AN INVESTIGATION OF THE ABILITY OF TSH AND GRAVES IMMUNOGLOBULIN-G TOINCREASE INTRACELLULAR CALCIUM IN HUMAN THYROID-CELLS, RAT FRTL-5 THYROID-CELLS AND EUKARYOTIC CELLS TRANSFECTED WITH THE HUMAN TSH RECEPTOR

The purpose of this study was to determine if immunoglobulin G prepara tions (IgGs) from patients with Graves disease can increase intracellu lar calcium in thyroid cells, as has been reported for TSH. Both TSH a nd Graves' IgGs (prepared by protein G affinity chromatography) increa sed calcium in a range of thyroid cells; however, the response seen, u sing Fura-2-loaded coverslips of cell monolayers, varied considerably. Chinese hamster ovary (CHO/JPO9) cells transfected with a high number of human TSH receptors showed the greatest response: TSH (10 mU/ml) i ncreased calcium in 46% of experiments and 18 out of 25 (72%) Graves' IgGs increased calcium at 0.1 mg/ml (significantly greater, P<0.001, t han for control IgGs where cells responded to 2 out of 13 preparations ). Rat FRTL-5 cells only responded to TSH in 22% of experiments and to 2 out of 8 (25%) of Graves' IgGs. Similarly, human thyroid cells resp onded to TSH in 22% of experiments and to 2 out of 9 (22%) of Graves' IgGs. (When studying cyclic AMP responses in JPO9 cells, much higher c oncentrations of Graves' IgGs were required (1-3 mg/ml).) However, hig her concentrations (0.3 mg/ml) of both Graves' IgGs, and to a lesser e xtent of control IgGs, were capable of increasing calcium in cells bot h with and without TSH receptors (control CHO cells and normal human d ermal fibroblasts). We conclude that relatively low concentrations of patient IgGs can be distinguished from control IgGs in JPO9 cells on t he basis of their ability to increase calcium, but that additionally a ll IgG preparations possibly contain another factor which can increase calcium in a range of cells independent of the presence of the TSH re ceptor.