How potentially autoreactive T cells are prevented from being 'switched on' is reported in a paper published online this week in Nature Immunology. Explaining how these potentially harmful cells are activated could lead to new therapies for the prevention of autoimmune diseases, such as diabetes.

Previous work showed that PD-1, a protein expressed on autoreactive T lymphocytes, is essential to prevent autoimmunity and maintain immune cell tolerance for self proteins in mice.

Using a mouse model of type 1 diabetes, Brian Fife and co-workers found that blockade of PD-1 caused a slowdown in the movement of autoreactive T cells. This decreased spontaneous movement allowed autoreactive T cells the opportunity to recognize pancreatic islet cell components. The subsequent release of proinflammatory mediators caused islet cell destruction and clinical diabetes.

Whether these findings are relevant to other T cell-driven autoimmune diseases remains to be seen.