Differences in TSH receptor binding and thyroid-stimulating properties between TSH and Graves' IgG. Slowly-acting TSH receptor antibody moieties in Graves' sera affect assay data.
We analyzed TSH receptor (TSHR) effects, both binding and thyroid-stimulation, of TSH and Graves' IgG. A new TRAb assay system utilizes rhTSHR coated tubes and is comprised of two step incubation, the first incubation with patient serum followed by a second incubation with 125I-bTSH. We called TRAb measured by this method as hTRAb. 125I-bTSH binding capacity of the tube was found close to saturation at 1 hr with 200 microl of 125I-bTSH. Up to 5 hr of first incubation for hTRAb assay revealed significant increases in all hTRAb activities. hTRAb was not affected by second incubation time or dose of 125I-bTSH. When 1 step incubation with 125I-bTSH and Graves' serum was performed, hTRAb again increased significantly with time. A simple competitive equilibrium model could not be applied to these ligands. Second, Graves' IgG and bTSH were compared for in vitro thyroid-stimulation sequentially up to 24 hr, measuring cAMP generation from cultured porcine thyrocytes. While bTSH yielded peak cAMP generation by 8 hr, TSAb revealed more cAMP generation by 24 hr than at 8 hr. We concluded that individual Graves' sera contain heterogeneous TRAb of variable avidities, and that slow-acting TRAb, which may lack biological activity, can be detected by prolonged incubation.
Saiki
Yasuhiko
Y
Department of Nuclear Medicine, Kobe City General Hospital, Minatojima-nakamachi, Kobe, Japan.
Ishihara
Takashi
T
Ikekubo
Katsuji
K
Mori
Toru
T
D000818:Animals; D001323:Autoantibodies / Q000097:blood*; D001667:Binding, Competitive; D000242:Cyclic AMP / Q000096:biosynthesis; D006111:Graves Disease / Q000097:blood / Q000503:physiopathology*; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism*; D018828:Immunoglobulins, Thyroid-Stimulating / Q000494:pharmacology; D011989:Receptors, Thyrotropin / Q000097:blood / Q000378:metabolism*; D013552:Swine; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology*; D013972:Thyrotropin / Q000378:metabolism* / Q000494:pharmacology; D013997:Time Factors
D001323:Autoantibodies; D007074:Immunoglobulin G; D018828:Immunoglobulins, Thyroid-Stimulating; D011989:Receptors, Thyrotropin; C094372:thyrotropin-binding inhibitory immunoglobulin; D013972:Thyrotropin; D000242:Cyclic AMP