Elevated 1-α Hydroxylase Activity in Monocytes from Patients with Active Tuberculosis

A uremic patient developed hypercalcemia after tuberculosis infection, and his ionized calcium levels correlated with 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) levels. We performed further studies to determine whether monocytes are alternative sites of 1,25(OH)(2)D(3) conversion beyond renal tubular cells. Using an ex vivo bioassay, in this study, we found that 1-α hydroxylase (CYP27B1) activity in monocytes is significantly higher in patients with active tuberculosis (TB) than in those with frequent TB contact. However, when monocytes from patients with active TB were restimulated with antigen derived from Mycobacterium tuberculosis, less 1,25(OH)(2)D(3) was observed. In contrast, the level of 1,25(OH)(2)D(3) was unchanged in those with frequent TB contact. We conclude that monocytes may be an alternative source of 1-α hydroxylase that could convert 25-hydroxyvitamin D(3) to the more active 1,25(OH)(2)D(3).