Expression of retinaldehyde dehydrogenase enzymes in mucosal dendritic cells and gut-draining lymph node stromal cells is controlled by dietary vitamin A

The vitamin A metabolite retinoic acid (RA) plays a crucial role in mucosal immune responses. We demonstrate in this study that RA-producing retinaldehyde dehydrogenase (RALDH) enzymes are postnatally induced in mesenteric lymph node (MLN) dendritic cells (DCs) and MLN stromal cells. RALDH enzyme activity in lamina propria-derived CD103(+) MLN-DCs did not depend on TLR signaling. Remarkably, RA itself could directly induce RALDH2 in both DCs and stromal cells in vitro. Furthermore, upon provision of a vitamin A-deficient diet, it was found that RA-mediated signaling was strongly reduced within the small intestines, while RALDH2 mRNA and RALDH enzyme activity in lamina propria DCs and MLN-DCs, as well as RALDH2 mRNA expression in MLN stromal cells, were strongly diminished. Moreover, supply of vitamin A to vitamin A-deficient mice restored RA-mediated signaling in the intestine and RALDH activity in lamina propria-derived CD103(+) MLN-DCs. Our results show that RA-dependent signaling within the intestine is indispensable for RALDH activity in the draining MLN.