[Thyrocytes contribute to their own demise: the role of interleukin-18 in Hashimoto's thyroiditis].

Objective To investigate the IL-18 expression in the thyroid tissues of Hashimoto's thyroiditis (HT) and its cellular localization and the effect of interferon-γ(IFN-γ) on the interleukin- (IL)-18 expression in thyrocytes. Methods RT-PCR and immunohistoehemistry were used to detect the IL-18 expression and its cellular localization in the thyroid tissues biopsy specimens of 6 HT patients with normal thyroid function, 6 normal thyroid specimens resected from patients with pharyngeal carcinoma, and 16 specimens of thyroid tissues adjacent to the thyroid adenoma obtained during operation. Thyrocytes were isolated, cultured, and exposed to IL-1β, tumor necrosis factor-α (TNF-α), or IFN-γ for 48 h. RT-PCR and Western blotting were used to detect the IL-18 expression. Results IL-18 mRNA expression was at an extremely low levels in the normal thyroid tissues and at a significantly higher level in the thyroid tissues of HT. Immunohistoehemical staining showed that IL-18 expression was augmented in the thyroid tissues of HT and was mainly localized in the thyroid follicular cells. The IL-18 mRNA expression in the isolated human thyrocytes was dose-dependently elevated by IFN-γ rather than TNF-α or IL-1β. Western blotting showed that pro-IL-18, but not mature IL-18, was detected in the lysates of the cultured human thyrocytes and the expression of pro-IL-18 was increased by IFN-γ. Conclusion IL-18 expression is elevated in the thyroid follicular cells of HT. IL-18 is constitutively expressed in the isolated human thyrocytes and its expression is up-regulated by IFN-γ. Therefore, interplay between IL-18 and IFN-γ may have an important role in the thyrocyte destruction in HT. Key words: Thyroiditis, autoimmune;  Interleukin-18;  Thyrocyte