TSH receptor antibodies

Molecular pathway and mechanism responsible for the progress of thyroid-associated orbitopathy

PURPOSE

Our study aims to summarize the current knowledge concerning the molecular pathway and mechanism responsible for the progress of orbitopathy in the thyroid.

METHOD

A thorough investigation of the literature was conducted using Scopus, Elsevier, PubMed, ScienceDirect, and Web of Science databases, covering studies published between 2000 and 2024. The inclusion criteria focused on clinical trials, preclinical research, and ethnopharmacological studies that investigated the effects of traditional medicines on "orbitopathy in thyroid," "molecular pathway," "mechanism," "Medicinal Plants," "Mechanism of Action," and "Active Constituents." Studies were excluded if they lacked specific data on orbitopathy in thyroid, focused solely on orbitopathy in thyroid, or had inconclusive methodologies.

RESULTS

Our findings indicate that TSHR autoantibodies drive orbital fibroblast activation, leading to inflammation, adipogenesis, and glycosaminoglycan accumulation. Elevated IL-17 and TNF-α levels contribute to immune dysregulation, while IGF-1R signaling enhances fibroblast proliferation and cytokine release. Biomarker analysis suggests that miR-146a, miR-155, and HLA-DR3 polymorphisms may serve as potential indicators for disease severity and progression.

CONCLUSION

Early diagnostic markers and targeted therapies, including offer promising avenues for improved TAO management. A multidisciplinary, personalized approach integrating biomarker-driven treatment decisions may help optimize patient outcomes.

Graves' Disease: Is It Time for Targeted Therapy? A Narrative Review

Current therapies for Graves' disease (GD) primarily aim to manage hyperthyroidism through synthetic antithyroid drugs, radioiodine, or surgery. However, these approaches are often limited by their incomplete efficacy and the risk of inducing hypothyroidism. The latest advances in understanding the autoimmune mechanisms driving GD have paved the way for novel therapies targeting the thyrotropin receptor (TSH-R) or immune pathways. Overall, key targets include cluster of differentiation 20 (CD20), cluster of differentiation 40 (CD40), protein tyrosine phosphatase non-receptor type 22 (PTPN22), cytotoxic T lymphocyte antigen-4 (CTLA-4), B cell-activating factor (BAFF), and the Fc receptor-like protein 3 (FcRL3). Recent preclinical studies and clinical trials testing targeted therapies have shown promising results in terms of efficacy and safety. Here, we present a narrative review of the literature on emerging therapeutic approaches for GD that are currently under investigation.

Severe Acquired Hypothyroidism and Van Wyk-Grumbach Syndrome in Two Children

The primary manifestations of chronic hypothyroidism in children include growth arrest, delayed skeletal maturity, and delayed puberty. In 1960, Van Wyk and Grumbach reported three girls with hypothyroidism and a combination of incomplete isosexual precocious puberty (early breast development, menstruation, and absence of pubic hair), galactorrhea, delayed bone age, and pituitary enlargement. All abnormalities regressed after appropriate thyroid hormone replacement therapy. Over the years, an increasing number of reported cases has allowed for a more precise understanding of the clinical, biochemical, and radiological phenotypes of the Van Wyk-Grumbach syndrome (VWGS). These varying clinical manifestations are thought to result from a unique pathophysiological process where the thyroid-stimulating hormone (TSH) is a key element. We describe the cases of two patients (a boy and a girl) with severe autoimmune thyroiditis and VWGS. The clinical, biochemical, and radiological imaging characteristics were similar in both patients and included growth failure, absence of clinical goiter, markedly elevated TSH concentrations >100 mIU/L, undetectable free thyroxine levels, "normal" thyroglobulin levels, high follicle-stimulating hormone (FSH) and prolactin levels, prepubertal levels of luteinizing hormone (LH), delayed bone age, and hyperplasia of the pituitary gland. The two patients displayed differences, especially in the absence of clinical pubertal development, moderate anemia, abnormal renal function, and moderate goiter detected via ultrasonography (in the female patient). Thyroxine replacement therapy reversed the VWGS phenotype and hypothyroidism, with satisfactory growth velocity, strictly normal thyroid function, and normal pituitary size detected via magnetic resonance imaging at the 6-month follow-up visit.

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.

Laboratory Thyroid Tests: A Historical Perspective

Background: This review presents a timeline showing how technical advances made over the last seven decades have impacted the development of laboratory thyroid tests. Summary: Thyroid tests have evolved from time-consuming manual procedures using isotopically labeled iodine as signals (¹³¹I and later ¹²⁵I) performed in nuclear medicine laboratories, to automated nonisotopic tests performed on multianalyte instruments in routine clinical chemistry laboratories. The development of isotopic radioimmunoassay techniques around 1960, followed by the advent of monoclonal antibody technology in the mid-1970s, led to the development of a nonisotopic immunometric assay methodology that forms the backbone of present-day thyroid testing. This review discusses the development of methods for measuring total thyroxine and triiodothyronine, direct and indirect free thyroid hormone measurements and estimates (free thyroxine and free triiodothyronine), thyrotropin (TSH), thyroid autoantibodies (thyroperoxidase, thyroglobulin [Tg] and TSH receptor autoantibodies), and Tg protein. Despite progressive improvements made in sensitivity and specificity, current thyroid tests remain limited by between-method differences in the numeric values they report, as well as nonspecific interferences with test reagents and interferences from analyte autoantibodies. Conclusions: Thyroid disease affects ∼10% of the U.S. population and is mostly managed on an outpatient basis, generating 60% of endocrine laboratory tests. In future, it is hoped that interferences will be eliminated, and the standardization/harmonization of tests will facilitate the establishment of universal test reference ranges.

B Cells and Autoantibodies in AIRE Deficiency

Autoimmune polyendocrine syndrome type 1 (APS-1) is a rare but severe monogenetic autoimmune endocrine disease caused by failure of the Autoimmune Regulator (AIRE). AIRE regulates the negative selection of T cells in the thymus, and the main pathogenic mechanisms are believed to be T cell-mediated, but little is known about the role of B cells. Here, we give an overview of the role of B cells in thymic and peripheral tolerance in APS-1 patients and different AIRE-deficient mouse models. We also look closely into which autoantibodies have been described for this disorder, and their implications. Based on what is known about B cell therapy in other autoimmune disorders, we outline the potential of B cell therapies in APS-1 and highlight the unresolved research questions to be answered.

Evaluation of choroidal circulation and stromal features in Graves' disease

PURPOSE

This study aimed to evaluate choroidal thickness (CT) and choroidal vascularity index (CVI) in patients with Graves' disease (GD) without ocular involvement.

METHODS

Fifty patients diagnosed with GD and 50 age and gender matched healthy control subjects were retrospectively evaluated. Measurements were taken from five different points on CT images. Choroid images were classified as lumen regions (LA) and stromal regions (SA) using the image binarization method. CVI was calculated by dividing LA by the total choroidal area (TCA). The effects of Thyrotropin Receptor Antibody (TRAb), age, GD duration, blood pressure, axial length measurements, and intraocular pressure were analyzed on CT and CVI measurements.

RESULTS

Mean age was 40.1 ± 13.5 years in the patient group and 39.3 ± 13.6 years in the control group (p = 0.89). There was no significant difference between the GD group and control group in terms of CT measurements. There was a significant difference between the mean CVI measurements of the GD group and control group (68.03 ± 3.41 and 66.62 ± 3.11, respectively) (p < 0.001). Univariate linear regression analysis revealed a positive correlation between TRAb and CVI (p = 0.013).

CONCLUSION

While there was no significant difference between the CT measurements of the GD group and the control group, the GD group had significantly higher CVI measurements.

Thyrotropin receptor antibodies and Graves' orbitopathy

CONTEXT AND PURPOSE

The thyrotropin receptor (TSHR) is the key autoantigen in Graves' disease (GD) and associated orbitopathy (GO). Antibodies targeting the TSHR (TSHR-Ab) impact the pathogenesis and the course of GO. This review discusses the role and clinical relevance of TSHR-Ab in GO.

METHODS

Review of the current and pertinent literature.

