细胞与分子免疫学课程课件示范

细胞与分子免疫学课程课件细胞与分子免疫学课程课件细细胞与分子免疫学胞与分子免疫学课课程程课课件件1（优选）细胞与分子免疫学课程课件（优选优选）细细胞与分子免疫学胞与分子免疫学课课程程课课件件23Chapter7LymphocyteMaturationandExpressionofAntigenReceptorGenes3Chapter734nGeneralFeaturesofLymphocyteMaturation ThematurationofBandTlymphocytesconsistsof:1.Lineagecommitmentandproliferation2.Expressionofantigenreceptorgenes3.Selectionofthematurerepertories4GeneralFeaturesofLymphocyt45pEarlymaturation:1.Pluripotentstemcellsgiverisetoalllineagesofbloodcells1)Itisdifficulttopreciselydefinethemechanismsbywhichstemcellsbecometothelymphoidlineage.2)Bcell:boneborrowTcell:thymus3)Bythegenemutationsinexperimentalanimalsorhumanpatients.i.Transcriptionfactorsii.Growthfactorsiii.Growthfactorsreceptor5Earlymaturation:Pluripotent56Example1Bubbleboydisease1.MutatedinIL-7geneandIL-7receptorgenehaveprofounddeficienciesinmatureTandBcells.2.MutationsinachainoftheIL-2receptorg gchain,leadstoanimmunodeficiencydisease:X-linkedseverecombinedimmunodeficiencydisease,bubbleboy.6Example1Bubbleboydisease167pAntigenReceptorGeneRecombinationandExpression1.Theremaybe107ormoredifferentTandBlymphocyteclonesinoneindividual,eachcloneproduceonespecificantigenreceptor.2.Bysomaticrecombination,eachindividualdoesnotneedtohavesuchenormouslygenes.3.Duringthepre-Bcellorpre-Tcellstage,animmatureformofantigenreceptorisformedwhichtotransducesignalstoinducefurthermaturation4.Inmorematurelymphocytes,completeantigenreceptorexpressed,whichpromotecellmaturation.7AntigenReceptorGeneRecomb78pSelectionProcessThatShapetheBandTLymphocyteRepertoires1.Thepreservationofusefulspecificitiesiscalledpositiveselection:Tcellsinthymus.Bcellsmaturingarenotwellknown.2.Negativeselectionistheprocessthateliminatesdevelopinglymphocyteswithstrongbindingtoself-antigen.8SelectionProcessThatShape89pAcquisitionofFunctionalCompetence1.Bcellscansecreteantibodies.2.TcellscandifferentiateintodistinctsubsetsofTcells.3.Expressionofavarietyofcellsurfaceandintracellularmoleculesthatparticipateinlymphocyteactivationandeffectorfunctions.9AcquisitionofFunctionalCom910nFormationofFunctionalAntigenReceptorGenesinBandTLymphocytesElucidationofthemechanismsofantigenreceptorgeneexpressionisoneofthelandmarkachievementsofmordernimmunology1胚系理论胚系理论(GermlineTheory)在胚系基因组中包含了免疫基因库，可对外界的众多抗在胚系基因组中包含了免疫基因库，可对外界的众多抗原发生应答，并能遗传。原发生应答，并能遗传。Whataretheproblemswiththistheory?2体细胞突变理论（体细胞突变理论（SomaticMutationModel）基因组中的免疫球蛋白基因相对较少，抗体的多样性主基因组中的免疫球蛋白基因相对较少，抗体的多样性主要是由体细胞基因突变引起的。要是由体细胞基因突变引起的。Whataretheproblemswiththistheory?10FormationofFunctionalAnt1011胚系理论与体细胞突变理论所遇到的问题胚系理论与体细胞突变理论所遇到的问题1胚系理论胚系理论1）基因的种类少于抗体的多样性）基因的种类少于抗体的多样性Somanyspecificitiessofewgenes2体细胞突变理论（体细胞突变理论（SomaticMutationModel）1）部分编码）部分编码V区基因有众多的变化但部分编码区基因有众多的变化但部分编码C区的区的基因却相对稳定。基因却相对稳定。2）不同类的同型的免疫球蛋白具有相同的）不同类的同型的免疫球蛋白具有相同的V区。区。Samevariableregionsondifferentisotypes11胚系理胚系理论论与体与体细细胞突胞突变变理理论论所遇到的所遇到的问题问题1胚系理胚系理论论11123DreyerBennett假说：假说：免疫球蛋白单一的肽链是由两个分隔的基因编码：免疫球蛋白单一的肽链是由两个分隔的基因编码：每个免疫球蛋白类基因可能只有单个每个免疫球蛋白类基因可能只有单个C区基因，在胚区基因，在胚系基因组中与系基因组中与V区基因是分隔开的。