Major Histocompatibility Complex (MHC) and its encoding molecules

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1 Major Histocompatibility Complex (MHC) and its encoding molecules
IMMUNOLOGY Major Histocompatibility Complex (MHC) and its encoding molecules Xiaojian Wang 科研楼B819

2 Structure of MHC genes and products Polymorphism of MHC
Introduction Structure of MHC genes and products Polymorphism of MHC Interactions of MHC molecules with antigenic peptides Biological function of MHC molecules MHC and clinical medicine

3 Introduction The ability to accept grafts between individuals. MHC
1. Histocompatibility antigen The Ags primarily responsible for rejection of genetically different tissues are known as histocompatibility Ags. Histocompatibility The ability to accept grafts between individuals. 2. Histocompatibility antigen system Major histocompatibility antigen Minor histocompatibility antigen

4 3.Major histocompatibility complex,MHC
A cluster of genes on chromosome 6 in humans, encoding major histocompatibility antigen which regulates immune response. 4. Human: Human leukocyte antigens (HLA) mouse: H-2

5 Mouse MHC = H-2 human MHC = HLA Mouse MHC = H-2 Ir基因
MHC生物学功能的研究。MHC及其分子的研究开始于对移植抗原的研究。 40年代末戈尔（ Gorer）和斯莱尔（ Snell）等对小鼠的主要移植抗原（H－2抗原）系统的研究揭示了H－2抗原的多样性以及编码H－2抗原的基因是一个紧密连锁的基因群，现称为主要组织相容性复合体（ Major Histocompatibility Complex， MHC）。与此同时多塞（ Dausset）等对人的 HLA进行了相同的研究；班拉塞拉夫（ Beracerraf）等对 H-2内控制免疫应答的基因（Ir基因）进行了研究，这些研究成果使斯莱尔、多塞和班拉塞拉夫获得1980年的诺贝尔奖。 Mouse MHC = H-2 Ir基因 human MHC = HLA Mouse MHC = H-2

6 1996 Nobel Prize (MHC restriction)
显然，如此复杂的基因复合物（MHC）的存在决不仅仅是编码移植抗原，以引导移植排斥，它必然有更重要的生理功能，目前已知，MHC分子是一种抗原提呈分子，抗原肽只有与MHC分子结合才能被T细胞识别，引发T细胞介导的免疫应答。多赫迪（Doherty）和辛克拉杰（Zinkernagel）对MHC功能的研究获得1996年诺贝尔奖。

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8 Organization and Structure of MHC Genes and Products
1. Organization of MHC genes 2. Products of MHC class I and MHC class II genes---HLA molecules 3. Immune function related genes

9 1. Organization of MHC genes
H K AβAα EβEα C4 Bf C2 D L IA IE Ⅰ Ⅱ Ⅱ Ⅲ Ⅰ Ⅰ 1500kb Chromosome 17 (mouse)

10 Organization of MHC genes
HLA DP DQ DR C B C A B A B A B B A B A Bf C2 Ⅱ Ⅱ Ⅱ Ⅲ Ⅰ Ⅰ Ⅰ HLA复合体位于第六对染色体的短臂上（跨度约3600kb Chromosome 6 (human)6p21.31

11 Organization of MHC genes

12 2. Products of MHC class I and class II genes---HLA molecules

13 MHC 1) HLA class I molecules 编码B2-M位于第15号染色体

14 1) HLA class I molecules Genes: A, B, C Distribution: every nucleated cell Structure: α chain (45kD) β2m (12kD) chromosome 15 peptide-binding cleft: α1+α2 CD8 binding: α3 Function: recognize and present the endogenous Ags to CD8+ T cells

15 MHC HLA class I molecule

16 Structure of HLA I molecule
MHC Structure of HLA I molecule HLA I molecule

17 2) HLA class II molecules
MHC 2) HLA class II molecules

18 2) HLA class II molecules
MHC 2) HLA class II molecules Genes: DR, DQ, DP Distribution: APC (B, DC, MΦ) thymic epithelial cell, activated T cell Structure: α chain (35kD) β chain (28kD) peptide-binding cleft: α1+β1 CD4 binding: β2 Function: recognize and present the exogenous Ags to CD4+ T cells

