From the diet to the nucleus: Vitamin A and TGF-β join efforts at the mucosal interface of the intestine

The vitamin A metabolites, including retinoic acid (RA), form ligands for retinoic acid-related nuclear receptors and together they play pleiotropic roles in various biological processes. Recently, we described that RA also functions as a key modulator of transforming growth factor-beta (TGF-β)-driven immune deviation, capable of suppressing the differentiation of interleukin-17 secreting T helper cells (TH17) and conversely promoting the generation of Foxp3+ T regulatory (Treg) cells. This review will focus on the role of RA in the reciprocal TGF-β-driven differentiation of TH17 and Treg and on the importance of such regulatory mechanism to control a functional immune system, in particular at the mucosal interface of the intestine.