Human monoclonal antibodies have been generated from heterohybridomas obtained by fusing mouse myeloma cells with peripheral lymphocytes from patients with active Graves disease. This report characterizes four antibodies as presumptive thyrotropin receptor antibodies because they specifically inhibit thyrotropin binding and competitively inhibit thyrotropin-induced cAMP levels in human thyroid cells. Two of these antibodies, 208F7 and 206H3, are representative of autoimmune stimulators in Graves disease sera because they stimulate thyroid function in all assays, including the mouse bioassay; their ability to inhibit thyrotropin-induced cAMP increases in thyroid cells competitively is complemented by more than additive agonism at low (10 pM) thyrotropin concentrations. These stimulating antibodies interact more potently with human thyroid ganglioside preparations than with bovine thyroid or brain gangliosides; in contrast, they are poor inhibitors of 125I-labeled thyrotropin binding to liposomes containing the glycoprotein component of the human thyrotropin receptor. Antibodies 129H8 and 122G3 appear to be representative of inhibiting or "blocking" antibodies in Graves disease sera. Thus they have no intrinsic stimulatory action in assays of thyroid function but rather inhibit thyrotropin activity in the assays tested. These two antibodies do not react with human thyroid gangliosides but are strong inhibitors of thyrotropin binding to liposomes containing the high-affinity glycoprotein component from human, bovine, and rat thyroid membranes. The data unequivocally establish the pluritopic nature of the immunoglobulins in Graves disease and relate individual components or determinants of the thyrotropin receptor structure with specific autoimmune immunoglobulins.
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