Bioassay of thyrotropin receptor antibodies with Chinese hamster ovary cells transfected with recombinant human thyrotropin receptor: clinical utility in children and adolescents with Graves disease

Thyrotropin receptor antibodies and Graves' orbitopathy

CONTEXT AND PURPOSE

The thyrotropin receptor (TSHR) is the key autoantigen in Graves' disease (GD) and associated orbitopathy (GO). Antibodies targeting the TSHR (TSHR-Ab) impact the pathogenesis and the course of GO. This review discusses the role and clinical relevance of TSHR-Ab in GO.

METHODS

Review of the current and pertinent literature.

RESULTS

GO is the most common extrathyroidal manifestation of GD and is caused by persistent, unregulated stimulation of TSHR-expressing orbital target cells (e.g. fibroblasts and pre-adipocytes). Serum TSHR-Ab and more specifically, the stimulatory Ab (TSAb) are observed in the vast majority of patients with GD and GO. TSHR-Ab are a sensitive serological parameter for the differential diagnosis of GO. TSHR-Ab can be detected either with conventional binding immunoassays that measure binding of Ab to the TSHR or with cell-based bioassays that provide information on their functional activity and potency. Knowledge of the biological activity and not simply the presence or absence of TSHR-Ab has relevant clinical implications e.g. predicting de-novo development or exacerbation of pre-existing GO. TSAb are specific biomarkers of GD/GO and responsible for many of its clinical manifestations. TSAb strongly correlate with the clinical activity and clinical severity of GO. Further, the magnitude of TSAb indicates the onset and acuity of sight-threatening GO (optic neuropathy). Baseline serum values of TSAb and especially dilution analysis of TSAb significantly differentiate between thyroidal GD only versus GD + GO.

CONCLUSION

Measurement of functional TSHR-Ab, especially TSAb, is clinically relevant for the differential diagnosis and management of GO.

Comparison of a Novel Homogeneous Cyclic Amp Assay and a Luciferase Assay for Measuring Stimulating Thyrotropin-Receptor Autoantibodies

OBJECTIVE

Stimulating thyrotropin-receptor antibodies (TSAb) cause Graves' disease (GD). We tested a novel homogeneous fluorescent 3',5' cyclic adenine monophosphate (cAMP) assay for the detection of TSAb in a bioassay.

METHODS

Chinese hamster ovary (CHO) cell lines expressing either a chimeric (MC4) or wild-type (WT) TSH-R were incubated with the adenyl cyclase activator forskolin, a human TSAb monoclonal antibody (M22), and with sera from GD patients. Intracellular cAMP levels were measured using a Bridge-It® cAMP assay, and the results were compared with a luciferase-based bioassay.

RESULTS

Both cell lines were stimulated with forskolin concentrations (0.006-200 µM) in a dose-dependent manner. The linear range in the MC4 and WT cells was 0.8-25 and 3.1-50 µM, respectively. Levels of cAMP and luciferase in forskolin-treated MC4 and WT cells were positively correlated (r = 0.91 and 0.84, both p < 0.001). The 50% maximum stimulatory concentration of forskolin was more than 16-fold higher for the CHO-WT cells than the CHO-MC4 cells in the cAMP assay and 4-fold higher in the luciferase assay. Incubation of both cell lines with M22 (0.006-50 ng/mL) resulted in a dose-dependent increase in cAMP levels with linear ranges for the MC4 and WT cells of 0.8-12.5 and 0.2-3.125 ng/mL, respectively. Comparison of cAMP and luciferase levels in M22-treated MC4 and WT cells also showed a positive correlation (r = 0.88, p < 0.001 and 0.75, p = 0.002). A positive correlation was also noted when using patient samples (r = 0.96, p < 0.001) that were all TSH-R-Ab binding assay positive.

CONCLUSION

The novel, rapid, simple-to-perform cAMP assay provides TSAb-mediated stimulatory results comparable to a luciferase-based bioassay.

