Thyroid Stimulating Immunoglobulin Activity Research Articles

Role of Maternal Thyroid-Stimulating Immunoglobulin in Graves' Disease for Predicting Perinatal Thyroid Dysfunction.

Objective To assess maternal thyroid-stimulating immunoglobulin (TSI) as a predictor of neonatal thyroid hyperthyroidism in pregnancies complicated by Graves' disease. Methods This is a 10-year retrospective study of patients with a history of Graves' disease and elevated TSI activity level defined as 1.3 times the normal. All subjects underwent cordocentesis for ultrasound findings of suspected fetal thyrotoxicosis (fetal tachycardia, oligohydramnios, hydrops, and thyromegaly). Neonatal diagnosis was made based on neonatal thyroid function testing or symptoms. Results Fourteen patients were included in the study, seven with active Graves' disease requiring antithyroid drug (“ATD group”) and seven with iatrogenic hypothyroidism on levothyroxine (“levothyroxine group”). Four cases (57%) of neonatal thyrotoxicosis were diagnosed in the levothyroxine group compared with two cases (28%) in the ATD group. The lowest maternal TSI level at which a neonate did not develop hyperthyroidism was 2.6 for the levothyroxine group and 2.5 for the ATD group. The odds ratio of a neonate from the levothyroxine group developing hyperthyroidism compared with one from the ATD group is 3.3 (95% confidence interval: 0.4–30.7). Conclusion For patients with Graves' disease, those with iatrogenic hypothyroidism and TSI > 2.5 times the basal level are at the highest risk for neonatal thyrotoxicosis.

Immunogenicity of a unique region of the human thyrotropin receptor.

Clarifying the role of the TSH receptor protein in the autoimmune process may be the key to understanding the development of Graves' disease. In the present study we used a 16 amino acid peptide of the human TSH receptor (hTSHR) to immunize rabbits. A comparable, but theoretically less immunogenic, peptide was injected into other rabbits. The antibody response against these and other peptides, as well as against solubilized human thyroid membrane (TM) and guinea pig fat cell membrane (GPF) proteins, was tested using ELISA and Western blots. The GPF and TM binding pattern of rabbits' sera was compared to that of Graves' patients' sera. We have identified an area of antigenic cross-reactivity between GPF and TM; a 63 kD protein was present in both GPF and TM, and this protein uniformly bound IgG-s of the rabbits' postimmunization sera and one of eight Graves' patient's serum. We have shown that i) a theoretically immunogenic 16 amino acid peptide was indeed highly immunogenic in rabbits, ii) antibodies binding to GPF and TM were detected after immunization, and iii) the peak of thyroid stimulating immunoglobulin activity of sera was followed by a transient elevation of serum triiodothyronine levels. Further studies investigating the immunogenic epitopes of the hTSHR as well as characterizing the 63 kD protein are indicated.

TSH Receptor Antibody in Hyperthyroid Patients due to Graves' Disease Treated with Antithyroid Drugs

As an immunologic process, TSH receptor antibody (TRab) may be synthesized by the lymphocytes within the thyroid gland. Two techniques were devised to express this TRap activity: a) thyroid stimulating immunoglobulin (TSI) expressed as thyroid c AMP synthesis and b) TSH binding inhibiting immunoglobulin (TBII) expressed as TSH displacement. In general, serum TSI and TBII activity correlated well with each other in hyperthyroid patients. Measurement of TSI and TBII is useful to assess improvement of immunologic abnormality induced by antithyroid drugs. The data so far gathered indicated that TRab disappears from the blood in about 70-80% of hyperthyroid patients in response to antithyroid drugs. However, this does not indicate that intrathyroidal TRab synthesis has ceased, since thyroglobulin is still secreted supernormally and T3 fails to suppress the thyroid in some patients. On the other hand, normalization of thyroglobulin and absence of TRab in the blood indicated complete normalization in the patients as evidenced by positive T3 suppressibility. By using a number of new drugs, further efforts must be made to completely normalize immunologic abnormality in 100% of patients. Recurrence of hyperthyroidism of Graves' disease is generally associated with re-appearance of TRab in the blood in most of the recurrent patients after discontinuation of antithyroid drugs.

Bioassay of thyroid-stimulating immunoglobulin in cryopreserved human thyroid cells: optimization and clinical evaluation.

