ABSTRACT
Vitamin A is essential for many biological functions, including maintaining growth and vision. Vitamin A deficiency impairs many aspects of innate and adaptive immunity, leading to an increased severity of infections and increased risk of death for infants and young children in areas of the world with a high burden of infection and a high risk of vitamin A deficiency. The role of vitamin A in enhancing mucosal immunity by affecting immune cell development and targeting to mucosal sites presumably accounts for some of this beneficial effect of vitamin A, and it might also be beneficial in diminishing chronic inflammation. The innate immune system is comprised of barrier defenses that typically involve the response of a class of leukocytes termed myeloid cells, in contrast to the lymphoid cells, which comprise the principal cellular component of the adaptive immune system. The adaptive immune system is comprised primarily of lymphocytes, including T-cells and B-cells.