Thyrotropin Receptor Blocking Antibodies

Autoantibodies (Ab) against the thyroid-stimulating hormone receptor (TSHR) are frequently found in autoimmune thyroid disease (AITD). Autoantibodies to the TSHR (anti-TSHR-Ab) may mimic or block the action of TSH or be functionally neutral. Measurement of anti-TSHR-Ab can be done either via competitive-binding immunoassays or with functional cell-based bioassays. Antibody-binding assays do not assess anti-TSHR-Ab functionality, but rather measure the concentration of total anti-TSHR binding activity. In contrast, functional cell-based bioassays indicate whether anti-TSHR-Ab have stimulatory or blocking activity. Historically bioassays for anti-TSHR-Ab were research tools and were used to study the pathophysiology of Graves' disease and Hashimoto's thyroiditis. In the past, bioassays for anti-TSHR-Abs were laborious and time-consuming and varied widely in performance from laboratory to laboratory. Recent advances in the development of cell-based assays, including the application of molecular engineering, have led to significant improvements that have enabled bioassays to be employed routinely in clinical laboratories. The prevalence and functional significance of TSHR blocking autoantibodies (TBAb) in autoimmune hypothyroidism has been less well investigated compared to TSHR stimulating Ab. There is an increasing body of data, however, that demonstrate the clinical utility and relevance of TBAb, and thus the importance of TBAb bioassays, in the diagnosis and management of patients with AITD. In the present review, we summarize the different methods used to measure TBAb, and discuss their prevalence and clinical relevance.

Thyroid Stimulating Hormone Receptor Antibodies in Thyroid Eye Disease-Methodology and Clinical Applications

BACKGROUND

Thyroid stimulating hormone receptor antibodies (TSHR-Ab) cause autoimmune hyperthyroidism and are prevalent in patients with related thyroid eye disease (TED).

PURPOSE

To provide a historical perspective on TSHR-Ab and to present evidence-based recommendations for clinical contemporary use.

METHODS

The authors review the recent literature pertaining to TSHR-Ab in patients with TED and describe the various immunoassays currently used for detecting TSHR-Ab and their clinical applications.

RESULTS

We provide a historical summary and description of the various methods used to detect TSHR-Ab, foremost, the functional TSHR-Ab. Increasing experimental and clinical data demonstrate the clinical usefulness of cell-based bioassays for measurements of functional TSHR-Ab in the diagnosis and management of patients with autoimmune TED and in the characterization of patients with autoimmune-induced hyperthyroidism and hypothyroidism. Thyroid stimulating hormone receptor antibodies, especially the functional stimulating antibodies, are sensitive, specific, and reproducible biomarkers for patients with autoimmune TED and correlate well with clinical disease activity and clinical severity. Unlike competitive-binding assays, bioassays have the advantage of indicating not only the presence of antibodies but also their functional activity and potency.

CONCLUSIONS

Measurement of TSHR-Ab (especially stimulating antibodies) is a clinically useful tool for the management of patients with TED.

Diagnosis of pediatric hyperthyroidism: technetium 99 uptake versus thyroid stimulating immunoglobulins

BACKGROUND

Treatment with antithyroid drugs is effective in conditions of increased thyroid hormone production (mostly Graves' Disease; GD), but not in subacute thyroiditis (SAT) or autoimmune thyroiditis (AIT). Positive thyroid stimulating immunoglobulins (TSI) make GD likely. However, not all children with GD have increased TSI. Uptake studies with (123)I or (99)Tc ((99m)Tc) provide accurate and rapid diagnosis but are expensive and involve radiation exposure. Our objective was to compare TSI with (99m)Tc uptake for diagnosis of pediatric hyperthyroidism.

METHODS

We performed a retrospective chart review of hyperthyroid children who had both TSI estimation and (99m)Tc uptake assessment at presentation. Based on subsequent laboratory studies and follow-up, 37 had GD and 10 had non-GD thyroiditis. The TSI index was considered positive (TSI+) when it was above the upper limit of normal. (99m)Tc uptake was considered positive (Tc+) for any uptake >0.4% and negative (and low) (Tc-) for uptake ≤0.4%.

