Adenovirus-mediated gene delivery of interleukin-10, but not transforming growth factor beta, ameliorates the induction of Graves' hyperthyroidism in BALB/c mice

Murine Thyroid IL-4 Expression Worsens Hypothyroidism on Iodine Restriction and Mitigates Graves Disease Development

Cytokines are known to perturb thyroid function and the role of interleukin-4 (IL-4) in the pathogenesis of Graves disease (GD) remains controversial. In our mouse model overexpressing IL-4 in thyrocytes (Thyr-IL4), we have reported that adult mice preserved normal serum thyroxine despite an iodide uptake defect. In the present work, we evaluated if iodine restriction could uncover the thyroid deficiency in Thyr-IL4 animals as well as the role of pendrin overexpression as a compensatory mechanism. Moreover, using an experimental model of GD we investigated the effect of a local expression of IL-4 on the incidence of hyperthyroidism. Thyr-IL4 mice developed more rapidly elevated serum thyrotropin under low-iodine supply with thyroid enlargement and classical histological modifications. These hallmarks of hypothyroidism were all enhanced in Thyr-IL4 mice with complete pendrin invalidation. Following immunization, a lower proportion of Thyr-IL4 animals developed hyperthyroidism. Surprisingly, immunized Thyr-IL4 animals presented numerous leukocyte infiltrates, associated with increased intrathyroidal expression of IFN-γ. We have demonstrated that thyroid deficiency in Thyr-IL4 mice is partially compensated for by the excessive iodide content of the standard chow and the overexpression of pendrin in these animals. Furthermore, we have shown that the local expression of IL-4 in the thyroid attenuates GD progression, which was associated with enhanced thyroid infiltration by immune cells that could negatively affect thyroid function.

A transgenic mouse that spontaneously develops pathogenic TSH receptor antibodies will facilitate study of antigen-specific immunotherapy for human Graves' disease

Graves' hyperthyroidism can be treated but not cured. Antigen-specific immunotherapy would accomplish this goal, for which purpose an animal model is an invaluable tool. Two types of animal models are available. First, pathogenic TSHR antibodies (TSHRAb) can be induced by injecting mice with fibroblasts co-expressing the human TSHR (hTSHR) and MHC class II, or in mammals using plasmid or adenovirus vectors encoding the hTSHR or its A-subunit. Second, a mouse model that spontaneously develops pathogenic TSHRAb resembling those in human disease was recently described. This outcome was accomplished by transgenic intrathyroidal expression of the hTSHR A-subunit in NOD.H2^h4 mice that are genetically predisposed to develop thyroiditis but, without the transgene, do not generate TSHRAb. Recently, novel approaches to antigen-specific immunotherapy have been tested, primarily in the induced model, by injecting TSHR A-subunit protein or cyclic TSHR peptides. T-cell tolerance has also been induced in "humanized" HLA-DR3 mice by injecting synthetic peptides predicted in silico to mimic naturally processed TSHR T-cell epitopes. Indeed, a phase 1 study based on the latter approach has been conducted in humans. In the spontaneous model (hTSHR/NOD.H2^h mice), injection of soluble or nanoparticle-bearing hTSHR A-subunits had the unwanted effect of exacerbating pathogenic TSHRAb levels. A promising avenue for tolerance induction, successful in other conditions and yet to be tested with the TSHR, involves encapsulating the antigen. In conclusion, these studies provide insight into the potential outcome of immunotherapeutic approaches and emphasize the importance of a spontaneous model to test future novel, antigen-specific immunotherapies for Graves' disease.

Comparative Assessment of Female Mouse Model of Graves' Orbitopathy Under Different Environments, Accompanied by Proinflammatory Cytokine and T-Cell Responses to Thyrotropin Hormone Receptor Antigen

We recently described a preclinical model of Graves' orbitopathy (GO), induced by genetic immunization of eukaryotic expression plasmid encoding human TSH receptor (TSHR) A-subunit by muscle electroporation in female BALB/c mice. The onset of orbital pathology is characterized by muscle inflammation, adipogenesis, and fibrosis. Animal models of autoimmunity are influenced by their environmental exposures. This follow-up study was undertaken to investigate the development of experimental GO in 2 different locations, run in parallel under comparable housing conditions. Functional antibodies to TSHR were induced in TSHR A-subunit plasmid-immunized animals, and antibodies to IGF-1 receptor α-subunit were also present, whereas control animals were negative in both locations. Splenic T cells from TSHR A-subunit primed animals undergoing GO in both locations showed proliferative responses to purified TSHR antigen and secreted interferon-γ, IL-10, IL-6, and TNF-α cytokines. Histopathological evaluation showed orbital tissue damage in mice undergoing GO, manifest by adipogenesis, fibrosis, and muscle damage with classic signs of myopathy. Although no inflammatory infiltrate was observed in orbital tissue in either location, the appearances were consistent with a "hit-and-run" immune-mediated inflammatory event. A statistically significant increase of cumulative incidence of orbital pathology when compared with control animals was shown for both locations, confirming onset of orbital dysimmune myopathy. Our findings confirm expansion of the model in different environments, accompanied with increased prevalence of T cell-derived proinflammatory cytokines, with relevance for pathogenesis. Wider availability of the model makes it suitable for mechanistic studies into pathogenesis and undertaking of novel therapeutic approaches.

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.

