Chronic exposure in vivo to thyrotropin receptor stimulating monoclonal antibodies sustains high thyroxine levels and thyroid hyperplasia in thyroid autoimmunity-prone HLA-DRB1*0301 transgenic mice

Thyroid Hemiagenesis: Narrative Review and Clinical Implications

Thyroid Hemiagenesis (THA) is an uncommon, congenital anomaly defined by the absence of one thyroid lobe with or without the isthmus. Reports suggest it may be found more often in regions endemic for hypothyroidism. Genetic abnormalities are thought to have a role based on findings in monozygotic twins. Most cases are sporadic, however familiar clusters have also been documented. It is found more frequently in females. A majority of patients report no symptoms and THA is found incidentally during investigations or intraoperatively. THA is usually associated with normal thyroid function, but it can present with thyroid hypofunction.

Since a majority of patients are asymptomatic, there are no specific recommendations for management. Ultrasound imaging and thyroid scintigraphy using technetium or iodine are useful in diagnosis. Its clinical importance occurs when the remnant thyroid lobe requires excision leading to the lifelong requirement for thyroxine supplementation.

Published English literature (Medline, PubMed, and Embase databases) was searched. Medical subject headings (MeSH) terms used were “thyroid hemiagenesis,” “one thyroid lobe,” and “thyroid aplasia”. Case reports, case series, and original articles were selected to provide a framework for this review.

Articles reviewed were published in the past 20 years. The association of THA with thyroid cancer was explored. In this group, the F:M ratio was 3.25:1. Left THA constituted 53% of cases, right THA in 29.4%, and isthmus absence in 17.6% of cases. Also, the authors investigated the link between THA and hyperparathyroidism, both left and right THA are seen in an equal number of cases in the hyperparathyroidism subgroup. In patients with THA and Grave’s disease, left THA was seen in a majority of cases (86.7%), while an equal number of left and right THA was observed in patients with Hashimoto’s thyroiditis. In addition, congenital abnormalities associated with THA were observed, the left THA was seen in 60% and right THA in 40% of cases of this subgroup.

The summative review provided a detailed insight into the epidemiology, aetiopathogenesis, genetics, symptomatology, diagnosis, and treatment for THA by combining findings and results from almost a hundred research papers from around the world. THA remains a poorly understood, often incidentally detected, abnormality in euthyroid patients undergoing investigations and treatment for other thyroid disorders.

HLA transgenic mice: application in reproducing idiosyncratic drug toxicity

Various types of transgenic mice carrying either class I or II human leukocyte antigen (HLA) molecules are readily available, and reports describing their use in a variety of studies have been published for more than 30 years. Examples of their use include the discovery of HLA-specific antigens against viral infection as well as the reproduction of HLA-mediated autoimmune diseases for the development of therapeutic strategies. Recently, HLA transgenic mice have been used to reproduce HLA-mediated idiosyncratic drug toxicity (IDT), a rare and unpredictable adverse drug reaction that can result in death. For example, abacavir-induced IDT has successfully been reproduced in HLA-B*57:01 transgenic mice. Several reports using HLA transgenic mice for IDT have proven the utility of this concept for the evaluation of IDT using various HLA allele combinations and drugs. It has become apparent that such models may be a valuable tool to investigate the mechanisms underlying HLA-mediated IDT. This review summarizes the latest findings in the area of HLA transgenic mouse models and discusses the current challenges that must be overcome to maximize the potential of this unique animal model.

Noninflammatory Diffuse Follicular Hypertrophy/Hyperplasia of Graves Disease: Morphometric Evaluation in an Experimental Mouse Model

OBJECTIVES

Experimental models of Graves hyperthyroid disease accompanied by Graves orbitopathy (GO) can be efficiently induced in susceptible inbred strains of mice by immunization by electroporation of heterologous human TSH receptor (TSHR) A-subunit plasmid. The interrelated pathological findings in the thyroid glands of Graves disease (GD) that explain the core changes classically include diffuse follicular hyperplasia and multifocal mild lymphocytic infiltrate. However, the relative contributions of different thyroid tissue components (colloid, follicular cells, and stroma) have not been previously evaluated. In this study, we characterize the thyroid gland of an experimental mouse model of autoimmune GD. Our objective was to define the relative contribution of the different thyroid tissue components to the pathology of glands in the experimental model.

