Retinoic Acid and Immunity

Abstract

Vitamin A and its active metabolite retinoic acid (RA) are key players in the regulation of the immune response, especially at the mucosal borders, where RA is particularly abundant. Retinoic acid receptors (RARs), via their transcriptional activity, modulate the expression of many genes in many types of immune cells, such as T cells, B cells, macrophages or dendritic cells. Among the pleiotropic effects on immune cells, the ability of RA and RARs to confer gut tropism and to promote the generation of regulatory T cells (Tregs) are undoubtedly the most prominent. However, depending on the physiopathological context, RA can also promote inflammation. These multiple and sometimes paradoxical properties of RA reflect the importance of this nutrient‐derived molecule in the fine‐tuning of the immune system. Key Concepts Retinoic acid is the active metabolite of Vitamin A, a nutrient essential for many biological processes. Retinoic acid receptors act as transcription factors to regulate the expression of several genes. Retinoic acid induces the expression of gut homing receptors on several immune cells. Retinoic acid induces the generation of regulatory T cells that control the immune and inflammatory response. In certain physiopathological contexts, retinoic acid can act as an adjuvant to promote inflammation.

Pharmacological Modulation of Immune Responses by Nutritional Components

“…There are three RAR isoforms, RARa, b, and c (Cunningham and Duester, 2015). RAR has the ability to modify the expression of numerous genes in multiple immune-cell types, such as T cells, B cells, macrophages, and dendritic cells, via transcriptional activity and downstream signaling pathway activation (Larange, 2017). The RAR/RXR receptor is involved in wound healing, development of the nervous and skeletal systems, myeloid development, and embryonic development (Nagy et al, 2012).…”