Antibodies that promote thyroid growth. A distinct population of thyroid-stimulating autoantibodies

We used a strain of differentiated rat-thyroid cells in continuous culture (the FRTL-5 strain) to detect the presence of growth-promoting antibodies in serum samples from patients with autoimmune thyroid disease. We found that IgG preparations from 17 of 20 patients (85 per cent) with active Graves' disease and two of five patients (40 per cent) with Hashimoto's thyroiditis could augment thyroid-cell growth. In parallel with IgG-induced elevations in intracellular cyclic AMP levels in the same cell line, all 20 of the patients with active Graves' disease had thyroid-stimulatory antibodies. Patients' IgG preparations fell into three subclasses: those with both potent cyclic AMP stimulation and potent growth-promoting activity; those with potent cyclic AMP stimulation but low-level growth promotion; and those with potent growth promotion and low-level cyclic AMP action. Growth-promoting antibodies were not detected in patients with Graves' disease in remission (seven patients), nodular goiter (seven), subacute thyroiditis (five), or atrophic thyroiditis (one). Simultaneous assays of growth promotion and cyclic AMP stimulation may be useful in the care of patients with autoimmune thyroid disease.