Antigen-presenting cell activation: a link between infection and autoimmunity?

The onset of autoimmune diseases such as type I diabetes and multiple scler osis is often thought to be associated with infection. This has led to stud ies of molecular mimicry between infectious agents and the self-antigens as sociated with autoimmunity. Despite many claims, however, a single causativ e infectious agent for autoimmunity has not been found. An alternative poss ibility is that many infectious agents are capable of non-specifically enha ncing the likelihood of an autoimmune attack. Here we show how infectious a gents may activate antigen-presenting cells leading to the activation of au toreactive T cells by otherwise innocuous antigens. The mechanism of activa tion involves upregulation of co-stimulatory molecules on the antigen-prese nting cell resulting in a lowering of the threshold required for activation . These results help explain how diverse infectious agents could cause auto immune disease in susceptible individuals. (C) 2001 Academic Press.