Defining the major antibody epitopes on the human thyrotropin receptor in immunized mice: evidence for intramolecular epitope spreading

Cepharanthine blocks TSH receptor peptide presentation by HLA-DR3: Therapeutic implications to Graves' disease

We have previously identified a signature HLA-DR3 pocket variant, designated HLA-DRβ1-Arg74 that confers a high risk for Graves' Disease (GD). In view of the key role of HLA-DRβ1-Arg74 in triggering GD we hypothesized that thyroid-stimulating hormone receptor (TSHR) peptides that bind to the HLA-DRβ1-Arg74 pocket with high affinity represent key pathogenic TSHR peptides triggering GD, and that blocking their presentation to CD4⁺ T-cells can be used as a novel therapeutic approach in GD. There were several previous attempts to identify the major pathogenic TSHR peptide utilizing different methodologies, however the results were inconsistent and inconclusive. Therefore, the aim of our study was to use TSHR peptide binding affinity to HLA-DRβ1-Arg74 as a method to identify the key pathogenic TSHR peptides that trigger GD. Using virtual screening and ELISA and cellular binding assays we identified 2 TSHR peptides that bound with high affinity to HLA-DRβ1-Arg74 - TSHR.132 and TSHR.197. Peptide immunization studies in humanized DR3 mice showed that only TSHR.132, but not TSHR.197, induced autoreactive T-cell proliferation and cytokine responses. Next, we induced experimental autoimmune Graves' disease (EAGD) in a novel BALB/c-DR3 humanized mouse model we created and confirmed TSHR.132 as a major DRβ1-Arg74 binding peptide triggering GD in our mouse model. Furthermore, we demonstrated that Cepharanthine, a compound we have previously identified as DRβ1-Arg74 blocker, could block the presentation and T-cell responses to TSHR.132 in the EAGD model.

The Most N-Terminal Region of THSD7A Is the Predominant Target for Autoimmunity in THSD7A-Associated Membranous Nephropathy

Background Thrombospondin type 1 domain-containing 7A (THSD7A) has been identified as a pathogenic autoantigen in membranous nephropathy (MN). However, the THSD7A epitopes targeted by patient autoantibodies are unknown.Methods We performed an in silico analysis of the THSD7A multidomain structure, expressed the folded domains in HEK293 cells, and tested for domain reactivity with 31 serum samples from patients with THSD7A-associated MN using Western and native blotting. Immunogenicity of the antigen domains was further investigated by cDNA immunization of rabbits and mice.Results We characterized the extracellular topology of THSD7A as a tandem string of 21 thrombospondin type 1 domains. Overall, 28 serum samples (90%) recognized multiple epitope domains along the molecule. Detailed epitope mapping revealed that the complex consisting of the first and second N-terminal domains (amino acids 48-192) was recognized by 27 of 31 patient serum samples (87%). Serum recognizing one or two epitope domains showed lower anti-THSD7A antibody levels than serum recognizing three or more epitope domains. During follow-up, a loss of epitope recognition was observed in seven of 16 patients, and it was accompanied by decreasing antibody levels and remission of proteinuria. In four of 16 patients, epitope recognition patterns changed during follow-up. Notably, immunization experiments in rabbits and mice revealed that induced antibodies, like patient autoantibodies, preferentially bound to the most N-terminal domains of THSD7A.Conclusions Our data show that the immune response in THSD7A-associated MN is polyreactive and that autoantibodies predominantly target the most N-terminal part of THSD7A.

Thyrotropin Receptor Epitope and Human Leukocyte Antigen in Graves' Disease

Graves' disease (GD) is an organ-specific autoimmune disease, and thyrotropin (TSH) receptor (TSHR) is a major autoantigen in this condition. Since the extracellular domain of human TSHR (TSHR-ECD) is shed into the circulation, TSHR-ECD is a preferentially immunogenic portion of TSHR. Both genetic factors and environmental factors contribute to development of GD. Inheritance of human leukocyte antigen (HLA) genes, especially HLA-DR3, is associated with GD. TSHR-ECD protein is endocytosed into antigen-presenting cells (APCs), and processed to TSHR-ECD peptides. These peptide epitopes bind to HLA-class II molecules, and subsequently the complex of HLA-class II and TSHR-ECD epitope is presented to CD4+ T cells. The activated CD4+ T cells secrete cytokines/chemokines that stimulate B-cells to produce TSAb, and in turn hyperthyroidism occurs. Numerous studies have been done to identify T- and B-cell epitopes in TSHR-ECD, including (1) in silico, (2) in vitro, (3) in vivo, and (4) clinical experiments. Murine models of GD and HLA-transgenic mice have played a pivotal role in elucidating the immunological mechanisms. To date, linear or conformational epitopes of TSHR-ECD, as well as the molecular structure of the epitope-binding groove in HLA-DR, were reported to be related to the pathogenesis in GD. Dysfunction of central tolerance in the thymus, or in peripheral tolerance, such as regulatory T cells, could allow development of GD. Novel treatments using TSHR antagonists or mutated TSHR peptides have been reported to be effective. We review and update the role of immunogenic TSHR epitopes and HLA in GD, and offer perspectives on TSHR epitope specific treatments.

B cell epitope spreading: mechanisms and contribution to autoimmune diseases. Immunol Lett. 2015;163:56-68. [PMID: 25445494 DOI: 10.1016/j.imlet.2014.11.001]

While a variety of factors act to trigger or initiate autoimmune diseases, the process of epitope spreading is an important contributor in their development. Epitope spreading is a diversification of the epitopes recognized by the immune system. This process happens to both T and B cells, with this review focusing on B cells. Such spreading can progress among multiple epitopes on a single antigen, or from one antigenic molecule to another. Systemic lupus erythematosus, multiple sclerosis, pemphigus, bullous pemphigoid and other autoimmune diseases, are all influenced by intermolecular and intramolecular B cell epitope spreading. Endocytic processing, antigen presentation, and somatic hypermutation act as molecular mechanisms that assist in driving epitope spreading and broadening the immune response in autoimmune diseases. The purpose of this review is to summarize our current understanding of B cell epitope spreading with regard to autoimmunity, how it contributes during the progression of various autoimmune diseases, and treatment options available.

