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 (p110δD910A/D910A) are reduced despite enhanced Treg selection in the thymus. p110δD910A/D910A CD4+CD25+Foxp3+ Tregs showed attenuated suppressor function in vitro and failed to secrete IL-10. In adoptive transfer experiments, p110δD910A/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.

Neutrophils are abundant, short-lived leukocytes, and their death by apoptosis is central to hemostasis and the resolution of inflammation, yet the trigger for their entry into apoptosis is unknown. We show here that death receptor signaling, including CD95 death-inducing signaling complex (DISC) formation and caspase 8 activation, occurred early in neutrophil apoptosis. However, death receptor ligation was not required for apoptosis, suggesting a novel mechanism for caspase 8 activation. We detected ceramide generation and clustering of CD95 in lipid rafts early in neutrophil apoptosis, and neutrophil apoptosis and ceramide generation were both significantly inhibited in acid sphingomyelinase knockout (ASM ؊/؊ ) mice compared to wild-type littermates. Further studies revealed that ceramide generation, CD95 clustering, and neutrophil apoptosis were dependent on reactive oxygen species (ROSs) and were preceded by a fall in reduced glutathione levels. We propose that accumulation of ROSs, as a consequence of altered redox status, initiates ligand-independent death receptor signaling via activation of ASM and clustering of preformed DISC components in lipid rafts and is therefore a primary factor limiting neutrophil life span.