Impaired Vitamin A-Mediated Mucosal IgA Response in IL-5 Receptor-Knockout Mice

To clarify actions of vitamin A on mucosal immunity associated with interleukin-5 (IL-5), we examined effects of vitamin A on mucosal IgA level in IL-5 receptor α-chain-knockout (IL-5Rα−/−) mice. Daily supplementation of retinyl acetate (1 mg/mouse) increased Th2 cytokine levels and a number of their positive cells in the small intestinal mucosa of IL-5Rα−/− mice, as observed in wild-type or IL-5Rα+/− mice. Wild-type and heterozygous mice increased the IgA level and a number of IgA-containing cells in the mucosa in response to the vitamin A treatment, but not in IL-5Rα−/− mice. Retinyl acetate increased anti-cholera toxin (CT) IgA level in the mucosa of wild-type mice, improving their survival rate after an exposure to 0.4 mg of CT. However, retinyl acetate failed to induce resistance to CT toxicity in IL-5Rα−/− mice. Our results suggest that IL-5 may play an important role in an action of vitamin A on mucosal IgA system.