区基因是分隔开的。在抗体产生细胞的发育过程中，其中一个独立的在抗体产生细胞的发育过程中，其中一个独立的V区区基因序列将与基因序列将与C区序列结合成为完整的区序列结合成为完整的VC基因，然基因，然后在细胞内表达。后在细胞内表达。两个基因两个基因一条多肽链：一条多肽链：此模型可以解释如下问题：此模型可以解释如下问题：1）一个基因的部分片断是多变的，而另一部分相对不）一个基因的部分片断是多变的，而另一部分相对不变。变。2）一个）一个V区可以与不同类的区可以与不同类的C区结合，产生出不同类区结合，产生出不同类型的抗体。型的抗体。123DreyerBennett假假说说：免疫球蛋白：免疫球蛋白单单12134 The genetic foundation of antibody diversityThe Nobel Prize in Physiology or Medicine 1987for his discovery of the genetic principle for generation of antibody diversity“in1976.Susumu Tonegawa Japan Massachusetts Institute of Technology(MIT)Cambridge,MA,USA b.1939134Thegeneticfoundationof1314ProofoftheDreyer-BennetthypothesisVVVVVVVVVVVVVA mechanism to rearrange V and C genes in the genome so that they can fuse to form a complete Immunoglobulin gene.CVCA single C region gene encoded in the germline and separate from the multiple V region genesFind a way to show the existence of multiple V genes and rearrangement to the C gene14ProofoftheDreyer-Bennet1415ProofoftheDreyer-BennetthypothesisVVVCVVVVVVSize fractionate by gel electrophoresisCVVVVVVVVVCVVVVVVVVVCut germline DNA with restriction enzymesVVVVVVVVVCArangeoffragmentsizesisgeneratedBlot with a V region probeBlot with a C region probeThefollowingexampledescribeseventsononlyONEofthechromosomes15ProofoftheDreyer-Bennet15C:two C genes in each of the human TCR b and TCR g chain,one C gene in each of TCR a,d chain.The thymus is the major site of maturation of T cells.Tolerance induced in immature lymphocytes by recognition of self antigen in the generative lymphoid organs is also called central tolerance.Vb-to-DJb rearrangements occur在抗体产生细胞的发育过程中，其中一个独立的V区基因序列将与C区序列结合成为完整的VC基因，然后在细胞内表达。The stimuli come from cells including:Maturation of T lymphocytes3)RAG proteins are first expressedSo many specificities so few genesmembrane-bound antigen receptor is not expressed;In three separate loci:在抗体产生细胞的发育过程中，其中一个独立的V区基因序列将与C区序列结合成为完整的VC基因，然后在细胞内表达。Mature B cellInfluence the specificities of the T cells.AT GTGACAC2 体细胞突变理论（Somatic Mutation Model）其中P碱基与N碱基的加入是导致抗体出现多样性的主要原因：RAG-1 and RAG-2 are first expressed.Organization of Ig Gene LociElucidation of the mechanisms of antigen receptor gene expression is one of the landmark achievements of mordern immunology16CVVVVVCVVVVVSize fractionate by gel electrophoresisVVVVCVBlot with a V region probeBlot with a C region probeCut mature B cell DNA with restriction enzymesVVVBlot with a V region probeBlot with a C region probeCVVVVVVSize fractionate by gel electrophoresis-compare the pattern of bandswith germline DNAV and C probes detect the same fragmentSome V regions are missingThe C fragment has got largerVVVVCVEvidenceforgenerecombinationC:twoCgenesineachofthe1617OrganizationofIgandTCRGenesintheGermline1.OrganizationofIgGeneLoci1)ThreeseparatelociencodetheIgchains.chromosome14:Hchainlocuschromosome2:k