Cutting edge: the phosphoinositide 3-kinase p110 delta is critical for the function of CD4+CD25+Foxp3+ regulatory T cells.

CD4 + CD25 + Foxp3 + regulatory T cells (Tregs) contribute to the maintenance of peripheral tolerance by inhibiting the expansion and function of conventional T cells. Treg development and homeostasis are regulated by the Ag receptor, costimulatory receptors such as CD28 and CTLA-4, and cytokines such as IL-2, IL-10, and TGF-β. Here we show that the proportions of Tregs in the spleen and lymph nodes of mice with inactive p110δ PI3K (p110δ D910A/D910A ) are reduced despite enhanced Treg selection in the thymus. p110δ D910A/D910A CD4 + CD25 + Foxp3 + Tregs showed attenuated suppressor function in vitro and failed to secrete IL-10. In adoptive transfer experiments, p110δ D910A/D910A T cells failed to protect against experimental colitis. The identification of p110δ as an intracellular signaling protein that regulates the activity of CD4 + CD25 + Foxp3 + Tregs may facilitate the further elucidation of the molecular mechanisms responsible for Treg-mediated suppression.