T reg cells get specific

Naturally occurring regulatory T (T reg) cells suppress T cell–driven autoimmunity and chronic inflammation. Although the origin and function of these cells has been widely studied, the specificity of their T cell receptors (TCRs)—whether for self or foreign antigens on target cells—remains a matter of debate. Prevailing opinion comes down on the side of self-antigen. But now Suffia and colleagues (page 777) show that a majority of these T reg cells, at least those that congregate at the site of chronic parasite infection in mice, recognize the bug, not the mouse.

In earlier work, the group showed that this kind of T reg cell accumulated in the skin of mice infected with the parasite Leishmania major, thus hampering the response of effector...