Activity of thyroid stimulating antibody and thyroid stimulation blocking antibody determined by radioiodine uptake into FRTL-5 cells

US-based, Prospective, Blinded Study of Thyrotropin Receptor Antibody in Autoimmune Thyroid Disease

CONTEXT

Bioassays provide information on the functionality of thyrotropin receptor antibodies (TSH-R-Ab) and thus may offer more clinical utility than binding assays.

OBJECTIVE

In this prospective, blinded, US-based study, the clinical performance of several TSH-R-Ab assays was compared.

SETTING

US endocrinology clinic.

SUBJECTS

One hundred sixty-two unselected, consecutive, well-documented patients with various thyroid diseases and healthy controls.

INTERVENTION(S)

Blinded TSH-R-Ab measurements.

MAIN OUTCOME MEASURE(S)

Sensitivity and specificity of 4 TSH-R-Ab assays.

RESULTS

The 4 TSH-R-Ab assays were negative in all 42 patients without autoimmune thyroid disease (AITD). In 104 patients with Graves' disease (GD), irrespective of the disease duration, TSH-R-Ab positivity was present in 65 (63%), 67 (65%), and 87 (84%) for the Cobas and Immulite binding assays and stimulatory TSH-R-Ab [thyroid-stimulating immunoglobin (TSI)] bioassay, respectively (TSI vs Immulite P < .0025, TSI vs Cobas P < .0009). Fifteen newly diagnosed GD patients were all positive in the TSI bioassay, but only 11 (73%) were positive in the Cobas and Immulite binding assays. Nine GD patients with biochemical subclinical hyperthyroidism were TSI-positive but Immulite- and Cobas-negative. Two GD patients were blocking TSH-R-Ab [thyroid-blocking immunoglobin (TBI)]-positive and TSI-negative, and the Immulite and Cobas were positive in both. Additional serum samples from AITD patients that consisted of 30 TBI-positive and 10 TSI-positive samples were blindly tested in the binding assays. Only 6 of the 10 TSI-positive samples were positive in both binding assays, and 30 and 28 of the TBI-positive samples were positive in the Cobas and Immulite assays, respectively.

CONCLUSION

Binding TSH-R-Ab assays are less sensitive than TSI bioassays and are not specific for stimulating antibodies. Measuring the function of TSH-R-Ab in a bioassay can provide useful information to clinicians.

Bioassays for thyrotropin receptor autoantibodies

Bioassays using animal models were essential tools in the discovery of thyrotropin and in enhancing our understanding of the physiology of the pituitary-thyroid axis. These same bioassays were also instrumental in the discovery of autoantibodies to the thyrotropin receptor (TSH-R-Ab) and in identifying their role in the pathophysiology of Graves' disease. The development of cell-based bioassays led to further advances in our knowledge of the functional activity of TSH-R-Ab and to the discovery that TSH-R-Ab can be either thyroid-stimulating or thyroid blocking, and that they occur in other types of autoimmune thyroid diseases (AITD) besides Graves' disease. More recently, TSH-R-Ab bioassays have been advanced from research tools to clinical laboratory tests. Whereas TSH-R-Ab can be measured with competitive-binding immunoassays, these assays do not provide information on the functional activity of TSH-R-Ab. Bioassays, in contrast, can differentiate between the stimulatory or blocking activity of TSH-R-Ab which provides clinically useful information that can inform the management of patients with AITD. The clinical use of TSH-R-Ab bioassays, however, has been limited to-date by their inherent complexity and long turn-around-time. Recent advances in biosensors have been applied to the development of TSH-R-Ab bioassays that are rapid and simple to perform. We now are entering an era in which bioassays for TSH-R-Ab can be measured routinely by virtually any clinical laboratory.

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.

