1α,25-Dihydroxyvitamin D.

1α,25-Dihydroxyvitamin D [1α,25(OH)D] is a steroid hormone that regulates calcium metabolism. Besides, 1α,25(OH)Dalso has pronounced immunomodulatory effects: it strongly inhibits dendritic cell (DC) maturation and impairs IL-12 production. We studied the effect of 1α,25(OH)Don the antibody response to pneumococcal capsular polysaccharide (caps-PS) serotype 3. 1α,25(OH)D inhibited the IgG2a antibody response to caps-PS serotype 3. Besides, 1α,25(OH)D also inhibited IL-12 production and maturation of DC. Anti-IL-12 and exogenous IL-12, respectively, inhibited and stimulated the IgG2a antibody response to caps-PS serotype 3. Exogenous IL-12 abrogated the effect of 1α,25(OH)D on the IgG2a antibody response to caps-PS serotype 3, indicating that the effect of 1α,25(OH)D on the IgG2a antibody response to caps-PS serotype 3 was mediated through IL-12. In conclusion, we demonstrate that 1α,25(OH)D has an inhibitory effect on the IgG2a antibody response to caps-PS serotype 3, and that this effect was mediated trough IL-12. [ABSTRACT FROM AUTHOR]