A novel murine model of Graves' hyperthyroidism with intramuscular injection of adenovirus expressing the thyrotropin receptor

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

Interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) are well known anti-inflammatory cytokines. We have studied the effect of adenovirus-mediated IL-10 and TGF-beta gene delivery on the induction of Graves' hyperthyroidism in our mouse model that involves repeated injections of adenovirus expressing the thyrotropin receptor A subunit (AdTSHR). We first constructed adenoviruses encoding the two cytokines (AdIL10 and AdTGF(beta)) and confirmed expression by in vitro infection of COS cells. Susceptible BALB/c mice were injected twice with AdTSHR alone or together with AdIL10 or AdTGF(beta), and bled two weeks after the second immunization. Significantly elevated serum thyroxine levels were seen in 26% of mice immunized with AdTSHR and AdIL10 versus 61% with AdTSHR alone. Levels of thyroid stimulating antibody, but not nonstimulating antibody, were also decreased, and TSHR-specific splenocyte secretion of interferon-gamma in recall assays was impaired in mice treated with AdIL10. In contrast, AdTGF(beta) had little effect on hyperthyroidism. Overall, our findings demonstrate that gene delivery of IL-10, but not TGF-beta, suppresses the induction of Graves' hyperthyroidism in a mouse model. However, the effect of IL-10 is less powerful than we observed previously with T helper type 2-inducers including adenovirus expressing IL-4, Shistosoma mansoni infection or alpha-galactosylceramide.

Monoclonal antibodies to the thyrotropin receptor

The thyrotropin receptor (TSHR) is a seven transmembrane G-protein linked glycoprotein expressed on the thyroid cell surface and which, under the regulation of TSH, controls the production and secretion of thyroid hormone from the thyroid gland. This membrane protein is also a major target antigen in the autoimmune thyroid diseases. In Graves' disease, autoantibodies to the TSHR (TSHR-Abs) stimulate the TSHR to produce thyroid hormone excessively. In autoimmune thyroid failure, some patients exhibit TSHR-Abs which block TSH action on the receptor. There have been many attempts to generate human stimulating TSHR-mAbs, but to date, only one pathologically relevant human stimulating TSHR-mAb has been isolated. Most mAbs to the TSHR have been derived from rodents immunized with TSHR antigen from bacteria or insect cells. These antigens lacked the native conformation of the TSHR and the resulting mAbs were exclusively blocking or neutral TSHR-mAbs. However, mAbs raised against intact native TSHR antigen have included stimulating mAbs. One such stimulating mAb has demonstrated a number of differences in its regulation of TSHR post-translational processing. These differences are likely to be reflective of TSHR-Abs seen in Graves' disease.

Animal models of Graves' hyperthyroidism

Graves' disease is a common organ-specific autoimmune disease characterized by overstimulation of the thyroid gland with agonistic anti-thyrotropin (TSH) receptor autoantibodies, which leads to hyperthyroidism and diffuse hyperplasia of the thyroid gland. Several groups including us have recently established several animal models of Graves' hyperthyroidism using novel immunization approaches, such as in vivo expression of the TSH receptor by injecting syngeneic living cells co-expressing the TSH receptor, the major histocompatibility complex (MHC) class II antigen and a costimulatory molecule, or genetic immunization using plasmid or adenovirus vectors coding the TSH receptor. This breakthrough has made it possible for us to study the pathogenesis of Graves' disease in more detail and has provided important insights into our understanding of disease pathogenesis. The important new findings that have emerged include: (i) the shed A subunit being the major autoantigen for TSAb, (ii) the significant role played by dendritic cells (DCs) as professional antigen-presenting cells in initiating disease development, (iii) contribution of MHC and particularly non-MHC genetic backgrounds in disease susceptibility, and (iv) influence of some particular infectious pathogens on disease development. However, the data regarding Th1/Th2 balance of TSH receptor-specific immune response or the association of Graves' hyperthyroidism with intrathyroidal lymphocytic infiltration are rather inconsistent. Future studies with these models will hopefully lead to better understanding of disease pathogenesis and help develop novel strategies for treatment and ultimately prevention of Graves' disease in humans.

A Graves' disease-associated Kozak sequence single-nucleotide polymorphism enhances the efficiency of CD40 gene translation: a case for translational pathophysiology

We analyzed the mechanism by which a Graves' disease-associated C/T polymorphism in the Kozak sequence of CD40 affects CD40 expression. CD40 expression levels on B cells in individuals with CT and TT genotypes were decreased by 13.3 and 39.4%, respectively, compared with the levels in CC genotypes (P = 0.012). Similarly, Rat-2 fibroblasts transfected with T-allele cDNA expressed 32.2% less CD40 compared with their C-allele-transfected counterparts (P = 0.004). Additionally, an in vitro transcription/translation system showed that the T-allele makes 15.5% less CD40 than the C-allele (P < 0.001), demonstrating that the effect of the single-nucleotide polymorphism (SNP) on CD40 expression is at the level of translation. However, the SNP did not affect transcription, because the mRNA levels of CD40, as measured by quantitative RT-PCR, were independent of genotype. Therefore, our results may suggest that the C allele of the CD40 Kozak SNP, which is associated with Graves' disease, could predispose to disease by increasing the efficiency of translation of CD40 mRNA.

TSH receptor-adenovirus-induced Graves' hyperthyroidism is attenuated in both interferon-gamma and interleukin-4 knockout mice; implications for the Th1/Th2 paradigm

The role of the Th1/Th2 balance in the pathogenesis of murine Graves' hyperthyroidism is controversial. In BALB/c mice injected with adenovirus expressing TSH receptor (TSHR-adeno model), we found that suppression of TSHR-specific Th1 immune responses by exogenous interleukin-4 (IL-4), alpha-galactosylceramide or helminth (Schistosoma mansoni) infection was associated with inhibition of hyperthyroidism, indicating the critical role for Th1 cytokines. In contrast, BALB/c IL-4 knockout (KO), but not interferon-gamma (IFN-gamma) KO mice failed to develop Graves' hyperthyroidism when injected with TSHR-expressing M12 B lymphoma cells (TSHR-M12 model), suggesting the importance of Th2 cytokine IL-4. To reconcile differences in these two models, we used IL-4 KO and IFN-gamma KO BALB/c mice in the TSHR-adeno model. Unlike wild-type (wt) BALB/c mice in which 60% developed hyperthyroidism, only 13 and 7% of IL-4 KO and IFN-gamma KO mice, respectively, became hyperthyroid. Thyroid stimulating antibodies were positive in most hyperthyroid mice. TSHR antibody titres determined by TSH binding inhibition and ELISA were comparable in all three groups. IgG1 and IgG2a TSHR antibody titres were similar in IFN-gamma KO and wt mice, whereas IgG1 TSHR antibody titres and TSHR-specific splenocyte IFN-gamma secretion were lower in IL-4 KO than in IFN-gamma KO and wt mice, respectively. Our results clearly implicate both IFN-gamma and IL-4 in development of hyperthyroidism in the TSHR-adeno model. These data, together with the previous report, also indicate different cytokine requirements in these two Graves' models, with IFN-gamma being more important in the TSHR-adeno than the TSHR-M12 model. Moreover, our previous and present observations indicate a difference in the role of exogenous versus endogenous IL-4 in TSHR-adenovirus induced Graves' hyperthyroidism.