Prevalence and clinical relevance of thyroid stimulating hormone receptor-blocking antibodies in autoimmune thyroid disease

The prevalence and clinical relevance of thyroid stimulating hormone (TSH) receptor (TSHR) blocking antibodies (TBAb) in patients with autoimmune thyroid disease (AITD) was investigated. Serum TBAb were measured with a reporter gene bioassay using Chinese hamster ovary cells. Blocking activity was defined as percentage inhibition of luciferase expression relative to induction with bovine TSH alone (cut-off 40% inhibition). All samples were measured for TSHR stimulatory antibody (TSAb) and TSHR binding inhibiting immunoglobulins (TBII). A total of 1079 unselected, consecutive patients with AITD and 302 healthy controls were included. All unselected controls were negative for TBAb and TSAb. In contrast, the prevalence of TBAb-positive patients with Hashimoto's thyroiditis and Graves' disease was 67 of 722 (9·3%) and 15 of 357 (4·2%). Of the 82 TBAb-positive patients, thirty-nine (48%), 33 (40%) and 10 (12%) were hypothyroid, euthyroid and hyperthyroid, respectively. Ten patients were both TBAb- and TSAb-positive (four hypothyroid, two euthyroid and four hyperthyroid). Thyroid-associated orbitopathy was present in four of 82 (4·9%) TBAb-positive patients, with dual TSHR antibody positivity being observed in three. TBAb correlated positively with TBII (r = 0·67, P < 0·001) and negatively with TSAb (r = -0·86, P < 0·05). The percentage of TBII-positive patients was higher the higher the level of inhibition in the TBAb assay. Of the TBAb-positive samples with  > 70% inhibition, 87% were TBII-positive. Functional TSHR antibodies impact thyroid status. TBAb determination is helpful in the evaluation and management of patients with AITD. The TBAb assay is a relevant and important tool to identify potentially reversible hypothyroidism.

Significance of thyroid blood flow as a predictor of methimazole sensitivity in untreated hyperthyroid patients with Graves' disease

OBJECTIVE

The peak systolic velocity (PSV) of the inferior thyroid artery (ITA) is increased in untreated hyperthyroid patients with Graves' disease (GD). We investigated the clinical significance of the ITA-PSV and its determinants in hyperthyroid GD patients.

PATIENTS AND METHODS

ITA-PSV, together with thyroid volume, was measured by ultrasonography in untreated hyperthyroid GD patients (n=49) and healthy subjects (n=22). Established markers of GD activity such as TSH receptor antibody (TRAb), thyroid stimulating antibody (TSAb), vascular endothelial growth factor (VEGF) and immunoglobulin E (IgE) were simultaneously determined.

RESULTS

ITA-PSV, thyroid volume, VEGF and IgE were significantly higher in hyperthyroid GD patients than in normal subjects. ITA-PSV in hyperthyroid GD patients was correlated positively with serum levels of FT(3), FT(4) and IgE, smoking index and thyroid volume, and negatively with total, HDL- and LDL-cholesterols, but did not correlate significantly with age, triglyceride, TRAb, TSAb or VEGF. In stepwise regression analysis, ITA-PSV showed significant positive and negative associations with IgE and LDL-cholesterol, respectively, in hyperthyroid GD patients. In the pre-treatment hyperthyroid state, FT(4) and ITA-PSV, but not IgE, were found to be significantly and positively associated with the maintenance dose of methimazole (MMI) required to keep serum TSH within normal range for at least 12 months.

CONCLUSION

These results suggest that ITA-PSV in untreated hyperthyroid GD patients may reflect GD activity and thus MMI sensitivity.

A young boy with a thyroid yo-yo

We describe a boy with Hashimoto's thyroiditis and Addison's disease who was initially hypothyroid, developed hyperthyroidism and eventually became euthyroid. A rise and fall in thyroid binding inhibitory immunoglobulin and thyroid stimulating antibodies were demonstrated to have correlated with the appropriate changes in thyroid status. The fact that Hashimoto's thyroiditis can evolve in such a way emphasizes the importance of lifetime follow-up in these patients.

The effect of adding a surfeit of autologous CD8+ T cells to SCID mice after secondary rexenografts of Graves' thyroid tissue

