Viral infection and innate pattern recognition receptors in induction of Hashimoto's thyroiditis

Hashimoto's thyroiditis, a common organ-specific autoimmune disease, is multifactorial in which both genetic susceptibility and environmental factors including infection play a critical role in its pathogenesis. Viral infection activates both the innate and adaptive immunity and is implicated as a trigger of Hashimoto's thyroiditis. Candidate viruses include hepatitis C virus and human parvovirus B19. Viral components, which are recognized by innate receptors including Toll-like receptors (TLRs), are detected in thyroid tissues and sera of patients with Hashimoto's thyroiditis. While conflicting results have been obtained regarding the role of TLRs in autoimmune diseases, our preliminary study suggested a contribution of TLR2 and dectin-1 in combination, TLR4, or TLR7 to the production of anti-thyroglobulin antibody in nonobese diabetic mice, a mouse model of Hashimoto's thyroiditis. Despite interesting circumstantial evidence, however, whether viral infection and innate receptors are involved in the development of Hashimoto's thyroiditis remains largely unclear. In this review, we summarize our knowledge regarding the role of viral infection and innate receptors in the etiology of Hashimoto's thyroiditis.