Innate immune activation and thyroid autoimmunity

CONTEXT

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

EVIDENCE ACQUISITION

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

EVIDENCE SYNTHESIS

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

CONCLUSION

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

Heritability of levels of autoantibodies to thyroid antigens using the method of plotting regression of offspring on midparent (ROMP)

Only a few methods can be applied in a simple manner to estimate the genetic control of autoimmunity in humans. Here we examined the heritability of autoantibodies to two thyroid antigens; thyroglobulin (Tg) and thyroperoxidase (TPO, formerly known as thyroid microsomal antigen), using methods of regression of offspring on mid-parental values (ROMP). With the data sets available, affected and unaffected siblings were compared by this rapid screening method using results determined by hemagglutination (HA). The presence of both types of autoantibodies showed positive heritability in patients with Graves' thyrotoxicosis (TT), but it was not observed in chronic lymphocytic or Hashimoto's thyroiditis (CLT) patients. Since these assays have been extensively used over the years by most diagnostic and research laboratories, they should provide some insight as to which quantifiable parameters may be usefully accumulated to help select groups of patients and their families for further genetic study. ROMP may also be useful to determine the sequential appearance of different types of antibody in predicting disease onset in other family members, and in distinguishing maternal and paternal effects on imprinting. The method may be extended to study epitope spreading and other measures of disease progression.

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.

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.

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.

Evidence for intramolecular B-cell epitope spreading during experimental immunization with an immunogenic thyroglobulin peptide

Thyroglobulin (Tg) is a target autoantigen in autoimmune thyroid diseases, such as Graves' disease (GD) and Hashimoto's thyroiditis. In a previous study we identified three 20mer Tg peptides bearing epitopes of autoantibodies associated with GD (TgP15, TgP26 and TgP41: sequences 2339-2358, 2471-2490 and 2651-2670 of human Tg, respectively). In the present study, we investigated the antigenicity of the above peptides in experimental immunization with Tg, the immunogenicity of antigenic peptides and the possibility of intramolecular B-cell epitope spreading during peptide immunization. For this purpose, two rabbits were injected with human Tg in CFA six times, every three weeks. Two control animals were injected only with CFA. Testing of antisera and of affinity-purified antibodies, by ELISA against the three peptides, revealed reactivity only to TgP41. This synthetic peptide was subsequently administered to two rabbits, in its free form (100 micro g in CFA six times, every two weeks). A strong serological response was developed not only against TgP41, but also to intact human and rabbit Tg. Immunization with TgP41 induced intramolecular B-cell epitope spreading, i.e. production of antibodies to sites on Tg other than that corresponding to TgP41, as revealed by immunoadsorption and competitive ELISA. Histopathological studies did not reveal any infiltration in thyroid glands. We conclude that peptide TgP41 encompasses not only an epitope of disease-associated autoantibodies, but also a dominant immunogenic epitope of experimentally induced Tg-specific antibodies, able to drive B-cell epitope spreading.

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.

Graves' disease: a host defense mechanism gone awry

In this report we summarize evidence to support a model for the development of Graves' disease. The model suggests that Graves' disease is initiated by an insult to the thyrocyte in an individual with a normal immune system. The insult, infectious or otherwise, causes double strand DNA or RNA to enter the cytoplasm of the cell. This causes abnormal expression of major histocompatibility (MHC) class I as a dominant feature, but also aberrant expression of MHC class II, as well as changes in genes or gene products needed for the thyrocyte to become an antigen presenting cell (APC). These include increased expression of proteasome processing proteins (LMP2), transporters of antigen peptides (TAP), invariant chain (Ii), HLA-DM, and the co-stimulatory molecule, B7, as well as STAT and NF-kappaB activation. A critical factor in these changes is the loss of normal negative regulation of MHC class I, class II, and thyrotropin receptor (TSHR) gene expression, which is necessary to maintain self-tolerance during the normal changes in gene expression involved in hormonally-increased growth and function of the cell. Self-tolerance to the TSHR is maintained in normals because there is a population of CD8- cells which normally suppresses a population of CD4+ cells that can interact with the TSHR if thyrocytes become APCs. This is a host self-defense mechanism that we hypothesize leads to autoimmune disease in persons, for example, with a specific viral infection, a genetic predisposition, or even, possibly, a TSHR polymorphism. The model is suggested to be important to explain the development of other autoimmune diseases including systemic lupus or diabetes.

A novel mouse model of Graves' disease: implications for a role of aberrant MHC class II expression in its pathogenesis

Mice immunized with fibroblasts expressing an MHC class II molecule and human thyrotropin receptor (TSHR), but not either alone, develop major features characteristic of Graves' disease (GD), such as thyroid-stimulating autoantibodies directed against TSHR, increased serum thyroid hormone levels, and enlarged thyroid glands. The results indicate the need for the simultaneous expression of a class II molecule and the TSHR on the surface of the fibroblasts to develop stimulating anti-TSHR antibodies and full-blown GD in our model. A T cell line established from a mouse with hyperthyroidism proliferates in response to fibroblasts expressing a class II molecule and TSHR, but not to the fibroblasts expressing only TSHR, indicating that the class II molecules on the fibroblasts present TSHR-derived peptide(s) to T cells. These results strongly suggest that the acquisition of antigen-presenting ability by thyrocytes can lead to the induction or progression of GD. We identified a T cell epitope of TSHR by the proliferative response of spleen cells from mice immunized with fibroblasts expressing a class II molecule and TSHR to 80 overlapping peptides spanning the extracellular domain of human TSHR. The identification of a major T cell epitope provides an important clue to a novel therapy of GD.