To investigate the effect of adding a surfeit of CD8+ T cells as a potential immunoregulator in Graves' disease (GD), thyroid tissues from 4 patients with GD and 2 normal subjects (N) were initially xenografted into nude mice. Eight weeks after xenografting, the thyroid tissues, which were then devoid of lymphocytes and appeared normal, were retrieved from the nude mouse, and rexenografted (rexenografts) into severe combined immuno-deficient (SCID) mice; 20 x 10(6) of autologous peripheral blood mononuclear cells (PMBC) or 20 x 10(6) of CD8(+)-depleted PBMC ("non-CD8 cells," i.e., CD4-enriched PBMC) were simultaneously engrafted into SCID mice with thyroid rexenografts. In addition, 20 x 10(6) of CD8(+)-enriched PBMC ("CD8-doubled" cells, which were prepared to double the percentage of CD8+ T cells compared to that of PBMC) were engrafted into SCID mice with rexenografts from 2 GD and 2 N; finally, 20 x 10(6) of PBMC plus an extra 10 x 10(6) of CD8+ T cells ("extra-CD8 added" cells, total 30 x 10(6) of CD8-enriched cells) were engrafted into separate SCID mice with rexenografts from 2 GD. The reengraftment of GD rexenografts or N rexenografts alone did not result in the detection of thyroperoxidase (TPO)-antibodies (Abs), thyroglobulin (Tg)-Abs, thyroid-stimulating Ab (TSAb) production, human IgG, or lymphocytic infiltration in the xenografts. However, the engraftment of either autologous PBMC or non-CD8 cells from patients with GD and N into SCID mice with rexenografts caused human IgG to become detectable and then rise further in 10 of 17 SCID mice; when human IgG, TPO-Ab, Tg-Ab, and TSAb were quantitated, GD rexenografts plus non-CD8 cells engrafted into SCID mice showed a higher production of each antibody and human IgG than in GD rexenografts plus PBMC, or GD rexenografts plus CD8-doubled cells, or GD rexenografts plus extra "CD8-added" cells. Moreover, when CD8-doubled cells or extra CD8-added cells with rexenografts were engrafted to SCID mice with rexenografts, they showed generally lower production of human IgG and thyroid antibodies compared to SCID mice into which PBMC were engrafted with rexenografts, despite the fact that 50% more cells (30 x 10(6)) were engrafted in the preparations of extra CD8-added cells. In conclusion, CD8+ T cells from patients with GD appeared to suppress the induction of thyroid antibodies, TSAb, and human IgG. The CD8+ cells thus are acting as suppressor or regulatory T cells. Such cells might be important in the pathogenesis of autoimmune thyroid disease.

Effect of FK-506 on xenografted human Graves' thyroid tissue is severe combined immunodeficient mice

OBJECTIVE

We studied the macrolide antibiotic FK-506, an immunosuppressive agent, in an attempt to ameliorate the lesion of autoimmune thyroid disease in human thyroid tissue xenografted into severe combined immunodeficient (SCID) mice. It was not felt appropriate to employ this agent directly in patients with autoimmune thyroid disease because adequate therapeutic modalities are available and the introduction of new, experimental agents could not be justified. Moreover, the study of the tissue before and after treatment could not have been undertaken directly in patients.

DESIGN

Human thyroid xenografts from four patients with Graves' disease and two normal persons were xenografted into SCID mice. Two weeks after xenografting, human immunoglobulin G (IgG) was detectable in all SCID mice xenografted with Graves' thyroid tissue. Mice were divided into two groups with human IgG levels similar to each other. Mice in the first group were treated with FK-506 daily for 6 weeks; mice in the second (similar) group were given phosphate-buffered saline (PBS) only (control group).

MEASUREMENTS

Blood samples were taken every 2 weeks from the tail veins for human IgG, thyroid stimulating antibody, thyroperoxidase antibodies, thyroglobulin antibodies, and interferon-gamma (IFN-gamma). After 8 weeks treatment, animals were sacrificed; thyroid tissue was examined histologically and for thyrocyte HLA-DR expression. FK-506 was also added to thyrocytes in in-vitro tissue culture conditions.

RESULTS

After 4-6 weeks of FK-506 therapy, human IgG, all thyroid antibodies and IFN-gamma were suppressed, while the levels remained elevated in the control group. Lymphocytic infiltration virtually disappeared in the human thyroid tissue of the FK-506-treated mice and thyrocyte HLA-DR expression markedly declined; in the control mice, lymphocytic infiltration remained heavy and HLA-DR expression remained high. On the other hand, FK-506 added directly to thyrocytes in vitro (without lymphocytes) did not reduce thyrocyte HLA-DR expression.

CONCLUSIONS

FK-506 appears to suppress the activation of intrathyroidal lymphocytes, but not thyrocytes. From these observations, it is concluded that this agent, by its action on intrathyroidal lymphocytes, is able to ameliorate the immunologically mediated histological and serological disturbance in human autoimmune thyroid disease, at least under these circumstances.

