Peripheral tolerance

In <a href="/facts/Immunology/vylm0L8e">immunology</a>, peripheral tolerance is the second branch of <a href="/facts/Immune_tolerance/hvDqPHTP">immunological tolerance</a>, after <a href="/facts/Central_tolerance/2dUAKATR">central tolerance</a>. It takes place in the immune periphery (after <a href="/facts/T_cell/5z6PQ9UN">T</a> and <a href="/facts/B_cell/6Y1tgwwp">B cells</a> egress from <a href="/facts/Primary_lymphoid_organ/yw5QLgMT">primary lymphoid organs</a>). Its main purpose is to ensure that <a href="/facts/Reactive_lymphocyte/QS6mkyqN">self-reactive</a> T and B cells which escaped central tolerance do not cause <a href="/facts/Autoimmune_disease/sojBeQ7t">autoimmune disease</a>. Peripheral tolerance can also serve a purpose in preventing an immune response to harmless food <a href="/facts/Antigen/9JlAernG">antigens</a> and <a href="/facts/Allergen/bnM4cttq">allergens</a>.
Self reactive cells are subject to clonal deletion or clonal diversion. Both processes of peripheral tolerance control the presence and production of self reactive immune cells. Deletion of self-reactive T cells in the thymus is only 60-70% efficient, and <a href="/facts/Naive_T_cell/QEl3A7Yh">naive T cell</a> repertoire contains a significant portion of low-avidity self-reactive T cells. These cells can trigger an autoimmune response, and there are several mechanisms of peripheral tolerance to prevent their activation. Antigen-specific mechanisms of peripheral tolerance include persistent of T cell in quiescence, ignorance of antigen and direct inactivation of effector T cells by either clonal deletion, conversion to <a href="/facts/Regulatory_T_cell/1ECRAGMg">regulatory T cells</a> (Tregs) or induction of <a href="/facts/Clonal_anergy/nc2QNDqf">anergy</a>. Tregs, which are also generated during thymic T cell development, further suppress the effector functions of conventional lymphocytes in the periphery. <a href="/facts/Dendritic_cell/19KBuKFK">Dendritic cells</a> (DCs) participate in the negative selection of autoreactive T cells in the thymus, but they also mediate peripheral immune tolerance through several mechanisms.
Dependence of a particular antigen on either central or peripheral tolerance is determined by its abundance in the organism. B Cells have a lower probability that they will express cell surface markers to pose the threat of causing an autoimmune attack. Peripheral tolerance of B cells is largely mediated by B cell dependence on T cell help. However, B cell peripheral tolerance is much less studied.

Peripheral tolerance open-in-new

Peripheral tolerance