A human monoclonal autoantibody to the thyrotropin receptor with thyroid-stimulating blocking activity

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.

Non-thionamide antithyroid drug options in Graves' hyperthyroidism

INTRODUCTION

The thionamide anti-thyroid drugs namely carbimazole, methimazole, and propylthiouracil, have been the predominant therapy modality for Graves' hyperthyroidism for over 60 years. Although these agents have proven efficacy and favorable side-effect profiles, non-thionamide alternatives are occasionally indicated in patients who are intolerant or unresponsive to thionamides alone. This review examines the available non-thionamide drug options for the control of Graves' hyperthyroidism and summarizes their clinical utility, efficacy, and limitations.

AREAS COVERED

We reviewed existing literature on mechanisms, therapeutic utility, and side-effect profiles of non-thionamide anti-thyroid drugs. Established non-thionamide agents act on various phases of the synthesis, release, and metabolism of thyroid hormones and comprise historical agents such as iodine compounds and potassium perchlorate as well as drug repurposing candidates like lithium, glucocorticoids, beta-blockers, and cholestyramine. Novel experimental agents in development target key players in Graves' disease pathogenesis including B-cell depletors (Rituximab), CD40 blockers (Iscalimab), TSH-receptor antagonists, blocking antibodies, and immune-modifying peptides.

EXPERT OPINION

Non-thionamide anti-thyroid drugs are useful alternatives in Graves' hyperthyroidism and more clinical trials are needed to establish their safety and long-term efficacy in hyperthyroidism control. Ultimately, the promise for a cure will lie in novel approaches that target the well-established immunopathogenesis of Graves' disease.

Thyrotropin receptor antagonists and inverse agonists, and their potential application to thyroid diseases

The thyrotropin receptor (TSHR) plays critical roles in thyroid growth and function and in the pathogenesis of several thyroid diseases including Graves' hyperthyroidism and ophthalmopathy, non-autoimmune hyperthyroidism and thyroid cancer. Several low-molecular weight compounds (LMWCs) and anti-TSHR monoclonal antibodies (mAbs) with receptor antagonistic and inverse agonistic activities have been reported. The former binds to the pocket formed by the receptor transmembrane bundle, and the latter to the extracellular TSH binding site. Both are effective inhibitors of TSH/thyroid stimulating antibody-stimulated cAMP and/or hyaluronic acid production in TSHR-expressing cells. Anti-insulin-like growth factor 1 inhibitors are also found to inhibit TSHR signaling. Each agent has advantages and disadvantages; for example, mAbs have a higher affinity and longer half-life but are more costly than LMWCs. At present, mAbs appear most promising, yet the development of more efficacious LMWCs is desirable. These agents are anticipated to be efficacious not only for the above-mentioned diseases but also for resistance to thyroid hormone and have utility for thyroid cancer radionuclide scintigraphy/therapy as a new theranostic.

2021 update on thyroid-associated ophthalmopathy

PURPOSE

Our understanding of thyroid-associated ophthalmopathy (TAO, A.K.A Graves' orbitopathy, thyroid eye disease) has advanced substantially, since one of us (TJS) wrote the 2010 update on TAO, appearing in this journal.

METHODS

PubMed was searched for relevant articles.

RESULTS

Recent insights have resulted from important studies conducted by many different laboratory groups around the World. A clearer understanding of autoimmune diseases in general and TAO specifically emerged from the use of improved research methodologies. Several key concepts have matured over the past decade. Among them, those arising from the refinement of mouse models of TAO, early stage investigation into restoring immune tolerance in Graves' disease, and a hard-won acknowledgement that the insulin-like growth factor-I receptor (IGF-IR) might play a critical role in the development of TAO, stand out as important. The therapeutic inhibition of IGF-IR has blossomed into an effective and safe medical treatment. Teprotumumab, a β-arrestin biased agonist monoclonal antibody inhibitor of IGF-IR has been studied in two multicenter, double-masked, placebo-controlled clinical trials demonstrated both effectiveness and a promising safety profile in moderate-to-severe, active TAO. Those studies led to the approval by the US FDA of teprotumumab, currently marketed as Tepezza for TAO. We have also learned far more about the putative role that CD34+ fibrocytes and their derivatives, CD34+ orbital fibroblasts, play in TAO.

CONCLUSION

The past decade has been filled with substantial scientific advances that should provide the necessary springboard for continually accelerating discovery over the next 10 years and beyond.

Brief Report - Monoclonal Antibodies Illustrate the Difficulties in Measuring Blocking TSH Receptor Antibodies

TSH receptor (TSHR) antibodies are the cause of Graves' disease and may also be found in patients with Hashimoto's thyroiditis. They come in at least three varieties: thyroid stimulating, thyroid blocking and neutral. The measurement of TSH receptor antibodies in Graves' disease and Hashimoto's thyroiditis is a common clinical activity and can be useful in diagnosis and prognosis. We show that it is not possible to detect the blocking variety of TSHR antibody in patients with Graves' disease because the stimulating antibody may overwhelm the measurement of blocking in the bioassays available for their measurement and may blind the valid interpretation of the results. To help explain this in more detail we show a series of studies with monoclonal TSHR antibodies which support this conclusion.

Potential Roles of CD34+ Fibrocytes Masquerading as Orbital Fibroblasts in Thyroid-Associated Ophthalmopathy

CONTEXT

Orbital tissues in thyroid-associated ophthalmopathy exhibit particular reactivity and undergo characteristic remodeling. Mechanisms underlying these changes have remained largely unexplained. Studies have characterized orbital connective tissues and derivative fibroblasts to gain insights into local manifestations of a systemic autoimmune syndrome.

EVIDENCE ACQUISITION

A systematic search of PubMed was undertaken for studies related to thyroid-associated ophthalmopathy (TAO), orbital fibroblasts, and fibrocytes involved in pathogenesis.

EVIDENCE SYNTHESIS

Orbital tissues display marked cellular heterogeneity. Fibroblast subsets, putatively derived from multiple precursors, inhabit the orbit in TAO. Among them are cells displaying the CD34+CXC chemokine receptor 4+collagen I+ phenotype, identifying them as fibrocytes, derived from the monocyte lineage. Their unique presence in the TAO orbit helps explain the tissue reactivity and characteristic remodeling that occurs in the disease. Their unanticipated expression of several proteins traditionally thought to be thyroid gland specific, including the TSH receptor and thyroglobulin, may underlie orbital involvement in Graves disease. Although no currently available information unambiguously establishes that CD34+ orbital fibroblasts originate from circulating fibrocytes, inferences from animal models of lung disease suggest that they derive from bone marrow. Further studies are necessary to determine whether fibrocyte abundance and activity in the orbit determine the clinical behavior of TAO.

