医学免疫学：09 T淋巴细胞及细胞免疫

1、DEPARTMENT OF IMMUNOLOGYT淋巴细胞(T lymphocyte)T淋巴细胞概述T淋巴细胞的分化发育T淋巴细胞的表面分子及其作用T淋巴细胞亚群T淋巴细胞的功能主要内容T细胞 (T lymphocyte)淋巴细胞概述T细胞是由一群功能不同的异质性淋巴细胞组成，由于它在胸腺内分化成熟故称为T细胞。成熟T细胞由胸腺迁出，移居于周围淋巴组织中淋巴节的副皮质区和脾白髓小动脉的周围。T细胞执行特异性细胞免疫应答并在TD-Ag诱导的体液免疫应答中发挥重要作用淋巴细胞概述基本概念成年人骨髓每天约产生109个淋巴细胞成年人体内约1012个淋巴细胞，童贞细胞寿命约57周，效应细胞 ：几天90存

2、在于外周淋巴器官或组织中外周血循环中淋巴细胞约占白细胞总数的2045T细胞占60，B细胞30，NK细胞10T细胞在免疫器官中的比例：淋巴液90，胸腺85，淋巴结75，脾脏35基本数据淋巴细胞的显著特征：异质性（heterogeneity）发育过程涉及复杂的：发育生物学（developmental biology）研究方法：表型鉴定、各种动物模型建立基本特性T淋巴细胞的分化发育T细胞在胸腺的发育T细胞在外周淋巴器官中的分化发育T细胞受体(TCR)的发育T细胞发育过程中的阳性选择T细胞发育过程中的阴性选择thymic corpuscle T细胞在胸腺发育胸腺微环境是诱导并调控T细胞分化发育的关键因

3、素 胸腺基质细胞（TSC） 细胞因子 胸腺激素T细胞在胸腺发育TCR的发育DN: b链基因开始重排 前细胞替代a链pTapTa:b受体表达于preT表面preT增殖活跃分化为DP细胞IL-7pTa:b表达下调细胞停止增殖a链基因重排开始表达有功能的TCR双阴性期（DN） 原T细胞（pro-T）、前T细胞（pre-T）TCR 、CD3 /low 、CD4 、CD8 双阳性期（DP）TCR 、CD3low、CD4 、CD8 单阳性期（SP）TCR 、CD3 、CD4 TCR 、CD3 、CD8 成熟T细胞，具有识别抗原、介导免疫应答及参与免疫调节的功能1. T细胞发育的阳性选择（positive

4、selection）CD4+CD8+T细胞胸腺基质细胞（表面MHC分子）如果与MHC-I结合，最终分化为CD8+T细胞如果与MHC-II结合则最终分化为CD4+T细胞如果与MHC分子不结合则在胸腺皮质中凋亡胸腺细胞经阳性选择赋予成熟T细胞在识别抗原时具有MHC限制性2. T细胞发育的阴性选择（negative selection）其TCR识别胸腺基质细胞表面高亲和力的MHC或MHC-自身抗原肽的T细胞克隆将发生凋亡经阴性选择可清除自身反应性T细胞克隆获中枢耐受DP或经阳性选择的SP的T细胞T细胞在胸腺中的阳性选择和阴性选择 T细胞在外周淋巴器官中的分化发育初始细胞细胞亚群调节性细胞记忆细胞T淋

5、巴细胞表面分子及其作用T细胞表面受体 T细胞表面抗原 粘附分子T细胞表面标志MHC抗原 所有T细胞表达MHC-I 活化T细胞表达MHC-II类分化抗原（CD , cluster of differentiation） 与T细胞识别和激活有关：CD3、CD4、CD8、CD2、CD28家族、CD40L、CD45等T细胞表面抗原TCR-CD3 complexTCR-CD3复合物是T细胞抗原受体与一组CD3（Gamma DeltaEpsilon Zeta Eta ）分子以非共价键结合而形成的复合物，是T细胞识别抗原和转导信号的主要单位。TCR特异识别由MHC分子提呈的抗原肽，CD3分子转导T细胞活化的