RESULTS

Forty-seven youth (83% females), aged 12.3±4.6 years, presented with a suppressed thyrotropin (TSH) and elevated free thyroxine and total triiodothyronine. All 37 patients with GD were Tc+ (100% sensitivity and specificity). The sensitivity of TSI for diagnosing GD was 84%, and the specificity was 100%. Six patients with GD were discordant with Tc+ but TSI-. Elevated TSI correlated with Tc+ (p=0.01) with a degree of agreement (kappa) of 0.69.

CONCLUSION

(99m)Tc has excellent specificity and sensitivity in diagnosing GD. Given additional costs of (99m)Tc (two and a half times as much as TSI), it is reasonable to reserve (99m)Tc uptake assessment for hyperthyroidism of unclear etiology and negative TSI.

Clinical relevance of thyroid-stimulating autoantibodies in pediatric graves' disease-a multicenter study

CONTEXT AND OBJECTIVE

The incidence of TSH receptor (TSHR) stimulating autoantibodies (TSAbs) in pediatric Graves' disease (GD) is controversial. This large, multicenter study evaluated the clinical relevance of TSAbs in children with GD both with Graves' orbitopathy (GO) and without orbital disease.

DESIGN

We conducted a cross-sectional retrospective study.

SETTING

Sera were collected in seven American and European academic referral centers and evaluated in a central laboratory. PATIENTS AND SAMPLES: A total of 422 serum samples from 157 children with GD, 101 control individuals with other thyroid and nonthyroid autoimmune diseases, and 50 healthy children were studied.

MAIN OUTCOME MEASURES

TSAbs were measured using a novel, chimeric TSHR bioassay and a cAMP response element-dependent luciferase. TSH binding-inhibitory Ig (TBII) and parameters of thyroid function were also determined.

RESULTS

In 82 untreated children with GD, sensitivity, specificity, and positive and negative predictive values for TSAb and TBII were: 100 and 92.68% (P = .031), 100 and 100%, 100 and 100%, and 100 and 96.15%, respectively. TSAb and TBII were present in 147 (94%) and 138 (87.9%) of the 157 children with GD (P < .039), respectively; and in 247 (94%) and 233 (89%) of the 263 samples from this group (P < .0075), respectively. In children with GD and GO, TSAb and TBII were noted in 100 and 96% (P < .001), respectively. Hyperthyroid children with GD and GO showed markedly higher TSAb levels compared to those with thyroidal GD only (P < .0001). No significant differences were noted for TBII between the two groups. After a 3-year (median) medical treatment, the decrease of TSAb levels was 69% in GD vs 20% in GD and GO (P < .001). All 31 samples of euthyroid children with GO were TSAb positive; in contrast, only 24 were TBII positive (P = .016). All children with Hashimoto's thyroiditis, nonautoimmune hyperthyroidism, type 1 diabetes, and juvenile arthritis and the healthy controls were TSAb and TBII negative.

CONCLUSIONS

Serum TSAb level is a sensitive, specific, and reproducible biomarker for pediatric GD and correlates well with disease severity and extrathyroidal manifestations.

Thyroid stimulating immunoglobulin is often negative in children with Graves' disease

BACKGROUND

The diagnosis of Graves' disease (GD) is typically confirmed with a thyroid stimulating immunoglobulin (TSI) titer. While TSI is reported to be positive in >90% of patients with GD, our anecdotal experience suggests that TSI negative GD may be more common in children.

AIM

To investigate the incidence of TSI negative GD in our population and to compare patients with TSI negative vs TSI positive GD.

METHODS

Charts of children with GD seen in our pediatric endocrinology clinic over the past 5 years were reviewed.

RESULTS

Fifty-seven patients with GD were included. TSI was negative in 43% of patients. No significant differences were found in children with TSI negative vs TSI positive GD.

CONCLUSIONS

In patients with GD, the finding of a negative TSI titer usually creates diagnostic uncertainty. However, the fact that nearly half of our patients with GD were TSI negative suggests that this is common in children.

