The contribution of transcription factor IRF1 to the interferon-γ–interleukin 12 signaling axis and TH1 versus TH-17 differentiation of CD4+ T cells

Interleukin-12 (IL-12) and interferon-γ (IFN-γ) drive T helper type 1 (TH1) differentiation, but the mechanisms underlying the regulation of the complicated gene networks involved in this differentiation are not fully understood. Here we show that the IFN-γ-induced transcription factor IRF1 was essential in TH1 differentiation by acting on Il12rb1, the gene encoding the IL-12 receptor β1 subunit (IL-12Rβ1). IRF1 directly interacted with and activated the Il12rb1 promoter in CD4+ T cells. Notably, the IRF1-dependent induction of IL-12Rβ1 was essential for IFN-γ–IL-12 signaling but was dispensable for IL-23–IL-17 signaling. Because both IL-12 and IL-23 bind to and transmit signals through IL-12Rβ1, our data suggest that distinct thresholds of IL-12Rβ1 expression are required for TH1 versus TH-17 differentiation.