Effects of Iodine excess,polyinosinic-polycytidylic acid and thyroglobulin induced thyroiditis in mice on Toll-like receptor 3 expression

Objective To observe the effect of iodine excess(HI),polyinosinic-polycytidylic acid[Poly(I:C),Poly]and thyroglobulin(TG)on the thyroid of mice by the expression of Toll-like receptor 3(TLR3)to reveal the functional role of TLR3 in autoimmune thyroiditis.Methods Forty-two non-obese diabetic mice,body weight (20±3)g,were divided into six groups:control group,HI group,Poly group,TG group,HI+TG group,HI+Poly group. Fed with deionized water and injected intraperitoneally with physiological saline 0.1 ml each day for a week, the mice in control group were injected with physiological saline every other day at the same dose for 1 week before they were sacrificed; HI group drank 0.05% NaI water and were injected intraperitoneally with physiological saline same as control group; Poly group drank deionized water and were injected intraperitoneally with poly 0.1 ml (1 g/L)each day of the week, then the mice were injected with Poly every other day at the same dose for 1 week before they were sacrificed; TG group drank deionized water and were injected intraperitoneally with physiological saline same as control group, immunized with 0.1 mg TG by subcutaneously injecting and the immunization was enhanced after they were fed half dose for 4 and 8 weeks separately. In HI + Poly group, the treatment was the same as HI group and Poly group; HI + TG group: the treatment was the same as HI group and TG group. Eight weeks later, mice were sacrificed and thyroids were taken to make frozen sections, Hematoxylin-Eosin (HE) staining was employed to observe the morphological change of the thyroids. The expression of TLR3 of thyroids was observed under fluorescence microscope after Immumofluorescence using TLR3 antibody and TR3-positive cells were analyzed in the thyroid density. Results HE staining showed thyroids of Poly group had no inflammation under microscope.There were different degrees of inflammatory cell infiltration in HI group and TG group. The inflammatory cell infiltration and the damage of follicular thyroid of HI + TG group and HI + Poly group were serious, and the degrees of inflammation were higher over "++". Thyroid follicular epithelial cell with TLR3 expression could be seen in Poly group and HI group, meanwhile, there were TLR3 strong positive inflammatory cells in HI group under fluorescent microscope. Using stereological analysis of TLR3-positive cell density in the thyroid, the difference between groups was statistically significant(F=7.870, P<0.01 ). TLR3-positive cell density in the thyroid of HI + Poly group was higher[ (9.287 ± 0.522)mm2] than control group[ (0.062 ± 0.025)mm2, P < 0.01] significantly, meanwhile, the density in HI + Poly group was higher than HI group [ (2.574 ± 0.257 )mm2] and Poly group[ (1.361 ± 0.148 )mm2, all P < 0.01]. The density in HI + TG group[ (4.843±0.405)mm2] was higher than HI group and TG group[(1.601 ±0.268)mm2, all P < 0.01 )]. Conclusions Excessive iodine and thyroglobulin can induce thyroiditis, and stimulate the expression of TLR3 in the thyroid follicular epithelial, Poly aggravated thyroiditis induced by iodine excess in NOD mice; TLR3 positive inflammatory cells also appeared in inflammatory region, suggesting that TLR3 is involved in the pathogenesis of autoimmune thyroiditis Key words: Iodine; Polyinosinic-polycytidylic acid; Thyroglobulin; Autoimmune thyroid diseases; Toll-like receptor 3