Limitations of the semisynthetic library approach for obtaining human monoclonal autoantibodies to the thyrotropin receptor of Graves' disease

Graves' disease (GD) is characterized by the presence of autoantibodies against the TSH-receptor (TSH-R) which are pathogenic and, upon binding to the receptor, trigger intracellular signal transduction. The autoantibodies are oligoclonal and as they are responsible for disease activity, their characterization would lead to a better understanding of the development of GD. Attempts to isolate anti-TSH-R antibodies from patients have proved to be difficult due to the exceedingly low serum levels due to rarity of these B cells, together with difficulties in obtaining purified TSH-R capable of interacting with patients autoantibodies. We employed phage antibody display technology and performed selection with a previously characterized semisynthetic antibody library on the purified extracellular ectodomain of the TSH-R. We report the isolation of six different anti-TSH-R monoclonal phage antibodies (moPhabs) from this library. All the moPhabs recognized TSH-R and its recombinant fragments by Western blotting, but failed to recognize the native TSH-R by flow cytometry. Consequently, the moPhabs did not lead to TSH-R activation. As these were the first moPhabs to TSH-R, they were analysed in terms of nucleotide and amino acid sequence and epitope specificity on the receptor. The moPhabs used immunoglobulin VH1 and VH3 germ line genes, all associated with Vlambda3 genes. Interestingly, the CDR3 regions of all moPhabs were remarkably similar, though not identical. In light of the common CDR3 usage, the epitopes recognized on TSH-R appeared to be restricted to amino acids residues 405-411 and 357-364. In summary, our results show that semisynthetic libraries may be limited in isolating human monoclonal antibodies that resemble pathogenic antithyrotropin receptor autoantibodies present in patients with GD. It is likely that until preparations of purified TSH-R that can be recognized by patients autoantibodies become available, similar to the recently described glycosylphosphatidylinositol (GPI) anchored TSH-R ectodomain, monoclonal antibodies from phage antibody display to TSH-R will be limited for isolating the rare, pathogenic antibodies of GD.

Comparison of immune responses to extracellular domains of mouse and human thyrotropin receptor

The mouse and human thyrotropin receptors show greater than 87% homology in their amino acid sequences. However, glycosylated extracellular domains of mouse (mET-gp) and human (hET-gp) thyrotropin receptors showed differences in their ability to react with patient autoantibodies to thyrotropin receptor (TSHR). To test for potential differences in their immunogenicity, we immunized BALB/c mice with either gel pure non-glycosylated ectodomain of human TSHR (ETSHR II), or hET-gp (hET-gp III), or mET-gp (mET-gp III). Alternatively, mice were primed with gel pure hET-gp or mET-gp and subsequently immunized with insect cells expressing hET-gp (hET-gp II) or mET-gp (mET-gp II) respectively. All groups of mice immunized with TSHR developed high titers of antibodies against the respective immunogens. As shown earlier, sera obtained from mice immunized with ETSHR showed strong reactivity to peptide 1 (aa 22-41) and weak reactivity to peptides 23 (aa 352-371), 24 (aa 367-386), 25 (aa 382-401), and 26 (aa 397-415). Mice immunized with hET-gp or mET-gp showed comparable titers to peptides 1 and 23 and lower reactivity to other peptides. Mice immunized with hET-gp showed higher TBII reactivity (52.2%) compared to mice immunized with either ETSHR (20.9%) or mET-gp (34.5%). Peptides from the C-terminal region of ETSHR could neutralize the TBII activities of sera from mice immunized with ETSHR or hET-gp but not mET-gp. Compared to corresponding control mice, T4 levels in mET-gp II mice were only marginally higher. These data suggested that outcome of immunization with mouse ETSHR is comparable to that seen after immunization with human ETSHR.

Glycosylated ectodomain of the human thyrotropin receptor induces antibodies capable of reacting with multiple blocking antibody epitopes

Recently, we showed that the glycosylated ectodomain of the human thyrotropin receptor (hET-gp) reacts with autoantibodies from autoimmune thyroid disease (AITD) patients' sera. To better understand the effects of glycosylation of thyrotropin receptor (TSHR) in antibody induction, we immunized rabbits with hET-gp protein. The rabbits developed relatively high titers of antibodies with highly potent TSH binding inhibitory immunoglobulin (TBII) and thyroid stimulatory blocking antibody (TSBAb) activities. Both the hET-gp and a nonglycosylated ectodomain of the human TSHR (hETSHR) protein significantly reversed the TBII as well as TSBAb activity. Based on the ability of synthetic peptides to significantly reverse the functional activity of these rabbit antisera, we identified three discrete regions of the TSH R, represented by amino acids 202-221, 292-311 and 367-386, as TBII epitopes and four regions represented by amino acids 352-371, 367-386, 382-401 and 392-415 as TSBAb epitopes. These data demonstrate that rabbit antibodies that bind to amino acids 367-386 mediate their TSBAb activity by inhibiting the binding of TSH to TSHR; whereas, antibodies to regions 352-415, excluding aa 367-386, exert their TSBAb activity by affecting a step subsequent to TSH binding. Coincident with the elevation of TBII and TSBAb activity, serum total T4 levels declined and thus suggested that the antibodies exerted functional effects on thyroid in vivo. Together, these data demonstrate that glycosylated hET-gp protein is a more potent immunogen and it can induce a broader antibody response directed against multiple TBII and TSBAb epitopes.

