T cell and Cell-mediated immunity Lu Linrong ( 鲁林荣 ) PhD Laboratory of Immune Regulation Institute of Immunology Zhejiang University, it School of Medicine i Medical Research Building B815-819 Email: Lu.Linrong@gmail.com Website: http://mypage.zju.edu.cn/llr
T lymphocyte a key player in the immune system Absence or hyperactivation of T cells leads to immunodeficiency, respectively chronic inflammation or autoimmune disorders.
T Cell Belongs to Lymphocytes Can be distinguished by the expression of T cell receptor (TCR) Function: mediate cellular immunity; Thymus-derived d lymphocyte: T cell Origin: bone marrow stem cell Distributing: T Zone of secondary lymph node and peripheral blood (65-75% of total lymphocytes)
Outline 1. Development of T cells 2. T cell surface markers 3. T cell subsets 4. Functions of T cells 5. Cell-mediated d immunityit
1. Development of T cells
T cells develop in Thymus
Geography of the thymus: Thymic epithelial cells control the maturation of thymocytes
Factors promoting T cell development in the thymus Cytokines (IL-1, IL-6, IL-7) and hormones secreted by thymic stroma cells and thymocytes y themselves. Interaction of cell adhesion molecules between immature thymocytes and thymic stroma cells
The cortical epithelium of the thymus is critical for T cell development The nude mouse strain is athymic due to a mutation in the Foxn1nu gene that encodes FOXN1, a transcription factor of the forkhead box family. FOXN1 is preferentially expressed in the skin and thymus. Alteration ti of its expression in the thymus underlies the manifestation of severe immunodeficiency resulting from total absence of T cell development.
Sequential development of thymocytes Pre-T cells: no T cell marker expression Double negative cells (DN): CD4 - CD8 - ; cytoplasmic CD3 + Double positive cells (DP): CD4 + CD8 +, CD3 +, γδtcrr low, αβtcr low Mature T cells (single positive T cells): CD4 + or CD8 +, CD3 +, TCR +
Stages of T cell development defined by surface markers
Stages of Thymocytes development in Thymus
Surface marker for αβ thymocyte t development The distinct stages of αβ thymocytes can be identified by FACS analysis in respect to the expression of the CD4 and CD8 coreceptors. Percentages of the distinct cell populations are indicated in the respective quadrants (CD4 SP: upper left, DP: upper right, CD8 SP: lower right, DN: lower left).
Surface marker for αβ thymocyte development CD25 CD8 CD44 CD4
VDJ recombination and TCR expression is essential for Thymocytes development
VDJ recombination and TCR expression is essential for Thymocytes development
Thymocytes development driven by stage-specific expression of Key molecules
Positive and negative selection Positive selection: DP cells that bind, with moderate affinity, to MHC-Ag on thymic stroma cells survive----mhc restriction MHC I----CD8 + T cells MHC II----CD4 + T cells Negative selection: Cells that bind to MHC-Ag on thymic stroma cells (or auto-reactive T cells, ART) with high affinity will undergo apoptosis Formation of central immune tolerance
Positive and negative selection Downloaded from: StudentConsult (on 1 June 2006 01:58 PM) 2005 Elsevier
2. T cell surface markers
CDs on T cells
CD3 1.Consists of 5 proteins that are designated as γ, δ, ε, ζ and η. Three dimers: γε, δε, ζζ (ζη) 2.The cytoplasmic domain contains ITAM (immunoreceptor r tyrosinebased activation motif) YxxL/V 3.Function: transduction of signals that lead to T cell activation.
transmembrane glycoprotein co-receptor of T cell CD4 and CD8 *CD4: first and second domains bind to nonpolymorphic region of MHC Ⅱmolecules CD8: IgV-like domain of α chain binds to nonpolymorphic α3 region of MHCⅠmolecules function: function: mediate adhesion; mediate signal trans 赌场提哦呢 : lck activation first V-like domain of CD4 ---specific receptor of HIV APC
CD28 and CD152 (CTLA-4) CD28 + cell ---all CD4 + T cell and 50% CD8 + T cell; CTLA-4 + cell --- activated T cell binding to B7-1 (CD80) and B7-2 (CD86) on the surface of APC *CD28: provide an co-stimulatory signal for T cell * CTLA 4 lifi ti f ti t d T ll (b i * CTLA-4:suppress amplification of activated T cell (bring into play negative regulation )
Interaction of CD28 with B7 provide 2 nd signal for T cell activation
CD40 and CD40L (CD154)
Other surface markers ICOS: expressed on activated T cells CD2: SRBC receptor, LFA-2 PD-1: ligand PD-L1,PD-L2 LFA-1 and ICAM-1: mediate adhesion between APC (or target cells or endothelial cells) and T cells or other leukocytes.
