北大醫(yī)學(xué)研究生課程-分子免疫學(xué)-MHC課件

主要組織相容性復(fù)合體MHC〔Majorhistocompatibilitycomplex〕一.概念

組織相容：不同個(gè)體間的組織的相容性

MHC是受遺傳控制的，代表個(gè)體特異性的主要組織抗原系統(tǒng)，參與器官移植排斥，免疫應(yīng)答調(diào)控。除無(wú)頜類以外，所有脊椎動(dòng)物都擁有MHC人的MHC通常稱為HLA〔humanleukocyteantigen〕

MHC的發(fā)現(xiàn)20世紀(jì)40－50年代的研究確定，小鼠近交系之間皮膚移植物的排斥主要由定位在17號(hào)染色體上的H-2基因決定建立兩個(gè)遺傳背景不同的小鼠近交系〔如A、B兩個(gè)品系〕A與B雜交后代與親本回交建立小鼠同類系〔congenicmice，即除特定基因外遺傳背景高度一致的近交系小鼠品系〕，通過(guò)后代小鼠能否接受某一親本的皮膚移植物來(lái)確定組織相容性基因〔histocompatibilitygenes〕的染色體位置發(fā)現(xiàn)位于17號(hào)染色體的H-2(histocompatibility-2)基因是主要的控制移植排斥的基因H-2基因特點(diǎn)：在移植排斥中起主要作用；本身含多個(gè)功能相近的基因座位，形成一復(fù)合體－－引入“主要組織相容性復(fù)合體〞的概念CONGENICMOUSESTRAINSStrainAStrainA.BSelectedLocusIntra-H2RecombinantCongenicMouseStrainsStrainAStrainA.BStrainA.B(R1)StrainA.B(R2)K I S DStrainBH2MHC是決定同種移植排斥的主要抗原二.MHC基因及分子人MHCHLA〔Humanleukocyteantigen〕位于6號(hào)染色體短臂，共3400kb通過(guò)大規(guī)?；驕y(cè)序，99年10月28日在Nature雜志報(bào)道了HLA全基因序列已發(fā)現(xiàn)在此區(qū)域有約224個(gè)基因，多數(shù)基因尚不知功能2004年增加延伸的〔extended〕MHCI類和II類基因區(qū)，即xMHC區(qū)，約7.6Mb小鼠MHCH2，位于17號(hào)染色體狗MHCDLA，兔MHCRLA人HLA復(fù)合體的結(jié)構(gòu)ClassIIClassIIIClassIDPDQDRC4BC4AB1C2HSPTNFBCEAGFRINGDPDMLMP2LMP7DQDRB2A2B1A1ABTAP1TAP2B2A2B3B1A1B*AClassIIClassIIIClassI第六對(duì)染色體HumanxMHCGeneMap傳統(tǒng)上分為MHCI，II，III類基因；近年來(lái)傾向于分為以下兩類：經(jīng)典的MHCI，II類：基因產(chǎn)物的主要生理功能是呈遞抗原，多態(tài)性豐富；即通常所說(shuō)的“MHC基因〞免疫功能相關(guān)基因：傳統(tǒng)的MHCIII類基因，非經(jīng)典MHCI，II基因。xMHC基因區(qū)主要兩大基因簇：組蛋白基因簇和tRNA基因簇分類：(一)經(jīng)典MHCI類和II類基因小鼠H-2：定位于17號(hào)染色體；I類基因：K、D、L；II類基因：Ab、Aa、Eb、Ea。人HLA基因：定位于6號(hào)染色體；I類基因：B、C、A；II類基因：DP、DQ、DR亞區(qū)，每個(gè)亞區(qū)由兩個(gè)或兩個(gè)以上基因座組成，分別編碼分子量相近的α鏈和β鏈(二)HLA分子1、HLAI類分子：鏈和2微球蛋白〔2-microglobin〕組成的異源二聚體；鏈胞外有3個(gè)結(jié)構(gòu)域1，2，3，1，2組成抗原肽結(jié)合槽；所有有核細(xì)胞表達(dá)。2微球蛋白基因不在MHC基因區(qū)，人2微球蛋白基因的位于15號(hào)染色體；小鼠在2號(hào)染色體。MHC與抗原形成復(fù)合物2、HLAII類分子：分子量相似的鏈和鏈組成的異二聚體分子；1，1形成抗原肽結(jié)合槽；B,DC,M等表達(dá)。HLAII類分子的結(jié)構(gòu)MHCclassIMHCclassIICleftgeometryPeptideisheldinthecleftbynon-covalentforces〔三〕免疫功能相關(guān)基因〔一〕血清補(bǔ)體成份編碼基因：C4B，C4A，BF，C2。〔二〕抗原加工提呈相關(guān)基因：1、低分子量多肽基因：LMP2，LMP7；2、抗原加工相關(guān)轉(zhuǎn)運(yùn)體基因：TAP1，TAP2；3、TAP相關(guān)蛋白基因；4、HLA-DM，DO基因?！踩撤墙?jīng)典的I類基因：HLA-E(殺傷細(xì)胞外表抑制性受體CD94/NKG2A,CD94/NKG2C的配體)，HLA-G(殺傷細(xì)胞免疫球蛋白樣受體KIR的配體)。〔四〕炎癥相關(guān)基因：TNF家族，IkB基因，MICA/B，HSP70等。1

