Presence of both stimulating and blocking types of TSH-receptor antibodies in sera from three patients with primary hypothyroidism

Shift in Dominance from Blocking to Stimulating Type of Thyrotropin Receptor Antibodies, Resulting in Conversion from Hypothyroidism to Hyperthyroidism during Late Pregnancy

A 20-year-old woman with a 10-month history of treatment for Graves' disease (GD), developed hypothyroidism with a high level of thyrotropin (TSH) receptor-blocking antibodies (TBAbs). She conceived at 28 years old and was clinically euthyroid in the first and second trimester, while taking L-thyroxine. However, at 28 weeks she became hyperthyroid with an unexpected rise in TSH receptor-stimulating antibody (TSAb) levels. She was diagnosed with GD, and methimazole was initiated. Her thyroid function normalized, but the neonate became hyperthyroid. We herein report the first case of a shift in dominance from TBAbs to TSAbs in late pregnancy.

Autoimmune alternating hypo- and hyperthyroidism in children

Two children presented with autoimmune alternating hypo- and hyperthyroidism related to the presence of blocking and stimulating thyroid antibodies. It was difficult to control their thyroid function adequately with an appropriate single drug regimen, and both children underwent total thyroidectomy with subsequent stable management with levothyroxine replacement therapy postsurgically. Although this phenomenon is well described in adults, this report is the first of such occurrence in children. The possible mechanism for the variation in the type of clinical presentation and options for management are discussed.

Epitope heterogeneity of thyrotropin receptor-blocking antibodies in Graves' patients as detected with wild-type versus chimeric thyrotropin receptors

The stable transfectants of wild-type (W25) and mutant thyrotropin-receptor (TSH-R) allow detection of the bioactivities of TSH-R antibodies in Graves' patients. A mutant Chinese hamster ovary (CHO) cell line (Mc1+2) transfected with a chimeric construct, where residues 8 to 165 of the TSH-R are replaced with residues 10 to 166 of the lutropin/choriogonadotropin (LH/CGR) receptor, lacks the cyclic adenosine monophosphate (cAMP) response to most thyrotropin stimulating antibodies (TSAb), yet retains the response to TSH and acquires the response to LH/CG. We compared Mc1+2 cells with wild-type W25 cells for their ability to detect TSAb as well as thyrotropin-blocking antibodies (TBAb) in Graves' sera. Eighteen normal and 39 Graves' sera were tested for TSAb and TBAb levels by in vitro bioassays using W25 and Mc1+2 cells. In addition, these sera were also tested for thyrotropin-binding inhibitory activity (TBII) by a radioreceptor assay. Eighteen (47%) Graves' sera had TBAb activity measured with W25 cells but not with Mc1+2 cells. These TBAbs were, therefore, a population of antibodies with functional epitopes on the N-terminus of the extracellular domain. This TBAb activity by W25 cells exhibited a high degree of correlation with TBII levels by a radioreceptor assay (r = 0.70, p = 0.001). Ten (25.6%) Graves' sera had positive TBAb activity in both W25 and Mc1+2 cells; moreover, their activity in both assays was similar (r = 0.83, p < 0.001). The TBAb activity in these sera, however, did not correlate with TBII activity. Eleven (28%) Graves' sera had no TBAb activity. Overall, thyroid-stimulating antibodies were detected in 87% and 28% of the 39 Graves' sera by W25 and Mc1 +2 cells, respectively. Thus, using the 2 cell lines, at least 2 distinct populations of TBAbs were detected. One is detected in a similar fashion by both W25 and Mc1+2 cell lines and likely interacts with the epitopes residing in the unaltered C-terminus of the TSH-R. The other is reactive in W25 cells only, indicating the loss of TBAb epitope in the chimeric receptor located in the N-terminus of the TSH-R. Furthermore, our results indicate that the TBAb binding epitope in 8-165 residues of the native TSH-R is highly associated with TBII activity in Graves' disease. These results indicate that patients with Graves' disease harbor TBAbs with epitope heterogeneity and favor the notion that there are different sites and mechanisms by which TBAbs act in Graves' patients. It remains to be determined whether or not TBAb subtyping will have a useful predictive role in the management of patients with Graves' disease.

