Control of autoimmunity by naturally arising regulatory CD4+ T cells

Naturally acquired immunological self-tolerance is not entirely accounted for by clonal deletion, anergy, and ignorance. It is now well established that the T cell-repertoire of healthy individuals harbors self-reactive lymphocytes with a potential to cause autoimmune disease and these lymphocytes are under dominant control by a unique subpopulation of CD4(+) T cells now called regulatory T cells. Efforts to delineate these Treg cells naturally present in normal individuals have revealed that they are enriched in the CD25(+)CD4(+) population. The identification of the CD25 molecule as a useful marker for naturally arising CD4(+) regulatory T cells has made it possible to investigate many key aspects of their immunobiology, including their antigen specificities and the cellular/molecular pathways involved in their development and their mechanisms of action. Furthermore, reduction or dysfunction of the CD25(+)CD4(+) regulatory T cell population can be responsible for certain autoimmune diseases in humans.