Michael Kanitz

Analytical Performance and Clinical Utility of a Bioassay for Thyroid-Stimulating Immunoglobulins

The analytical performance and the clinical utility of a thyrotropin receptor (TSHR)-stimulating immunoglobulin (TSI) bioassay were compared with those of a TSHR-binding inhibitory immunoglobulin (TBII) assay. Limits of detection (LoD) and quantitation (LoQ), assay cutoff, and the half-maximal effective concentration (EC(50)) were measured. Dilution analysis was performed in sera of hyperthyroid patients with Graves disease (GD) during antithyroid treatment (ATD). Titer was defined as the first dilution step at which measurement of TSI or TBII fell below the assay cutoff. The LoD, LoQ, cutoff, and EC(50) of the bioassay were 251-, 298-, 814-, and 827-fold lower than for the TBII assay. There were 22%, 42%, 23%, and 14% more positive samples in the TSI bioassay at dilutions of 1:3, 1:9, 1:27, and 1:81 (P < .0001), respectively. Responders to ATD demonstrated marked differences in titers compared with nonresponders. The bioassay detected lower levels of TSHR autoantibodies, and the dilution analysis provided similar predictive values of both assays in GD.

Thyroid Stimulating Antibodies Are Highly Prevalent in Hashimoto's Thyroiditis and Associated Orbitopathy

CONTEXT Thyroid-associated orbitopathy (TAO) rarely occurs in patients with Hashimotos thyroiditis (HT). OBJECTIVE There is evidence that TSH receptor stimulating antibodies (TSAb) play a role in the pathogenesis of TAO. In this report, the prevalence of TSAb in HT patients with and without TAO was studied. DESIGN This is a longitudinal observational study. SETTING The study took place in an academic joint thyroid-eye clinic. SUBJECTS A total of 1055 subjects were included. METHODS TSAb was measured with a Food and Drug Administration-cleared bioassay that uses Chinese hamster ovary cells expressing a chimeric TSH receptor and a cAMP response element-dependent luciferase. Results of TSAb activity were reported as percentage of specimen-to-reference ratio (SRR%, cutoff >140%). MAIN OUTCOME MEASURE We measured the association of TSAb with the risk of TAO in patients with HT. RESULTS Of 700 consecutive and unselected patients with HT, 44 (6%) had overt TAO. Patients with HT+TAO were older (P < .001), heavier smokers (P = .032), and clustered less with autoimmune diseases (P = .005). All healthy controls were TSAb negative. In contrast, serum was TSAb positive in 30/44 (68.2%) and 36/656 (5.5%, P < .001) patients with HT+TAO and HT, respectively. Compared to patients with HT only, serum TSAb levels were higher in HT+TAO (median SRR%, 25th and 75th percentiles): 45, 35-65 vs 192.5, 115-455.3, P < .001. Highest TSAb values were noted in patients with active and severe TAO vs those with mild and inactive TAO: 486, 392-592 vs 142, 73-192.5; P < .001. The odds ratio of TSAb positivity for the risk of TAO adjusted for gender and age was 55.9 (95% confidence interval [CI], 24.6-127, P < .0001), whereas the odds ratio per 10-fold change in TSAb SRR% (quantitative TSAb) was 133 (95% CI, 45-390, P < .0001). The area under the receiver operating characteristic curve for qualitative and quantitative TSAb was 87.2% (95% CI, 80.6-93.8) and 89.4% (95% CI, 84.1-94.7), respectively. CONCLUSIONS TSAb is strongly associated with TAO in HT and TSAb may contribute to the pathophysiology of TAO.

Analytical Performance and Validation of a Bioassay for Thyroid-Blocking Antibodies

BACKGROUND AND OBJECTIVE A cell-based bioassay for the measurement of thyroid blocking autoantibodies (TBAb) has been recently reported. The analytical performance and validation of this bioassay is assessed and described. METHODS Chinese hamster ovary cells expressing a chimeric thyrotropin receptor were treated with bovine (b) TSH and different concentrations of an immunoglobulin G (IgG) monoclonal human TBAb (K1-70). TBAb was measured as a function of luciferase activity relative to bTSH alone and expressed as percent inhibition. Results obtained in the chimeric cell line were compared with those of a wild-type cell line. Analytical performance studies were subsequently performed with the chimeric cell line only. RESULTS Immunodepletion of K1-70 IgG by using a protein G-Sepharose column showed that positive percent inhibition in the TBAb bioassay was detectable from K1-70 IgG only. The limit of blank was determined to be 12.2%. The limit of detection was 14% inhibition, equivalent to 0.4 ng/mL K1-70, while the limit of quantitation was 22% (coefficient of variation [CV] 12%) equivalent to 0.625 ng/mL K1-70. The dynamic range was between 14 ± 3.7 (mean % inhibition ± standard deviation) and 101 ± 2.6, equivalent to 0.4-10 ng/mL K1-70. The linear range was between 22 ± 2.6 and 93 ± 0.6 inhibition, equivalent to 0.625-5 ng/mL K1-70. The upper limit of the 99th percent reference range was 34% inhibition. In two laboratories, CV values for the intra- and inter-assay precisions for K1-70 ranged from 2% to 12% and from 1.7% to 14.5%, respectively. For patient sera, the CV values for the intra- and inter-assay precisions ranged from 3% to 9% and from 3% to 11%, respectively. No interference was found when follicle-stimulating hormone, luteinizing hormone, and human chorionic gonadotrophin were tested in the TBAb bioassay. The median of % inhibition values in 40 TBAb positive sera from patients with autoimmune thyroid disease were 93.5 (range 25-103) and 92 (range 64-107) for the wild type and chimeric cell lines, respectively. Further, all 40 samples of patients with various non-thyroidal autoimmune diseases were TBAb negative. CONCLUSIONS This TBAb bioassay exhibits excellent analytical performance and high level of reproducibility.