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三、MHC基因的多態(tài)性現(xiàn)象相關(guān)概念多態(tài)性：是指在一隨機(jī)分配的群體中，染色體同一基因座位〔或多態(tài)性標(biāo)記位點(diǎn)〕有兩種以上基因型。復(fù)等位基因：位于一對(duì)同源染色體上對(duì)應(yīng)位置的一對(duì)基因稱為等位基因。在群體中占據(jù)某同源染色體同一座位的兩個(gè)以上的、決定同一性狀的基因經(jīng)典的MHCI類和MHCII類基因是基因組中多態(tài)性最豐富的基因

某些MHCIII類基因也具有高度多態(tài)性，如Bf基因已檢出20多種變異體MHC多態(tài)性能防止快速進(jìn)化的病原微生物針對(duì)宿主的攻擊，保護(hù)生物群體的生存。SomeMHCGenesareHighlyPolymorphic#AllelesClassIClassIIHLA的復(fù)等位基因的命名NomenclatureIndicatesHLAtheHLAregionandprefixforanHLAgeneHLA-DRB1aparticularHLAlocusi.e.DRB1HLA-DRB1*13agroupofalleleswhichencodetheDR13antigenHLA-DRB1*13:01aspecificHLAalleleHLA-DRB1*13:01Nanullallele,anallelewhichisnotexpressed

HLA-DRB1*13:01:02anallelewhichdiffersbyasynonymousmutationHLA-DRB1*13:01:01:02anallelewhichcontainsamutationoutsidethecodingregionHLA的復(fù)等位基因的命名HLA-A*24:09NANullallele,anallelewhichisnotexpressed

HLA-A*30:14LAnalleleencodingaproteinwithsignificantlyreducedor'Low'cellsurfaceexpressionHLA-A*24:02:01:02LAnalleleencodingaproteinwithsignificantlyreducedor'Low'cellsurfaceexpression,wherethemutationisfoundoutsidethecodingregionHLA-B*44:02:01:02SAnalleleencodingaproteinwhichisexpressedasa'Secreted'moleculeonlyHLA-A*32:11QAnallelewhichhasamutationthathaspreviouslybeenshowntohaveasignificanteffectoncellsurfaceexpression,butwherethishasnotbeenconfirmedanditsexpressionremains'Questionable'HLA的復(fù)等位基因的命名〔續(xù)〕L：anallelewhichhasbeenshowntohave'Low'cellsurfaceexpressionwhencomparedtonormallevels.S：anallelespecifyingaproteinwhichisexpressedasasoluble'Secreted'moleculebutisnotpresentonthecellsurface.C：analleleproductwhichispresentinthe'Cytoplasm'butnotonthecellsurface.A：'Aberrant'expressionwherethereissomedoubtastowhetheraproteinisexpressed.Q：analleleis'Questionable'giventhatthemutationseenintheallelehaspreviouslybeenshowntoeffectnormalexpressionlevels#PROTEINSHLA基因的多態(tài)性現(xiàn)象－－與普通多態(tài)性基因的差異典型MHC基因的多態(tài)性較普通的多態(tài)性基因復(fù)雜得多〔如與ABO血型抗原基因比較〕不同復(fù)等位基因間差異明顯多態(tài)性變異較為集中于HLA分子與抗原肽結(jié)合部位的結(jié)構(gòu)域1210864220406080100120140160180200220a1a2CP,TM,CHLA－DRβ分子的多態(tài)性四、MHC基因復(fù)合體遺傳特征單元型〔haplotypes〕遺傳方式單元型：同一條染色體上緊密相連基因的組合HLA單元型：同一條染色體上不同HLA基因的組合。HLA基因在體細(xì)胞兩條染色體上的組合稱為基因型。某一個(gè)體HLA抗原特異性型別稱為表型。共顯性：一對(duì)等位基因的兩個(gè)成員在雜合體中都表達(dá)的遺傳現(xiàn)象。連鎖不平衡子女與父母有一半HLA相同子妹間1/4機(jī)率完全相同；1/2機(jī)率一半HLA相同162352401016abcdacadbcbd162401610162352402351016

