A novel transcription factor, T-bet, directs Th1 lineage commitment

Naive T helper cells differentiate into two subsets, Th1 and Th2, each with distinct functions and cytokine profiles. Here, we report the isolation of T-bet, a Th1-specific T box transcription factor that controls the express ion of the hallmark Th1 cytokine, IFN gamma. T-bet expression correlates wi th IFN gamma expression in Th1 and NK cells. Ectopic expression of T-bet bo th transactivates the IFN gamma gene and induces endogenous IFN gamma produ ction. Remarkably, retroviral gene transduction of T-bet into polarized Th2 and Tc2 primary T cells redirects them into Th1 and Tc1 cells, respectivel y, as evidenced by the simultaneous induction of IFN gamma and repression o f IL-4 and IL-5. Thus, T-bet initiates Th1 lineage development from naive T hp cells both by activating Th1 genetic programs and by repressing the oppo sing Th2 programs.