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.