Thyroid-stimulating antibody bioassay using porcine thyroid cells cultured in follicles

Isolated porcine thyroid cells were cultured in agarose-coated dishes and allowed to reform follicles with normal polarity. The thyroid cells reaggregated into follicles were compared with cells cultured in monolayer for cAMP responsiveness to TSH and thyroid-stimulating antibody (TSAb). The cells in follicles were sensitive to TSH stimulation and responded to the hormone at concentrations as low as 3.3-10 microU/ml with an increase in cAMP production. In contrast, 10-50 microU/ml TSH were required to elicit a cAMP response in cells cultured in monolayer using identical conditions. cAMP responsiveness to TSAb also was greater in the cells organized into follicles. TSAb was detected in serum from 89.4% of 66 untreated patients with hyperthyroid Graves' disease using thyroid follicles, but TSAb was detected in serum from only 60% of the patients when assayed using cells in monolayer. The assay using thyroid follicles was used to measure TSAb in 27 euthyroid patients who were euthyroid while receiving thionamide therapy and compared with 20-min thyroid 131I uptake after T3 suppression. TSAb was present in 11 of 12 nonsuppressible patients and in 5 of 15 suppressible patients. TSAb was positively correlated with 20-min 131I thyroid uptake. We conclude that thyroid cells cultured in follicles are suitable for measuring TSAb.