Increase of serum interleukin-10 in intractable Graves' disease.

The intractability of Graves' disease (GD) and the severity of Hashimoto's disease (HD) vary among patients. We previously reported that peripheral immunoglobulin (Ig) G3-secreting cells were increased in patients with intractable GD (i.e., requiring continuous antithyroid drug therapy). Isotype switching to IgG3 is induced by interleukin (IL)-4 and IL-10. To clarify which of these cytokines is related to the intractability or severity of autoimmune thyroid disease (AITD), we examined the serum concentrations of IL-10 and IL-4 by enzyme immunoassay in 166 patients with AITD and in 53 healthy controls. The serum IL-10 concentration was significantly higher in patients with GD and continuously positive for thyrotropin (TSH) receptor antibody (TRAb) despite more than 5 years of antithyroid drugs treatment than in patients with GD in remission. The serum IL-4 concentration did not differ between these two groups of patients. However, the serum IL-10 concentration was not related to the severity of HD. These results indicate that IL-10, but not IL-4, is related to the intractability of GD, but not to the severity of HD.