Studies on the action of thyroid stimulation blocking antibody (TSBAb) on thyroid cell membrane

The effect of thyroid stimulation blocking antibody (TSBAb) on stimulated cyclic AMP (cAMP) production induced by adenylate cyclase stimulators in porcine thyroid membrane (PTM) and porcine thyroid cells (PTC) has been studied. Ten TSBAbs with high TSH binding inhibitory immunoglobulin (TBII) activities significantly blocked TSH-stimulated cAMP production in PTC. The blocking effect of TSBAb on the cAMP increase induced by forskolin or GTP-gamma S stimulation in PTC was found in a few cases. However, there was no blocking action of TSBAb on the cAMP increase stimulated by forskolin, GTP gamma S, or NaF in isolated PTM. When TSBAb-globulin was absorbed with PTM or guinea pig epididymal fat membrane (GPFM), the TBII activity in TSBAb-globulin was significantly absorbed by these membranes. A decrease of TSBAb activity (blocking activity for TSH-stimulated cAMP production in PTC) by PTM absorption, but no decrease by GPFM absorption, was found in six cases. This suggests that the potent TSBAb-neutralizing component may be associated with a non-TSH receptor site in the thyroid membrane. The other four cases showed a decrease of TSBAb activity by absorption with both PTM and GPFM. This suggests that the TSBAb-neutralizing activity may be associated with the TSH receptor site of both PTM and GPFM. The results of the present study suggest that TSBAb may block TSH action either via the TSH receptor itself or via a non-TSH receptor component of the thyroid membrane and not at a postreceptor level.

Studies of human thyroid xenografts from Hashimoto's thyroiditis in severe combined immunodeficient (SCID) mice: detection of thyroid stimulation-blocking antibody

Human thyroid xenografts from 7 patients with Hashimoto's thyroiditis (HT) and 3 normal persons (N) were xenografted into severe combined immunodeficient (SCID) mice to study the intrathyroidal lymphocytes that were expected to survive in these animals. Human IgG was detected in all mice engrafted with HT thyroid tissue peaking at 6-10 weeks after xenografting. Thyroperoxidase-antibody (TPO-Ab) was also detected in all mice with HT thyroid grafts peaking at 4-6 weeks after xenografting, reaching up to 44% of donors' original concentrations. In contrast, maximal thyroglobulin (Tg)-Ab production in some SCID mice with HT thyroid grafts was higher than the donors' original level, and was detectable in mice with thyroid grafts from Tg-Ab-negative HT donors. Thyroid stimulation-blocking antibody (TSBAb) was found in 2 mice with thyroid xenografts from 1 HT patient whose original serum TSBAb and thyrotropin-binding inhibitor immunoglobulin (TBII) had been positive; the maximal TSBAb level in SCID mice exceeded the donor's original level. TSBAb production in SCID mice reached its peak at 10 weeks after xenografting, i.e., later than that of thyroid-stimulating antibody (TSAb) observed in our recent report, suggesting the existence of distinct intrathyroidal B cell autoreactive clones of different life span responsible for secreting TSAb or TSBAb. When autologous peripheral blood mononuclear cells (PBMC) were engrafted alone (without thyroid tissue), TSBAb was undetectable.(ABSTRACT TRUNCATED AT 250 WORDS)

Human chorionic gonadotropin induces c-myc mRNA expression via TSH receptor in FRTL-5 rat thyroid cells

To elucidate the gene regulation of the thyroid-cell growth-promoting activity by human chorionic gonadotropin (hCG), we investigated the effect of hCG on c-myc proto-oncogene expression in cultured rat FRTL-5 cells by the Northern blot method. hCG induced c-myc mRNA expression, which peaked at 60-120 min. A dose-dependent increase in c-myc mRNA levels was also ascertained. In the presence of crude immunoglobulin G (IgG) from 2 patients with primary hypothyroidism who had blocking type TSH-receptor antibody, c-myc mRNA expressions induced by hCG were decreased to 82% and 62%, compared with that in the presence of normal IgG. The present results suggest that the expression of c-myc mRNA is a part of the molecular mechanism through which hCG regulates the proliferation of thyroid cells, and that hCG-induced c-myc mRNA expression is presumed to be mediated in part by TSH receptors.