Predicting the likelihood of remission in children with Graves' disease: a prospective, multicenter study

OBJECTIVE

The optimal treatment for Graves' disease in children is controversial. Antithyroid medications are often used initially, but many children eventually require alternative therapies. We evaluated predictors of remission after 2 years of antithyroid medication use.

METHODS

We prospectively studied children who had Graves' disease and were treated with antithyroid medications. We compared children who achieved remission after 2 years with those who had persistent disease to determine which variables were associated with remission; multiple logistic regression and binary recursive partitioning analyses were used to evaluate interactions among predictive variables.

RESULTS

Of 51 children who completed the study, 15 (29%) achieved remission. Children who achieved remission had lower thyroid hormone concentrations at presentation than those with persistent disease (free thyroxine: 6.17 +/- 3.10 vs 9.86 +/- 7.54 ng/dL; total triiodothyronine: 431 +/- 175 vs 561 +/- 225 ng/dL). Children who achieved remission were also more likely to be euthyroid within 3 months of initiating propylthiouracil (82% vs 29%). Binary recursive partitioning analysis identified rapid achievement of euthyroid status after initiation of propylthiouracil, lower initial triiodothyronine, and older age as significant predictors of remission. CONCLUSIONS; Thyroid hormone concentrations at diagnosis, age, and initial response to propylthiouracil can be used to stratify patients according to the likelihood of remission after 2 years of antithyroid medication use. These data provide a useful guide for clinical decision-making regarding Graves' disease in children.

Persistence of thyrotropin (TSH) receptor antibodies in children and adolescents with Graves' disease treated using antithyroid medication

OBJECTIVE

To determine the course of thyrotropin (thyroid-stimulating hormone [TSH]) receptor antibodies (TRAbs) in children and adolescents with Graves' disease treated using antithyroid drugs (ATDs).

DESIGN

Retrospective, cross-sectional study of 86 children and adolescents with Graves' disease treated medically for >3 years. Patients with Hashimoto's thyroiditis and idiopathic short stature (n = 30) served as controls. A second-generation enzyme-linked immunosorbent assay (ELISA) for TRAbs was used.

MAIN OUTCOMES

Twenty-two out of 23 (95.7%) patients with newly diagnosed Graves' disease, but 0/30 controls, had detectable TRAbs (22.0 +/- 13.5 U/L [mean +/- SD] vs. 0.9 +/- 0.9 U/L, p < 0.0001). Mean TRAb levels decreased with duration of therapy, but even after 13-24 months, TRAbs had normalized in only 3/16 (18.8%) patients. The initial TRAb titer correlated significantly with severity of the initial hyperthyroidism, but did not predict the response to therapy as indicated by the dosage of ATD required to control the hyperthyroidism at 6 and 12 months.

CONCLUSION

Unlike adults, most children and adolescents with Graves' disease require >2 years of ATD treatment before TRAbs are normalized. Although initial TRAb activity reflects disease severity, it does not predict the response to medical therapy. Recommendations as to treatment duration developed for adult patients should not be applied to the young.

Assays for thyroid-stimulating antibodies and thyrotropin-binding inhibitory immunoglobulins in children with Graves' disease

Studies on thyrotropin receptor autoantibodies (TRAb) by measurement of both thyroid-stimulating antibodies (TSAb) and thyrotropin-binding inhibitory immunoglobulins (TBII) in serum from children with Graves' disease are limited in number of studies. The aim of this study was to investigate the levels of serum TSAb and TBII in children with Graves' disease, and to evaluate the clinical significance of these antibodies. We measured the serum TSAb and TBII at diagnosis and during management in 65 children with Graves' disease. Patients were divided into four groups according to their metabolic state: those with untreated active Graves' disease, those receiving treatment with antithyroid drugs, those in remission, and those in relapse. At diagnosis, both TSAb and TBII assays had high sensitivities and high specificities. In follow-up, the levels of both TSAb and TBII paralleled the course of the disease. There was a strong positive correlation between TSAb and TBII. TBII levels were significantly higher in the patients with ophthalmopathy than those without ophthalmopathy in untreated Graves' children. It was concluded that TSAb and TBII measurements are valuable in the diagnosis and management of children with Graves' disease.

