Augmentation of thyrotropin-induced iodide uptake in FRTL-5 cells by immunoglobulins containing blocking thyrotropin-receptor antibodies under NaCl-depleted conditions

Abstract

Takeuchi R, Kasagi K, Hidaka A, Miyamoto S, Misaki T, lida Y, Konishi J. Augmentation of thyrotropin-induced iodide uptake in FRTL-5 cells by immunoglobulins containing blocking thyrotropin-receptor antibodies under NaCl-depleted conditions. Eur J Endocrinol 1995;132:109–17. ISSN 0804–4643 We have found recently that Graves' immunoglobulins (Igs) are more active under NaCl-free conditions to increase iodide uptake in FRTL-5 thyroid cells. The present study was designed to examine the effect of blocking-type thyrotropin (TSH)-receptor antibodies (TR-abs) in the same assay. FRTL-5 cells were incubated with crude Ig fractions from 13 patients with primary hypothyroidism having blocking TR-abs and 100 mU/l bovine TSH in NaCl-free Hanks' balanced salt solution (HBSS) supplemented with 274 mmol/l sucrose (HBBS(−)-sucrose to keep isotonicity for 3 days, followed by the determination of 60 min of 125I uptake in the cells. Thyrotropin alone increased the uptake to 3.3-to 5.2-fold of the basal. When the highest concentration (250 ml serum equivalent (eq.)/l) of the Ig was used, the TSH-stimulated 125I uptake was decreased to 0–42% in 11 of the 13 cases. When the lower concentrations (0.4–50 ml serum eq./l) were used, however, 125I uptake was enhanced (1.4- to 11.4-fold) unexpectedly in all 13 cases. Such an enhancement was specific to blocking TR-abs, because the effect was duplicated by the purified IgG but not by Igs from 10 healthy control subjects or from three TR-ab-negative hypothyroid patients. When Graves' Igs, instead of TSH, were used as a stimulator, the similar stimulatory effect of the Ig with blocking activity was observed on the 125I uptake induced by three Graves' Igs but not on the response to one Graves' Ig. These Igs alone displayed no stimulating activity. When isotonic 5H medium was used instead of HBSS(−)-sucrose, effects of these 13 Igs were only inhibitory on the TSH-stimulated 125I uptake. In summary, Igs containing blocking TR-abs from patients with primary hypothyroidism showed a variable effect on TSH- or Graves' Ig-induced 125I uptake, depending on their concentration and the presence of NaCl. Together with our recent reports that both stimulating and blocking TR-abs exist simultaneously in some patients, these observations suggest that the two types of TR-abs and TSH may play a more complicated role in disease expression than what has been suggested as merely a net activity. Kanji Kasagi, Department of Nuclear Medicine, Kyoto University School of Medicine, 54 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto 606-01, Japan