title: A novel bioreporter assay for thyrotropin receptor antibodies using a chimeric thyrotropin receptor (mc4) is more useful in differentiation of Graves' disease from painless thyroiditis than conventional thyrotropin-stimulating antibody assay using porcine thyroid cells.
abstract: BACKGROUND
  Graves' disease (GD) is caused by thyrotropin (TSH) receptor antibodies (TSHRAbs) that bind to TSHR and activate thyrocytes. The measurement of TSHRAbs therefore has been used to assist in the diagnosis and management of GD.
  
  
  METHODS
  In this study, we evaluated the clinical significance of a newly developed bioreporter assay for the detection of TSHRAbs (Thyretain). The Thyretain bioreporter assay utilizes a chimeric receptor (Mc4), in which residues 262-335 of TSHR are replaced with a rat lutropin-choriogonadtropin receptor segment. This bioreporter is designed to specifically detect stimulating TSHRAbs (Mc4-TSHRAbs).
  
  
  RESULTS
  The Mc4-TSHRAb level of sera obtained from 110 normal healthy controls, 103, 99, and 50 patients with untreated GD, painless Hashimoto's thyroiditis (PT), and subacute thyroiditis (SAT) were 27.3% +/- 11.3%, 327.8% +/- 105.9%, 48.9% +/- 48.5%, and 24.9% +/- 13.4%, respectively. Compared with the Mc4-TSHRAb levels of patients with PT and SAT, and normal healthy controls, the Mc4-TSHRAb levels of untreated GD patients were significantly higher (p < 0.01). The sensitivity and specificity of the Thyretain bioreporter assay for GD and PT were 95.1% and 96.0%, respectively, at the optimal cut-off value of 128%. Measurement of TSHRAbs with a bioassay that uses porcine thyroid cells (TSH-stimulating antibody [TSAb]) showed a positive correlation (r = 0.472, p < 0.001) with the Thyretain assay for untreated GD, and strong positive correlation (r = 0.821, p < 0.001) for the entire untreated GD, PT, and SAT population. The positive rate of Mc4-TSHRAbs for GD was significantly higher than that of TSAb (95.1% vs. 89.3%, p < 0.05) and the negative rate of PT by Mc4-TSHRAbs was also significantly higher than that of TSAb (96.0% vs. 86.9%, p < 0.01). As a result, Mc4-TSHRAbs showed statistically better (p < 0.01) diagnostic accuracy in differentiating GD from PT than TSAb.
  
  
  CONCLUSIONS
  These data suggest that the Thyretain bioreporter assay with a chimeric TSHR (Mc4) is more useful in the differential diagnosis of GD from PT than the bioassay with wild-type TSHR on porcine thyroid cells.
authors.affiliation: Kamijo Thyroid Clinic and Kamijo Thyroid Research Institute , Sapporo, Japan. katt@cocoa.ocn.ne.jp
authors.forename: Keiichi
authors.initials: K
authors.lastname: Kamijo
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Murayama
authors.forename: Takahiro
authors.initials: T
authors.lastname: Uzu
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Togashi
authors.forename: George J
authors.initials: GJ
authors.lastname: Kahaly
mesh_terms: D000328:Adult; D000818:Animals; D001681:Biological Assay; D016466:CHO Cells; D006063:Chorionic Gonadotropin / Q000737:chemistry; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D017930:Genes, Reporter; D006111:Graves Disease / Q000175:diagnosis / Q000276:immunology* / Q000378:metabolism; D050031:Hashimoto Disease / Q000097:blood / Q000276:immunology; D006801:Humans; D007986:Luteinizing Hormone / Q000737:chemistry; D008297:Male; D051381:Rats; D011989:Receptors, Thyrotropin / Q000737:chemistry* / Q000276:immunology*; D013552:Swine; D013961:Thyroid Gland / Q000378:metabolism; D013968:Thyroiditis, Subacute / Q000097:blood
chemical_list: D006063:Chorionic Gonadotropin; D011989:Receptors, Thyrotropin; D007986:Luteinizing Hormone