Insight into Graves' hyperthyroidism from animal models

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

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

Polymorphisms of the T-cell immunoglobulin and mucin domain molecule-3 are not associated with autoimmune Graves' disease in a Chinese Han Population

OBJECTIVES

This study aimed to investigate the association between polymorphisms of T-cell immunoglobulin and mucin domain molecule-3 (TIM-3) and Graves' disease (GD) in a Chinese population.

DESIGN AND METHODS

Genomic DNA was extracted from peripheral blood cells of the 182 GD patients and 150 control subjects. The TIM-3 gene polymorphic sites were genotyped. We also analyzed the relationships between the genotypes of each SNP and serum specific clinical variables. To detect whether the variants were associated with the TIM-3 expression, we further studied 40 patients by using the method of real-time quantitative reverse-transcription polymerase chain reaction (real-time RT-PCR).

RESULTS

The genotype and allele frequency of each polymorphic site were not significantly different between GD and control individuals. Furthermore, it also showed no relationship between the variants and TIM-3 mRNA expression.

CONCLUSIONS

Our results demonstrated that the polymorphisms of TIM-3 gene may not contribute to GD susceptibility in the Chinese Han population.

Prophylactic and therapeutic efficacies of a selective inhibitor of the immunoproteasome for Hashimoto's thyroiditis, but not for Graves' hyperthyroidism, in mice

Major histocompatibility complex (MHC) class I-restricted T cell epitopes are generated mainly by the immunoproteasome in antigen-presenting cells. Therefore, inhibition of activity of this proteolytic complex molecule is thought to be a potential treatment for cell-mediated autoimmune diseases. We therefore studied the efficacy of an immunoproteasome inhibitor, ONX 0914 (formerly PR-957), for the treatment of autoimmune thyroid diseases, including cell-mediated Hashimoto's thyroiditis and autoantibody-mediated Graves' hyperthyroidism using mouse models. Our data show that ONX 0914 was effective prophylactically and therapeutically at suppressing the degree of intrathyroidal lymphocyte infiltration and, to a lesser degree, the titres of anti-thyroglobulin autoantibodies in non-obese diabetic (NOD)-H2(h4) mice, an iodine-induced autoimmune thyroiditis model. It also inhibited differentiation of T cells to T helper type 1 (Th1) and Th17 cells, effector T cell subsets critical for development of thyroiditis in this mouse strain. In contrast, its effect on the Graves' model was negligible. Although ONX 0914 exerts its immune-suppressive effect through not only suppression of immune proteasome but also other mechanism(s), such as inhibition of T cell differentiation, the present results suggest that the immunoproteasome is a novel drug target in treatment of Hashimoto's thyroiditis in particular and cell-mediated autoimmune diseases in general.

Role of insulin-like growth factor-1 (IGF-1) pathway in the pathogenesis of Graves' orbitopathy

The etiology of Graves' orbitopathy (GO) remains enigmatic and thus controversy surrounds its pathogenesis. The role of the thyroid stimulating hormone receptor (TSHR) and activating antibodies directed against it in the hyperthyroidism of Graves' disease (GD) is firmly established. Less well elucidated is what part the TSHR pathway might play in the development of GO. Also uncertain is the participation of other cell surface receptors in the disease. Elevated levels of insulin-like growth factor-1 receptor (IGF-1R) have been found in orbital fibroblasts as well as B and T cells from patients with GD. These abnormal patterns of IGF-1R display are also found in rheumatoid arthritis and carry functional consequences. In addition, activating IgGs capable of displacing IGF-1 from IGF-1R have also been detected in patients with these diseases. IGF-1R forms a complex with TSHR which is necessary for at least some of the non-canonical signaling observed following TSHR activation. Functional TSHR and IGF-1R have also been found on fibrocytes, CD34⁺ bone marrow-derived cells from the monocyte lineage. Levels of TSHR on fibrocytes greatly exceed those found on orbital fibroblasts. When ligated by TSH or M22, a TSHR-activating monoclonal antibody, fibrocytes produce extremely high levels of several cytokines and chemokines. Moreover, fibrocytes infiltrate both the orbit and thyroid in GD. In sum, based on current evidence, IGF-1R and TSHR can be thought of as "partners in crime". Involvement of the former probably transcends disease boundaries, while TSHR may not.

Innate immune activation and thyroid autoimmunity

CONTEXT

Autoimmune thyroid disease (AITD) is the archetypal organ-specific autoimmune disorder and is characterized by the production of thyroid autoantibodies. However, the underlying mechanisms by which specific antibodies against thyroid proteins are produced are largely unknown.

EVIDENCE ACQUISITION

Published peer-reviewed basic and clinical literatures on immunology and autoimmune diseases were identified through searches of PubMed for articles published from January 1971 to May 2011. Articles resulting from these searches and relevant references cited in those articles were reviewed. All the relevant articles were written in English.

EVIDENCE SYNTHESIS

Recent studies have indicated that innate immune responses induced by both exogenous and endogenous factors affect the phenotype and severity of autoimmune reactions. One of the recent topics is the effect of self-genomic DNA fragments on immune activation. Expression of major histocompatibility complex class II on the autoimmune target cells seems to play an important role in the presentation of endogenous antigens. Accumulated evidence from animal models has generated new insights into the pathogenesis of AITD.

CONCLUSION

AITD develops by a combination of genetic susceptibility and environmental factors. Innate immune responses are associated with thyroid dysfunction, tissue destruction, and the likely development and perpetuation of AITD. In addition to the other factors, cell injury may contribute to the activation of innate immune response and the development of AITD.

The significance of immune-related molecule expression profiles in an animal model of Graves' disease

BACKGROUND

The thyrotropin receptor (TSHR) A-subunit has been reported to be a critical autoantigen in the generation of thyroid-stimulating antibodies, thereby causing Graves' disease (GD). However, immune mechanisms associated with GD animal models induced by TSHR A-subunit are poorly understood until now.

