性： 生理、病理生理、病理5）反应的局限性：）反应的局限性： 易失活、抗体、抑制成分易失活、抗体、抑制成分 理化性质理化性质l对热对热不稳定，不稳定，56 °C 30分钟即被灭活分钟即被灭活l体液中体液中C3含量最高含量最高l多数补体属多数补体属 球蛋白球蛋白 补体代谢l来源：主要由肝细胞和巨噬细胞产生主要由肝细胞和巨噬细胞产生l合成的调节：组织特异性；多因素调节l分解代谢：快于其他血浆蛋白 第第2节节 补体的激活补体的激活•经典途径经典途径(classical pathway)•替代途径替代途径(alternative pathway)•凝集素途径凝集素途径(lectin pathway) 激活物：激活物：免疫复合物（免疫复合物（IC））条件：条件： ①① C1仅与仅与IgM的的CH3或或 IgG1-3的的CH2结合结合 ②②每一个每一个C1与两个以上与两个以上Ig补体结合位点结合补体结合位点结合 Ab必需必需与与Ag结合结合 激活过程激活过程 ：：1、识别阶段、识别阶段—C1S（（C1酯酶）形成酯酶）形成 2、活化阶段、活化阶段—C5转化酶形成转化酶形成 3、膜攻击阶段、膜攻击阶段—MAC形成形成 识别阶段识别阶段参与成分：参与成分：C1q、、C1r、、C1s过程：过程： Ag与与Ab结合结合 补体结合位点补体结合位点（（IgG的的CH2；；IgM的的CH3））暴露暴露 C1q激激活活 C1r活化活化 C1s脂酶形成。
脂酶形成 IgM（（未与未与Ag结合）结合）IgM（（已与已与Ag结合）结合） 活化阶段活化阶段参与成分：参与成分：C4、、C2、、C3目的：目的：形成形成C5转化酶转化酶过程：过程：C4 C4b+C4aC2 C2b+C2aC4b2bC3C3b+C3aC4b2b3bC1SC1S 活化阶段活化阶段 膜攻击阶段膜攻击阶段参与成分：参与成分：C5、、C6、、C7、、C8、、C9目的：目的：形成形成MAC 膜膜攻击复合物攻击复合物membrane attack complex, MAC组成：组成：C5b678 (9)n ，，其中其中C9分子可有分子可有12-15个个大小：大小：10-11 nm 内径的小孔内径的小孔效应：胞内渗透压降低，细胞溶解效应：胞内渗透压降低，细胞溶解致死量钙离子被动向胞内弥散，细胞死亡致死量钙离子被动向胞内弥散，细胞死亡 激活物：激活物：MBLMBL产生：产生：感染感染 巨噬细胞、中性粒巨噬细胞、中性粒细胞活化产生细胞活化产生TNF、、IL-1、、IL-6等因子等因子 肝细胞激活肝细胞激活 合成分泌期急性蛋白（包括合成分泌期急性蛋白（包括MBL、、C反应蛋白等）反应蛋白等）MBL特点：特点：Ca离子依赖蛋白，可与甘露糖残基离子依赖蛋白，可与甘露糖残基结合，结构与结合，结构与 C1q类似，具有活化类似，具有活化C1q 同样的生同样的生物学功能。
物学功能 激活物质：激活物质：Gˉ菌内毒素，聚合菌内毒素，聚合IgA、、IgG4等等参与成分：参与成分：D、、B、、P因子，因子，C3、、C5~C9特特 点点 感染早期发生有效防御感染早期发生有效防御 形成放大机制形成放大机制 可识别自己和异己可识别自己和异己 第第3节节 补体活化的调控补体活化的调控 自身衰变调控自身衰变调控C 3转化酶（转化酶（C 4b2b和和C 3bBb））C 4 b、、 C 3b 、、C 5b仅在与固相结合时状态才较稳定仅在与固相结合时状态才较稳定 调节因子调控调节因子调控负调节因子：负调节因子：C 1INH 、、 C 4结合蛋白结合蛋白 、、I因因子子 、、H因子、因子、MAC、、DAF等等正调节因子：正调节因子：P因子、因子、C3 肾炎因子（抗肾炎因子（抗C3转转化酶化酶Ab、、稳定稳定C 3bBb）） C1INH的作用的作用 C4BP的作用的作用 DAF因子的作用因子的作用H因子的作用因子的作用 DAF因子的作用因子的作用 S蛋白的作用蛋白的作用 同源限制因子的作用同源限制因子的作用 第第4节节 补体受体补体受体lCR1（（C3b/C4bR):抑制补体激活；调理作用；抑制补体激活；调理作用；清除免疫复合物；免疫调节清除免疫复合物；免疫调节lCR2(C3dR,CD21)：：免疫调节；是免疫调节；是EB病毒受体病毒受体lCR3(iC3bR,CD18)/ CR4(iC3bR/C3dg,CD18) ：：参与吞噬细胞生物学作用；凝集素活性；参参与吞噬细胞生物学作用；凝集素活性；参与黏附作用与黏附作用 第第5节节 补体的生物学活性补体的生物学活性MAC介导细胞溶解介导细胞溶解活性片段的生物学活性片段的生物学效应效应 调理作用调理作用 引起炎症反应引起炎症反应 清除免疫复合物清除免疫复合物清除凋亡细胞清除凋亡细胞 免疫调节作用等免疫调节作用等 一、参与宿主早期抗感染免疫一、参与宿主早期抗感染免疫 1 1 1 1、溶解细胞、细菌和病毒、溶解细胞、细菌和病毒、溶解细胞、细菌和病毒、溶解细胞、细菌和病毒补体活化形成的补体活化形成的MAC可导致靶细胞溶解，是机可导致靶细胞溶解，是机体抵抗微生物感染的重要防御机制。
体抵抗微生物感染的重要防御机制 2、调理作用、调理作用 C3b/C4b为中间桥梁，通过其为中间桥梁，通过其N端与细菌等颗端与细菌等颗粒性抗原或免疫复合物结合后，再通过其粒性抗原或免疫复合物结合后，再通过其C端与端与具有补体受体（具有补体受体（CRI））的吞噬细胞结合，由此增的吞噬细胞结合，由此增强吞噬细胞的吞噬作用称为补体的调理作用；强吞噬细胞的吞噬作用称为补体的调理作用； 细菌或免疫复合物激活补体，结合细菌或免疫复合物激活补体，结合C3b/C4b后，后，若与具有补体受体（若与具有补体受体（CRI））的的RBC和血小板结合，和血小板结合，则可形成较大的聚合物，这种效应称为免疫黏附则可形成较大的聚合物，这种效应称为免疫黏附作用 调理作用调理作用 3、炎症介质作用、炎症介质作用过敏毒素样作用：过敏毒素样作用：可使表面具有相应补体受体的肥可使表面具有相应补体受体的肥大细胞和嗜碱性粒细胞等脱颗粒，释放组胺等血管大细胞和嗜碱性粒细胞等脱颗粒，释放组胺等血管活性物质，引起血管扩张、通透性增强、平滑肌收活性物质，引起血管扩张、通透性增强、平滑肌收缩和支器官痉挛等的作用，称缩和支器官痉挛等的作用，称过敏毒素样作用过敏毒素样作用。