Role of self-tolerance and chronic stimulation in the long-term persistence of adenovirus-induced thyrotropin receptor antibodies in wild-type and transgenic mice

BACKGROUND

Graves'-like disease, reflected by thyrotropin receptor (TSHR) antibodies and hyperthyroidism in some mouse strains, can be induced by immunization with adenovirus-expressing DNA for the human TSHR or its A-subunit. The conventional approach involves two or three adenovirus injections at 3-week intervals and euthanasia 10 weeks after the first injection. To investigate TSHR antibody persistence in mice with differing degrees of self-tolerance to the TSHR A-subunit, we studied the effect of delaying euthanasia until 20 weeks after the initial immunization.

METHODS

Wild-type (WT) mice and transgenic (tg) mice expressing low intrathyroidal levels of the human TSHR A-subunit were immunized with A-subunit-adenovirus on two occasions; a second group of mice was immunized on three occasions. Sera obtained 4, 10, and 20 weeks (euthanasia) after the initial immunization were tested for thyrotropin (TSH) binding inhibition (TBI), antibody binding to TSHR A-subunit protein-coated enzyme-linked immunosorbent assay (ELISA) plates, and thyroid stimulating antibody activity (TSAb; cyclic adenosine monophosphate [cAMP] generation). Serum thyroxine (T4) and thyroid histology were studied at euthanasia.

RESULTS

THE majority of WT mice retained high TSHR antibody levels measured by TBI or ELISA at euthanasia but only about 50% were TSAb positive. Low-expressor tgs exhibited self-tolerance, with fewer mice positive by TBI or ELISA and antibody levels were lower than in WT littermates. In WT mice, antibody persistence was similar after two or three immunizations; for tgs, only mice immunized three times had detectable TSAb at 20 weeks. Unlike our previous observations of hyperthyroidism in WT mice examined 4 or 10 weeks after immunization, all mice were euthyroid at 20 weeks.

CONCLUSIONS

Our findings for induced TSHR antibodies in mice, similar to data for human thyroid autoantibodies, indicate that the parameters that contribute to the concentration of the antibody and thereby play a critical role in long-term persistence of TSHR antibodies are the degree of self-tolerance to the TSHR and chronic stimulation.

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.

Attenuation of induced hyperthyroidism in mice by pretreatment with thyrotropin receptor protein: deviation of thyroid-stimulating to nonfunctional antibodies

Graves'-like hyperthyroidism is induced by immunizing BALB/c mice with adenovirus expressing the thyrotropin receptor (TSHR) or its A-subunit. Nonantigen-specific immune strategies can block disease development and some reduce established hyperthyroidism, but these approaches may have unforeseen side effects. Without immune stimulation, antigens targeted to the mannose receptor induce tolerance. TSHR A-subunit protein generated in eukaryotic cells binds to the mannose receptor. We tested the hypothesis that eukaryotic A-subunit injected into BALB/c mice without immune stimulation would generate tolerance and protect against hyperthyroidism induced by subsequent immunization with A-subunit adenovirus. Indeed, one sc injection of eukaryotic, glycosylated A-subunit protein 1 wk before im A-subunit-adenovirus immunization reduced serum T(4) levels and the proportion of thyrotoxic mice decreased from 77 to 22%. Prokaryotic A-subunit and other thyroid proteins (thyroglobulin and thyroid peroxidase) were ineffective. A-subunit pretreatment reduced thyroid-stimulating and TSH-binding inhibiting antibodies, but, surprisingly, TSHR-ELISA antibodies were increased. Rather than inducing tolerance, A-subunit pretreatment likely expanded B cells that secrete nonfunctional antibodies. Follow-up studies supported this possibility and also showed that eukaryotic A-subunit administration could not reverse hyperthyroidism in mice with established disease. In conclusion, glycosylated TSHR A-subunit is a valuable immune modulator when used before immunization. It acts by deviating responses away from pathogenic toward nonfunctional antibodies, thereby attenuating induction of hyperthyroidism. However, this protein treatment does not reverse established hyperthyroidism. Our findings suggest that prophylactic TSHR A-subunit protein administration in genetically susceptible individuals may deviate the autoantibody response away from pathogenic epitopes and provide protection against future development of 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.

Treatment of autoimmune hyperthyroidism in a murine model of Graves' disease with tumor necrosis factor-family ligand inhibitors suggests a key role for B cell activating factor in disease pathology

Hyperthyroid Graves' disease is a common autoimmune disorder mediated by agonistic antibodies to the TSH receptor, termed thyroid stimulating antibodies (TSAbs). Recently members of the TNF superfamily, B cell activating factor (BAFF) and a proliferation-inducing ligand (APRIL), have been identified along with their receptors, B cell maturation antigen and transmembrane activator and calcium-modulator and cyclophilin ligand interactor, and the BAFF-specific receptor. BAFF is a fundamental B cell survival/maturation factor, and both BAFF and APRIL have been implicated in antibody production. We investigated the effect of interfering with BAFF- and APRIL-mediated signals in an induced model of Graves' disease by blockade of these factors using soluble decoy receptors. In a therapeutic setting in mice with established hyperthyroidism, we show that blockade of BAFF or BAFF+APRIL with BAFF-specific receptor-Fc and B cell maturation antigen-Fc, respectively, leads to significant reductions in the induced hyperthyroidism. This was supported by a parallel pattern of declining TSAbs in the responding animals. Histopathological analysis of splenic sections from treated animals revealed marked reductions in the B cell follicle regions, but staining with anti-CD138 revealed the persistence of plasma cells. Thus, the reductions in TSAbs in the treated animals were not related to overall plasma cell numbers in the secondary lymphoid organs. Our results are the first to demonstrate attenuation of established hyperthyroidism by therapeutic intervention aimed at autoreactive B cells and indicate that both BAFF and APRIL appear to play important roles in the development and survival of the autoantibody producing cells in this model.

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.