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Thyrocytes Express a Functional Toll-Like Receptor 3: Overexpression Can Be Induced by Viral Infection and Reversed by Phenylmethimazole and Is Associated with Hashimoto’s Autoimmune Thyroiditis

Edison Biotechnology Institute (N.H., C.J.L., K.M., U.B.-P., X.S., L.D.K.), the Department of Biomedical Sciences (L.D.K.), College of Osteopathic Medicine, and the Department of Chemical Engineering (D.J.G.), Ohio University, Athens, Ohio 45701; Medstar Research Institute (V.V., M.D.R., M.S.), Washington Hospital Center, Washington, D.C. 20010; The Ohio State University (V.V., M.D.R., M.S.), Arthur G. James Cancer Center and Richard J. Solove Research Institute, Columbus, Ohio 43210; and Section of Endocrinology (C.G., G.N.), Department of Science of Aging, Università degli Studi "G.D. Annunzio," Faculty of Medicine and Surgery, 66100 Chieti, Italy

Address all correspondence and requests for reprints to: L. D. Kohn, Edison Biotechnology Institute, Ohio University, Athens, Ohio 45701.

Toll-like receptors (TLRs) initiate an innate immune response. TLR3 on dendritic cells recognize double-stranded (ds) RNA and then signal increases in cytokines and recognition molecules important for immune cell interactions. In this report, we demonstrate TLR3 mRNA and protein are expressed on Fisher rat thyroid cell line-5 (FRTL-5) thyroid cells and are functional because incubating cells with polyinosine-polycytidylic acid causes 1) transcriptional activation of both the nuclear factor B (NF-B)/Elk1 and interferon (IFN) regulatory factor-3/IFN-ß signal paths, 2) posttranscriptional activation of NF-B and ERK1/2, and 3) increased IFN-ß mRNA. TLR3 can be overexpressed, along with dsRNA-dependent protein kinase, major histocompatibility complex-I or II, and IFN regulatory factor-1, by transfecting dsRNA into the cells, infection with Influenza A virus, or incubation with IFN-ß, but not by incubation with dsRNA or IFN, or by dsDNA transfection. A methimazole (MMI) derivative, phenylmethimazole, to a significantly greater degree than MMI, prevents overexpression by inhibiting increased transcriptional activation of IRF-3 and of IFN-stimulated response elements, phosphorylation of signal transducers and activation of transcription (STAT-1), but not NF-B activation. TLR3 can be functionally overexpressed in cultured human thyrocytes by dsRNA transfection or IFN-ß treatment. Immunohistochemical studies show that TLR3 protein is overexpressed in human thyrocytes surrounded by immune cells in 100% of patients with Hashimoto’s thyroiditis examined, but not in normal or Graves’ thyrocytes. We conclude that functional TLR3 are present on thyrocytes; TLR3 downstream signals can be overexpressed by pathogen-related stimuli; overexpression can be reversed by phenylmethimazole to a significantly greater extent than MMI by inhibiting only the IFN regulatory factor-3/IFN-ß/signal transducers and activation of transcription arm of the TLR3 signal system; and TLR3 overexpression can induce an innate immune response in thyrocytes, which may be important in the pathogenesis of Hashimoto’s thyroiditis and in the immune cell infiltrates.

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