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

HLA transgenic mice: application in reproducing idiosyncratic drug toxicity

Various types of transgenic mice carrying either class I or II human leukocyte antigen (HLA) molecules are readily available, and reports describing their use in a variety of studies have been published for more than 30 years. Examples of their use include the discovery of HLA-specific antigens against viral infection as well as the reproduction of HLA-mediated autoimmune diseases for the development of therapeutic strategies. Recently, HLA transgenic mice have been used to reproduce HLA-mediated idiosyncratic drug toxicity (IDT), a rare and unpredictable adverse drug reaction that can result in death. For example, abacavir-induced IDT has successfully been reproduced in HLA-B*57:01 transgenic mice. Several reports using HLA transgenic mice for IDT have proven the utility of this concept for the evaluation of IDT using various HLA allele combinations and drugs. It has become apparent that such models may be a valuable tool to investigate the mechanisms underlying HLA-mediated IDT. This review summarizes the latest findings in the area of HLA transgenic mouse models and discusses the current challenges that must be overcome to maximize the potential of this unique animal model.

New approaches for predicting T cell-mediated drug reactions: A role for inducible and potentially preventable autoimmunity

Adverse drug reactions (ADRs) are commonplace and occur when a drug binds to its intended pharmacologic target (type A ADR) or an unintended target (type B ADR). Immunologically mediated type B ADRs, such as drug hypersensitivity syndrome, drug reaction with eosinophilia and systemic symptoms syndrome, and Stevens-Johnson syndrome/toxic epidermal necrolysis, can be severe and result in a diverse set of clinical manifestations that include fever and rash, as well as multiple organ failure (liver, kidney, lungs, and/or heart) in the case of drug hypersensitivity syndrome. There is increasing evidence that specific HLA alleles influence the risk of drug reactions. Several features of T cell-mediated ADRs are strikingly similar to those displayed by patients with autoimmune diseases like type I diabetes, such as strong HLA association, organ-specific adaptive immune responses, viral involvement, and activation of innate immunity. There is a need to better predict patient populations at risk for immunologically mediated type B ADRs. Because methods to predict type 1 diabetes by using genetic and immunologic biomarkers have been developed to a high level of accuracy (predicting 100% of subjects likely to progress), new research strategies based on these methods might also improve the ability to predict drug hypersensitivity.

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.

cDNA immunization of mice with human thyroglobulin generates both humoral and T cell responses: a novel model of thyroid autoimmunity

Thyroglobulin (Tg) represents one of the largest known self-antigens involved in autoimmunity. Numerous studies have implicated it in triggering and perpetuating the autoimmune response in autoimmune thyroid diseases (AITD). Indeed, traditional models of autoimmune thyroid disease, experimental autoimmune thyroiditis (EAT), are generated by immunizing mice with thyroglobulin protein in conjunction with an adjuvant, or by high repeated doses of Tg alone, without adjuvant. These extant models are limited in their experimental flexibility, i.e. the ability to make modifications to the Tg used in immunizations. In this study, we have immunized mice with a plasmid cDNA encoding the full-length human Tg (hTG) protein, in order to generate a model of Hashimoto's thyroiditis which is closer to the human disease and does not require adjuvants to breakdown tolerance. Human thyroglobulin cDNA was injected and subsequently electroporated into skeletal muscle using a square wave generator. Following hTg cDNA immunizations, the mice developed both B and T cell responses to Tg, albeit with no evidence of lymphocytic infiltration of the thyroid. This novel model will afford investigators the means to test various hypotheses which were unavailable with the previous EAT models, specifically the effects of hTg sequence variations on the induction of thyroiditis.

Antibodies to thyroid peroxidase arise spontaneously with age in NOD.H-2h4 mice and appear after thyroglobulin antibodies

Hashimoto's thyroiditis, a common autoimmune disease, is associated with autoantibodies to thyroglobulin (Tg) and thyroid peroxidase (TPO). TPO, unlike abundant and easily purified Tg, is rarely investigated as an autoantigen in animals. We asked whether antibodies (Abs) develop to both TPO and Tg in thyroiditis that is induced (C57BL/6 and DBA/1 mice) or arises spontaneously (NOD.H-2h4 mice). Screening for TPOAbs was performed by flow cytometry using mouse TPO-expressing eukaryotic cells. Sera were also tested for binding to purified mouse Tg and human TPO. The antibody data were compared with the extent of thyroiditis. Immunization with mouse TPO adenovirus broke self-tolerance to this protein in C57BL/6 mice, but thyroiditis was minimal and TgAbs were absent. In DBA/1 mice with extensive granulomatous thyroiditis induced by Tg immunization, TPOAbs were virtually absent despite high levels of TgAbs. In contrast, antibodies to mouse TPO, with minimal cross-reactivity with human TPO, arose spontaneously in older (7-12 months) NOD.H-2h4 mice. Unexpectedly, TgAbs preceded TPOAbs, a time course paralleled in relatives of probands with juvenile Hashimoto's thyroiditis. These findings demonstrate a novel aspect of murine and human thyroid autoimmunity, namely breaking B cell self-tolerance occurs first for Tg and subsequently for TPO.