METHODS

Female BALB/c mice (n = 23) were randomly divided into two groups, and GD presentation was monitored following injection with either 50 μl phosphate-buffered saline containing 10(9) particles of adenovirus expressing the human TSHR A-subunit (Ad-TSHR289) or the Ad-LacZ control. Expressions of CD40, CD40L, CD80, CD86, CD28, CTLA-4, FOXP3 and IL-17A in various tissues were assessed by quantitative RT-PCR and immunohistochemical assays.

RESULTS

Compared with control group, mice of the hyperthyroid group showed significant elevation of expression in the thyroid of CD40 and CD86, expression in the heart of CD28, CD40 and CD40L and expression in the liver of CD28, CD40 and CD86. Conversely, there was significantly diminished expression of CTLA-4 in the thymus of mice in the hyperthyroid group. Expression of all genes examined was not significantly different in the spleens of mice from either of the groups and CD40L and FOXP3 expression was not detected in the thyroids of hyperthyroid mice.

CONCLUSIONS

The expression profile of multiple immune-related molecules differed in mice in the GD group following Ad-TSHR289 immunization, suggesting that these molecules played a potential role in GD pathogenesis.

Role of cytokines in the pathogenesis and suppression of thyroid autoimmunity

Autoimmune thyroid diseases (AITD) are one of the most common organ-specific autoimmune disorders, of which Hashimoto's thyroiditis (HT) and Graves' disease (GD) are 2 of the most common clinical expressions. HT is characterized by hypothyroidism that results from the destruction of the thyroid by thyroglobulin-specific T cell-mediated autoimmune response. In contrast, GD is characterized by hyperthyroidism due to excessive production of thyroid hormone induced by thyrotropin receptor-specific stimulatory autoantibodies. Cytokines play a crucial role in modulating immune responses that affect the balance between maintenance of self-tolerance and initiation of autoimmunity. However, the role of cytokines is often confusing and is neither independent nor exclusive of other immune mediators. A regulatory cytokine may either favor induction of tolerance against thyroid autoimmune disease or favor activation and/or exacerbation of autoimmune responses. These apparently contradictory functions of a given cytokine are primarily influenced by the nature of co-signaling delivered by other cytokines. Consequently, a thorough understanding of the role of a particular cytokine in the context of a specific immune response is essential for the development of appropriate strategies to modulate cytokine responses to maintain or restore health. This review provides a summary of recent research pertaining to the role of cytokines in the pathogenesis of AITD with a particular emphasis on the therapeutic applications of cytokine modulation.

An attempt to induce "Graves' disease of the gonads" by immunizing mice with the luteinizing hormone receptor provides insight into breaking tolerance to self-antigens

BACKGROUND

Gonadotropin receptors, unlike the thyrotropin receptor (TSHR), are not cleaved into disulfide-linked A- and B-subunits, nor do they shed A-subunits. Heavily glycosylated TSHR A-subunits initiate or amplify responses leading to stimulating TSHR-autoantibodies and Graves' hyperthyroidism.

METHODS

To investigate the possibility that mice immunized with luteinizing hormone receptor (LHR) would develop functional antibodies, we constructed adenoviruses expressing the rat-LH holoreceptor (LHR-Ad) and an LHR A-subunit equivalent (LHR-289-Ad). Female BALB/c mice were immunized with high doses (10(11) particles) of LHR-Ad, LHR-289-Ad, or control (Con)-Ad. Sera were tested using LHR-expressing eukaryotic cells for antibody binding by flow cytometry and for bioactivity by measuring cyclic adenosine monophosphate (cAMP) stimulation.

RESULTS

Elevated serum binding to LHR cells in some LHR-Ad and LHR-289-Ad immunized mice was not specific for LHR-expressing cells. Moreover, sera lacked bioactivity, consistent with unchanged serum estradiol and ovary histology. The difference between rat and mouse LHR-ectodomains is relatively small (3% at the amino-acid level). In contrast, despite amino-acid identity, immunization of mice with adenovirus expressing membrane-bound mouse thyroid peroxidase (TPO), but not soluble mouse TPO ectodomain, elicited strong TPO-specific antibodies.

CONCLUSIONS

Our investigations provide insight into antibody responses to self-antigens. First, antibodies are induced to large self-antigens like mouse-TPO when membrane bound. Second, lesser amino acid homology between the immunogen and mouse protein (91% vs. 97% for the human-TSHR and rat-LHR, respectively) favors antibody induction. Finally, from previous studies demonstrating the immunogenicity of the highly glycosylated human TSHR A-subunit versus our present data for the nonimmunogenic less glycosylated rat LHR, we suggest that the extent of glycosylation contributes to breaking self-tolerance.

Exceptional hyperthyroidism and a role for both major histocompatibility class I and class II genes in a murine model of Graves' disease

Autoimmune hyperthyroidism, Graves' disease, can be induced by immunizing susceptible strains of mice with adenovirus encoding the human thyrotropin receptor (TSHR) or its A-subunit. Studies in two small families of recombinant inbred strains showed that susceptibility to developing TSHR antibodies (measured by TSH binding inhibition, TBI) was linked to the MHC region whereas genes on different chromosomes contributed to hyperthyroidism. We have now investigated TSHR antibody production and hyperthyroidism induced by TSHR A-subunit adenovirus immunization of a larger family of strains (26 of the AXB and BXA strains). Analysis of the combined AXB and BXA families provided unexpected insight into several aspects of Graves' disease. First, extreme thyroid hyperplasia and hyperthyroidism in one remarkable strain, BXA13, reflected an inability to generate non-functional TSHR antibodies measured by ELISA. Although neutral TSHR antibodies have been detected in Graves' sera, pathogenic, functional TSHR antibodies in Graves' patients are undetectable by ELISA. Therefore, this strain immunized with A-subunit-adenovirus that generates only functional TSHR antibodies may provide an improved model for studies of induced Graves' disease. Second, our combined analysis of linkage data from this and previous work strengthens the evidence that gene variants in the immunoglobulin heavy chain V region contribute to generating thyroid stimulating antibodies. Third, a broad region that encompasses the MHC region on mouse chomosome 17 is linked to the development of TSHR antibodies (measured by TBI). Most importantly, unlike other strains, TBI linkage in the AXB and BXA families to MHC class I and class II genes provides an explanation for the unresolved class I/class II difference in humans.

