Introduction: Multiple sclerosis (MS) is a chronic autoimmune disease with unknown etiology affecting the central nervous system. The prevalence of MS is highest where environmental supplies of vitamin D are lowest. Some studies have shown a strong protective effect of vitamin D3 in experimental autoimmune encephalomyelitis (EAE) a model of MS. However, it is not known whether vitamin D3 has a protective effect in EAE. Vitamin D3 may be inhibit EAE by having an effect on TH1 and TH2 immune responses. To address this question, the effect of vitamin D3 on cellular immune responses in C57BL/6 mice with experimental autoimmune encephalomyelitis was investigated. Methods: Male C57BL/6 mice matched in age and weight were placed in two therapeutic groups (n=10 per group) as follows: Vitamin D3-treated EAE mice (5μg/kg/every two days of vitamin D3 given i.p from day -3 until day +19 after disease induction). Non-treated EAE mice (EAE control) received vehicle alone with same schedule. 20 days after immunization, the mononuclear cells (MNCs) of the spleen were isolated from mice and cultured in the presence and absence of MOG35-55 for 96 hours. The supernatant of cultured cells was collected and produced cytokines (IL-10 and IFN-γ) were assayed by ELISA. Results: The results showed that vitamin D3-treated mice had less severe clinical signs and synptoms of EAE (3.2±0.8) than non-treated EAE induced mice (5.3±0.44), (p=0.001). Also, there was a significant difference regarding the day of onset of disease in the vitamin D3-treated and non treated EAE-induced mice (day 15±1 and day 11±1, respectively). There was no significant difference in IFN-γ production between treated and non-treated mice, but the amount of IL-10 production in the D3-treated mice was higher than the non-treated group (p=0.001). Conclusion: Considering the role of TH1 in the pathogenesis of EAE and MS, it is suggested that vitamin D3 can reduce or delay the onset of EAE by shifting immune responses to TH2 and IL-10 production. Thus, vitamin D3 as an immune modulatory agent is potentially important for treatment of MS

Keywords: Multiple Sclerosis, Experimental Autoimmune Encephalomyelitis, Vitamin D3, MOG35-55 peptide, C57BL/6 mice

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