中科院细胞与分子免疫学课程chapter8.ppt

中科院细胞与分子中科院细胞与分子免疫学课程免疫学课程chapter8chapter8uT淋巴细胞的成熟：淋巴细胞的成熟：祖祖T细胞，前细胞，前T细胞，双阳性阶段，单阳性阶段，成熟阶段细胞，双阳性阶段，单阳性阶段，成熟阶段两次选择：两次选择：1.阳性选择：阳性选择：2.阴性选择：阴性选择：Chapter 8 Activation of T lymphocytesHow to activate the T cell?1.In peripheral lymphoid organs,Nave T lymphocytes recognize antigens and are activated.2.In lymphoid organs or in nonlymphoid tissues,effector T cells recognize antigens and are activated.3.The activation of T cells requires a.antigen presented by APC b.costimulators c.cytokines produced by the APCs and by the T cells.4a.Nave T cells require activation by dendritic cells;4b.Effector T cells can respond to antigens presented by a wider variety of APC.What the activated T cells can do?1.Proliferation 2.Differentiation into Effector Cells CD4+T cell:Th1 and Th2Th1:Stimulate cytokine(IL-12 and IFN-g),g),secrete cytokines:IL-2,INF-g g and TNF-b.b.Th2:Stimulate cytokine:IL-4,secrete cytokines:IL-4,5,6,10,13.CD8+T cell differentiate into functional CTL.3.Differentiation into Memory Cells4.Decline of T Cell ResponsesRole of Costimulators in T Cell Activation1.Costimulators:CD28:B7-1 and B7-22.The expression of costimulators is regulated to make sure the correct time and place expressionThe expression of B7 costimulators is increased2a.by microbial products,2b.by cytokines of innate immunity 3.Mature dendritic cells express the highest levels of costimulators.4.Adjuvants are products of microbes that stimulate the expression of costimulators.5.Previously activated effector and memory T cells are less dependent on costimulation by the B7:CD28 pathway than are nave cells.Role of CD40 in T cell activation1.Activated T cells express CD40L2.APCs express CD403.CD40L binding to CD40 can deliver signals that enhance the expression of B7 costimulators on the APCs.4.Secretion of cytokines IL-12 is increased upon CD40L interaction with CD40.Signal Transduction by the TCR Complex1.What is the goal:activate the transcription of genes that are silent in nave cells,these proteins mediate the responses and functions of activated T cells.2.How is signal transduction triggered:by ligation of multiple antigen receptors and coreceptors.3.What happened after signal transduction in cell:clustering of membrane receptors,tyrosine phosphorylation of several protein,and recruitment and activation of adapter proteins.4.What the important biochemical pathways in the activation of T cells:1)Ras-MAP kinase pathway 2)the protein kinase C pathwayMajor steps in signaling by the TCREarly membrane events:1.Formation of the Immunological Synapse:1)Immunological synapse:the region of physical contact between the T cells and the APC2)T cell components participated in are:TCR complex,coreceptors(CD4 or CD8),CD28,the enzymes and adaptor proteins.3)The formation is triggered by antigen recognition4)Brings signaling molecules into proximity to one another The formation of synapse was demonstrated by confocal microscopy.2.Activation of Tyrosine Kinases1)Tyrosines residues in:CD3,z z chain.2)Tyrosine kinases:Lck,that is associated with the cytoplasmic tails of CD4 and CD8.3)Fyn,another tyrosine kinase in physical association with the CD3 molecules.4)ZAP-70,attached to the tyrosine phosphorylated ITAMs z z chain.ZAP-70 is only expressed in T and NK cells.2.Activation of Tyrosine KinasesProcedure:1)Lck is activated by autophosphorylation,then the active Lck phosphorylates the tyrosines in the ITAM of the CD3 and the z z chain2)ZAP-70 binding to two phosphorylated tyrosine residues of each ITAMs in the z z chain3)Lck phosphorylates the tyrosines of ZAP-70.4)ZAP-70 acquires its own tyrosine kinase activity.5)Multiple ZAP-70 could be recruited to the multiple phosphorylated ITAMs.3.Recruitment and Activation of Adapter Proteins1)Adapter proteins bring the signaling molecules into specific cellular compartments.2)Can bind other proteins.3)ZAP-70 phosphorylated tyrosines of LAT.4)Activated LAT binds phospholipase Cg 1,g 1,SLP-76,and Grb-2.5)Serves to bring a variety of downstream components of TCR signaling pathways close to their upstream activators.Ras-MAP Kinase Signaling Pathways in T lymphocytesProteins that were needed in the pathway:1.Ras:a member of a family of 21-kD guanine nucleotide-binding proteins,(small G protein)has a lot of activation responses in different cell types.The reason is that Ras can recruit or activate various cellular enzymes.2.MAP kinases:ERK,extracellular receptor-activated kinaseJNK,c-Jun N-terminal kinase also called stress-activated protein.P38Ras-MAP Kinase Signaling Pathways in T lymphocytes1.LAT can bind Grb-2,then the Grb-2 recruits the