Autoantibodies to insulin are present in sera of patients with autoimmune thyroid disease

It has been clinically suspected that patients with autoimmune thyroid disease are at an increased risk of developing other autoimmune diseases later in life. To determine the presence and potential importance of a more generalized deregulation of immune response in patients with Grave's disease and Hashimoto's disease, sera from 33 patients with Graves' disease and 16 patients with Hashimoto's disease were screened for the presence of anti-insulin antibodies and anti-insulin-receptor antibodies. An enzyme-linked immunosorbent assay was used to identify the presence of IgG against human insulin. The optical density indicating the presence of IgG against insulin in sera from patients with Graves' disease averaged .172 +/- .024 (mean +/- SE; range .010-.802), compared to the mean normal value of .098 +/- .0009 (range .012-.238) in 33 control subjects. Ten of 33 patients with Graves' disease had values greater than .200, whereas control sera values were less than .200 in all but one case (P less than .005, Graves' sera vs. controls). The sera from patients with Hashimoto's disease had a mean optical density of .110 +/- .016, with 15 of 16 values between .010 and .200. These values were not significantly different from controls with an insulin-binding inhibition assay. Anti-insulin-receptor antibodies were not detected in any of 33 patients with Graves' disease, and cytoplasmic islet cell antibodies were not detected in sera from seven patients with Graves' disease who had insulin-binding antibodies. These data support the hypothesis that the immunologic response in autoimmune thyroid disease may be more heterogeneous and polyclonal than previously believed.