Regulation and transfer of a murine model of thyrotropin receptor antibody mediated Graves' disease

In order to replicate a recently described murine model of Graves' disease, we immunized AKR/N (H-2k) mice i.p., every 2 weeks, with either a clone of fibroblasts expressing both the human TSH receptor (hTSHR) and murine major histocompatibility complex (MHC) class II molecules or with fibroblasts expressing the MHC class II molecules alone. Mice were bled, and their thyroid hormone levels measured, at 6, 12, and up to 18 weeks after the first immunization. Between 11-12 weeks after immunization, a significant number of mice began to die spontaneously and were found to have developed large goiters. Thirty to 40% of mice immunized with hTSHR transfected fibroblasts showed markedly increased serum T3 and T4 hormone levels by 12 weeks compared with controls, with the highest thyroid hormone levels being T3: 420 ng/dl (normal < 70) and T4: 16.5 microg/dl (normal < 5). The murine serum demonstrated the presence of antibodies to the TSHR, as evidenced by inhibition of labeled TSH binding to the hTSHR, and these sera had in vitro thyroid stimulating activity. Many of the hyperthyroid mouse exhibited weight loss and hyperactivity and, on examination, their thyroids had the histological features of thyroid hyperactivity including thyroid enlargement, thyroid cell hypertrophy, and colloid droplet formation--all consistent with Graves' disease. In contrast, a small number of mice (< 5%) developed hypothyroidism with low serum T4 levels and markedly increased TSH concentrations and evidence of thyroid hypoplasia. Both hyperthyroidism and hypothyroidism were successfully transferred to naive mice using ip cells of immunized mice. Surprisingly, hypothyroidism occurred in many recipient mice even after transfer from hyperthyroid donors. These results confirmed that immunization with naturally expressed hTSHR in mammalian cells was able to induce functional TSHR autoantibodies that either stimulated or blocked the mouse thyroid gland and induced hyperthyroidism or thyroid failure. Furthermore, both blocking and stimulating antibodies coexisted in the same mice as evidenced so clearly by the transfer of hypothyroidism from hyperthyroid mice. The addition of a Th2 adjuvant (pertussis toxin) caused approximately 50% of the animals to become hyperthyroid beginning early at 9 weeks, whereas a Th1 adjuvant (CFA) delayed the disease onset such that only 10% were hyperthyroid by 12 weeks. As with human autoimmune thyroid disease, the T cell control of this murine model may be critical and requires more extensive investigation.

Expansion of helper T-cell recognition in mice immunized with a synthetic peptide corresponding to the C-terminal thyrotropin receptor-specific insert

We previously reported that immunization with a synthetic peptide of human thyrotropin receptor (TSH-R) expanded humoral autoimmunity to TSH-R (Sugawa H, Ueda Y, Ueda M, Kosugi S, Ichiyama S, Mori T. Immunization with the 'immunogenic Peptide' of TSH receptor induces oligoclonal antibodies with various biological activities. Peptide 1998;19:1303-7.). In the present study, we examined this phenomenon at the T-cell level. Balb/c mice were immunized with a synthetic peptide corresponding to the C-terminal-specific insert of human TSH-R. Spleen cells were collected and subjected to antigen-specific ELISPOT assay. The number of interleukin 4-secreting cells specific to P354-367 increased within 3 weeks. Cells responding to the other peptides increased 7 weeks after immunization. This phenomenon was not observed in mice immunized with bovine serum albumin alone. During immunization, numbers of interferon-gamma-secreting lymphocytes were not changed significantly. These results indicated that immunization with C-terminal TSH-R-specific insert peptide causes fluctuation in the type 2 helper T-cell population but not type 1 Th cells against the TSH-R, and the recognition repertoire of type 2 helper T cell was expanded by the peptide.

Characterization of the murine immune response to the murine TSH receptor ectodomain: induction of hypothyroidism and TSH receptor antibodies

The thyrotropin receptor (TSHR) is the major autoantigen of human Graves' disease. In order to define the antigenicity of the TSHR in a defined model, we examined the immune response of BALB/c mice to immunization with a new bioactive, recombinant preparation of the ectodomain of the murine TSHR (mTSHR-ecd). Mice (n = 10) were immunized with 25-50 microg of insect cell expressed, purified and refolded, mTSHR-ecd in alum adjuvant containing pertussis toxin, on days 0, 21, 36, 50 and 70. Control mice received wild-type baculovirus-infected insect cell protein lysate, in a similar way. After 28 days, murine serum contained high titres of antibodies specific to mTSH-ecd and their titres continued to increase over 90 days. Antibody epitope mapping, using 26 peptides spanning the human TSHR-ecd, showed that a variety of regions of the ectodomain were antigenic. The earliest epitope included aa 22-41, but later two regions of reactivity were noted clustered towards the mid portion and carboxyl terminus of the ectodomain. The murine TSHR autoantibodies (TSHR-Abs) inhibited up to 78% of the binding of labelled TSH to native TSHR, demonstrating the presence of antibodies capable of blocking the native TSHR. We showed that these TSHR antibodies acted, in vitro, as TSH blocking antibodies, inhibiting TSH-induced generation of cyclic AMP in chinese hamster ovary (CHO) cells transfected with the hTSHR. Hence, the antibody response to mTSHR-ecd was potentially antagonistic in its influence on the TSHR. Assessment of thyroid function in the immunized mice showed a fall in serum total T3 by 90 days and markedly elevated murine TSH levels (from 64.0 to 239.6 ng/ml), confirming the onset of thyroid failure. However, thyroid histology remained grossly normal. These data demonstrate that mTSHR-ecd is a potent antigen with three major immunogenic regions. The induced mTSHR-Abs blocked TSH action in vivo and reduced murine thyroid function.

Induction of thyroiditis in mice with thyrotropin receptor lacking serologically dominant regions

Grave's disease (GD) is characterized by pathogenic autoantibodies to the human thyrotropin receptor (hTSH-R), and is frequently associated with a lymphocytic infiltrate of the thyroid gland. In attempts to establish a murine model of GD, we and others have previously shown that immunization of mice with recombinant preparations of the hTSH-R ectodomain induces high titres of specific antibodies, which, however, are not pathogenic, nor is the response accompanied by the development of thyroiditis. Since earlier reports identified the serological immunodominant determinants within the N- and C-terminal regions of hTSH-R ectodomain, we reasoned that immunization of mice with truncated fragments of ectodomain lacking these dominant regions might result in skewing of the response to other determinants of the molecule, with consequent induction of immunopathological features present in GD. We show here that multiple challenge of BALB/c mice with an amino acid fragment of residues 43-282 generates antibodies directed at hTSH-R peptides 37-56, 157-176, 217-236 and 232-251. This reactivity pattern is distinct from that induced previously with the whole ectodomain of hTSH-R in BALB/c animals. Thyroid function remained unaffected in these mice, suggesting that pathogenic antibodies were not being induced. Interestingly, some animals developed lymphocytic infiltration of the thyroid gland, clearly indicating the presence of pathogenic T cell determinants within the 43-282 fragment. Challenge with the related fragment 43-316 produced the same pattern of serological response to the synthetic peptides as fragment 43 282, but was not accompanied by thyroiditis. The results demonstrate: (i) the presence of thyroiditogenic determinants within hTSH-R, and (ii) that these pathogenic determinants are likely to be cryptic, as their effect is exhibited only when the hierarchy of immunodominance within hTSH-R is drastically altered.

