Effects of vitamin D3on helper T cell 1/helper T cell 2 cell balance and monocyte chemoattractant protein-1/cell surface chemokine receptor 2 signal in experimental autoimmune thyroiditis

Abstract:

Objective: To investigate the effect of vitamin D₃on inflammation, helper T cell 1/helper T cell 2 (Th1/Th2) and monocyte chemoattractant protein-1/cell surface chemokine receptor 2 (MCP-1/CCR2) signal in experimental autoimmune thyroiditis (EAT) rats. Methods: Lewis rats were randomly divided into the control group (n=10), the model group (n=15) and the treatment group (n=15). The rat model of EAT was established by immunizing porcine thyroglobulin (pTG). The treatment group received intraperitoneal injection of 1, 25- (OH) ₂vitamin D₃at the dose of 5 mg/kg, once every other day for consecutive four weeks, and the other two groups were given normal saline of equal volume. The morphological changes of thyroid tissue in rats were observed by hematoxylineosin (HE) staining. Serum thyroid stimulating hormone (TSH), anti-thyroglobulin antibody (TGAb), anti-thyroid peroxidase antibody (TPOAb) and cytokines interferon-γ (IFN-γ), interleukin-12 (IL-12), interleukin-14 (IL-4) and interleukin-10 (IL-10) were detected by enzyme-linked immunosorbent assay (ELISA). The relationship between TSH and autoantibodies and cytokines was analyzed by stepwise linear regression. NF-κB p65 in thyroid tissue was detected by immunohistochemistry. MCP-1/CCR2 signal axis in thyroid tissue was analyzed by Western blot. Results: In the model group, thyroid follicles were damaged and inflammatory cells were infiltrated, while the pathological changes of thyroid in the treatment group were significantly improved and tended to the control group. The levels of TSH, TGAb and TPOAb in the treatment group were significantly lower than those in the model group (t=4.000, 2.603, 5.279; P=0.000, 0.015, 0.000), but were still significantly higher than those in the control group (t=2.400, 2.216, 7.392; P=0.025, 0.037, 0.000). Compared with the model group, the levels of IL-4 and IL-10 were significantly increased in the treatment group (t=3.522, 2.432; P=0.001, 0.022), and the levels of IFN-γ, IL-12 and IFN-γ/IL-4 and IL-12/IL-10 were significantly decreased in the treatment group (t=2.940, 4.700, 5.416, 8.178; P=0.007, 0.000, 0.000, 0.000), which tended to the levels of the control group. Stepwise regression analysis showed that TSH was positively correlated with TGAb, TPOAb, IFN-γ and IL-12, and negatively correlated with IL-4 and IL-10 (r=0.872, 0.868, 0.731, 0.706, -0.557, -0.236, all P<0.001), among which TGAb, TPOAb and IL-12 had the most significant effect on TSH. Compared with the model group, the levels of NF-κB p65, MCP-1 and CCR2 in the thyroid tissues of rats in the treatment group were decreased, with statistically significant differences (t=2.432, 2.267, 5.143; P=0.000, 0.031, 0.000). Conclusion: Vitamin D₃may inhibit NF-κB pathway to down-regulate Th1 cytokines and up-regulate Th2 cytokines, thereby reducing Th1/Th2 ratio. Or, it reduces thyroiditis in EAT rats, improves thyroid function, inhibits thyroid antibody production and protects thyroid by inhibiting MCP-1/CCR2 signaling axis.