Role of Vitamin A in Gut Mucosal Immunity

Abstract

The deployment of immune cells is essential in the gut since it has a wide surface area directly facing to the outer world. In general, there are certain rules for lymphocytes to be deployed into tissues. Nave T cells can immigrate into the secondary lymphoid organs, but cannot immigrate into non-lymphoid tissues. However, once they are activated in a secondary lymphoid organ and become effector/memory T cells, they can selectively immigrate into the tissue associated with the secondary lymphoid organ where they were activated. For example, T cells activated in the gut-associated lymphoid organs, Peyer's patches and mesenteric lymph nodes, express the gut-homing receptors, integrin α4β7 and chemokine receptor CCR9, and become capable of immigrating into the small intestinal tissues. We found that dendritic cells in gut-associated lymphoid organs imprint gut-homing specificity on T cells by producing retinoic acid from vitamin A and giving it to T cells during antigen presentation. Furthermore, retinoic acid also plays a critical role in imprinting B cells with gut-homing specificity and inducing their differentiation to IgA-producing cells.