Regulatory T cells

A subpopulation of naive CD4+ T cells that coexpresses the interleukin (IL)-2 receptor α chain, CD25, has been shown to have potent suppressor activity [1–12]. Although they are present in both rodents and humans, the frequencies of CD4+CD25bright cells are higher in rodents than in humans (8%–12% versus 1%–3%, respectively, of CD4+ T cells). CD4+CD25+ cells have been shown to play a vital role in the induction and maintenance of peripheral self-tolerance by preventing the proliferation and activation of autoreactive T cells that have escaped thymic deletion or that recognize extrathymic antigens.