Abstract Interleukin 9 (IL-9)-producing helper T (Th9) cells have a crucial function in allergic
inflammation, autoimmunity, immunity to extracellular pathogens and anti-tumor immune
responses. In addition to Th9, Th2, Th17 and Foxp3+ regulatory T (Treg) cells produce IL-9.
A transcription factor that is critical for IL-9 induction in Th2, Th9 and Th17 cells has not been
identified. Here we show that the forkhead family transcription factor Foxo1 is required for IL-
9 induction in Th9 and Th17 cells. We further show that inhibition of AKT enhances IL-9 …