6、第一信号CD3 是T细胞所特有的表面标志 与 TCR以盐桥形式组成 TCR-CD3复合体TCR-CD3 复合体结构模式图 转导T细胞活化的第一信号 功能稳定TCR的结构负责抗原特异性信号传导参与T细胞发育CD4/CD8CD4：胸腺细胞、成熟TH细胞 巨噬细胞、DC等 CD8：胸腺细胞、成熟TC 细胞 NK细胞、T等表达CD4 结构单链跨膜糖蛋白分子，胞外区含有4个Ig样结构域分别为D1、D2、D3和D4CD4分子D1结构域可与HIV gp120结合，是HIV病毒的受体CD4分子的D4结构域能与IL-16结合，有可能为IL-16受体 IL-16: 刺激CD4T细胞、单核细胞及嗜酸性粒细胞的移行，

7、抑制HIV感染的T细胞CD4分子结构示意图lckCD4和CD8共受体分子模式图 CD8结构 或链以二硫键连接的二聚体，每条链具有一个IgV样结构域V样区与胞膜之间：富含脯氨酸、丝氨酸和苏氨酸的连接肽，广泛糖基化，保护多肽链免于蛋白酶的裂解CD4通过D1结构域侧面与MHC-II类2结构域结合CD8通过链V样结构域与MHC-I类3结构域结合稳定T细胞与APC或靶细胞间的结合CD4和CD8通过胞浆区的CxCP基序与p56lck酪氨酸激酶相连，参与T细胞活化和增殖信号转导 功能CD4与MHCII结合位点CD28-B7分子家族 CD28家族成员包括： CD28 CTLA-4 （cytotoxic T l

8、ymphocyte antigen-4） ICOS（inducible T-cell co-stimulator） PD-1（ programmed death 1） CD28家族分子配体均为B7家族分子 均属于IgSF B7家族成员包括：B7-1（CD80）B7-2（CD86）ICOSLPD-L1、PD-L2 CD28B7分子家族 同源二聚体胞外区单一IgSF V样结构域，具有高度保守的MYPPY基序胞浆区可与多种信号分子和激酶作用胞浆区SH3-激酶结合位点（PYAP），对细胞分化和IL-2的产生重要 CD28 CD28家族分子结构与CD28有31同源性，生物进化十分保守与B7分子结合必需的

9、MYPPY基序CTLA-4与B7结合的亲和力明显高于CD28胞浆区有ITIM（immunoreceptor tyrosine-based inhibition motif）基序，与SHP-2蛋白酪氨酸磷酸酶的SH2结构域结合，募集并活化PTP，阻断由PTK参与的活化信号转导通路 CTLA-4 （cytotoxic T lymphocyte antigen-4）分布和功能 CD28分布：组成性表达所有CD4T细胞和50CD8T细胞功能：1)与B7结合提供共刺激信号，促进T细胞活化2)转导信号与TCR转导信号起协同促进作用，显著减低有效活化T细胞所需的TCR数量 分布：初始T细胞不表达，活化后快速

10、上调表达与B7结合亲和力高功能：转导负调节信号，在调节外周T细胞耐受中发挥重要作用 体内阻断CTLA-4能增强抗肿瘤免疫，加剧自身免疫应答 CTLA-4CD28/CTLA-4B7-1/B7-2结合 ICOS（inducible T-cell co-stimulator）氨基酸水平：与CD28有39同源性胞外区有与ICOSL结合的FDPPPF基序胞浆区特殊基序，可与PI-3K的p85亚单位结合ICOS 区别CD28和ICOS分子及其功能的结构基础CD28有SH3-激酶结合位点（PYAP）ICOS缺乏此位点，NATURE REVIEWS，VOLUME 2 | FEBRUARY 2002 | 125

11、ICOS T细胞活化后快速诱导表达表达水平受到TCR和CD28信号的影响Th1，Th2分化早期，ICOS均上调表达生发中心中Th细胞高表达ICOS ICOS与CD28所产生的共刺激信号具有协同促进作用 ICOS主要调节已活化的或效应T细胞产生细胞因子增加多种细胞因子分泌不增加CTL的杀伤功能 ICOS对Th2分泌IL-4和IL-13发挥重要作用 ICOS上调Th2表达CD40L，可影响B细胞Ig类别转化在初始T细胞活化过程中阻断ICOS，能促进Th1的分化程序性死亡分子-1(programmed death -1, PD-1)无MYPPPY基序，有半胱氨酸残基，易形成二硫键而组成同源二聚体胞浆