Performance and Specificity of 6 Immunoassays for TSH Receptor Antibodies: A Multicenter Study

Background: The measurement of TSH receptor (TSHR) antibodies is warranted for diagnosis of Graves’ disease (GD). Objective: The performance, detection sensitivity, and specificity of 6 TSHR immunoassays were compared. Methods: Two bioassays and 4 binding assays (Kronus, Immulite, Kryptor, Dynex) were compared in a dilution study performed in patients with autoimmune thyroid disease. Both bioassays were compared to 2 binding assays using stimulatory (M22) and blocking (K1–70) monoclonal antibody (MAb) mixtures. Results: Thirty samples from stimulatory (TSAb)-positive/blocking (TBAb)-negative patients with GD were diluted serially and measured in all assays. Samples were positive until dilution 1:2,187 in the TSAb bioassay, 1:81 in the Immulite (p < 0.002 vs. bioassay) and Kronus ELISA (p = 0.039) assays, and 1:27 in the Kryptor and Dynex ELISA (p < 0.001 vs. bioassay). Ten samples from TBAb-positive/TSAb-negative patients with GD or Hashimoto’s thyroiditis were positive in all binding assays. None of the binding assays differentiated between TSAb and TBAb. Mixtures of 100% K1–70 (200 ng/mL), 80% K1–70 + 20% M22, 60% K1–70 + 40% M22, 40% K1–70 + 60% M22, 20% K1–70 + 80% M22, and 100% M22 (20 ng/mL) tested positive in both Immulite (26.4, 20.2, 15.2, 10.5, 6.3, 2.00 IU/L) and Kronus assays (27.1, 23.3, 19.3, 12.0, 5.7, 2.2 IU/L). These MAb mixtures were tested in the TBAb bioassay and showed 82, 61, 24 (negative), –26 (negative), –77 (negative), and –95% (negative) inhibition, respectively. Conclusions: The sample dilution study showed higher detection sensitivity for the TSAb bioassay, and the antibody mixture study demonstrated exclusive specificity of the bioassays over all automated and ELISA binding assays.

STIMULATORY TSH-RECEPTOR ANTIBODIES AND OXIDATIVE STRESS IN GRAVES' DISEASE.

Context We hypothesized that TSH-receptor (TSHR) stimulating antibodies (TSAbs) are involved in oxidative stress mechanisms in patients with Graves disease (GD). Methods Nicotinamide adenine dinucleotide phosphate oxidase, isoform 2 (NOX2); oxidative parameters; and oxidative burst were measured in serum, urine, and whole blood from patients with GD and control subjects. Superoxide production was investigated in human embryonic kidney (HEK)-293 cells stably overexpressing the TSHR. Lipid peroxidation was determined by immunodot-blot analysis for protein-bound 4-hydroxy-2-nonenal (4-HNE) in human primary thyrocytes and HEK-293-TSHR cells. Results Serum NOX2 levels were markedly higher in hyperthyroid untreated vs euthyroid treated patients with GD, hyperthyroid patients with toxic nodular goiter, and euthyroid healthy control subjects (all P < 0.0001). Urine oxidative parameters were increased in patients with GD vs patients with toxic goiter (P < 0.01) and/or control subjects (P < 0.001). The maximum of the zymosan A- and phorbol 12,13-dibutyrate-induced respiratory burst of leukocytes was 1.5-fold higher in whole blood from hyperthyroid patients with GD compared with control subjects (P < 0.001 and P < 0.05). Monoclonal M22 TSAbs stimulated cAMP (HEK cells) in a dose-dependent manner. M22 (P = 0.0082), bovine TSH (P = 0.0028), and sera of hyperthyroid patients with GD (P < 0.05) increased superoxide-specific 2-hydroxyethidium levels in HEK-293 TSHR cells after 48-hour incubation vs control subjects. In contrast, triiodothyronine (T3) did not affect reactive oxygen species (ROS) production. In primary thyrocytes, the 4-HNE marker was higher in patients with GD vs control subjects at 6 and 48 hours (P = 0.02 and P = 0.04, respectively). Further, after 48-hour incubation of HEK-293 TSHR cells with patient sera, 4-HNE was higher in patients with untreated GD compared with control subjects (P < 0.05). Conclusions Monoclonal M22 and polyclonal serum TSAbs augment ROS generation and/or induce lipid peroxidation.