Vitamin A and the immune system

Vitamin A is required in the diet of all vertebrates, and is metabolized intracellularly to retinoic acid (RA), which is well known as a regulator of cell proliferation and differentiation. RA activates nuclear retinoid receptors and regulates a wide variety of genes. This chapter first discusses vitamin A nutrition and metabolism, and then how inflammation affects the metabolism of vitamin A compounds. Clinically, RA and several analogs are used in the treatment of skin disorders. Vitamin A deficiency is a risk factor for infectious disease. This chapter discusses the role of vitamin A in the immune system, especially in the regulation of T cell differentiation and in innate immunity.