We have explored the method of Rapoport et al. (J Clin Endocrinol Metab 1984;58:332-8) for the bioassay of thyroid-stimulating immunoglobulin (TSI) in cultured human thyroid cells, to optimize the assay and to evaluate its utility in clinical diagnosis and management of patients with autoimmune thyroid disease. Here we describe the procedure ultimately adopted, its major properties, and the results it has yielded in various clinical states. Clinical sensitivity of the assay was established by demonstrating TSI activity in all of 60 cases of active Graves' disease. We observed in these patients a nonlinear correlation between concentrations of TSI and of triiodothyronine, as well as between TSI concentration and the clinical severity of the thyrotoxicosis. Specificity of the assay was demonstrated by finding no TSI bioactivity in 13 patients with toxic adenoma, five with cold nodule, and 18 of 19 with nontoxic goiter. Remission of Graves' disease in 25 patients was invariably accompanied by undetectable concentrations of TSI; evidently this assay may be useful in identifying patients who are likely to go into remission. TSI activity was present in eight of 11 patients with euthyroid ophthalmopathy (unilateral and bilateral) associated with a normal response to the thyrotropin-releasing hormone test and absence of increased titers of antithyroid antibodies, suggesting that this assay may provide a powerful tool in the clinical diagnosis of this disorder.

Thyroid stimulating immunoglobulin bioactivity during carbimazole therapy as measured by the cytochemical bioassay.

Most assays of thyroid stimulating immunoglobulin (TSI) are unsuitable for the quantitation of TSI during the treatment of Graves' hyperthyroidism because assay insensitivity results in some negative responses. Therefore the sensitive cytochemical bioassay was used to investigate the effect of carbimazole on TSI levels as a possible mechanism for the induction of the increased remission rate which is characteristic of thionamide therapy. Twelve patients were studied before therapy for de-novo Graves' hyperthyroidism; seven patients consented to a detailed prospectively study during block-replace therapy with carbimazole 10mg 6 hourly with a later addition of T3 20 micrograms 6 hourly when biochemically euthyroid. In addition thyroid hormone or T3 suppressed technetium (99m Tc) thyroidal uptake was monitored at between weekly and 3 monthly intervals, as well as the clinical findings, total T4 total T3, TSH, antimicrosomal antibody titers and immunoglobulins IgG, IgM and IgA. TSI was detected in all patients before treatment but there was no correlation with any other pretreatment measurements. During therapy TSI fell (in three different patterns) in 6 out of 7 patients studied for between 14-55 weeks (mean 29 weeks). TSI remained unchanged in one patient. Only the 99m Tc uptake correlated with TSI activity in the treated patients as a group (r = 0.71, p less than 0.001). TSI remained detectable in all patients, even in 4 patients in whom T3 suppression of 99m Tc was demonstrated. There is some evidence for a carbimazole effect lowering TSI activity, however relapse rate did not support this. T3 suppressed 99m Tc uptake may be a sensitive in vivo marker of TSI activity.

Toxic multinodular goiter: a variant of autoimmune hyperthyroidism.

The aim of this study was to examine whether at least a subgroup of patients with toxic multinodular goiter may have autoimmune thyroid disease. Thyroid-stimulating immunoglobulin (TSI) activity, measured by a sensitive bioassay employing cultured human thyroid cells, was determined in patients with toxic multinodular goiter and other thyroid disorders. All patients with active Graves' disease (n = 47) had detectable serum TSI activity, whereas TSI was undetectable in patients with thyroid disease not believed to be of autoimmune origin: toxic adenoma (n = 13), cold nodule (n = 5), and nontoxic goiter (n = 19), with a single exception in the latter group. Toxic multinodular goiter (n = 26) was diagnosed based on clinical and laboratory evidence of hyperthyroidism associated with a multinodular goiter on palpation and scintiscan. The toxic multinodular goiter group was then subclassified according to scintiscan pattern (type A, diffuse but uneven distribution of technetium uptake; type B, multiple discrete nodules of varying size and function). All but 1 of the 11 TSI-positive toxic multinodular goiter patients had a type A scintiscan pattern. The patients with the type A scintiscan pattern were younger and more often had elevated antithyroid antibody titers, ophthalmopathy, and concurrent development of goiter and hyperthyroidism (rather than long-standing goiter preceding hyperthyroidism) compared to the type B patients. Thus, a subgroup of patients with clinically defined toxic multinodular goiter (type A) probably have autoimmune hyperthyroidism (a variant of Graves' disease), while in another subgroup (type B) hyperthyroidism is not related to an autoimmune etiology (a variant of toxic adenoma).

Rabbits immunized with thyroid-stimulating hormone produce autoantiidiotypic thyroid-stimulating antibodies.