METHODS

Mice were immunized with human TSHR A-subunit plasmid. Antibodies induced to human TSHR were pathogenic in vivo due to their cross-reactivity to mouse TSHR.

RESULTS

Autoimmune thyroid disease in the model was characterized by histopathology of hyperplastic glands with large follicular cells. Further examination of thyroid glands of immunized animals revealed a significantly increased follicular area and follicle/stroma ratio, morphometrically correlated with a noninflammatory follicular hyperplasia/hypertrophy. The increased follicle/stroma ratio was the most relevant morphometrically variable summarizing the pathological changes for screening purposes.

CONCLUSION

GD thyroid glands are enlarged and characterized by a noninflammatory diffuse follicular cell hyperplasia/hypertrophy and a significant increase in the follicles with an increased follicle/stroma ratio. Overall, this mouse model is a faithful model of an early hyperthyroid status of GD (diffuse glandular involvement and follicular expansion).

Flexible peptide recognition by HLA-DR triggers specific autoimmune T-cell responses in autoimmune thyroiditis and diabetes

Autoimmune polyglandular syndrome 3 variant (APS3v) refers to the co-occurrence of autoimmune thyroiditis (AITD) and type 1 diabetes (T1D) within the same individual. HLA class II confers the strongest susceptibility to APS3v. We previously identified a unique amino acid signature of the HLA-DR pocket (designated APS3v HLA-DR pocket) that predisposes to APS3v. We hypothesized that both thyroid and islet peptides can be presented by the unique APS3v HLA-DR pocket, triggering AITD + T1D together. To test this hypothesis we screened islet and thyroid peptides for their ability to bind to the APS3v HLA-DR pocket. Virtual screen of all possible thyroglobulin (Tg), thyroid-stimulating hormone receptor (TSHR), thyroid peroxidase (TPO), insulin (Ins), and glutamic acid decarboxylase 65 (GAD65) peptides identified 36 peptides that bound to this unique pocket. In vitro binding assays using baculovirus-produced recombinant APS3v HLA-DR identified 11 thyroid/islet peptides (of the 36 predicted binders) that bound with high affinity. By immunizing humanized HLA-DR3 mice carrying the APS3v HLA-DR pocket we identified 4 peptides (Tg.1571, GAD.492, TPO.758, TPO.338) that were presented by antigen presenting cells and elicited T-cell response. We conclude that both thyroid and islet peptides can bind to this flexible APS3v HLA-DR pocket and induce thyroid and islet specific T-cell responses. These findings set the stage to developing specific inhibitors of the APS3v HLA-DR pocket as a precision medicine approach to treating or preventing APS3v in patients that carry this genetic HLA-DR pocket variant.

Does TSH Trigger the Anti-thyroid Autoimmune Processes? Observation on a Large Cohort of Naive Patients with Thyroid Hemiagenesis

