The immune system has various mechanisms to prevent the induction of autoimmunity against self-antigens and the subsequent production of an autoimmune disorder.
Central tolerance is the earliest prevention process that occurs within primary lymphoid tissue; immature B and T cells are exposed to a variety of self-antigens. The immature cells are "tested" for reactivity against self-antigens, and self-reactive cells will meet one of several fates. The self-reactive cells may die by clonal deletion, undergo receptor editing to produce a new receptor that does not bind the self-antigen, or the cell may become anergic and may be released into the body.
Peripheral tolerance is regulated by several factors outside primary lymphoid tissue:
- Regulatory T cells help inhibit and destroy self-reactive B and T cells
- Self-reactive cells are unable to receive the costimulatory signals required for their activation, thus resulting in their eventual death. Previously released self-reactive anergic cells will be eliminated by this mechanism.
- The presence of immunologically privileged sites and tissue barriers which prevent exposure to certain self-antigens that may induce an autoimmune response.
The loss of one or more of these mechanisms may influence the development of autoimmune disease.
