IL-12 inhibits the TGF-β-dependent T cell developmental programs and skews the TGF-β-induced differentiation into a Th1-like direction

The development and differentiation of T helper (Th) cell subsets is a highly plastic process which is strictly regulated by cytokines. Here we show that the transforming growth factor β (TGF-β)-dependent differentiation programs are negatively regulated by interleukin-12 (IL-12). The development of TGF-β-induced regulatory T cells (iTregs) or TGF-β/IL-6 activated Th17 cells from purified mouse CD4+CD25− T cells, stimulated with monoclonal antibody anti-CD3, was abrogated in the presence of IL-12 and a different developmental program was established. On the molecular level, IL-12 inhibited the expression of the lineage specific transcription factors Foxp3 and RORγt in developing Tregs and Th17 cells, respectively. Moreover, IL-12 was able to alter the development of iTregs and Th17 cells even when added to the differentiating cells after 48 h of the culture. The cells activated in the presence of TGF-β and IL-12 had an increased expression of the Th1 transcription factor T-bet, produced Th1 cytokines interferon γ and IL-2 and expressed IL-18 receptor and C-C chemokine receptor type 5 which are the phenotypic markers characteristic for Th1 cells. Furthermore, the cells activated in the presence of both TGF-β and IL-12, and not of TGF-β only, stimulated macrophages to produce nitric oxide. Altogether, these results indicate that IL-12 is a superior cytokine that has the ability to skew the already ongoing TGF-β-dependent iTreg or Th17 developmental program into Th1-like direction.