A TSHr-LH/CGr Chimera that Measures Functional TSAb in Graves' Disease

Abstract

Stimulating thyrotropin receptor (TSHr) autoantibodies (TSAb) are the cause of hyperthyroidism in Graves' disease. In a patient's serum, TSAb can coexist with antagonist TSHr autoantibodies that block TSAb stimulatory activity (TSBAb); both can vary in amount and time. The objective of the study was to create a functional assay that detects only TSAb, thus having an increased accuracy for diagnosing Graves' disease. A TSHr chimera (Mc4) that retains an agonist-sensitive TSAb epitope but replaces a TSBAb epitope was stably transfected in cells to establish the Mc4 assay. The study was conducted at the Chieti University (Outpatient Endocrine Clinic) and the University of Pisa (the Department of Endocrinology). The assay was validated using sera from 170 individuals with Graves' disease, Hashimoto's thyroiditis, and nonautoimmune hyperthyroidism and normal subjects from Chieti University. A second blinded study evaluated sera from 175 patients with autoimmune thyroid disease (mainly Graves' disease) from the University of Pisa. Interventions included the assessment of patients' sera using human wild-type TSHr (WT-TSHr), Mc4 chimera, and binding (TRAb) assays. The Mc4 assay has the best accuracy for diagnosing Graves' disease. The Mc4 assay has a better diagnostic accuracy than WT-TSHr and second-generation TRAb assays. Indeed, the sensitivity of the WT-TSHr, TRAb, and Mc4 assays was 97.3, 86.5, and 100%, respectively, whereas the specificity was 93.1, 97, and 98.5%, respectively. The Mc4 assay is a functional assay with improved sensitivity and specificity for the detection of TSAb and is clinically useful in diagnosing Graves' disease.