RESULTS

GO is the most common extrathyroidal manifestation of GD and is caused by persistent, unregulated stimulation of TSHR-expressing orbital target cells (e.g. fibroblasts and pre-adipocytes). Serum TSHR-Ab and more specifically, the stimulatory Ab (TSAb) are observed in the vast majority of patients with GD and GO. TSHR-Ab are a sensitive serological parameter for the differential diagnosis of GO. TSHR-Ab can be detected either with conventional binding immunoassays that measure binding of Ab to the TSHR or with cell-based bioassays that provide information on their functional activity and potency. Knowledge of the biological activity and not simply the presence or absence of TSHR-Ab has relevant clinical implications e.g. predicting de-novo development or exacerbation of pre-existing GO. TSAb are specific biomarkers of GD/GO and responsible for many of its clinical manifestations. TSAb strongly correlate with the clinical activity and clinical severity of GO. Further, the magnitude of TSAb indicates the onset and acuity of sight-threatening GO (optic neuropathy). Baseline serum values of TSAb and especially dilution analysis of TSAb significantly differentiate between thyroidal GD only versus GD + GO.

CONCLUSION

Measurement of functional TSHR-Ab, especially TSAb, is clinically relevant for the differential diagnosis and management of GO.

The intramolecular agonist is obligate for activation of glycoprotein hormone receptors

In contrast to most rhodopsin-like G protein-coupled receptors, the glycoprotein hormone receptors (GPHR) have a large extracellular N-terminus for hormone binding. The hormones do not directly activate the transmembrane domain but mediate their action via a, thus, far only partially known Tethered Agonistic LIgand (TALI). The existence of such an intramolecular agonist was initially indicated by site-directed mutation studies and activating peptides derived from the extracellular hinge region. It is still unknown precisely how TALI is involved in intramolecular signal transmission. We combined systematic mutagenesis studies at the luteinizing hormone receptor and the thyroid-stimulating hormone receptor (TSHR), stimulation with a drug-like agonist (E2) of the TSHR, and structural homology modeling to unravel the functional and structural properties defining the TALI region. Here, we report that TALI (a) is predisposed to constitutively activate GPHR, (b) can by itself rearrange GPHR into a fully active conformation, (c) stabilizes active GPHR conformation, and (d) is not involved in activation of the TSHR by E2. In the active state conformation, TALI forms specific interactions between the N-terminus and the transmembrane domain. We show that stabilization of an active state is dependent on TALI, including activation by hormones and constitutively activating mutations.

Prospective Trial of Functional Thyrotropin Receptor Antibodies in Graves Disease

CONTEXT

Scarce data exist regarding the relevance of stimulatory (TSAb) and blocking (TBAb) thyrotropin receptor antibodies in the management of Graves disease (GD).

OBJECTIVE

To evaluate the clinical utility and predictive value of TSAb/TBAb.

DESIGN

Prospective 2-year trial.

SETTING

Academic tertiary referral center.

PATIENTS

One hundred consecutive, untreated, hyperthyroid GD patients.

METHODS

TSAb was reported as percentage of specimen-to-reference ratio (SRR) (cutoff SRR < 140%). Blocking activity was defined as percent inhibition of luciferase expression relative to induction with bovine thyrotropin (TSH, thyroid stimulating hormone) alone (cutoff > 40% inhibition).

MAIN OUTCOME MEASURES

Response versus nonresponse to a 24-week methimazole (MMI) treatment defined as biochemical euthyroidism versus persistent hyperthyroidism at week 24 and/or relapse at weeks 36, 48, and 96.

RESULTS

Forty-four patients responded to MMI, of whom 43% had Graves orbitopathy (GO), while 56 were nonresponders (66% with GO; P < 0.01). At baseline, undiluted serum TSAb but not thyroid binding inhibitory immunoglobulins (TBII) differentiated between thyroidal GD-only versus GD + GO (P < 0.001). Furthermore, at baseline, responders demonstrated marked differences in diluted TSAb titers compared with nonresponders (P < 0.001). During treatment, serum TSAb levels decreased markedly in responders (P < 0.001) but increased in nonresponders (P < 0.01). In contrast, TBII strongly decreased in nonresponders (P = 0.002). All nonresponders and/or those who relapsed during 72-week follow-up period were TSAb-positive at week 24. A shift from TSAb to TBAb was noted in 8 patients during treatment and/or follow-up and led to remission.

CONCLUSIONS

Serum TSAb levels mirror severity of GD. Their increase during MMI treatment is a marker for ongoing disease activity. TSAb dilution analysis had additional predictive value.

Preclinical studies on the toxicology, pharmacokinetics and safety of K1-70TM a human monoclonal autoantibody to the TSH receptor with TSH antagonist activity

Background

The human monoclonal autoantibody K1-70™ binds to the TSH receptor (TSHR) with high affinity and blocks TSHR cyclic AMP stimulation by TSH and thyroid stimulating autoantibodies.

Methods

The preclinical toxicology assessment following weekly intravenous (IV) or intramuscular (IM) administration of K1-70™ in rats and cynomolgus monkeys for 29 days was carried out. An assessment of delayed onset toxicity and/or reversibility of toxicity was made during a further 4 week treatment free period. The pharmacokinetic parameters of K1-70™ and the effects of different doses of K1-70™ on serum thyroid hormone levels in the study animals were determined in rats and primates after IV and IM administration.

Results

Low serum levels of T3 and T4 associated with markedly elevated levels of TSH were observed in the study animals following IV and IM administration of K1-70™. The toxicological findings were attributed to the pharmacology of K1-70™ and were consistent with the hypothyroid state. The no observable adverse effect level (NOAEL) could not be established in the rat study while in the primate study it was 100 mg/kg/dose for both males and females.

Conclusions

The toxicology, pharmacodynamic and pharmacokinetic data in this preclinical study were helpful in designing the first in human study with K1-70™ administered to subjects with Graves’ disease.

A novel third-generation TSH receptor antibody (TRAb) enzyme-linked immunosorbent assay based on a murine monoclonal TSH receptor-binding antibody

TSH receptor (TSHR) autoantibody (TRAb) is the serological hallmark of Graves' disease (GD). Third-generation enzyme-linked immunosorbent assays (ELISAs) using monoclonal TRAbs instead of TSH have been found useful for TRAb analysis recently. For the first time, a mouse monoclonal antibody (mAb) against TSHR was analyzed for TRAb detection and compared with human mAb M22 and TSH by the same competitive binding assay technique. A mouse monoclonal antibody (T7) binding to the TSH receptor and inhibiting TSH binding was generated and used for TRAb analysis in a third-generation ELISA. Obtained TRAb levels were compared with a second-generation TRAb assay employing bovine TSH and a third-generation assay with human mAb M22 as TSHR-binding reagents by investigating 89 patients with GD, 56 with Hashimoto's thyroiditis (HT), 73 with non-autoimmune thyroid diseases, 17 with rheumatoid arthritis, and 100 healthy subjects. The T7-based TRAb ELISA did not reveal a significantly different assay performance (area under the curve [AUC]) in contrast to the TSH and M22-based TRAb ELISAs by receiver operating characteristic (ROC) curve analysis (AUC-T7 0.967, AUC-TSH 0.972, AUC-M22 0.958, p > 0.05, respectively). After adjustment of cutoffs by ROC, all three TRAb ELISAs demonstrated sensitivities and specificities above 89.9% and 96.0%, respectively. Both third-generation TRAb ELISAs showed a tendency for a higher prevalence of TRAb positives in HT in contrast to the second-generation ELISA. Mouse mAbs against the TSHR may be used for the reliable detection of TRAb by third-generation TRAb ELISA. The earlier reported higher sensitivity of third-generation TRAb ELISA in GD needs to be considered in the context of a slightly lower specificity regarding HT.

