1-alpha,25-Dihydroxyvitamin D3 (1,25(OH)(2)D(3)) hampers the maturation of fully active immature dendritic cells from monocytes.

OBJECTIVE

To study the effects of the active metabolite of vitamin D(3), 1,25(OH)(2)D(3), an immunomodulatory hormone, on the generation of so-called immature dendritic cells (iDCs) generated from monocytes (Mo-iDCs).

DESIGN AND METHODS

Human peripheral blood monocytes were cultured to iDCs in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-4 for 1 week, with or without the extra addition of 10(-8) M 1,25(OH)(2)D(3) to the culture. Their phenotypes (CD14, CD1a, CD83, HLA-DR, CD80, CD86 and CD40 expression) were examined by fluorescence-activated cell sorting, and their T-cell stimulatory potential was investigated in allogeneic mixed lymphocyte reaction (allo-MLR). Additionally, their in vitro production of IL-10, IL-12 and transforming growth factor beta (TGF-beta) were examined by using the enzyme-linked immunosorbent assay.

RESULTS

When 1,25(OH)(2)D(3) was added to monocytes in culture with GM-CSF and IL-4, it hampered the maturation of Mo-iDCs. First, the phenotype of the 1,25(OH)(2)D(3)-differentiated DCs was affected, there being impaired downregulation of the monocytic marker CD14 and impaired upregulation of the markers CD1a, CD83, HLA-DR, CD80 and CD40. CD86 was expressed on more 1,25(OH)(2)D(3)-differentiated DCs. Secondly, the T-cell stimulatory capability of 1,25(OH)(2)D(3)-differentiated DCs was upregulated relative to the original monocytes to a lesser degree than DCs differentiated without 1,25(OH)(2)D(3) when tested in an allo-MLR. With regard to the production of cytokines, Staphylococcus aureus cowan 1 strain (SAC)-induced IL-10 production, although not enhanced, remained high in 1,25(OH)(2)D(3)-differentiated DCs, but was strongly downregulated in DCs generated in the absence of 1,25(OH)(2)D(3). SAC/interferon-gamma-induced IL-12 production was clearly upregulated in both types of DC relative to those of the original monocytes, and TGF-beta production was downregulated.

CONCLUSION

Our data confirm earlier reports showing that 1,25(OH)(2)D(3) hampers the maturation of fully active immunostimulatory major histocompatibility complex (MHC) class II+, CD1a+, CD80+ DCs from monocytes. Our data supplement the data from other reports by showing that the expression of CD86 was upregulated in 1,25(OH)(2)D(3)-differentiated DCs, whilst the capacity for IL-10 production remained high. Collectively, these data are in line with earlier descriptions of suppressive activities of this steroid-like hormone with respect to the stimulation of cell-mediated immunity.