Characterisation of the antibody response to the extracellular region of recombinant thyrotropin receptor

Autoantibodies to the human thyrotropin receptor (TSH-R) are pathogenic in a number of autoimmune thyroid diseases including Graves' disease. We have characterised polyclonal antisera to TSH-R for antibodies which may mimic those present in autoimmune thyroid disease. For immunisations, recombinant extracellular region of human TSH-R which does not interact with its ligand TSH was used. The induced antibodies react with the full length membrane receptor in transfected mammalian cells by flow cytometry showing the presence of antibody capable of recognising the native functional receptor. The properties of the generated antibodies have been compared after two injections or following a multiple immunisation protocol with the receptor in adjuvant. High titre antisera were readily generated after the short injection protocol and further immunisations did not lead to any change in antibody titers. Analysis of the epitopes recognised using synthetic peptides confirmed previous observations that the immunodominant determinants localise to the amino and the carboxyl terminal part of the extracellular region of the receptor. Antisera from both rabbits contain TSH blocking antibody as assessed by inhibition of TSH mediated cAMP stimulation. There was an increase in TSH binding inhibitory immunoglobulin (TBII) activity with multiple injections. Furthermore, the increase in TBII activity was not related to spreading of the antibody response to new determinants on TSH-R. Our results support previous observations on the difficulties in reproducing, by adjuvant immunisation with recombinant TSH-R preparations, the fine specificity of antibodies to TSH-R present in autoimmune disorders such as Graves' disease or primary myxoedema.

The formation of thyrotropin receptor (TSHR) antibodies in a Graves' animal model requires the N-terminal segment of the TSHR extracellular domain

Immunization of AKR/N mice with murine fibroblasts, transfected with the TSH receptor (TSHR) and a murine major histocompatibility complex class II molecule having the same H-2k haplotype (but not either alone), induces immune thyroid disease with the humoral and histological features of human Graves', including the presence of two different TSHR antibodies (TSHRAbs): stimulating TSHRAbs, which cause hyperthyroidism; and TSH-binding-inhibiting immunoglobulins. The primary functional epitope for both types of antibodies in Graves' patients is on the N-terminal portion of the extracellular domain of the TSHR, residues 25 to 165; most require residues 90-165 to express TSHRAb activity, as evidenced in studies using chimeras of the TSHR and lutropin-choriogonadotropin receptor (LH-CGR). To evaluate the role of this region of the TSHR in the formation of Graves' TSHRAbs, we immunized AKR/N mice with fibroblasts transfected with three human TSHR chimeras with residues 9-165 (Mc1+2), 90-165 (Mc2), or 261-370 (Mc4) substituted by equivalent residues of the rat LH-CGR. Mice immunized with the Mc1+2 and Mc2 chimeras, with the N-terminal portion of the extracellular domain of the TSHR substituted by LH-CGR residues, did not develop TSHRAbs. Mice immunized with the Mc4 chimera, having a major portion of the C-terminal portion of the extracellular domain of the TSHR replaced by comparable LH-CGR residues, can develop TSHRAbs. The results suggest that the N-terminal segment of the TSHR extracellular domain is not only a critical functional epitope for Graves' TSHRAbs, but it is important also in their formation in a mouse model of Graves' disease.

Genetic Immunization Against the Human Thyrotropin Receptor Causes Thyroiditis and Allows Production of Monoclonal Antibodies Recognizing the Native Receptor

The generation of Abs recognizing the native structure of the human thyrotropin receptor (hTSHR) has been difficult because there is currently no method allowing the purification of correctly folded Ag in the amounts required by classical immunization protocols. The majority of Abs made against the hTSHR react preferentially with denatured molecules. We report that a humoral response against the native hTSHR, compatible with mAb production, is elicited in mice by immunization with a DNA construct encoding the receptor. BALB/c mice were inoculated in the anterior tibialis muscle with 100 μg of plasmid DNA harboring the hTSHR cDNA. Eleven weeks after the first injection, 10 mice of 14 showed by FACS analysis a strong IgG response against the hTSHR expressed at the surface of Chinese hamster ovary cells. A clear TSH-binding inhibiting Ig and thyrotropin-blocking Ab activity (competition with TSH binding and TSH activity, respectively) was demonstrated in the majority of sera tested. One serum exhibited a clear stimulating activity. Despite the maintenance of normal circulating free T4 levels in all mice, these bioactivities persisted until 18 wk, in which mice were sacrificed, their thyroids were examined histologically, and spleens from two animals were used for mAb production. All mice displayed a severe lymphocytic infiltration of their thyroids, composed mostly of activated B cells. Three mAbs were produced against conformational epitopes of the hTSHR. We conclude that genetic immunization is an efficient method of generating Abs recognizing the native structure of the hTSHR and a new way of inducing thyroiditis in mice murine.

