Vitamin A and retinoic acids immunomodulation on human gut lymphocytes.

Abstract Epidemiological studies have suggested an important immunomodulatory role for vitamin A and other related vitamin A compounds in adults and children. Although vitamin A is absorbed via the gastrointestinal tract, its affect on the gut mucosal immune cells has not been adequately investigated. We investigated the in-vitro effect of vitamin A (retinol) and its retinoid acid (RA) compounds (13- cis - and all trans -retinoic acids) on the human gut mucosal immune system as represented by colonic lamina propria lymphocyte (LPL) proliferation, and ornithine decarboxylase (ODC) activity. Results showed that retinol suppressed and trans -retinoic acid enhanced thymidine incorporation into LPL. 13- cis retinoic acid did not significantly affect LPL DNA synthesis. Similarly, retinol (0.025 μ/ml and 10 μg/ml) and 13- cis retinoic acid (conc. 10 μ/ml) suppressed, while all trans -retinoic acid (conc. 10 μg/ml) enhanced ODC activity in PHA-stimulated LPL. Interestingly, the effects of retinol and all trans -RA were abolished when LPL were previously depleted of macrophages. Addition of monocyte-associated lymphokines, IL-1 and IL-6, showed that IL-1 partially replaced the enhancing effect of all trans -RA previously observed on LPL thymidine incorporation. IL-6 did not affect LPL DNA synthesis irrespective of the vitamin A compound used. We conclude that retinol and retinoid acids (13- cis , all trans -) may alter the human colonic immune system possibly via IL-1 cytokine, but not via IL-6. The data suggest that vitamin A and its retinoid compounds may participate in the modulation of the gut immune system.