Increased circulating pro-inflammatory cytokines and Th17 lymphocytes in Hashimoto's thyroiditis

Th17 lymphocytes play an important role in different chronic inflammatory and autoimmune conditions.

The aim of the study was to explore the status of Th17 cells in patients with autoimmune thyroid diseases (AITD).

We assessed the serum levels and in vitro synthesis of IL-17 and IL-22 and of different cytokines (IL-6, IL-15, and IL-23) involved in the differentiation of Th17 cells in the peripheral blood and thyroid glands of 26 patients with AITD, eight with Graves' disease, and 18 with Hashimoto's thyroiditis (HT) as well as 10 healthy controls.

We found enhanced levels of T cells synthesizing IL-17 and IL-22 in the peripheral blood from AITD patients, mainly in those with HT. In addition, a stronger expression of IL-17 and IL-22 and an enhanced number of IL-23R(+) cells was detected in thyroid glands from HT patients compared with Graves' disease or controls. Furthermore, increased concentrations of IL-6 and IL-15 were detected in sera from HT patients, whereas serum levels of IL-23 tended to be higher in these patients. Finally, an enhanced in vitro differentiation of T lymphocytes into Th17 cells induced by IL-23/IL-6 was observed in AITD patients. Accordingly, a strong induction of RORC2 gene was detected in lymphocytes from HT patients when stimulated with IL-23.

Our results indicate that there is an increased differentiation of Th17 lymphocytes and an enhanced synthesis of Th17 cytokines in AITD, mainly in HT. These phenomena may have an important role in the pathogenesis of thyroid autoimmunity.