Naked TSH receptor DNA vaccination: A TH1 T cell response in which interferon-gamma production, rather than antibody, dominates the immune response in mice

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

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

Construction and characterization of monoclonal antibodies against the extracellular domain of B-lymphocyte antigen CD20 using DNA immunization method

To date, several new anti-CD20 monoclonal antibodies (mAbs) have been developed for potential efficacies compared with familiar mAb rituximab. Despite the recent advances in development of anti-CD20 mAbs for the treatment of B cell malignancies, the efforts should be continued to develop novel antibodies with improved properties. However, the development of mAbs against CD20 as a multi-transmembrane protein is challenging due to the difficulty of providing a lipid environment that can maintain native epitopes. To overcome this limitation, we describe a simple and efficient DNA immunization strategy for the construction of a novel anti-CD20 mAb with improved anti-tumour properties. Using a DNA immunization strategy that includes intradermal (i.d.) immunization with naked plasmid DNA encoding the CD20 gene, we generated the hybridoma cell line D4, which secretes functional mAbs against an extracellular epitope of CD20. Immunocytochemistry analysis and a cell-based enzyme-linked immunosorbent assay using a Burkitt's lymphoma cell line showed that D4 mAbs are capable of binding to native extracellular epitopes of CD20. Moreover, the binding specificity of D4 mAbs was determined by western blot analysis. Cell proliferation was examined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Apoptosis was detected by the annexin V/propidium iodide staining and dye exclusion assay. The results showed that D4 anti-CD20 mAbs produced by DNA immunization exhibit potent growth inhibitory activity and have superior direct B-cell cytotoxicity compared to rituximab. We propose that antibody-induced apoptosis is one of the mechanisms of cell growth inhibition. Taken together, the data reported here open the path to DNA-based immunization for generating pharmacologically active monoclonal antibodies against CD20. In addition, the data support future in vivo animal testing and subsequent procedures to produce a potential therapeutic mAb.

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

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

Modeling Graves' Orbitopathy in Experimental Graves' Disease

Graves' orbitopathy (GO), also known as thyroid eye disease is an inflammatory disease of the orbital tissue of the eye that arises as a consequence of autoimmune thyroid disease. The central feature of the disease is the production of antibodies to the thyrotropin hormone receptor (TSHR) that modulate the function of the receptor leading to autoimmune hyperthyroidism and GO. Over the years, all viable preclinical models of Graves' disease have been incomplete and singularly failed to progress in the treatment of orbital complications. A new mouse model of GO based upon immunogenic presentation of human TSHR A-subunit plasmid by close field electroporation is shown to lead to induction of prolonged functional antibodies to TSHR resulting in chronic disease with subsequent progression to GO. The stable preclinical GO model exhibited pathologies reminiscent of human disease characterized by orbital remodeling by inflammation and adipogenesis. Inflammatory lesions characterized by CD3+ T cells and macrophages were localized in the orbital muscle tissue. This was accompanied by extensive adipogenesis of orbital fat in some immune animals. Surprisingly, other signs of orbital involvement were reminiscent of eyelid inflammation involving chemosis, with dilated and congested orbital blood vessels. More recently, the model is replicated in the author's independent laboratories. The pre-clinical model will provide the basis to study the pathogenic and regulatory roles of immune T and B cells and their subpopulations to understand the initiation, pathophysiology, and progression of GO.

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.

Breaking tolerance in transgenic mice expressing the human TSH receptor A-subunit: thyroiditis, epitope spreading and adjuvant as a 'double edged sword'

Transgenic mice with the human thyrotropin-receptor (TSHR) A-subunit targeted to the thyroid are tolerant of the transgene. In transgenics that express low A-subunit levels (Lo-expressors), regulatory T cell (Treg) depletion using anti-CD25 before immunization with adenovirus encoding the A-subunit (A-sub-Ad) breaks tolerance, inducing extensive thyroid lymphocytic infiltration, thyroid damage and antibody spreading to other thyroid proteins. In contrast, no thyroiditis develops in Hi-expressor transgenics or wild-type mice. Our present goal was to determine if thyroiditis could be induced in Hi-expressor transgenics using a more potent immunization protocol: Treg depletion, priming with Complete Freund's Adjuvant (CFA) + A-subunit protein and further Treg depletions before two boosts with A-sub-Ad. As controls, anti-CD25 treated Hi- and Lo-expressors and wild-type mice were primed with CFA+ mouse thyroglobulin (Tg) or CFA alone before A-sub-Ad boosting. Thyroiditis developed after CFA+A-subunit protein or Tg and A-sub-Ad boosting in Lo-expressor transgenics but Hi- expressors (and wild-type mice) were resistant to thyroiditis induction. Importantly, in Lo-expressors, thyroiditis was associated with the development of antibodies to the mouse TSHR downstream of the A-subunit. Unexpectedly, we observed that the effect of bacterial products on the immune system is a “double-edged sword”. On the one hand, priming with CFA (mycobacteria emulsified in oil) plus A-subunit protein broke tolerance to the A-subunit in Hi-expressor transgenics leading to high TSHR antibody levels. On the other hand, prior treatment with CFA in the absence of A-subunit protein inhibited responses to subsequent immunization with A-sub-Ad. Consequently, adjuvant activity arising in vivo after bacterial infections combined with a protein autoantigen can break self-tolerance but in the absence of the autoantigen, adjuvant activity can inhibit the induction of immunity to autoantigens (like the TSHR) displaying strong self-tolerance.