A Modifying Autoantigen in Graves' Disease

The TSH receptor (TSHR) is the major autoantigen in Graves' disease (GD). Bioinformatic analyses predict the existence of several human TSHR isoforms from alternative splicing, which can lead to the coexpression of multiple receptor forms. The most abundant of these is TSHRv1.3. In silico modeling of TSHRv1.3 demonstrated the structural integrity of this truncated receptor isoform and its potential binding of TSH. Tissue profiling revealed wide expression of TSHRv1.3, with a predominant presence in thyroid, bone marrow, thymus, and adipose tissue. To gain insight into the role of this v1.3 receptor isoform in thyroid pathophysiology, we cloned the entire open reading frame into a mammalian expression vector. Immunoprecipitation studies demonstrated that both TSHR-stimulating antibody and human TSH could bind v1.3. Furthermore, TSHRv1.3 inhibited the stimulatory effect of TSH and TSHR-Ab MS-1 antibody on TSHR-induced cAMP generation in a dose-dependent manner. To confirm the antigenicity of v1.3, we used a peptide ELISA against two different epitopes. Of 13 GD samples, 11 (84.6%) were positive for a carboxy terminal peptide and 10 (76.9%) were positive with a junction region peptide. To demonstrate that intracellular v1.3 could serve as an autoantigen and modulate disease, we used double-transfected Chinese hamster ovary cells that expressed both green fluorescent protein (GFP)-tagged TSHRv1.3 and full-length TSHR. We then induced cell stress and apoptosis using a TSHR monoclonal antibody and observed the culture supernatant contained v1.3-GFP protein, demonstrating the release of the intracellular receptor variant by this mechanism.

Crystal structure of a ligand-free stable TSH receptor leucine-rich repeat domain

The crystal structures of the thyroid-stimulating hormone receptor (TSHR) leucine-rich repeat domain (amino acids 22-260; TSHR260) in complex with a stimulating human monoclonal autoantibody (M22TM) and in complex with a blocking human autoantibody (K1-70™) have been solved. However, attempts to purify and crystallise free TSHR260, that is not bound to an autoantibody, have been unsuccessful due to the poor stability of free TSHR260. We now describe a TSHR260 mutant that has been stabilised by the introduction of six mutations (H63C, R112P, D143P, D151E, V169R and I253R) to form TSHR260-JMG55TM, which is approximately 900 times more thermostable than wild-type TSHR260. These six mutations did not affect the binding of human TSHR monoclonal autoantibodies or patient serum TSHR autoantibodies to the TSHR260. Furthermore, the response of full-length TSHR to stimulation by TSH or human TSHR monoclonal autoantibodies was not affected by the six mutations. Thermostable TSHR260-JMG55TM has been purified and crystallised without ligand and the structure solved at 2.83 Å resolution. This is the first reported structure of a glycoprotein hormone receptor crystallised without ligand. The unbound TSHR260-JMG55TM structure and the M22 and K1-70 bound TSHR260 structures are remarkably similar except for small changes in side chain conformations. This suggests that neither the mutations nor the binding of M22TM or K1-70TM change the rigid leucine-rich repeat domain structure of TSHR260. The solved TSHR260-JMG55TM structure provides a rationale as to why the six mutations have a thermostabilising effect and provides helpful guidelines for thermostabilisation strategies of other soluble protein domains.

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.

Antigenic "Hot- Spots" on the TSH Receptor Hinge Region

The TSH receptor (TSHR) hinge region was previously considered an inert scaffold connecting the leucine-rich ectodomain to the transmembrane region of the receptor. However, mutation studies have established the hinge region to be an extended hormone-binding site in addition to containing a region which is cleaved thus dividing the receptor intoα | ' (A) and β (B) subunits. Furthermore, we have shown in-vitro that monoclonal antibodies directed to the cleaved part of the hinge region (often termed "neutral" antibodies) can induce thyroid cell apoptosis in the absence of cyclic AMP signaling. The demonstration of neutral antibodies in patients with Graves' disease suggests their potential involvement in disease pathology thus making the hinge a potentially important antigenic target. Here we examine the evolution of the antibody immune response to the entire TSHR hinge region (aa280-410) after intense immunization with full-length TSHR cDNA in a mouse (BALB/c) model in order to examine the immunogenicity of this critical receptor structure. We found that TSHR hinge region antibodies were detected in 95% of the immunized mice. The antibody responses were largely restricted to residues 352-410 covering three major epitopes and not merely confined to the cleaved portion. These data indicated the presence of novel antigenic "hotspots" within the carboxyl terminus of the hinge region and demonstrate that the hinge region of the TSHR contains an immunogenic pocket that is involved in the highly heterogeneous immune response to the TSHR. The presence of such TSHR antibodies suggests that they may play an active role in the immune repertoire marshaled against the TSHR and may influence the Graves' disease phenotype.

A New Highly Thyrotropin Receptor-Selective Small-Molecule Antagonist with Potential for the Treatment of Graves' Orbitopathy

BACKGROUND

The thyrotropin receptor (TSHR) is the target for autoimmune thyroid stimulating antibodies (TSAb) triggering hyperthyroidism. Whereas elevated thyroid hormone synthesis by the thyroid in Graves' disease can be treated by antithyroid agents, for the pathogenic activation of TSHR in retro-orbital fibroblasts of the eye, leading to Graves' orbitopathy (GO), no causal TSHR directed therapy is available.

METHODS

Due to the therapeutic gap for severe GO, TSHR inhibitors were identified by high-throughput screening in Chinese hamster ovary cells expressing the TSHR. Stereo-selective synthesis of the screening hits led to the molecule S37, which contains seven chiral centers. Enantiomeric separation of the molecule S37 resulted in the enantiopure molecule S37a-a micro-molar antagonist of thyrotropin-induced cyclic adenosine monophosphate accumulation in HEK 293 cells expressing the TSHR.

RESULTS

The unique rigid bent shape of molecule S37a may mediate the observed high TSHR selectivity. Most importantly, the closely related follitropin and lutropin receptors were not affected by this compound. S37a not only inhibits the TSHR activation by thyrotropin itself but also activation by monoclonal TSAb M22 (human), KSAb1 (murine), and the allosteric small-molecule agonist C2. Disease-related ex vivo studies in HEK 293 cells expressing the TSHR showed that S37a also inhibits cyclic adenosine monophosphate formation by oligoclonal TSAb, which are highly enriched in GO patients' sera. Initial in vivo pharmacokinetic studies revealed no toxicity of S37a and a remarkable 53% oral bioavailability in mice.

CONCLUSION

In summary, a novel highly selective inhibitor for the TSHR is presented, which has promising potential for further development for the treatment of GO.

Thyroid Stimulating Hormone Receptor Antibodies in Thyroid Eye Disease-Methodology and Clinical Applications

BACKGROUND

Thyroid stimulating hormone receptor antibodies (TSHR-Ab) cause autoimmune hyperthyroidism and are prevalent in patients with related thyroid eye disease (TED).

PURPOSE

To provide a historical perspective on TSHR-Ab and to present evidence-based recommendations for clinical contemporary use.

METHODS

The authors review the recent literature pertaining to TSHR-Ab in patients with TED and describe the various immunoassays currently used for detecting TSHR-Ab and their clinical applications.

RESULTS

We provide a historical summary and description of the various methods used to detect TSHR-Ab, foremost, the functional TSHR-Ab. Increasing experimental and clinical data demonstrate the clinical usefulness of cell-based bioassays for measurements of functional TSHR-Ab in the diagnosis and management of patients with autoimmune TED and in the characterization of patients with autoimmune-induced hyperthyroidism and hypothyroidism. Thyroid stimulating hormone receptor antibodies, especially the functional stimulating antibodies, are sensitive, specific, and reproducible biomarkers for patients with autoimmune TED and correlate well with clinical disease activity and clinical severity. Unlike competitive-binding assays, bioassays have the advantage of indicating not only the presence of antibodies but also their functional activity and potency.

CONCLUSIONS

Measurement of TSHR-Ab (especially stimulating antibodies) is a clinically useful tool for the management of patients with TED.

TSHR Gene Polymorphisms in the Enhancer Regions Are Most Strongly Associated with the Development of Graves' Disease, Especially Intractable Disease, and of Hashimoto's Disease

BACKGROUND

Graves' disease (GD) and Hashimoto's disease (HD) are autoimmune thyroid disorders distinguished by the presence or absence of antithyrotropin receptor (TSHR) antibodies (TRAb). TSHR gene polymorphisms determine the amount of TSHR expressed, which may in turn influence TRAb production. The FANTOM5 project identified six GD-associated single nucleotide polymorphisms (SNPs) within the enhancer regions of the TSHR and unknown genes. This study examined the association of 11 TSHR and unknown gene polymorphisms, five of which are located in TSHR enhancer regions, with the development and prognosis of GD and HD.

