The Transcription Factor T-bet Is Induced by Multiple Pathways and Prevents an Endogenous Th2 Cell Program during Th1 Cell Responses

T-bet is a critical transcription factor for T helper 1 (Th1) cell differentiation. To study the regulation and functions of T-bet, we developed a T-bet-ZsGreen reporter mouse strain, in which GFP faithfully reflects the expression of T-bet. By using this tool, we report that signals elicited by IL-12 and IFNg are redundant in inducing T-bet in mice infected with Toxoplasma gondii and that T-bet does not contribute to its own expression when induced by IL-12 and IFNg. While both T-bet and Stat4 are critical for IFNg production, IFNg signaling is dispensable. Strikingly, loss of T-bet results in activation of an endogenous Th2 program in cells expressing T-bet-ZsGreen. Genome-wide analyses suggest T-bet directly induces Th1-related genes but indirectly suppresses Th2-related genes. Our study revealed redundancy and synergy among several Th1-inducing pathways in regulating the expression of T-bet and IFNg, and a critical role of T-bet in suppressing an endogenous Th2 program. RNA-Seq experiments were performed using total RNAs isolated from both wild type and Tbx21-/- Th1 cells in duplicates. Tbet ChIP-seq was performed using wild type Th1 cells. H3K4me1 and H3K27me3 ChIP-seq was performed using both wild type and Tbx21-/- Th1 cells.