CONCLUSION

Evidence supports a role for fibrocytes in the pathogenesis of TAO. Recognition of their presence in the orbit now allows development of therapies specifically targeting these cells that ultimately could allow the restoration of immune tolerance within the orbit and perhaps systemically.

Thyrotrophin receptor antibody concentration and activity, several years after treatment for Graves' disease

OBJECTIVE

TSH receptor antibodies (TRAb) are responsible for autoimmune hyperthyroid disease (Graves' disease; GD) with TRAb levels tending to decrease following treatment. Measurement of TRAb activity during follow-up could prove valuable to better understand treatment effectiveness.

STUDY DESIGN

TRAb concentration and stimulating (TSAb) and blocking (TSBAb) activity of patient serum were assessed following different treatment modalities and follow-up length.

METHODS

Sixty-six subjects were recruited following treatment with carbimazole (n = 26), radioiodine (n = 27) or surgery (n = 13). TRAb, TPOAb, TgAb and GADAb were measured at a follow-up visit as well as bioassays of TSAb and TSBAb activity.

RESULTS

Forty-five per cent of all patients remained TRAb-positive for more than one year and 23% for more than 5 years after diagnosis, irrespective of treatment method. Overall, TRAb concentration fell from a median (IQR) of 6.25 (3.9-12.7) to 0.65 (0.38-3.2) U/L. Surgery conferred the largest fall in TRAb concentration from 11.4 (6.7-29) to 0.58 (0.4-1.4) U/L. Seventy per cent of TRAb-positive patients were positive for TSAb, and one patient (3%) was positive for TSBAb. TRAb and TSAb correlated well (r = 0.83). In addition, 38/66 patients were TgAb-positive, 47/66 were TPOAb-positive and 6/66 were GADAb-positive at follow-up.

CONCLUSIONS

TRAb levels generally decreased after treatment but persisted for over 5 years in some patients. TRAb activity was predominantly stimulatory, with only one patient demonstrating TSBAb. A large proportion of patients were TgAb/TPOAb-positive at follow-up. All treatment modalities reduced TRAb concentrations; however, surgery was most effective.

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.

Structure of a Thyrotropin Receptor Monoclonal Antibody Variable Region Provides Insight into Potential Mechanisms for its Inverse Agonist Activity

BACKGROUND

The high constitutive, or ligand-independent, activity of the thyrotropin receptor (TSHR) is of clinical importance in some thyroid conditions, particularly well-differentiated thyroid carcinoma remnants following incomplete ablative therapy (surgery and radioiodine). Under these conditions, even total suppression of TSH by thyroid hormone administration does not fully reduce TSHR activity, a driver of thyrocyte growth.

METHODS

CS-17 is a murine monoclonal antibody that has inverse agonist activity in that it suppresses TSHR constitutive activity. This study crystallized the CS-17 Fab and determined its atomic structure at a resolution of 3.4 Å.

RESULTS

In silico docking of this structure to that of the TSHR extracellular domain was accomplished by targeting to TSHR residue tyrosine 195 (Y195) known to contribute to the CS-17 epitope. High affinity interaction between these two molecules, primarily by the CS-17 immunoglobulin heavy chain, was validated by energetic analysis (K_D of 8.7 × 10^-11 M), as well as by previously obtained data on a number of individual TSHR amino acids in three regions whose mutagenesis reduced CS-17 binding as detected by flow cytometry.

CONCLUSIONS

Structural insight at atomic resolution of a TSHR antibody with inverse agonist activity opens the way for the development of a molecule with therapeutic potential, particularly in thyroid carcinoma. For this purpose, CS-17 will require "humanization" by substitution of its constant region (Fc component). In addition, with its epitope defined, the CS-17 affinity can be increased further by mutagenesis of selected amino acids in its heavy- and light-chain complementarity determining regions.

Nonthionamide Drugs for the Treatment of Hyperthyroidism: From Present to Future

Hyperthyroidism is a common endocrine disease. Although thionamide antithyroid drugs are the cornerstone of hyperthyroidism treatment, some patients cannot tolerate this drug class because of its serious side effects including agranulocytosis, hepatotoxicity, and vasculitis. Therefore, nonthionamide antithyroid drugs (NTADs) still have an important role in controlling hyperthyroidism in clinical practice. Furthermore, some situations such as thyroid storm or preoperative preparation require a rapid decrease in thyroid hormone by combination treatment with multiple classes of antithyroid drugs. NTADs include iodine-containing compounds, lithium carbonate, perchlorate, glucocorticoid, and cholestyramine. In this narrative review, we summarize the mechanisms of action, indications, dosages, and side effects of currently used NTADs for the treatment of hyperthyroidism. In addition, we also describe the state-of-the-art in future drugs under development including rituximab, small-molecule ligands (SMLs), and monoclonal antibodies with a thyroid-stimulating hormone receptor (TSHR) antagonist effect.

Mechanisms of Autoantibody-Induced Pathology

Autoantibodies are frequently observed in healthy individuals. In a minority of these individuals, they lead to manifestation of autoimmune diseases, such as rheumatoid arthritis or Graves' disease. Overall, more than 2.5% of the population is affected by autoantibody-driven autoimmune disease. Pathways leading to autoantibody-induced pathology greatly differ among different diseases, and autoantibodies directed against the same antigen, depending on the targeted epitope, can have diverse effects. To foster knowledge in autoantibody-induced pathology and to encourage development of urgently needed novel therapeutic strategies, we here categorized autoantibodies according to their effects. According to our algorithm, autoantibodies can be classified into the following categories: (1) mimic receptor stimulation, (2) blocking of neural transmission, (3) induction of altered signaling, triggering uncontrolled (4) microthrombosis, (5) cell lysis, (6) neutrophil activation, and (7) induction of inflammation. These mechanisms in relation to disease, as well as principles of autoantibody generation and detection, are reviewed herein.

