Serum IL-18 levels are not increased in patients with untreated Graves' ophthalmopathy

Objective: Cytokines play an important role in autoimmune thyroid diseases, and serum levels may reflect the activity of the immune process. This is particularly interesting in Graves' ophthalmopathy, where a reliable serum activity marker is warranted. Interleukin-18 (IL-18) is a potent Th1 cytokine, known to induce interferon (IFN)-gamma and the aim of this study was to evaluate serum IL-18 levels in Graves' ophthalmopathy. Methods: Serum IL-18 was measured by ELISA in 52 patients with untreated Graves' ophthalmopathy (who all had been rendered euthyroid with antithyroid drugs), 52 healthy controls matched for sex, age, and smoking habits, and 15 euthyroid patients who had been treated for Graves' hyperthyroidism and ophthalmopathy in the past. Results: Serum IL-18 (median values in pg/ml with range) levels did not differ between the untreated Graves' ophthalmopathy patients - 226 (61 - 704) pg/ml, matched healthy controls - 194 (17 - 802) pg/ml, and Graves' ophthalmopathy patients treated in the past - 146 (0-608) pg/ml. No correlation was observed between serum IL-18 levels and thyroid function or antithyroid antibodies. There was no correlation between serum IL-18 levels and smoking habits. Conclusion: We conclude that Graves' ophthalmopathy does not affect serum IL-18