Cloning of the TSH receptor: the story from a Brussels perspective

In the mid eighties, thyroglobulin and thyroperoxidase had been cloned and sequenced, and the obvious next target for thyroidologists was the TSH receptor. Many labs entered the race in a healthy (and fierce) competitive mood, exploiting all technologies available at that time. We present here the cloning of the TSH receptor and some of the main fall-out, as seen from the Brussels perspective.

Enhanced response to mouse thyroid-stimulating hormone (TSH) receptor immunization in TSH receptor-knockout mice

Graves-like hyperthyroidism is induced in BALB/c mice by immunization with adenovirus expressing the human TSH receptor (TSHR) A-subunit (amino acids 1-289). However, because of nonidentity between the human and mouse TSHR ( approximately 87% amino acid homology), we compared the responses of mice immunized with adenoviruses expressing either the mouse or the human TSHR A-subunit. Wild-type (wt) BALB/c mice immunized with the mouse A-subunit developed neither TSHR antibodies (measured by flow cytometry) nor thyroid lymphocytic infiltration. However, wt C57BL/6 mice developed sparse intrathyroidal lymphocyte infiltration without antibody production. Depletion of naturally occurring regulatory CD4(+)CD25(+) T cells had little effect. These results indicate the inability to break tolerance to the mouse TSHR in wt mice. In contrast, TSHR knockout (KO) BALB/c mice generated mouse TSHR antibodies in response to mouse A-subunit immunization and augmented human TSHR antibody response to human A-subunit immunization. Thyroid-stimulating antibody titers measured in a functional bioassay were comparable in human A-subunit immunized wt mice and in TSHR KO mice immunized with either the mouse or human A-subunit. In conclusion, immune response to the mouse TSHR is readily induced in TSHR KO but not in wt mice. Only in the former does immunization with adenovirus expressing the mouse A-subunit generate antibodies capable of activating the mouse TSHR. TSHR KO mice are, therefore, of value for future studies dissecting the autoimmune response to the mouse TSHR.

Distinct role of T helper Type 17 immune response for Graves' hyperthyroidism in mice with different genetic backgrounds

T helper type 17 (Th17) cells, a newly identified effector T-cell subset, have recently been shown to play a role in numerous autoimmune diseases, including iodine-induced autoimmune thyroiditis in non-obese diabetic (NOD)-H2(h4) mice, which had previously been thought Th1-dominant. We here studied the role of Th17 in Graves' hyperthyroidism, another thyroid-specific autoimmune disease, in a mouse model. Two genetically distinct BALB/c and NOD-H2(h4) strains with intact or disrupted IL-17 genes (IL-17(+/+) or IL-17(-/-)) were immunized with adenovirus (Ad) expressing the thyrotropin receptor (TSHR) A-subunit (Ad-TSHR289). Both IL-17(+/+) and IL-17(-/-) mice developed anti-TSHR antibodies and hyperthyroidism at equally high frequencies on the BALB/c genetic background. In contrast, some IL-17(+/+), but none of IL-17(-/-), mice became hyperthyroid on the NOD-H2(h4) genetic background, indicating the crucial role of IL-17 for development of Graves' hyperthyroidism in non-susceptible NOD-H2(h4), but not in susceptible BALB/c mice. In the T-cell recall assay, splenocytes and lymphocytes from the draining lymph nodes from either mouse strains, irrespective of IL-17 gene status, produced IFN-γ and IL-10 but not other cytokines including IL-17 in response to TSHR antigen. Thus, the functional significance of Th17 may not necessarily be predictable from cytokine expression patterns in splenocytes or inflammatory lesions. In conclusion, this is, to our knowledge, the first report showing that the role of Th17 cells for the pathogenesis of a certain autoimmune disease depends on the mouse genetic backgrounds.

Immunoglobulin heavy chain variable region genes contribute to the induction of thyroid-stimulating antibodies in recombinant inbred mice

Graves' hyperthyroidism is an autoimmune disease occurring spontaneously in humans and caused by autoantibodies that stimulate the thyrotropin receptor. In mice, inducing Graves'-like hyperthyroidism requires in vivo expression of the thyrotropin receptor using plasmid or adenovirus vectors. However, mice with different genetic backgrounds vary markedly in their susceptibility to induced hyperthyroidism. Further, in some strains major disparities exist between the induction of hyperthyroidism and detection of thyroid-stimulating antibodies. To break tolerance, virtually all Graves' mouse models involve immunization with human thyrotropin-receptor DNA and the standard thyroid-stimulating antibody bioassay uses cells expressing the human thyrotropin receptor. We hypothesized, and now report, that disparities between hyperthyroidism and thyroid-stimulating antibody bioactivity are explained, at least in part, by differential antibody recognition of the human vs the mouse thyrotropin receptor. The genetic basis for these species differences was explored using genotyped, recombinant-inbred mouse strains. We report that loci in the immunoglobulin heavy chain variable region as well as in the major histocompatibility complex region contribute in a strain-specific manner to the development of antibodies specific for the human or the mouse thyrotropin receptor. The novel finding of a role for immunoglobulin heavy chain variable region gene involvement in thyroid-stimulating antibody epitopic specificity provides potential insight into genetic susceptibility in human Graves' disease.

Graves' ophthalmopathy

Graves’ ophthalmopathy, also called Graves’ orbitopathy, is a potentially sight-threatening ocular disease that has puzzled physicians and scientists for nearly two centuries.1 –3 Generally occurring in patients with hyperthyroidism or a history of hyperthyroidism due to Graves’ disease, Graves’ ophthalmopathy is also known as thyroid-associated ophthalmopathy or thyroid eye disease, because it sometimes occurs in patients with euthyroid or hypothyroid chronic autoimmune thyroiditis. The condition has an annual adjusted incidence rate of 16 women and 3 men per 100,000 population.4

This review explores the perplexing relationship between Graves’ ophthalmopathy, hyperthyroidism, and thyroid dermopathy, the associated skin condition. I examine clinical features, histologic findings, and laboratory studies, with an emphasis on mechanisms that could be targeted in the development of new treatments for this debilitating disease.