Thyrotropin receptor antibodies: new insights into their actions and clinical relevance

The thyrotropin receptor (TSHR) is a G-protein-coupled receptor with a large ectodomain. TSH, acting via TSHR, regulates thyroid growth and thyroid hormone production and secretion. The TSHR undergoes complex post-translational processing involving dimerization, intramolecular cleavage, and shedding of its ectodomain, and each of these processes may influence the antigenicity of the TSHR. The TSHR is also the major autoantigen in Graves' disease, as well as a leading candidate autoantigen in both Graves' ophthalmopathy and pretibial myxedema. The naturally conformed TSHR is most effectively presented as an autoantigen to the immune system, causing the production of stimulating TSHR-Abs. There are also autoantibodies which block the TSHR from TSH action, and neutral TSHR-Abs which have no influence on TSH action. TSHR-Abs can be detected by competition assays of TSHR-Abs for labeled TSH, or monoclonal TSHR-Ab binding to solubilized TSHRs, or by bioassays using thyroid cells or mammalian cells expressing recombinant TSHRs.

Dissociation between iodide-induced thyroiditis and antibody-mediated hyperthyroidism in NOD.H-2h4 mice

NOD.H-2h4 mice are genetically predisposed to thyroid autoimmunity and spontaneously develop thyroglobulin autoantibodies (TgAb) and thyroiditis. Iodide administration enhances TgAb levels and the incidence and severity of thyroiditis. Using these mice, we investigated the interactions between TSH receptor (TSHR) antibodies induced by vaccination and spontaneous or iodide-enhanced thyroid autoimmunity (thyroiditis and TgAb). Mice were immunized with adenovirus expressing the TSHR A-subunit (or control adenovirus). Thyroid antibodies, histology, and serum thyroxine levels were compared in animals on a regular diet or on a high-iodide diet (0.05% NaI-supplemented water). Thyroiditis severity and TgAb levels were enhanced by iodide administration and were independent of the type of adenovirus used for immunization. In contrast, TSHR antibodies, measured by TSH-binding inhibition, thyroid-stimulating activity, and TSH-blocking activity, were induced in the majority of animals immunized with TSHR (but not control) adenovirus and were unaffected by dietary iodide. The NOD.2h4 strain of mice was less susceptible than BALB/c or BALB/k mice to TSHR adenovirus-induced hyperthyroidism. Nevertheless, hyperthyroidism developed in approximately one third of TSHR adenovirus-injected NOD.2h4 mice. This hyperthyroidism was suppressed by a high-iodide diet, probably by a nonimmune mechanism. The fact that inducing an immune response to the TSHR had no effect on thyroiditis raises the possibility that the TSHR may not be the target involved in the variable thyroiditis component in some humans with Graves' disease.

"Hijacking" the thyrotropin receptor: A chimeric receptor-lysosome associated membrane protein enhances deoxyribonucleic acid vaccination and induces Graves' hyperthyroidism

Naked DNA vaccination with the TSH receptor (TSHR) does not, in most studies, induce TSHR antibodies and never induces hyperthyroidism in BALB/c mice. Proteins expressed endogenously by vaccination are preferentially presented by major histocompatibility complex class I, but optimal T cell help for antibody production requires lysosomal processing and major histocompatibility complex class II presentation. To divert protein expression to lysosomes, we constructed a plasmid with the TSHR ectodomain spliced between the signal peptide and transmembrane-intracellular region of lysosome-associated membrane protein (LAMP)-1, a lysosome-associated membrane protein. BALB/c mice pretreated with cardiotoxin were primed intramuscularly using this LAMP-TSHR chimera and boosted twice with DNA encoding wild-type TSHR, TSHR A-subunit, or LAMP-TSHR. With each protocol, spleen cells responded to TSHR antigen by secreting interferon-gamma, and 60% or more mice had TSHR antibodies detectable by ELISA. TSH binding inhibitory activity was present in seven, four, and two of 10 mice boosted with TSHR A-subunit, LAMP-TSHR, or wild-type TSHR, respectively. Importantly, six of 30 mice had elevated T4 levels and goiter (5 of 6 with detectable thyroid-stimulating antibodies). Injecting LAMP-TSHR intradermally without cardiotoxin pretreatment induced TSHR antibodies detectable by ELISA but not by TSH binding inhibitory activity, and none became hyperthyroid. These findings are consistent with a role for cardiotoxin-recruited macrophages in which (unlike in fibroblasts) LAMP-TSHR can be expressed intracellularly and on the cell surface. In conclusion, hijacking the TSHR to lysosomes enhances T cell responses and TSHR antibody generation and induces Graves'-like hyperthyroidism in BALB/c mice by intramuscular naked DNA vaccination.

Dissecting linear and conformational epitopes on the native thyrotropin receptor

The TSH receptor (TSHR) is the primary antigen in Graves' disease. In this condition, autoantibodies to the TSHR that have intrinsic thyroid-stimulating activity develop. We studied the epitopes on the native TSHR using polyclonal antisera and monoclonal antibodies (mAbs) derived from an Armenian hamster model of Graves' disease. Of 14 hamster mAbs analyzed, five were shown to bind to conformational epitopes including one mAb with potent thyroid-stimulating activity. Overlapping conformational epitopes were determined by cell-binding competition assays using fluorescently labeled mAbs. We identified two distinct conformational epitopes: epitope A for both stimulating and blocking mAbs and epitope B for only blocking mAbs. Examination of an additional three mouse-derived stimulating TSHR-mAbs also showed exclusive binding to epitope A. The remaining nine hamster-derived mAbs were neutral or low-affinity blocking antibodies that recognized linear epitopes within the TSHR cleaved region (residues 316-366) (epitope C). Serum from the immunized hamsters also recognized conformational epitopes A and B but, in addition, also contained high levels of TSHR-Abs interacting within the linear epitope C region. In summary, these studies indicated that the natively conformed TSHR had a restricted set of epitopes recognized by TSHR-mAbs and that the binding site for stimulating TSHR-Abs was highly conserved. However, high-affinity TSHR-blocking antibodies recognized two conformational epitopes, one of which was indistinguishable from the thyroid-stimulating epitope. Hence, TSHR-stimulating and blocking antibodies cannot be distinguished purely on the basis of their conformational epitope recognition.