12、区含有2个酪氨酸，其中一个参与组成ITIMPD-1L和PD-2L为B7家族新成员，被确定为PD-1的配体 PD-1 PD-1 分布：表达于：活化T细胞、NK、B和髓系细胞表面功能：抑制T细胞增殖 主要机制：拮抗CD28-B7信号途径，抑制生长因子的分泌 CD2 CD2又称为淋巴细胞功能相关抗原-2（lymphocyte function associated antigen 2, LFA-2） 与其配体LFA-3 ( CD58 ) 结合CD2分布：胸腺细胞、 T细胞和NK细胞CD58分布：广泛，T细胞、APC、粒细胞、红细胞和血小板表面，某些上皮细胞、内皮细胞和成纤维细胞也可表达CD2和CD5

13、8分子结构相似，胞外区N端 ：IgSF V样区，近膜段：IgSF C2样区 CD2/CD58功能 增强T细胞与APC或靶细胞的粘附作用 促进T细胞识别抗原及其介导的信号转导p59fyn 胸腺细胞的分化成熟CD40L（CD154） 结构属于TNF超家族成员II型膜蛋白分子，C端在胞外区，N端在胞内区 以三聚体形式结合三聚体的CD40 分布活化的T细胞表面（主要CD4+T/部分CD8+T和 T）活化的B细胞、嗜碱性粒细胞、NK细胞、单核细胞等LFA-1/ICAM-1功能 介导T细胞与APC或靶细胞的粘附作用T细胞与APC细胞间的主要辅助分子4. 其它一些受体 丝裂原受体 细胞因子受体 病毒受体1）

14、初始T细胞、效应T细胞和记忆性T细胞 初始T细胞表达CD45RA,CD62Lhigh ， 效应T细胞表达IL-2R,整合素,CD44,CD45RO 记忆性T细胞表达CD45RO,黏附分子(整合素,CD44) NK1.1 T细胞 其TCR识别的抗原是由CD1分子提呈的脂类和糖脂类抗原三、T细胞亚群三、T细胞亚群2）根据TCR种类 T、T细胞在末梢血主要为T细胞可占95%，而T细胞只占1%10%。T细胞为主要参予免疫应答的T细胞，两者特性和功能均不相同。TCRT和TCRT细胞 TCR 分布 表型识别抗原MHC限制功能TCRT TCRT 极大多样性60-70,外周淋巴组织成熟CD2CD3CD4/CD

15、8817aa经典MHCTh、Tc较少多样性5-15,粘膜上皮成熟大多数CD2CD3简单多肽、 HSP、脂类、多糖MHC样分子Tc3）根据T细胞是否表达CD4或CD8分类 CD4+ T细胞或CD8+ T细胞TCRTCD4+细胞：CD2+、CD3+、CD4+、CD8-TCR识别抗原是MHC类分子限制性 TH0、Th1和Th2、行使Tc、Ts功能TCRTCD8+细胞：CD2+、CD3+、CD4-、CD8+TCR识别抗原是MHCI类分子限制性 行使Tc、Ts功能Th细胞 根据所分泌的细胞因子不同，将其分为Th1、Th2和Th17亚型。 Th3、I型调节性T细胞(Tr1)Tc细胞 杀伤、分泌IFN、IL

16、-4、IL-5和IL-10Treg4）功能性亚群：Th、Tc(CTL)、Treg初始T细胞效应T细胞记忆T细胞T细胞活化阶段abT细胞gdT细胞Th细胞CTL(Tc)Treg细胞CD8T+细胞CD4T+细胞TCR类型CD4/8功能Th1Th2Th17TregGeneration and conversion of Treg cells in the tumor microenvironmentTumor cells not only provide antigenic stimulation for T cell activation but also interact with tumor-

17、infiltrating innate immune cells to secrete crucial cytokines for T-cell differentiation. Nave CD4+ T cells can be differentiated into different subsets of CD4+ T cells, including Th1, Th2, Treg and IL-17-producing T cells (Th17), depending upon the strength of antigen stimulation and cytokine milie

18、u. It is known that combination of suboptimal antigen stimulation with TGF-b favors the conversion of naive T cells into Treg cells but blocks the generation of Th1 or Th2 cells. However, TGF-b plus IL-6 facilitate the conversion of naive T cells intoTh17 cells. Alternatively, naturally occurring CD

