Simultaneous measurement of TSH-binding inhibitor immunoglobulin and thyroid stimulating autoantibody activities using cultured FRTL-5 cells in patients with untreated Graves' disease

Author:

Lu Chao,Kasagi Kanji,Hidaka Akinari,Hatabu Hiroto,Iida Yasuhiro,Konishi Junji

Abstract

Abstract. A new and practical assay was developed using cultured FRTL-5 cells for simultaneous assessment of TS-ab and TSH-binding inhibitor immunoglobulin, allowing direct comparison of these two activities under the same conditions. Subsequent to the TS-ab assay in which extracellular cAMP concentration in Hanks' medium without NaCl was determined, [125I]bTSH in this medium was added to observe the ability of serum Ig to inhibit the binding of [125I]bTSH to FRTL-5 cells. We found a much higher specific binding of [125I]bTSH to FRTL-5 cells and a much greater inhibition of [125I]bTSH binding to the cells exposed to Graves' Ig in hypotonic NaCl-free than in NaCl containing Hanks' medium, indicating that the binding of both TSH and Graves' Ig to the TSH receptor was salt-sensitive. The inhibitory activity of [125I]bTSH binding to the cells was 0.2±4.6% (mean ±sd) in 45 normals. Inter-assay coefficients of variation in two positive controls with the mean values of 18.0 and 65.8% were 15.8 and 16.5%, respectively. Among 46 patients with untreated hyperthyroidism owing to Graves' disease, 45 (97.8%) were positive for TS-ab; 35 (76.1%) and 40 (87.0%) were positive for TSH-binding inhibitor in Ig assays using FRTL-5 cells and solubilized porcine thyroid membranes, respectively. TS-ab activities correlated less closely with TSH-binding inhibitory activities determined using FRTL-5 cells (r=0.576, p<0.001) than with those determined using porcine thyroid membranes (r=0.745, p<0.001). The correlation between TSH-binding inhibitory activities determined by the two methods, although statistically significant (r=0.537, p<0.001) was rather rough. Some patients clearly demonstrated discrepant results, suggesting the existence of heterogeneous populations of TSH receptor antibodies.

Publisher

Bioscientifica

Subject

Endocrinology,General Medicine,Endocrinology, Diabetes and Metabolism

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