IL23A and colitis: The ability of IL-23 to promote IFN-γ expression in Th17 cells is T-bet dependent in vitro (Lee et al., 2009), raising the possibility that in addition to driving conventional Th1 cell responses, the requirement for T-bet in T cell transfer colitis (Neurath et al., 2002) involves IL-23-dependent modulation of the Th17 cell phenotype.