Immune response of mice transgenic for human histocompatibility leukocyte Antigen-DR to human thyrotropin receptor-extracellular domain

BACKGROUND

Hyperthyroidism of Graves' disease is caused by auto-antibodies to human thyrotropin receptor (hTSH-R). To elucidate important T-cell epitopes in TSH-R, we studied three models of immunity to TSH-R in mice.

METHODS

Mice transgenic for histocompatibility leukocyte antigen DR3 or DR2 were immunized with cDNA for hTSH-R-extracellular domain (hTSH-R-ECD), or hTSH-R-ECD protein, or hTSH-R peptide epitopes. Proliferative responses of immunized splenocytes to epitopes derived from the hTSH-ECD sequence, anti-TSH-R antibody responses, serum thyroxine and TSH, and thyroid histology were recorded.

RESULTS

DR3 mice responded to genomic immunization with proliferative responses to several epitopes, which increased in intensity and spread to include more epitopes, during a 6-week immunization program. DR2 transgenic mice developed weak proliferative responses. Both types of mice developed anti-TSH-R antibodies measured by enzyme-linked immunosorbent assay or TSH-binding inhibition assay in 16-60% of animals. There was evidence of weak thyroid stimulation in one group of animals. Immunization of DR3 transgenic mice to hTSH-R-ECD protein induced a striking response to an epitope with sequence ISRIYVSIDVTLQQLES (aa78-94). Immunization to peptides derived from the TSH-R-ECD sequence (including aa78-94) caused strong responses to the epitopes, and development of immune responses to several other nonoverlapping epitopes within the hTSH sequence (epitope spreading) and antibodies reacting with hTSH-R. This implies that immunization with hTSH-R epitopes produced immunity to mouse TSH-R.

CONCLUSION

T-cell and B-cell responses to genetic immunization differ in DR3 and DR2 transgenic mice, and there is less genetic control of antibody than of T-cell responses. During both genomic and peptide epitope immunization there was evidence of epitope spreading during the immunization. Several functionally important epitopes are evident, especially aa78-94. However, if similar progressive epitope recruitment occurs in human disease, epitope-based therapy will be difficult to achieve.

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.

Thyroid antigens, not central tolerance, control responses to immunization in BALB/c versus C57BL/6 mice

BACKGROUND

Vaccination with cDNA for the human thyrotropin receptor (TSHR) in a plasmid, without adjuvant, induces TSHR antibodies in C57BL/6 but rarely in BALB/c mice. This outcome could be due to a difference between "high" versus "low" antibody responder mouse strains. However, unlike their poor response to TSHR-DNA vaccination, BALB/c mice vaccinated with thyroid peroxidase (TPO)-cDNA readily develop antibodies to TPO. We hypothesized that insight into these conundrums would be provided by the following differences in central tolerance: (i) between two mouse strains (C57BL/6 versus BALB/c) for the TSHR; and (ii) between two thyroid autoantigens (TPO and the TSHR) in one mouse strain (BALB/c).

METHODS

We studied autoantigen expression using real-time polymerase chain reaction to quantify mRNA transcripts for the TSHR, TPO, and thyroglobulin (Tg) in thymic tissue (as well as in thyroid) of young mice.

RESULTS

Our hypothesis was not confirmed. Intrathymic TSHR transcript expression was similar in BALB/c and C57BL/6 mice. Moreover, thymic mRNA transcripts for TSHR and TPO were comparable. Unlike the 10-fold differences for the autoantigens in thyroid tissue (Tg greater than TPO which, in turn was greater than the TSHR), intrathymic transcripts for TPO and the TSHR were similar, both being slightly lower than the level for Tg.

CONCLUSIONS

Central tolerance, assessed by measuring intrathymic transcripts of thyroid autoantigens, does not explain the different outcome of TSHR-DNA vaccination in BALB/c and C57BL/6 mice, or even susceptibility versus resistance to hyperthyroidism induced by TSHR-adenovirus. Instead, differences in MHC and TSHR T-cell epitopes likely contribute to TSHR antibody development (or not) following DNA plasmid immunization. The greater immunogenicity of TPO versus TSHR probably relates to the greater number of nonhomologous amino acids in the human and mouse TPO ectodomains (78 amino acids) than in the human and mouse TSHR ectodomains (58 amino acids). Overall, the autoantigens themselves, not central tolerance, control DNA plasmid-induced immunity to TPO and the TSHR.

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.

Association of Graves' disease and prevalence of circulating IFN-gamma-producing CD28(-) T cells

BACKGROUND

Peripheral blood CD4(+) and CD8(+) T-cell subsets lacking surface CD28 have been suggested to predispose patients to immune-mediated disorders.

MATERIALS AND METHODS

To determine the role of CD28(-) T-cell subset in Graves' disease (GD), we characterized peripheral blood CD4(+)CD28(-) and CD8(+)CD28(-) T cell from early onset GD patients.

RESULTS AND DISCUSSION

GD patients had significantly higher percentages of CD4(+)CD28(-) and CD8(+)CD28(-) T cells than did healthy donors. Both CD28(-) T cells expressed mostly CD45RO, suggesting that they are activated and/or are memory T cells. GD patient-derived CD4(+)CD28(-) and CD8(+)CD28(-) T cells produced more intracellular IFN-gamma than their counterparts from healthy donors. Furthermore, CD4(+)CD28(-) and CD8(+)CD28(-) T cells from GD patients with Graves' ophthalmopathy (GO) secreted higher level of intracellular IFN-gamma than those CD28(-) T cells from GD patients without GO. Retrospective analysis showed that the increased levels of CD4(+)CD28(-) T cells and their IFN-gamma-producing subgroups were positively correlated to the serum anti-thyrotropin receptor (TSHR) autoantibodies (TRAb). Our observations suggest that increased IFN-gamma-producing CD28(-) T cells in GD patients may play an important role in the pathogenesis of GD.

