In vivo upregulation of interleukin-4 is one mechanism underlying the immunoregulatory effects of 1,25-dihydroxyvitamin D₃¹

The active form of vitamin D (1,25-(OH)₂D₃) is a potent immune system regulator. In vivo the oral administration of 1,25-(OH)₂D₃ completely prevents experimental autoimmune encephalomyelitis (EAE), significantly prolongs allograft survival, and prevents collagen-induced arthritis. 1,25- (OH)₂D₃ given to mice increased IL-4 protein and transcript levels. We have now tested the efficacy of 1,25-(OH)₂D₃ on EAE development and allograft survival in IL-4-deficient [knockout (ko)] mice. 1,25-(OH)₂D₃ was found to be much less effective in the absence of IL-4, suggesting that IL-4 production is a significant factor in the action of 1,25-(OH)₂D₃ on the immune system. (C) 2000 Academic Press.