MHC的共顯性表達(dá)MouseMHC連鎖不平衡連鎖：處于同一條染色體上的基因遺傳時(shí)較多地聯(lián)系在一起的現(xiàn)象基因頻率：是指群體中攜帶某一等位基因的個(gè)體數(shù)目與攜帶該基因座位各等位基因個(gè)體數(shù)目總和的比例。假設(shè)兩個(gè)基因座的兩個(gè)等位基因，其頻率分別是p1和p2，假設(shè)它們之間的重組是隨機(jī)的，其聯(lián)合的頻率，即單元型頻率h是p1Xp2，這樣的結(jié)果即為連鎖平衡。如果h比預(yù)期的隨機(jī)重組值高或者低，說(shuō)明兩個(gè)基因座存在連鎖不平衡HLA連鎖不平衡舉例單元型頻率（％）ABD觀察值期望值A(chǔ)1B89.82.1A3B75.42.1B8Dw38.61.4B7Dw23.91.8HLA連鎖不平衡的可能起因緊密連鎖基因座的某些等位基因的組合使攜帶者具有選擇優(yōu)勢(shì)，因而可以長(zhǎng)期存在據(jù)推測(cè)傳染病是維持其多態(tài)性和連鎖不平衡的最重要選擇力量

五.MHC結(jié)合的分子MHCI類抗原結(jié)合抗原多肽〔8-10個(gè)氨基酸〕、TCR、CD8、殺傷細(xì)胞抑制性受體MHCII類抗原結(jié)合抗原多肽〔13-18個(gè)氨基酸〕、TCR、CD4抗原肽往往帶有兩個(gè)或兩個(gè)以上和MHC分子凹槽相結(jié)合的特定部位〔錨定位〕。該位置上的氨基酸殘基被稱為錨定殘基。AllelicVariationinMHCProteinsSurroundsPeptideBindingCleftJanewayetal.,Immunobiology,2001六、MHC分子表達(dá)的調(diào)節(jié)I類分子組成型表達(dá)于所有有核細(xì)胞外表，II類分子正常情況下只存在于B細(xì)胞、巨噬細(xì)胞、樹突狀細(xì)胞、內(nèi)皮細(xì)胞等少數(shù)細(xì)胞類型轉(zhuǎn)錄水平的調(diào)節(jié)MHC分子的表觀遺傳學(xué)調(diào)控：MHC基因的甲基化狀態(tài)在不同的組織中有所差異轉(zhuǎn)錄速度是MHC分子在細(xì)胞外表表達(dá)的重要決定因素各種MHC基因和分子的轉(zhuǎn)錄和表達(dá)同等地受到調(diào)節(jié)：如不位于MHC區(qū)域內(nèi)的β2m和Ii分別與I類的α鏈和II類的α、β鏈協(xié)同地被調(diào)節(jié)細(xì)胞因子可調(diào)節(jié)I類和II類基因在多種細(xì)胞內(nèi)的根本轉(zhuǎn)錄速度，這是T細(xì)胞應(yīng)答的重要放大機(jī)制，如IFN-γ可提高M(jìn)HC分子的表達(dá)CIITA缺陷－裸淋巴細(xì)胞綜合征淋巴細(xì)胞和胸腺細(xì)胞缺乏MHCII類分子表達(dá)，CD4T細(xì)胞很少能發(fā)育成熟，即使有少量發(fā)育成熟，也得不到抗原的有效刺激患者出現(xiàn)SCID表型(IFNstimulatedresponseelement〕〔IFN-γactivationsites〕ISGF-3:IFNstimulatedgenefactor-3細(xì)胞因子可促進(jìn)MHC基因在多種細(xì)胞表達(dá)轉(zhuǎn)錄后的調(diào)節(jié)：泛素介導(dǎo)的MHC分子降解IdentifiedE3sforMHCmolecules.KSHVMIR1andMIR2caninhibitsurfaceexpressionofMHCclassI(MHCI)throughubiquitinationofthecytoplasmictailoftheMHCIheavychain,thuspresumablyinhibitingrecognitionoftheinfectedcellbyviral-specificcytotoxicTcells(CTL).ThismechanismisproposedtobeoneofstrategiesusedbyKSHVforimmuneevasion.ThecellularMARCHs,c-MIR/MARCH-VIIIandMARCH-I,candownregulatethesurfaceexpressionofMHCclassII(MHCII)throughsimilarmechanisms.BothE3subiquitinatethecytoplasmictailoftheMHCIIbchain.Forcedexpressionofc-MIR/MARCH-VIIIcaninhibitTcell-dependentimmunity.Ub,ubiquitin;RINGv