T CELL ACTIVATION.pptx

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1. T CELL ACTIVATION

2. T CELL MATURATION

3. Negative selection : The process by which T cells are screened so that those with a high affinity for binding to self antigens (and potentially causing autoimmunity) are destroyed. Positive selection : The process by which T cells are screened so that only those capable of binding to MHC are kept alive.

4. THREE PHASES ANTIGEN RECOGNITION PHASE ACTIVATION AND DIFFERENTIATION PHASE EFFECTOR PHASE T CELL ACTIVATION AND DIFFERENTATION

5. T CELL ACTIVATION Activation of  T cells occurs through the simultaneous engagement of the T-cell receptor and a co-stimulatory molecule (like  CD4 or CD28 ) on the T cell by the major histocompatibility complex ( MHCII) peptide  and co-stimulatory molecules on the APC.  Both are required for production of an effective immune response; in the absence of co-stimulation, T cell receptor signalling alone results in  anergy . Anergy is a term in immunobiology that describes a lack of reaction by the body's defense mechanisms to foreign substances  

6. FIRST SIGNAL The first signal is provided by binding of the T cell receptor to its peptide presented on MHCII on an APC . P eptides presented to CD8 +  T cells by MHC class I molecules are 8–13 amino acids in length. P eptides presented to CD4 +  cells by MHC class II molecules are longer, usually 12–25 amino acids in length.

7. SECOND SIGNAL The second signal comes from co-stimulation . in which surface receptors on the APC are induced by a relatively small number of stimuli, usually products of pathogens, sometimes breakdown products of cells, such as necrotic-bodies or heat shock proteins.   T he second signal licenses the T cell to respond to an antigen. Without it, the T cell becomes  anergic , and it becomes more difficult for it to activate in future.

8. CD28