19 来源与APC 之外的抗原 ，如被吞噬的细胞、细菌。蛋白质抗原，
细胞内合成的抗原： 被病毒感染的病毒蛋白， 肿瘤抗原， 包内的自身成分。

20 Structure of HLA II molecule
MHC Structure of HLA II molecule HLA class II molecule

21 Structure of HLA molecule
MHC Structure of HLA molecule

22 HLA-Ⅰ、Ⅱ类抗原的分布 组织 MHC I类分子 MHC II类分子 T细胞 B细胞 巨噬细胞 树突状细胞 胸腺上皮细胞 肝细胞 肾脏细胞
脑细胞 红细胞 滋养层细胞 +++ + +- - +/- ++

23 3. Immune function related genes
MHC 3. Immune function related genes 1. Serum complement coded genes HLA class III C4B, C4A,Bf, C2 2. Antigen presenting function related genes HLA class II LMP (proteasome subunit beta type, psmb):LMP2/7 encoding proteosome beta subunit Function: process endogenous Ag TAP (transporter associated with Ag processing): TAP1, TAP2 Function: transport endogenous Ag peptides Tapasin (TAP associated protein) Function: : participate in the endogenous pathways , help the assemble of the MHCI in ER TAP: 抗原加工相关转运物

24 PSMB, 蛋白酶体B 亚单位 蛋白酶体是胞内大分子蛋白水解酶复合体， 具有酶活性的组分主要是B 亚单位。 TAP是一种由两个亚单位组成的异二聚体（TAP1/2）,各跨ER膜6次， 共同在ER膜上形成孔道。 选择性结合适合MHCI类分子的8-12个AA 的抗原肽。

25 HLA-DO: negative regulation to DM
MHC HLA-DM: DMA and DMB participate in the exogenous pathways, help the peptide binding to the MHCII HLA-DO: negative regulation to DM

26 The function of HLA-DM

27 HLA-DM catalyses the removal of CLIP
Replaces CLIP with a peptide antigen using a catalytic mechanism (i.e. efficient at sub-stoichiometric levels) Discovered using mutant cell lines that failed to present antigen HLA-DO may also play a role in peptide exchange MIIC compartment Sequence in cytoplasmic tail retains HLA-DM in endosomes HLA-DM HLA-DR

28 3. Non-classic class I gene (HLA Ib)
MHC 3. Non-classic class I gene (HLA Ib) HLA-E, HLA-G: inhibit NK cell activity ＊HLA-E： 结合NK细胞和部分CTL细胞表面的C型凝集素受体超家族CD94/NKG2家族.抑制NK 细胞功能 表达于各种组织细胞，在羊膜和滋养层细胞表面高表达。 功能： A.生理状态下NK处于抑制状态。 B.母胎耐受 由α链和β2m组成，有6种等位基因。表达于各 种组织细胞、在羊膜和滋养层细胞表面高表达

29 ＊HLA-G：由α链和β2m组成，有15种等位基因。
分布：主要分布于母胎界面绒毛外滋养层细胞， 受体：杀伤细胞免疫球蛋白样受体（KIR）家族和白细 胞免疫球蛋白样受体（LIR）家族的某些成员。 功能：在母胎耐受中发挥功能。

30 4. Inflammation related genes TNF gene family: TNF, LTA, LTB
MHC 4. Inflammation related genes TNF gene family: TNF, LTA, LTB Transcript factor gene family: I-κBL, ZNF173 MIC family: MIC A(高多态性), 激活NK 细胞性MIC B Heat shock protein gene family: HSP70 MHC I类相关基因家族， HSP 内源性抗原加工提呈

31 Immune function related genes
Complement encoding genes Non-classical MHC I genes Ag processing-related genes Inflammation-related genes 31

32 Polymorphism of MHC Concept of polymorphism
The phenomenon of having multiple allels at given genetic locus in the population

33 EMBL-EBI HLA Sequence Database
1.Mutiple-allele EMBL-EBI HLA Sequence Database ( HLA alleles: 3,201 (class I:2,215, class II: 986) (last updated:07/2010 ) HLA-A alleles HLA-DPA HLA-B HLA-DPB HLA-C HLA-DQA HLA-E HLA-DQB HLA-F HLA-DRA HLA-G HLA-DRB HLA-DRB HLA-DRB HLA-DRB HLA-DRB

34 Naming of HLA alleles Locus group number HLA-A* 02 01 HLA-DRB1* 1102
allele allele Locus group number HLA-A* HLA-DRB1* 1102

35 2. Codominant expression: MHC genes are codominantly expressed in each individual (therefore each individual has 6 class I and 6 class II MHC molecules), which means the alleles inherited from both parents are expressed equally. This maximizes the number of MHC molecules available to bind peptides for presentation to T cells.

