[Assay of circulating thyroid stimulator determined by I- efflux].

The thyroid stimulating antibodies (TSAb) have been widely used as a clinical marker for diagnosis of hyperthyroidism due to Graves' disease. Immunoglobulins (IgG) of Graves' patients as well as TSH is known to stimulate cAMP production in FRTL-5 cells, a cell-line derived from normal rat thyroid. On the other hand, it has been shown that TSH-induced I- efflux in these cells is associated with production of inositolphosphate as well as intracellular Ca2+ increase. An attempt was made to determine whether Graves' IgG also can mimic such TSH action as a cause of Graves' disease. Polyethyleneglycol precipitated serum fraction of Graves' patients were prepared. The cells grown in the presence of TSH were incubated for 3 weeks in a Ham's 10 medium containing 1% calf serum, insulin and hydrocortisone for TSH depletion. After preincubation with 125I-iodide for 50 min to label intracellular iodide, the cells were challenged by serum samples for 1 min. The addition of normal pooled serum hardly affected the I- efflux. The Graves' immunoglobulin G fractions stimulated I- efflux dose-dependently. The mean potency of 12 patient's sera relative to the values of the pooled serum as 100% was 217 +/- 56.4%, which was significantly higher (p < 0.001) than that for 8 normal subjects (110 +/- 16.1%). The results obtained herein indicate that IgG of Graves' patients activate both adenylate aclase-cAMP system and a phospholipid-Ca2 system. I- efflux stimulating immunoglobulins (IESI) activity is a useful marker in making a diagnosis or determining a remission of hyperthyroidism due to Graves' disease.