[Physiological autoimmunity]

The serum of normal individuals contains antibodies directed against their own antigens (autoantigens). These autoantibodies are the main and the best known component of normal autoimmunity. They mostly involve polyreactive (one antibody recognising several antigens) IgM, but also IgG, usually having low affinity for antigens. The role of natural autoimmunity is becoming better understood. It participates in the equilibrium of the immune system, contributing to controlled production of antibodies, accelerated elimination of external antigens or aged autoantigens, and to triggering of a specific immune response. Some data suggest that the action of autoantibodies in homeostasis can extend beyond the immune system. Many pathological states, of immune nature or not, are associated with an increase or diminution of the titre of natural autoantibodies. The mechanisms and consequences of these changes remain to be elucidated.