Graves' hyperthyroidism and the hygiene hypothesis in a mouse model

Graves' hyperthyroidism is an organ-specific autoimmune disease mediated by stimulatory autoantibodies against the TSH receptor (TSHR; thyroid-stimulating antibodies), causing thyroid hyperplasia and hyperthyroidism. Development of this ailment is well known to be under polygenic and environmental control. For example, we recently demonstrated that parasite helminth Schistosoma mansoni infection suppressed a T helper cell type 1 (Th1)-type anti-TSHR immune response and prevented disease development in our mouse model of Graves' disease using adenovirus coding for the TSHR. In the present study we examined the outcome of infection with Mycobacterium bovis bacillus Calmette-Guerin (BCG), a Th1-promoting infectious pathogen, on Graves' disease. Our results show that prior infection with M. bovis BCG differentiates the TSHR-specific immune response toward a Th1 phenotype, as demonstrated by enhanced secretion of a Th1 cytokine interferon-gamma and impaired production of a Th2 cytokine IL-10 from splenocytes stimulated in vitro with TSHR antigen. M. bovis BCG also significantly suppressed disease induction. These data together with our recent report that coinjection of adenovirus expressing the Th1 cytokine IL-12 induced a Th1-polarized, TSHR-specific immune response without affecting disease development support the hygiene hypothesis, rather than Th1-mediated disease suppression. Thus, some infectious pathogens may influence the development of Graves' disease regardless of their ability to modify the Th1/Th2 balance.

Susceptibility rather than resistance to hyperthyroidism is dominant in a thyrotropin receptor adenovirus-induced animal model of Graves' disease as revealed by BALB/c-C57BL/6 hybrid mice

We investigated why TSH receptor (TSHR) adenovirus immunization induces hyperthyroidism more commonly in BALB/c than in C57BL/6 mice. Recent modifications of the adenovirus model suggested that using adenovirus expressing the TSHR A subunit (A-subunit-Ad), rather than the full-length TSHR, and injecting fewer viral particles would increase the frequency of hyperthyroidism in C57BL/6 mice. This hypothesis was not fulfilled; 65% of BALB/c but only 5% of C57BL/6 mice developed hyperthyroidism. TSH binding inhibitory antibody titers were similar in each strain. Functional TSHR antibody measurements provided a better indication for this strain difference. Whereas thyroid-stimulating antibody activity was higher in C57BL/6 than BALB/c mice, TSH blocking antibody activity was more potent in hyperthyroid-resistant C57BL/6 mice. F(1) hybrids (BALB/c x C57BL/6) responded to A-subunit-Ad immunization with hyperthyroidism and TSHR antibody profiles similar to those of the hyperthyroid-susceptible parental BALB/c strain. In contrast, ELISA of TSHR antibodies revealed that the IgG subclass distribution in the F(1) mice resembled the disease-resistant C57BL/6 parental strain. Because the IgG subclass distribution is dependent on the T helper 1/T helper 2 cytokine balance, this paradigm can likely be excluded as an explanation for susceptibility to hyperthyroidism. In summary, our data for BALB/c, C57BL/6, and F(1) strains suggest that BALB/c mice carry a dominant gene(s) for susceptibility to induction of a thyroid-stimulating antibody/TSH blocking antibody balance that results in hyperthyroidism. Study of this genetic influence will provide useful information on potential candidate genes in human Graves' disease.

Superiority of thyroid peroxidase DNA over protein immunization in replicating human thyroid autoimmunity in HLA-DRB1*0301 (DR3) transgenic mice

Murine experimental autoimmune thyroiditis (EAT), characterized by thyroid destruction after immunization with thyroglobulin (Tg), has long been a useful model of organ-specific autoimmune disease. More recently, porcine thyroid peroxidase (pTPO) has also been shown to induce thyroiditis, but these results have not been confirmed. When (C57BL/6 x CBA)F(1) mice, recently shown to be susceptible to mouse TPO-induced EAT, were immunized with plasmid DNA to human TPO (hTPO) and cytokines IL-12 or GM-CSF, significant antibody (Ab) titres were generated, but minimal thyroiditis was detected in one mouse only from the TPO + GM-CSF immunized group. However, after TPO DNA immunization of HLA-DR3 transgenic class II-deficient NOD mice, thyroiditis was present in 23% of mice injected with TPO + IL-12 or GM-CSF. We also used another marker for assessing the closeness of the model to human thyroid autoimmunity by examining the epitope profile of the anti-TPO Abs to immunodominant determinants on TPO. Remarkably, the majority of the anti-TPO Abs was directed to immunodominant regions A and B, demonstrating the close replication of the model to human autoimmunity. TPO protein immunizations of HLA-DR3 transgenic mice with recombinant hTPO did not result in thyroiditis, nor did immunization of other mice expressing HLA class II transgenes HLA-DR4 or HLA-DQ8, with differential susceptibility to Tg-induced EAT. Moreover, our efforts to duplicate exactly the experimental procedures used with pTPO also failed to induce thyroiditis. The success of hTPO plasmid DNA immunization of DR3(+) mice, similar to our reports on Tg-induced thyroiditis and thyrotropin receptor DNA-induced Graves' hyperthyroidism, underscores the importance of DR3 genes for all three major thyroid antigens, and provides another humanized model to study autoimmune thyroid disease.

Naked deoxyribonucleic acid vaccination induces recognition of diverse thyroid peroxidase T cell epitopes

Recently, we observed that vaccination of BALB/c mice with thyroid peroxidase (TPO)-DNA in a plasmid is highly effective at inducing antibodies that interact with the immunodominant region recognized by human autoantibodies. We have now analyzed the TPO epitopes recognized by memory T cells in these animals. Splenocytes from TPO-DNA (not control DNA)-vaccinated mice responded to TPO protein antigen, as measured by interferon-gamma production. As a group, TPO-immunized mice recognized 35 of 55 overlapping synthetic peptides that encompass the 814-amino acid TPO ectodomain. In individual mice, between five and 10 peptides induced splenocyte responses. Two T cell epitopes were immunodominant, one of which is also recognized by patients with autoimmune thyroid disease. To explore a potential correlation between T and B cell epitopes, we analyzed serum TPO antibody epitopic fingerprints. No relationship was evident. However, the number of T cell epitopes recognized by individual mice was inversely proportional to recognition of an antibody epitopic subdomain. The diversity of TPO T cell epitopes is in striking contrast to the restricted number of TSH receptor (TSHR) peptides (four of 29) recognized by T cells, as is the paucity of antibodies in the same strain of mice vaccinated with TSHR-DNA. In conclusion, our data highlight differences for both antibody and T cell epitopic recognition in TPO- vs. TSHR-DNA-immunized BALB/c mice. These findings provide insight into mechanisms that may be involved in spontaneous immune responses to two major thyroid autoantigens in humans.

Schistosoma mansoniand α-Galactosylceramide: Prophylactic Effect of Th1 Immune Suppression in a Mouse Model of Graves’ Hyperthyroidism

Graves' hyperthyroidism, an organ-specific autoimmune disease mediated by stimulatory thyrotropin receptor (TSHR) autoantibodies, has been considered a Th2-dominant disease. However, recent data with mouse Graves' models are conflicting. For example, we recently demonstrated that injection of BALB/c mice with adenovirus coding the TSHR induced Graves' hyperthyroidism characterized by mixed Th1 and Th2 immune responses against the TSHR, and that transient coexpression of the Th2 cytokine IL-4 by adenovirus skewed Ag-specific immune response toward Th2 and suppressed disease induction. To gain further insight into the relationship between immune polarization and Graves' disease, we evaluated the effect of Th2 immune polarization by helminth Schistosoma mansoni infection and alpha-galactosylceramide (alpha-GalCer), both known to bias the systemic immune response to Th2, on Graves' disease. S. mansoni infection first induced mixed Th1 and Th2 immune responses to soluble worm Ags, followed by a Th2 response to soluble egg Ags. Prior infection with S. mansoni suppressed the Th1-type anti-TSHR immune response, as demonstrated by impaired Ag-specific IFN-gamma secretion of splenocytes and decreased titers of IgG2a subclass anti-TSHR Abs, and also prevented disease development. Similarly, alpha-GalCer suppressed Ag-specific splenocyte secretion of IFN-gamma and prevented disease induction. However, once the anti-TSHR immune response was fully induced, S. mansoni or alpha-GalCer was ineffective in curing disease. These data support the Th1 theory in Graves' disease and indicate that suppression of the Th1-type immune response at the time of Ag priming may be crucial for inhibiting the pathogenic anti-TSHR immune response.