Elocalcitol inhibits inflammatory responses in human thyroid cells and T cells

T-helper 1 (Th1) cell-mediated inflammatory responses predominate in the early pathogenesis of Graves' disease (GD), whereas Th2 cell-mediated immunity may play a role in later stages. The chemokine CXCL10 and its receptor CXCR3 are expressed in most thyroid glands of early GD patients. Circulating CXCL10 levels inversely correlate with disease duration; CXCL10 maximal expression also correlates with interferon (IFN)gamma levels in recent GD onset. Methimazole (MMI) reduces CXCL10 secretion by isolated thyrocytes, decreases serum CXCL10 levels, and promotes a transition from Th1 to Th2 dominance in patients in GD active phase. Vitamin D receptor agonists exhibit antiinflammatory properties and promote tolerance induction. We investigated the effects and the mechanism of action of a nonhypercalcemic vitamin D receptor agonist, elocalcitol (BXL-628), compared with MMI on CXCL10 secretion induced by proinflammatory cytokines. Furthermore, we studied the effects of both drugs on Th1, Th17, and Th2 cytokine secretion in CD4+ T cells. ELISA, cytometry, immunocytochemistry, Western blot, and quantitative real-time PCR were used for protein and gene analysis. In human thyrocytes, elocalcitol inhibited IFNgamma and TNFalpha-induced CXCL10 protein secretion more potently than MMI. Elocalcitol impaired both cytokine intracellular pathways, whereas MMI was effective only on the IFNgamma pathway. In CD4+ T cells, elocalcitol decreased Th1- and Th17-type cytokines, and promoted Th2-type cytokine secretion. Elocalcitol and MMI inhibited Th1 cytokine-mediated responses in thyrocytes and CD4+ T cells. In addition, elocalcitol promoted a shift toward a Th2 response. In conclusion, elocalcitol could represent a novel pharmacological tool in the treatment of autoimmune thyroid diseases.

Shared and unique susceptibility genes in a mouse model of Graves' disease determined in BXH and CXB recombinant inbred mice

Susceptibility genes for TSH receptor (TSHR) antibodies and hyperthyroidism can be probed in recombinant inbred (RI) mice immunized with adenovirus expressing the TSHR A-subunit. The RI set of CXB strains, derived from susceptible BALB/c and resistant C57BL/6 (B6) mice, were studied previously. High-resolution genetic maps are also available for RI BXH strains, derived from B6 and C3H/He parents. We found that C3H/He mice develop TSHR antibodies, and some animals become hyperthyroid after A-subunit immunization. In contrast, the responses of the F1 progeny of C3H/He x B6 mice, as well as most BXH RI strains, are dominated by the B6 resistance to hyperthyroidism. As in the CXB set, linkage analysis of BXH strains implicates different chromosomes (Chr) or loci in the susceptibility to induced TSHR antibodies vs. hyperthyroidism. Importantly, BXH and CXB mice share genetic loci controlling the generation of TSHR antibodies (Chr 17, major histocompatibility complex region, and Chr X) and development of hyperthyroidism (Chr 1 and 3). Moreover, some chromosomal linkages are unique to either BXH or CXB strains. An interesting candidate gene linked to thyroid-stimulating antibody generation in BXH mice is the Ig heavy chain locus, suggesting a role for particular germline region genes as precursors for these antibodies. In conclusion, our findings reinforce the importance of major histocompatibility complex region genes in controlling the generation of TSHR antibodies measured by TSH binding inhibition. Moreover, these data emphasize the value of RI strains to dissect the genetic basis for induced TSHR antibodies vs. their effects on thyroid function in Graves' disease.

Graves' animal models of Graves' hyperthyroidism

Fifty years after the discovery of thyroid autoimmunity, several animal models of Graves' hyperthyroidism are now available. All are inducible types, and diseases are elicited by injecting living cells (professional or nonprofessional antigen-presenting cells) expressing the recombinant thyrotropin receptor (TSHR) or by DNA vaccination with TSHR cDNA in plasmid or adenovirus vectors. Thus most Graves' models are attributed to the cloning of the TSHR cDNA and involve in vivo expression of the TSHR. These breakthroughs have provided us important insights into our understanding of the pathogenesis of Graves' disease, and also indispensable means to exploring the possibility of development of novel therapeutic modalities. In particular, recent studies have begun to scrutinize the genetic factors contributing to the susceptibility to this ailment, and to delineate the roles for central and peripheral tolerance and also for fine balance between autoreactive effector T cells and regulatory T cells in the pathophysiology of anti-TSHR autoimmunity and Graves' hyperthyroidism. Moreover, preliminary, but novel, therapeutic approaches have also been started to treat experimental hyperthyroidism.

Environmental factors and genetic background that interact to cause autoimmune thyroid disease

PURPOSE OF REVIEW

To provide an updated list of genetic and environmental causative factors of autoimmune thyroid disease, and report about the recent discoveries concerning their interaction in the pathogenesis of thyroid autoimmunity.

RECENT FINDINGS

Although significant discoveries have been made on genetic and environmental factors underlying the development of autoimmune thyroid disease, few data are available about the mechanisms by which they interact. The most interesting news in this field comes from research on molecular mimicry between microbial antigens and thyroid autoantigens. The molecular mimicry model postulates that, in predisposed subjects, a microbial antigen could trigger autoimmunity because of its structural similarity to an autoantigen of the host, and is a paradigmatic example of the multifactorial interaction of several genes and environmental factors to cause autoimmune diseases, including thyroid diseases.

SUMMARY

Recent findings help us to better understand the functional mechanisms of the immune system, which are still only partially known. Beyond the scientific interest, this knowledge has immediate repercussions on clinical practice because it can suggest possible therapeutic targets for new treatments, as well as better and more specific uses of currently available drugs and resources.