Regulation of major histocompatibility class II gene expression in FRTL-5 thyrocytes: opposite effects of interferon and methimazole

Aberrant expression of major histocompatibility complex (MHC) class II antigens is associated with autoimmune thyroid disease; aberrant expression duplicating the autoimmune state can be induced by interferon-gamma (IFNgamma). We have studied IFNgamma-induced human leukocyte antigen (HLA)-DR alpha gene expression in rat FRTL-5 thyroid cells to identify the elements and factors important for aberrant expression. Using an HLA-DR alpha 5'-flanking region construct from -176 to +45 bp coupled to the chloramphenicol acetyltransferase reporter gene, we show that there is no basal class II gene expression in FRTL-5 thyroid cells, that IFNgamma can induce expression, and, as is the case for antigen-presenting cells from the immune system, that IFNgamma-induced expression requires several highly conserved elements on the 5'-flanking region, which, from 5' to 3', are the S, X1, X2, and Y boxes. Methimazole (MMI), a drug used to treat patients with Graves' disease and experimental thyroiditis in rats or mice, can suppress the IFNgamma-induced increase in HLA-DR alpha gene expression as a function of time and concentration; MMI simultaneously decreases IFNgamma-induced endogenous antigen presentation by the cell. Using gel shift assays and the HLA-DR alpha 5'-flanking region from -176 or -137 to +45 bp as radiolabeled probes, we observed the formation of a major protein-DNA complex with extracts from FRTL-5 cells untreated with IFNgamma, termed the basal or constitutive complex, and formation of an additional complex with a slightly faster mobility in extracts from cells treated with IFNgamma. MMI treatment of cells prevents IFNgamma from increasing the formation of this faster migrating complex. Formation of both complexes is specific, as evidenced in competition studies with unlabeled fragments between -137 and -38 bp from the start of transcription; nevertheless, they can be distinguished in such studies. Thus, high concentrations of double stranded oligonucleotides containing the sequence of the Y box, but not S, X1, or X2 box sequences, can prevent formation of the IFNgamma-increased faster migrating complex, but not the basal complex. Both complexes involve multiple proteins and can be distinguished by differences in their protein composition. Thus, using specific antisera, we show that two cAMP response element-binding proteins, activating transcription factor-1 and/or -2, are dominant proteins in the upper or basal complex. The upper or basal complex also includes c-Fos, Fra-2, Ets-2, and Oct-1. A dominant protein that distinguishes the IFNgamma-increased lower complex is CREB-binding protein (CBP), a coactivator of cAMP response element-binding proteins. We, therefore, show that aberrant expression of MHC class II in thyrocytes, induced by IFNgamma, is associated with the induction or increased formation of a novel protein-DNA complex and that its formation as well as aberrant class II expression are suppressed by MMI, a drug used to treat human and experimental autoimmune thyroid disease. Its component proteins differ from those in a major, basal, or constitutive protein-DNA complex formed with the class II 5'-flanking region in cells that are not treated with IFNgamma and that do not express the class II gene.

Immunization with the "immunogenic peptide" of TSH receptor induces oligoclonal antibodies with various biological activities

Balb/c mice were immunized with a synthetic peptide (P354-14) corresponding to "the immunogenic peptide" of human thyrotropin receptor (hTSH-R). Through screening for binding to the peptide, we obtained several monoclonal antibodies with various biological activities: thyroid stimulation (SAb), inhibition of TSH stimulation (BAb) and no significant effect on cAMP production. One of the stimulatory clones was further studied. This clone enhanced cAMP production in Cos-7 cells transformed with the truncated TSH-R cDNA deleting the immunogenic peptide. These results indicated that the immunogenic peptide of the TSH-R induces oligoclonal anti-TSH-R antibodies, although the region is not essential for the functional epitope.

Thyroid iodide transporter: local sequence homologies with thyroid autoantigens

Here we show the existence of local amino acid (aa) sequence homologies between rat thyroid iodide transporter (Na+/l- symporter or NIS), whose gene was recently cloned, and known human thyroid autoantigens [thyroglobulin (Tg), thyroid peroxidase (TPO) and thyrotropin receptor (TSHR)] NIS sequences corresponding to the fourth (aa 264-282) and fifth extracellular loop (aa 386-414) are 15 to 40% identical and 30 to 60% similar to sequences corresponding to known or putative epitopes of Tg, TPO and TSHR. The sixth extracellular loop (aa 465-485) beared homology (44% identity, 52% similarity) only to a region of Tg which flanks one of its immunodominant domains. Sequences of thyroid autoantigens other than NIS shared homology, especially Tg and TPO. We conclude that in all likelihood NIS is an additional thyroid antigen, which shares common epitopes with the other thyroid autoantigens. Addendum: A study in abstract form appeared after submission of our paper finds experimental evidence for the antigenicity of two extracellular segments (aa 262-280 and 468-487) and of a portion of the intracellular C-terminus (aa 560-579).

Changes in epitopes for thyroid-stimulating antibodies in Graves' disease sera during treatment of hyperthyroidism: therapeutic implications

To determine whether there are changes in epitope recognition by stimulating TSH receptor antibodies (TSHRAbs) during treatment of hyperthyroidism and to evaluate the clinical relevance of such changes, we serially measured the activity of IgG preparations from 39 patients with Graves' disease over an 8-month period. To measure epitope changes of the stimulating TSHRAbs, we used Chinese hamster ovary (CHO) cells transfected with wild-type human TSHR (hTSHR) or TSHR chimeras with residues 90-165 (Mc2) substituted by equivalent residues of the rat LH/CG receptor. When initially examined, 37 of the 39 patients had significant stimulating TSHRAb activity measured with wild-type CHO-hTSHR cells. Serial measurements of stimulating TSHRAb activity in Mc2 chimera-transfected cells divided the 39 patients into three distinct groups. Thus, 10 patients (heterogeneous epitope group) exhibited low but significant activity in Mc2 chimera assays at the start of the study; 10 patients who were initially negative in Mc2 chimera assays remained negative (persistently homogeneous epitope group); and 19 patients who were initially negative in Mc2 chimera assays became transiently or persistently positive during treatment, despite a simultaneous decrease in TSHRAb activity measured with wild-type TSHR (changing epitope group). The functional stimulating TSHRAb epitope thus changed from residues 90-165 to residues outside this region in the last group, which comprises nearly two-thirds of the initially Mc2-negative patients (19 of 29) and one-half of all patients (19 of 39). Patients in the changing epitope group responded more quickly and to lower doses of methimazole than patients in the persistently homogeneous epitope group, behaving in this respect exactly as the patients in the heterogeneous epitope group. Additionally, although the decrease in stimulating TSHRAb activities during the 8-month treatment period was similar in the two groups, the thyrotropin binding inhibitor immunoglobulin (TBII) activities decreased more rapidly in patients in the persistently homogeneous epitope group than in patients in the changing epitope group (P < 0.05). There were no differences in initial stimulating TSHRAb or TBII activities, degree of hyperthyroidism, goiter size, or prior duration of symptoms between the persistently homogeneous epitope group and changing epitope group. In summation, we show that the epitopes of stimulating TSHRAbs in Graves' disease patients may change during their clinical course or treatment period, and that the change is from antibodies recognizing N-terminal TSHR residues 90-165 to antibodies recognizing other regions of the TSHR. We also show that the development of stimulating TSHRAbs with this heterogeneous epitope or their presence at the initial screening for disease activity seems to be associated with increased responsiveness to antithyroid drug therapy. We suggest, therefore, that Mc2 chimera assays may be useful to predict the response of patients to antithyroid drug therapy.