Concentration-dependent regulation of thyrotropin receptor function by thyroid-stimulating antibody

Thyrotropin receptor (TSHR) Ab's of the stimulating variety are the cause of hyperthyroid Graves disease. MS-1 is a hamster mAb with TSHR-stimulating activity. To examine the in vivo biological activity of MS-1, mice were treated with purified MS-1 intraperitoneally and the thyroid response evaluated. MS-1 induced a dose-dependent increase in serum thyroxine (T4), with a maximum effect after 10 proportional, variant g of MS-1 was administered. MS-1-secreting hybridoma cells were then transferred into the peritoneum of nude mice to study chronic thyroid stimulation. Serum MS-1 levels detected after 2 weeks were approximately 10-50 proportional, variant g/ml, and the serum TSH was suppressed in all animals. Serum triiodothyronine levels were elevated, but only in animals with low serum MS-1 concentrations. In addition, there was a negative correlation between serum T4 and the serum MS-1 concentrations. These in vivo studies suggested a partial TSHR inactivation induced by excessive stimulation by MS-1. We confirmed this inactivation by demonstrating MS-1 modulation of TSHR function in vitro as evidenced by downregulation and desensitization of the TSHR at concentrations of MS-1 achieved in the in vivo studies. Thus, inactivation of the TSHR by stimulating TSHR autoantibodies (TSHR-Ab's) in Graves disease patients may provide a functional explanation for the poor correlation between thyroid function and serum TSHR-Ab concentrations.

Induction of hyperthyroidism in mice by intradermal immunization with DNA encoding the thyrotropin receptor

Intramuscular injection with plasmid DNA encoding the human thyrotropin receptor (TSHR) has been known to elicit symptoms of Graves' disease (GD) in outbred but not inbred mice. In this study, we have examined, firstly, whether intradermal (i.d.) injection of TSHR DNA can induce hyperthyroidism in BALB/c mice and, secondly, whether coinjection of TSHR- and cytokine-producing plasmids can influence the outcome of disease. Animals were i.d. challenged at 0, 3 and 6 weeks with TSHR DNA and the immune response was assessed at the end of the 8th or 10th week. In two experiments, a total of 10 (67%) of 15 mice developed TSHR-specific antibodies as assessed by flow cytometry. Of these, 4 (27%) mice had elevated thyroxine (TT4) levels and goitrous thyroids with activated follicular epithelial cells but no evidence of lymphocytic infiltration. At 10 weeks, thyroid-stimulating antibodies (TSAb) were detected in two out of the four hyperthyroid animals. Interestingly, in mice that received a coinjection of TSHR- and IL-2- or IL-4-producing plasmids, there was no production of TSAbs and no evidence of hyperthyroidism. On the other hand, coinjection of DNA plasmids encoding TSHR and IL-12 did not significantly enhance GD development since two out of seven animals became thyrotoxic, but had no goitre. These results demonstrate that i.d. delivery of human TSHR DNA can break tolerance and elicit GD in inbred mice. The data do not support the notion that TSAb production is Th2-dependent in murine GD but they also suggest that codelivery of TSHR and Th1-promoting IL-12 genes may not be sufficient to enhance disease incidence and/or severity in this model.

HLA and H2 class II transgenic mouse models to study susceptibility and protection in autoimmune thyroid disease

Using single H2 and HLA class II transgenic mice, in the absence of endogenous H2 class II molecules, we have studied the permissiveness of class II molecules for experimental autoimmune thyroiditis (EAT). Resistant strains expressing susceptible class II molecules, H2Ak or HLA-DR3, developed EAT, clearly demonstrating the importance of class II gene inheritance. Polymorphism for HLA-DRB1 was observed, as DR3, but not DR2 or DR4, molecules were permissive for EAT induction with either mouse (m) or human (h) thyroglobulin (Tg). HLA-DQ polymorphism was also detectable, as hTg-induced EAT developed in DQ8+, but not DQ6+, mice. Class II gene interactions leading to reduced EAT severity were observed in H2 transgenic mice, when H2E transgene was expressed in H2A+ mice or H2A molecules were introduced into our novel H2A- E+ transgenic model. Similarly, in DR3+ mice, only the DQ8 transgene reduced EAT severity, depending on both background genes (C57BL/10 or NOD) and Tg species. Based on computer-predicted, class II-binding motifs, potential pathogenic Tg peptides, either unique to hTg (H2A- E+ model) or shared between mTg and hTg (HLA-DR3+ model), were identified. We have also developed a Graves' disease model by immunizing DR3+ mice with TSH receptor DNA. Thus, transgenic models are excellent tools to study human autoimmune thyroid diseases in the context of murine EAT.

Evidence that factors other than particular thyrotropin receptor T cell epitopes contribute to the development of hyperthyroidism in murine Graves' disease

Immunization with thyrotropin receptor (TSHR)-adenovirus is an effective approach for inducing thyroid stimulating antibodies and Graves' hyperthyroidism in BALB/c mice. In contrast, mice of the same strain vaccinated with TSHR-DNA have low or absent TSHR antibodies and their T cells recognize restricted epitopes on the TSHR. In the present study, we tested the hypothesis that immunization with TSHR-adenovirus induces a wider, or different, spectrum of TSHR T cell epitopes in BALB/c mice. Because TSHR antibody levels rose progressively from one to three TSHR-adenovirus injections, we compared T cell responses from mice immunized once or three times. Mice in the latter group were subdivided into animals that developed hyperthyroidism and those that remained euthyroid. Unexpectedly, splenocytes from mice immunized once, as well as splenocytes from hyperthyroid and euthyroid mice (three injections), all produced interferon-gamma in response to the same three synthetic peptides (amino acid residues 52-71, 67-86 and 157-176). These peptides were also the major epitopes recognized by TSHR-DNA plasmid vaccinated mice. We observed lesser responses to a wide range of additional peptides in mice injected three times with TSHR-adenovirus, but the pattern was more consistent with increased background 'noise' than with spreading from primary epitopes to dominant secondary epitopes. In conclusion, these data suggest that factors other than particular TSHR T cell epitopes (such as adenovirus-induced expression of conformationally intact TSHR protein), contribute to the generation of thyroid stimulating antibodies with consequent hyperthyroidism in TSHR-adenovirus immunized mice.