TSHR as a therapeutic target in Graves' disease

INTRODUCTION

Graves' disease (GD) and thyroid-associated ophthalmopathy (TAO) are thought to result from actions of pathogenic antibodies mediated through the thyrotropin receptor (TSHR). This leads to the unregulated consequences of the antibody-mediated receptor activity in the thyroid and connective tissues of the orbit. Recent studies reveal antibodies that appear to be directed against the insulin-like growth factor-I receptor (IGF-IR). Areas covered: In this brief article, I attempt to review the fundamental characteristics of the TSHR, its role in GD and TAO, and its relationship to IGF-IR. Strong evidence supports the concept that the two receptors form a physical and functional complex and that IGF-IR activity is required for some of the down-stream signaling initiated through TSHR. Recently developed small molecules and monoclonal antibodies that block TSHR and IGF-IR signaling are also reviewed in the narrow context of their potential utility as therapeutics in GD and TAO. The Pubmed database was searched from its inception for relevant publications. Expert opinion: Those agents that can interrupt the TSHR and IGF-IR pathways possess the potential for offering more specific and better tolerated treatments of both hyperthyroidism and TAO. This would spare patients exposure to toxic drugs, ionizing radiation and potentially hazardous surgeries.

Current trends in antithyroid drug treatment of Graves' disease

INTRODUCTION

Graves' hyperthyroidism is associated with significant morbidity and mortality risk. The thionamides, methimazole, its pro-drug derivative carbimazole, and propylthiouracil, remain a cornerstone of management. Yet despite decades of use, optimal strategies for maximising treatment response and curtailing adverse effect risk remains uncertain.

AREAS COVERED

We reviewed the current literature on the evidence based medical management of Graves' disease. Specifically, we evaluated current approaches to the use of thionamides, adjunctive therapies, and potential novel agents for controlling Graves' hyperthyroidism.

EXPERT OPINION

Primary medical therapy is successful in less than 50% of cases and so careful selection of patients for medical treatment based on a combination of pathological and pragmatic considerations is essential. Carbimazole or methimazole is the treatment of choice in the non-pregnant population driven by its more favourable pharmacokinetic and adverse effect profile over propylthiouracil. In pregnancy the choice of treatment is less straightforward and an approach that minimises undue fetal exposure to all thionamides should be adopted. Additional data is needed on the value of adjunctive therapies including potassium perchlorate, iodides, glucocorticoids, lithium, and cholestyramine. Novel agents directed against pathogenetic targets including TSH receptor blocking monoclonal antibodies and small molecule antagonists may hold promise for the future.

Modeling Graves' Orbitopathy in Experimental Graves' Disease

Graves' orbitopathy (GO), also known as thyroid eye disease is an inflammatory disease of the orbital tissue of the eye that arises as a consequence of autoimmune thyroid disease. The central feature of the disease is the production of antibodies to the thyrotropin hormone receptor (TSHR) that modulate the function of the receptor leading to autoimmune hyperthyroidism and GO. Over the years, all viable preclinical models of Graves' disease have been incomplete and singularly failed to progress in the treatment of orbital complications. A new mouse model of GO based upon immunogenic presentation of human TSHR A-subunit plasmid by close field electroporation is shown to lead to induction of prolonged functional antibodies to TSHR resulting in chronic disease with subsequent progression to GO. The stable preclinical GO model exhibited pathologies reminiscent of human disease characterized by orbital remodeling by inflammation and adipogenesis. Inflammatory lesions characterized by CD3+ T cells and macrophages were localized in the orbital muscle tissue. This was accompanied by extensive adipogenesis of orbital fat in some immune animals. Surprisingly, other signs of orbital involvement were reminiscent of eyelid inflammation involving chemosis, with dilated and congested orbital blood vessels. More recently, the model is replicated in the author's independent laboratories. The pre-clinical model will provide the basis to study the pathogenic and regulatory roles of immune T and B cells and their subpopulations to understand the initiation, pathophysiology, and progression of GO.

Mechanisms of Action of TSHR Autoantibodies

The availability of human monoclonal antibodies (MAbs) to the TSHR has enabled major advances in our understanding of how TSHR autoantibodies interact with the receptor. These advances include determination of the crystal structures of the TSHR LRD in complex with a stimulating autoantibody (M22) and with a blocking type autoantibody (K1-70). The high affinity of MAbs for the TSHR makes them particularly suitable for use as ligands in assays for patient serum TSHR autoantibodies. Also, M22 and K1-70 are effective at low concentrations in vivo as TSHR agonists and antagonists respectively. K1-70 has important potential in the treatment of the hyperthyroidism of Graves' disease and Graves' ophthalmopathy. Small molecule TSHR antagonists described to date do not appear to have the potency and/or specificity shown by K1-70. New models of the TSHR ECD in complex with various ligands have been built. These models suggest that initial binding of TSH to the TSHR causes a conformational change in the hormone. This opens a positively charged pocket in receptor-bound TSH which attracts the negatively charged sulphated tyrosine 385 on the hinge region of the receptor. The ensuing movement of the receptor's hinge region may then cause activation. Similar activation mechanisms seem to take place in the case of FSH and the FSHR and LH and the LHR. However, stimulating TSHR autoantibodies do not appear to activate the TSHR in the same way as TSH.

Constitutive activities in the thyrotropin receptor: regulation and significance

The thyroid-stimulating hormone receptor (TSHR, or thyrotropin receptor) is a family A G protein-coupled receptor. It not only binds thyroid-stimulating hormone (TSH, or thyrotropin) but also interacts with autoantibodies under pathological conditions. The TSHR and TSH are essential for thyroid growth and function and thus for all thyroid hormone-associated physiological superordinated processes, including metabolism and development of the central nervous system. In vitro studies have found that the TSHR permanently stimulates ligand-independent (constitutive) activation of Gs, which ultimately leads to intracellular cAMP accumulation. Furthermore, a vast variety of constitutively activating mutations of TSHR-at more than 50 different amino acid positions-have been reported to enhance basal signaling. These lead in vivo to a "gain-of-function" phenotype of nonautoimmune hyperthyroidism or toxic adenomas. Moreover, many naturally occurring inactivating mutations are known to cause a "loss-of-function" phenotype, resulting in resistance to thyroid hormone or hyperthyrotropinemia. Several of these mutations are also characterized by impaired basal signaling, and these are designated here as "constitutively inactivating mutations" (CIMs). More than 30 amino acid positions with CIMs have been identified so far. Moreover, the permanent TSHR signaling capacity can also be blocked by inverse agonistic antibodies or small drug-like molecules, which both have a potential for clinical usage. In this chapter, information on constitutive activity in the TSHR is described, including up- and downregulation, linked protein conformations, physiological and pathophysiological conditions, and related intracellular signaling.

