Objective To investdgatethe effect of alpha 1,25 - dihydroxy vitamin D3(VitD3) on the differentiation of Th cells and its
possi.ble mechanism. Methods spleen cells derived from BALB/c mice were isolated and stimulated by 2.5μg/ml of ConA. VitD3 at different concentrations was added at different time. The
proliferation of spleen cells was measured by 3H-TdR incorporation assay, and the expression level of mRNA of the cytokines involved in differentiation of Th cells was detected by RT-PCR. Results VitD3 inhibited the ConA-induced proliferation of
lymphocytes in a dose - dependent manner and the inhibitory effect of the VitD3 of the 10-5mol/L on the proliferation of lymphocytes was the strongest. The inhibitory effect of VitD3 was associated with the time when VitD3 added. When VitD3 was added 24 hours after ConA - induced lymphocytes activation,the inhibitory effiect of VitD3 was the most significant. Furthermore,the more the cells were activated,the stronger the inhibitory effect was. VitD3 enhanced mRNA of genes involved in Th 2 development (IL-4, IL-6) and decreased mRNA of genes involved in Th 1 development (IFN -γ TNF -α) signincandy ( P < 0.05). Conclusions VitD3 can inhibit the ConA - induced the proliferation of lymphocytes and enhance the development of Th 2. The some evidences for the clinical application of VitD3 to therapy of some diseases of dysfunction of T cells are provided.