kchainchromosome22:l l chain2)Multiplecopiesofatleastthreedifferenttypesofgenesegments:V:300base,separatebynoncodingDNA,atthe5endofeachVregionisanucleotidesequencewhichiscalledleaderpeptide.17OrganizationofIgandTCRG1718C,eachIglocushasadistinctarrangementandnumberofCgene.Inhuman:Igk k lightchain:asingleCgeneIg l l lightchain:fourfunctionalCgenesIgHheavychain:ninedifferentIgisotypesandsubtypes.Jsegments,30-50basepairslong.Dsegments,inthehumanIgheavychainlocus.1.OrganizationofIgGeneLoci18C,eachIglocushasadist18192.OrganizationofTCRGeneLociInthreeseparateloci:TCRa,da,dchain:chromosome14TCRb b chain:chromosome7TCRg gchain:chromosome7V:likeIgVgeneC:twoCgenesineachofthehumanTCRb b andTCRg g chain,oneCgeneineachofTCRa,da,dchain.J:inallTCRloci,betweenVandCgenes.D:inTCR b bchainandd d chain.192.OrganizationofTCRGene1920AntigenReceptorGeneRecombinationDiversityofantigenreceptorgenes20AntigenReceptorGeneRecomb2021MechanismsofSomaticRecombinationofAnitgenReceptorGenes1.有限的有限的DNA是怎样产生无限的专一是怎样产生无限的专一性的性的?2.V区是怎样找到区是怎样找到J区的？为什么区的？为什么V区不与区不与V区相连？区相连？3.DNA是怎样断裂的？是怎样断裂的？4.DNA是怎样重新组合的？是怎样重新组合的？21MechanismsofSomaticRecomb2122RSS(重排信号序列重排信号序列)，recombinase(重组酶重组酶)，12-23 rule(一个一个规则规则)。1、Recombination Signal Sequences(RSS),重排信号序列：重排信号序列：v基因片断两端存在两个特基因片断两端存在两个特异的保守序列：异的保守序列：7聚体与聚体与9聚体。聚体。v 7聚体与聚体与9聚体之间间隔聚体之间间隔是是23bp或者是或者是12bp。vRSS:7聚体聚体-间隔间隔-九聚九聚体体(The heptamer The heptamer spacer spacer nonamer)nonamer)MechanismsofSomaticRecombinationofAnitgenReceptorGenes22RSS(重排信号序列重排信号序列)，recombinase(重重组组2223 RSS（重排信号序列（重排信号序列）23RSS（重排信号序列）（重排信号序列）23242、重组酶：、重组酶：一组参与一组参与V、（、（D）、）、J基因片断重组的酶，包括以下几种：基因片断重组的酶，包括以下几种：RAG-1与与RAG-2(recombination-activatinggenes):一种内切酶，只一种内切酶，只表达在表达在T和和B淋巴细胞淋巴细胞不成熟阶段。不成熟阶段。末端脱氧核苷酸转移酶末端脱氧核苷酸转移酶(terminaldeoxynucleotidyltransferase,TdT)：表达于：表达于T、B细胞前体，此酶可将数个核苷酸通过不细胞前体，此酶可将数个核苷酸通过不需要模板的方式加到需要模板的方式加到DNA的断段。的断段。其他其他切开发夹结构的内切酶，参与修复切开发夹结构的内切酶，参与修复DNA双链断段的双链断段的DNA外切酶、外切酶、DNA合成酶等，如合成酶等，如DNA连接酶连接酶IV，DNA依赖的蛋白依赖的蛋白激酶。激酶。242、重、重组组酶酶：2425 重组酶所催化的重排步骤1.RAG蛋白复合物结合蛋白复合物结合到到RSS。2.蛋白复合物拉近将要蛋白复合物拉近将要相连的相连的DNA片断。片断。3.互补链切断，发夹结互补链切断，发夹结构形成。构形成。4.其他其他DNA修饰蛋白结修饰蛋白结合到发夹结构剪切合到发夹结构剪切RSS末端。末端。5.发夹结构被随机剪切，发夹结构被随机剪切，碱基或者增加或者减碱基或者增加或者减少。少。6.DNA连接酶连接产生连接酶连接产生编码连接点和信号连编码连接点和信号连接。接。25重重组组酶酶所催化的重排步所催化的重排步骤骤RAG蛋白复合物蛋白复合物结结合到合到RSS。252623-mer=two turns12-mer=one turn3、Molecularexplanationofthe12-23ruleIntervening DNAof any length23V9712D J792623-mer=twoturns12-mer=o262723-mer12-merLoop of interveningDNA is excisedTheshapegeneratedbytheRSSsactsasatargetforrecombinases7997V1V2V3V4V8V7V6V5V9D JV1D JV2V3V4V8V7V6V5V9Anappropriateshapecannotbeformediftwo23-merflankedelementsattemptedtojoin(i.e.the12-23rule)3.Molecularexplanationofthe12-23rule2723-mer12-merLoopofinterven2728Thisrulecanexplainwhyinheavychain,theVcannotdirectlybindtoJ.28Thisrulecanexplainwhyin28AGCTGCAATATA7聚体与9聚体之间间隔是23bp或者是12bp。