METHODS

SNPs of the TSHR and unknown genes were genotyped in 180 GD patients, including 62 patients with intractable GD and 48 patients with GD in remission; 151 HD patients, including 65 patients with severe HD and 40 patients with mild HD; and 111 healthy controls.

RESULTS

The rs4411444 GG genotype and G allele, the rs2300519 AA genotype, and the rs179247 AA genotype and A allele were more frequent in GD patients than they were in controls. These same genotypes and alleles, in addition to the rs2300519 A allele and rs4903961 GG genotype and G allele, were more frequent in patients with intractable GD than they were in controls and patients with GD in remission. Interestingly, the rs2300519 TT genotype and T allele, rs4903961 CC genotype and C allele, and rs179247 GG genotype, all of which are minor genotypes and alleles among the evaluated SNPs, were more frequent in HD patients than they were in controls, but there were no differences in the frequencies of these genotypes and alleles between patients with severe HD and mild HD. Among the evaluated SNPs, the rs4411444 GG genotype and the rs4903961 C allele in the enhancer regions of the TSHR gene were most strongly associated with the development of GD, especially intractable disease, and that of HD, respectively.

CONCLUSIONS

Among the evaluated TSHR gene SNPs, the rs4411444 GG genotype and the rs4903961 C allele in the enhancer regions of the TSHR gene were most strongly associated with the development of GD, especially intractable disease, and that of HD, respectively.

A baby with congenital hypothyroidism born to a hypothyroid mother who expressed undiagnosed thyroid stimulation blocking antibody

In adults, hypothyroidism caused by thyroid stimulation blocking antibody (TSB Ab) is rare, and confirmed cases are even fewer, as TSB Ab levels are rarely assayed. However, this may create problems in babies, as the transplacental passage of maternal TSB Ab can cause a rare type of hypothyroidism in the infant. Prompt levothyroxine replacement for the baby starting immediately after birth is important. We describe a congenital hypothyroid baby born to a hypothyroid mother who was not aware of the cause of her hypothyroid condition, which turned out to be associated with the expression of TSB Ab. This cause was confirmed in both the infant and mother using a series of thyroid function tests and measurements of autoantibody levels, including TSB Ab. During periodic follow-up, the TSB Ab and thyroid stimulating hormone receptor antibody titers became negative in the baby at 8 months of age, but remained positive in the mother. Evaluation of hypothyroidism and its cause in mothers during pregnancy is important for both maternal and child health.

Association of polymorphisms of rs179247 and rs12101255 in thyroid stimulating hormone receptor intron 1 with an increased risk of Graves' disease: A meta-analysis

The polymorphisms of thyroid stimulating hormone receptor (TSHR) intron 1 rs179247 and rs12101255 have been found to be associated with Graves' disease (GD) in genetic studies. In the present study, we conducted a meta-analysis to examine this association. Two reviewers systematically searched eligible studies in PubMed, Web of Science, Embase and China Biomedical Literature Database (CBM). A meta-analysis on the association between GD and TSHR intron 1 rs179247 or rs12101255 was performed. The odd ratios (OR) were estimated with 95% confidence interval (CI). Meta package in R was used for the analyses. Seven articles (13 studies) published between 2009 and 2014, involving 5754 GD patients and 5768 controls, were analyzed. The polymorphism of rs179247 was found to be associated with an increased GD risk in the allele analysis (A vs. G: OR=1.40, 95% CI=1.33-1.48) and all genetic models (AA vs. GG: OR=1.94, 95% CI=1.73-2.19; AA+AG vs. GG: OR=1.57, 95% CI=1.41-1.74; AA vs. AG+GG: OR=1.54, 95% CI=1.43-1.66). The site rs12101255 also conferred a risk of GD in the allele analysis (T vs. C: OR=1.50, 95% CI=1.40-1.60) and all genetic models (TT vs. CC: OR=2.22, 95% CI=1.92-2.57; TT+TC vs. CC: OR=1.66, 95% CI=1.50-1.83; TT vs. TC+CC: OR=1.74, 95% CI=1.53-1.98). Analysis of the relationship between rs179247 and Graves' ophthalmopathy (GO) showed no statistically significant correlation (A vs. G: OR=1.02, 95% CI=0.97-1.07). Publication bias was not significant. In conclusion, GD is associated with polymorphisms of TSHR intron 1 rs179247 and rs12101255. There is no association between rs179247 SNPs and GO.

Genetic associations of the thyroid stimulating hormone receptor gene with Graves diseases and Graves ophthalmopathy: A meta-analysis

Graves' disease (GD) is a common thyroid disease, and Graves ophthalmopathy(GO) is the most common extra-thyroidal manifestation of GD. Genetic associations of the thyroid stimulating hormone receptor (TSHR) gene with GD and GO have been studied in different population groups for a long time. We aimed to obtain a more precise estimation of the effects of TSHR single nucleotide polymorphisms (SNPs) on GD/GO using a meta-analysis. Publications were searched on Pub Med and EMBASE up to December 30, 2015. Eight studies involving three SNPs (rs179247, rs12101255, and rs2268458), which included 4790 cases and 5350 controls, met the selection criteria. The pooled odds ratios (OR) and the 95% confidence intervals (CI) were estimated. SNPs rs179247 (dominant model [GG + GA vs. AA]: OR = 0.66, 95%CI: 0.61-0.73, P = 0.000, I(2) = 0%) and rs12101255 (dominant model [TT + TC vs. CC]: OR = 1.67, 95%CI: 1.53-1.83, P = 0.000, I(2) = 0%) were significantly associated with GD in all of the genetic models. TSHR rs12101255 and rs2268458 polymorphisms had no association between GO and GD (GD without GO). The results indicate that rs179247 and rs12101255 are likely to be genetic biomarkers for GD. Further studies with different population groups and larger sample sizes are needed to confirm the genetic associations of the TSHR gene with GD/GO.

Agonistic antibodies reveal the function of GPR56 in human glioma U87-MG cells

GPR56 is a member of the adhesion G protein-coupled receptor (GPCR) and is highly expressed in parts of tumor cells. The involvement of GPR56 in tumorigenesis has been reported. We generated agonistic monoclonal antibodies against human GPR56 and analyzed the action and signaling pathway of GPR56. The antibodies inhibited cell migration through the Gq and Rho pathway in human glioma U87-MG cells. Co-immunoprecipitation analysis indicated that the interaction between the GPR56 extracellular domain and transmembrane domain was potentiated by agonistic antibodies. These results demonstrated that functional antibodies are invaluable tools for GPCR research and should open a new avenue for therapeutic treatment of tumors.

Excessive Cytosolic DNA Fragments as a Potential Trigger of Graves' Disease: An Encrypted Message Sent by Animal Models

Graves' hyperthyroidism is caused by autoantibodies directed against the thyroid-stimulating hormone receptor (TSHR) that mimic the action of TSH. The establishment of Graves' hyperthyroidism in experimental animals has proven to be an important approach to dissect the mechanisms of self-tolerance breakdown that lead to the production of thyroid-stimulating TSHR autoantibodies (TSAbs). "Shimojo's model" was the first successful Graves' animal model, wherein immunization with fibroblasts cells expressing TSHR and a major histocompatibility complex (MHC) class II molecule, but not either alone, induced TSAb production in AKR/N (H-2^k) mice. This model highlights the importance of coincident MHC class II expression on TSHR-expressing cells in the development of Graves' hyperthyroidism. These data are also in agreement with the observation that Graves' thyrocytes often aberrantly express MHC class II antigens via mechanisms that remain unclear. Our group demonstrated that cytosolic self-genomic DNA fragments derived from sterile injured cells can induce aberrant MHC class II expression and production of multiple inflammatory cytokines and chemokines in thyrocytes in vitro, suggesting that severe cell injury may initiate immune responses in a way that is relevant to thyroid autoimmunity mediated by cytosolic DNA signaling. Furthermore, more recent successful Graves' animal models were primarily established by immunizing mice with TSHR-expressing plasmids or adenovirus. In these models, double-stranded DNA vaccine contents presumably exert similar immune-activating effect in cells at inoculation sites and thus might pave the way toward successful Graves' animal models. This review focuses on evidence suggesting that cell injury-derived self-DNA fragments could act as Graves' disease triggers.

