Session 14 - T Cell Activation and Differentiation revised.pptx

T Cell Activation And Differentiatio n PBC 9700 Session 14 Randal K. Gregg, PhD Learning Objectives 1) Identify the three signals provided by antigen presenting cells to T cells for activation and differentiation. 2) Recall the stimuli that promote expression of antigen presenting cell signals two a...

T Cell Activation And Differentiatio n PBC 9700 Session 14 Randal K. Gregg, PhD Learning Objectives 1) Identify the three signals provided by antigen presenting cells to T cells for activation and differentiation. 2) Recall the stimuli that promote expression of antigen presenting cell signals two and three. 3) Identify the signaling molecules downstream of the TCR leading to activation. 4) Recognize the cell markers for T cells during activation by antigen. What is the role of these surface markers? 5) Recall the mechanisms of memory formation in T cells. Cell-mediated immunity initiates with T cell activation If an infecting pathogen successfully resists control and elimination by the innate immune response – adaptive immune response is triggered with the activation of T cells Naïve, mature T cells are presented and activated with Ag resulting in signals that instruct the cells to proliferate into a clone army and differentiate into effector cells Cell-mediated immunity part 1 examines the process of T cell activation or T cell priming Recall that tissue DC capture/process Ag and migrate to the lymph nodes Tissue dendritic cells (DC) survey the local environment for Ags If an infectious agent is present pattern recognition receptors (PRR) of epithelial cells, macrophages and DC will be activated Resulting cytokine production by epithelial cells and macrophages can trigger inflammation Cytokines such as TNF-and PRR ligation can induce maturation of the DC At the same time, DC have captured components of the infectious agent and are processing the Ag into peptides to display on the cell surface bound to MHC Maturing DC migrate to the draining lymph nodes in order to encounter T cells 3 signals are essential for T cell activation “SIGNAL 3” + Naïve T Cell “SIGNAL 1”Activated + T Cell + T Cell ACTIVATED “Effector” “SIGNAL 2” Antigen presenting cells, mainly DC are responsible for providing these 3 signals The antigen source (peptide binding to TCR) provides SIGNAL 1 PRR Immature DC MHC “SIGNAL 1” Antigen Microbe Cytokine Receptor Microbial components can also bind to “detecting” PRR PRR Immature DC Microbe Cytokine Receptor Macrophages and Neutrophils produce cytokines (such as TNF- ) to activate DC Immature DC Neutrophil Macrophage Cytokine Receptor Microbial components and/or cytokines induce B7 expression or SIGNAL 2 Microbe component PRR Maturing APC “SIGNAL 2” B7 Cytokine Cytokine Also called Receptor (CD80, CD86) “costimulat ion” Microbial components and/or cytokines induce cytokine production or SIGNAL 3 Microbe component Innate Receptor Cytokine “SIGNAL 3” Mature APC B7 Cytokine Receptor(CD80, CD86) Cytokine SIGNALS 1+2 = Proliferation (clone army) SIGNAL 3 = Differentiation (weapons) “SIGNAL 3” PRR Mature“SIGNAL DC 1” T Cell + + CD28 Cytokine B7 Receptor “SIGNAL 2” – microbial + Cytokine Receptor T Cell ACTIVATED “Effector” Cytokine Cytotoxic molecules A few activated T cells develop into “memory” T cells for long-term protection Most T cells become “effector” T cells and leave the node to access the blood TO BLOOD Exploring the signaling in T cells that initiates from signals 1 and 2 Ag recognition activates CD4/CD8 associated Lck Lck (lymphocyte-specific protein tyrosine kinase) ITAM (immunoreceptor tyrosine-based activation motif) Lck associated with cytoplasmic tails of CD4 and CD8 Short amino acid sequence motif with tyrosine residues that can be phosphorylated Phosphorylates the ITAMs of CD3 and Zeta ( ) chains Provides binding sites for enzymes and other