Contrasting roles of IFN-gamma in murine models of autoimmune thyroid diseases

Interferon-gamma (IFN-gamma), a prototypic proinflammatory cytokine produced by several different cell types, including the Th1 subset of CD4(+) T cells, plays an important role in inflammation and autoimmune diseases. This review focuses on the varied and often contrasting roles of IFN-gamma in three murine models of autoimmune thyroid disease, experimentally induced autoimmune thyroiditis, the model of iodine-induced spontaneous autoimmune thyroiditis in NOD.H-2h4 mice and several different murine models of Graves' disease.

The NLR network and the immunological disease continuum of adaptive and innate immune-mediated inflammation against self

The nucleotide-binding domain, leucine-rich repeat containing family (NLR) network has provided pivotal genetic and molecular insights into diseases that were hitherto regarded as autoimmune. The NLR-related disorders include rare monogenic autoinflammatory diseases collectively termed cryopyrin-associated periodic syndromes, Crohn's disease which is a common polygenic disease and also an association at the mechanistic level with gout and pseudogout. Unlike the classical autoimmune diseases where disease immunopathogenesis is played out primarily in the primary and secondary lymphoid organs, the immunopathogenesis of the NLR-related disorders is played out in the tissues where inflammation arises. As the genetic mutations or molecular cascades associated with the NLR-related disorders have a widespread cellular distribution, it has been somewhat enigmatic why these disorders attack certain territories, but not others. This implies that tissue-specific factors in the target organs themselves contribute to disease expression. Such examples include the high abundance of NOD2 expressing cells in the part of the gut most typically afflicted by Crohn's disease and the preferential deposition of crystals in the joints to where inflammation localises in gout and pseudogout. The NLR network is associated principally with increases in TNF or IL-1 production, both of which are key players in innate immunity. Therefore, the NLR network identifies at the genetic and molecular level a robust paradigm for innate immune activation against self. This tissue-specific-factor-associated inflammation is the diametric opposite of classical autoimmunity. Of note, the MHC class-I-associated diseases including psoriasis (HLA-Cw6) and ankylosing spondylitis (HLA-B27) show striking clinical overlaps with Crohn's disease and also some rare monogenic diseases. Thus, the NLR innate immune pathway allows the full spectrum of inflammation against self to be viewed along an immunological disease continuum with autoantibody-associated disease at one end, innate immune diseases at the other and MHC class-1-related disorders as an intermediate.

Dysregulation of TNF/TNFR superfamily members: a systemic link between intra- and extrathyroidal manifestations in Graves' disease

Graves' disease (GD) coincides with the occurrence of disease-associated intrathyroidal dendritic cells (DC) and intraorbital inflammatory macrophages (Mphi). Physiologically, tumour necrosis factor-alpha (TNF-alpha) strongly affects the differentiation of DC and Mphi from monocytic precursors; we thus hypothesized that dysregulation of the TNF/TNFR superfamilies may provide a systemic pathogenic link in GD. In patients without eye symptoms, percentages of TNF-alpha-stimulated blood monocytes were highly significantly (P < 0.001) elevated, corresponding to both intrathyroidal DC maturation as well as increases in mature blood DC (MHC-II(hi)/CD40+/RFD1(hi)) and B cells (CD20(hi)/CD40+). GD patients also displaying eye symptoms revealed a striking reduction in blood monocytes, yet significantly (P < 0.05) increased CD40(hi) and TNF-alpha(hi) leucocytes. These findings suggest for GD that excess TNF-alpha induces monocytes to differentiate into hyperactivated thyroidal DC that, once emigrated, initiate systemic humoral autoimmunity associated with CD40/TNF-alpha upregulation. Such overexpression may instigate differentiation of periorbital inflammatory Mphi from CD14(hi)/CD16+ monocytes as a likely precursor subset. These results indicate that dysregulation of TNF/TNFR superfamily members provides a systemic pathogenic link in GD in that hyperactivated circulating monocytic precursors give rise to locally restricted, disease-associated DC and Mphi. Monocytes, therefore, may serve as a suitable target to therapeutically address the common precursor of key promoters of GD.

Differential Susceptibility of BALB/c and BALB/cBy mice to Graves' hyperthyroidism

BALB/c mice are susceptible to the induction of Graves' hyperthyroidism. To investigate the susceptibility of BALB/c substrains of mice to the induction of hyperthyroidism, we immunized BALB/cJ and BALB/cByJ mice with an adenovirus expressing amino acid residues 1-289 of thyrotropin receptor (TSHR). The data presented in this article showed that 17 of 26 (65%) BALB/c and only 4 of 30 (13%) BALB/cBy mice developed hyperthyroidism. Hyperthyroid mice displayed characteristics of Graves' disease, such as thyroid-stimulating antibodies and enlarged thyroid glands. To explore the differences in the susceptibility of these substrains for hyperthyroidism, we examined the TSHR antibodies in three different assays. The TSHR antibodies determined in a radioreceptor assay (TSH binding inhibitory immunoglobulins) were similar in both of these BALB/c substrains. The TSHR antibody titers of total IgG, IgG1, and IgG2a were measured by an enzyme-linked immunosorbent assay and were found to be similar in these mice. There were no significant differences between these two groups of mice in the thyroid-stimulating antibody activity. However, BALB/cBy mice had significantly higher TSH-blocking antibody activity compared to BALB/c mice. TSHR-specific proliferation of splenocytes and secretion of cytokines interferon-gamma and interleukin-4 by spleen cells were comparable in both the groups. BALB/cJ and BALB/cByJ mice both belong to same MHC haplotype, H-2(d), but differ in the Qa-2 region of class Ib molecule. This report shows the importance of other genes, such as Qa-2 region of class Ib molecule in addition to MHC class II, in the susceptibility of Graves' hyperthyroidism.

Blockade of costimulation between T cells and antigen-presenting cells: an approach to suppress murine Graves' disease induced using thyrotropin receptor-expressing adenovirus

OBJECTIVE

Immune responses require costimulatory interactions between molecules on antigen-presenting cells and T cells: CD40 binding to CD40 ligand and B7 binding to CD28. Graves' hyperthyroidism is induced in BALB/c mice by immunization with thyrotropin receptor (TSHR) A-subunit adenovirus (Ad-A-subunit). We attempted to modulate Ad-A-subunit-induced Graves' disease using adenoviruses expressing costimulation "decoys": CD40-IgG-Fc (CD40-Ig) to block CD40:CD40-ligand interactions and CTLA4-Fc (CTLA4-Ig) to prevent B7:CD28 binding.