Thyrotropin Receptor Epitope and Human Leukocyte Antigen in Graves' Disease

Graves' disease (GD) is an organ-specific autoimmune disease, and thyrotropin (TSH) receptor (TSHR) is a major autoantigen in this condition. Since the extracellular domain of human TSHR (TSHR-ECD) is shed into the circulation, TSHR-ECD is a preferentially immunogenic portion of TSHR. Both genetic factors and environmental factors contribute to development of GD. Inheritance of human leukocyte antigen (HLA) genes, especially HLA-DR3, is associated with GD. TSHR-ECD protein is endocytosed into antigen-presenting cells (APCs), and processed to TSHR-ECD peptides. These peptide epitopes bind to HLA-class II molecules, and subsequently the complex of HLA-class II and TSHR-ECD epitope is presented to CD4+ T cells. The activated CD4+ T cells secrete cytokines/chemokines that stimulate B-cells to produce TSAb, and in turn hyperthyroidism occurs. Numerous studies have been done to identify T- and B-cell epitopes in TSHR-ECD, including (1) in silico, (2) in vitro, (3) in vivo, and (4) clinical experiments. Murine models of GD and HLA-transgenic mice have played a pivotal role in elucidating the immunological mechanisms. To date, linear or conformational epitopes of TSHR-ECD, as well as the molecular structure of the epitope-binding groove in HLA-DR, were reported to be related to the pathogenesis in GD. Dysfunction of central tolerance in the thymus, or in peripheral tolerance, such as regulatory T cells, could allow development of GD. Novel treatments using TSHR antagonists or mutated TSHR peptides have been reported to be effective. We review and update the role of immunogenic TSHR epitopes and HLA in GD, and offer perspectives on TSHR epitope specific treatments.

TSH Receptor Signaling Abrogation by a Novel Small Molecule

Pathological activation of the thyroid-stimulating hormone receptor (TSHR) is caused by thyroid-stimulating antibodies in patients with Graves' disease (GD) or by somatic and rare genomic mutations that enhance constitutive activation of the receptor influencing both G protein and non-G protein signaling. Potential selective small molecule antagonists represent novel therapeutic compounds for abrogation of such abnormal TSHR signaling. In this study, we describe the identification and in vitro characterization of a novel small molecule antagonist by high-throughput screening (HTS). The identification of the TSHR antagonist was performed using a transcription-based TSH-inhibition bioassay. TSHR-expressing CHO cells, which also expressed a luciferase-tagged CRE response element, were optimized using bovine TSH as the activator, in a 384 well plate format, which had a Z score of 0.3-0.6. Using this HTS assay, we screened a diverse library of ~80,000 compounds at a final concentration of 16.7 μM. The selection criteria for a positive hit were based on a mean signal threshold of ≥50% inhibition of control TSH stimulation. The screening resulted in 450 positive hits giving a hit ratio of 0.56%. A secondary confirmation screen against TSH and forskolin - a post receptor activator of adenylyl cyclase - confirmed one TSHR-specific candidate antagonist molecule (named VA-K-14). This lead molecule had an IC₅₀ of 12.3 μM and a unique chemical structure. A parallel analysis for cell viability indicated that the lead inhibitor was non-cytotoxic at its effective concentrations. In silico docking studies performed using a TSHR transmembrane model showed the hydrophobic contact locations and the possible mode of inhibition of TSHR signaling. Furthermore, this molecule was capable of inhibiting TSHR stimulation by GD patient sera and monoclonal-stimulating TSHR antibodies. In conclusion, we report the identification of a novel small molecule TSHR inhibitor, which has the potential to be developed as a therapeutic antagonist for abrogation of TSHR signaling by TSHR autoantibodies in GD.

The Activation Mechanism of Glycoprotein Hormone Receptors with Implications in the Cause and Therapy of Endocrine Diseases

Glycoprotein hormones (GPHs) are the main regulators of the pituitary-thyroid and pituitary-gonadal axes. Selective interaction between GPHs and their cognate G protein-coupled receptors ensure specificity in GPH signaling. The mechanisms of how these hormones activate glycoprotein hormone receptors (GPHRs) or how mutations and autoantibodies can alter receptor function were unclear. Based on the hypothesis that GPHRs contain an internal agonist, we systematically screened peptide libraries derived from the ectodomain for agonistic activity on the receptors. We show that a peptide (p10) derived from a conserved sequence in the C-terminal part of the extracellular N terminus can activate all GPHRs in vitro and in GPHR-expressing tissues. Inactivating mutations in this conserved region or in p10 can inhibit activation of the thyroid-stimulating hormone receptor by autoantibodies. Our data suggest an activation mechanism where, upon extracellular ligand binding, this intramolecular agonist isomerizes and induces structural changes in the 7-transmembrane helix domain, triggering G protein activation. This mechanism can explain the pathophysiology of activating autoantibodies and several mutations causing endocrine dysfunctions such as Graves disease and hypo- and hyperthyroidism. Our findings highlight an evolutionarily conserved activation mechanism of GPHRs and will further promote the development of specific ligands useful to treat Graves disease and other dysfunctions of GPHRs.

Association between TSHR gene polymorphism and the risk of Graves' disease: a meta-analysis

Thyroid stimulating hormone receptor (TSHR) is thought to be a significant candidate for genetic susceptibility to Graves' disease (GD). However, the association between TSHR gene polymorphism and the risk of GD remains controversial. In this study, we investigated the relationship between the two conditions by meta-analysis. We searched all relevant case-control studies in PubMed, Web of Science, CNKI and Wanfang for literature available until May 2015, and chose studies on two single nucleotide polymorphisms (SNPs): rs179247 and rs12101255, within TSHR intron-1. Bias of heterogeneity test among studies was determined by the fixed or random effect pooled measure, and publication bias was examined by modified Begg's and Egger's test. Eight eligible studies with 15 outcomes were involved in this meta-analysis, including 6,976 GD cases and 7,089 controls from China, Japan, Poland, UK and Brazil. Pooled odds ratios (ORs) for allelic comparisons showed that both TSHR rs179247A/G and rs12101255T/C polymorphism had significant association with GD (OR=1.422, 95%CI=1.353–1.495, P<0.001, P_{heterogeneity}=0.448; OR=1.502, 95%CI: 1.410–1.600, P<0.001, P_{heterogeneity}=0.642), and the associations were the same under dominant, recessive and co-dominant models. In subgroup analyses, the conclusions are also consistent with all those in Asian, European and South America subgroups (P<0.001). Our meta-analysis revealed a significant association between TSHR rs179247A/G and rs12101255T/C polymorphism with GD in five different populations from Asia, Europe and South America. Further studies are needed in other ethnic backgrounds to independently confirm our findings.

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.

TSH-receptor-expressing fibrocytes and thyroid-associated ophthalmopathy

Thyroid-associated ophthalmopathy (TAO) is a vexing and undertreated ocular component of Graves disease in which orbital tissues undergo extensive remodelling. My colleagues and I have introduced the concept that fibrocytes expressing the haematopoietic cell antigen CD34 (CD34(+) fibrocytes), which are precursor cells of bone-marrow-derived monocyte lineage, express the TSH receptor (TSHR). These cells also produce several other proteins whose expression was traditionally thought to be restricted to the thyroid gland. TSHR-expressing fibrocytes in which the receptor is activated by its ligand generate extremely high levels of several inflammatory cytokines. Acting in concert with TSHR, the insulin-like growth factor 1 receptor (IGF-1R) expressed by orbital fibroblasts and fibrocytes seems to be necessary for TSHR-dependent cytokine production, as anti-IGF-1R blocking antibodies attenuate these proinflammatory actions of TSH. Furthermore, circulating fibrocytes are highly abundant in patients with TAO and seem to infiltrate orbital connective tissues, where they might transition to CD34(+) fibroblasts. My research group has postulated that the infiltration of fibrocytes into the orbit, their unique biosynthetic repertoire and their proinflammatory and profibrotic phenotype account for the characteristic properties exhibited by orbital connective tissues that underlie susceptibility to TAO. These insights, which have emerged in the past few years, might be of use in therapeutically targeting pathogenic orbit-infiltrating fibrocytes selectively by utilizing novel biologic agents that interfere with TSHR and IGF-1R signalling.