The influence of alpha1-acid glycoprotein (orosomucoid) and its glycoforms on the function of human thyrocytes and CHO cells transfected with the human TSH receptor

Local immunological reactions might influence the structure of alpha1-acid glycoprotein (AGP, orosomucoid) leading to a pathological condition in e.g. the thyroid. The aim of this study was to investigate whether the AGP molecule had a direct effect on thyroid cell function in vitro. The influence of AGP and its three glycoforms, TSH (1.0 U/l), serum samples and several sugars (methyl-mannose, methyl-glycoside, N-acetyl-D-galactose, N-acetyl-D-glycoside, neuramidase) were studied with respect to their influence on the function of the Chinese Hamster Ovary (CHO) cell line transfected with the human TSH receptor (hTSHr) and on human thyroid follicular epithelial cells (TFEC) in secondary cultures. We found that low concentrations of AGP (0.001-0.05 microg/l) stimulated while high concentrations of AGP (0.25-1.0 microg/l) inhibited cAMP accumulation in both cell systems (n=24, P<0.0002). In CHO cells (JP26) and TFEC glycoforms 1 (n=9), 2 (n=12) or 3 (n=11) significantly inhibited the TSH stimulated cAMP production, respectively, compared to controls (P<0.0001) and was partially reversed by mannose (P<0.0004). Control CHO cells (JP02) without the hTSHr showed no response. The specificity of the reaction was further confirmed by binding of biotinylated glycoforms and streptavidin conjugated FITC to both cell systems. This is the first report demonstrating that AGP and/or its glycoforms affects thyroid cell function in vitro and that it does so by influencing the second messenger cAMP probably by interacting directly with the TSH receptor.

Prevalence of thyroid peroxidase, thyroglobulin and thyrotropin receptor antibodies in a long-term follow-up of juvenile Graves disease

OBJECTIVE

To relate the presence of thyroid peroxidase antibodies (TPO ab), thyroglobulin antibodies (Tg ab) and thyrotropin receptor antibodies (TSH-R ab) to the clinical course in a long-term follow-up of patients with juvenile Graves' disease (JGD).

DESIGN

Patients with JGD were drawn from a Danish retrospective study and reexamined.

RESULTS

A number of 105 patients were reexamined 4-21 years (median 10 years) after diagnosis. Three groups were formed: Gr.1: euthyroid patients with anti-thyroid drug (ATD) cessation more than 12 months before reexamination (n=41). Gr.2: patients still on ATD (n=24). Gr.3: subtotally thyroidectomized patients (n=40). Positive TPO ab titers were found in 75% of the patients. In 13% of the patients the titers were very high: >10,000 U/ml. Positive Tg ab were found in 51%. The prevalence of TPO ab and Tg ab was the lowest in group 3. Stimulating TSH-R ab titers were found in 13%. No patients had blocking TSH-R ab. The prevalence of TSH-R ab was 3% in the euthyroid patients, without surgery performed. 15% in the surgical patients, and 25% in the patients still on ATD.

CONCLUSIONS

Many JGD patients were euthyroid at the long-term follow-up in spite of high TPO ab and Tg ab titers. Stimulating TSH-R ab were rare (13%). According to this presence of TPO ab, Tg ab or TSH-R ab does not predict the final outcome of JGD. Further studies are needed.

[Neonatal hyperthyroidism in a premature infant born to a mother with Grave's disease]

BACKGROUND

Neonatal thyrotoxicosis is most commonly due to transplacental transfer of maternal thyroid-stimulating hormone receptor antibodies (TRAb). Bioassay of thyrotropin receptor antibodies may help to determine the risk for neonatal hyperthyroidism.

CASE REPORT

Thyrotoxicosis developed in a premature infant born to a mother with Graves' disease, with a low level of TRAb by bioassay. The infant was treated with carbimazole for two months, until TRAb had disappeared.

CONCLUSION

Bioassay TRAb is not always reliable for predicting the development of neonatal hyperthyroidism in infants born to mothers with Graves' disease. Thyroid function should be measured in all these neonates.