T cells in thymus.Ig l light chain:four functional C genesThe nicked strand flips outCytokines:thymic stromal cells including epithelial cells,Stimulate the proliferation of immature T cells,especially IL-7.The stimuli come from cells including:The nucleotides that flip out,become part of the complementary DNA strandThe pre-T cell receptor was formed.TA CACTGTG-compare the pattern of bandsRecombination activating gene products,(RAG1&RAG 2)and high mobility group proteins bind to the RSSIn terms of G to C and T to A pairing,the new nucleotides are palindromic.Thymocytes can not recognize self MHC-restricted will die by apoptosis.Maturation of T lymphocytes蛋白复合物拉近将要相连的DNA片断。5)Ig a and Ig b of BCR complex starts to express.一组参与V、（D）、J基因片断重组的酶，包括以下几种：Find a way to show the existence of multiple V genes and rearrangement to the C geneGrowth factors receptorTCR a gene recombination commences.29V7239D7129JV723972397129D7129J72397129VDJRecombinationactivatinggeneproducts,(RAG1&RAG2)andhighmobilitygroupproteinsbindtotheRSSThetwoRAG1/RAG2complexesbindtoeachotherandbringtheVregionadjacenttotheDJregion互补链断裂，发夹结构形成互补链断裂，发夹结构形成4.StepsofIggenerecombinationAGCTGCAATATA29V7239D7129JV72392930VDJ72397129Anumberofotherproteins,(Ku70:Ku80,XRCC4andDNAdependentproteinkinases)bindtothehairpinsandtheheptamerends.VDJThehairpinsattheendoftheVandDregionsareopened,andexonucleasesandtransferasesremoveoraddrandomnucleotidestothegapbetweentheVandDregionVDJ7 2397129DNAligaseIVjoinstheendsoftheVandDregiontoformthecodingjointandthetwoheptamerstoformthesignaljoint.4.StepsofIggenerecombination30VDJ72397129Anumberofother3031V1V2V3V4V9D JLooping out works if all V genes are in the same transcriptional orientationV1V2V3V9D J缺失性重排缺失性重排D J7129V47239V17239D7129JHow does recombination occur when a V gene is in opposite orientation to the DJ region?V45.重排方式以重链重排为例非非缺失性重排缺失性重排LL31V1V2V3V4V9DJLoopingoutwork3132D J7129V47239V4andDJinoppositetranscriptionalorientationsD J7129V472391.D J7129V472393.D J7129V472392.D J7129V472394.Non-deletionalrecombination32DJ7129V47239V4andDJinopp3233D J7129V472391.D JV4712972393.V to DJ ligation-coding joint formationD J7129V472392.Heptamer ligation-signal joint formationD JV471297239Fully recombined VDJ regions in same transcriptional orientationNo DNA is deleted4.33DJ7129V472391.DJV4712972393.33347D129J6.GenerationofDiversityoftheBandTCellRepertoiresJunctionaldiversity:Pnucleotideadditions7V239D7129JV7239TC CACAGTGAG GTGTCACAT GTGACACTA CACTGTGThe recombinase complex makes single stranded nicks at random sites close to the ends of the V and D region DNA.7D129J7V239CACAGTGGTGTCACGTGACACCACTGTGTCAGATTADJVTCAGATTAUUThe 2nd strand is cleaved and hairpins form between the complementary bases at ends of the V and D region.347D129J6.GenerationofDivers3435V2V3V4V8V7V6V5V97239CACAGTGGTGTCAC7129GTGACACCACTGTGVTCAGUDJATTAUHeptamers