HLA class II transgenic mice mimic human inflammatory diseases

Population studies have shown that among all the genetic factors linked with autoimmune disease development, MHC class II genes on chromosome 6 accounts for majority of familial clustering in the common autoimmune diseases. Despite the highly polymorphic nature of HLA class II genes, majority of autoimmune diseases are linked to a limited set of class II-DR or -DQ alleles. Thus a more detailed study of these HLA-DR and -DQ alleles were needed to understand their role in genetic predisposition and pathogenesis of autoimmune diseases. Although in vitro studies using class-II restricted CD4 T cells and purified class II molecules have helped us in understanding some aspects of HLA class-II association with disease, it is difficult to study the role of class II genes in vivo because of heterogeneity of human population, complexity of MHC, and strong linkage disequilibrium among different class II genes. To overcome this problem, we pioneered the generation of HLA-class II transgenic mice to study role of these molecule in inflammatory disease. These HLA class II transgenic mice were used to develop novel in vivo disease model for common autoimmune diseases such as rheumatoid arthritis, multiple sclerosis, insulin-dependent diabetes mellitus, myasthenia gravis, celiac disease, autoimmune relapsing polychondritis, autoimmune myocarditis, thyroiditis, uveitis, as well as other inflammatory disease such as allergy, tuberculosis and toxic shock syndrome. As the T-cell repertoire in these humanized HLA transgenic mice are shaped by human class II molecules, they show the same HLA restriction as humans, implicate potential triggering mechanism and autoantigens, and identify similar antigenic epitopes seen in human. This review describes the value of these humanized transgenic mice in deciphering role of HLA class II molecules in immunopathogenesis of inflammatory diseases.

Application of HLA class II transgenic mice to study autoimmune regulation

In the past decade, we participated in the increased use of HLA class II transgenic mice to delineate genetic control in autoimmune diseases. Our studies began with individual class II transgenes to determine permissiveness for experimental autoimmune thyroiditis (EAT), first in resistant strains and then in the absence of endogenous H2 class II molecules. Polymorphism for HLA-DRB1 was observed, as DR3, but not DR2 or DR4, molecules serve as a determinant for EAT induction with either mouse thyroglobulin (mTg) or human thyroglobulin (hTg). This delineation enabled identification of pathogenic Tg peptides, based on DR3-binding motifs. HLA-DQ polymorphism was also detectable; hTg induced moderate EAT in DQ8(+), but not DQ6(+), mice. Coexpressing permissive and nonpermissive alleles, DR3(+) mice showed reduced EAT severity in the presence of DQ8, but not DQ6, DR2, or DR4. Determining the regulatory T cell (Treg) influences showed that Treg depletion increased thyroiditis incidence and severity without altering the major histocompatibility complex-based hierarchy in susceptibility. This increase after Treg depletion can also be observed in NaI-induced thyroiditis in DR3(+) mice, a means to study a major environmental factor in thyroid autoimmunity. DR3(+) mice were also immunized with human thyroid peroxidase cDNA, resulting in thyroiditis and an antibody (Ab) profile resembling patient antibodies (Abs). Similar immunization with human TSH receptor cDNA resulted in thyroid-stimulating Abs and elevated T(4) levels with moderate thyroiditis in some animals, suggesting a potential Graves' disease model that due to thyroid lesions is more complete than other models. Recently, Treg manipulation in cancer immunotherapy trials has triggered various autoimmune disorders. Thus, DR3(+) mice are being used to monitor a known risk factor for autoimmune thyroid disease in attempts to enhance tumor immunity.

