As a homologous system is required to evaluate the effect of thyroid-stimulating antibody (TSAb) present in the serum of Graves' patients, primary cultures obtained from normal human thyroid gland have been used and the stimulatory effect measured as an increase of cAMP intracellular levels.
Monolayer cell cultures were stimulated by IgG purified from sera of Graves' patients or control subjects and compared to the effect of bovine TSH. Bovine TSH produced a dose-dependent increase in cAMP intracellular levels between 0·05 mU and 2·5 mU/ml, reaching a maximal value after 30 min with higher doses. While normal IgG had no effect, IgG prepared from untreated patients with frank Graves' disease elicited a significant increase in cAMP accumulation at a concentration between 0·05 and 0·5 mg/ml within 60 min in thirteen out of fourteen patients. A longer incubation period showed no further increase in cAMP values, even if in one case a higher concentration (5·0 mg/ml) of Graves' IgG had a delayed response. When the cAMP intracellular level modifications produced by Graves' IgG preparations in thyroid cell cultures were compared to those evoked in thyroid slices, an identical percentage (93%) of positive cases was obtained, without a coincidence of negative cases. Using thyroid slices the cAMP intracellular increase above basal levels was higher, if considered as a percentage, but in cultured cells a very low IgG concentration was sufficient to detect the presence of TSAb. No correlation between the two assays was found.
In conclusion, normal human cultured thyroid cells appeared to be a more suitable substrate when compared to human thyroid slices for detecting the presence of TSAb in Graves' disease and for studying its effect on thyroid cells. However, a 100% TSAb positivity was present in our Graves' patient series only when both assays were used.