Eye muscle antibodies in Graves' ophthalmopathy: pathogenic or secondary epiphenomenon?

The extra ocular (eye) muscles are one of the principal tissues involved in the autoimmune-mediated inflammation of Graves' ophthalmopathy (GO). Several eye muscle proteins are targeted by autoantibodies or sensitized T lymphocytes, or both, and include: G2s, which is now identified as the terminal 141 amino acids of the winged-helix transcription factor FOXP1, the flavoprotein (Fp) subunit of the mitochondrial enzyme succinate dehydrogenase, the so-called "64kDa protein", a non-tissue specific membrane protein called 1D and the calcium binding protein calsequestrin. Of these, antibodies against G2s and Fp are the most sensitive markers of eye muscle damage in patients with thyroid autoimmunity even though neither antigen is specific to eye muscle and neither antibody is specific to GO. However, the recent finding that the calsequestrin gene is 4.7 times more expressed in eye muscles than other skeletal muscles suggests that we should reconsider the possible role of anti-calsequestrin autoantibodies in ophthalmopathy. GO may comprise two main subtypes with different pathogenetic mechanisms, namely ocular myopathy in which eye muscle inflammation predominates and congestive ophthalmopathy where inflammatory changes occur in the periorbital connective tissues in the absence of eye muscle dysfunction. Anti-G2s and anti-Fp antibodies are closely associated with the ocular myopathy subtype of GO while antibodies targeting type XIII collagen, the only member of the collagen family to have a transmembrane domain, are closely linked to congestive ophthalmopathy. Since both G2s and Fp are intracellular antigens it is unlikely that either antibody causes eye muscle fiber damage in GO, although a role in the later stages of the disease when the fiber has released its cellular contents has not been excluded. Eye muscle antibodies that are cytotoxic to eye muscle cells in antibody-dependent cell-mediated cytotoxicity (ADCC) are more likely to play a role in eye muscle fiber damage since they target a putative eye muscle cell membrane antigen, the identity of which is currently being investigated. While anti-G2s and anti-Fp antibodies are probably secondary to an underlying reaction, such as cytotoxic T lymphocyte targeting of an eye muscle membrane antigen that has yet to be identified, they are reliable markers of immunologically mediated eye muscle fiber damage in patients with Graves' hyperthyroidism. In conclusion, while a pathogenic role for eye muscle antibodies has not been excluded, they are most likely secondary to cytotoxic T cell reactions in GO and, as such, good markers of this autoimmune disease.

Thyrotrophin receptor-specific memory T cell responses require normal B cells in a murine model of Graves' disease

The role of B cells as antigen-presenting cells is being recognized increasingly in immune responses to infections and autoimmunity. We compared T cell responses in wild-type and B cell-deficient mice immunized with the thyrotrophin receptor (TSHR), the major autoantigen in Graves' disease. Three B cell-deficient mouse strains were studied: JHD (no B cells), mIgM (membrane-bound monoclonal IgM+ B cells) and (m + s)IgM (membrane-bound and secreted monoclonal IgM). Wild-type and B cell-deficient mice (BALB/c background) were studied 8 weeks after three injections of TSHR or control adenovirus. Only wild-type mice developed IgG class TSHR antibodies and hyperthyroidism. After challenge with TSHR antigen, splenocyte cultures were tested for cytokine production. Splenocytes from TSHR adenovirus injected wild-type and mIgM-mice, but not from JHD- or (m + s)IgM- mice, produced interferon (IFN)-gamma in response to TSHR protein. Concanavalin A and pokeweed mitogen induced comparable IFN-gamma secretion in all groups of mice except in the JHD strain in which responses were reduced. The absence in (m + s)IgM mice and presence in mIgM mice of an anamnestic response to TSHR antigen was unrelated to lymphoid cell types. Surprisingly, although TSHR-specific antibodies were undetectable, low levels of serum IgG were present in mIgM- but not (m + s)IgM mice. Moreover, IFN-gamma production by antigen-stimulated splenocytes correlated with IgG levels. In conclusion, T cell responses to TSHR antigen developed only in mice with IgG-secreting B cells. Consequently, in the TSHR-adenovirus model of Graves' disease, some normal B cells appear to be required for the development of memory T cells.

Graves' hyperthyroidism and thyroiditis in HLA-DRB1*0301 (DR3) transgenic mice after immunization with thyrotropin receptor DNA

Familial and twin studies in Caucasians have established that the MHC class II allele HLA-DRB1*0301 (DR3) is a strong susceptibility gene in Graves' hyperthyroid disease (GD). To determine if a DR3 transgene could help establish an animal model for GD, we expressed DR3 molecules in class II-knockout NOD mice (H2Ag7-). DR3+g7- mice were given cardiotoxin prior to immunization on weeks 0, 3 and 6 with plasmid DNA encoding human thyrotropin receptor (TSHR). Two groups of mice were also coimmunized with plasmid DNA for IL-4 or GM-CSF. Serial bleeds on weeks 8, 11 and 14 showed that approximately 20% of mice produced thyroid-stimulating antibodies (Abs), and approximately 25% had elevated T4 levels. In particular, a subset displayed both signs of hyperthyroidism, resulting in approximately 30% with some aspect of GD syndrome. Additional mice had thyroid-stimulating blocking Abs and/or TSH-binding inhibitory immunoglobulins, while most mice showed strong labelling of TSHR+ cells by flow cytometry. Interestingly, lymphocytic infiltration with thyroid damage and Abs to mouse thyroglobulin were also noted. Vector controls were uniformly negative. Thus, DR3 transgenic mice can serve as a model for GD, similar to our earlier reports that this allele is permissive for the Hashimoto's thyroiditis model induced with human thyroglobulin.

Low-dose immunization with adenovirus expressing the thyroid-stimulating hormone receptor A-subunit deviates the antibody response toward that of autoantibodies in human Graves' disease

Immunization with adenovirus expressing the TSH receptor (TSHR) induces hyperthyroidism in 25-50% of mice. Even more effective is immunization with a TSHR A-subunit adenovirus (65-84% hyperthyroidism). Nevertheless, TSHR antibody characteristics in these mice do not mimic accurately those of autoantibodies in typical Graves' patients, with a marked TSH-blocking antibody response. We hypothesized that this suboptimal antibody response was consequent to the standard dose of TSHR-adenovirus providing too great an immune stimulus. To test this hypothesis, we compared BALB/c mice immunized with the usual number (10(11)) and with far fewer viral particles (10(9) and 10(7)). Regardless of viral dose, hyperthyroidism developed in a similar proportion (68-80%) of mice. We then examined the qualitative nature of TSHR antibodies in each group. Sera from all mice had TSH binding-inhibitory (TBI) activity after the second immunization, with TBI values in proportion to the viral dose. After the third injection, all groups had near-maximal TBI values. Remarkably, in confirmation of our hypothesis, immunization with progressively lower viral doses generated TSHR antibodies approaching the characteristics of autoantibodies in human Graves' disease as follows: 1) lower TSHR antibody titers on ELISA and 2) lower TSH-blocking antibody activity without decrease in thyroid-stimulating antibody activity. In summary, low-dose immunization with adenovirus expressing the free TSHR A-subunit provides an induced animal model with a high prevalence of hyperthyroidism as well as TSHR antibodies more closely resembling autoantibodies in Graves' disease.

