Serum interferon gamma levels in autoimmune thyroid disease.

The lymphokine, interferon gamma (IFN gamma) is considered to play an important role in the development of autoimmune thyroid disease (AITD); the main source of IFN gamma has been shown to be CD4 cells when stimulated by soluble antigen. We have measured the serum IFN gamma concentration in 42 patients with AITD (24 Graves' disease and 18 Hashimoto's thyroiditis) and 9 normal control subjects, using a sandwich enzyme-linked immunosorbent assay (ELISA) (detectable limit, 1 IU/ml). One of normal controls, 14 of the 24 patients with Graves' disease, and 5 of the 18 patients with Hashimoto's thyroiditis had detectable IFN gamma levels. Patients with Graves' disease were found to have higher concentrations of serum IFN gamma (11.6 +/- 15.8 IU/ml, mean +/- SD) than normal controls (1.1 +/- 0.3 IU/ml). However, the values in patients with Hashimoto's thyroiditis (9.4 +/- 15.5 IU/ml) were not significant when compared to those in normal controls. Serum IFN gamma values in patients with AITD did not correlate with serum anti thyroid autoantibodies (antithyroglobulin, antithyroid microsomal antibody, or TSH binding inhibitory immunoglobulin activity) or with thyroid function. Thus, increased in vivo production of IFN gamma in Graves' disease as evidenced in these serum concentrations might reflect T cell activity, but does not appear to be an accurate reflection of intrathyroidal events.