Changes

===Peripheral Tolerance===

===Peripheral Tolerance===

It is inevitable that some self-reactive T cells will get through the thymic selection process and into the periphery, as:

It is inevitable that some self-reactive T cells will evade the thymic selection process and enter the peripheral circulation, bacause some self-antigens are not expressed in the thymus, and others will not show sufficient affinity to MHC to form the MHC:self-peptide complex required for negative selection in the thymus. Conversely some T cell receptors will not have enough affinity for their respective self-antigen to induce apoptosis. Peripheral tolerance describes an unresponsiveness towards self-antigen which is developed outside the primary lymphoid organs. There are four ways this may be achieved in T cells:

*Some self-antigens are not expressed in the thymus

*Some antigens will not show sufficient affinity to MHC to form the MHC:self-peptide complex required for negative selection in the thymus

*Conversely some T cell receptors will not have enough affinity for their respective self-antigen to induce apoptosis

Peripheral tolerance is the process in which unresponsiveness towards self-antigen is developed outside the primary lymphoid organs. There are four ways this may be achieved in T cells:

* Ignorance

* Ignorance

* Anergy

* Anergy