Blocking type TSH receptor antibodies

TSH receptor (TSHR) autoantibodies (TRAbs) play a key role in the pathogenesis of Graves' disease. In the majority of patients, TRAbs stimulate thyroid hormone synthesis via activation of the TSHR (stimulating TRAbs, TSHR agonists). In some patients, TRAbs bind to the receptor but do not cause activation (blocking TRAbs, TSHR antagonists). Isolation of human TSHR monoclonal antibodies (MAbs) with either stimulating (M22 and K1-18) or blocking activities (5C9 and K1-70) has been a major advance in studies on the TSHR. The binding characteristics of the blocking MAbs, their interaction with the TSHR and their effect on TSHR constitutive activity are summarised in this review. In addition, the binding arrangement in the crystal structures of the TSHR in complex with the blocking MAb K1-70 and with the stimulating MAb M22 (2.55 Å and 1.9 Å resolution, respectively) are compared. The stimulating effect of M22 and the inhibiting effect of K1-70 on thyroid hormone secretion in vivo is discussed. Furthermore the ability of K1-70 to inhibit the thyroid stimulating activity of M22 in vivo is shown. Human MAbs which act as TSHR antagonists are potentially important new therapeutics. For example, in Graves' disease, K1-70 may well be effective in controlling hyperthyroidism and the eye signs caused by stimulating TRAb. In addition, hyperthyroidism caused by autonomous TSH secretion should be treatable by K1-70, and 5C9 has the potential to control hyperthyroidism associated with TSHR activating mutations. Furthermore, K1-70 has potential applications in thyroid imaging as well as targeted drug delivery to TSHR expressing tissues.

Thyrotropin-blocking autoantibodies and thyroid-stimulating autoantibodies: potential mechanisms involved in the pendulum swinging from hypothyroidism to hyperthyroidism or vice versa

BACKGROUND

Thyrotropin receptor (TSHR) antibodies that stimulate the thyroid (TSAb) cause Graves' hyperthyroidism and TSHR antibodies which block thyrotropin action (TBAb) are occasionally responsible for hypothyroidism. Unusual patients switch from TSAb to TBAb (or vice versa) with concomitant thyroid function changes. We have examined case reports to obtain insight into the basis for "switching."

SUMMARY

TBAb to TSAb switching occurs in patients treated with levothyroxine (LT4); the reverse switch (TBAb to TSAb) occurs after anti-thyroid drug therapy; TSAb/TBAb alterations may occur during pregnancy and are well recognized in transient neonatal thyroid dysfunction. Factors that may impact the shift include: (i) LT4 treatment, usually associated with decreased thyroid autoantibodies, in unusual patients induces or enhances thyroid autoantibody levels; (ii) antithyroid drug treatment decreases thyroid autoantibody levels; (iii) hyperthyroidism can polarize antigen-presenting cells, leading to impaired development of regulatory T cells, thereby compromising control of autoimmunity; (iv) immune-suppression/hemodilution reduces thyroid autoantibodies during pregnancy and rebounds postpartum; (v) maternally transferred IgG transiently impacts thyroid function in neonates until metabolized; (vi) a Graves' disease model involving immunizing TSHR-knockout mice with mouse TSHR-adenovirus and transfer of TSHR antibody-secreting splenocytes to athymic mice demonstrates the TSAb to TBAb shift, paralleling the outcome of maternally transferred "term limited" TSHR antibodies in neonates. Finally, perhaps most important, as illustrated by dilution analyses of patients' sera in vitro, TSHR antibody concentrations and affinities play a critical role in switching TSAb and TBAb functional activities in vivo.

CONCLUSIONS

Switching between TBAb and TSAb (or vice versa) occurs in unusual patients after LT4 therapy for hypothyroidism or anti-thyroid drug treatment for Graves' disease. These changes involve differences in TSAb versus TBAb concentrations, affinities and/or potencies in individual patients. Thus, anti-thyroid drugs or suppression/hemodilution in pregnancy reduce initially low TSAb levels even further, leading to TBAb dominance. In contrast, TSAb emergence after LT4 administration may be sufficient to counteract TBAb inhibition. The occurrence of "switching" emphasizes the need for careful patient monitoring and management. Finally, whole genome screening of relatively rare "switch" patients and appropriate Graves' and Hashimoto's controls could provide unexpected and valuable information regarding the basis for thyroid autoimmunity.

TSH and Thyrotropic Agonists: Key Actors in Thyroid Homeostasis

This paper provides the reader with an overview of our current knowledge of hypothalamic-pituitary-thyroid feedback from a cybernetic standpoint. Over the past decades we have gained a plethora of information from biochemical, clinical, and epidemiological investigation, especially on the role of TSH and other thyrotropic agonists as critical components of this complex relationship. Integrating these data into a systems perspective delivers new insights into static and dynamic behaviour of thyroid homeostasis. Explicit usage of this information with mathematical methods promises to deliver a better understanding of thyrotropic feedback control and new options for personalised diagnosis of thyroid dysfunction and targeted therapy, also by permitting a new perspective on the conundrum of the TSH reference range.

Immune manipulation for Graves' disease: re-exploring an unfulfilled promise with modern translational research

Although Graves' disease is the commonest autoimmune thyroid disorder, current therapeutics typically center on the eradication of the antigenic stimulus (i.e. thyroid gland) rather than radically tackling the underlying autoimmune processes. Consequently, it is not a surprising fact that Graves' disease remains essentially a chronic drug-dependent ailment afflicting untold numbers worldwide for decades despite progress in deciphering its autoimmune nature. Addressing the latter is key to a future cure as underscored by appropriate, albeit crude, proof-of-concept scenarios of clinical remissions achieved with hematopoietic stem cell transplantation, immune down-regulation during pregnancy, use of corticosteroids or immunosuppressives, and cytokine biologics in animal models. Ongoing basic and translational research to further elucidate and refine our understanding of the pathogenesis of Graves' disease holds the promise of unraveling novel immune manipulative techniques that will bring the world a step closer to the elusive cure of the underlying autoimmunity amidst skepticisms on the value of the science from the present lack of paralleled advances at the bedside. We review the updated literature and describe the forms of immune manipulation hitherto explored that will offer a route to a future cure, from thionamides, hematopoietic stem cell transplantation to the latest immunomodulatory agents.