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.

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.

Animal Models of Graves' Hyperthyroidism

An animal model of Graves' disease (GD) will help us to clearly understand the role of thyroid-stimulating hormone receptor (TSHR)-specific T cells and TSHR-Abs during the development of GD and to develop TSHR-specific immunotherapy. This review focuses on four different recent approaches towards the development of an animal model of GD. These approaches are: (1) Immunization of AKR/N mice with fibroblasts coexpressing syngeneic major histocompatibility complex (MHC) class II and TSHR. (2) Immunization of selected strains of mice with an expression vector containing TSHR cDNA. (3) Immunization of BALB/c mice with syngeneic M12 cells or xenogenic HEK-293 cells expressing full-length or extracellular domain of TSHR (ETSHR). (4) Injection of adenovirus-expressing TSHR into BALB/c mice.

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.

Role of the transgenic human thyrotropin receptor A-subunit in thyroiditis induced by A-subunit immunization and regulatory T cell depletion

Transgenic BALB/c mice that express intrathyroidal human thyroid stimulating hormone receptor (TSHR) A-subunit, unlike wild-type (WT) littermates, develop thyroid lymphocytic infiltration and spreading to other thyroid autoantigens after T regulatory cell (T(reg)) depletion and immunization with human thyrotropin receptor (hTSHR) adenovirus. To determine if this process involves intramolecular epitope spreading, we studied antibody and T cell recognition of TSHR ectodomain peptides (A-Z). In transgenic and WT mice, regardless of T(reg) depletion, TSHR antibodies bound predominantly to N-terminal peptide A and much less to a few downstream peptides. After T(reg) depletion, splenocytes from WT mice responded to peptides C, D and J (all in the A-subunit), but transgenic splenocytes recognized only peptide D. Because CD4(+) T cells are critical for thyroid lymphocytic infiltration, amino acid sequences of these peptides were examined for in silico binding to BALB/c major histocompatibility complex class II (IA-d). High affinity subsequences (inhibitory concentration of 50% < 50 nm) are present in peptides C and D (not J) of the hTSHR and mouse TSHR equivalents. These data probably explain why transgenic splenocytes do not recognize peptide J. Mouse TSHR mRNA levels are comparable in transgenic and WT thyroids, but only transgenics have human A-subunit mRNA. Transgenic mice can present mouse TSHR and human A-subunit-derived peptides. However, WT mice can present only mouse TSHR, and two to four amino acid species differences may preclude recognition by CD4+ T cells activated by hTSHR-adenovirus. Overall, thyroid lymphocytic infiltration in the transgenic mice is unrelated to epitopic spreading but involves human A-subunit peptides for recognition by T cells activated using the hTSHR.

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.

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.

Insight into Graves' hyperthyroidism from animal models

Graves' hyperthyroidism can be induced in mice or hamsters by novel approaches, namely injecting cells expressing the TSH receptor (TSHR) or vaccination with TSHR-DNA in plasmid or adenoviral vectors. These models provide unique insight into several aspects of Graves' disease: 1) manipulating immunity toward Th1 or Th2 cytokines enhances or suppresses hyperthyroidism in different models, perhaps reflecting human disease heterogeneity; 2) the role of TSHR cleavage and A subunit shedding in immunity leading to thyroid-stimulating antibodies (TSAbs); and 3) epitope spreading away from TSAbs and toward TSH-blocking antibodies in association with increased TSHR antibody titers (as in rare hypothyroid patients). Major developments from the models include the isolation of high-affinity monoclonal TSAbs and analysis of antigen presentation, T cells, and immune tolerance to the TSHR. Studies of inbred mouse strains emphasize the contribution of non-MHC vs. MHC genes, as in humans, supporting the relevance of the models to human disease. Moreover, other findings suggest that the development of Graves' disease is affected by environmental factors, including infectious pathogens, regardless of modifications in the Th1/Th2 balance. Finally, developing immunospecific forms of therapy for Graves' disease will require painstaking dissection of immune recognition and responses to the TSHR.

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.

"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.

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.

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.

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.

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.

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.

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.

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.