Characteristic epitope recognition pattern of autoantibodies against eukaryotic ribosomal protein L7 in systemic autoimmune diseases

OBJECTIVE

To define the epitope-recognition pattern and the fine specificity of the autoantibody response to protein L7 in patients with rheumatic diseases.

METHODS

The epitope-recognition pattern was studied by enzyme-linked immunosorbent assay utilizing overlapping fragments of L7. The fine specificity was examined by binding inhibition and isoelectric focusing.

RESULTS

We observed a disease-specific epitope-recognition pattern of anti-L7 autoantibodies. There was one immunodominant epitope that was recognized by all anti-L7-positive sera from patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and systemic sclerosis (SSc). Additional recognition of minor epitopes was observed; it arises by intramolecular epitope spreading and was correlated with disease activity in SLE patients. SSc patients differed from SLE and RA patients in that their sera did not recognize certain minor epitopes. The major epitope was recognized by high-affinity autoantibodies of limited heterogeneity. Minor epitopes were recognized by heterogeneous low-affinity autoantibodies.

CONCLUSION

The anti-L7 autoantibody response is oligoclonal. Additional B cell clones are activated by antigen during active phases of disease.

Folding-dependent binding of thyrotropin (TSH) and TSH receptor autoantibodies to the murine TSH receptor ectodomain

The mouse TSH receptor ectodomain (mTSHR-ecd) was amplified from murine thyroid complementary DNA and ligated into the pAcGP67B insect cell vector, and the nucleotide sequence was confirmed. Employing a baculovirus-insect cell system, the mTSHR-ecd (amino acids 22-415) was expressed as a fusion protein with the gp67 insect cell signal sequence at the NH2-terminus and a C-terminal six-histidine tag. Protein expression was assessed by Western blot using a murine monoclonal antibody (recognizing amino acids 22-35) and a rabbit antipeptide antibody (recognizing amino acids 397-415). These antibodies detected two principal species of mTSHR-ecd, one glycosylated (66 kDa) and one nonglycosylated (52 kDa), in cell lysates of infected insect cells. More than 10% of these species were present in a water-soluble (cytosolic) fraction. This fraction was then used to purify, under native conditions, 100-microg amounts of mTSHR-ecd using nickel-nitrilo-triacetic (Ni-NTA) resin chromatography. The purified cytosolic mTSHR-ecd migrated as a homogeneous 66-kDa band visible on Coomassie blue-stained gels and was confirmed by Western blotting. We also purified the mTSHR-ecd from total cell lysates under denaturing conditions, followed by "in vitro" refolding on the Ni-NTA column. Under these conditions, milligram amounts of soluble mTSHR-ecd were obtained. This material consisted primarily of the 66-kDa glycosylated form, but in addition contained four or five lower molecular mass, partially glycosylated intermediates and the 52-kDa nonglycosylated form. Deglycosylation with either endoglycosidase F or H, reduced all mTSHR-ecd glycosylated species to a 52-kDa nonglycosylated form. Both the cytosolic and refolded mTSHR-ecd preparations inhibited the binding of [125I]TSH to the full-length human TSHR expressed in Chinese hamster ovary cells in a dose-dependent manner, with similar affinities. The affinity of such interactions was 3 orders of magnitude less than observed with native porcine TSHR and was further reduced by unfolding the mTSHR-ecd preparations. The cytosolic and refolded mTSHR-ecd were also recognized by hTSHR autoantibodies in the serum of patients with hyperthyroid Graves' disease. Such autoantibody binding to mTSHR-ecd was also markedly reduced by unfolding the antigen. These results demonstrated the successful production of large quantities of well characterized, biologically active, mTSHR-ecd antigen. In addition, the data showed that although the ectodomain of the mTSHR bound TSH, intact holoreceptor may be required for high affinity ligand binding. Whether the transmembrane region is required for direct ligand binding, as seen for other G protein-linked receptors, or whether it is needed to stabilize the ligand binding to the ectodomain and maintain a correctly folded state, remains unclear.

Thyrotropin receptor autoantibodies in serum are present at much lower levels than thyroid peroxidase autoantibodies: analysis by flow cytometry