OUTCOME

Unexpectedly, coimmunizing mice with Ad-A-subunit and excess control adenovirus (1:10 Ad-A-subunit:Ad-control) reduced TSHR antibody levels (thyrotropin binding inhibition [TBI]). Furthermore, only 15% of mice developed hyperthyroidism versus 75% using the same Ad-A-subunit dose (10(8) particles) without Ad-control. This effect was related to the dose of control adenovirus but not to the adenovirus insert, the timing or immunization site. Increasing the Ad-subunit dose (10(9) particles) and decreasing the control adenovirus dose (10:1 Ad-A-subunit:Ad-control) induced high TBI levels and 80% of mice were hyperthyroid. Coimmunization with Ad-CD40-Ig (but not Ad-CTLA4-Ig) reduced the incidence of hyperthyroidism to 40%.

CONCLUSIONS

Using appropriate controls and adenovirus ratios, our data suggest the importance of CD40:CD40-ligand interactions for inducing Graves' hyperthyroidism by Ad-A-subunit. Furthermore, our observations emphasize the potential pitfalls of non-specific inhibition by coimmunization with two adenovirus species.

Regulation of Graves' hyperthyroidism with naturally occurring CD4+CD25+ regulatory T cells in a mouse model

Graves' hyperthyroidism can be efficiently induced in susceptible mouse strains by repeated immunization with recombinant adenovirus coding the TSH receptor (TSHR). This study was designed to evaluate the role(s) played by naturally occurring CD4(+)CD25(+) regulatory T cells in the development of Graves' hyperthyroidism in resistant C57BL/6 and susceptible BALB/c mice. Depletion of CD4(+)CD25(+) T cells rendered some C57BL/6 mice susceptible to induction of hyperthyroidism. Thus, hyperthyroidism developed in 30% of the CD4(+)CD25(+) T cell-depleted C57BL/6 mice immunized with adenovirus expressing the TSHR A-subunit (AdTSHR289) vs. 0% of those immunized with AdTSHR289 alone. This immunological manipulation also enhanced disease severity in susceptible BALB/c mice, as reflected by a significant increase in mean T(4) levels by CD4(+)CD25(+) T cell depletion. The immunoenhancing effect of CD4(+)CD25(+) T cell depletion appears to be attributable to an increase in thyroid-stimulating antibody production and/or a decrease in thyroid-blocking antibody synthesis, but not immune deviation to either T helper 1 or 2 cells. Interestingly, unlike BALB/c mice, some hyperthyroid C57BL/6 mice showed some intrathyroidal lymphocytic infiltration with follicular destruction. These results indicate that CD4(+)CD25(+) T cells play a role in disease susceptibility and severity in adenovirus-TSHR-induced Graves' hyperthyroidism. Overall, the imbalance between effector and regulatory T cells appears to be crucial in the pathogenesis of Graves' disease.

A low molecular weight agonist signals by binding to the transmembrane domain of thyroid-stimulating hormone receptor (TSHR) and luteinizing hormone/chorionic gonadotropin receptor (LHCGR)

Many cognate low molecular weight (LMW) agonists bind to seven transmembrane-spanning receptors within their transmembrane helices (TMHs). The thienopyrimidine org41841 was identified previously as an agonist for the luteinizing hormone/chorionic gonadotropin receptor (LHCGR) and suggested to bind within its TMHs because it did not compete for LH binding to the LHCGR ectodomain. Because of its high homology with LHCGR, we predicted that thyroid-stimulating hormone receptor (TSHR) might be activated by org41841 also. We show that org41841 is a partial agonist for TSHR but with lower potency than for LHCGR. Analysis of three-dimensional molecular models of TSHR and LHCGR predicted a binding pocket for org41841 in common clefts between TMHs 3, 4, 5, 6, and 7 and extracellular loop 2 in both receptors. Evidence for this binding pocket was obtained in signaling studies with chimeric receptors that exhibited improved responses to org41841. Furthermore, a key receptor-ligand interaction between the highly conserved negatively charged E3.37 and the amino group of org41841 predicted by docking of the ligand into the three-dimensional TSHR model was experimentally confirmed. These findings provide the first evidence that, in contrast to the ectodomain binding of cognate ligands, a LMW agonist can bind to and activate glycoprotein hormone receptors via interaction with their transmembrane domain.

Cathepsin S is not crucial to TSHR processing and presentation in a murine model of Graves' disease

By regulating invariant (Ii) chain processing and MHC class II peptide loading, the endosomal protease cathepsin S (Cat S) has a potential role in autoimmune susceptibility. Indeed, Cat S null mice are resistant to I-Ab-restricted experimental myasthenia gravis due to inadequate peptide presentation. To explore the role of Cat S in a Graves' disease model, I-Ad-restricted wild-type (WT) and Cat S(-/-) mice were immunized with adenovirus encoding the A subunit of thyroid stimulating hormone receptor (TSHR). TSHR adenovirus immunized mice develop Th1 T cells, TSHR antibodies, and a proportion become overtly hyperthyroid. Although TSHR presentation in vitro was initially impaired in Cat S(-/-) mice, subsequent TSHR presentation in vitro and disease development were similar in both groups but with higher antibody responses in Cat S null mice. WT and Cat S(-/-) mice recognized similar T cell epitopes from a panel of overlapping TSHR peptides. TSHR responses were found to be I-Ad-restricted and Cat S(-/-) I-Ad B cells had marked defects in Ii processing. These data imply that loading of TSHR peptides critical to TSHR antibody responses becomes Ii-independent. Contrasting findings among organ-specific murine autoimmune models imply that potential uses of Cat S inhibitors to ameliorate autoimmunity must be determined empirically.

