CASR and vitamin D deficiency: The present study was therefore designed to explore (i) whether an easy distinction of CaSR expression in normal human circulating monocytes could be made between that found in the entire cell and that found on cell surface alone, (ii) whether CaSR expression could be changed by correction of vitamin D deficiency, and (iii) whether in vitro exposure to vitamin D sterols and/or Ca2+ and/or pro-inflammatory cytokines could modify CaSR expression using the monocyte U937 cell line.