Ras GTP/GDP exchange factor-Sos(son of sevenless)2.Sos catalyzes GTP for GDP exchange on Ras.3.Ras.GTP activates mitogen activated protein(MAP)kinases-ERK4.The ERK phosphorylates a protein called ELK,and stimulates transcription of Fos,5.Two other MAP kinases:Rac.GTP activates JNK,JNK phosphorylates c-Jun,another component of transcription factor.p38,is too activated by Rac.GTP and in turn activates various transcription factor.Pathway:Calcium-and protein Kinase C-Mediated Signaling Pathways in T lymphocytes1.PLCg1g1 is recruited to phosphorylated LAT,PLCg1 g1 is a cytosolic enzyme specific for inositol（肌糖）（肌糖）phospholipids（磷脂质）（磷脂质）.2.PLCg1 g1 is phosphorylated by ZAP-70.3.Phosphorylated PLCg1g1catalyzes the hydrolysis of a plasma membrane phospholipid called PIP2（磷脂酰肌醇二磷酸）（磷脂酰肌醇二磷酸generating two products:IP3（三（三磷酸肌醇）磷酸肌醇）and DAG（二酰基甘油）（二酰基甘油）.Signal pathway of IP3:1)IP3 binds to the receptor of ER and stimulates release of membrane-sequestered calcium stores.2)Calcium ion concentration increased,and binding to a calcium-dependent regulatory protein called calmodulin（钙调（钙调蛋白蛋白）.3)Calcium-calmodulin complexes activated calcineurin（钙调磷酸（钙调磷酸酶）酶）that is important for transcription factor.Calcium-and protein Kinase C-Mediated Signaling Pathways in T lymphocytesCalcium-and protein Kinase C-Mediated Signaling Pathways in T lymphocytes1.DAG is hydrophobic,and remains in the membrane where it is formed.2.The elevated free cytosolic calcium and DAG activates membrane-associated PKC（蛋白激酶（蛋白激酶C）.3.PKC q q isoform localizes to the immunological synapse.4.PKC q q activates the nuclear translocation of the NF-k kB transcription factor.Signal pathway of DAG:Activation of Transcription Factors that Regulate T Cell Gene Expression1.The requirement for multiple transcription factors accounts for the need to activate multiple signal transduction pathways.2.For example IL-2:three factors(NFAT,AP-1,NF kB)kB)are needed,and all the sites must be occupied for maximal transcription of IL-2 gene.3.These three factors are critical for most T cell responses.Activation of Transcription Factors that Regulate T Cell Gene Expression1.NFAT:1)A transcription factor required for the expression of IL-2,IL-4 and other cytokines.2)Four types of NFAT,NFAT1 and 2 in T cells.3)In resting T cells,NFAT presents in an inactive,serine phosphorylated form in the cytoplasm.4)It is activated by the calcium-calmodulin-dependent phosphatase calcineurin.5)Calcineurin dephosphorylates cytoplasmic NFAT,uncovering a nuclear localization signal.Activation of Transcription Factors that Regulate T Cell Gene Expression2.AP-11)A transcription factor found in many cell types,and is specifically activated in T lymphocytes by TCR mediated signals.2)It is composed of Fos and Jun.3)From the Erk and PKC pathway,Fos gene was generated.4)JNK phosphorylates c-Jun,Fos and phosphorylated c-Jun consisted AP-1.Activation of Transcription Factors that Regulate T Cell Gene Expression3.NF kBkB1)A transcription factor that is activated in response to TCR signals and is essential for cytokine synthesis.2)In resting T cells,NF kB kB is present in the cytoplasm in a complex with a inhibitors IkB.kB.After phosphorylation of IkB,kB,ubiquitin attach to the protein and be degraded.3)NF kB kB is released and translocated to the nucleus.抗原抗原MHC复合体复合体T淋巴细胞激活：淋巴细胞激活：共刺激信号共刺激信号细胞因子细胞因子T淋巴细胞被激活淋巴细胞被激活佐剂佐剂免疫突免疫突触形成触形成T细胞内信号细胞内信号转导激活转导激活T细胞内信号转导激活细胞内信号转导激活：CD4 分子上分子上Lck 自身磷酸化自身磷酸化CD3分子分子ITAM酪氨酸基序磷酸化酪氨酸基序磷酸化ZAP70结合结合ZAP70被磷酸化并且酪氨酸激酶被磷酸化并且酪氨酸激酶活性激活活性激活多个多个ZAP聚集聚集LAT蛋白被磷酸化蛋白被磷酸化LAT蛋白被蛋白被磷酸化磷酸化磷脂酶磷脂酶Cg1g1活化活化Grb-2活化活化PIP2IP3DAGPKCNFkBNFATERKELKFosJNKJUNAP-1Biochemistry of Costimulation1.CD28 can activate MAP kinase pathway,including ERK and Jun.2.Can activate NFk kB to bind to IL-2 gene promoter.3.May also block inhibitory signals in T cells.4.CTLA-4 blocks normal phosphorylation of TCR associated z z chain.Not known1.How is this choice made?KnownOne possibility:CTLA-4 binds to B7-1 and B7-2 with 50-fold higher affinity than does CD28.Altered peptide Ligands:1.The TCR on an individual T cell contact only a few amino acid residues of a particular MHC-bound peptide.2.If one or two TCR contact residues have been changed,the responses will be different from the native peptide.2a:may induce a subset of the functional responses.2b:others deliver negative signals to specific T cells that inhibit responses to native peptides.P10P11P2(Tyr53),P5(Leu56),P8(Asn59),P10(Arg61)and P11(Trp62)3.APLs:Peptides with altered TCR contact residues that elicit different responses4.Utilization:microbes produce altered versions that inhibit host immune responses.