Blocking Type Antithyrotropin Receptor Antibody in Patients with Nongoitrous Hypothyroidism: Its Incidence and Characteristics of Action

The incidence, characteristics of action, and pathogenetic importance of blocking type anti-TSH receptor antibody were examined in patients with autoimmune thyroiditis. Serum immunoglobulin G (IgG) from 8 of 20 patients with nongoitrous hypothyroidism contained substantial amounts of TSH binding inhibitor immunoglobulin (TBII) activity. Newborn infants of a patient with the greatest TBII activity had neonatal transient hypothyroidism. In sera of patients with goitrous hypothyroidism and euthryoid chronic thyroiditis, only weakly positive or negative TBII activity was found. IgGs of these patients and those of nongoitrous hypothyroid patients without strongly positive TBII activity did not inhibit TSH stimulation of thyroid adenylate cyclase activity. Seven of 8 IgGs which had strongly positive TBII activity significantly inhibited cAMP generation induced by 9.1 mU/ml TSH, and the eighth IgG inhibited stimulation with 0.5 mU/ml TSH. Although the modes of TSH binding inhibition were variable, markedly close correlation was found between TSH binding- and TSH stimulation-inhibiting activities of these 8 IgGs (r = 0.90; P < 0.01). These IgGs may exert their inhibitory effects on adenylate cyclase activity by inhibiting TSH binding to its receptor.