Autoimmune diseases such as rheumatoid arthritis and Type 1 diabetes are thought to arise when people with a genetic susceptibility to autoimmunity encounter something in the environment that triggers their immune systems to attack their own bodies. Scientists have made progress in identifying genetic factors that put people at risk, but the environmental triggers have proven more elusive. Researchers at Washington University School of Medicine in St. Louis have now discovered that a viral infection can set a destructive process in motion, culminating in autoimmunity long after the infection has resolved. The researchers investigated the impact of viral infection on T cells, a group of immune cells that play a key role in many autoimmune conditions. In the study, which was conducted in mice, the researchers showed that murine roseolovirus infects the thymus--the organ where self-destructive T cells are identified and eliminated--and disrupts the screening process in the organ. Months after infection, the mice develop an autoimmune disease of the stomach driven by self-destructive T cells.