Retinoic Acid in the Immune System

On occasion, emerging scientific fields intersect and great discoveries result. In the last decade, the discovery of regulatory T cells (Treg) in immunity has revolutionized our understanding of how the immune system is controlled. Intersecting the rapidly emerging field of Treg function, has been the discovery that retinoic acid (RA) controls both the homing and differentiation of Treg. Instantly, the wealth and breadth of knowledge of the molecular basis for RA action, its receptors, and how it controls cellular differentiation can and will be exploited to understand its profound effects on Treg. Historically, vitamin A deprivation and repletion and RA agonists have been shown to profoundly affect immunity. Now these findings can be interpreted in light of the revelations that RA controls leukocyte homing and Treg function.