In a healthy gut, a thin layer of mucus-lined intestinal wall separates billions of beneficial bacteria from the immune system. But in the throes of an intestinal infection, the walls are breached and both infectious and beneficial microbes penetrate the intestinal wall.
Immunologist Timothy Hand of the National Institute of Allergy and Infectious Diseases in Bethesda, Md., and his colleagues show online August 23 in Science that in mice these breaches cause immune cells to lose their tolerance for the beneficial bacteria. Worse yet, the T cells form long-lasting memory cells that harbor the ability to bring the beneficial bacteria under friendly fire in subsequent encounters.
The new findings suggest a role for misdirected T cells in inflammatory bowel ailments such as Crohn’s disease, in which there is evidence of barrier breaching and T cell dysfunction. In this way, gut infections might prime T cells for a subsequent destructive role and, Hand suggests, predispose some people to the disease.