Interaction of Thyroid-Stimulating Antibodies With the Human Thyrotrophin Receptor

Using a radioligand receptor assay the sera of 46 patients with myasthenia gravis (MG) were tested for the presence of circulating TSH-binding inhibiting immunoglobulins (TBII). In addition thyroid function was evaluated on the basis of T3, T4, TBG and TSH radioimmunoassays including the TRH stimulation test. Circulating antimicrosomal and antithyroglobulin thyroid antibodies were measured by haemagglutination techniques. Two patients had concomitant Graves' disease (GD), 5 were euthyroid with autonomously functioning thyroid tissue due to non-immunogenic multinodular goitre and 39 myasthenic patients were euthyroid with normal pituitary thyroid axis. Only 1 patient with GD had strongly positive TBII-activity and 3 euthyroid MG patients were TBII borderline-positive.

mentioning

confidence: 99%

Circulating TSH-binding inhibiting immunoglobulins in myasthenia gravis

Kiessling

Finke²,

Kotulla³

et al. 1982

“…Furthermore, the interassay variability can be monitored easily by means of standard 1.6 M ASP. A TSH-equivalent or [iU TSH value per mg IgG in 1.6 M ASP from patients with Graves' disease can be calculated, as suggested before by Smith et al (1977b) and Arikawa et al (1980), after the necessary correction for the TSHequivalent value of normal IgG. Finally, this pro¬ cedure may be applied to any serum fraction to be studied.…”

Section: Resultsmentioning

confidence: 98%

Standardization of the radioreceptor assay against anti-thyrotrophin receptor antibodies in Graves' disease

Bruin

Król

Heide

1982

We studied the possibility of standardizing the radioreceptor assay for the detection of anti-thyrotrophin receptor antibodies, also called thyrotrophinbinding inhibitor immunoglobulins (TBII), to circumvent the problem of inter-assay variability in TBII index calculations. We developed a procedure for conversion of the thyrotrophin-binding inhibition caused by standard amounts (10 mg IgG/ml) of 1.6 m ammonium sulphate precipitates into thyrotrophin-equivalents, i.e. the amount of thyrotrophin required to cause the same thyrotrophin-binding inhibition. We were able to determine a normal range for thyrotrophin-binding inhibition which exhibited little inter-assay variability and was applicable to individual radioreceptor assays. The normal range, expressed in thyrotrophin-equivalents or the logarithm of \g=m\U thyrotrophin, was 2.616\p=n-\3.645, which corresponds to 413\p=n-\4420\g=m\U. The thyrotrophin-binding inhibition by 1.6 m ammonium sulphate precipitates from sera of 17 untreated patients with Graves' disease was also expressed in thyrotrophin-equivalents. For 15 patients (88%) the thyrotrophin-equivalent values were above the normal range, whereas only 10 patients (59%) had a positive TBII index (using the same sample). This indicated that 5 patients had anti-thyrotrophin receptor antibodies in spite of their negative TBII index. Standardization based on the IgG content of the test samples therefore seems to be imperative. Pig serum 1.6 m ammonium sulphate precipitates, which were tested in a porcine assay system, yielded thyrotrophin-equivalent values that corresponded closely to the normal range for the human assay system, suggesting that the normal range of thyrotrophin-binding inhibition is in the same order of magnitude in porcine and human assay systems.

“…1 Therefore we cannot draw any conclusion on the physiological relevance of the kinetic behaviour of TSH binding sites in the presence of normal gam¬ maglobulins. On the other hand, the well-known so-called 'aspecific' TSH-binding inhibition caused by normal gammaglobulins in the radio-receptor assay for TSH-binding inhibitor immunoglobulins (TBII) (Smith et al 1977b;Endo et al 1978;) is easily explained by assuming that the observed decrease in R high and R low leads to a reduction in TSH binding sites available for the [125I]bTSH tracer.…”

Section: Resultsmentioning

confidence: 99%

“…It is generally assumed (Hall et al 1975;Adams 1980) that the serum of patients with Graves' disease contains antibodies which bind to thyroid TSH receptors (Manley et al 1974;Smith et al 1977b; Mehdi & Kriss 1978;Endo et al 1981); by mimicking the biological actions of TSH these antibodies could be responsible for the hyperfunctioning of the thyroid gland in Graves' disease (Adams et al 1974;Orgiazzi et al 1976;Shishiba et al 1978;Zakarija 1980). Recently we demonstrated that anti-TSH receptor antibodies in Graves' dis¬ ease indeed bind to the TSH receptor but may be directed towards different determinants on the TSH receptor than the TSH binding site itself (de Bruin & van der Heide 1983).…”

mentioning

confidence: 99%

Anti-TSH receptor antibodies in Graves' disease modulate the kinetic behaviour of autologous thyroid TSH receptors. Evidence of the IgG-induced cross-linkage of autologous TSH receptors

Bruin

Heide

Król

1984

The effect of the anti-TSH receptor antibodies present in the sera of 8 patients with Graves' disease on the affinity constant (Ka) and the number (R) of TSH receptors in autologous human thyroid plasma membranes was investigated. Kinetic analysis of [125I]bTSH binding to human thyroid plasma membranes in the presence of autologous Graves' and normal gammaglobulins was carried out by means of a computer fitting programme. Analysis of the TSH-TSH receptor interaction in the presence of TSH alone yielded curvilinear Scatchard plots, indicating the existence of two independent classes of binding sites (high affinity Ka: 8.5 \ m=+-\4.8 \m=x\108 m\ m=-\ 1; low affinity Ka: 5.3 \m=+-\2.7 \m=x\106 m\ m=-\ 1). Similarly the Scatchard plot for this interaction in the presence of normal gammaglobulins is also curvilinear. Linear Scatchard plots, indicating the existence of only one class of high affinity TSH binding sites (Ka: 3.5 \m=+-\1.8 \m=x\108 m\ m=-\ 1), were obtained for both autologous gammaglobulins and pure IgG from 8 patients with Graves' disease. The number of high affinity TSH binding sites in the presence of Graves' gammaglobulins had increased on the average by a factor 3.76 \ m=+-\0.74 (sd) with respect to the number found in the presence of normal gammaglobulins. This marked change in the kinetic behaviour of the TSH binding sites provided evidence that there is a direct interaction between anti-TSH receptor antibodies and autologous TSH receptors.Divalency of Graves' IgG or linkage of Fab fragments by anti-Fab antiserum proved to be necessary to produce this specific change in the kinetic behaviour of TSH binding sites. Graves' IgG monovalent Fab and Fc fragments had no effect. We suggest that the mechanism by which anti-TSH receptor antibodies in Graves' disease mimick the biological action of TSH is the IgG-induced cross-linkage ofTSH receptors.