Thyrotrophin receptor antibody characteristics in a woman with long-standing Hashimoto's who developed Graves' disease and pretibial myxoedema

CONTEXT

Sequential conversion of Hashimoto's thyroiditis (HT) to Graves' disease (GD) is uncommon. Distinct immune paradigms, paucity of functioning tissue in long-standing HT, and infrequent conversion of blocking (TBAb) to stimulating (TSAb) thyrotrophin receptor antibody (TRAb) may account for this. Molecular and crystal structure analysis helps delineate TSH receptor (TSHR)/TRAb interactions in detail. Such 'fingerprinting' helps determine the behaviour and characteristics of TRAb in longitudinal studies.

PATIENT

An 80-year-old woman taking thyroxine for long-standing HT became hyperthyroid. This persisted despite thyroxine withdrawal - free T3 was 7·3 pmol/l (2·6-5·7) and TSH < 0·01 mU/l (0·2-4·5) and TRAb highly positive. She had a goitre (ultrasound - HT), pretibial myxoedema, with mild inactive Graves' orbitopathy. She had RAI treatment and is on thyroxine replacement.

MEASUREMENTS AND RESULTS

Blood samples at presentation (A) and 1 year (B) showed high TSAb and TPOAb activity but no TBAb. Experiments involving TSHR mutations confirmed that (i) TRAb had stable characteristics over 1 year; (ii) TSHR mutation R255D caused complete inhibition and (iii) R109A caused marked reduction of cAMP production by M22 (TSHR-stimulating human monoclonal antibody) and A and B; (iv) mutations R80A, E107A and K129A while affecting M22 had little effect on A and B.

CONCLUSIONS

The reasons for an immunological paradigm shift in this elderly woman remain speculative. We believe that de-novo TSAb synthesis occurred converting her long-standing HT to GD although the mechanisms responsible remain unexplained. TRAb analysis confirmed stable autoantibody characteristics over 1 year and variable effects of TSHR mutations on TRAb and M22 function.

Autoimmunity and Graves' disease

Current treatment options for Graves' hyperthyroidism and the related ophthalmopathy (GO) are not uniformly effective and carry with them potentially serious side effects. As a result, efforts have been focused on the development of novel therapies. Progress has been made, particularly in the production of thyroid-stimulating hormone receptor (TSHR) antagonists, as either monoclonal blocking antibodies or small-molecule ligands. In addition, rituximab (RTX) is the first targeted biological therapy to be studied as treatment for these conditions.

Insights into differential modulation of receptor function by hinge region using novel agonistic lutropin receptor and inverse agonistic thyrotropin receptor antibodies

We report two antibodies, scFv 13B1 and MAb PD1.37, against the hinge regions of LHR and TSHR, respectively, which have similar epitopes but different effects on receptor function. While neither of them affected hormone binding, with marginal effects on hormone response, scFv 13B1 stimulated LHR in a dose-dependent manner, whereas MAb PD1.37 acted as an inverse agonist of TSHR. Moreover, PD1.37 could decrease the basal activity of hinge region CAMs, but had varied effects on those present in ECLs, whereas 13B1 was refractory to any CAMs in LHR. Using truncation mutants and peptide phage display, we compared the differential roles of the hinge region cysteine box-2/3 as well as the exoloops in the activation of these two homologus receptors.

Congenital disorders of the thyroid: hypo/hyper

This article summarizes the ontogenesis and genetics of the thyroid with regards to its possible congenital dysfunction and briefly refers to the roles of the mother-placenta-fetal unit, iodine effect, and organic and functional changes of the negative feedback mechanism, as well as maturity and illness, in some forms of congenital hypo- and hyperthyroidism. This article also describes the published literature and the authors' data on the clinical aspects of congenital hypothyroidism, on the alternating hypo- and hyperthyroidism in the neonatal period, and on neonatal hyperthyroidism.

In vivo effects of a human thyroid-stimulating monoclonal autoantibody (M22) and a human thyroid-blocking autoantibody (K1-70)

PURPOSE

To study in vivo effects of the human monoclonal TSH receptor (TSHR) autoantibodies M22 (stimulating type) and K1-70 (blocking type) on thyroid hormone levels in rats.

METHODS

Serum levels of total T4, free T4, M22 and K1-70 were measured following intramuscular injection of M22 IgG (2-4 μg/animal), K1-70 IgG (10-200 μg/animal) or both into rats. Thyroid pathology was assessed in M22-injected rats.

RESULTS

Serum levels of total T4 and free T4 increased in a dose-dependent manner following injection of M22 IgG. Thyroid follicular cell hypertrophy was dependent on the dose of M22 IgG. K1-70 IgG caused a dose dependent decrease of total T4 and free T4 levels in rats receiving K1-70 only. The stimulating effects of M22 IgG on T4 levels in rats were completely inhibited by K1-70 IgG.

CONCLUSION

M22 is a potent stimulator of thyroid hormone secretion in vivo. In contrast, K1-70 inhibits thyroid hormone secretion in vivo. Furthermore, K1-70 has the ability to inhibit the stimulating activity of M22 in vivo and as such has potential as a new drug to block TSHR stimulation by autoantibodies in Graves' disease.

Mutations that silence constitutive signaling activity in the allosteric ligand-binding site of the thyrotropin receptor

The thyrotropin receptor (TSHR) exhibits elevated cAMP signaling in the basal state and becomes fully activated by thyrotropin. Previously we presented evidence that small-molecule ligands act allosterically within the transmembrane region in contrast to the orthosteric extracellular hormone-binding sites. Our goal in this study was to identify positions that surround the allosteric pocket and that are sensitive for inactivation of TSHR. Homology modeling combined with site-directed mutagenesis and functional characterization revealed seven mutants located in the allosteric binding site that led to a decrease of basal cAMP signaling activity. The majority of these silencing mutations, which constrain the TSHR in an inactive conformation, are found in two clusters when mapped onto the 3D structural model. We suggest that the amino acid positions identified herein are indicating locations where small-molecule antagonists, both neutral antagonists and inverse agonists, might interfere with active TSHR conformations.

Monoclonal autoantibodies to the TSH receptor, one with stimulating activity and one with blocking activity, obtained from the same blood sample

OBJECTIVE

Patients who appear to have both stimulating and blocking TSHR autoantibodies in their sera have been described, but the two activities have not been separated and analysed. We now describe the isolation and detailed characterization of a blocking type TSHR monoclonal autoantibody and a stimulating type TSHR monoclonal autoantibody from a single sample of peripheral blood lymphocytes.

