Guarding the immune system:: Suppression of autoimmunity by CD4+CD25+ immunoregulatory T cells

CD4(+)CD25(+)Foxp3(+) T cells (CD25(+) T regulatory [Treg] cells) are a naturally occurring suppressor T-cell population that regulates a wide variety of immune responses. A major function of CD25(+) Treg cells is to inhibit the activity of self-reactive T cells that can potentially cause autoimmune disease. This review examines the recent advances in CD25(+) Treg cell biology, with particular focus on the thymic and peripheral development of CD25(+) Treg cells, the signals that promote their expansion and maintenance in the periphery and the mechanism by which they mediate their suppressor activity in peripheral lymphoid tissues. An understanding of these issues is likely to facilitate the development of CD25(+) Treg-cell-based therapies for the treatment of autoimmune disease.