,RINGvariantdomain.CurrentOpinioninImmunology2021,21:78–83PossiblecontributionofMARCH-Itoimmuneresponses.Inthesteadystate,MARCH-I(shownas‘E3’)isconstitutivelyexpressedinAPCsandregulatestheexpressionofMHCIIthroughubiquitination-mediatedlysosomaldegradation(leftpanel).OnceAPCsareactivatedbyinfection,MARCH-Iexpressionoritsenzymaticactivityisdownregulated,andpathogen-derivedpeptidesarepresentedbyMHCIIstabilizedowingtolossofubiquitination.CurrentOpinioninImmunology2021,21:78–83DifferentialdistributionofMHCmoleculesCellactivationaffectsthelevelofMHCexpressionThepatternofexpressionreflectsthefunctionofMHCmolecules:ClassIisinvolvedinanti-viralimmuneresponsesClassIIinvolvedinactivationofothercellsoftheimmunesystemTissue MHCclassI MHCclassIITcells +++ +/- Bcells +++ +++Macrophages +++ ++OtherAPC +++ +++Epithelialcellsofthymus + +++Neutrophils +++ -Hepatocytes + -Kidney + -Brain + -Erythrocytes - -七.MHC功能介導(dǎo)T細(xì)胞的抗原識(shí)別T細(xì)胞在胸腺的分化調(diào)控NK細(xì)胞功能免疫應(yīng)答的遺傳控制：不同個(gè)體表現(xiàn)出差異性移植排斥與某些疾病具有關(guān)聯(lián)關(guān)系MHCI類分子的非免疫功能MHCII類分子的非經(jīng)典生物學(xué)功能介導(dǎo)T細(xì)胞的抗原識(shí)別MHCI類抗原介導(dǎo)內(nèi)源性抗原的呈遞MHCII類抗原介導(dǎo)外源性抗原的呈遞交叉呈遞：可引起交叉啟動(dòng)或交叉耐受，對(duì)于某些幼稚CD8+T細(xì)胞的活化、及T細(xì)胞發(fā)育的中樞耐受有重要作用MHCI類抗原介導(dǎo)外源性抗原的呈遞MHCII類抗原介導(dǎo)內(nèi)源性抗原的呈遞MHC限制〔MHCrestriction〕Zinkernagel&Doherty'sexperment

蛋白酶體對(duì)內(nèi)源性抗原的水解。

通過(guò)TAP復(fù)合物轉(zhuǎn)運(yùn)至內(nèi)質(zhì)網(wǎng)。

與MHCI類分子裝配成復(fù)合物。

轉(zhuǎn)運(yùn)至高爾基體。

轉(zhuǎn)運(yùn)至細(xì)胞膜。NascentclassIMHCheavychainsand

2-microglobulinareassembledwithassistancefromnumerouschaperones(a).TheMHCheterodimeristhenrecruitedintotheTAP-containingPLCviainteractionswithtapasin(b).Peptidesgeneratedbyubiquitin–proteasome-mediatedproteinturnover(c),somesubsequentlytrimmedbycytosolicpeptidases,aretransportedbyTAPfromthecytosolintotheERlumen(d).ThesepeptidesareboundbyclassIMHC,someafterfurthertrimmingintheERbyERAP,causingthefullyfoldedclassIMHC-peptidecomplexestoshedER-associatedchaperones(e).Thepeptide-MHCmoleculesmigratetothecellsurface(fandg)wheretheyarescannedbyCD8+Tcells.

