T-bet binds to and represses the transcription of Socs1, Socs3, and Tcf7. (A) RNA was isolated from WT and T-bet–deficient primary CD4⁺ T cells either directly ex vivo or after polarization in Th1 conditions for 7 d. Socs1, Socs3, and Tcf7 transcript levels were analyzed by quantitative RT-PCR. Results were normalized to the values obtained for Actb and are expressed as a ratio relative to the T-bet^−/− sample. (B) RNA was isolated from T-bet^−/− CD4⁺ T cells transduced with an empty expression vector or one containing T-bet. Transcript levels were determined by quantitative RT-PCR, and the data were normalized and represented as in A. (C) T-bet association with the promoters of Socs1, Socs3, and Tcf7 was assessed by ChIP. Chromatin was isolated from either WT or T-bet^−/− CD4⁺ T cells stimulated under Th1 conditions for 7 d. Chromatin samples were immunoprecipitated with antibodies to T-bet or a nonspecific antibody control. After purification, immunoprecipitated DNA was quantitated by qPCR. qPCR signals were normalized to the nonspecific antibody control as well as a standardized aliquot of the input chromatin. (A–C) Data represent the mean of three (A and B) or five (C) independent experiments (error bars indicate SEM).