Interleukin-2 is essential for CD4+CD25+ regulatory T cell function.

Constitutive expression of CD25, the IL-2 receptor alpha-chain, defines a distinct population of CD4+ T cells (Treg) with suppressive activity in vitro and in vivo. IL-2 has been implicated in the generation and maintenance of Treg, however, a functional contribution of the IL-2 receptor during suppression is thus far unknown. We show that IL-2 is required for Treg function in vitro, since suppression is completely abrogated by selective blocking of the IL-2 receptor on Treg during co-culture with responder T cells.