Thyroid peroxidase as an autoantigen

Thyroid peroxidase (TPO) evokes high-affinity, IgG-class autoantibodies [TPO autoantibodies (TPOAbs)] and TPO-specific T cells that are markers of thyroid infiltration or implicated in thyroid destruction, respectively. A diverse repertoire of human monoclonal TPOAbs, unparalleled in other autoimmune diseases, provides invaluable probes for investigating antibody epitopes. Human TPOAbs recognize an immunodominant region comprising overlapping A and B domains on conformationally intact TPO. Amino acids recognized by TPOAbs are located in the regions with homology to myeloperoxidase (MPO) and the complement control protein (CCP) but not in the epidermal growth factor (EGF)-like region. T cells recognize epitopes in the MPO-like region but not in the CCP- or EGF-like regions in humans. Monoclonal human TPOAbs modulate processing of TPO protein to provide peptides for some T cells. A human T cell clone expressed transgenically in mice induces lymphocytic infiltration and hypothyroidism. This T cell's epitope is only generated by thyrocyte processing of endogenous TPO. Further, intact TPO expressed in vivo is also required for induction of TPOAbs in mice that resemble human autoantibodies. Overall, some TPO-specific T cells and the majority of autoantibodies in humans develop in response to TPO presented by thyroid cells, rather than to TPO released by damaged thyrocytes.

A radioligand binding assay to measure anti-thyroperoxidase autoantibodies in mice

Autoimmune (Hashimoto's) thyroiditis is a chronic inflammatory disease which affects >3% of the population and shows an increasing prevalence with increasing age. Anti-thyroid autoantibodies, particularly against thyroperoxidase (also known as thyroid peroxidase or TPO), occur commonly in humans with autoimmune thyroid disease, and assays for anti-TPO autoantibodies are used in clinical diagnosis. In contrast anti-TPO autoantibodies have not been observed in classical mouse models of autoimmune thyroiditis, except in cases where mice were deliberately immunized with TPO. In the past, detection of anti-TPO autoantibodies in mice has relied on an indirect immunofluorescence assay (iIFA) which screens for thyroid follicle membrane staining in frozen sections of mouse thyroid glands. Since recent transgenic mouse models of autoimmune thyroiditis spontaneously develop anti-TPO autoantibodies, an assay other than serial dilution and iIFA would be useful to detect and quantify these autoantibodies. In this paper we describe such an assay, based on the capacity of autoimmune mouse sera to bind to the extracellular domain of mouse TPO which was produced in a radioactively labeled form using a coupled in vitro transcription/translation system. The same approach, using human TPO, could provide a highly sensitive method to detect anti-TPO autoantibodies in humans.

HLA-DR3 transgenic mice immunized with adenovirus encoding the thyrotropin receptor: T cell epitopes and functional analysis of the CD40 Graves' polymorphism

The major histocompatibility (MHC) molecule HLA-DR3 is a susceptibility gene for Graves' disease (GD) in Caucasians. Mice lacking murine MHC and expressing human HLA-DR3 develop thyrotropin receptor (TSHR) antibodies and sometimes hyperthyroidism after vaccination with TSHR-DNA. MHC molecules present peptides processed from antigens to T cells. Therefore, we used DR3-transgenic mice to investigate recognition of TSHR ectodomain peptides. After immunization with TSHR A-subunit adenovirus (A-subunit-Ad) but not control-adenovirus (Control-Ad), splenocytes from DR3 mice responded to A-subunit protein in culture by producing interferon-gamma (IFN-gamma). When challenged with 29 overlapping TSHR peptides, splenocytes from A-subunit-Ad- or Control-Ad-immunized mice responded to several peptides. However, in splenocytes from A-subunit-Ad but not Control-Ad mice, a peptide containing TSHR residues 142-161 induced significantly more IFN-gamma than the same splenocytes in medium alone. Immunized DR3 mice also permitted testing the TSHR-specific function of the CD40 single nucleotide polymorphism (C vs. T) associated with GD. Of three human DR3 human Epstein-Barr virus lines (EBVL), two had C in both alleles (CC) and one was CT. However, these EBVL presented peptides poorly and there was no difference between CC vs. CT EBVL in peptide presentation to splenocytes from immunized mice. A peptide corresponding to residues 145-163 is one of seven suggested to be important in GD based on HLA-binding affinities, T-epitope algorithms, and human studies. Consequently, as in human GD, TSHR amino acids 142-161 appear to include a major T cell epitope in HLA-DR3 transgenic mice immunized with A-subunit-Ad.

