Clinical usefulness of TSAb assay with high polyethylene glycol concentrations

Antibody to immunoglobulin G and polyethylene glycol augment cyclic adenosine monophosphate production by TSH receptor antibody bound to porcine thyroid cells

Anti-immunoglobulin G (IgG) augments cyclic adenosine monophosphate (cAMP) production by thyroid-blocking antibody (TBAb) bound to porcine thyroid cells (PTC). This is described as a conversion phenomenon. We reported the effect of polyethylene glycol (PEG) to augment thyroid-stimulating antibody (TSAb) activity in a PTC assay. In the present experiment we examined the effect of anti-immunoglobulin G (IgG) and PEG on cAMP production from TBAb or TSAb bound to PTC. TBAb bound to PTC was separated from unbound TBAb by centrifugation after a first incubation (0.5 hour at 37 degrees C) of TBAb-IgG with PTC. TBAb bound to PTC were incubated with anti-human (h)IgG or hIgG fragments [F(ab')(2), Fc, Fd, H chain or L-chain] for 4 hours at 37 degrees C in the second incubation. Anti-IgG or anti-IgG fragments increased cAMP production. No conversion was caused by protein A, protein L, or PEG (5%). PEG did not augment cAMP production by these IgG antibodies. PEG augmented cAMP production during incubation of TSAb-IgG bound to PTC, but anti-IgG did not. PEG significantly augmented cAMP production by coincubation of TSAb-IgG bound to PTC and the unbound TSAb-IgG (obtained from the first incubation). A similar augmentative effect of PEG was also observed in experiments using TSAb-F(ab')(2) and TSAb-Fab. cAMP production by PTC bound by both TBAb- and TSAb-IgG was increased by co-incubation with anti-IgG, but was not increased by PEG. In conclusion, anti-IgG specifically increased cAMP production from TBAb bound to PTC (conversion phenomenon) and PEG specifically increased cAMP production by TSAb bound to PTC. Different mechanisms enhance cAMP production by TSAb and conversion of TBAb.

Antithyrotropin receptor antibody: an update

Numerous studies have reported the characteristics and significance concerning antithyrotropin receptor antibodies (TSHR-Abs), which cause Graves' disease and in some cases primary hypothyroidism. However, many unsolved questions concerning those antibodies remain. Here, recent developments in the study of TSHR-Abs are reviewed based on three aspects: mechanisms of TSHR-Ab production, antibody binding epitopes, and clinical TSHR-Ab assays. Mechanisms of TSHR-Ab production are discussed from five points of view: aberrant expression of the major histocompatibility complex, dysregulation of T cells, molecular mimicry, bystander effect, and expansion of autoreactive B cells. Regarding epitopes, unique TSHR-Abs have been reported that may explain the complicated pathophysiology of patients with TSHR-Ab diseases. Finally, recent efforts to improve TSHR-Ab measurements are introduced. Such efforts will contribute to clinical examinations and treatments for thyroid diseases as well as experimental methods of thyroidology.

Graves' ophthalmopathy in the absence of elevated free thyroxine and triiodothyronine levels: prevalence, natural history, and thyrotropin receptor antibody levels

The aims of this study were to (a) determine the prevalence of patients without elevated thyroid hormone levels in Graves' ophthalmopathy (GO) using current generation free thyroid hormone assays, (b) measure the prevalence of thyrotropin receptor antibodies (TRAb) in these cases, and (c) identify possible predictors of hyperthyroidism. Over a 30-month period, 1020 cases of thyroid eye disease were evaluated, of which only 19 (1.9%) met the diagnostic criteria. Ten (1%) had subclinical thyrotoxicosis, 7 (0.7%) were euthyroid, and 2 (0.2%) were hypothyroid as determined by a third-generation thyrotropin (TSH) assay. TRAb levels were measured in 16 of these 19 patients. The prevalence of TRAb varied according to the assay used. Polyethylene glycol-extracted thyroid-stimulating immunoglobulin (PEG-TSI), unfractionated thyroid-stimulating immunoglobulin (uTSI), first-generation porcine TSH-binding inhibitory immunoglobulin (pTBII), and second-generation human TSH-binding inhibitory immunoglobulin (hTBII) assays were positive in 93.8%, 50%, 18.8%, and 81.3% of patients, respectively. TRAb was detected by at least one method in all patients. Patients were followed up for 15 to 45 months. Hyperthyroidism developed in 4 patients (25%). Suppressed TSH levels and elevated TBII were predictors of hyperthyroidism. When sensitive assays are used, the prevalence of GO patients without elevated thyroid hormone levels is extremely low. The sensitivities of assays for TRAb detection differ substantially in these cases. PEG extraction improves the detection rate of TSI (p = 0.02), and hTBII assays improve the detection of TBII in these patients (p = 0.002). The high prevalence of TRAb in such cases supports a role for these antibodies in the pathogenesis of thyroid-associated eye disease.

Augmentative effect of polyethylene glycol, polyvinyl alcohol and dextran on thyroid-stimulating antibody stimulated cAMP production in FRTL-5 cells and CHO cells expressing human TSH receptor

Previously we reported the augmentative effect of nonionic hydrophilic polymers such as polyethylene glycol (PEG), polyvinyl alcohol (PVA) and dextran on thyroid-stimulating antibody (TSAb) activity in porcine thyroid cell assays. We examined whether a similar phenomenon occurs in FRTL-5 thyroid cells and CHO cells expressing the human (h) TSH receptor (CHO-hTSHR cells). As with porcine thyroid cells, PEG 22.5% precipitated crude IgG from serum of patients with Graves' disease, significantly increased cAMP production as compared with PEG 12.5% precipitated crude IgG in both FRTL-5 cells and CHO-hTSHR cells. PEG 5% augmented purified-TSAb-IgG-stimulated cAMP production in both cell assays. TSAb activities and positivity by the direct assay using whole serum (0.05 ml) in the presence of 5% PEG in untreated Graves' patients were significantly increased as compared with the absence of 5% PEG. The augmentative effects of PVA 10% or dextran T-70 10% on TSAb-IgG-stimulated cAMP production were also observed in both cell assays. PVA 10% did not augment TSH-stimulated cAMP production in spite of weak augmentation by dextran 10% in both cell assays. Lack of the augmentative effects of PEG 5%, PVA 10% and dextran 10% on cAMP produced by GTPgammaS, forskolin and pituitary adenylate cyclase activating polypeptide was observed in both cell assays. The augmentative effects of these polymers in both cell assays similar to porcine thyroid cells suggest that there is no apparent species specificity among human, porcine and rat thyroid cells as far as TSH receptor linked cAMP production in cell membranes existed.