Inhibitory effect of 1alpha,25-dihydroxyvitamin D3 on allogeneic lymphocyte stimulation and Langerhans cell maturation.

1alpha,25-Dihydroxyvitamin D3 (calcitriol) has been shown to inhibit the proliferation of peripheral blood mononuclear cells induced by allogeneic Langerhans cells in a human mixed epidermal cell lymphocyte reaction. The potent antigen-presenting function of Langerhans cells is gained during culture. We tried to dissect the effect of calcitriol on lymphocyte proliferation and Langerhans cell maturation in a murine mixed epidermal cell lymphocyte reaction using unfractioned epidermal cells as a source for Langerhans cells. First, calcitriol was added upon setup of the mixed epidermal cell lymphocyte reaction using cultured epidermal cells as antigen-presenting cells, and this was found to inhibit the proliferation of lymphocytes in a time- and concentration-dependent manner. When calcitriol was added only during preculture of freshly isolated epidermal cells, the subsequent mixed epidermal cell lymphocyte reaction was also inhibited. In addition, the growth of keratinocytes and the production of granulocyte/macrophage colony-stimulating factor during preculture of epidermal cells was completely inhibited. Supplementation with this growth factor only partially restored the proliferative response of lymphocytes. These results suggest that calcitriol inhibits both the alloantigen-driven stimulation of naive T cell and Langerhans cells maturation. Further experiments with purified Langerhans cells are required to elucidate the mechanism of action of calcitriol on Langerhans cell maturation.