Epithelial retinoic acid receptor β regulates serum amyloid A expression and vitamin A-dependent intestinal immunity

Vitamin A is a dietary component that is essential for the development of intestinal immunity. Vitamin A is absorbed and converted to its bioactive derivatives retinol and retinoic acid by the intestinal epithelium, yet little is known about how epithelial cells regulate vitamin A-dependent intestinal immunity. Here we show that epithelial cell expression of the transcription factor retinoic acid receptor beta (RA beta) is essential for vitamin A-dependent intestinal immunity. Epithelial RAR beta activated vitamin A-dependent expression of serum amyloid A (SAA) proteins by binding directly to Saa promoters. In accordance with the known role of SAAs in regulating Th17 cell effector function, epithelial RAR beta promoted IL-17 production by intestinal Th17 cells. More broadly, epithelial RAR beta was required for the development of key vitamin A-dependent adaptive immune responses, including CD4(+) T-cell homing to the intestine and the development of IgA-producing intestinal B cells. Our findings provide insight into how the intestinal epithelium senses dietary vitamin A status to regulate adaptive immunity, and highlight the role of epithelial cells in regulating intestinal immunity in response to diet.