Abstract
This paper addresses the molecular mechanisms by which vitamin A (retinol) could influence the immune system, and the relationships of these mechanisms to the better known mechanisms in which retinol affects other non-immune biological phenomena, such as epithelial cell differentiation, embryogenesis, and organ development. In many tissues, the sequential molecular actions of the reti-noids have been well defined. However, major questions remain about the action of retinoids on lymphocytes. Much evidence indicates an important role for vitamin A molecules (called retinoids) in the function of both the cellular and the humoral arms of the immune system.
Attention should also be paid to the nuclear retinoic acid receptors (RAR) in various cells. These protein receptors are similar to those which bind steroids, thyroid hormones, and vitamin D. The nuclear retinoic acid receptors, and another analogous receptor family initially called “orphan receptor” now designated “nuclear RXR receptors,” together with other described cellular binding proteins, appear to be involved in regulating, as well as transmitting, the effects of the retinoids on the molecular machinery of various body cells, including the lymphocytes.