36 the set of MHC alleles on each chromosome
Linkage disequilibrium and haplotype Linkage disequilibrium: the phenomenon that certain MHC alleles at different loci are inherited together more frequently than would be predicted by random assortment. e.g., DRB1* DQB1*0701 15.6% % % (0.156×0.219=3.4%) 分属两个或两个以上基因座位的等位基因，同时出现在一条染色体的几率高于随机出现的频率，称连锁不平衡（linkage disequlibrium）。 MHC单元型 ＊ 更加复杂化。染色体上MHC不同座位等位基因的特定组合称单元型（haplotype）。 ＊ 利用单元型可进行人种和地理族的分析以及HLA配型分析。中国汉族人特征性的HLA单元型为A2-B46-Cw3-DR9-Dw23和A33-B17-Cw3-DR3-DQ2-Dw3。 ＊ 利用单元型进行疾病相关基因的分析 从无血缘关系人群中寻找HLA相匹配的供受体 the set of MHC alleles on each chromosome A2-B46-Cw3-DR9-DQ9-Dw23 36

37 MHC

38 HLA多态性 ＊产生基础为变异，涉及基因突变、基因重组（染色体同源部分的交换）和基因转换（染色体非同源部分DNA片段的转移）等。
＊MHC变异属于偶发事件，这些偶发变异能否以新等位基因的形式被遗传下来，取决于自然选择。

39 例如：HLA-B53在抗疟疾流行中的作用 白种人和黄种人频率低不到1％，中非人高达28-40％，当地疟疾患者中B53的频率明显降低（17％）——B53具有保护作用。 白种人和黄种人群中，没有持续的疟疾流行，B53基因不显示“优越性”，没有保留下来。在中非的疟疾流行区，B53的保护作用引起阳性自然选择效应，构成选择压力，使得B53基因频率上升。

40 MHC The significance of MHC polymorphism:
Almost all of the polymorphism among MHC alleles involves amino acid residues located in and around the peptide-binding groove. As a result, each allelic form has its own unique peptide-binding properties. Affect the ability to make immune responses (e.g. resistance or susceptibility to infectious diseases) ＊等位基因及其产物结构上的差异，主要表现在构成抗原结合槽的氨基酸残基在组成和序列上的不同。 Ⅰ类分子的α1和α2，Ⅱ类分子的 α1和β1 ＊HLA分型：采用PCR技术针对性地扩增相应的基因片段之后，通过测序或用显示等位基因特异性的探针与之杂交，确定不同个体的等位基因特异性。 RFLP, PCR/SSO, PCR/SSP… ＊意义：寻找合适的器官移植供受体、分析疾病易感基因和法医学上的亲子鉴定。 不同的MHC 等位基因产物可以提呈结构不同抗原肽， 诱发出特异性和强度不同的免疫应答。

41 Interactions of MHC molecules with antigenic peptides
1. Molecular basis (1) Antigen-binding cleft class I Molecules: 1/2 closed at both ends 8~10 amino acids class II Molecules: 1/1 open at both ends 13~17 amino acids

42 Cleft geometry b2-M a-chain Peptide a-chain b-chain Peptide
MHC class I accommodate peptides of 8-10 amino acids MHC class II accommodate peptides of amino acids

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44 HLA-Ⅰ,Ⅱ类分子抗原肽复合物的三维图

45 (2) Anchor site and anchor residue
MHC (2) Anchor site and anchor residue anchor site anchor residue consensus motif ＊锚定位（anchor site）： 抗原肽中与MHC分子凹槽结合的特定部位，称为锚定位，所在位置的氨基酸残基称为锚定残基(anchor residue)。 ＊与同一类MHC分子结合的抗原肽，其锚定位和锚定残基往往相同和相似。 ＊ HLA-A*0201 结合的9肽： x-L/M-x-x-x-x-x-x-L/V （亮氨酸/甲硫氨酸） （亮氨酸/颉氨酸）