C3a、、C4a、、C5a有此作用有此作用 趋化作用：趋化作用：C3a和和C5a等能吸引具有相应受体的中等能吸引具有相应受体的中性粒细胞和单核吞噬细胞向补体激活的炎症区域游性粒细胞和单核吞噬细胞向补体激活的炎症区域游走和聚集，增强炎症反应走和聚集，增强炎症反应 二、维护机体内环境稳定二、维护机体内环境稳定l清除免疫复合物（清除免疫复合物（IC）：）：补体抑制新的补体抑制新的IC形成；形成；可溶解已沉积的可溶解已沉积的IC；； IC活化补体，借助活化补体，借助C3b与与血细胞结合，而被肝细胞清除血细胞结合，而被肝细胞清除l清除凋亡细胞：清除凋亡细胞：C1q、、C3b、、iC3b可识别和结可识别和结合凋亡细胞，并通过与吞噬细胞受体相互作用合凋亡细胞，并通过与吞噬细胞受体相互作用而清除这些细胞而清除这些细胞 清除免疫复合物清除免疫复合物 三、连接天然免疫与获得性免疫的桥梁三、连接天然免疫与获得性免疫的桥梁l参与免疫应答的诱导：参与免疫应答的诱导：C3b参与捕捉、固定抗原，参与捕捉、固定抗原，是抗原易被是抗原易被APC处理处理与提呈l参与免疫细胞的增殖、分化：补体多种成分参与免疫细胞的增殖、分化：补体多种成分与与多种免疫细胞相互作用，调节细胞的增殖分化多种免疫细胞相互作用，调节细胞的增殖分化。
l参与免疫应答的效应：如细胞毒性、调理作用参与免疫应答的效应：如细胞毒性、调理作用及清除及清除ICl参与免疫记忆参与免疫记忆 四、补体与其他酶系统的相互作用四、补体与其他酶系统的相互作用l补体与凝血、纤溶、激肽系统间存在着十分密补体与凝血、纤溶、激肽系统间存在着十分密切的相互影响及相互调节关系切的相互影响及相互调节关系 补体遗传缺陷可导致的疾病补体遗传缺陷可导致的疾病缺陷蛋白缺陷蛋白 影影 响响 功功 能能 相相 关关 疾疾 病病C1、、C2、、C4 免疫复合物清除缺陷免疫复合物清除缺陷 SLE、、化脓性感染化脓性感染 补体传统激活途径活化缺陷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、肾小球肾炎化脓性感染、肾小球肾炎 C1INH 炎性炎性介质产生失控介质产生失控 遗传性血管水肿遗传性血管水肿DAF、、CD59 补体对宿主细胞毒作用补体对宿主细胞毒作用 阵发性夜间血红蛋白尿阵发性夜间血红蛋白尿CR3 外周血单核细胞黏附缺陷外周血单核细胞黏附缺陷 感染（绿脓杆菌、假单胞菌等感染（绿脓杆菌、假单胞菌等））H因子因子 替代激活途径活化失控致低替代激活途径活化失控致低C3血症血症 SLE、、化脓性感染、肾小球肾炎化脓性感染、肾小球肾炎 complement complementlclassical name: heat-labile component of plasma which ‘complements’ antibody opsonisation and killing of bacterialplasma proteins most of which circulate as inactive zymogens and are activated at sites of inflammation initiating an enzyme cascadelcontribution of the complement system to disease in which complement is inappropriately activated, inhibited or deficient nomenclaturelC1,C2,C3………C9lB,D,P (factor)lI,H factor for regulationla ,b ( peptide fragment )lC4bC2a, C3bBb (the complex that have enzymatic activity) Activation pathwaylthe classical pathwaylthe alternative pathwaylthe lectin pathway classical pathwaylinitiated by antigen—antibody complexes lectin pathwaylmannan binding lectin(MBL)pathway lmannan binding lectin(MBL) is a acute protein, a member of the collectin group of proteins that recognize repeating sugar patterns，as might occur on the carbohydrate capsule of bacteria．lPAMP (pathogen associated molecular pattern) alternative pathwaylphylogenetically it probably is the older activation pathway lIt does not absolutely require antibody for activation． lthree pathways proceed identically through binding of the terminal components to form a membrane attack complex，which ultimately causes cell lysis Simple view EffectorlC3a, C4a, C5a inflammatory cell chemotaxis, mast-cell degranlC3bopsonin via C3bR, solubilisation of i-clC5b-C8, C9 membrane attack complex - cell lysisRegulatory proteinslcontrol the amplification cascade lshort enzyme half life C3 central molecule of the complement systemlConserved molecule – in echinoderms (ancient 700M years), long before Ig.lThe most versatile and multifunctional molecule described to datelCan interact specifically with at least 25 different molecules C3 lPromotes phagocytosislSupports local inflammatory reactions against