Vitamin D receptor quantitation in human blood mononuclear cells in health and disease

Vitamin D receptor (VDR) concentration was quantitated in human peripheral blood mononuclear cells (PBMC) from patients with absorptive hypercalciuria (AH) and patients with high 1,25(OH)₂D₃ due to acquired or transient disease states and the results compared to those in normal subjects. VDR concentration in resting cells was not different between the three groups and represented constitutive receptor expression of monocytes. Following activation with phytohemagglutinin, patients with hypercalcitriolemia demonstrated significantly greater VDR concentrations. Patients with AH demonstrated a normal value for the group, but 6 patients had significantly greater concentrations of VDR despite normal plasma 1,25(OH)₂D₃ in four of the patients. Proliferation, as assessed from [³H]thymidine incorporation was inversely correlated with serum 1,25(OH)₂D₃ and was significant (R = -0.299, p = 0.048). Taken together, the results suggest that PBMC provide a useful system for studying VDR status in transient or acquired states of hypercalcitriolemia. Furthermore, the studies in patients with absorptive hypercalciuria disclosed it to be a heterogenous disorder, characterized by both vitamin D-dependent and D-independent forms of receptor up-regulation.