Using Chinese hamster ovary (CHO) cells that express high numbers of TSH receptor (TSHR) on their surface, we studied the feasibility of detecting directly by flow cytometry the binding of autoantibodies in patients' sera to the native TSHR. After using a serum (BBI) with high potency in the TSH binding inhibition (TBI) assay to establish the protocol, we studied an additional 38 sera: 10 without TBI activity (1-4.2% inhibition), 10 with moderately high TBI values (17.3-39.4% inhibition), 10 with high TBI levels (52-95.1% inhibition), 4 from normal individuals without autoimmune thyroid disease, and 4 from patients with systemic lupus erythematosus. We observed that a number of sera, including some without thyroid autoantibodies, contain antibodies against unknown antigens on CHO cells. Preadsorption with untransfected CHO cells before addition to the TSHR-10,000 cells eliminated or greatly reduced this nonspecific background. None of the sera from normal individuals, subjects with negative TBI values, or patients with systemic autoimmunity generated a positive signal on flow cytometry with TSHR-10,000 cells relative to the signal on untransfected cells. Remarkably, only 4 of 21 TBI-positive sera (including BBI) unequivocally recognized the TSHR on flow cytometry. In contrast, when thyroid peroxidase (TPO) autoantibodies in the same sera were studied using CHO cells overexpressing TPO on their surface, all 20 sera with TPO autoantibodies clearly elicited positive net fluorescence relative to untransfected cells. Study of the potent serum, BBI, revealed similar fluorescence (approximately 250 U) for TPO autoantibodies and TSHR autoantibodies at dilutions of 1:1000 and 1:10, respectively. Thus, by flow cytometry, the titer of TPO autoantibodies in the BBI serum is about 100-fold higher than that for TSHR autoantibodies in the same serum. In conclusion, the present data provide the strongest support for the idea that TSHR autoantibodies in the sera of patients with autoimmune thyroid disease are present at much lower levels than are TPO autoantibodies. This finding has important implications for the diagnostic detection of TSHR autoantibodies and for understanding the pathogenesis of Graves' disease.

Characterization of soluble, disulfide bond-stabilized, prokaryotically expressed human thyrotropin receptor ectodomain

To study the interaction of TSH receptor (TSHR) autoantibodies with receptor protein; it is necessary first to express the receptor in the proper conformation including the formation of correct disulfide bridges. However, the reducing environment of the Escherichia coli (E. coli) cytoplasm prevents the generation of protein disulfide bonds and limits the solubility and immunoreactivity of recombinant human TSHR (hTSHR) products. To circumvent these limitations, hTSHR complementary DNA encoding the extracellular domain (hTSHR-ecd; amino acids 21-415) was inserted into the vector pGEX-2TK by directional cloning and used to transform the thioredoxin reductase mutant strain of E. coli (Ad494), which allowed formation of disulfide bonds in the cytoplasm. After induction, the expressed soluble hTSHR-ecd fusion protein was detected by Western blot analysis using a monoclonal antibody directed against hTSHR amino acids 21-35. This showed that over 50% of the expressed hTSHR-ecd was soluble in contrast to expression in a wild-type E. coli (strain alpha F'), where the majority of the recombinant receptor was insoluble. The soluble recombinant receptor was affinity purified and characterized. Under nonreducing SDS-PAGE conditions, the soluble hTSHR-ecd migrated as refolded, disulfide bond-stabilized, multimeric species, whose formation was independent of fusion partner protein. This product was found to be biologically active as evidenced by the inhibition of the binding of 125I-TSH to the full-length hTSHR expressed in transfected CHO cells and was used to develop a competitive capture enzyme-linked immunosorbent assay for mapping of hTSHR antibody epitopes. Hence, hTSHR-ecd produced in bacteria with a thioredoxin reductase mutation was found to be highly soluble and biologically relevant.

Induction of Graves-like disease in mice by immunization with fibroblasts transfected with the thyrotropin receptor and a class II molecule

Graves disease is an autoimmune thyroid disease characterized by the presence of antibodies against the thyrotropin receptor (TSHR), which stimulate the thyroid to cause hyperthyroidism and/or goiter. By immunizing mice with fibroblasts transfected with both the human TSHR and a major histocompatibility complex class II molecule, but not by either alone, we have induced immune hyperthyroidism that has the major humoral and histological features of Graves disease: stimulating TSHR antibodies, thyrotropin binding inhibiting immunoglobulins, which are different from the stimulating TSHR antibodies, increased thyroid hormone levels, thyroid enlargement, thyrocyte hypercellularity, and thyrocyte intrusion into the follicular lumen. The results suggest that the aberrant expression of major histocompatibility complex class II molecules on cells that express a native form of the TSHR can result in the induction of functional anti-TSHR antibodies that stimulate the thyroid. They additionally suggest that the acquisition of antigen-presenting ability on a target cell containing the TSHR can activate T and B cells normally present in an animal and induce a disease with the major features of autoimmune Graves.

Influence of adjuvants on the induction of autoantibodies to the thyrotropin receptor

To determine the influence of adjuvant on the induction of antibodies to thyrotropin receptor (TSHR), we immunized BALB/c mice with a extracellular domain of the TSHR (ETSHR) protein in complete Freund's adjuvant (CFA), Titer Max (TM) and Gerbu. Similarly, control groups of mice were immunized with bovine serum albumin (BSA) in each of the different adjuvants. As determined by ELISA, ETSHR given along with CFA elicited high titers of antibodies to ETSHR which were mainly restricted to the IgG1 subclass. Mice immunized with ETSHR in TM also developed high titers of anti-ETSHR antibodies but had higher levels of both IgG1 and IgG2a. However, immunization with ETSHR in Gerbu resulted in low titers of antibodies, restricted to IgG1 subclass. Immunization of mice with BSA in each of the three adjuvants induced higher antibody titers to BSA. The subclass of antibodies in mice immunized with BSA in CFA and TM were predominantly IgG1 and IgG2a with lower levels of IgG2b, whereas in Gerbu treated group, antibody to BSA was restricted to IgG1 subclass. Analysis of specificity of antibodies against ETSHR, in mice immunized with ETSHR, revealed that irrespective of the adjuvant used, the dominant reactivity was against peptide 1 (AA 22-41) with weaker reactivity against several other. peptides. The only exception was in mice immunized with ETSHR in TM which also showed significant reactivity against peptide 23 (AA 352-371). Mice immunized with the ETSHR in CFA or in TM showed elevated levels of serum TSH binding inhibitory immunoglobulins (TBII). However, mice immunized with ETSHR in Gerbu, which had lower titers of antibodies to ETSHR, showed normal TBII levels. These studies showed that adjuvant composition could influence the titer, subclass and fine specificity of antibodies to ETSHR which in turn could affect the development of TBII activity.