| Objective:To observe the effects of the active form of vitamin D,1,25(OH)2D3, on the incidence of diabetes,insulitis and serum IL-4, IFN-γ ,N0 level and the subsets of T cells in spleen of female nonobese diabetic (NOD) mice.Furthermore, to investigate the immuno-regulatoy mechanisms involved in the prevention of diabetes by this substance.Methods:80 Female NOD mice on day 21, the time of weaning,were randomly divided into two groups.The 1,25(OH)2D3 was dissolved in arachis oil.Group 1(n=40) received 1, 25(OH)2D3(5μg/kg) i p 0. 1ml every other day, stopped on day 69;Group 2(n=40) received arachis oil 0.1ml instead of 1,25(OH)2D3 for the same period as the control group.Both two groups mice were administered a single cyclophosphamide (CY) at 70 days old to accelerate diabetes, one week after CY administration ,15 mice of each group were killed to detect serum IL-4, IFN-γ byELISA, NO level by colorimetry and the subsets of T cells in spleen by flow cytometry quantitative analysis. At the age of the onset of diabetes or one month after CY administration ,mice in two groups were killed to observe pancreatic histopathology ,the incidence of diabetes and serum calcium levels. Results:The incidence of diabetes in the 1,25(OH)2D3 group was 12% which was obviously less than 56% in the arachis oil group (p<0.01).The insulitis score decreased markedly (p<0.01) in the 1,25(OH)2D3 group than in the control group, and the severity of insulitis in 1,25(OH)2D3 group was lower than that of the control group. ELISA revealed significantly lower levels of IFN-r and higher levels of IL-4 in the 1,25(OH)2D3 group compared to the control group. (IL-4 52.47± 9. 13pg/ml vs 32.53±3.34 pg/ml, IFN-r 70.75± 15.55 pg/ml vs 141.38±10.67 pg/ml, P all<0. 01). Serum NO level in NOD mice was reduced after i.p administrated 1,25(OH)2D3 compared to the control group (77.50±28.22μ mol/1 vs 118.21±18.71μmol/1p<0.01). The number of CD4+,CD8+ subsets in splenocytes of the 1,25(OH)2D3 group was respectively higher than that of the control group (p<0.01, p<0.05). The CD4+/CD8+ ratio show no significent difference between these two groups. The serum calcium levels of 1,25(OH)2D3 group is a little higher than that of the control group,but the NOD mice can be well tolerated.Conclusion: 1,25(OH)2D3 can prevent cyclophophamide-induced type 1 diabetes and reduce the severity of insulitis in female NOD mice.Its mechanisms seem to be related to the increasing of the systematic expression of Th2 type cytokine such as IL-4 and to the decreasing of the systematic expression of Th1 type cytokine such as IFN-r, also related to the increasing the number of CD8+ T cell, and regulating the subsets of T cells in spleen. In this study, 1,25(OH)2D3 has not major side effects , such as high serum calcium levels. The study also proved the onset of the diabetes is closed related to the serum NO level.
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