Explain the meaning of MHCrestrictionSolutionMHC restriction

Explain the meaning of MHC-restriction.

Solution

MHC restriction

The ability of T cells to recognise antigens when associated with the organism’s own MHC haplotype, providing a dual recognition system critical to T-cell function.
MHCR occurs in the thymus before a T cell becomes a functional antigen-specific cell in the peripheral immune system; the selection process operates on the / heterodimer of the T-cell receptor, assuring that the T cells will react with the product of the MHC, and not with self-antigens (i.e., the process is “self-tolerant”).T helper cells only recognize an antigen that is presented with class II major histocompatibility antigens whereas T cytotoxic cells usually only recognize a processed antigen in conjunction with class I major histocompatibility antigens.

FURTHER ADDITIONAL INSIGHT

difference between MHC restriction and self-tolerance is. This is one of the central concepts of immunology. As you know, most T lymphocytes (T cells) need to see cognate peptide + MHC in order to be activated. There are also other types of T cells that can recognize lipids and/or lipopeptides in the context of CD1 or other antigen- presenting molecules, but for the purposes of this question, we will not discuss these T cells. The fact that T cells need to see antigen (peptide) in the context of a particular MHC is called \"MHC restriction.\" This is the result of the fact that the T cell receptor (TCR) makes contact with both the MHC molecule itself, as well as the peptide that is bound into the MHC groove.

In an unmanipulated animal, T cells are restricted to self MHC. This restriction is imposed in the thymus, where T cells must undergo \"positive selection\" to not die from neglect. T cells with a TCR that cannot recognize self MHC (bound to self peptide) in the thymus do not receive a survival signal and die. This removes useless T cells from the repertoire, ones that cannot recognize MHC + antigen. Positive selection, however, poses a potential problem: the T cells in the thymus are selected on MHC+self peptide. This means of ensuring functionality also holds the seeds of autoimmunity. Therefore a second selection step must take place: negative selection.

Negative selection is achieved as the thymocytes move deeper into the thymic cortex and to the corticomedullary junction. In this case, if T cells bind too tightly/well to self peptide + MHC, they will receive a strong stimulatory signal and die by apoptosis. This process removes most self-reactive T cells. After the newly formed T cells are released into the circulation and the periphery, they are also somewhat sensitive to deletion, allowing the generation of peripheral tolerance to antigens not expressed in the thymus.

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