1 alpha,25-dihydroxyvitamin D3 inhibits pokeweed mitogen-stimulated human B-cell activation: an analysis using serum-free culture conditions.

The effect of 1 alpha,25-dihydroxyvitamin D3 (1,25-(OH)2D3) on pokeweed mitogen-induced generation of human immunoglobulin-secreting cells (ISC) was studied in serum-free culture. Human peripheral blood mononuclear cells (1.75 X 10(6)/ml) were cultured in 200 microliter microculture wells containing Iscove's MEM supplemented with 20 micrograms/ml of human transferrin, 20 micrograms/ml of soybean lecithin and 1 mg/ml of delipidated bovine albumin. The culture supported ISC generation of all isotypes, and the optimal concentration of pokeweed mitogen was 1 microgram/ml. After stimulation with a suboptimal concentration (0.3 micrograms/ml) of pokeweed mitogen, 1,25-(OH)2D3 suppressed the ISC generation at a dose range between 10(-9) M and 10(-7) M, and maximal inhibition was obtained at 10(-7) M. 1,25-(OH)2D3 had no effect on the spontaneous ISC generation. The effect was specific for 1,25-(OH)2D3 and no suppression was obtained by 24R,25-dihydroxyvitamin D3 or 25-hydroxyvitamin D3.