Immune Suppressive Activity and Lack of T Helper Differentiation Are Differentially Regulated in Natural Regulatory T Cells

The mechanism for controlling Th cytokine expression in natural regulatory T (nTreg) cells is unclear. Here, it was found that under polarizing conditions Foxp3 did not affect Th1 cell, partially inhibited Th17 cell, but greatly inhibited Th2 cell differentiation of conventional CD4 T cells. Under the polarizing conditions, nTreg cells failed to differentiate into Th2 and Th17 cells, but differentiated into IFN-gamma-producing cells. Such Foxp3-transduced CD4 T cells and nTreg cells expressed T-bet, GATA-3, or retinoic acid-related orphan receptor (ROR)gamma t, and retroviral GATA-3 and ROR gamma t could not induce Th2 and Th17 differentiation from nTreg cells. However, regardless of their cytokine profiles, the Foxp3-transduced CD4 T cells and nTreg cells remained immune suppressive. These results suggested that it is possible to convert pathogenic Th cells to Treg-like cells for therapeutic application. In conclusion, our studies show that Foxp3 is sufficient for immune suppression, whereas the inhibition of cytokine expression requires additional mechanisms. The Journal of Immunology, 2009, 183: 3583-3590.