Immunoregulatory Effect of Calcitriol on Experimental Autoimmune Encephalomyelitis (EAE) Mice

Previous studies noted an imbalance in T helper (Th) 17 and regulatory T cells (Tregs) in experimental autoimmune encephalomyelitis (EAE), a multiple sclerosis animal model. calcitriol, vitamin D's active form, was found to ameliorate EAE symptoms by favoring Tregss over Th17 cells, suggesting immunomodulatory effects. This study aimed to assess calcitriol's impact on EAE manifestations and cytokine profile in mice. In this study, we recruited twenty-eight C57BL/6 mice and divided them into 4 groups: healthy controls, EAE, EAE with calcitriol treatment, and healthy mice with calcitriol treatment. CD4+ T cells were isolated from splenocytes using magnetic-activated cell sorting. Real-time polymerase chain reaction was employed to quantify the genes associated with Th9 cells (i.e., SPI1 encoding PU.1 and IL9 encoding interleukin [IL]-9). Moreover, the levels of IL-17 and transforming growth factor beta (TGF-β) were evaluated through enzyme-linked immunosorbent assay in the supernatant of CD4+ T cell culture stimulated by anti-CD3 and anti-CD28 antibodies for 72 hours. In the supernatant of CD4+ T cell cultures, the levels of interleukin-17 (IL-17) were significantly increased, while the levels of transforming growth factor beta (TGF-β) were decreased in the EAE Group compared to the healthy control group. Calcitriol treatment reversed these changes and attenuated EAE symptoms, as confirmed in hematoxylin and eosin, and luxol fast blue stains. Notably, calcitriol increased IL9 gene expression in both EAE and healthy mice.  This study provides further evidence of the anti-inflammatory effects of calcitriol and its role in attenuating EAE.