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===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:
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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
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