TheclassIassemblypathwayandformationofpeptideloadingcomplex(PLC)CurrentOpinioninImmunology2021,20:75–81AmodelofpeptidetransportbeginswithTAPinaninward/cytosol-facingconformationwiththeNBDs(nucleotide-bindingdomains)open.Apeptidebindsacytosol-facingcavityformedbytheTMDs(transmembranedomains),causingaconformationalchangethatistransmittedtotheNBDs.ThisconformationalchangepermitsATP-dependentNBDclosure,perhapsbyfacilitatingexchangeofADPonTAP2forATP.AstheNBDsclose,thepeptide-bindingcavityclosestothecytosolandopenstotheERlumen,creatingtheclosed,outward-facingconformationofTAP.Peptideaffinityismarkedlyreducedinthisconformation,andthepeptideishencereleasedintotheER.ATPhydrolysisintheconsensusATPasesiteissufficienttodestabilizetheclosedNBDs(hydrolysismayalsooccurinthedegenerateATPasesite,butthisisnotessential),whichre-opentogeneratetherestingconformation.CurrentOpinioninImmunology2021,21:84–91TAP1和TAP2〔抗原處理相關(guān)的轉(zhuǎn)運(yùn)蛋白，transporterassociatedwithantigenprocessing〕屬于膜轉(zhuǎn)運(yùn)蛋白質(zhì)，含有6-10個(gè)疏水性穿膜區(qū)，形成異源雙聚體，可將抗原多肽從胞漿轉(zhuǎn)運(yùn)至內(nèi)質(zhì)網(wǎng)局部腫瘤細(xì)胞TAP1表達(dá)下降，TAP1基因?qū)胫委熜〖?xì)胞肺癌TAP1和TAP2基因突變可引起MHCI類分子缺陷，患者?；己粑兰?xì)菌性感染而不是病毒感染LMP2和LMP7〔lowmolecularweightprotein〕蛋白酶體〔Proteasome〕的主要活性成分，可水解抗原分子，使其成為小分子多肽。鈣連接蛋白〔Calnexin〕分子伴侶，在內(nèi)質(zhì)網(wǎng)與MHCI類分子結(jié)合，形成穩(wěn)定復(fù)合物外源性抗原被內(nèi)吞，在內(nèi)體〔Endosome〕和溶酶體被變性、水解成多肽。MHCII類分子合成后與Ii分子形成3聚體，在內(nèi)質(zhì)體和溶酶體內(nèi)被蛋白酶水解形成MHCII和CLIP復(fù)合物。HLA-DM催化CLIP從MHC解離，促進(jìn)MHCII類分子與抗原多肽形成復(fù)合物。轉(zhuǎn)運(yùn)至細(xì)胞膜。MHCclassIIcompartment,MIIC〔MHCII類小室〕：一種富含MHCII類分子的溶酶體樣細(xì)胞器SchematicrepresentationofMIICs.InprofessionalAPCs,bothmultivesicular(MVB)andmultilamellar(MLB)MIICshavebeendescribed.Theopen/emptyconformationofHLA-DR(red)hasonlybeenobservedintheMLBtype.HLA-DM(green)isexpressedinbothcompartments,albeitparticularlyabundantinMLB.ThecarboxyandaminoterminalsofinvariantchainsarestillevidentinMVBswhereasaremostlyprocessedinMLBs.Electrondensebodies(EDBs)arelysosomal-likeMIICs,andhavebeenobservedinhumanmonocytesandinGM-CSFdifferentiatedmonocytes.CurrentOpinioninImmunology2006,18:64–69Ii〔Invariantchain〕：非多態(tài)性的分子伴侶〔Chaperone〕，與MHCII類抗原形成復(fù)合物，參與MHCII類抗原的裝配和轉(zhuǎn)運(yùn)。防止II類分子復(fù)合物到達(dá)內(nèi)體前，肽與肽結(jié)合槽結(jié)合引導(dǎo)II類分子復(fù)合物進(jìn)入內(nèi)體抑制蛋白酶水解CLIP〔ClassIIassociatedIipeptide〕：Ii結(jié)合MHCII類抗原的活性片段。HLA-DM：低多態(tài)性的MHC樣蛋白質(zhì)，雙體結(jié)構(gòu)，能夠催化CLIP分子與MHCII類分子解離，有利于抗原多肽與MHCII類分子形成復(fù)合物。