19、4+CD25+ Treg cells directly derived from the thymus can cross-react with some antigens expressed by cancer cells, thus promoting their expansion and accumulation in the tumor microenvironment.T-helper-cell differentiationHuman IL-17 and IL-17R key featuresa Two isoforms (long and short). Therapeutic

20、 targets for autoimmune inflammatory diseases are associated preferentially with the IL-23/Th17 pathway The pathogenic role for IL-23, not IL-12, in mouse models of autoimmunityStudies by Cua and co-workers have demonstrated that disease development requires IL-23, but not IL-12, in EAE and CIA. Com

21、pared with wild-type susceptible mice, mice deficient for IL-23 (Il23p19/) and both IL-23 and IL-12 (Il12p40/) failed to develop disease after antigenic challenge, whereas mice deficient for IL-12 (Il12p35/) developed more severe disease.Model of Th1 versus Th17 lineage development from naive CD4 T

22、cell precursors (Tn)This model emphasizes the distinct lineages leading to mature Th1 and Th17 effector cells (see main body of text for details). Question marks denote speculative or unknown aspects of Th17 differentiation that are yet to be defined.Antagonistic cytokine networks control CD4 effect

23、or T-cell differentiationRecent studies have established that Th1 and Th2 effector cytokines, IFNg and IL-4, respectively, potently inhibit Th17 development. Furthermore, TGF-b, a cytokine previously implicated in Treg development and function, appears to be required for Th17 development, both throu

24、gh indirect effects (blockade of IFNg and IL-4 production by cells of the innate immune system) and through direct effects on naive CD4 T-cell precursors (Tn).CD4+T细胞分化和免疫调节细胞因子网络模式简图Although functional CD4 T cell development has been dominated by the Th1-Th2 paradigm for nearly two decades, the num

25、ber of defined lineages has now increased. The cytokines associated with arrows indicate dominant cytokines involved in specification of each of the indicated lineages. The cytokines listed below each cell type indicate key effector or regulatory cytokines produced by differentiated cells of that li

26、neage or, in the case of nTreg, a contact-dependent mechanism of suppression. Tn: naive, postthymic CD4 T cell precursors; Tp: thymic precursors.Dotted lines represent less well-defined lineage relationships.Diversification of CD4 T Cell LineagesModel of Branching Th17 and Adaptive Treg Lineage Deve

27、lopmentThis model emphasizes distinct pathways leading to mature Th17 effector cells or Foxp3+ adaptive Tregs (aTreg), induced by a common requirement for TGF-b but differential effects of IL-6 and IL-23. Naive CD4 T cells (Tn) activated by antigen presented on immature DCs that do not produce IL-6

28、production are induced by TGF-b to express Foxp3 and develop into aTregs (top panel). Tns activated bymature,TLR-activatedDCsthat produceIL-6 are induced by TGF-b to upregulate IL-23R and become competent for IL-17 production and IL-23 signaling. IL-23 signaling induces responsiveness to IL-18 and I

29、L-1, which can act synergistically with IL-23 to induce Th17 cytokineproductionindependently ofTCRstimulation.Alternatively, TCR stimulation by antigen can induce Th17 cytokine production directly,without a requirement for IL-23, IL-1, or IL-18.Dotted lines indicate possible positive feedback loops

30、by which cytokine products of Th17 (IL-6) or aTreg cells (TGF-b1) may reinforce lineage development. CD4辅助性T细胞的功能 CD8杀伤性T细胞的功能调节性T细胞的功能四、T细胞功能细胞因子对Th1和Th2细胞的调节作用Naturally occurring CD4+CD25+ Treg cells (56%) GITR and Foxp3 a cellcell contact mechanismAntigen-induced Tr1 and Th3 cells (IL-10) and/or

31、(TGF-b) ck-dependent mechanism no specific marker has been identified. Adaptively induced CD4+ Treg cells GITR and Foxp3 a cell contact dependent or soluble factor-dependent (other than IL-10and/or TGF-b) mechanismglucocorticoid-induced TNFRfamily related gene (GITR)CD8+ Treg cellsNKT regulatory T c

