Relationships Among Immunoglobulin Markers in Graves' Disease*

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Abstract
TSH-binding inhibitory activity (TBIA), LATS, and LATS-protector (LATS-P) were examined in sera of 17 patients with untreated Graves' disease (UGD), 17 patients treated for Graves' disease (TGD) and rendered euthyroid, 4 TGD cases not yet euthyroid, 12 patients with euthyroid Graves' disease (EGD), 14 patients with Hashimoto's thyroiditis, and 14 euthyroid relatives of Graves' disease patients. TBIA, LATS, and LATS-P were positive in 69%, 29%, and 100% of UGD sera so studied. Frequency of positive TBIA, LATS, or LATS-P was much less in EGD than in UGD. These activities were undetectable in sera of all patients with Hashimoto's thyroiditis. LATS-P was demonstrable in one Graves' relative, while TBIA or LATS were undetectable in all 14 of them so studied. TBIA was strongly positive in all 10 LATS-positive sera (5 UGD, 4 TGD, and 1 EGD) in this study. It was negative, however, in many sera (5 of 12 UGD, all 7 TGD, all 4 EGD, and the 1 Graves' relative) which were positive for LATS-P without LATS. There was a good correlation (r = 0.59; P < 0.001) between LATS (log response index) and TBIA in 38 Graves' disease sera (17 UGD, 17 TGD, and 4 TGD but still hyperthyroid). However, the r of 0.28 between LATS-P (percentage of protection) and TBIA in 29 LATS-negative sera so studied was not statistically significant (P < 0.2). A patient with Graves' disease demonstrated normally suppressible 24-h thyroid radioiodine uptake after propylthiouracil therapy at a time when TBIA was demonstrable in serum. Similarly, two EGD patients and a relative of a patient with Graves' disease had normal thyroid radioiodine suppression tests in association with a clearly positive LATS-P in the serum. The various data suggest that 1) LATS-P is a more sensitive marker of Graves' disease than LATS or TBIA, and 2) TBIA correlates well with LATS but not as well with LATS-P. The latter finding is consistent with the idea that LATS-P and TBIA are separate activities in Graves' disease, but technical problems prevent a definite conclusion. Additionally, findings in this and other studies of positive LATS-P, TBIA, and/or LATS in some cases with normally suppressible thyroid function raise a question aboutthe significance of these activities, as now estimated, as the sole cause of hyperthyroidism in Graves' disease. (J Clin Endocrinol Metab48: 381, 1979)