DESIGN, PATIENTS AND MEASUREMENTS

Two heterohybridoma cell lines secreting TSHR autoantibodies were isolated using standard techniques from the lymphocytes of a patient with hypothyroidism and high levels of TSHR autoantibodies (160 units/l by inhibition of TSH binding). The ability of the two new monoclonal antibodies (MAbs; K1-18 and K1-70) to bind to the TSHR and compete with TSH or TSHR antibody binding was analysed. Furthermore, the effects of K1-18 and K1-70 on cyclic AMP production in Chinese hamster ovary cells (CHO) cells expressing the TSHR were investigated.

RESULTS

One MAb (K1-18) was a strong stimulator of cyclic AMP production in TSHR-transfected CHO cells and the other (K1-70) blocked stimulation of the TSHR by TSH, K1-18, other thyroid-stimulating MAbs and patient serum stimulating type TSHR autoantibodies. Both K1-18 (IgG1 kappa) and K1-70 (IgG1 lambda) bound to the TSHR with high affinity (0.7 x 10(10) l/mol and 4 x 10(10) l/mol, respectively), and this binding was inhibited by unlabelled K1-18 and K1-70, other thyroid-stimulating MAbs and patient serum TSHR autoantibodies with stimulating or blocking activities. V region gene analysis indicated that K1-18 and K1-70 heavy chains used the same V region germline gene but different D and J germline genes as well as having different light chains. Consequently, the two antibodies have evolved separately from different B cell clones.

CONCLUSIONS

This study provides proof that a patient can produce a mixture of blocking and stimulating TSHR autoantibodies at the same time.

A small molecule inverse agonist for the human thyroid-stimulating hormone receptor

Small molecule inverse agonists for the TSH receptor (TSHR) may be used as probes of the role of basal (or agonist-independent or constitutive) signaling and may have therapeutic potential as orally active drugs to inhibit basal signaling in patients with thyroid cancer and in some patients with hyperthyroidism. We describe the first small-molecule ligand [1;2-(3-((2,6-dimethylphenoxy)methyl)-4-methoxyphenyl)-3-(furan-2-ylmethyl)-2,3-dihydroquinazolin-4(1H)-one] that exhibits inverse agonist properties at TSHR. 1 inhibits basal and TSH-stimulated signaling, measured as cAMP production, by TSHRs in HEK-EM 293 cells stably expressing wild-type TSHRs; the antagonism of TSH-mediated signaling is competitive. 1 also inhibits basal signaling by wild-type TSHRs, and four constitutively active mutants of TSHR expressed transiently in HEK-EM 293 cells. 1 was active under more physiologically relevant conditions in primary cultures of human thyrocytes expressing endogenous TSHRs where it inhibited basal levels of mRNA transcripts for thyroglobulin, thyroperoxidase, sodium iodide symporter, and TSHR. These data serve as proof of principle that small, drug-like molecules can inhibit basal signaling by TSHR. We suggest that this small molecule is a lead compound for the development of higher-potency inverse agonists that can be used as probes of TSHR biology with therapeutic potential.

Thyrotropin receptor autoantibody measurement following radiometabolic treatment of hyperthyroidism: comparison between different methods

BACKGROUND

TSH receptor antibodies (TRAb) play a crucial role in the pathogenesis of Graves' disease (GD). The use of human recombinant TSH-receptor far improved the analytical performance of TRAb assays (2nd-generation assays). The 3rd-generation assay is based on the inhibition of binding of a human biotin-labeled monoclonal thyroid- stimulating antibody (M22) to TSH-receptor by the autoantibodies present in the serum.

AIM

We aimed to assess the ability of the 2nd- and 3rd-generation assays to detect serum TRAb following radioiodine therapy for hyperthyroidism.

METHODS

Sera from 47 hyperthyroid (25 autoimmune, 22 non-autoimmune) patients were tested using the two different assays before and at different time intervals after radioiodine therapy. The modifications of TRAb were evaluated, as well as the correlation between the two methods.

RESULTS

The results obtained by the two methods proved to be closely correlated. A rise in TRAb was invariably observed in GD patients following radioiodine, with a median peak at 6 months, irrespective of their initial clinical status, presence of ophthalmopathy, smoking habits or other variables. Such a rise was nearly superimposable using both methods. No TRAb appearance was observed in patients with non-autoimmune hyperthyroidism.

CONCLUSIONS

The use of methods of higher sensitivity with respect to that formerly used indicate that nearly all GD patients develop TRAb following radioiodine, and that this phenomenon is transient and not related to baseline conditions and clinical outcome/efficacy of treatment.

Constitutively active thyrotropin and thyrotropin-releasing hormone receptors and their inverse agonists

Receptors for thyrotropin-releasing hormone (TRH) and thyrotropin (thyroid-stimulating hormone-TSH) are important regulators of the function of the TSH-producing cells of the anterior pituitary gland and the thyroid gland, respectively, and thereby play a central role in thyroid hormone homeostasis. Although the roles of TRH- and TSH-stimulated signaling in these endocrine glands are well understood, these receptors are expressed in other sites and their roles in these extraglandular tissues are less well known. Moreover, one of the two subtypes of TRH receptors (TRH-R2) and the single TSH receptor (TSHR) exhibit constitutive signaling activity and the roles of constitutive signaling by these receptors are poorly understood. One approach to studying constitutive signaling is to use inverse agonists. In this chapter, we will describe the experimental procedures used to measure constitutive signaling by TRH-R2 and TSHR and the effects of their specific inverse agonists.

TSH receptor monoclonal antibodies with agonist, antagonist, and inverse agonist activities

