Bioassay of thyroid-stimulating immunoglobulins using human thyroid cell cultures: optimization and clinical assessment.

Primary monolayer cultures of human thyroid cells have been used to investigate the intracellular cyclic AMP response to thyroid-stimulating immunoglobulins (TSIg) prepared from the sera of patients with Graves' disease. In particular, attention was directed towards dose-response characteristics obtained under differing incubation conditions, and an optimized incubation procedure based upon conditions consistent with the maximal precision of TSIg measurement was developed. The magnitude of the cyclic AMP response to a tested TSIg preparation was shown to be greatest after the longest incubation period investigated, 16 h, for all doses of TSIg investigated. The greatest precision of TSIg measurement, as determined by the lowest relative error, was obtained at an immunoglobulin (Ig) dose of 1 mg/ml, and when incubated at this dose level for 16 h, all Ig-enriched fractions prepared from the sera of 28 newly-diagnosed patients with Graves' disease significantly (P less than 0.05) raised the intracellular cyclic AMP level of thyroid cell monolayers. After thionamide drug therapy, the incidence of TSIg detection declined to 42% (5 of 12 patients). TSIg bioactivity was also found in 9 of 14 (64%) patients with euthyroid exophthalmos and in 4 of 11 (36%) cases of non-toxic goitre. In contrast, Ig's prepared from the sera of normal euthyroid volunteers were devoid of TSIg bioactivity.