Temporal dissection of T-bet functions.

T-bet is a transcription factor of the T-box family that regulates the expression of numerous immune system-associated genes. T-bet directs the acquisition of the Th1-associated genetic program in differentiating CD4(+) lymphocytes. It also influences the development of NK and NKT cells through its regulation of the IL-2/IL-15Rbeta-chain (CD122) and the trafficking of these lymphocytes through CxCR3. The temporal requirements of T-bet activity for the production of IFN-gamma and the regulation of CD122 and CxCR3 expression remain undefined. We produced an ectopically controllable form of T-bet by fusing its C-terminal domain with a mutated ligand-binding domain of human estrogen receptor alpha. By temporally controlling the expression of T-bet-estrogen receptor alpha by the addition or removal of 4-hydroxytamoxifen (4-HT), we show that IFN-gamma, CD122, and CxCR3 are direct gene targets of T-bet whose expression are acutely regulated by T-bet activity.