Standardization of a bioassay for thyrotropin receptor stimulating autoantibodies

BACKGROUND

Cell-based bioassays for functional thyroid stimulating autoantibodies (TSAb) are sensitive diagnostic tools. However, there is no bioassay available that is standardized with international reference material. We aimed to promote the standardization of the test results among laboratories that perform TSAb bioassays and calibrate TSAb levels against the second international standard (IS) 08/204 from the National Institute for Biological Standards and Control (NIBSC).

METHODS

Serum TSAb activity was measured with a FDA-cleared bioassay that utilizes CHO cells expressing a chimeric thyrotropin receptor (TSHR) and a c-AMP response-element-dependent luciferase. The IS was applied for calibration. TSAb results were reported as percentage of specimen-to-reference ratio (SRR%) and converted into mIU/L.

RESULTS

The IS dose-response curve was obtained using concentrations from 0.3125 to 200 mIU/L. Mean TSAb SRR%±standard deviation (SD) values for the IS concentrations 0.3125, 0.625, 1.25, 2.5, 5, 10, 20, 40, 60, 80, 100, 120, 160, and 200 mIU/L were 63±4 (CV 6.3%), 63±4 (6.3), 67±2 (3.0), 76±6 (7.9), 91±8 (8), 134±8 (5.9), 201±13 (6.5), 294±12 (4.1), 336±10 (3.0), 348±8 (2.3), 360±14 (3.8), 371±15 (4.0), 381±9 (2.4), and 389±10 (2.6), respectively. A total of 127 dilution experiments were performed using 12 high TSAb-positive sera from patients with Graves' disease. When diluting TSAb-positive sera, IS concentrations within the linear range 5, 10, 20, 40, and 80 mIU/L were used for the calibration curve. All standard curves had R(2) values >0.95. Low coefficient of variation (CV %) values for the IS calibration curve (4-6%) were obtained. Compared to bovine TSH, no significant differences were noted using either a pool of healthy donors or a normal serum as reference controls. The average IU measured value for the assay cutoff (SRR 140%) corresponded to 9.54±1.68 mIU/L, and clinical application was shown in 60 Graves' patients.

CONCLUSIONS

The TSAb bioassay demonstrated excellent performance in terms of linear range, limit of quantitation, and imprecision. The dilution experiments showed a high correlation coefficient and excellent reproducibility. Thus, TSAb levels can be reliably converted from SRR% to IU/L. These results offer the perspective of standardizing TSAb levels among laboratories and enable more accurate comparison of TSAb studies.

Differentiation of postpartum Graves' thyrotoxicosis from postpartum destructive thyrotoxicosis using antithyrotropin receptor antibodies and thyroid blood flow

BACKGROUND

Postpartum thyroid dysfunction occurs in approximately 5-10% of women in the general population within one year of delivery. Differentiation of postpartum Graves' thyrotoxicosis (PPGr) from postpartum destructive thyrotoxicosis (PPDT) is essential because of the difference in treatment measures between the two. However, it is sometimes difficult because radioactive iodine uptake is contraindicated when patients are lactating. We examined the usefulness of determining the time of onset postpartum and measurement of antithyrotropin (anti-TSH) receptor antibodies and thyroid blood flow.

METHODS

Forty-two patients with newly developed thyrotoxicosis after delivery were examined: 18 had Graves' disease and 24 had destructive thyrotoxicosis. Serum free thyroxine (fT4), free triiodothyronine (fT3), and TSH were measured by chemiluminescent immunoassays. Anti-TSH receptor antibodies (TRAb), antithyroglobulin antibodies (TgAb), and antithyroid peroxidase antibodies (TPOAb) were measured by the Elecsys electrochemiluminescence immunoassay. Thyroid volume and blood flow (TBF) were measured quantitatively by color flow Doppler ultrasonography.

RESULTS

Onset of thyrotoxicosis was distributed from 2 to 12 months postpartum. Twelve (85.7%) of 14 patients who developed thyrotoxicosis at three months or earlier after delivery had PPDT. On the other hand, all 11 patients who developed thyrotoxicosis at 6.5 months or later had PPGr. All patients with PPGr had positive TRAb (14.9±14.9 IU/L, mean±standard deviation (SD)) and all patients with PPDT had negative TRAb (0.1±0.3 IU/L, p<0.0001). Fifteen (83.3%) of 18 PPGr patients had high TBF of more than 4.0% (8.9±4.4), and all PPDT patients had low TBF of <4.0% (1.6±1.0, p<0.0001). The fT3/fT4 ratio was higher in PPGr (64.0±23.9) than in PPDT (38.9±13.1, p<0.0002), but absolute values overlapped between the two.

CONCLUSION

Early onset of thyrotoxicosis postpartum was associated mainly with PPDT, and a late onset was suggestive of PPGr. Positive TRAb and high TBF >4.0% are indicators of postpartum onset of Graves' disease.

Methods for the investigation of thyroid function

In the developed world, all routine clinical laboratories should be able to perform tests for the assessment of the pituitary-thyroid axis. Testing strategies usually involve the measurement of thyroid-stimulating hormone (TSH), either alone or in combination with free thyroxine (FT4), which itself should also be measured when TSH is abnormal or if there is a suspicion of pituitary disease. Based on these findings, clinical history and medications such as amiodarone, free tri-iodothyronine (FT3), thyroid-binding globulin (TBG), and/or autoantibodies may then be measured. All these assays have their individual challenges. For example, sensitivity of a TSH assay is of crucial importance for improving distinction between eu- and hyperthyroidism. In the measurement of free hormones, there is the potential disturbance of the equilibrium between free and bound moieties by separating systems. There are a number of commercial diagnostic kits available for each of these tests. This chapter presents various representative assays and their principles. With the exception of FT4 determination by equilibrium dialysis, those that employ a 96-well plate format and use non-isotopic techniques have been described. Attention has been paid to limitations of the assays, standardization of assay kits, imprecision, recovery, detection limit, and ease of use. The assays described have been given as typical and reliable examples, but it is the responsibility of assayists to choose methods that are best suited to their needs.

The role of osteopontin in the induction of the CD40 ligand in Graves' disease

OBJECTIVE

Graves' disease (GD) is a common autoimmune disease involved autoantibody production. Although we previously reported that osteopontin (OPN), a proinflammatory protein, affected development of GD through NF-κB activation, little is known about the role of OPN in regulating immunoglobulin production in GD. CD40 Ligand (CD40L) is expressed on the surface of activated CD4+T cells and costimulates CD40 on B cells, stimulating production of immunoglobulins, a process which has been reported to play a vital role in immunological signalling transduction in several autoimmune diseases. This study sought to characterize the relationship between CD40L and GD development, as well as investigating the role of OPN in modulating immunoglobulin production in GD via CD40L.

METHODS

Forty incident patients with GD, twenty-one patients with GD in remission and twenty-seven healthy controls were recruited. Both membrane-bound and soluble forms of CD40L were measured, and their correlations with clinical parameters were studied. In addition, correlation between OPN and CD40L level was also examined. Furthermore, we studied the regulatory effect of OPN on CD40L in CD4+T cells.

RESULTS

We demonstrated that the CD40L levels were enhanced in patients with GD and recovered in patients with GD in remission. CD40L levels correlated with clinical GD diagnostic parameters and OPN concentration. Moreover, human recombinant OPN and plasma samples from patients with GD increased CD40L expression, which could be significantly suppressed by OPN monoclonal antibody. In addition, CD40L antibody blocked the immunoglobulin production augmented by OPN in cultured peripheral blood mononuclear cells (PBMCs), isolated from patients with GD and healthy subjects.

CONCLUSION

These results indicate that CD40L is induced by OPN and serves as the downstream effector of OPN for immunoglobulin production in GD development.

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.

Nongoitrous autoimmune thyroiditis with facial palsy

We report a case of severe hypothyroidism with nongoitrous, autoimmune thyroiditis and pituitary hyperplasia in a 13-year-old boy, who presented with sudden palsy on the left side of his face. Prednisolone and antiviral medication was administered. However, the facial palsy did not improve completely. The medications were replaced with thyroxine, and the facial palsy recovered. Endocrinological testing showed severe hypothyroidism as follows: thyroid stimulating hormone (TSH) level >100 µIU/mL, T4 of 1.04 µg/dL, T3 of 0.31 ng/mL, and free T4 of 0.07 ng/dL. Level of serum antithyroid peroxidase antibodies was 1,933.39 IU/mL, and that of antithyroglobulin antibodies was 848.16 IU/mL. Level of TSH receptor antibodies was >40 IU/L. Bioassay result for TSH receptor stimulating antibodies was negative. Thyroid sonography revealed no increase in the size or vascularity of the bilateral gland. Thyroid scintigraphy with 99mTc showed decreased uptake, and magnetic resonance imaging demonstrated an enlarged pituitary gland.

