Concentration-dependent regulation of thyrotropin receptor function by thyroid-stimulating antibody

Abstract

Thyrotropin receptor (TSHR) Ab's of the stimulating variety are the cause of hyperthyroid Graves disease. MS-1 is a hamster mAb with TSHR-stimulating activity. To examine the in vivo biological activity of MS-1, mice were treated with purified MS-1 intraperitoneally and the thyroid response evaluated. MS-1 induced a dose-dependent increase in serum thyroxine (T4), with a maximum effect after 10 μg of MS-1 was administered. MS-1-secreting hybridoma cells were then transferred into the peritoneum of nude mice to study chronic thyroid stimulation. Serum MS-1 levels detected after 2 weeks were approximately 10-50 μg/ml, and the serum TSH was suppressed in all animals. Serum triiodothyronine levels were elevated, but only in animals with low serum MS-1 concentrations. In addition, there was a negative correlation between serum T4 and the serum MS-1 concentrations. These in vivo studies suggested a partial TSHR inactivation induced by excessive stimulation by MS-1. We confirmed this inactivation by demonstrating MS-1 modulation of TSHR function in vitro as evidenced by downregulation and desensitization of the TSHR at concentrations of MS-1 achieved in the in vivo studies. Thus, inactivation of the TSHR by stimulating TSHR autoantibodies (TSHRAb's) in Graves disease patients may provide a functional explanation for the poor correlation between thyroid function and serum TSHR-Ab concentrations.

A Unique Mouse Strain That Develops Spontaneous, Iodine-Accelerated, Pathogenic Antibodies to the Human Thyrotrophin Receptor

“…Moreover, the IgM TSAb transgenic mouse model requires LPS administration to expand the transgenic B cell population. Other animal models have involved the intraperitoneal injection of hybridoma cells secreting a potent hamster monoclonal TSAb (44) or injection of purified, extremely potent, mouse monoclonal TSAb IgG (45). Valuable insights were obtained from all three studies into (for example) immune parameters and/or the pathogenic changes accompanying TSAb-induced hyperthyroidism.…”

“…H2 h4 mice is the restoration of tolerance to the TSHR. Methods used to induce hyperthyroidism in mice, unsuitable for inducing self-tolerance to the TSHR, include: TSH injection (for example 48), TSAb mAb injection (45), hamster TSAb mAb hybridoma injection (44), TSHR immunization approaches to express TSHR in mice (5–9), hamsters (10) and rhesus monkeys (11), and expressing TSAb (B6B7) in a transgenic mouse (42,43). Confounding effects of hyperthyroidism on the immune system include altering the phenotype and function of antigen-presenting dendritic cells (46) and polarizing dendritic cells leading to impaired function of regulatory T-cells (Treg), a major change that may influence the emergence of pathogenic autoantibodies (47).…”

Delineating the autoimmune mechanisms in Graves’ disease

“…Experimentally produced blocking TSHR-mAbs have been shown to bind to independent linear or conformational epitopes [44] on the α subunit although at least one linear epitope on the β subunit has been described [33]. TSHR autoantibodies from patients with GD or HT have been shown to compete with a blocking TSHR-mAb to the N-terminus of the TSHR β subunit (amino acids 382-415) [45].…”

Prediction for recurrence following antithyroid drug therapy for Graves’ hyperthyroidism

“…In some patients who had recurrence of hyperthyroidism after ATD withdrawal, the TRAb titer remained high (21). This was also indicated by a study in mice showing that excessive autoantibody stimulation reduces the sensitivity of the thyroid gland to TRAb through downregulating TSH receptors (22). This might be due to a change in thyroid gland responsiveness to TRAb, which may be caused by the progression of cell-mediated autoimmune destruction during the disease process of GD (18).…”