Signaling pathways involved in thyroid hyperfunction and growth in Graves' disease

The elucidation of the multiple signaling cascades coupled to the TSH receptor has offered new approaches in the understanding of the pathogenesis of Graves' disease. Here we review findings showing that immunoglobulins from Graves' patients are heterogeneous, bind to different epitopes and, similarly to TSH, activate different signaling pathways, including adenylyl cyclase, phospholipase C and phospholipase A2. Evidence that the multiplicity of signals correlates with the different manifestations of the disease is also summarized. We believe that the dissection of the molecular mechanisms involved in the pathogenesis of Graves' disease offers the basis for developing novel therapeutical approaches to this disease.

Thyroid stimulating hormone-receptor overexpression in brain of patients with Down syndrome and Alzheimer's disease

Thyroid hormone abnormalities are strongly associated with Down Syndrome (DS) with elevated thyroid stimulating hormone (TSH) levels as the most consistent finding. Using subtractive hybridization for gene hunting we found significant overexpression of mRNA levels for the TSH-receptor (TSH-R) in brain of a fetus with DS. Based upon this observation we determined TSH-R protein levels in five brain regions of patients with DS (n=8), Alzheimer disease (AD, n=8) and controls (C, n=8). Western blots revealed significantly elevated immunoreactive TSH-R protein(s) 40 kD and 61 kD in temporal and frontal cortex of patients with DS and, unexpectedly, in AD. Levels for the 40 kD protein in temporal cortex were 1.00+/-0.036 (arbitrary units+/-SD) in C, 1.35+/-0.143 in DS, 1.52+/-0.128 in AD; in frontal cortex: 1.00+/-0.046 in C, 1.10+/-0.03 in DS, 1.10+/-0.038 in AD. Levels for the 61 kD protein in temporal cortex were 1.01+/-0.015 in C, 1.47+/-0.013 in DS, 1.623+/-0.026 in AD; in frontal cortex: 1.02+/-0.020 in C, 1.18 +/-0.123 in DS, 1.48+/-0.020 in AD. These results show that elevated brain immunoreactive TSH-R is not specific for DS and maybe reflecting apoptosis, a hallmark of both neurodegenerative disorders, as it is well-documented that the thyroid hormone system is involved in the control of programmed cell death.

TSH receptor antibody-associated thyroid dysfunction following subacute thyroiditis

OBJECTIVE

Autoimmunity plays an important role in the development of thyrotrophin (TSH) receptor antibodies and the pathogenesis of Graves' disease and Hashimoto's thyroiditis. On the other hand, subacute thyroiditis is a self-limited inflammatory disease of presumed viral aetiology. The aim of this study was to examine whether subacute thyroiditis triggers TSH receptor antibody-associated thyroid disorders.

PATIENTS

We reviewed 1,697 patients with subacute thyroiditis seen between 1985 and 1995.

DESIGN AND MEASUREMENTS

We measured antibodies which inhibit the TSH binding to the TSH receptor (TBIAb), thyroid stimulating antibodies (TSAb) and antibodies that block TSH action (TBAb). Other thyroid autoantibodies were also determined.

RESULTS

TBIAb became positive in 38 patients following subacute thyroiditis. Thyroid function after the development of TBIAb appeared to be influenced by the bioactivity of the antibody. Hyperthyroidism developed in the presence of TSAb, and so did hypothyroidism in the presence of TBAb, although 21 patients did not have thyroid dysfunction despite high titres of TBIAb. Fifteen out of 17 patients recovered from hyperthyroidism or hypothyroidism after the disappearance of TBIAb sometimes even without medication. TBIAb-positive patients had a high incidence of a family history of thyroid disease and positive anti-thyroid microsomal antibodies. An ophthalmopathy similar to Graves' disease was also observed in 3 patients.

CONCLUSIONS

Subacute thyroiditis may trigger autoreactive B cells to produce TSH receptor antibodies, resulting in TSH receptor antibody-associated thyroid dysfunction in some patients.

