A novel bioassay for anti-thyrotrophin receptor autoantibodies detects both thyroid-blocking and stimulating activity

Abstract

SummaryAutoantibodies to the thyrotrophin (TSH) receptor (anti-TSHR) are unique, in that they are involved directly in the pathophysiology of certain autoimmune thyroid diseases (AITD). Thyroid-stimulating antibodies (TSAb) act as agonists that activate the thyroid gland and cause Graves' disease. Other anti-TSHR antibodies block TSH and can cause hypothyroidism. Thyroidblocking antibodies (TBAb) have not been studied as extensively as TSAb. We developed a TBAb bioassay based on a cell line that expresses a chimeric TSHR. The 50% inhibitory concentration of the chimeric Chinese hamster ovary (CHO)-Luc cells was more than five-fold lower compared with the wild-type CHO-Luc cells. We tested the performance of this bioassay using a thyroid-blocking monoclonal antibody K1-70, established an assay cut-off and detected TBAb in 15 of 50 (30%) patients with AITD. Interestingly, the assay detects both TSAb and TBAb and measures the net activity of a mixture of both types of antibodies. There was a high correlation (R 2 0·9, P < 0·0001) between the results of the TSAb assay and the negative percentage inhibition of the TBAb assay. The TBAb bioassay was approximately 20-fold more sensitive than a commercially available TSHR binding assay (TRAb). In contrast to TRAb, sera with high levels of TBAb activity were able to be diluted several hundred-fold and still exhibit blocking activity above the cut-off level. Thus, this TBAb bioassay provides a useful tool for measuring the activity of anti-TSHR antibodies and may help clinicians to characterize the diverse clinical presentations of patients with AITD.

Prevalence, Phenotype, and Psychosocial Well-Being in Euthyroid/Hypothyroid Thyroid-Associated Orbitopathy

“…As the eu-/hypothyroid TAO patients were TRAb-negative in the present study, besides orbital magnetic resonance imaging-sensitive laboratory assays (i.e. cell-based bioassays), may, as previously shown (35)(36)(37)(38), significantly improve diagnostics of TAO.…”

Conformational inactivation induces immunogenicity of the receptor-binding pocket of a bacterial adhesin

“…Interestingly, they often are abundant in patients with autoimmune syndromes in which a humoral response is directed against receptor proteins, e.g., autoantibodies against the thyrotropin receptor in Graves' disease or insulin receptor-specific antibodies in insulin autoimmune syndrome (26,27). By mimicking the functions of the ligands (thyroid hormone and insulin, respectively), these antibodies are directly involved in in the pathophysiology of hyperthyroidism and hypoglycemia.…”

Autoimmune thyroid disorders

“…The identification of the bioactivity of TRAbs requires a bioassay using cellular systems carrying functional TSH receptors [59]. Blocking antibodies are detected using a modified bioassay [60,61]. Blocking TRAbs are mostly detected in a fraction of patients with AT.…”