STAT6 inhibits TGF-β1-mediated Foxp3 induction through direct binding to the Foxp3 promoter, which is reverted by retinoic acid receptor

It has been shown that transforming growth factor beta (TGF-beta 1) is critical in the generation of CD4(+)CD25(+)Foxp3(+) -inducible regulatory T cells (iTregs) from naive CD4(+)T cells. However, in contrast to natural Tregs, TGF-beta 1-induced iTregs rapidly lose both Foxp3 expression and suppression activity. We found that TGF-beta 1-induced Foxp3 levelswere maintained by the addition of the anti-interleukin 4 (IL-4) antibody or by STAT6 gene deletion. Thus, IL-4 is an important suppressor of Foxp3 induction, and T helper 2 development is a major cause for the disappearance of iTreg during long culture. Using promoter analysis in EL4 cells and primary T cells, we identified a silencer region containing a STAT6 binding site. STAT6 binding to this site reduced TGF-beta 1-mediated Foxp3 promoter activation and chromatin modification. Retinoic acid has also been shown to suppress loss of Foxp3 induced by TGF-beta 1 Retinoic acid in the presence of TGF-beta 1 reduced STAT6 binding to the Foxp3 promoter and enhanced histone acetylation, thereby reverting the effect of IL-4. We propose that antagonistic agents for neutralizing IL-4 could be a novel strategy to facilitate inducible Treg cell generation and the promotion of tolerance in Th2-dominated diseases such as allergy.