Use of cells expressing the human thyrotropin (TSH) receptor for the measurement of thyroid stimulating and TSH-blocking antibodies.

A clone of Chinese hamster ovary cells (CHO) transfected with the cDNA of the human thyrotropin (TSH) receptor (CHO-R) was used to optimise assays for TSH receptor antibodies with either thyroid stimulating (TSAb) or TSH blocking (TSH-blocking Ab) activity. The study group included 89 patients with Graves' disease, 38 patients with goitrous Hashimoto's thyroiditis (HT) and 47 subjects with atrophic thyroiditis (AT). In the HT group, 8 patients had subclinical hypothyroidism (HT-SH) and 30 had overt hypothyroidism (HT-H). In the assay for TSAb, CHO-R cells were incubated with 1mg/ml of the immunoglobulin G (IgG) from patients with Grave's disease, while in the assay for TSH-blocking Ab cells were incubated with IgGs from patients with HT or AT alone (1mg/ml), or IgGs plus TSH (10 mU/L). After 2 h of incubation the extracellular cAMP was measured by a RIA. In these conditions a significant stimulation by Graves' IgG was obtained in patients with active hyperthyroidism (33/35, 94% untreated; 21/23, 91% relapsed after a course of medical treatment), in 12/20 (60%) patients euthyroid under methimazole and in 4/11 (36%) euthyroid after a course of antithyroid drugs. TSH-blocking Ab were detected in 1/8 (12.5%) patients with HT-SH, in 7/30 (23.3%) with HT-H and in 16/47 (34.0%) patients with AT. TSAb and TSH-blocking Ab coexisted in 4 IgGs that belonged to patients in whom spontaneous hypothyroidism developed after hyperthyroidism, or viceversa. TSAb and TSH-blocking Ab were also tested on FTRL-5 cells. TSAb were positive in both assays in 43/58 (74%) patients with active Graves' disease, negative in both assays in 3 (5%), negative in FRTL-5 and positive in CHO-R in 11 (19%), negative in CHO-R and positive in FRTL-5 in 1 (1.7%). In FTRL-5 cells TSH-blocking Ab were detected in 1/8 (12.5%) patients with HT-SH, in 5/30 (16.6%) with HT-H and in 15/47 (31.9%) with AT. The results of cAMP stimulation in FRTL-5 and CHO-R showed a fairly good correlation in TSAb (r = 0.60, p < 0.0001) and in TSH-blocking Ab (r = 0.74, p < 0.0001) assays. In conclusion, CHO cells transfected with the cloned human TSH receptor are suitable for the clinical assay of TSAb and TSH-blocking Ab. The sensitivity of this assay is higher than that obtained using FRTL-5 cells, having the additional advantages of expressing the human TSH receptor and requiring less cumbersome procedures for cell culture.