Regulatory effects of 1α-25-dihydroxyvitamin D3 on the cytokine production of human peripheral blood lymphocytes

We studied the possible regulatory effects of 1 alpha,25-dihydroxyvitamin D-3 [1 alpha,25-(OH)(2)D-3] On cytokine production and differentiation of subsets of CD4(+) [T helper 1 (Th1) and Th2] and CD8(+) [T cytotoxic 1 (Tc1) and Tc2] lymphocytes at the single cell level. PBMC from healthy donors were cultured with or without 1 alpha,25-(OH)(2)D-3 for up to 21 days. On days 0, 7, 14, and 21, the percentage of cytokine-producing T lymphocytes was analyzed by intracellular cytokine detection with mAb and flow cytometry. Simultaneous staining for cell surface markers allowed discrimination of CD4(+) and CD8+ T cell subsets. After culture with 1 alpha,25-(OH)(2)D-3 (10(-8) mol/L), no significant effects on the proportion of interferon-gamma (IFN gamma)- or interleubin-4 (IL-4)-producing cells were detected, whereas reduced frequencies of IL-2-producing cells in the CD4(+) as well as in the CD8(+) population were found. An increase in the low percentage of CD4(+) and CD8(+) T cells producing the Th2 cytokine IL-13 was noticed. Most interestingly, IL-6-producing CD4(+) and CD8(+) T cells could only be detected in cultures with 1 alpha,25-(OH)(2)D-3, reaching a plateau after 14 days. The percentage of IL-6-producing T cells induced by 1 alpha,25-(OH)(2)D-3 after a given time period remained stable for at least 7 weeks. Studies of cytokine coexpression revealed that about 70% of IL-6-producing CD4(-) and CD8(+) cells were also positive for IL-2, but more than 90% were negative for IFN gamma, IL-4, or IL-13, respectively. This suggests that the IL-6-producing population does not match the Th1/Tc1-like (IFN gamma(+)) or Th2/Tc2-like (IL-4(+) or IL-13(+)) subset. The influence of 1 alpha,25-(OH)(2)D-3 on cytokine production by lymphocytes is probably an important point of intersection between the endocrine and the immune system.