Peripheral tolerance

Peripheral tolerance is the second branch of immunological tolerance, after central tolerance. It takes place in the immune periphery (after T and B cells egress from primary lymphoid organs). Its main purpose is to ensure that self-reactive T and B cells which escaped central tolerance do not cause autoimmune disease. Peripheral tolerance is the second branch of immunological tolerance, after central tolerance. It takes place in the immune periphery (after T and B cells egress from primary lymphoid organs). Its main purpose is to ensure that self-reactive T and B cells which escaped central tolerance do not cause autoimmune disease. Mechanisms of peripheral tolerance include direct inactivation of effector T cells by either clonal deletion, conversion to regulatory T cells (Tregs) or induction of anergy. Tregs, which are also generated during thymic T cell development, further suppress the effector functions of conventional lymphocytes in the periphery. Dependence of a particular antigen on either central or peripheral tolerance is determined by its abundance in the organism. B cell peripheral tolerance is much less studied and is largely mediated by B cell dependence on T cell help. Antigens, which are present in generally low numbers can be ignored by the immune system without any further mechanism, since T cells have to be activated, prior to their migration to non-lymphoid tissues. Specialized mechanisms ensuring ignorance by the immune system have developed in so-called immunoprivileged organs.