Autoantibodies in autoimmune thyroid disease (AITD) bind to the TSH receptor (TSHR) and can act as either agonists, mimicking the biological activity of TSH, or as antagonists inhibiting the action of TSH. Furthermore, some antibodies with antagonist activity can also inhibit the constitutive activity of the TSHR, that is, act as inverse agonists. The production of animal TSHR monoclonal antibodies (MAbs) with the characteristics of patient autoantibodies and the isolation of human autoantibodies from patients with AITD has allowed us to analyze the interactions of these antibodies with the TSHR at the molecular level. In the case of animal MAbs, advances such as DNA immunization allowed the production of the first MAbs which showed the characteristics of human TSHR autoantibodies (TRAbs). Mouse MAbs (TSMAbs 1-3) and a hamster MAb (MS-1) were obtained that acted as TSHR agonists with the ability to stimulate cyclic AMP production in CHO cells expressing the TSHR. In addition, a mouse TSHR MAb (MAb-B2) that had the ability to act as an antagonist of TRAbs and TSH was isolated and characterized. Also, a mouse TSHR MAb that showed TSH antagonist and TSHR inverse agonist activity (CS-17) was described. Furthermore, a panel of human TRAbs has been obtained from the peripheral blood lymphocytes of patients with AITD and extensively characterized. These MAbs have all the characteristics of TRAbs and are active at ng/mL levels. To date, two human MAbs with TSHR agonist activity (M22 and K1-18), one human MAb with TSHR antagonist activity (K1-70) and one human MAb (5C9) with both TSHR antagonist and TSHR inverse agonist activity have been isolated. Early experiments showed that the binding sites for TSH and for TRAbs with thyroid stimulating or blocking activities were located on the extracellular domain of the TSHR. Extensive studies using TSHRs with single amino acid mutations identified TSHR residues that were important for binding and biological activity of TSHR MAbs (human and animal) and TSH. The structures of several TSHR MAb Fab fragments were solved by X-ray crystallography and provided details of the topography of the antigen binding sites of antibodies with either agonist or antagonist activity. Furthermore stable complexes of the leucine-rich repeat domain (LRD) of the TSHR with a human MAb (M22) with agonist activity and with a human MAb (K1-70) with antagonist activity have been produced and their structures solved by X-ray crystallography at 2.55 and 1.9Å resolution, respectively. Together these experiments have given detailed insights into the interactions of antibodies with different biological activities (agonist, antagonist, and inverse agonist) with the TSHR. Although the nature of ligand binding to the TSHR is now understood in some detail, it is far from clear how these initial interactions lead to functional effects on activation or inactivation of the receptor.

The influence of hepatitis C infection and interferon-alpha therapy on thyrotropin blocking and stimulating autoantibodies in Graves' ophthalmopathy: a case report

Background

Hepatitis C virus is a highly immunogenic pathogen often inducing autoimmune activation changes and this can often be further exacerbated by Interferon therapy. As HCV is lymphocytotropic, it can modulate T cell and B cell antibody responses, affecting many endocrine organs, most commonly the thyroid.

Case presentation

We hereby describe a case of fluctuating and wavering thyrotropin autoantibodies of both stimulating and blocking nature in the setting of Graves's ophthalmopathy, hepatitis C infection and interferon-α, causing hypo- and subsequently hyper-thyroidism. The autoantibody profile was clearly modified during interferon therapy and settled into a new equilibrium at the completion of treatment.

Conclusion

The case highlights the possible existence of a dual thyroid autoantibody population associated with hepatitis C, and its modulation by interferon therapy, which further compounds the difficulties in the assessment thyroid disease in this setting.

Human TSH receptor ligands as pharmacological probes with potential clinical application

The biologic role of thyroid-stimulating hormone (TSH; thyrotropin) as an activator (agonist) of the TSH receptor (TSHR) in the hypothalamic-pituitary-thyroid axis is well known and activation of TSHR by recombinant human TSH is used clinically in patients with thyroid cancer. TSHR ligands other than TSH could be used to probe TSHR biology in thyroidal and extrathyroidal tissues, and potentially be employed in patients. A number of different TSHR ligands have been reported, including TSH analogs, antibodies and small-molecule, drug-like compounds. In this review, we will provide an update on all these classes of TSHR agonists and antagonists but place emphasis on small-molecule ligands.

Clonal relationships between thyroid-stimulating hormone receptor-stimulating antibodies illustrate the effect of hypermutation on antibody function

Graves' disease is characterized by production of agonist antibodies to the thyroid-stimulating hormone receptor (TSHR), but knowledge of the genetic and somatic events leading to their aberrant production is limited. We describe the genetic analysis of two monoclonal antibodies (mAbs) with thyroid-stimulating activity (TSAb) obtained from a single mouse with experimental Graves' disease. The mAbs were class switched, but used the same rearrangement of immunoglobulin heavy chain, variable region (IGHV) and immunoglobulin light chain, variable region (IGLV) germline genes, implying a clonal relationship and derivation from a single precursor B-cell clone. The IGHV-region genes of the two mAbs underwent high degrees of somatic hypermutation by sharing numerous mutations before diverging, while the IGLV genes evolved separately. Interestingly, the mutations were present in both the complementarity-determining regions (CDRs) and the framework regions. The cloned IGHV and IGLV genes were confirmed to have TSAb properties in experiments in which they were expressed as recombinant Fabs (rFabs). In other experiments, we swapped the IGLV genes with IGHV genes by constructing chimeric rFabs and showed that the chimeras retained TSAb activities, confirming the close functional relatedness of the V-region genes. Importantly, the IGLV genes in chimeric rFabs had a dominant stimulatory effect at low concentrations, while the IGHV genes had a dominant effect at higher concentrations. Our findings demonstrate that, in experimentally immunized mice, multiple pathogenic antibodies to TSHR can arise from a single clone by a series of somatic mutations in the V-region genes and may give an insight into how such antibodies develop spontaneously in autoimmune Graves' disease.

Congenital disorders of the thyroid: hypo/hyper

This article summarizes the ontogenesis and genetics of the thyroid with regards to its possible congenital dysfunction and briefly refers to the roles of the mother-placenta-fetal unit, iodine effect, and organic and functional changes of the negative feedback mechanism, as well as maturity and illness, in some forms of congenital hypo- and hyperthyroidism. This article also describes the published literature and the authors' data on the clinical aspects of congenital hypothyroidism, on the alternating hypo- and hyperthyroidism in the neonatal period, and on neonatal hyperthyroidism.

Autoimmune thyroid disease: unlocking a complex puzzle

PURPOSE OF REVIEW

The autoimmune thyroid diseases (AITD), Graves' disease and chronic lymphocytic thyroiditis (CLT) are amongst the most common endocrine diseases in childhood and adolescence. The application of molecular biology has permitted an unparalleled insight into susceptibility genes that predispose to their development and has allowed enhanced understanding of their complex immune pathophysiology.

RECENT FINDINGS

The susceptibility genes that predispose to AITD can be subdivided into those that affect the immune response in general and thyroid-specific antigens. Both known and new susceptibility genes have been the focus of recent attention. Although there is no known human leukocyte antigen (HLA) association in CLT, recent work has demonstrated an association with a specific amino acid pocket signature irrespective of the HLA-DR class. In Graves' disease a specific combination of polymorphisms for thyroglobulin and HLA-DR markedly increases the odds ratio for developing disease. The availability of recombinant antigen [particularly thyroid peroxidase and thyrotropin (TSH) receptor] and of high affinity monoclonal antibodies has provided insight into the specific epitopes recognized by antibodies in AITD and has confirmed the increased affinity of stimulating TSH receptor antibodies for the shed A subunit rather than the holoreceptor.

