Vitamin D and Adaptive Immunology in Health and Disease

Abstract The adaptive immune system provides antigen-specific long-lasting immune responses that are mediated by T and B lymphocytes and are highly sensitive to modulation by vitamin D. In particular, vitamin D has been shown to suppress type 1 (IFNγ-mediated) and type 17 (IL-17A-mediated) T effector lymphocyte responses both in vitro and in vivo, while enhancing T regulatory lymphocyte responses. The latter are vital for preventing inappropriate pathological immune responses that can drive diseases such as multiple sclerosis and asthma. Notably, each of these conditions is detrimentally associated with vitamin D insufficiency. Vitamin D can regulate lymphocytes through direct genomic actions and also indirectly by acting on other cells of the immune microenvironment, which interact with lymphocytes. The reported actions of vitamin D on the adaptive immune system are diverse, and at times contrary, suggesting that the effects of vitamin D on immune responses are context-dependent. Vitamin D appears to act as a temporal regulator of adaptive immune responses to maintain health in the face of the threat of disease.