Expression of 1,25-dihydroxyvitamin D₃ receptor in the immune system

In addition to its role in calcium and skeletal homeostasis, there is increasing evidence that the hormonal form of vitamin D, 1,25- dihydroxyvitamin D₃, appears to serve as a modulator of the immune system. We have determined the level of the 1,25-dihydroxyvitamin D₃ receptor (VDR) in resting and activated lymphocytes by immuno- and ligand-binding assays. As expected from previous work, the total T lymphocyte population contains VDR whose levels are increased when activated and treated with 1,25- dihydroxyvitamin D₃. Surprisingly, the highest concentrations of VDR are found in CD8 lymphocytes, although significant amounts are also present in CD4 lymphocytes. Furthermore, B lymphocytes do not contain detectable amounts of VDR. Cells of the monocyte/macrophage lineage possess small amounts of VDR that are not affected by activation but are increased by treatment with 1,25- dihydroxyvitamin D₃. These results suggest that CD8 lymphocytes may be a major site of 1,25-dihydroxyvitamin D₃ action, while B lymphocytes are likely not directly regulated by 1,25-dihydroxyvitamin D₃. (C) 2000 Academic Press.