Increased oxygen consumption observed in phorbol 12-myristate 13-acetate stimulated human cultured promonocytic U937 cell lines treated with calcitriol and retinoic acid.

Objective: To investigate the effect of phorbol 12-myristate 13-acetate (PMA) and formyl-methionyl-leucyl-phenylalanine (FMLP) on oxygen consumption of differentiated and non-differentiated immune cell lines by retinoic acid and calcitriol treatment which might be useful in subsequent elicitation of immunological action during immunosuppressive states.

Methods: PMA and FMLP were used to artificially stimulate reactive oxygen production in cultured promonocytic U937 cell line. Paralleled samples of the cultured cells were separately prepared with calcitriol (1, 25- dihydroxyvitamin D3) and retinoic acid followed by a 72-hour incubation period. The rate of respiratory burst was measured using the Clark oxygen electrode.

Results: The average increase in cell concentrations per mL observed was significantly higher in retinoic acid-treated cells (9×10(6) cells/mL) when compared with calcitriol-treated samples (4×10(6) cells/mL). There was a marked increase in oxygen consumption of the calcitriol-treated cell lines against the retinoic acid-treated ones. Exposure of differentiated U937 cells to PMA and FMLP increased significantly (P<0.05) in their oxygen consumption when compared with the control. PMA calcitriol-treated cells resulted in 55% oxygen consumption more than the control while FMLP oxygen consumption increased 78% by comparison with the control.

Conclusions: The result demonstrated that calcitriol may serve as a physiological promoter of normal differentiation of precursor cells which may exert an immunological action. This effect could elicit a marker potential and increase immune cell activity of the host especially in immunosuppressed diseased states.