Paper Topic:

`T-cells are MHC restricted`. Discuss this statement.

/Naive_T_cell " \o "Naive T cell " napve responses , although B-cells and macrophages can be important APCs

Since antibody cannot enter infected cells and phagocytes cannot detect that they are infected , cytotoxic T-cells must be activated to recognize and kill the infected cells . To be activated by endogenous antigen , CD8 T-cells use their T-cell receptor TCR to bind endogenous antigen peptides presented on membrane Class I MHC proteins of target or infected cells . T-cell precursors however arrive to the thymus from the Bone Marrow

T-cells are Major Histocompatibility Complex MHC-restricted in their

ability to see antigen , they only recognize it presented by syngeneic or self MHC on APC . CD4 T-cells bind exogenous antigen on Class II MHC of professional APC , macrophages and B-cells . T-cell receptor TCR binds both peptide plus Class II MHC domains . CD8 T-cells recognize antigen on Class I MHC of cells infected with endogenous pathogens . Unlike B-cells T-cells do not recognize antigens directly . They see ' antigen as peptides only in association with host surface Major Histocomptability MHC molecules . Since MHC molecules can only bind peptide molecules of 7-15 amino acids long , T-cells only recognize their specific antigen in the form of small peptides . The antigen presenting cells such as macrophages and B-cells take up antigen and partially degrade it into peptides which then occupy the antigen-presenting groove in MHC-I and MHC-II molecules (Decker Janet M , 2006

T-cells cannot recognize whole ' intact antigens or non-proteinaceous antigens such as carbohydrates . The two classes of MHC molecule MHC class I , which primarily present intracellular antigens and MHC class II , which primarily present extra cellular antigens . CD8 T-cells can only recognize antigen in association with MHC I . The role of the CD8 molecule would be to bind MHC I and thus strengthen this association Without interaction with CD8 , T-cells will not be activated...

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