Specific effects of radioiodine treatment on TSAb and TBAb levels in patients with Graves' disease

Radioactive iodine (RAI)-induced changes in the levels of antibodies to the thyroid-stimulating hormone (TSH) receptor (TRAb) in patients undergoing treatment for autoimmune thyroid disease have been well documented. Previous studies have reported effects on the overall level of the antibodies present, TSH-binding inhibitory immunoglobulins (TBII), without detailed studies of specific effects on the levels of thyroid-stimulating (TSAb) or thyroid-blocking antibodies (TBAb). More detailed studies have been reported only in individual cases. In this study, the values of TSAb, TBAb, and TBII were measured longitudinally in 33 patients (27 females and 6 males) who received RAI. The bioassays for TSAb and TBAb were performed in JPO9 cells. Following RAI, there were significant and immediate effects on the values of TBII in 70% of patients. TBII levels fell in 7 patients (20%) (Group 1), rose in 16 patients (48%) (Group 2) or remained unchanged but elevated in 10 patients (32%) (Group 3). In the Group 1 patients, only TSAb were detectable and none of these patients became hypothyroid after treatment. In the 16 patients in Group 2, increases in TBII were attributable to specific increases in TSAb in 7 (44%), in TBAb in 3 (19%), and in both TSAb and TBAb in 3 (19%). There were 3 patients (19%) in this group in whom there was no detectable TSAb or TBAb activity despite the increase in TBII. Six patients from this group became hypothyroid within 6 months of RAI treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Scintigraphic findings of the thyroid in hypothyroid patients with blocking-type TSH-receptor antibodies

The present study was designed to analyse the scintigraphic appearance of the thyroid in hypothyroid patients with blocking-type TSH receptor antibodies (TRAbs). Eleven hypothyroid patients with autoimmune thyroiditis positive for TSH binding inhibitor immunoglobulins (TBII) [80% +/- 12 (SD)%; normal < 11%] and for thyroid stimulation-blocking antibodies (TSBAbs) (90% +/- 9%: normal < 32%) were studied. Thyroid scanning was performed using technetium-99m or iodine-123, when the patients were hypothyroid. Analysis of the scan images revealed the presence of localized functioning areas in six patients (group 1), and no visualization of the thyroid in the remaining five patients (group 2). Patients in group 1 showed significantly higher uptake of 99mTc than those in group 2 (P < 0.05). Interestingly, three patients in group 1 were positive for thyroid-stimulating antibodies (TSAbs) (249% +/- 17%; normal < 145%), which were not detected in the remaining eight patients. Antibodies against thyroglobulin and microsomal antigens were detected in nine nine (81.8%) and 11 (100%) patients, respectively, but neither of these titres correlated with the scan image. Three patients in group 1 underwent scintigraphy again after treatment with thyroxine, at which time the functioning lesion was not noted. Fourteen hypothyroid patients with negative TBII displayed no such scintigraphic findings. Chronic stimulation of the thyroid by TSAbs and/or TSH might be responsible for the presence of the functioning lesion, but clarification of the mechanism requires further studies. In summary (1) TSAbs were detected in three (27.3%) of 11 hypothyroid patients with blocking TRAbs; (2) thyroid scintigraphy revealed the presence of localized functioning area(s) in approximately half of these cases.

Thyrotropin stimulation of the lutropin/choriogonadotropin receptor: different sites mediate agonist activity and high affinity binding

