Suppressive Effect of 1α,25-Dihydroxyvitamin D3 on Type I IFN-Mediated Monocyte Differentiation into Dendritic Cells: Impairment of Functional Activities and Chemotaxis

Abstract

Dendritic cells (DCs) generated by a single-step exposure of human monocytes to type I IFN and GM-CSF (IFN-DCs) are endowed with potent immunostimulatory activities and a distinctive migratory response to specific chemokines. In this study, we evaluated the effects of 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3), the biologically active metabolite of vitamin D3, on the DC differentiation/activation induced by type I IFN. We found that 1,25(OH)2D3 prevented the generation of IFN-DCs when added to freshly isolated monocytes, and was capable of redirecting already differentiated IFN-DCs toward a more immature stage, as revealed by their immunophenotype, reduced allostimulatory activity, and impaired LPS-induced production of Th1-polarizing cytokines. Control and 1,25(OH)2D3-treated IFN-DCs exhibited a similar expression of vitamin D receptor, as well as comparable cell death rates. Furthermore, the chemotactic response of IFN-DCs to CCL4 and CCL19 was markedly reduced or completely abrogated by 1,25(OH)2D3. Despite these changes in the IFN-DC migratory behavior, the expression of CCR5 and CCR7 and the calcium fluxes triggered by CCL4 and CCL19 were not affected. These findings indicate that, in this innovative single-step DC generation model from monocytes, the suppressive effect of 1,25(OH)2D3 is associated with a potent impairment of DC migration in response to inflammatory and lymph node-homing chemokines, thus unraveling a novel mechanism involved in 1,25(OH)2D3-mediated immunomodulation.