The paradoxical effects of vitamin D on type 1 mediated immunity

Low vitamin D status is associated with an increased risk of Th1 mediated autoimmune diseases like inflammatory bowel disease. 1,25(OH)2D3 treatments have been shown to suppress Th1 mediated immunity and protect animals from experimental autoimmunity. Th1 mediated immunity is important for clearance of a number of different infectious diseases. For tuberculosis 1,25(OH)2D3 treatment is associated with decreased Th1 mediated immunity but increased bactericidal activity. Systemic candidiasis is unaffected by 1,25(OH)2D3 treatment. The seemingly paradoxical effects of 1,25(OH)2D3 and vitamin D on Th1 mediated autoimmunity versus infectious immunity point to a broad array of vitamin D targets in the immune system. The interplay of these vitamin D targets and their impact on the host-immune response then dictate the outcome.