signaling molecules, which upon binding, can be activated Phosphorylated ITAMs recruit ZAP-70 (phosphorylates LAT) ZAP-70 = Zeta chain associated protein kinase 70 AT = linker for activation of T cells ZAP-70 is phosphorylated and activated by Lck Phosphorylated LAT activates the Ras pathway and Phospholipase C (PLC) Ras-GTP Rac-GTP PLC breaks down phospholipid into DAG (diacylglycerol) and IP3 (inositol triphosphate) DAG activates PKC IP3 opens Ca2+ channels Phospholipase C 1 (PLC 1) DAG Ca2+ (cytosolic) Inositol Triphosphate (IP3) Protein Kinase C (PKC) Protein Kinase C (PKC) NF- B PKC activates I B kinase phosphorylates I B bound to NF- B (nuclear factor kappa beta) P-I B releases NF- B NF- B then moves into the nucleus and promotes transcription of several “accessible” genes Glucocorticoids o Administered to reduce inflammation associated with allergies, asthma, autoimmune disease and sepsis o Blocks NF- B activation o Suppresses T cell responses Calcium ions NFAT Calcium ions bind to calmodulin Calmodulin activates calcineurin Calcineurin removes inhibitory phosphates from NFAT (Nuclear Factor of Activated T cells) NFAT migrates to the nucleus to activate gene expression Cyclosporine o Used in organ transplant patients o Inhibits calcineurin activity MAPK pathway AP-1 Ras-GTP/Rac-GTP initiate enzyme cascades This activates MAPK (mitogen-activated protein kinase) pathway: o ERK (Extracellular signal-regulated kinase) o JNK (c-Jun amino-terminal kinase) Leads to the expression of c-Fos (via ERK) and phosphorylation of c-Jun (via JNK) c-Fos + c-Jun = AP-1 (activating protein-1) which enhances transcription of several genes related to: o Differentiation (cytokines) o Proliferation o Apoptosis (Fas ligand) Activation of T cells results in IL-2 production 1) Clonal Expansion T cells proliferate about 100,000-fold 2) Survival Induce expression of anti-apoptotic proteins (Bcl) Increases gene expression of IL-2 receptor alpha chain (IL-2Ror CD25) o CD25 + IL-2 receptor beta chain (CD122) + common gamma chain ( c) = IL-2 receptor 3) Prepares cells for differentiation Promotes gene expression of CD40 ligand and cytokine receptors for type 1 and 2 responses (i.e. Th1, Th2) IL-2 / CD25 = T cell clonal expansion Temporal expression of T cell proteins following activation CD40L = DC cytokines + B7 molecules Temporal expression of T cell proteins following activation CTLA-4 / PD-1 = T cell contraction Temporal expression of T cell proteins following activation CTLA-4 PD-1 CTLA-4 outcompetes CD28 for B7 PD-1 ligands bind to PD-1 on T cells Both CTLA-4 and PD-1 results in phosphatase activation and blockade of TCR signaling This leads to cell cycle arrest T cell proliferation slows CTLA-4 = Cytotoxic T lymphocyte antigen 4 PD-1 = Programmed Death-1 Activated T cells migrate to tissues Cytokines activate endothelia Activated T cells express selectin ligands and integrins induced by DC cytokines in the lymphoid tissue T cells extravasate into tissue TISSUE Memory T cells form during the activation of T cells DC activation of T cells leads to clonal expansion (driven by IL-2) CTLA-4/PD-1 signaling after 3 days of expansion results in slowing of proliferation Fas-Fas ligand interactions lead to contraction of T cells Smal number of the activated T cells differentiate memory T cells Memory T cells maintain IL-7R expression Leave the lymph nodes to infiltrate the tissues (immediate response) - IL-7R IL-7R+ Naïve T cell CCR7- Undergo apoptosis Effector T cell IL-7R+ Central Memory T cell (TCM) CCR7 + Remain in the lymph nodes (reservoir) Activated to generate more TEM if response not sufficient in tissues Memory T cell Effector Memory T cell (TEM) CCR7- Leave the lymph nodes to infiltrate the tissues (local recall response) T cell activation requires 3 signals from APC Cytokines T follicular helper (TFH) are produced in the thymus to aid B cell activation