69 THE CLINICAL SIGNIFICANCE OF THYROID STIMULATION-BLOCKING IMMUNOGLOBULINS

Abstract

Immunoglobulin G (IgG) fractions from three mothers with primary myxedema, who delivered neonates, 6 patients with goitrous Hashimoto's disease and one adolescent girl with primary myxedema were tested for their ability to alter TSH stimulation of cAMP production in porcine thyroid follicles of suspension culture and the binding of TSH to its receptor in Smith's assay. The results suggested the presence of at least two types of IgG: 1) one inhibits TSH-stimulated CAMP responses and TSH binding to its receptors; 2) the other inhibits TSH-stimulated cAMP responses but does not inhibit TSH binding to its receptors. The former was detected in all three mothers and the thyroid stimulation-blocking activity of the IgG was most significant in the mother of transient neonatal hypothyroidism. The latter was detected in 5 patients with goitrous thyroiditis. The accumulation of CAMP by 1 mU/ml TSH decreased with increasing quantities of both IgGs (the dose range 1-15 mg/ml). The present study suggests that one of the IgGs which inhibits TSH-stimulated CAMP responses may be responsible for thyroid dysfunction in primary myxedema and also for transient neonatal hypothyroidism. However, the clinical significance of another blocking IgG which does not inhibit TSH binding to its receptors should be clarified.