Hyperthyroid monkeys: a nonhuman primate model of experimental Graves' disease

Graves' disease (GD) is a common organ-specific autoimmune disease with the prevalence between 0.5 and 2% in women. Several lines of evidence indicate that the shed A-subunit rather than the full-length thyrotropin receptor (TSHR) is the autoantigen that triggers autoimmunity and leads to hyperthyroidism. We have for the first time induced GD in female rhesus monkeys, which exhibit greater similarity to patients with GD than previous rodent models. After final immunization, the monkeys injected with adenovirus expressing the A-subunit of TSHR (A-sub-Ad) showed some characteristics of GD. When compared with controls, all the test monkeys had significantly higher TSHR antibody levels, half of them had increased total thyroxine (T₄) and free T₄, and 50% developed goiter. To better understand the underlying mechanisms, quantitative studies on subpopulations of CD4+T helper cells were carried out. The data indicated that this GD model involved a mixed Th1 and Th2 response. Declined Treg proportions and increased Th17:Treg ratio are also observed. Our rhesus monkey model successfully mimicked GD in humans in many aspects. It would be a useful tool for furthering our understanding of the pathogenesis of GD and would potentially shorten the distance toward the prevention and treatment of this disease in human.

Angiotensin receptor agonistic autoantibodies and hypertension: preeclampsia and beyond

Hypertensive disorders are life-threatening diseases with high morbidity and mortality, affecting billions of individuals worldwide. A multitude of underlying conditions may contribute to hypertension, thus the need for a plethora of treatment options to identify the approach that best meets the needs of individual patients. A growing body of evidence indicates that (1) autoantibodies that bind to and activate the major angiotensin II type I (AT₁) receptor exist in the circulation of patients with hypertensive disorders, (2) these autoantibodies contribute to disease pathophysiology, (3) antibody titers correlate to the severity of the disease, and (4) efforts to block or remove these pathogenic autoantibodies have therapeutic potential. These autoantibodies, termed AT₁ agonistic autoantibodies have been extensively characterized in preeclampsia, a life-threatening hypertensive condition of pregnancy. As reviewed here, these autoantibodies cause symptoms of preeclampsia when injected into pregnant mice. Somewhat surprisingly, these auto antibodies also appear in 3 animal models of preeclampsia. However, the occurrence of AT₁ agonistic autoantibodies is not restricted to pregnancy. These autoantibodies are prevalent among kidney transplant recipients who develop severe transplant rejection and malignant hypertension during the first week after transplantation. AT₁ agonistic autoantibodies are also highly abundant among a group of patients with essential hypertension that are refractory to standard therapy. More recently these autoantibodies have been seen in patients with the autoimmune disease, systemic sclerosis. These 3 examples extend the clinical impact of AT₁ agonistic autoantibodies beyond pregnancy. Research reviewed here raises the intriguing possibility that preeclampsia and other hypertensive conditions are autoimmune diseases characterized by the presence of pathogenic autoantibodies that activate the major angiotensin receptor, AT₁. These pathogenic autoantibodies could serve as presymptomatic biomarkers and therapeutic targets, thereby providing improved medical management for these conditions.

Thyroid autoantibodies in pregnancy: their role, regulation and clinical relevance

Autoantibodies to thyroglobulin and thyroid peroxidase are common in the euthyroid population and are considered secondary responses and indicative of thyroid inflammation. By contrast, autoantibodies to the TSH receptor are unique to patients with Graves' disease and to some patients with Hashimoto's thyroiditis. Both types of thyroid antibodies are useful clinical markers of autoimmune thyroid disease and are profoundly influenced by the immune suppression of pregnancy and the resulting loss of such suppression in the postpartum period. Here, we review these three types of thyroid antibodies and their antigens and how they relate to pregnancy itself, obstetric and neonatal outcomes, and the postpartum.

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.

Autoimmune thyroiditis in childhood

Autoimmune thyroiditis (AIT) is the most common thyroid disorder in the pediatric age range. The disease results from an as yet poorly characterized defect or defects in immunoregulation and a cascade of events progressing from lymphocyte infiltration of the thyroid, to T-cell- and cytokine-mediated thyroid follicular cell injury, and apoptotic cell death. Approximately 70% of disease risk has been attributed to genetic background with environmental factors being important in triggering disease in susceptible individuals. The contribution of individual genes is small and probably polymorphisms in multiple genes play a role. Some immuno susceptibility genes affect immune recognition or response in general, while others are thyroid-specific. Environmental agents may act through an epigenetic mechanism. Antibodies (Abs) to a variety of thyroid-specific antigens are detectable in a majority of patients, but the role of Abs in mediating cell injury and death is unclear and only thyrotropin (TSH) receptor Abs significantly affect thyroid function by interfering with (or stimulating) the action of TSH. Nonetheless, thyroid peroxidase (TPO) Abs and thyroglobulin (Tg) Abs, present in a majority of patients, are valuable diagnostically as markers of underlying autoimmune thyroid destruction. TSH receptor blocking Abs are found in ~18% of children and adolescents with severe hypothyroidism and, when persistent, may identify an adolescent likely to have a baby with TSH receptor blocking Ab-induced congenital hypothyroidism. AIT may coexist with other organ-specific autoimmune diseases. Although the most common age at presentation is adolescence, the disease may occur rarely in children <1 year of life.

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.

TSH receptor autoantibody immunoassay in patients with Graves' disease: improvement of diagnostic accuracy over different generations of methods. Systematic review and meta-analysis

BACKGROUND

TSH receptor antibodies (TRAb) are the diagnostic hallmark of Graves' disease (GD) and immunoassays for their detection have been available for more than 30 years over three generations of laboratory methods. Despite a growing body of data produced by clinical and laboratory research which demonstrates its elevated sensitivity and specificity, TRAb testing is poorly used for diagnosing GD. The aim of our systematic review and meta-analysis is to verify the diagnostic performance of TRAb detected with 2nd and 3rd generation immunoassay methods.

METHODS

We searched for English articles using MEDLINE with the search terms "TSH receptor antibody assay", "TSH Receptor antibody tests" and "Graves' disease". We analyzed studies reporting on TSH receptor antibody tests performed by quantitative immunoassays, on untreated patients with GD as the index disease (sensitivity) and on a control group of either healthy subjects or patients affected by other thyroid diseases (specificity). A total of 681 titles were initially identified with the search strategy described. 560 publications were excluded based on abstract and title. Full-text review was undertaken as the next step on 111 publications providing data on TRAb testing; 58 articles were subsequently excluded because they did not include untreated GD patients, or used either bioassays or 1st generation immunoassays. 32 were also excluded because they included data only on sensitivity or only on specificity of the assay, or were duplicates. Finally, 21 articles were selected for meta-analysis. Extraction of data from selected articles was performed by two authors independently, using predefined criteria: the number of patients with GD and the number of healthy or diseased controls; specification of the analytical method used to detect TRAb; sensitivity and specificity of the assay.

RESULTS

The meta-analysis showed that the overall pooled sensitivity and specificity of the 2nd and 3rd generation TRAb assays are 97.1% and 97.4%, and 98.3% and 99.2%, respectively, with little difference between the types of immunoassay methods employed (human or porcine receptor, manual or automated procedure). The likelihood of a TRAb-positive individual to have GD is 1367- to 3420-fold greater (depending upon the type of assay) compared to a TRAb-negative person.

CONCLUSIONS

Data from the meta-analysis showed that TRAb measured with 2nd and 3rd generation immunoassay methods have very high sensitivity and specificity in the diagnosis of GD. The difference between 2nd and 3rd generation methods is small and is equally useful. In contrast with recommendations made by clinical endocrinologists who are not familiar with the state of the art in diagnostic technologies of autoimmunology laboratories, we propose a wide application of these tests in clinical practice to screen all hyperthyroid patients.

