Autoimmunity as a special case of immunity: removing threats from within.

The function of the adaptive immune response against exogenous (non-self) agents is to help the innate arm of the immune system (represented by phagocytic cells) to fight and eliminate these agents. We suggest that the body also protects itself against potentially harmful self components using mechanisms similar to those used for fighting and eliminating non-self agents, and that the protective immune activity against self-components competes with the activity of self-destructive compounds. Tolerance to self is thus not a lack of response to self, but the ability to tolerate an active defense response to self without developing an autoimmune disease.