Summary of T cell surface markers
3. T cell subsets 1. Naive T cells, effector T cells and memory T cells; 2.TCRαβ T cells and TCRγδ T cells; 3.CD4 + T and CD8 + T cells; 4.Th, Tc and Treg
T-cell response
Naïve vs memory T cells
αβ vs γδ T cells
CD4 vs CD8 T cells
T cell differentiation
4. Functions of T cells 1. CD4 + helper T cells (Th): Th0:Th cells that secrete broad spectrum of cytokines at low level. Th1: produce IL-2 and IFN-γ, but not IL-4. They are chiefly responsible for cell-mediated immune responses, but can also help B cells to produce IgG2a, but not much IgG1 or IgE; Th2: secrete IL-4, 5, 10, 13, but not IL-2 and IFN-γ, are,,,, γ, very efficient helper cells for production of antibody, especially of IgG1 and IgE ;
Th1 vs Th2
CD4 T cell mediate immunity effecter functions
2. CD8 + cytotoxic T cells (CTL) Function: directly kill target cells (cytotoxicity)
CTL Mechanisms 1. Cytolysis (necrosis) i) ------ three stages: a. contact phase: recognition of antigen in the context of MHC class I molecules b. secretory phase: release of cytolytic granules (perforin and granzymes) c. lysis phase: osmotic death
CTL Mechanisms CTL 2. Cell apoptosis: a. FasL-Fas: CTLs express FasL interaction with Fas on target cells activation of caspase 8 apoptosis Target
3. CD4 + CD25 + regulatory T cells (Tr) Foxp3 positive Function: Down-regulation of immune response by inhibiting the activation and proliferation of CD4 + or CD8 + T cells. Mechanisms: Direct inhibition by contacting target cells. Inhibitory cytokines:il-10,tgf-β,et al.
5. T cell-mediated immune response
Introduction Cell-mediated immunity is the arm of the adaptive immune response whose role is to combat infection of intracellular pathogens, such as intracellular l bacteria (mycobacteria, listeria monocytogens), viruses, protozoa, etc.
3 Phases of T cell responses Antigen recognition phase Activation,proliferation and differentiation phase Effector phase
Antigen recognition Ag presentation by APC
Interaction between APC and T cell Non specific binding of APC and Tcell Specific binding of APC and T cell TCR-peptide-MHC co-receptor-mhc co-stimulatory molecules T cell synapse or immunological synapse
Ligand-receptor pairs involved in T cell activation Adhesion Antigen recognition Signal Signal transduction Signal transduction transduction Adhesion
Activation, proliferation and differentiation The first signal: TCR-antigen peptide-mhc (double recognition) CD4-MHC II or CD8-MHC I The second signal (co-stimulatory signal): Interactions between co-stimulatory molecules APC and corresponding receptors on T cells CD28 B7 on The third signal: Cytokines in T cell activation
Two signals ensure T cell activation Co-stimulation provides signal II self antigen
Other requirements for T cell mediated response --Cytokine signal as signal III
Signal transduction ti in T cell activation 1.Synapse formation 2.Activation of Src family PTK(p59 fyn, p56 lck ) 3.Phoisphorylation tyrosine of CD3 ITAM 4.Recruitment and activation of Syk family PTK(ZAP- 70) 5.Phoisphorylation of adaptor LAT and SLP 6.Activation of TF:NFAT, AP-1, NF-κB, Oct-1 7.Transcription and expression of gene :IL-2 et al
1, Formation of the Immunological Synapse When the TCR complex recognizes MHC-associated peptides on an APC, several T cell surface proteins and intracellular signaling molecules are rapidly mobilized to the site of T cell-apc contact. This region of physical contact between the T cell and the APC has been called the immunological synapse csmac : central supramolecular activation cluster (TCR/CD3, CD2, CD28, PKC θ, lck) psmac : peripheral supramolecular activation cluster (LFA-1, Talin, CD43, CD45, CD148)
2.Activation of Src family PTK(p59 fyn, p56 lck ) 3.Phoisphorylation tyrosine of CD3 ITAM
4.Recruitment and activation of Syk family PTK(ZAP- 70) 5.Phoisphorylation of adaptor LAT and SLP
6.Activation of signal pathways and TFs
Major signaling pathways & Gene expression 1) PLC-γ γ TCR-CD3 ITAM ZAP-70 LAT, SLP-76 PLC-γ IP 3 Ca 2+ calcineurin NFAT PIP 2 { DAG PKC NF-κB 2) Ras-MAP ZAP-70 phosphorylation of LAT and SLP-76 Grb-2 and Sos Ras MAPKK MAPK AP-1 Target genes activated by transcription factors CKs and their receptors CAMs MHC
Differentiation of T cells 1) CD4 + T cells: Th, Tr, Treg,Th17,Tm, regulated by cytokines (signal 3) 2) CD8 + T cells: Tc Th-dependent Th-independent: virus infected DC that highly express co-stimulatory molecules can directly stimulate t CD8 + T cells.
Differentiation of CD8 T cells
Effector functions of activated T cells 1) CD4 + T cells Activate macrophages Th1: secrete IFN-γ, etc. express CD40L express FasL, kill Fas + target cells effect on lymphocytes: IL-2 effect on neutrophil: TNF-α α,β Th2: promote B cell growth and Ig production mediate hypersensitivity Th17: IL 17 IL 8TNF α: enhance leukocyte recruitment Th17: IL-17,IL-8,TNF-α: enhance leukocyte recruitment and inflammation
Effector functions of CD4 T cells Activation of macrophages by T lymphocytes
Activation of Macrophage by Th1 cells
2). Effector functions of CD8 + T cells Cytotoxicity: kill target cells a. necrosis: perforin and granzyme b. apoptosis: granzyme, FasL Characteristics of CD8 + T cell cytotoxicity a. Specificity it b. MHC I restriction c. High efficiency
3) memory T cells 1) CD45RA - CD45RO +, 2) Long-lived memory to specific antigen 3) Mediate faster, stronger and more effective immune response 4) Mechanism: low dependent on costimulatory molecules or more sensitivity to cytokines
Summary 1. Development of T cells: Markers and stages, Essentials; 2. T cell surface markers: Related to Functions 3. T cell subsets: αβ vs γδ; CD4 vs CD8; Ths.. 4. Functions of T cells: Th1, Th2, CTL; 5. Cell-mediated immunity: Activation of T cells Effector of T cells