Serum levels of interleukin 6 and tumor necrosis factor-alpha in hyperthyroid patients before and after propylthiouracil treatment.

Contrary to the usual inhibitory role of tumor necrosis factor-alpha (TNF-alpha) in thyroid metabolism, it also has specific stimulatory effects in autoimmune thyroid disorders, including induction of HLA class II antigen-presenting cell-T cell interaction. Despite high intrathyroidal concentrations, various studies were not able to demonstrate high serum levels of TNF-alpha in patients with Graves' disease. To investigate this discrepancy we determined TNF-alpha and interleukin 6 (IL-6) levels in 25 hyperthyroid patients who responded to propylthiouracil treatment (16 with Graves' disease and nine with toxic multinodular goiter) and compared them with the levels found in euthyroid patients with simple diffuse goiter (n = 15) and normal healthy controls (n = 15). Median IL-6 levels were high in both Graves' disease and toxic multinodular goiter patients before propylthiouracil treatment (23 and 26.5 pg/ml, respectively). After restoring euthyroidism there was a statistically significant decline to near-normal levels (3 and 10 pg/ml, respectively). On the other hand, median serum TNF-alpha levels were high only in Graves' disease patients (20 pg/ml) and could not be normalized with antithyroid medication (20 pg/ml) compared to that of controls (5 pg/ml). Tumor necrosis factor-alpha, but not IL-6, was found to be high in the sera of Graves' disease patients when euthyroid, which may be due to an ongoing antigen-antibody interaction, a feature of autoimmune attack. It remains to be determined whether the degree of TNF-alpha and/or IL-6 elevation will be a predictor of disease recurrence.