Surprisingly, thyrotropin (TSH) can increase cAMP and inositol phosphate (IP) levels in Cos-7 cells transfected with the lutropin (LH)/choriogonadotropin (CG) receptor (LH/CGR) as well as LH or CG, as evidenced by similar EC50 and maximal stimulation values. Additionally surprising, TSH activation is evident, despite markedly reduced levels of high affinity TSH binding by comparison to CG (Hidaka A, et al. 1993 Biochem Biophys Res Commun 196:187-195). In this report, we questioned whether the unusual TSH activity, as well as the discrepancy between TSH activity and binding, might reflect the existence of distinct agonist and binding sites on the LH/CGR extracellular domain and the ability of TSH to interact with the former despite a minimal interaction with the latter. We evaluated this possibility by using two chimeras spanning the extracellular domain of the TSHR and the LH/CGR:Mc1 + 2, where residues 8-165 of the TSHR are substituted, and Mc2 + 3 + 4, where residues 90-370 are replaced with the corresponding peptide segment from the LH/CGR. After transfection in Cos-7 cells, Mc2 + 3 + 4 exhibits higher affinity for CG than wild-type LH/CGR, but has no CG agonist response in assays measuring cAMP or inositol phosphate (IP) levels. Conversely, the Mc1 + 2 chimera exhibits significantly decreased affinity for CG, but CG agonist activity is comparable to wild-type LH/CGR in cAMP and IP assays. These data show that the extracellular domain of the LH/CGR does have distinct sites for CG binding and agonist activity: the C-terminus in Mc2 + 3 + 4 is important for high affinity CG binding, whereas the N-terminus in Mc1 + 2 is able to exhibit a CG agonist response, despite low affinity binding. When evaluated using TSH, Mc1 + 2, with the C-terminus of the TSHR present, exhibits high affinity TSH binding comparable to wild-type TSHR. Unexpectedly, Mc1 + 2, with the substitution of the N-terminus of the extracellular domain of the LH/CGR, exhibits even better TSH agonist activity than wild-type TSHR, not a loss of activity. Thus, the N-terminus of the extracellular domain of the LH/CGR can couple TSH binding to signal transduction events even better than the N-terminus of the TSHR. This may, in part, explain why TSH has an unusual agonist activity in cells transfected with LH/CGR, despite relatively low affinity binding. Although distinct agonist and binding sites exist in the linear sequence of the extracellular domain, the activity of the two sites is interdependent.(ABSTRACT TRUNCATED AT 400 WORDS)

Characteristics and clinical correlates of a novel thyroid-stimulating autoantibody

We reported a patient who gave birth to 3 children with transient neonatal hypothyroidism. She had 3 different antibodies (Ab) to the thyrotropin receptor (TSHR) in her serum, viz., TSH binding-inhibiting (TBIAb), thyroid-stimulating (TSAb) and an additional stimulating Ab (SAb). The SAb differed from TSAb in that its in vitro stimulating effect in human thyroid and FRTL5 cells was not inhibited by TBIAb [similar data now obtained with Chinese hamster ovary (CHO) cells transfected with cloned human TSHR]. Because of symptomatic goiter enlargement the patient underwent subtotal thyroidectomy. About 50% of the gland was infiltrated with lymphocytes; thyroid follicles had columnar epithelium, despite suppression of TSH by thyroxine and the presence of the potent TBIAb. Fifteen months later, when all 3 Ab showed a decline of approximately 3 fold, she gave birth to hypothyroid twins. These data support the following conclusions: 1) thyroidectomy and immunosuppression of pregnancy do not prevent neonatal thyroid disease if TSHR Ab (TRAb) are of high titer; 2) the thyroid is not a major site of TRAb production; 3) SAb is a thyroid stimulator, distinct from TSAb in that it does not share binding epitopes on the TSHR with either TSH or TBIAb; 4) SAb was the probable cause of thyroid growth in this patient.

Fluctuating thyroid function depending on the balance between stimulating and blocking types of TSH receptor antibodies: a case report

A 41-year-old hyperthyroid woman visited the hospital in April 1989. She spontaneously developed hypothyroidism in August 1989 and recurrent hyperthyroidism in November 1991. TSH binding inhibitor immunoglobulins (TBII) and thyroid-stimulating antibodies (TSAb) activities were 34.7% (normal range, < 11.0%) and 295.0% (normal range, < 145.0%), respectively, at her first visit. When she was hypothyroid, TBII were 85.9-90.0%, TSAb were 75-190%, and thyroid stimulation-blocking antibodies (TSBAb) activities were 80.0-96.6% (normal range, < 32.2%). When she became hyperthyroid again, TSAb activities were markedly increased to 1108% with TBII and TSBAb activities being 82.2 and 62.8%, respectively. The results indicate that both stimulating and blocking types of TSH receptor antibodies were present in her serum and that her fluctuating thyroid function could be explained by alterations in the balance between the activities of these two types of antibodies.