Current perspective on the pathogenesis of Graves' disease and ophthalmopathy

Graves' disease (GD) is a very common autoimmune disorder of the thyroid in which stimulatory antibodies bind to the thyrotropin receptor and activate glandular function, resulting in hyperthyroidism. In addition, some patients with GD develop localized manifestations including ophthalmopathy (GO) and dermopathy. Since the cloning of the receptor cDNA, significant progress has been made in understanding the structure-function relationship of the receptor, which has been discussed in a number of earlier reviews. In this paper, we have focused our discussion on studies related to the molecular mechanisms of the disease pathogenesis and the development of animal models for GD. It has become apparent that multiple factors contribute to the etiology of GD, including host genetic as well as environmental factors. Studies in experimental animals indicate that GD is a slowly progressing disease that involves activation and recruitment of thyrotropin receptor-specific T and B cells. This activation eventually results in the production of stimulatory antibodies that can cause hyperthyroidism. Similarly, significant new insights have been gained in our understanding of GO that occurs in a subset of patients with GD. As in GD, both environmental and genetic factors play important roles in the development of GO. Although a number of putative ocular autoantigens have been identified, their role in the pathogenesis of GO awaits confirmation. Extensive analyses of orbital tissues obtained from patients with GO have provided a clearer understanding of the roles of T and B cells, cytokines and chemokines, and various ocular tissues including ocular muscles and fibroblasts. Equally impressive is the progress made in understanding why connective tissues of the orbit and the skin in GO are singled out for activation and undergo extensive remodeling. Results to date indicate that fibroblasts can act as sentinel cells and initiate lymphocyte recruitment and tissue remodeling. Moreover, these fibroblasts can be readily activated by Ig in the sera of patients with GD, suggesting a central role for them in the pathogenesis. Collectively, recent studies have led to a better understanding of the pathogenesis of GD and GO and have opened up potential new avenues for developing novel treatments for GD and GO.

Thyrotropin receptor-DNA vaccination of transgenic mice expressing HLA-DR3 or HLA-DQ6b

Graves' disease in Caucasians is associated with the major histocompatibility (MHC) antigen HLA-DR3. One approach to studying the role of susceptibility genes involves the use of mice that lack murine MHC and instead express human HLA antigens. Although Graves' disease does not arise spontaneously in animals, thyrotropin receptor (TSHR) antibodies can be induced in mice by vaccination with TSHR-DNA in a plasmid. In the present study, we characterized TSHR antibodies and thyroiditis developing in HLA-DR3 transgenic mice vaccinated with TSHR-DNA. As controls, we used mice transgenic for HLA-DQ6b, an MHC antigen rarely associated with Graves' disease. We observed that approximately 30% of DR3-, but none of DQ6b-transgenic mice, developed TSHR antibodies detectable by enzyme-linked immunosorbent assay (ELISA). The cysteine-rich amino terminal peptide was the dominant linear antibody epitope in DR3 mice, as in other strains vaccinated with TSHR-DNA. Sera from some vaccinated DR3 mice were positive on flow cytometry using intact cells expressing the TSHR, demonstrating recognition of the native TSHR on the cell surface. Although none of the these mice had thyroid stimulating antibodies or were hyperthyroid, a few developed lymphocytic infiltration of the thyroid. These data, together with information for other mouse strains, demonstrate that MHC (human and murine) and non-MHC genes contribute to the outcome of TSHR-DNA vaccination and indicate the potential value of DR3 transgenic mice for dissecting immune responses to the TSHR.

The thyrotropin receptor autoantigen in Graves disease is the culprit as well as the victim

Graves disease, a common organ-specific autoimmune disease affecting humans, differs from all other autoimmune diseases in being associated with target organ hyperfunction rather than organ damage. Clinical thyrotoxicosis is directly caused by autoantibodies that activate the thyrotropin receptor (TSHR). The etiology of Graves disease is multifactorial, with nongenetic factors playing an important role. Of the latter, there is the intriguing possibility that the molecular structure of the target antigen contributes to the development of thyroid-stimulatory autoantibodies (TSAb's). Among the glycoprotein hormone receptors, only the TSHR undergoes intramolecular cleavage into disulfide-linked subunits with consequent shedding of some of the extracellular, autoantibody-binding A subunits. Functional autoantibodies do not arise to the noncleaving glycoprotein hormone receptors. Recently, TSAb's were found to preferentially recognize shed, rather than attached, A subunits. Here we use a new adenovirus-mediated animal model of Graves disease to show that goiter and hyperthyroidism occur to a much greater extent when the adenovirus expresses the free A subunit as opposed to a genetically modified TSHR that cleaves minimally into subunits. These data show that shed A subunits induce or amplify the immune response leading to hyperthyroidism and provide new insight into the etiology of Graves disease.

Insight into antibody responses induced by plasmid or adenoviral vectors encoding thyroid peroxidase, a major thyroid autoantigen

Plasmid and adenoviral vectors have been used to generate antibodies in mice that resemble human autoantibodies to the thyrotrophin receptor. No such studies, however, have been performed for thyroid peroxidase (TPO), the major autoantigen in human thyroiditis. We constructed plasmid and adenovirus vectors for in vivo expression of TPO. BALB/c mice were immunized directly by intramuscular injection of TPO-plasmid or TPO-adenovirus, as well as by subcutaneous injection of dendritic cells (DC) infected previously with TPO-adenovirus. Intramuscular TPO-adenovirus induced the highest, and TPO-plasmid the lowest, TPO antibody titres. Mice injected with TPO-transfected DC developed intermediate levels. Antibodies generated by all three approaches had similar affinities (Kd approximately 10(-9)M) and recognized TPO expressed on the cell-surface. Their epitopes were analysed in competition assays using monoclonal human autoantibodies that define the TPO immunodominant region (IDR) recognized by patients with thyroid autoimmune disease. Surprisingly, high titre antibodies generated using adenovirus interacted with diverse TPO epitopes largely outside the IDR, whereas low titre antibodies induced by DNA-plasmid recognized restricted epitopes in the IDR. This inverse relationship between antibody titre and restriction to the IDR is likely to be due to epitope spreading following strong antigenic stimulation provided by the adenovirus vector. However, TPO antibody epitope spreading does not occur in Hashimoto's thyroiditis, despite high autoantibody levels. Consequently, these data support the concept that in human thyroid autoimmunity, factors besides titre must play a role in shaping an autoantibody epitopic profile.