Thyroid hemiagenesis (THA) is a rare abnormality characterized by the absence of one thyroid lobe. Elevated thyroid stimulating hormone (TSH) level and higher incidence of thyroid diseases were reported in THA. The aim of the study is to evaluate the thyroid autoimmunity incidence in patients with THA and influence of higher than average TSH level on thyroid volume (TV) and its change with age. The study included a group of naive patients with THA and a control group of subjects with bilobate thyroid. All patients underwent clinical examination, thyroid ultrasound, scintiscan and laboratory tests. In the studied and control group the presence of thyroid autoantibodies (TAb) was evaluated. The THA group consisted of 65 patients. In THA group 53.85 % of patients were positive for TAb. Patients with positive TAb were older (46.0 ± 18.3 years) than those with negative (35.0 ± 19.8 years); p = 0.02. The incidence of TAb was lower in controls (13.85 %, p < 0.0001). In the study group, positive correlation between the age and TV (r = 0.46, p = 0.0001), and negative correlations between the age and TSH level (r = −0.31, p = 0.01), and TSH concentration and TV (r = −0.35, p = 0.004) were found. In a subgroup of 30 patients with THA negative for TAb, even stronger correlations were observed. The median single lobe volume and median TSH level were higher in patients with THA when compared to controls (13.60 vs 8.20 ml, p < 0.0001; 3.23 vs 1.48 µU/ml, p < 0.0001, respectively). Patients with THA constitute an in vivo model of long-term thyroid TSH overstimulation. Further studies are needed to reveal, whether TSH overstimulation may be the trigger for thyroid autoimmunity.

A unique mouse strain that develops spontaneous, iodine-accelerated, pathogenic antibodies to the human thyrotrophin receptor

Abs that stimulate the thyrotropin receptor (TSHR), the cause of Graves' hyperthyroidism, only develop in humans. TSHR Abs can be induced in mice by immunization, but studying pathogenesis and therapeutic intervention requires a model without immunization. Spontaneous, iodine-accelerated, thyroid autoimmunity develops in NOD.H2(h4) mice associated with thyroglobulin and thyroid-peroxidase, but not TSHR, Abs. We hypothesized that transferring the human TSHR A-subunit to NOD.H2(h4) mice would result in loss of tolerance to this protein. BALB/c human TSHR A-subunit mice were bred to NOD.H2(h4) mice, and transgenic offspring were repeatedly backcrossed to NOD.H2(h4) mice. All offspring developed Abs to thyroglobulin and thyroid-peroxidase. However, only TSHR-transgenic NOD.H2(h4) mice (TSHR/NOD.H2(h4)) developed pathogenic TSHR Abs as detected using clinical Graves' disease assays. As in humans, TSHR/NOD.H2(h4) female mice were more prone than male mice to developing pathogenic TSHR Abs. Fortunately, in view of the confounding effect of excess thyroid hormone on immune responses, spontaneously arising pathogenic human TSHR Abs cross-react poorly with the mouse TSHR and do not cause thyrotoxicosis. In summary, the TSHR/NOD.H2(h4) mouse strain develops spontaneous, iodine-accelerated, pathogenic TSHR Abs in female mice, providing a unique model to investigate disease pathogenesis and test novel TSHR Ag-specific immunotherapies aimed at curing Graves' disease in humans.

Breaking tolerance to thyroid antigens: changing concepts in thyroid autoimmunity

Thyroid autoimmunity involves loss of tolerance to thyroid proteins in genetically susceptible individuals in association with environmental factors. In central tolerance, intrathymic autoantigen presentation deletes immature T cells with high affinity for autoantigen-derived peptides. Regulatory T cells provide an alternative mechanism to silence autoimmune T cells in the periphery. The TSH receptor (TSHR), thyroid peroxidase (TPO), and thyroglobulin (Tg) have unusual properties ("immunogenicity") that contribute to breaking tolerance, including size, abundance, membrane association, glycosylation, and polymorphisms. Insight into loss of tolerance to thyroid proteins comes from spontaneous and induced animal models: 1) intrathymic expression controls self-tolerance to the TSHR, not TPO or Tg; 2) regulatory T cells are not involved in TSHR self-tolerance and instead control the balance between Graves' disease and thyroiditis; 3) breaking TSHR tolerance involves contributions from major histocompatibility complex molecules (humans and induced mouse models), TSHR polymorphism(s) (humans), and alternative splicing (mice); 4) loss of tolerance to Tg before TPO indicates that greater Tg immunogenicity vs TPO dominates central tolerance expectations; 5) tolerance is induced by thyroid autoantigen administration before autoimmunity is established; 6) interferon-α therapy for hepatitis C infection enhances thyroid autoimmunity in patients with intact immunity; Graves' disease developing after T-cell depletion reflects reconstitution autoimmunity; and 7) most environmental factors (including excess iodine) "reveal," but do not induce, thyroid autoimmunity. Micro-organisms likely exert their effects via bystander stimulation. Finally, no single mechanism explains the loss of tolerance to thyroid proteins. The goal of inducing self-tolerance to prevent autoimmune thyroid disease will require accurate prediction of at-risk individuals together with an antigen-specific, not blanket, therapeutic approach.

