Fig. 1.

The three components of the intestinal mucosal barrier and the impact of diet and specific immune mechanisms involved in maintaining the integrity of the barrier. Diet can reinforce both the structure and function of the intestinal barrier, for example, through the production of short-chain fatty acids (SCFAs) by the gut microbiota, which are used by the colonic epithelium as a source of energy and can, independently, induce immune tolerance via T regulatory (Treg) cells. As another example, metabolites in diet can activate innate lymphoid cells (ILCs) to produce IL-22, which, in turn, can enhance the production of mucin and antimicrobial peptides (AMPs) by the intestinal epithelium to fortify gut barrier function. Plasma cells, a component of the mucosal immune system, can also produce IgA, which is secreted into the intestinal mucus layer. In this manner, the intestinal epithelium, the most important component of the intestinal barrier, has both structural and functional components to protect the host from the luminal contents of the intestinal tract. Th17, T helper type 17. [Modified from Kamada and Núñez (108) with permission.]