SUMMARY

Powerful molecular tools have been developed that have shed light on the nature of the susceptibility genes for and the pathophysiology of AITD. These have already led to improved diagnostic tools and, hopefully, will permit the development of more specific immune therapy in the future.

A monoclonal antibody with thyrotropin (TSH) receptor inverse agonist and TSH antagonist activities binds to the receptor hinge region as well as to the leucine-rich domain

Monoclonal antibody CS-17 is a TSH receptor (TSHR) inverse agonist (suppresses constitutive activity) and a TSH antagonist. Elucidation of the CS-17 epitope will provide insight into TSHR structure and function. Present information on its epitope conflicts with recent data regarding another TSHR inverse agonist antibody. To characterize further the CS-17 epitope, we exploited the observation that CS-17 does not recognize a chimeric receptor with TSHR hinge region residues 261-289 replaced with homologous rat LH receptor residues (13 mismatches). We generated individual and double TSHR mutations corresponding to these mismatches. On flow cytometry, only T273L/R274V reduced CS-17 recognition. No mutation affected TSH-stimulated cAMP generation. Because the immunogen for CS-17 generation was highly glycosylated, we also investigated whether the glycan moiety at N198, topologically adjacent to Y195 (a previously identified epitopic component), could contribute to the CS-17 epitope. Elimination of this N-linked glycan (mutations of N198 and T200) abrogated CS-17 binding without altering TSH responsiveness. However, studies with tunicamycin suggested that these mutations affected CS-17 binding by altering the polypeptide backbone rather than eliminating the glycan moiety. TSHR residues N198 and T200, like Y195, are on the convex facet of the leucine-rich domain. In summary, the present data indicate that the discontinuous epitope of CS-17, a TSHR inverse agonist and TSH antagonist, includes a component in the hinge region as well as the convex surface of the TSHR leucine-rich domain. These findings expand our present concept of glycoprotein hormone binding and function.

Clinical value of M22-based assays for TSH-receptor antibody (TRAb) in the follow-up of antithyroid drug treated Graves' disease: comparison with the second generation human TRAb assay

BACKGROUND

We compared the clinical performances of two new M22-based assays for TSH-receptor antibody (TRAb) with those of the human TRAb assay (hTRAK) in Graves' disease patients at the end of treatment.

PATIENTS AND METHODS

Sera were obtained from 128 Graves' patients treated for 18 months with antithyroid drugs. Sixty-six remained in remission and sixty-two had relapse of hyperthyroidism in a 3-year follow-up after discontinuing treatment. TRAbs were measured using two M22-based methods (electrochemiluminescence using the Cobas or ELISA using the Medizym TRAb clone) and with the hTRAK.

RESULTS

At T18, the results were significantly higher by the Cobas assay (median: 2.7 IU/L, range: 1.1-18.5 IU/L) or lower by ELISA (median: 0.56 IU/L, range: 0.22-14.8 IU/L) than those obtained for the hTRAK (median: 1.5 IU/L, range: 0.9-9.8 IU/L). The use of cut-off limits at 1.9 IU/L, 3.2 IU/L and 0.94 IU/L gave similar and higher prevalences of TRAb-positive patients in the group of relapse as compared to the remission group. However, some patients remained misclassified in each remission or relapse group.

CONCLUSIONS

The M22-based TRAb assays did not improve the predictive value of relapse obtained with the hTRAK measured at the end of treatment. High inter-method variability requires assay harmonization for correct interpretation of results.

Characterization of thyrotropin receptor antibody-induced signaling cascades

The TSH receptor (TSHR) is constitutively active and is further enhanced by TSH ligand binding or by stimulating TSHR antibodies (TSHR-Abs) as seen in Graves' disease. TSH is known to activate the thyroid epithelial cell via both Galphas-cAMP/protein kinase A/ERK and Galphaq-Akt/protein kinase C coupled signaling networks. The recent development of monoclonal antibodies to the TSHR has enabled us to investigate the hypothesis that different TSHR-Abs may have unique signaling imprints that differ from TSH ligand itself. We have, therefore, performed sequential studies, using rat thyrocytes (FRTL-5, passages 5-20) as targets, to examine the signaling pathways activated by a series of monoclonal TSHR-Abs in comparison with TSH itself. Activation of key signaling molecules was estimated by specific immunoblots and/or enzyme immunoassays. Continuing constitutive TSHR activity in thyroid cells, deprived of TSH and serum for 48 h, was demonstrated by pathway-specific chemical inhibition. Under our experimental conditions, TSH ligand and TSHR-stimulating antibodies activated both Galphas and Galphaq effectors. Importantly, some TSHR-blocking and TSHR-neutral antibodies were also able to generate signals, influencing primarily the Galphaq effectors and induced cell proliferation. Most strikingly, antibodies that used the Galphaq cascades used c-Raf-ERK-p90RSK as a unique signaling cascade not activated by TSH. Our study demonstrated that individual TSHR-Abs had unique molecular signatures which resulted in sequential preferences. Because downstream thyroid cell signaling by the TSHR is both ligand dependent and independent, this may explain why TSHR-Abs are able to have variable influences on thyroid cell biology.

Implications of new monoclonal antibodies and the crystal structure of the TSH receptor for the treatment and management of thyroid diseases

Autoantibodies to the thyroid-stimulating hormone receptor (TSHR) cause the hyperthyroidism of Graves’ disease and contribute to Graves’ eye signs. Human monoclonal TSHR autoantibodies prepared from patients’ lymphocytes have important clinical applications in terms of their ability to stimulate TSHR-containing tissues. Also, TSHR monoclonal antibodies that act as antagonists may well be useful in treating Graves’ eye disease. Recently, the high-resolution (2.55 Å) crystal structure of the TSHR in complex with a monoclonal thyroid-stimulating autoantibody has been determined, and this provides key insights into how the autoantibodies interact with the receptor. Furthermore, the structure can be used in the rational design of small molecules that will disrupt receptor binding by thyroid-stimulating autoantibodies, thus providing new strategies to control TSHR activation in addition to monoclonal antibodies.