Clinical studies on abnormal thyroid stimulators in patients with Graves' disease. I. A sensitive assay for thyroid-stimulating antibodies using cultured porcine thyroid cells and polyethylene glycol precipitation of serum

Abstract

The activities of thyroid-stimulating antibody (TSAb) in serum from patients with Graves' disease were measured by a sensitive assay, using cultured porcine thyroid cells and the precipitation from serum with polyethylene glycol (PEG), and the activities were compared with those of thyrotropin binding inhibitor immunoglobulin (TBII), measured by the commercial assay kit. Porcine thyroid cells after digestion were cultured for 15-18 hours with TSH of 1-10,000 microU/ml or the precipitations of sera from normal subjects and patients with Graves' disease or Hashimoto's thyroiditis, and then the cAMP levels in the culture medium were determined by the commercial RIA assay kit (Yamasa). The precipitation was obtained by adding 0.5 ml of 30% PEG solution to 0.5 ml serum, and was resuspended with 0.6 ml of Hanks' medium without NaCl, containing 1.5% bovine serum albumin, 20mM Hepes and 0.5 mM 3-isobutyl-1-methylxanthine. The precipitation contained about 85% of immunoglobulin and 63% of albumin of the original amount of the serum, as well as substantial TSH, when the original serum contained TSH more than 40 microU/ml. When the PEG precipitations from 10 normal subjects were incubated with the thyroid cells of 4 X 10(5) cells, the cAMP releases into the medium ranged from 83 to 124%, when the mean value was calculated as 100%. Therefore, the cAMP release of more than 130% of the amount released into the culture medium incubated with normal IgG was judged as positive TSAb activity. The minimum detectable quantities were regarded as about 5 microU/ml TSH equivalent. TSAb and TBII activities were detected in 48 (92%) and 50 (96%) of 52 patients with untreated hyperthyroid Graves' disease, respectively, and either TSAb or TBII activities were detected in 16 (80%) of 20 patients with Graves' disease maintained in a clinically euthyroid state by treatment with antithyroid drugs. TBII was positive in 10(50%) of these patients. Some patients showed distinct discrepancies in these two activities, although there was a significant positive correlation between TSAb and TBII activities (r = 0.53, p less than 0.01) in patients with untreated Graves' disease. In these patients, TSAb activities showed a significant positive correlation with values for 99mTc thyroid uptake, determined 30 min after the injection. However, they did not show any significant correlation with serum T4 or T3 concentrations. Similarly, TBII showed significant correlations with goiter size and 99mTc thyroid uptake. To conclude, the present assay for TSAb is sensitive and reproducible.(ABSTRACT TRUNCATED AT 400 WORDS)