Yersinia enterocolitica provides the link between thyroid-stimulating antibodies and their germline counterparts in Graves' disease

Graves' disease results from thyroid-stimulating Abs (TSAbs) activating the thyrotropin receptor (TSHR). How TSAbs arise from early precursor B cells has not been established. Genetic and environmental factors may contribute to pathogenesis, including the bacterium Yersinia enterocolitica. We developed two pathogenic monoclonal TSAbs from a single experimental mouse undergoing Graves' disease, which shared the same H and L chain germline gene rearrangements and then diversified by numerous somatic hypermutations. To address the Ag specificity of the shared germline precursor of the monoclonal TSAbs, we prepared rFab germline, which showed negligible binding to TSHR, indicating importance of somatic hypermutation in acquiring TSAb activity. Using rFab chimeras, we demonstrate the dominant role of the H chain V region in TSHR recognition. The role of microbial Ags was tested with Y. enterocolitica proteins. The monoclonal TSAbs recognize 37-kDa envelope proteins, also recognized by rFab germline. MALDI-TOF identified the proteins as outer membrane porin (Omp) A and OmpC. Using recombinant OmpA, OmpC, and related OmpF, we demonstrate cross-reactivity of monoclonal TSAbs with the heterogeneous porins. Importantly, rFab germline binds recombinant OmpA, OmpC, and OmpF confirming reactivity with Y. enterocolitica. A human monoclonal TSAb, M22 with similar properties to murine TSAbs, also binds recombinant porins, showing cross-reactivity of a spontaneously arising pathogenic Ab with Y. enterocolitica. The data provide a mechanistic framework for molecular mimicry in Graves' disease, where early precursor B cells are expanded by Y. enterocolitica porins to undergo somatic hypermutation to acquire a cross-reactive pathogenic response to TSHR.

Reporting the Implementation of the Three Rs in European Primate and Mouse Research Papers: Are We Making Progress?

It is now more than 20 years since both Council of Europe Convention ETS123 and EU Directive 86/609?EEC were introduced, to promote the implementation of the Three Rs in animal experimentation and to provide guidance on animal housing and care. It might therefore be expected that reports of the implementation of the Three Rs in animal research papers would have increased during this period. In order to test this hypothesis, a literature survey of animal-based research was conducted. A randomly-selected sample from 16 high-profile medical journals, of original research papers arising from European institutions that featured experiments which involved either mice or primates, were identified for the years 1986 and 2006 (Total sample = 250 papers). Each paper was scored out of 10 for the incidence of reporting on the implementation of Three Rs-related factors corresponding to Replacement (justification of non-use of non-animal methods), Reduction (statistical analysis of the number of animals needed) and Refinement (housing aspects, i.e. increased cage size, social housing, enrichment of cage environment and food; and procedural aspects, i.e. the use of anaesthesia, analgesia, humane endpoints, and training for procedures with positive reinforcement). There was no significant increase in overall reporting score over time, for either mouse or primate research. By 2006, mouse research papers scored an average of 0 out of a possible 10, and primate research papers scored an average of 1.5. This review provides systematic evidence that animal research is still not properly reported, and supports the call within the scientific community for action to be taken by journals to update their policies.