are ligated by DNA ligase IVV and D regions juxtaposedVTCAGUD JATTAU35V2V3V4V8V7V6V5V97239CACAGTG73536VTCAGUD JATTAUEndonuclease cleaves single strand at random sites in V and D segmentVTCGAAGD JATTATAThe nucleotides that flip out,become part of the complementary DNA strand6.1GenerationofthepalindromicsequenceIn terms of G to C and T to A pairing,the new nucleotides are palindromic.The nucleotides GA and TA were not in the genomic sequence and introduce diversity of sequence at the V to D join.VTCAGUD JATTAURegions to be joined are juxtaposedThe nicked strand flips out 36VTCUDJATUEndonucleasecleave36376.2JunctionalDiversityNnucleotideadditionsVTCGAAGD JATTATATerminal deoxynucleotidyl transferase(TdT)adds nucleotides randomly to the P nucleotide ends of the single-stranded V and D segment DNACACTCCTTATTCTTGCAAVTCGAAGD JATTATACACACCTTATTCTTGCAAComplementary bases annealVD JDNA polymerases fill in the gaps with complementary nucleotides and DNA ligase IV joins the strandsTCGAAGATTATACACACCTTATTCTTGCAAD JTATAExonucleases nibble back free endsVTCGACACACCTTATTCTTGCAAVTCDTAGTTATATAGC376.2JunctionalDiversityN3738VDJTCGACGTTATATAGCTGCAATATAJunctionalDiversityNNNNNNNNNNNNNNNGermline-encoded nucleotidesPalindromic(P)nucleotides-not in the germlineNon-template(N)encoded nucleotides-not in the germlineCreates an essentially random sequence between the V region,D region and J region in heavy chains and the V region and J region in light chains.38VDJTCGACGTTATATAGCTGCAATATAJ3839JunctionalDiversity39JunctionalDiversity39Ig k light chain:a single C geneFor the nonproductive one,the second allelic chromosomes can recombine.Immature B cellThe coexpression of IgM and IgD make the B cell acquire the functional competence.Maturation of T lymphocytesMHC molecules in thymus are important.V and C probes detect the same fragmentThymus donorImmature B cell蛋白复合物拉近将要相连的DNA片断。Mature B cell1）部分编码V区基因有众多的变化但部分编码C区的基因却相对稳定。5)Ig a and Ig b of BCR complex starts to express.In terms of G to C and T to A pairing,the new nucleotides are palindromic.Maturation of T lymphocytesAT GTGACACRecombination activating gene products,(RAG1&RAG 2)and high mobility group proteins bind to the RSS3)RAG proteins are first expressed40MaturationofBLymphocytes1.Pro-Bcell2.Pre-Bcell3.ImmatureBcell4.MatureBcellIgklightchain:asingleCg4041MaturationofBLymphocytes41MaturationofBLymphocytes4142StagesofBLymphocyteMaturation:1.Pro-Bcell:1)notproduceIg2)Maker:CD19andCD103)RAGproteinsarefirstexpressed4)TdTenzymeisexpressedmostabundantly5)Iga aandIg b b of BCRcomplexstartstoexpress.6)FirstrecombinationofIggenesoccursinheavychains42StagesofBLymphocyteMatur4243RecombinationinPro-Bcell:43RecombinationinPro-Bcel43442.Pre-BcellAprimarytranscriptthatincludestherearrangedVDJcomplexandtheproximalCgenesisproduced;FunctionalmRNAforthem mheavychainisproduced;m m proteininpre-Bcellsaretranslated;membrane-boundantigenreceptorisnotexpressed;Pre-Bcellreceptorsareexpressedonthecellsurfaceatlowlevels.Onlyinhematopoietictissues;442.Pre-BcellAprimarytrans44454545468)Thepre-BCRregulatesfurthersomaticrecombinationofIggenesintwoways:8.1)Fortheproductiverearrangements:allelicexclusionexsits.Forthenonproductiveone,thesecondallelicchromosomescanrecombine.468)Thepre-BCRregulatesfur4647刘老师：刘老师：您好！