Dendritic cell modulation by 1α,25 dihydroxyvitamin D₃ and its analogs: A vitamin D receptor-dependent pathway that promotes a persistent state of immaturity in vitro and in vivo

Dendritic cells (DCs) play a central role in regulating immune activation and responses to self. DC maturation is central to the outcome of antigen presentation to T cells. Maturation of DCs is inhibited by physiological levels of 1α,25 dihydroxyvitamin D₃ [1α,25(OH)₂D₃] and a related analog, 1α,25(OH)₂-16-ene-23-yne-26,27-hexafluoro-19-nor-vitamin D₃ (D₃ analog). Conditioning of bone marrow cultures with 10^-10 M _D3 analog resulted in accumulation of immature DCs with reduced IL-12 secretion and without induction of transforming growth factor β1. These DCs retained an immature phenotype after withdrawal of D₃ analog and exhibited blunted responses to maturing stimuli (CD40 ligation, macrophage products, or lipopolysaccharide). Resistance to maturation depended on the presence of the 1α,25(OH)₂D₃ receptor (VDR). In an in vivo model of DC-mediated antigen-specific sensitization, D₃ analog-conditioned DCs failed to sensitize and, instead, promoted prolonged survival of subsequent skin grafts expressing the same antigen. To investigate the physiologic significance of 1α,25(OH)₂D₃/VDR-mediated modulation of DC maturity we analyzed DC populations from mice lacking VDR. Compared with wild-type animals, VDR-deficient mice had hypertrophy of subcutaneous lymph nodes and an increase in mature DCs in lymph nodes but not spleen. We conclude that 1α,25(OH)₂D₃/VDR mediates physiologically relevant inhibition of DC maturity that is resistant to maturational stimuli and modulates antigen-specific immune responses in vivo.