Antibodies focused on the human autoantibody immunodominant region are induced by B lymphocytes that constitutively express thyroid peroxidase diverted to the major histocompatibility complex II pathway

We addressed the question of why naturally occurring, polyclonal thyroid peroxidase (TPO) autoantibodies have a restricted epitopic repertoire to an immunodominant region (IDR). We hypothesized that immunizing BALB/c mice with major histocompatibililty complex (MHC) class II compatible B lymphocytes (A20 cells) preferentially diverting TPO to the MHC class II pathway would produce TPO antibodies with an epitopic specificity similar to human autoantibodies, namely to the IDR. For this purpose we stably expressed in A20 cells a fusion protein of TPO sandwiched between the signal peptide and transmembrane/cytoplasmic tail of the lysosome- associated membrane protein (LAMP) 1. Expression of LAMP1-TPO in A20 B cells was confirmed by flow cytometry using a TPO monoclonal antibody. Mice injected intraperitoneally with LAMP1-TPO A20 B cells developed TPO antibodies detected by enzyme-linked immunosorbent assay (ELISA), flow cytometry and (125)I-TPO precipitation. However, TPO antibody levels were low. Most important, competition for TPO antibody binding by recombinant human TPO autoantibody Fab indicated that more than 80% of the polyclonal TPO antibodies in the immunized mice were to the human autoantibody IDR. In summary, injecting mice with B lymphocytes that constitutively express TPO diverted to the MHC class II pathway generates antibodies with epitopes similar to those of human TPO autoantibodies, namely to the autoantibody IDR. However, these antibodies are of low titer that is itself associated with this epitopic bias.

Relationship between thyroid peroxidase T cell epitope restriction and antibody recognition of the autoantibody immunodominant region in human leukocyte antigen DR3 transgenic mice

We investigated the relationship between thyroid peroxidase (TPO) antibody and T lymphocyte epitopes in TPO-adenovirus (TPO-Ad) immunized BALB/c mice and mice transgenic for the human class II molecule DR3 associated with human thyroid autoimmunity. TPO autoantibodies are largely restricted to an immunodominant region (IDR). BALB/c mice immunized with fewer (10(7) vs. 10(9)) TPO-Ad particles developed TPO antibodies with lower titers that displayed greater restriction to the IDR. However, as with higher-dose TPO-Ad immunization, T cell epitopes (assessed by splenocyte interferon-gamma response to TPO in vitro) were highly diverse and variable in different animals. In contrast, DR3 mice immunized the higher TPO-Ad dose (10(9) particles) had high TPO antibody levels that showed relative focus on the IDR. Moreover, T cell epitopes recognized by splenocytes from DR3 mice showed greater restriction than BALB/c mice. Antibody affinities for TPO were higher in DR3 than in BALB/c mice. The present study indicates that weak TPO-Ad immunization of BALB/c mice (with consequent low TPO antibody titers) is required for enhanced IDR focus yet is not associated with T cell epitopic restriction. Humanized DR3 transgenic mice, despite stronger TPO-Ad immunization, develop higher titer TPO antibodies that do focus on the autoantibody IDR with T cells that recognize a more limited range of TPO peptides. These data suggest a relationship between major histocompatibility complex class II molecules and the development of antibodies to the IDR, a feature of human thyroid autoimmunity.

Structural and functional aspects of thyroid peroxidase

Thyroperoxidase (TPO) is the enzyme involved in thyroid hormone synthesis. Although many studies have been carried out on TPO since it was first identified as being the thyroid microsomal antigen involved in autoimmune thyroid disease, previous authors have focused more on the immunological than on the biochemical aspects of TPO during the last few years. Here, we review the latest contributions in the field of TPO research and provide a large reference list of original publications. Given this promising background, scientists and clinicians will certainly continue in the future to investigate the mechanisms whereby TPO contributes to hormone synthesis and constitutes an important autoantigen involved in autoimmune thyroid disease, and the circumstances under which the normal physiological function of this enzyme takes on a pathological role.

Pathogenic human thyroglobulin peptides in HLA-DR3 transgenic mouse model of autoimmune thyroiditis

To identify pathogenic epitopes on human thyroglobulin (hTg), a homodimer of 660kDa, we have applied a computer-based algorithm to predict potential HLA-DR3-binding peptides and have tested them in DR3-transgenic mice. Of the 39 peptides selected, four stimulated a proliferative response from hTg-primed cells of DR3+ mice, but not DQ8+ mice. Of the four peptides, one, hTg2079, was consistently pathogenic. Thyroiditis was not only produced by adoptive transfer of hTg-primed, hTg2079-activated cells but also by direct immunization with the peptide. These results demonstrate the utility of using this computer-based algorithm with synthetic peptides to help identify pathogenic T cell epitopes on hTg.