上节课讲到内切酶在您好！上节课讲到内切酶在V和和D上随机切开增加了上随机切开增加了VD间连接间连接的多样性。那么这个区域将来编码成蛋白质即抗体后，并不位的多样性。那么这个区域将来编码成蛋白质即抗体后，并不位于于V片段的片段的CDR区，如何能够增加抗体的多态性？区，如何能够增加抗体的多态性？还有一个问题是还有一个问题是TdT随机增加几个碱基从而增加了基因的多态随机增加几个碱基从而增加了基因的多态性，那么在重排机制中如何保证随机增加碱基后使得重排的基性，那么在重排机制中如何保证随机增加碱基后使得重排的基因的碱基数依旧是因的碱基数依旧是3的倍数而不发生编码错误？如果编码的不是的倍数而不发生编码错误？如果编码的不是3的倍数，是否是在转录水平上随机添加碱基的倍数，是否是在转录水平上随机添加碱基U来使编码恢复正来使编码恢复正常。常。谢谢老师！来自崔雪晶谢谢老师！来自崔雪晶47刘老刘老师师：4748C,eachIglocushasadistinctarrangementandnumberofCgene.Inhuman:Igk k lightchain:asingleCgeneIg l l lightchain:fourfunctionalCgenesIgHheavychain:ninedifferentIgisotypesandsubtypes.Jsegments,30-50basepairslong.Dsegments,inthehumanIgheavychainlocus.1.OrganizationofIgGeneLoci48C,eachIglocushasadist48492.OrganizationofTCRGeneLociInthreeseparateloci:TCRa,da,dchain:chromosome14TCRb b chain:chromosome7TCRg gchain:chromosome7V:likeIgVgeneC:twoCgenesineachofthehumanTCRb b andTCRg g chain,oneCgeneineachofTCRa,da,dchain.J:inallTCRloci,betweenVandCgenes.D:inTCR b bchainandd d chain.492.OrganizationofTCRGene49508)Thepre-BCRregulatesfurthersomaticrecombinationofIggenesintwoways:8.1)Fortheproductiverearrangements:allelicexclusionexsits.Forthenonproductiveone,thesecondallelicchromosomescanrecombine.508)Thepre-BCRregulatesfur5051上堂课回顾：上堂课回顾：1Ig与与TCR基因在染色体基因座位上的排列特点基因在染色体基因座位上的排列特点2重排机制重排机制1）一个信号序列）一个信号序列2）一个原则）一个原则3）一组酶）一组酶其中其中P碱基与碱基与N碱基的加入是导致抗体出现多样性的主要原因：碱基的加入是导致抗体出现多样性的主要原因：VDJTCGACGTTATATAGCTGCAATATAVTCAGUD JATTAU51上堂上堂课课回回顾顾：VDJTCGACGTTATATAGCTGCA51524）缺失性重排）缺失性重排5）非缺失性重排）非缺失性重排3、B细胞的成熟：祖细胞的成熟：祖B细胞，前细胞，前B细胞，非成熟细胞，非成熟B细胞，成熟细胞，成熟B细胞细胞524）缺失性重排）缺失性重排3、B细细胞的成熟：祖胞的成熟：祖B细细胞，前胞，前B细细胞，非胞，非52534、B细胞表面受体的重排：细胞表面受体的重排：重链：等位基因排斥重链：等位基因排斥轻链：同种型的排斥轻链：同种型的排斥534、B细细胞表面受体的重排：胞表面受体的重排：5354Pro-BcellPre-Bcell54Pro-BcellPre-Bcell54558.2)thepre-BCRregulatessomaticrecombinationisbystimulatinglightchaingenerearrangement.3.ImmatureBcell1)1)k k chainandl l chaingenearerearranged.2)IgMisexpressed.3)InasimilarmannerasintheIgheavychainlocus.4)k kchainrearrangesafterheavychainrearrangementandbeforel lchain.5)Lightchainisotypeexclusion.6)TheassembledIgMmoleculesareexpressedonthecellsurfaceinassociationwithIga a andIgb.b.7)ImmatureBcellsdonotproliferateanddifferentiateinresponsetoantigens.558.2)thepre-BCRregulatess55565656574.MatureBcell1)Coexpressedm m andd dheavychainsinassociationwiththek k andl l light