Background Excessive iodine intake and viral infection are recognized as both critical factors associated with autoimmune thyroid diseases.Toll-like receptors (TLRs) have been reported to play an important role in autoimmune and inflammatory disorders.In this study,we aimed to clarify the possible mechanism of TLR3 involved in polyinosinepolycytidylic acid (poly(l:C)) promoting excessive iodine intake induced thyroiditis in non-obese diabetic (NOD) mice.Methods Both NOD and BALB/c mice were randomly assigned to four groups:control group (n=5),high iodine intake (HI) group (n=7),poly(l:C) group (n=7) and combination of excessive iodine and poly(l:C) injection (HIP) group (n=7).After 8 weeks,mice were weighed and blood samples were collected.All the mice were sacrificed before dissection of spleen and thyroid gland.Then,thyroid histology,thyroid secreted hormone,expression of CD3+ cells and TLR3 as well as inflammatory mRNA level were evaluated.Results Both NOD and BALB/c mice from HI and HIP group represented goiter and increasing thyroid relative weight.Thyroid histology evidence indicated that only HIP group of NOD mice showed severe thyroiditis with lymphocytes infiltration in majority of thyroid tissue,severe damage of follicles and general fibrosis.Immunofluorescence staining results displayed a large number of CD3+ cells in HIP NOD mice.Real-time polymerase chain reaction (PCR) results suggested interferon (IFN)-αincreased over 30 folds and IFN-γ expression was doubled compared with control group,but interleukin (IL)-4 remained unchanged in HIP group of NOD mice thyroid.Meanwhile,over one third decrease of blood total thyroxine (TT4) and increased thyroid-stimulating hormone (TSH) was observed in HIP group of NOD mice.Only HIP group of NOD mice represented significantly elevation of TLR3 expression.Conclusion Poly(l:C) enhanced excessive dietary iodine induced thyroiditis in NOD mice through increasing TLR3 mediated inflammation.