Prevention of autoantibody-mediated Graves'-like hyperthyroidism in mice with IL-4, a Th2 cytokine

Graves' hyperthyroidism has long been considered to be a Th2-type autoimmune disease because it is directly mediated by autoantibodies against the thyrotropin receptor (TSHR). However, several lines of evidence have recently challenged this concept. The present study evaluated the Th1/Th2 paradigm in Graves' disease using a recently established murine model involving injection of adenovirus expressing the TSHR (AdCMVTSHR). Coinjection with adenovirus expressing IL-4 (AdRGDCMVIL-4) decreased the ratio of Th1/Th2-type anti-TSHR Ab subclasses (IgG2a/IgG1) and suppressed the production of IFN-gamma by splenocytes in response to TSHR Ag. Importantly, immune deviation toward Th2 was accompanied by significant inhibition of thyroid-stimulating Ab production and reduction in hyperthyroidism. However, in a therapeutic setting, injection of AdRGDCMVIL-4 alone or in combination with AdCMVTSHR into hyperthyroid mice had no beneficial effect. In contrast, coinjection of adenoviruses expressing IL-12 and the TSHR promoted the differentiation of Th1-type anti-TSHR immune responses as demonstrated by augmented Ag-specific IFN-gamma secretion from splenocytes without changing disease incidence. Coinjection of adenoviral vectors expressing IL-4 or IL-12 had no effect on the titers of anti-TSHR Abs determined by ELISA or thyroid-stimulating hormone-binding inhibiting Ig assays, suggesting that Ab quality, not quantity, is responsible for disease induction. Our observations demonstrate the critical role of Th1 immune responses in a murine model of Graves' hyperthyroidism. These data may raise a cautionary note for therapeutic strategies aimed at reversing Th2-mediated autoimmune responses in Graves' disease in humans.

A major role for non-major histocompatibility complex genes but not for microorganisms in a novel murine model of Graves' hyperthyroidism

The etiology of Graves' disease is multifactorial. We investigated the role of genetic and environmental factors on the susceptibility to Graves' hyperthyroidism using a new murine model. Intramuscular injection of recombinant adenovirus expressing the thyrotropin receptor (AdCMVTSHR) induces Graves'-like hyperthyroidism (thyrotropin receptor [TSHR] antibodies, elevated thyroxine, and diffuse goiter) in more than 50% of female BALB/c mice. The relative contributions of major histocompatibility complex (MHC) and non-MHC genes on the susceptibility to hyperthyroidism were studied by immunizing BALB/c (H-2d), BALB.K (H-2k), and DBA/2J (H-2d) mice with AdCMVTSHR. Hyperthyroidism developed in approximately 50% of BALB/c and BALB.K mice but only 5% of DBA/2J mice, indicating a major role for non-MHC genes in disease development. The effect of environmental microorganisms was evaluated by comparing disease incidence in BALB/c mice maintained in pathogen-free conditions versus those in nonsterile, conventional housing, as well as by coadministering microorganism components (Escherichia coli lipopolysaccharide or yeast zymosan A) as adjuvants with AdCMVTSHR. Neither type of exposure to environmental pathogens influenced disease induction. In conclusion, non-MHC genes, but not infectious organisms, play a major role in the etiology of this novel murine model of Graves' disease.

Induction of thyroid-stimulating hormone receptor autoimmunity in hamsters

Female Chinese hamsters (n = 10) were immunized with Chinese hamster ovary (CHO) cells that expressed the human TSH receptor (TSHR) to generate a model of Graves' disease. TSHR-autoantibodies (TSHR-Ab) were determined by CHO-TSHR. Two hamsters with stimulating TSHR-Ab showed thyrocyte hypertrophy associated with a focal lymphocytic infiltration. CHO-TSHR were then stimulated with interferon gamma to enhance major histocompatibility complex class II expression. However, after immunization no stimulating TSHR-Ab were detected, but blocking TSHR-Ab were found in three of five animals. The thyroid glands from these hamsters showed marked thinning of thyroid epithelial cells, indicative of early thyroid atrophy consistent with a TSHR blocking antibody, but no lymphocytic infiltration. Lastly, female Armenian hamsters were immunized with an adenovirus construct incorporating wild-type TSHR. High titers of TSHR-Ab were induced effectively, but the thyroid hypertrophy observed was not associated with a lymphocyte infiltration. In summary, we demonstrated that the hamster could serve as a model of TSHR autoimmunity and that an adenoviral vector produced higher levels of TSHR-Ab than more conventional immunization with cells. The data also indicated that the intrathyroidal cellular immunity in this model was not related to TSHR-Ab formation and was an independent reflection of the T-cell immune response to TSHR antigen.

Dendritic cells infected with adenovirus expressing the thyrotrophin receptor induce Graves' hyperthyroidism in BALB/c mice

Dendritic cells (DCs) are the most potent antigen-presenting cells and a prerequisite for the initiation of primary immune response. This study was performed to investigate the contribution of DCs to the initiation of Graves' hyperthyroidism, an organ-specific autoimmune disease in which the thyrotrophin receptor (TSHR) is the major autoantigen. DCs were prepared from bone marrow precursor cells of BALB/c mice by culturing with granulocyte macrophage-colony stimulating factor and interleukin-4. Subcutaneous injections of DCs infected with recombinant adenovirus expressing the TSHR (but not beta-galactosidase) in syngeneic female mice induced Graves'-like hyperthyroidism (8 and 35% of mice after two and three injections, respectively) characterized by stimulating TSHR antibodies, elevated serum thyroxine levels and diffuse hyperplasitc goiter. TSHR antibodies determined by ELISA were of both IgG1 (Th2-type) and IgG2a (Th1-type) subclasses, and splenocytes from immunized mice secreted interferon-gamma (a Th1 cytokine), not interleukin-4 (a Th2 cytokine), in response to TSHR antigen. Surprisingly, IFN-gamma secretion, and induction of antibodies and disease were almost completely suppressed by co-administration of alum/pertussis toxin, a Th2-dominant adjuvant, whereas polyriboinosinic polyribocytidylic acid, a Th1-inducer, enhanced splenocyte secretion of IFN-gamma without changing disease incidence. These observations demonstrate that DCs efficiently present the TSHR to naive T cells to induce TSHR antibodies and Graves'-like hyperthyroidism in mice. In addition, our results challenge the previous concept of Th2 dominance in Graves' hyperthyroidism and provide support for the role of Th1 immune response in disease pathogenesis.

Contrasting activities of thyrotropin receptor antibodies in experimental models of Graves' disease induced by injection of transfected fibroblasts or deoxyribonucleic acid vaccination

The development of experimental models of autoimmune hyperthyroid Graves' disease has proved a difficult challenge, but recently two novel methods have led to their successful development in mice. We describe our studies on replicating the adjuvant modified, human TSH receptor (TSHR) and major histocompatibility complex class II transfected fibroblast injection system, and the plasmid DNA vaccination method as models resembling the human disorder. The fibroblast injection model in female AKR/N (H-2k) mice led to 70% of the animals developing thyroid-stimulating antibodies and their thyroid glands showed large goiters with histological features of thyroid cell activation characteristic of Graves' glands. Consistent with the clinical homolog, there was no inflammatory cell infiltrate of the thyroid gland. Detailed studies on the anti-TSHR antibodies such as thyroid-stimulating blocking antibody, antibodies to the native TSHR by flow cytometry, and TSH-binding inhibiting Ig showed that they were heterogeneous and did not correlate with disease activity, thus resembling those present in patients with Graves' disease. In contrast, the plasmid DNA vaccination model in female BALB/c (H-2d) mice led to the generation of low levels of anti-TSHR antibodies by flow cytometry, which were undetectable for thyroid-stimulating antibodies, TSH-stimulating blocking antibodies, and TSH-binding inhibiting Ig activity. Moreover, this model too was not accompanied by lymphocytic cell infiltration. The data demonstrate the high incidence of hyperthyroid disease induced in the adjuvant modified, transfected fibroblast model in AKR/N mice to allow pathological mechanisms of disease to be studied.

