The disrupted autoimmune response in Hashimoto's
thyroiditis (HT) has long been considered to be dominantly T helper type 1 (Th1) mediated. Recent advances in the field of immunology have introduced a new class of effector T cells, named 'Th17', which plays important roles in autoimmune disorders once thought to be merely Th1 mediated. We aimed to examine the levels of major Th17
cytokines in patients with HT in this study. We studied serum
interleukin 17 (IL-17) and
interleukin 23 (IL-23) levels in 46 newly diagnosed, untreated patients with HT (40 women and 6 men, aged 40.0 ± 11.8 years) divided into euthyroid (n=22) and hypothyroid (n=24) groups and compared them with age and sex matched 26 healthy euthyroid controls without HT (21 women and 5 men; aged 36.0 ± 12.9 years). Serum
IL-17 and
IL-23 levels were significantly different among euthyroid and hypothyroid HT patients and controls, with highest levels obtained in the euthyroid HT group (p=0.041 for IL-17 and p<0.001 for IL-23). TSH was negatively and FT4 was positively correlated with
IL-17 (p=0.016 for TSH and p=0.004 for FT4) and
IL-23 (p<0.001 for TSH and p=0.003 for FT4) levels. There were no correlations between thyroid volumes calculated on thyroid ultrasonography and
IL-17 (p=0.630) or
IL-23 (p=0.321) levels. In conclusion, the levels of
IL-17, one of the major effector
cytokines of the Th17 system, and
IL-23, which had been implicated in the generation, survival and expansion of Th17 cells, are altered in HT. How
thyroid hormone status and the course of disease affect Th17 system in chronic
autoimmune thyroiditis needs to be determined with further studies.