pathogenslInstructs the adaptive immune responselUnregulated activation causes tissue damagelUsed by pathogens for immune evasion The Fab of IgG or IgM bind to epitopes on an antigen. C1q, C1r, and C1s then assembles on the Fc portion of the antibodies to form C1, the first enzyme of the classical complement pathway. The enzyme C1 is able to cleave C4 into C4a and C4b, as well as C2 into C2a and C2b. initiation IgG2 C3 C3 ConvertaseConvertase The enzyme C1 is able to cleave C4 into C4a and C4b. The C4b binds to adjacent proteins and carbohydrates on the surface of the antigen. C2 then binds to the C4b and C1 cleaves C2 into C2a and C2b. The C4b2a functions as a C3 convertase that can subsequently cleave hundreds of molecules of C3 into C3a and C3b. C5 C5 ConvertaseConvertase Much of the C3b binds to adjacent proteins and carbohydrates on the antigen to participate in opsonization while C3a can stimulate inflammatory responses. Some of the C3b binds to C4b2a to form C4b2a3b, a C5 convertase that can cleave C5 into C5a and C5b. The Membrane Attack Complex (MAC) Causing Cell Lysis This C5b6789n, or membrane attack complex (MAC), puts pores into lipid bilayer membranes of human cells to which antibodies have bound. This results in cell lysis. MAC can also damage the envelope of enveloped viruses and put pores in the outer membrane and cytoplasmic membrane of gram-negative bacteria causing their lysis. lThe electron micrograph shows holes punched through the cell wall of the bacterium Shigella dysenteriae by the terminal components of the complement system. Some of the holes are larger than expected for C9 channels and probably were enlarged later by the action of lysozyme Alternative (innate) pathwayslThere is a spontaneous conversion of C3 to C3b. Ordinarily the C3b is quickly inactivated: the C3b binds to inhibitory proteins and sialic acid present on the surface of body's own cells, and the process is aborted. lHowever, bacteria and other foreign materials that may get into the body lack these proteins and have little or no sialic acid. So the C3b binds a protein called Factor B forming a complex of C3b•Bb. lC3b•Bb is also a C3 convertase acting on more C3 to form: 1.C3b•Bb•C3b, which is a C5 convertase and can start the assembly of the MAC. 2.more C3b [a positive feedback loop], amplifying what might have started as a small reaction (the formation of C3b by either or both the classical and alternative pathways) into a massive production of C3b. Activation of the Alternative Complement Pathway and Formation of C3 Convertase lActivation of the alternative complement pathway begins when C3b (or C3i) binds to the cell wall and other surface components of microbes. Alternative pathway protein Factor B then combines with the cell-bound C3b to form