Vitamin A and the Immune System

Vitamin A (retinol) is a lipid-soluble vitamin essential to multiple biological processes such as vision, reproduction, embryogenesis, and development of the nervous system. Retinoic acid (RA), the biologically active form of vitamin A, plays a crucial role in the development and regulation of the immune system. Recent evidence indicates that RA influences the functions of various populations of cells of innate and adaptive immune system. Vitamin A deficiency (VAD) has been shown to confer defects in both innate and adaptive immune compartments, and therefore impair immunity against pathogens. RA contributes to immune tolerance by suppressing effector T cell responses, which result in inhibition of tissue inflammation in autoimmune diseases. Moreover, RA can cause gut tropism by inducing the expression of gut-tropic integrins on T cells. This chapter discusses the effect of RA on the immune system in infectious and autoimmune diseases. Also, how RA affects the interplay between effector and regulatory T cells is addressed.