Why does the body's immune system turn on it, creating autoimmune diseases like diabetes ? Emil Unanue, M.D., of Washington University School of Medicine in St. Louis, believes the answer can be found in an improved understanding of two features of the Immune system. First, the nature of the immune response, triggered when small pieces of protein from foreign cells are picked up by specialized cells of the immune system. Second, the way the body "trains" its immune system and eliminates dangerous cells.

In an autoimmune disease such as diabetes, it is clear that the pieces from the person's own proteins bind to the immune cells, causing a reaction not to an enemy but to the beta cells of the pancreas. It is this reaction that kills the beta cells and stops insulin production, causing diabetes. In studying this process at the cellular level in diabetes for the first time, researchers have found that the chemical bond formed in an autoreactive response that involved the person's own proteins is very weak compared to normal immune response bonds.

This weak bond presents a problem in the thymus, where the immune system literally gets rid of immune cells that have bound to proteins. The weak bond releases quickly, making it difficult for the thymus to catch the renegade T cells. This allows them to survive, to cause disease later on. Dr. Unanue's team will examine the nature of the T-cell bond in diabetes and look for a genetic link to increased risk.