It has been suggested recently that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] is involved in the regulation of the immune functions of lymphocytes and in the differentiation of monocytic cells. This report examined the possibility that 1,25(OH)2D3 influences immune functions mediated by monocytic cells by studying its effect on the murine myelomonocytic line WEHI-3. We found that WEHI-3 cells possess 3.3S receptor proteins with high affinity (Kd = 3.3 X 10(-10) M) for 1,25(OH)2D3 that are capable of binding to DNA. Also we found that 1,25(OH)2D3 enhances the interferon-gamma (IFN-gamma)-induced expression of the class II major histocompatibility complex antigens (Ia molecules), and such enhancement leads to increased capacity of the WEHI-3 cells to stimulate antigen-specific Ia-restricted T cell activation. Finally, 1,25(OH)2D3 inhibits the proliferation of WEHI-3 cells, and this inhibition is enhanced in the presence of IFN-gamma. The 1,25(OH)2D3 modulation of IFN-gamma induction of Ia antigens suggests that the hormone might promote monocytes to function more efficiently as antigen-presenting cells.

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