A novel hypothesis for the etiology of Graves' disease: TSAb may be thyroid stimulating animal IgG-like hormone and TBAb may be the precursor of TSAb

There are doubtful points about the theory that autoimmunity with auto-antibody (Ab) to TSH receptor (R) causes hyperthyroidism in Graves' disease (GD). A main doubtful point is no curative effect of corticosteroid on Graves' hyperthyroidism in spite of curative effect of corticosteroid for all autoimmune diseases. Recently we demonstrated the immunological similarity of TSAb and TBAb-IgG to animal IgGs, except for human (h)IgG, by neutralization and purification of TSAb and TBAb-IgG using (1) heterophilic Ab to animal IgG in GD sera and (2) experimentally generated anti-animal IgG Abs [such as dog (d), bovine (b), porcine (p), and rabbit (rb)]. Furthermore, greater immunological similarity of Fab- and F(ab')(2)-portion of TSAb- and TBAb-IgG to bovine Fab, compared to hFab, was demonstrated using goat anti-bovine F(ab')(2) Ab. Existence of b and p TSH-like portions in the LATS-IgG molecule (probably Fab portion) was suggested by a previous report of neutralization of LATS activity by anti-b- or anti-p-TSH Ab. We suggested the existence of a mammalian animal-TSH-like structure, excepting hTSH, in the TSAb-IgG molecule (probably Fab portion), by discovery of anti-mammalian TSH Ab (such as d, b, p, guinea-pig, rat, whale, except h) in sera of GD. Lately, similar TSHR binding of H- and L-chain of human stimulating monoclonal TSHR Ab (M22)-Fab with TSH-α and-β subunit was reported. This evidence suggests that Fab portion of TSAb has a structure like mammalian TSH, but not hTSH. IgG-λ type of d, horse, b, p, goat, ovine is 95% and IgG-κ type is 5%, while human κ and λ chain is 60:40. Previous report that LATS (TSAb)-IgG composed of predominant λ type is supporting evidence that TRAb-IgG has immunological similarity with these animal IgGs compared to hIgG. We speculate that TSAb-IgG may be referred as a mermaid consisted in face (Fab) and trunk-leg (Fc). Face may be a kind of hormone with animal TSH-like structure and trunk-leg has animal IgG-like structure (in spite of no antibody function). There are many reports for co-existence of TSAb and TBAb-IgG in sera of GD. We reported conversion from TBAb (non-thyroid stimulating type IgG) to TSAb by co-incubation of anti-hIgG Ab (containing anti-animal IgG Ab as a cross-reaction) with TBAb-bound porcine thyroid cells. Thus, we suggest that TBAb may be the precursor form of TSAb.

Autoimmune thyroid disease

PURPOSE OF REVIEW

Autoimmune thyroid disorders (AITDs) are the most common organ-specific autoimmune disorders. The genetics as well as clinical and laboratory manifestations of AITDs are reviewed.

RECENT FINDINGS

We discuss the association between specific rheumatologic disorders and AITDs and manifestations of AITDs that mimic rheumatologic disorders. The recently discovered common molecular pathways involved in these processes are discussed.

SUMMARY

AITDs and rheumatologic disorders have significant commonalities both clinically and etiologically. This information is important for rheumatologists and primary care physicians who care for patients with these disorders.

Thyroid physiology

The thyroid gland produces thyroid hormone, which has clinically important actions practically in every system in the human body. Detailed knowledge of the physiology of the thyroid gland is critical for the proper management of thyroid disorders. The molecular biology of thyroid function is being studied in great detail. Clinically important molecules, such as the thyroid-stimulating hormone receptor and the sodium/iodide symporter, have been identified and well characterized. Such discoveries have significantly improved our understanding of thyroid physiology. As a result, new diagnostic and therapeutic approaches for the management of thyroid disorders are now available or in development.

Updated assessment of the prevalence, spectrum and case definition of autoimmune disease

Autoimmune diseases are heterogeneous with regard to prevalence, manifestations, and pathogenesis. The classification of autoimmune diseases has varied over time. Here, we have compiled a comprehensive up-to-date list of the autoimmune diseases, and have reviewed published literature to estimate their prevalence. We identified 81 autoimmune diseases. The overall estimated prevalence is 4.5%, with 2.7% for males and 6.4% for females. For specific diseases, prevalence ranges from 1% to <1/10(6). Considering all diseases in the class, the most common mean age-of-onset was 40-50 years. This list of autoimmune diseases has also yielded information about autoantigens. Forty-five autoimmune diseases have been associated with well-defined autoantigens. Of the diseases with known autoantigens, 33.3% had highly repetitive sequences, 35.6% had coiled-coil arrangements and 57.8% were associated with cellular membranes, which means that based on these structural motifs alone, autoantigens do not appear to be a random sample of the human proteome. Finally, we identified 19 autoimmune diseases that phenocopy diseases arising from germline mutations in the corresponding autoantigen. Collectively, our findings lead to a tentative proposal for criteria for assigning autoimmune pathogenesis to a particular disease.

Immunological similarity of thyroid stimulating antibody (TSAb) and thyroid blocking antibody (TBAb) with animal IgG

Previously we reported neutralization and partial purification of TSAb and TBAb activity using heterophilic antibody (Ab) to animal IgG from Graves' disease. Thus, we examined immunological similarity of TSAb and TBAb with animal IgG using experimentally generated anti-animal IgG [dog (d), bovine (b), porcine (p) and rabbit (rb)] Abs. TBII activity of TSAb- and TBAb-positive serum was neutralized by these anti-animal IgG Abs. Applied TSAb- or TBAb-IgG protein (purified by Protein A) on these anti-animal IgG Abs-bound column was found mainly in the unbound fraction (UF) (>65%) and partially in the bound fraction(BF) (<35%). The TBII and TSAb activity of TSAb-IgG in the BF showed significantly higher than the UF. Thus, the ratio of TBII activity (U/L)/mg protein in the BF/UF was high. TBII activity of TBAb-IgG was similarly purified by this column. We examined immunological characteristics of TSAb-and TBAb-Fab or F(ab')₂ using rabbit anti-bF(ab')₂ Ab. TBII and TSAb activity of TSAb-Fab or- F(ab')₂ and TBII activity of TBAb-Fab or -F(ab')₂ were neutralized by anti-bF(ab')₂ Ab. Partial purification of TSAb- or TBAb-Fab and -F(ab')₂ by anti-bF(ab')₂ Ab-bound column was also possible. Immunological similarity of TSAb- and TBAb-IgG with animal IgG such as d, b, p, rb by anti-animal IgG Ab, and TSAb- or TBAb-Fab and -F(ab')₂ with bFab by anti-bF(ab')₂ Ab were demonstrated. These fact suggest that both Fab and Fc portion of TSAb- and TBAb-IgG molecule have immunological similarity with animal IgG.

Association between thyroid stimulating hormone receptor gene intron polymorphisms and autoimmune thyroid disease in a Chinese Han population

Autoimmune thyroid disease (AITD) is a multifactorial disease with a genetic susceptibility and environmental factors. The thyroid stimulating hormone receptor gene (TSHR) which is expressed on the surface of the thyroid epithelial cell is thought to be the main auto-antigen and a significant candidate for genetic susceptibility to AITD. This case-control study aimed at evaluating the association between single nucleotide polymorphisms (SNP) of TSHR and AITD in a Chinese Han population. We recruited 404 patients with Graves' disease (GD), 230 patients with Hashimoto's thyroiditis (HT) and 242 healthy controls. The Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometer (MALDI-TOF-MS) Platform was used to detect five SNPs (rs179247, rs12101255, rs2268475, rs1990595, and rs3783938) in TSHR gene. The frequencies of allele T and TT genotype of rs12101255 in GD patients were significantly increased compared with those of the controls (P=0.004/0.015, OR=1.408/1.446). The allele A frequency of rs3783938 was greater in HT patients than in the controls (P=0.025, OR=1.427). The AT haplotype (rs179247-rs12101255) was associated with an increased risk of GD (P=0.010, OR=1.368). The allele A of rs179247 was associated with ophthalmopathy in GD patients. These data suggest that the polymorphisms of rs12101255 and rs3783938 are associated with GD and HT, respectively.