We immunized rabbits with thyroid-stimulating hormone (TSH) to investigate the hypothesis that such immunization could result in production of thyroid-stimulating autoantiidiotypic antibodies to anti-TSH. Thyroid-stimulating immunoglobulin (TSI) appeared in the serum of several rabbits after immunization. At 160 d, TSI equivalent to 6-18 microU TSH/1.5 mg IgG was present in two of six human (h)TSH-, two of six hTSH beta chain-, and two of the four surviving bovine (b)TSH-immunized animals. Control (human serum albumin-immunized rabbits) serum TSI was 4.3 +/- 0.4 (mean +/- SD) at this time. Antiidiotypic antibodies that could bind to monoclonal anti-hTSH were found in the sera of the bTSH-immunized rabbits. The peak TSI activity occurred 3 mo after a TSH booster immunization and declined gradually during subsequent weeks. Evidence that antiidiotypic antibodies to anti-TSH can cause thyroid stimulation strengthens the notion that such antibodies may be the cause of Graves' hyperthyroidism.

Thyroid stimulating immunoglobulin bioassay using cultured normal human thyroid cells

It is currently believed that the thyroid stimulating immunoglobulin (TSI) of Graves' disease is involved in the pathogenesis of hyperthyroidism through the stimulation of the adenylate cyclase-cyclic AMP system. To evaluate this mechanism, TSI in the serum of patients with Graves' disease was determined by its ability to generate cyclic AMP (cAMP) in monolayer cells prepared from a normal thyroid gland. The thyroid tissue was digested with collagenase, and the liberated follicles were collected from the supernatant and cultured for 7 days. One gram of thyroid tissue yielded more than 1 X 10(7) monolayer cells which were stored in aliquots at -80C. Cells (1 approximately 2 X 10(4)/0.28 cm2 microtiter well) were incubated for 4 hours in 0.2 ml Hanks solution poor in NaCl, with various amounts of bovine TSH (bTSH) or 1.5 mg/ml Graves' serum IgG extracted by polyethylene glycol. cAMP accumulated in medium and cells was measured by RIA. Total cAMP (both medium and cells) was about 4 times higher when NaCl was deleted from Hanks solution. Moreover, as more than 90% of the cAMP was released into the medium, it was possible to omit the measurement of cellular cAMP, which requires extraction. The increase in medium cAMP concentration was dependent upon the number of cells, incubation time, and dose of bTSH. Time course and dose response curves in medium cAMP stimulated by IgG from 3 Graves' patients paralleled those of bTSH equivalent units. Accordingly, TSI activity could be expressed in bTSH equivalent units (bTSH microUeq). The assay could detect 1.0 or 3.3 microU/ml of bTSH and was highly reproducible. TSI activity in all of 16 IgGs from normal subjects was under 3.3 bTSH microUeq/ml, while it was greater than 3.3 bTSH microUeq/ml in IgGs from 33 of 37 (89%) untreated patients with Graves disease. Of the 13 patients followed for 2 to 7 months while on antithyroid drugs, 12 had greater than 3.3 bTSH microUeq/ml and, with the exception of one, all showed a decrease in their TSI activity. Moreover, 5 of 12 patients treated continuously for more than 1 year were TSI negative (less than 3.3 bTSH microUeq/ml), and except for one case, all had TSI values below 8 bTSH microUeq/ml (a value found in only 25% of untreated patients). This in vitro bioassay for TSI is simple and sensitive. It detects the presence of TSI in virtually 90% of untreated patients with Graves' disease. TSI activity showed a clear decrease during the course of antithyroid drug therapy.

Clinical experience with a human thyroid cell bioassay for thyroid-stimulating immunoglobulin.

A sensitive, specific, and practical bioassay for thyroid-stimulating immunoglobulin (TSI) is now available for clinical use. Fifty-seven of 61 patients with untreated hyperthyroid Graves' disease were TSI positive (sensitivity, 93%). TSI was undetectable in all normal subjects and in patients with Hashimoto's thyroiditis (without concurrent Graves' ophthalmopathy), nontoxic goiter, and toxic nodular goiter (specificity, 100%). The prevalence of TSI in serum declined after therapy, particularly during methimazole or propylthiouracil treatment. TSI correlated well with relapse or remission after antithyroid drug therapy. All 12 patients who were TSI negative at the time of discontinuing antithyroid drug therapy remained in remission (average follow-up of 10 months). TSI values in Graves' disease correlated better with thyroid dysfunction than with ophthalmopathy. Prenatal TSI activity tended to be higher in mothers of infants who developed neonatal Graves' disease than in at-risk mothers who delivered normal infants. However, there was considerable overlap between the two groups.