非典型MHCII類分子位于內(nèi)體/溶酶體HLA-DO：低多態(tài)性的MHC樣蛋白質(zhì)，雙體結(jié)構(gòu)，在B細(xì)胞中與HLA-DM形成復(fù)合物，參與催化CLIP分子與MHCII類分子解離PotentialmechanismsofcrosspresentationofMHCI.(a)Thevacuolarpathway.MHCclassImoleculessamplepeptidesthataregeneratedinphagosomesinaTAP-independentmanner.(b)Phagosome-to-cytosol-to-phagosomepathway.PhagosomesacquireMHCclassI,TAP,Sec61andotherERmoleculesthroughfusionwiththeER.Internalizedantigenisexported(possiblybySec61)tothecytosol,hydrolyzedbyproteasomesandtheresultingpeptidesarethenre-importedintophagosomesbyTAP,wheretheybindMHCclassImolecules.(c)Phagosome-to-cytosolpathway.Antigeninternalizedintophagosomesisexportedtothecytosol,hydrolyzedbyproteasomesandtheresultingpeptidesarethentransportedtoMHCclassImoleculesintheERbyTAP.(d)GAPjunctionpathway.APCsacquirepeptidesfromothercellsthroughGAPjunctions.(e)Endosome-to-ERpathway.AntigeninendosomesistransportedintotheERandthendegradedinthecytosolbytheERassociateddegradationpathway(ERAD).TheresultingpeptidesaretransportedtoclassImoleculesintheERbyTAP.CurrentOpinioninImmunology2006,18:85–91ArmedeffectorCD8+TcellsinstructedbyDCsthroughcross-primingkillviralinfectedcellsintheperiphery.CurrentOpinioninImmunology2021,22:94–108MHCII類分子處理及呈遞抗原的可能途徑。(a)經(jīng)典的內(nèi)吞途徑(b)通過(guò)微自噬處理胞漿可溶性組分(c)通過(guò)大自噬處理胞質(zhì)組分(d)通過(guò)分子伴侶介導(dǎo)的自噬處理胞內(nèi)組分AutophagyassistsantigenprocessingonMHCclassIandclassIImolecules.(a)MacroautophagydeliverscytosolicantigenstoMHCclassIIloadingcompartments(MIIC)forlysosomaldegradationandpresentationtoCD4+Tcells.(b)Chaperone-mediatedautophagymightdelivercytosolicantigensdirectlyintoMIICsforloadingandpresentationonMHCclassIImolecules.(c)Macroautophagyassistsendosomefusionwithlysosomes,possiblyviarecruitingautophagosomestoendosomes.Thisdeliversendosomalcargomoreefficientlyforlysosomaldegradation,possiblyenhancingMHCclassIIpresentation.(d)Theremightbealsoapathway,bywhichantigencanleaveautophagosomesforproteasomaldegradationinthecytosol,followedbyloadingandpresentationonMHCclassImolecules.(e)MacroautophagyseemsrequiredintheantigendonorcellforefficientcrosspresentationonMHCclassImolecules,possiblybyassistingexosomegenerationafterautophagicdeliveryofantigenstomultivesicularbodies(MVB)CurrentOpinioninImmunology2021,22:89–93.介導(dǎo)T細(xì)胞在胸腺的分化陽(yáng)性選擇胸腺深皮質(zhì)區(qū)雙陽(yáng)性細(xì)胞胸腺皮質(zhì)上皮細(xì)胞與上皮細(xì)胞外表MHC-肽有效結(jié)合的雙陽(yáng)性細(xì)胞繼續(xù)發(fā)育為單陽(yáng)性細(xì)胞：CD4+或CD8+未與上皮細(xì)胞外表MHC-肽有效結(jié)合的雙陽(yáng)性細(xì)胞發(fā)生程序性細(xì)胞死亡〔大局部〕陽(yáng)