Increased risk of thyroid pathology in patients with thyroid hemiagenesis: results of a large cohort case-control study

OBJECTIVE

Thyroid hemiagenesis (THA) is an anomaly resulting from the developmental failure of one thyroid lobe. Etiopathogenesis, clinical significance, and management of patients in whom THA is diagnosed are still a matter of debate. The aim of the study is to provide the first systematic analysis of a large cohort of subjects with THA.

DESIGN

Forty patients with THA are described in comparison to a control group of 80 subjects with fully developed thyroid gland.

METHODS

Serum concentrations of thyrotropin (TSH), free thyroxine (FT(4)), free triiodothyronine (FT(3)), and thyroid autoantibodies were measured. In 37 patients, thyroid ultrasonography and Tc-99m thyroid scintiscan were performed, followed by fine-needle aspiration biopsy if indicated. The remaining archival three cases were diagnosed with the use of I-131 scintiscan under basal conditions and after TSH stimulation.

RESULTS

Patients with THA, while usually clinically euthyroid, presented with significantly higher levels of TSH and FT(3) as well as with higher FT(3)/FT(4) concentration in comparison to the control group. Furthermore, a higher incidence of associated functional, morphological, and autoimmune thyroid disorders in patients with THA was observed when compared to subjects with bilobate thyroid (P<0.05).

CONCLUSIONS

Our results revealed that individuals with THA are more likely to develop thyroid pathology. The observed high incidence of associated pathologies is presumably due to long-lasting TSH overstimulation. Therefore, THA diagnosis should be followed by systematic observation and adequate levothyroxine treatment in patients with elevated TSH level.

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.

Toward better models of hyperthyroid Graves' disease

Graves' disease affects only humans. Although it is a treatable illness, medical therapy with antithyroid drugs is imperfect, showing high rates of recurrence. Furthermore, the etiology and treatment of the associated ophthalmopathy still represent problematic issues. Animal models could contribute to the solution of such problems by providing a better understanding of the underlying pathogenesis and could be used for evaluating novel therapeutic strategies. This article discusses the pursuit of a better experimental model for hyperthyroid Graves' disease and outlines how this research has clarified the immunology of the disease.

Recent insights into the pathogenesis and management of thyroid-associated ophthalmopathy

PURPOSE OF REVIEW

To identify and critique the most recent experimental findings regarding the pathogenesis and therapy of thyroid-associated ophthalmopathy.

RECENT FINDINGS

Much of the recent work in this field has focused on identifying genetic alterations associated with the phenotypes of Graves' disease and thyroid-associated ophthalmopathy and investigating their functional consequences. Identified candidate genes include CD40, cytotoxic T-lymphocyte antigen-4, protein tyrosine phosphatase-22, human leukocyte antigen-major histocompatibility complex and those associated with the X-chromosome. Efforts to generate a complete rodent model of Graves' disease continue with little progress. These uniformly involve the immunization of animals with the thyrotropin receptor. Studies conducted in vitro have focused on the actions of cytokines in orbital fibroblasts, the potential role of the insulin-like growth factor-1 receptor and activating antibodies directed against it as a fibroblast and T cell activation pathway. Reports continue to appear examining the potential relationship between the thyrotropin receptor and orbital adipogenesis. Regarding therapy for thyroid-associated ophthalmopathy, small molecules and antibodies disrupting cytokine pathways and lymphocyte function are currently under examination and have yielded promising albeit preliminary results.

SUMMARY

Thyroid-associated ophthalmopathy remains a vexing medical problem, the pathogenesis of which remains uncertain. A number of obstacles continue to plague major advances, not least of which is the absence of a robust animal model. A few new insights seem to represent departure from traditional thinking about this disease and may herald important innovation.