C3bB. Factor D then splits the bound Factor B into Bb and Ba, forming C3bBb. A serum protein called properdin then binds to the Bb to form C3bBbP that functions as a C3 convertase capable of enzymatically splitting hundreds of molecules of C3 into C3a and C3b. MannanMannan-binding -binding lectinlectin (MBL) (MBL)MBL recognises C3- and C4-hydroxyl groups of mannose, glucose, fucose and N-acetyglucosamine, and activates the classical complement pathway via MBL-associated serine proteases 1 and 2 Recognition of carbohydrates on microbes but not on self because lthe structure is common on microbes but is absent on self lbinding requires multiple associations between the recognition lectin domains and the repetitive carbohydrate structure on microbes which are not on mammalian membranes Pathogen-associated molecular patterns (PAMP). lessential surface molecules which serve non-redundant functions, and are therefore conservedlthese are the basis of an evolved non-specific recognition by host cells. These molecular patterns are recognised by pattern recognition receptors (PRR) on host cells Examples of PAMPs arellipopolysaccharides (LPS or endotoxin) Gram-negative bacteriallipoteichoic acidGram-positive bacterialformyl-peptidesbacterialmannansyeastlglycolipidsmycobacterialdouble-stranded RNA, poly ICviruses Benefits of C5a and C3b Most C3b binds to antigens on the microbial surface. Some C3b combines with C2a and C4b to form the third enzyme of the complement pathway that is able to split C5 into C5a and C5b. C5a stimulates mast cells to release histamine for inflammation and diapedesis. It also functions as a chemoattractant for phagocytes. The phagocytes are then able to bind to the C3b attached to the surface of the microorganism allowing for opsonization (enhanced attachment). complement recognition molecules and receptorscomplement recognition molecules and receptorslCR1 (CD35) mono/macs, PMN, lymphocytes, RBC C3b/4b phagocytosislCR2 (CD21)B-cells, FDC iC3b, C3daugments B cell activationlCR3 (CD11b/18) mono/macs, PMN, NKiC3b, LPSadhesion, clearancelCRPCa++ dependent C1q binding,activates classical comp, phagocytosis, apoptosis complement : structure and functioncomplement : structure and functionInitiating pathways:lclassical pathwaylmannan-binding lectin pathwaylalternative pathwayEffector pathwaylC3a, C4a, C5a inflammatory cell chemotaxis, mast-cell degranlC3bopsonin via C3bR, solubilisation of i-clC5b-C8, C9 membrane attack complex - cell lysisRegulatory proteinslcontrol the amplification cascade lshort enzyme half life, Regulatory proteins Anaphylaxis - laryngeal oedema Biological consequence of complement activationlCell lysis lOpsonization and phagocytosislViral neutralizationlInflammationlRegulation of cellslClearance of immune complex 。