Several reports have been published on the anti-
TSH receptor antibody in putative autoimmune thyroid disorders using a radioreceptor assay. We have carried out correlative studies between the ability of serum
immunoglobulins to displace radiolabeled TSH from the thyroid plasma membrane
receptor [TSH-displacing activity (TDA)] and that of actual stimulation of the human thyroid gland [human thyroid-stimulating activity (hTSA)] in Graves' and other
thyroid diseases and in control subjects. TDA was assayed by the use of a radioligand technique, while the activation of
adenylate cyclase in human thyroid slices was measured as an index of hTSA. The same
immunoglobulins were employed for both assays. In this series, positive TDA and hTSA values were found in 70.4% and 81.5% of the samples in active untreated
Graves' disease, respectively. Samples from normal persons and from several patients with toxic
nodular goiter gave generally negative results in both assays; in a small proportion of patients with either
subacute thyroiditis or Hashimoto's
thyroiditis, the TDA was positive but hTSA proved to be negative. In
Graves' disease (including those patients on
propylthiouracil) in remission and treated with 131I, the correlation between TDA and hTSA was not significant (r = 0.309; P greater than 0.1); even when the procedures were compared in the untreated group alone, there was no significant correlation between the two activities (r = 0.309, P greater than 0.1). These studies indicate that 1) significant TDA and hTSA are observed in
Graves' disease; nevertheless, the correlation between them is not significant; 2) the hTSA assay appears to be more sensitive and specific than the TDA assay; and 3) TDA may not be synonymous with thyroid stimulation.