Autoimmune disease is the consequence of an immune response against self-antigens that results in the damage and eventual dysfunction of target organs. Although the triggering event in most autoimmune diseases is unknown, an infectious cause has long been postulated to explain the development of autoimmunity. Molecular mimicry is one mechanism by which infectious agents (or other exogenous substances) may trigger an immune response against autoantigens. According to this hypothesis a susceptible host acquires an infection with an agent that has antigens that are immunologically similar to the host antigens but differ sufficiently to induce an immune response when presented to . . .