chaintoproduceIgMandIgD.2)ThecoexpressionofIgMandIgDmaketheBcellacquirethefunctionalcompetence.3)ItsuggeststhatIgDistheessentialactivatingreceptorofmatureBcells.4)Canresponsetoantigens.5)Withoutantigens,theywilldieinafewdaysorweeks.6)ThemajorityofBcellsareIgD+IgM+.574.MatureBcellCoexpressed5758585859SelectionoftheMatureBcellRepertoire1)TherepertoireofmatureBcellsispositivelyselectedfromthepoolofimmaturecellsbeforeleavingtheboneborrow.isdifferentfromtheTcellsselection,perhapsservetopreserveallthecellswiththecapacitytorecognizeantigens,regardlessofspecificity.59SelectionoftheMatureBce59602)Negativeselection:SelfantigensdeliverstrongsignalstoIgMexpressingimmatureBlymphocytesthathappentoexpressreceptorsspecificfortheseselfantigens.AntigenrecognitionleadstoapoptoticdeathofimmatureBcells.SomeimmatureBcellsthatrecognizeselfantigensmaybeinducedtochangetheirspecificitiesbyaprocesscalledreceptorediting.602)Negativeselection:6061B-1CellsBcellsdescribedto-date:B-2cellsAsecondpopulationofBcellsexists,calledB-1cellsAccountforapproximately5%totalBcellsinhumansFoundpredominantlyinperitonealandpleuralcavitiesRelationshiptoB-2cellsnotunderstoodUsealimitedsetofVgenesegmentsSynthesizelow-affinityIgMinresponsetomanybacteriaThoughttohaveanimportantroleasafirstlineofdefenseagainstmanypathogens;maybepartofinnateimmunity?ExpresstheCD5molecule.B-1cellsspontaneouslysecreteIgMantibodiesthatoftenreactwithmicrobialpolysaccharidesandlipids.61B-1CellsBcellsdescribedt6162B-1SubsetofBlymphocytes62B-1SubsetofBlymphocytes6263MaturationofTlymphocytes1.Pro-Tcell2.Pre-Tcell3.Doublepositive4.Singlepositive5.NavematureTcell63MaturationofTlymphocytesP63641.Pro-Tcell1)Recentarrivalsfromtheboneborrow.2)ContainTCRgenesintheirgermlineconfiguration,withoutexpressionofTCR,CD3orz z chainsorCD4orCD83)RAG-1andRAG-2arefirstexpressed.4)Db b-to-Jb b rearrangementsoccurfirst641.Pro-TcellRecentarrivals64656565662.Pre-Tcellstage:1)Vb b-to-DJb b rearrangementsoccur2)PrimaryRNAandmRNA3)Thepromoterinthe5flankingregionsofVb bgenesfunctiontogetherwithapowerfulenhancerthatislocated3oftheCb2b2 gene.4)Thepre-Tcellreceptorwasformed.5)Signalsfromthepre-TCRstimulateproliferationofthepre-Tcells,recombinationatthea achainlocus.6)Fromthedouble-negativetothedouble-positivestage.662.Pre-Tcellstage:Vb-to-DJ66676767683.Doublepositive1)ThymocytesexpressbothCD4andCD8molecules.2)TherearrangementoftheTCRa achaingenesandtheexpressionofTCRab ab heterodimersoccurinthedouble-positivepopulation.3)TCRa agenerecombinationcommences.4)Pre-TCRhasnoallelicexclusionof a achain.30.30%ofmatureperipheralTcellsdoexpresstwodifferentTCRs,withdifferenta a chainsbutthesameb b chains.683.DoublepositiveThymocytes68696969704.Singlepositive1)Afterselection,cellsmatureintoCD4+orCD8+Tcells.2)CD4+cellsacquiretheabilitytoproducecytokines3)CD8+cellsbecomecapableofproducingmoleculesthatkillothercells.704.SinglepositiveAftersele7071RoleofthethymusinTcellMaturation1)ThethymusisthemajorsiteofmaturationofTcells.2)Tlymphocytesoriginatefromprecursorsbutseedthethymus.Selectionp