Fig. 2: Dietary vitamin A stimulates retinoic acid-producing dendritic cell differentiation in the gut.
From: The role of retinoic acid in the production of immunoglobulin A
Dietary vitamin A is metabolized by intestinal epithelial cells (IECs) into retinoic acid (RA). Close interaction of intestinal dendritic cells (DCs) with the epithelium skews the DCs into an RA-DC phenotype characterized by the expression of CD103 and active ALDH enzymes. These local DCs provide RA to LP-residing IgM+ B cells, allowing them to undergo class switching to IgA. Moreover, RA-DCs migrate from the LP into the mesenteric lymph nodes (MLNs) to provide RA to B cells. Dietary vitamin A is also important in the development of tolerogenic RA-DCs within Peyer’s patches (PPs). Within organized lymphoid organs, the production of RA primes B lymphocytes to express the gut-homing receptor α4β7 and undergo IgA class switching. Activated B cells leave the PPs and MLNs, recirculate via the bloodstream and finally enter the gut using α4β7, where they populate the LP and become resident IgA-secreting plasma cells. Locally, IgA is produced as a dimeric molecule and transported through the epithelial layer, where it binds to the microbiota, thereby regulating its composition.