Generation of a mouse monoclonal TSH receptor antibody with stimulating activity

A Balb/c mouse was subjected to genetic immunization with a cDNA construct encoding the human thyrotropin receptor (TSHr). The immune response of the mouse resulted in the production of immunoglobulins recognizing the TSHr in three different assays: (1) flow immunocytometry (FACS) with CHO cells expressing the receptor; (2) receptor-dependent stimulation of cAMP production in the same cell line; and (3) competition with labeled TSH for binding to the receptor. One thousand hybridomas were generated from the spleen of the mouse and their supernatants were screened. A single monoclonal, IRI-SAb1, scored positive in all three assays and was studied further. It stimulated 13-fold cAMP production in TSHr-expressing CHO cells, with an EC50 in the low nanomolar range. When compared with bovine TSH, IRI-SAb1 behaved as a partial agonist. Contrary to the expectation from the characteristic of autoantibodies of Graves' patients, IRI-SAb1 recognized a linear epitope, which was localized in a segment encompassing the first 281 residues of the receptor.

Thyroid-stimulating monoclonal antibodies

Thyrotropin (TSH) receptor monoclonal antibodies (TSHR mAbs) were obtained from cDNA-immunized NMRI mice. Three mAb immunoglobulin Gs (IgGs) (TSmAbs 1-3) that had distinct V(H )and V(L) region sequences stimulated cyclic adenosine monophosphate (cAMP) production in isolated porcine thyroid cells greater than 10x basal and as little as 20 ng/mL (0.13 nmol/L) of TSmAb 1 IgG caused a 2x basal stimulation. TSmAb 1 and 2 Fab fragments were also effective stimulators and thyroid-stimulating activities of the IgGs and Fabs were confirmed using TSHR transfected Chinese hamster ovary (CHO) cells. The TSmAbs also inhibited (125)I-labeled TSH binding to TSHR-coated tubes by 50% or more at concentrations of 1 microg/mL or less and gave 15%-20% inhibition at 20-50 ng/mL. (125)I-labeled TSmAbs bound to TSHR-coated tubes with high affinity (approximately 10(10) L/mol) and this binding was inhibited by TSHR autoantibodies with both TSH agonist and antagonist activities. Inhibition of labeled TSmAb binding by Graves' sera correlated well with inhibition of TSH binding (r = 0.96; n = 18; p < 0.001 for TSmAb 2). The TSmAbs have considerable potential as (1) new probes for TSHR structure-function studies, (2) reagents for new assays for TSHR autoantibodies, and (3) alternatives to recombinant TSH in various in vivo applications.

A monoclonal thyroid-stimulating antibody

The thyrotropin receptor, also known as the thyroid-stimulating hormone receptor (TSHR), is the primary antigen of Graves disease. Stimulating TSHR antibodies are the cause of thyroid overstimulation and were originally called long-acting thyroid stimulators due to their prolonged action. Here we report the successful cloning and characterization of a monoclonal antibody (MS-1) with TSHR-stimulating activity. The thyroid-stimulating activity of MS-1 was evident at IgG concentrations as low as 20 ng/ml. MS-1 also competed for radiolabeled TSH binding to the native TSHR and was able to compete for TSH-induced stimulation. MS-1 recognized a conformational epitope within the TSHR alpha (or A) subunit but excluding the receptor cleavage region. Using an assay measuring loss of antibody recognition after cleavage we demonstrated that MS-1, in contrast to TSH, was unable to enhance TSHR posttranslational cleavage. Since receptor cleavage is followed by alpha subunit shedding and receptor degradation, the functional half-life of the receptor may be extended. The isolation and characterization of MS-1 provides a novel explanation for the prolonged thyroid stimulation in this disease which may be secondary to the lack of receptor cleavage in addition to the prolonged half-life of IgG itself.

Peptide scanning for thyrotropin receptor T-cell epitopes in mice vaccinated with naked DNA

Vaccinating mice with DNA encoding the thyrotropin receptor (TSHR), the major autoantigen in Graves' disease, induces memory T cells that secrete interferon-gamma (IFN-gamma) in response to TSHR antigen. We used a panel of 29 synthetic TSHR peptides encompassing the ectodomain and three extracellular loops to identify T-cell epitopes after TSHR-DNA vaccination of BALB/c, NOD.H-2h4, and AKR/N mice. These strains were chosen because of their previous use in animal models of thyroid autoimmunity. In initial studies, challenge of splenocytes with TSHR protein induced IFN-gamma and tumor necrosis factor-alpha (TNF-alpha) production in all three strains of mice. BALB/c mice recognized three peptides, all in the TSHR A subunit. These peptides differed from the four peptides recognized by nonobese diabetic (NOD mice NOD H-2h4). Three of the latter were also in the A subunit. The fourth was within the intervening C peptide region excised on TSHR cleavage into A and B subunits. Because of high and erratic responses in AKR/N mice, their TSHR T-cell epitopes could not be determined. In summary, we report that TSHR DNA vaccination of BALB/c and NOD.H-2h4 mice, with different major histocompatibility complex (MHC) class II genes (I-Ad and I-Ak, respectively), recognize restricted, nonoverlapping TSHR T-cell epitopes, nearly all in the TSHR A subunit.

Thyroid-stimulating autoantibodies in Graves disease preferentially recognize the free A subunit, not the thyrotropin holoreceptor

Graves disease is directly caused by thyroid-stimulating autoantibodies (TSAb's) that activate the thyrotropin receptor (TSHR). We observed upon flow cytometry using intact cells that a mouse mAb (3BD10) recognized the TSHR ectodomain with a glycosidylphosphatidylinositol (ECD-GPI) anchor approximately tenfold better than the same ectodomain on the wild-type TSHR, despite the far higher level of expression of the latter. The 3BD10 epitope contains the N-terminal cysteine cluster critical for TSAb action. Consequently, we hypothesized and confirmed that TSAb (but not thyrotropin-blocking autoantibodies [TBAb's]) also poorly recognize the wild-type TSHR relative to the ECD-GPI. Despite poor recognition by TSAb of the holoreceptor, soluble TSHR A subunits (known to be shed from surface TSHR) fully neutralized autoantibody-binding activity. These data indicate that the epitope(s) for TSAb's, but not for TBAb's, are partially sterically hindered on the holoreceptor by the plasma membrane, the serpentine region of the TSHR, or by TSHR dimerization. However, the TSAb epitope on the soluble A subunit is freely accessible. This observation, as well as other evidence, supports the concept that A subunit shedding either initiates or amplifies the autoimmune response to the TSHR, thereby causing Graves disease in genetically susceptible individuals.