New insights into antibody-mediated hyperthyroidism

The most common cause of hyperthyroidism is Graves' disease, which represents a typical example of an organ-specific autoimmune condition. The exact triggers for the disease remain unknown, but are likely to involve a complex interaction between multiple environmental factors in a genetically predisposed individual. The main feature of the condition is the presence of thyroid-stimulating antibodies, which activate the thyroid- stimulating hormone receptor, resulting in hyperthyroidism. These antibodies may also be involved in the extrathyroidal complications of the disease. The recent generation of thyroid-stimulating antibodies in animal models and the isolation of monoclonal thyroid-stimulating antibodies from a patient with Graves' disease should allow the detailed study of thyroid-stimulating antibodies-thyroid-stimulating hormone receptor interactions. This will help to shed more light on disease pathogenesis and may offer new treatment strategies in difficult cases, particularly in patients with extrathyroidal complications.

Stress and autoimmune thyroid diseases

Autoimmune thyroid diseases (AITD) are the far most common autoimmune disorders, their prevalence in Western countries exceeding 5% of the general population. In the large majority of individual cases the clinical impact of AITD is not severe, however, their widespread diffusion renders them a significant health problem. AITD are heterogeneous in their clinical presentation: the two main forms are autoimmune thyroiditis (AT) and Graves' disease (GD). Although they probably share, at least in part, a common genetic background and may occur in the same family as well as in the same individual, they are definitely two distinct diseases both in their clinical presentation and their pathophysiology. In fact, AT causes structural thyroid damage (mainly via cell-mediated immune destruction of thyroid follicular cells) which results, as a rule, in functional impairment (hypothyroidism); however, depending on clinical variants, evolution towards hypothyroidism may be very low, or thyroid function impairment occurs after an initial phase of mild thyrotoxicosis due to relatively rapid gland destruction. GD patients have hyperthyroidism, often severe, due to autoantibody-mediated thyrotropin receptor stimulation, with thyroid cell hyperplasia and hyperfunction. Such a functional heterogeneity is a key feature for the clinical management: as a matter of fact, therapy of AITD is mainly therapy of thyroid dysfunction. Moreover, since hyperthyroidism is quite early perceived by the patient as a cause of discomfort, the timing of the natural history of GD is relatively well defined; on the other hand, AT may be asymptomatic for a long time and defining its natural history in a single patient may be difficult. In some AITD patients (mainly, but not exclusively, with GD), clinical features not directly related to thyroid dysfunction, such as orbitopathy, are present. Graves' orbitopathy is probably related, at least in part, to autoantibodies directed to thyrotropin receptor; it may be, in a minority of patients, severe and sight-threatening, and represents an independent clinical problem.

Gene expression profiles differ markedly in mouse strains that are (or are not) susceptible to hyperthyroidism induced using thyrotropin receptor-expressing adenovirus

BALB/c mice are susceptible and C57BL/6 mice are resistant to Graves' hyperthyroidism induced by immunization with adenovirus encoding the thyrotropin receptor (TSHR) A-subunit. Both strains develop comparable levels of TSHR antibodies, but potent TSH blocking antibody activity in C57BL/6 mice likely blocks development of hyperthyroidism. We used microarrays to compare gene expression in spleens of mice immunized with A-subunit adenovirus (TSHR-Ad) or control adenovirus (Con-Ad). To preclude the effects of variable thyroxine (T(4)) levels, mice were studied when euthyroid as follows: BALB/c mice immunized three times with TSHR-Ad or Con-Ad and C57BL/6 mice immunized three times with TSHR-Ad or Con-Ad. Among the 14,000 expressed probe sets, there were no statistically significant differences in gene expression in BALB/c mice immunized with TSHR-Ad versus Con-Ad. In contrast, expression of 57 transcripts (representing 40 genes) changed in response to TSHR-Ad in C57BL/6 mice. Diverse genes were identified, including proteins involved in immune responses, inflammation, and cell cycling as well as heat-shock proteins and proteases. Down-regulation of chitinase 3- and-4 gene expression likely reflects cytokines produced by T-helper 2 (Th2) type cells. Indeed, the immunoglobulin (IgG) subclass for TSHR antibodies reflects a deviation away from Th2 cytokines and toward Th1 in C57BL/6 mice. In conclusion, TSHR-Ad immunization altered gene expression profiles in C57BL/6, but not in BALB/c, mice. This response primarily involved reduced gene expression. In C57BL/6 mice, decreased expression of genes such as cathelicidin, calgranulins, and lipocalin following TSHR A-subunit adenovirus immunization suggests the importance of innate immunity in this response.

Adenovirus encoding the thyrotropin receptor A-subunit improves the efficacy of dendritic cell-induced Graves' hyperthyroidism in mice

Stimulating the immune system by in vivo expression of the thyrotropin receptor (TSHR) is an efficient means to induce Graves' disease experimentally. For example, BALB/c mice injected with dendritic cells (DCs) infected with adenovirus encoding the full-length TSHR (AdTSHR) develop hyperthyroidism, albeit at a low incidence (36%). Recent observations suggest that the shed TSHR A-subunit, rather than the full-length receptor, is the autoantigen responsible for initiating/enhancing immune responses leading to thyroid stimulating antibodies (TSAb) and hyperthyroidism. Therefore, we attempted to improve the efficacy of the DC-based approach for Graves' disease using adenovirus encoding the TSHR A-subunit (AdTSHR289). Three injections of DCs infected with AdTSHR289 induced hyperthyroidism in 70% of BALB/c mice, approximately twice the disease induction rate with AdTSHR. TSAb activity was detected in most hyperthyroid mice, whereas virtually all immunized mice developed antibodies that inhibit [125I]TSH binding to the TSHR or recognize linear or conformational epitopes on the TSHR. TSHR antibodies were of IgG1 and IgG2a, indicating mixed T-helper type 1 (Th1)/Th2 immune responses. In conclusion, immunization with DC infected with adenovirus expressing the TSHR A-subunit is a highly efficient protocol to induce Graves' hyperthyroidism in BALB/c mice. This improved model will permit studies of the pathogenic role and therapeutic potential of DCs in Graves' hyperthyroidism.