Application of new therapies in Graves' disease and thyroid-associated ophthalmopathy: animal models and translation to human clinical trials

Most current approaches for treating Graves' disease are based essentially upon regimes developed nearly 50 years ago. Moreover, therapeutic approaches for complications such as thyroid-associated ophthalmopathy (TAO) and dermopathy are singularly dependent on conventional approaches of nonspecific immunosuppression. The recent development of an induced model of experimental Graves' disease, although incomplete as it lacks the extrathyroidal manifestations, provided opportunities to investigate immune intervention strategies, including influence upon the autoreactive B and T cell players in the autoimmune process. These major advances are generating new possibilities for therapeutic interventions for patients with Graves' disease and TAO.

HLA class II transgenic mice mimic human inflammatory diseases

Population studies have shown that among all the genetic factors linked with autoimmune disease development, MHC class II genes on chromosome 6 accounts for majority of familial clustering in the common autoimmune diseases. Despite the highly polymorphic nature of HLA class II genes, majority of autoimmune diseases are linked to a limited set of class II-DR or -DQ alleles. Thus a more detailed study of these HLA-DR and -DQ alleles were needed to understand their role in genetic predisposition and pathogenesis of autoimmune diseases. Although in vitro studies using class-II restricted CD4 T cells and purified class II molecules have helped us in understanding some aspects of HLA class-II association with disease, it is difficult to study the role of class II genes in vivo because of heterogeneity of human population, complexity of MHC, and strong linkage disequilibrium among different class II genes. To overcome this problem, we pioneered the generation of HLA-class II transgenic mice to study role of these molecule in inflammatory disease. These HLA class II transgenic mice were used to develop novel in vivo disease model for common autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, insulin-dependent diabetes mellitus, myasthenia gravis, celiac disease, autoimmune relapsing polychondritis, autoimmune myocarditis, thyroiditis, uveitis, as well as other inflammatory disease such as allergy, tuberculosis and toxic shock syndrome. As the T-cell repertoire in these humanized HLA transgenic mice are shaped by human class II molecules, they show the same HLA restriction as humans, implicate potential triggering mechanism and autoantigens, and identify similar antigenic epitopes seen in human. This review describes the value of these humanized transgenic mice in deciphering role of HLA class II molecules in immunopathogenesis of inflammatory diseases.

Application of HLA class II transgenic mice to study autoimmune regulation

In the past decade, we participated in the increased use of HLA class II transgenic mice to delineate genetic control in autoimmune diseases. Our studies began with individual class II transgenes to determine permissiveness for experimental autoimmune thyroiditis (EAT), first in resistant strains and then in the absence of endogenous H2 class II molecules. Polymorphism for HLA-DRB1 was observed, as DR3, but not DR2 or DR4, molecules serve as a determinant for EAT induction with either mouse thyroglobulin (mTg) or human thyroglobulin (hTg). This delineation enabled identification of pathogenic Tg peptides, based on DR3-binding motifs. HLA-DQ polymorphism was also detectable; hTg induced moderate EAT in DQ8(+), but not DQ6(+), mice. Coexpressing permissive and nonpermissive alleles, DR3(+) mice showed reduced EAT severity in the presence of DQ8, but not DQ6, DR2, or DR4. Determining the regulatory T cell (Treg) influences showed that Treg depletion increased thyroiditis incidence and severity without altering the major histocompatibility complex-based hierarchy in susceptibility. This increase after Treg depletion can also be observed in NaI-induced thyroiditis in DR3(+) mice, a means to study a major environmental factor in thyroid autoimmunity. DR3(+) mice were also immunized with human thyroid peroxidase cDNA, resulting in thyroiditis and an antibody (Ab) profile resembling patient antibodies (Abs). Similar immunization with human TSH receptor cDNA resulted in thyroid-stimulating Abs and elevated T(4) levels with moderate thyroiditis in some animals, suggesting a potential Graves' disease model that due to thyroid lesions is more complete than other models. Recently, Treg manipulation in cancer immunotherapy trials has triggered various autoimmune disorders. Thus, DR3(+) mice are being used to monitor a known risk factor for autoimmune thyroid disease in attempts to enhance tumor immunity.