46 2. Characteristics of peptide-MHC binding
(1) Specificity: special anchor residue The important point is that peptide binding by a given MHC protein. (2) Flexibility: a series of antigenic peptides with consensus motif can be presented by a given MHC molecule. is somewhat selective but mush less specific than antigen binding by a TCR or an Ig. ＊MHC借助共同基序选择性结合抗原肽——一定的专一性Specificity 不同的MHC分子可选择性结合不同锚定位和锚定残基的肽段，故不同MHC等位基因产物可能提呈同一抗原的不同部位，导致不同个体对同一抗原的免疫应答在质与量上的差异 。 ＊包容性Flexibility ： ①共同基序中以x表示的氨基酸，顺序和结构可变； ②同一MHC分子锚定残基往往不止一种氨基酸，可以结合多种抗原肽。 ③不同MHC分子接纳的抗原肽，也可以拥有相同的共同基序：如一个MHC家族的不同成员可共同识别拥有相同或相似锚定残基的抗原肽。

47 Consensus binding motif
HLA molecules bind to different peptides with the same consensus binding motif HLA molecules Consensus binding motif Class I A*0201 B*2705 Class II DRB1*0405 X I F Y V L M R E N S T Q D 47

48 Biological function of MHC
Participate in the adaptive immune response serving as antigen presenting molecules T cells recognize both the antigenic peptide and MHC molecules by TCR (double recognition)

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51 T细胞以其TCR实现对抗原肽和MHC分子的双重识别：
＊ MHC 限制性：TCR在特异性识别APC所提呈的抗原多肽的过程中，必须同时识别与抗原多肽形成复合物的MHC分子。 ＊ CD4 Th细胞识别MHCⅡ类分子提呈的外源性抗原肽 CD8 CTL识别MHCⅠ类分子提呈的内源性抗原肽

52 MHCI present endogenous antigen

53 MHCII present enxogenous antigen
CLIP:Class II-associated invariant chain peptide

54 MHC molecules can present both autoantigens and allogenic MHC molecules
MHC molecules participate in selection and differentiation of T cells in the thymus.

55 4) MHC is the crucial determinant of disease susceptibility in different individuals；
5) MHC contributes to the genetic heterogeneity of the population

56 2. Participate in the innate immunity serving as regulatory molecules
Classical MHC class III genes encode complement, hereby participating in complement reaction and the pathogenesis of some immune diseases. Non-classical HLA class I molecules (HLA-E, G) regulate the activity of NK cells. Inflammation related genes initiate and control inflammation. They also play a role in stress. (such as HSP).

57 HLA/MHC and clinical medicine
1. HLA and transplantation HLA typing; cross-match 2. Abnormal expression of HLA Tumor: class I molecule↓ Autoimmune diseases: class II molecule↑ 3. HLA and disease susceptibility Ankylosing apondylitis: B27 58%-97% 4. HLA and medical jurisprudence B27阳性个体较阴性患AS 要大55倍-376种。

58 一、 HLA与器官移植 ＊ HLA等位基因的匹配程度直接影响器官移植的成败。
HLA-DR对移植排斥最为重要，其次是HLA-B和HLA-A。

59 二、HLA分子的异常表达和临床疾病 ＊恶变细胞表达I类分子下调或缺如，造成免疫逃逸；
＊自身免疫性疾病中，原先不表达II类分子的组织细胞诱导表达II类分子，导致免疫应答的异常激活和病理作用。 如胰岛素依赖性糖尿病中的胰岛β细胞、乳糜泻中的肠道细胞、萎缩性胃炎中的胃壁细胞等。

60 三、HLA与疾病的关联 1、HLA是机体对疾病易感的主要免疫遗传成分
＊如HLA-B27与强直性脊柱炎呈阳性关联，高达58－97％，而健康人群仅为1－8％。相对风险程度（RR）为55～376。

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62 HLA与输血反应 抗HLA 五. HLA与亲子鉴定和法医学 利用HLA系统的多基因性和多态性进行亲子鉴定和法医学鉴定。

63 Thanks for your attention!
MHC more…? Thanks for your attention!

64 思考题(MHC)： 问答题： MHC分子的生物学功能。 2. HLA 1 类和II 类抗原的结构，组织分布和功能特点