Changes in stimulating and blocking TSH receptor antibodies in a patient undergoing three cycles of transition from hypo to hyper-thyroidism and back to hypothyroidism

We report a patient who underwent, over a mere 3-year period, three successive cycles of oscillation from hypo to hyper-thyroidism and back to hypothyroidism. This unusual sequence of events originated in a rare passage of primary hypothyroidism to hyper-thyroidism. The hyperthyroidism seemed typical of the autoimmune subgroup of toxic multinodular goitre. Stimulating and blocking TSH receptor antibody activities were measured (by cAMP functional bioassays using cultured human thyrocytes) during the course of the fluctuating phases of hypo and hyper-thyroidism. Measurement of such antibody activities revealed the coexistence of both stimulatory and blocking types of antibody in several serum samples from the patient. Throughout the whole course of alterations in thyroid function, thyroid stimulating antibodies were present. This was not the case with thyrotrophin receptor antibodies exhibiting TSH antagonist activity which seemed to appear and disappear. Monitoring such activity indicated that the emergence of blocking antibody seems to herald the onset of hypothyroidism.

Thyroid-stimulating antibodies and thyroid stimulation-blocking antibodies during the pregnancy and postpartum period: a case report

This report describes a unique pattern of changes in thyroid function and thyroid antibodies in a woman during the course of two pregnancies and two postpartum periods. A 25-year-old woman developed hypothyroidism in the postpartum period after the delivery of her first child. She was found to have potent thyroid stimulation-blocking antibodies (TSBAb) in the serum. One year later, she became pregnant again, and during the pregnancy, TSBAb had decreased to an undetectable level. She gave birth to the second healthy child and developed postpartum thyrotoxicosis, probably due to destruction of the thyroid gland, which gradually resolved. In this postpartum period, serum TSBAb levels increased. Eight months postpartum, she developed what appeared to be Graves' disease with an elevated 123I-thyroid uptake. Serum thyroid-stimulating antibodies (TSAb) were found at that time, and the TSBAb had disappeared from her serum.

Heterogeneity of thyrotropin binding inhibitor immunoglobulins in serum from untreated patients with hyperthyroid Graves' disease

We have previously established an assay for the simultaneous assessment of thyrotropin (TSH) binding inhibitor immunoglobulin (TBII) and thyroid stimulating autoantibody activities in cultured rat thyroid cells (FRTL-5 cell), and found a discrepancy in some patients with untreated Graves' disease between the activities of TBII measured in FRTL-5 cells (TBII-rc) and in solubilized thyroid membranes (TBII-pm). In three selected patients with untreated Graves' disease, the different dose-response relationship between TBII-rc and TBII-pm clearly indicated the heterogeneous populations of TBII-pm in patients' sera, with different binding affinities for TSH receptor in intact cells.

Heterogeneity of circulating TSH-receptor antibodies in thyroid disease demonstrated directly by chromatography

The heterogeneity of circulating TSH-receptor antibodies (TRAb) has been demonstrated directly by affinity chromatography on the dye Remazol Yellow-GGL. The technique resolved these antibodies into discrete peaks within the general serum immunoglobulin background. Peaks were detected initially by a binding (radioreceptor) assay and then characterized by their ability to stimulate the uptake of iodine-125 into FRTL-5 cells. Thirteen subjects with high serum levels of TRAb were studied. The two hypothyroid patients each produced a single peak of TRAb activity with no ability to stimulate uptake of iodine-125 into cultured cells. The remaining 11 patients had Graves' disease; their sera produced a range of elution profiles after chromatography with TRAb activity resolved into as many as five peaks. Considerable differences were seen in the relative abilities of the resolved TRAb components to bind to receptors and to stimulate cellular uptake of iodine-125 both between and within individual samples. No two patients produced components which chromatographed in the same position on the gradients employed for elution from the dye.