32、ellsMultiple subsets of Treg cellsNaturally occurring CD4+CD25+Foxp3+ Tregs Development and function of naturally occurring CD4+CD25+ FoxP3+ regulatory T cells (nTregs). Development:bone marrow-derived CD4+ T cell precursors develop naturallyinto nTregs upon beneficial TCR engagement by self-peptide

33、MHC complexes and Foxp3 induction in the thymus. Upon instruction in the thymus, nTregs emigrate into the periphery asfunctionally fully competent cells. Mode of action: upon TCR cross-linking, peripheral nTregs suppress the proliferation and IL-2 production by responder CD25CD4+ or CD8+ T cells in

34、acontact-dependent manner either (a) directly or (b) indirectly via the APC. In addition: nTregs may (c) condition DC to become tolerogenic and turn down the response of conventional T cellson her partExtrathymic induction and function of adaptive regulatory T cells. Adaptive regulatory T cells (aTr

35、egs) differentiate from naive conventional CD4+ T cells either as a result of suboptimal antigenic stimulation by resting/immature DC, theinfluence of suppressive cytokines like IL-10, TGF-b or cell contact-dependent interaction with activated nTregs (infectious tolerance). Their mode of action invo

36、lves both cell contactdependent (Tr1 cells) and contact-independent suppressive activities (Th3 cells). Through the production of IL-10 and TGF-b they convert immature DC into tolerizing APCFig. 3 Role of Tregs in early and late stages of microbial infections. In the stages of an immune response aga

37、inst a microbial infection Tregs behave differently. A Throughout the early phase of the response the suppressive activity of Tregs is turned down by effector T cell-derived IL-2 and microbial components such as TLR-ligands. Tregs respond to the stimulation by mature DC and proliferate.b At the late

38、 stage of the response, when the invading organism is cleared from the host, Tregs regain their suppressive function and participate in the silencing of the T cell response by acting on effector T cells and DC. Possibly, this late activity is also for the proper development ofmemory T cellsTreg-base

39、d immune intervention strategies. Selective manipulation of Treg function is an emerging target for immune intervention strategies to either boost responses in cancer and microbial diseases or suppress those unwanted in autoimmunity, allergy, transplantation and pregnancy disorders. The transientdep

40、letion of Tregs as well as their modulation by microbial agents may allow a transient reduction of Treg activity and enforce anti-tumor responses and immunity against viral infections. On the other hand their selective activation could diminishchronic pathological immune responses掌握TCR分型与结构掌握T细胞发育过程

41、掌握T细胞分群及不同亚群的生物学特性熟悉T细胞表面主要膜分子及其作用了解TCRT细胞和TCRT细胞的异同点教学要求T淋巴细胞对抗原的识别及免疫应答 一、T细胞对抗原的识别 二、T细胞活化的过程 三、效应性T细胞的应答效应 免疫应答的基本过程 抗原识别 抗原受体与抗原的特异性结合免疫应答 抗原识别、反应、效应的全过程免疫反应 免疫效应物质与抗原结合的过程 一、T细胞对抗原的识别T 细胞抗原受体及其识别抗原的特点 只识别表达于APC表面并与MHC分子结合 成复合物的多肽 只识别氨基酸一级序列的多肽线性决定簇 TCR识别抗原受到MHC的限制 CD4+T只识别与MHC-II分子结合的肽段 CD8+T只

42、识别与MHC-I分子结合的肽段T细胞与APC间的相互作用 （一）T细胞与APC的非特异性结合T细胞与APC的非特异性结合 （二）T细胞与APC的特异性结合TCR与APC的特异性稳定结合 （三）T细胞和APC表面共刺激分子的结合CD28/B7、LFA-1/ICAM-1、CD2/CD58等（四）免疫突触（immunological synapse）中心是TCR和抗原肽-MHC复合物周围是细胞黏附分子对“筏”状结构，相互靠拢成簇（一）T细胞活化的第一信号二、T细胞活化的信号要求CD4+T细胞的双识别（二）T细胞激活的第二信号CD28/B7LFA-1/ICAM-1或ICAM-2CD2/LFA-3CD40/CD40L等T细胞活化的双信号 CD28/B7促进IL-2基因转录、合成缺乏时，T细胞失能（anergy）CTLA4与CD28高同源性，与B7亲和力比CD28高20倍，结合后启动抑制信号，有效制约特异性T细胞克隆的过度增殖（三）细