Graves' disease is caused by stimulating
autoantibodies against the
thyrotropin receptor inducing uncontrolled overproduction of
thyroid hormones. A Bridge Assay is presented for direct detection of these
thyroid-stimulating immunoglobulins using
thyrotropin receptor chimeras. A capture receptor, formed by replacing aa residues 261-370 of the human
thyrotropin receptor with residues 261-329 from rat
lutropin/
choriogonadotropin receptor and fixed to microtiter plates, binds one arm of the
autoantibody. The second arm bridges to the signal receptor constructed from
thyrotropin receptor (aa 21-261) and secretory
alkaline phosphatase (aa 1-519) inducing chemiluminescence. The working range of the assay is from 0.3 IU/l to 50 IU/l with a cutoff of 0.54 IU/l and functional sensitivity of 0.3 IU/l. Sensitivity and specificity are 99.8 and 99.1%, respectively, with a diagnostic accuracy of 0.998. The low grey zone is from 0.3-0.54 IU/l. The stimulatory character of the assayed
antibodies is shown through a good correlation (r=0.7079, p<10(-7)) to serum T4 levels of untreated patients. In
Graves' disease, titers are increased in associated
eye disease. In 3 hypothyroid patients with sera positive in the
thyrotropin receptor competition assay and in the blocking bioassay,
antibodies are not detected by the Bridge Assay, while the monoclonal blocking antibody K1-70 was detected. In
Hashimoto disease thyrotropin receptor autoantibodies are detected in some patients, but not in
goiter. This Bridge Assay delivers good diagnostic accuracy for identification of
Graves' disease patients. Its high sensitivity may facilitate early detection of onset, remission, or recurrence of
Graves' disease enabling timely adaption of the treatment.Human genes: TSHR, Homo sapiens, acc. no. M31774.1.