The effect of 1,25-dihydroxyvitamin D3 on in vitro immunoglobulin production in human B cells.

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) dose-dependently suppressed immunoglobulin (Ig) production of human B cells, as evaluated by IgG-plaque-forming cells (IgG-PFC) in the culture of pokeweed mitogen (PWM)-activated B cells. Similar suppressive effect of 1,25(OH)2D3 on Ig production of B cells was observed in the Staphylococcus aureus Cowan I(SAC)-induced Ig-producing system. The mean percentage of inhibitions at a concentration of 10(-9) M were 60.0 +/- 8.2% (mean +/- SE, n = 6) and 65.1 +/- 4.7% (n = 10) in PWM- and SAC-stimulated cultures, respectively. The suppression was strongly exhibited only when 1,25(OH)2D3 was added at the start of the 6-day culture, accompanied by a decrease in DNA synthesis of B cells in both culture systems. On the other hand, the addition of 1,25(OH)2D3 on day 4, when DNA synthesis reached at plateau and IgG-PFC began to be detectable, had no noticeable affect on either the number of PFC or DNA synthesis of B cells. Furthermore, 1,25(OH)2D3 suppressed Ig production even when B cells were exposed to the agent for 4 hr after the activation with PWM or SAC, but not before the activation. These results indicate that 1,25(OH)2D3 inhibits B cell proliferation before differentiation to Ig-secreting cells, consequently reducing Ig production; and that its action appears to be mediated by the cytosol receptors expressed on activated B cells. Thus, the agent may serve as an immunoregulating hormone in vivo, as well as in vitro.