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

Autoimmune thyroid disease and type 1 diabetes mellitus: same pathogenesis; new perspective?

Autoimmune thyroid disease (AITD) and type 1 diabetes mellitus (T1DM) are two common autoimmune diseases that can occur concomitantly. In general, patients with diabetes have a high risk of AITD. It has been proposed that a complex genetic basis together with multiple nongenetic factors make a variable contribution to the pathogenesis of T1DM and AITD. In this paper, we summarize current knowledge in the field regarding potential pathogenic factors of T1DM and AITD, including human leukocyte antigen, autoimmune regulator, lymphoid protein tyrosine phosphatase, forkhead box protein P3, cytotoxic T lymphocyte-associated antigen, infection, vitamin D deficiency, and chemokine (C-X-C motif) ligand. These findings offer an insight into future immunotherapy for autoimmune diseases.

Phagocytosis Deficiency of Macrophages in NOD.H-2h4 Mice Accelerates the Severity of Iodine-Induced Autoimmune Thyroiditis

Apoptosis occurs in many autoimmune diseases. Excess iodine induces thyrocyte apoptosis and increases the incidence and prevalence of autoimmune thyroiditis (AIT). However, the sequence of events between the appearance of thyrocyte apoptosis and the occurrence of thyroiditis remains uncharacterized. Furthermore, few studies have investigated the role of macrophage phagocytosis in the development of AIT. Therefore, we evaluated the relationship between apoptosis and inflammatory infiltration in NOD.H-2^h4 mouse thyroids by comparing the sequence of events in tissue samples. We also investigated the role of macrophages by comparing macrophage phagocytosis function in BALB/c, C57BL/6, and NOD.H-2^h4 mice treated with different levels of iodine. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays and thyroid inflammatory scores revealed that apoptosis (2 weeks) occurred before inflammatory infiltration (4 weeks). Phosphatidylserine (PS) expression on the extracellular surface of the cell membrane and double-stranded DNA fragments associated with apoptosis appeared at 2 and 8 weeks, respectively. Additionally, although apoptosis was enhanced in the thyroids of mice supplemented with excess iodine (0.05 ± 0.12 vs 1.63 ± 0.82% for BALB/c, 0.09 ± 0.14 vs 1.51 ± 0.34% for C57BL/6, and 0.07 ± 1.11 vs 4.72 ± 0.62% for NOD.H-2^h4 mice), only NOD.H-2^h4 mouse thyroids presented with inflammation. Furthermore, macrophages from NOD.H-2^h4 mice (44.46 ± 1.79%) exhibited decreased phagocytotic activity relative to that in BALB/c (54.21 ± 4.58%) and C57BL/6 (58.96 ± 4.04%) mice. There were no differences in phagocytosis function between NOD.H-2^h4 mice supplemented with excess iodine or left untreated (24.50 ± 2.66 vs 21.71 ± 1.79%, p = 0.06). In conclusion, deficiencies in the apoptosis clearance of macrophages in NOD.H-2^h4 mice may constitute an early pathogenic mechanism in AIT that is not influenced by iodine intake.

Both positive and negative effects on immune responses by expression of a second class II MHC molecule

It is perplexing why vertebrates express a limited number of major histocompatibility complex (MHC) molecules when theoretically, having a greater repertoire of MHC molecules would increase the number of epitopes presented, thereby enhancing thymic selection and T cell response to pathogens. It is possible that any positive effects would either be neutralized or outweighed by negative selection restricting the T cell repertoire. We hypothesize that the limit on MHC number is due to negative consequences arising from expressing additional MHC. We compared T cell responses between B6 mice (I-A(+)) and B6.E(+) mice (I-A(+), I-E(+)), the latter expressing a second class II MHC molecule, I-E(b), due to a monomorphic Eα(k) transgene that pairs with the endogenous I-Eβ(b) chain. First, the naive T cell Vβ repertoire was altered in B6.E(+) thymi and spleens, potentially mediating different outcomes in T cell reactivity. Although the B6 and B6.E(+) responses to hen egg-white lysozyme (HEL) protein immunization remained similar, other immune models yielded differences. For viral infection, the quality of the T cell response was subtly altered, with diminished production of certain cytokines by B6.E(+) CD4(+) T cells. In alloreactivity, the B6.E(+) T cell response was significantly dampened. Finally, we observed markedly enhanced susceptibility to experimental autoimmune encephalomyelitis (EAE) in B6.E(+) mice. This correlated with decreased percentages of nTreg cells, supporting the concept of Tregs exhibiting differential susceptibility to negative selection. Altogether, our data suggest that expressing an additional class II MHC can produce diverse effects, with more severe autoimmunity providing a compelling explanation for limiting the expression of MHC molecules.

Delineating the autoimmune mechanisms in Graves' disease

The immunologic processes involved in autoimmune thyroid disease (AITD), particularly Graves' disease (GD), are similar to other autoimmune diseases with the emphasis on the antibodies as the most unique aspect. These characteristics include a lymphocytic infiltrate at the target organs, the presence of antigen-reactive T and B cells and antibodies, and the establishment of animal models of GD by antibody transfer or immunization with antigen. Similar to other autoimmune diseases, risk factors for GD include the presence of multiple susceptibility genes, including certain HLA alleles, and the TSHR gene itself. In addition, a variety of known risk factors and precipitators have been characterized including the influence of sex and sex hormones, pregnancy, stress, infection, iodine and other potential environmental factors. The pathogenesis of GD is likely the result of a breakdown in the tolerance mechanisms, both at central and peripheral levels. Different subsets of T and B cells together with their regulatory populations play important roles in the propagation and maintenance of the disease process. Understanding different mechanistic in the complex system biology interplay will help to identify unique factors contributing to the AITD pathogenesis.

Fine epitope mapping within the pathogenic thyroglobulin peptide 2340-2359: minimal epitopes retaining antigenicity across various MHC haplotypes are not necessarily immunogenic

We have previously reported that the 20-mer peptide p2340 (amino acids 2340-2359), of human thyroglobulin (Tg) has the unique feature that it causes experimental autoimmune thyroiditis (EAT) in mouse strains bearing high-responder (HR) or low-responder (LR) MHC haplotypes in Tg-induced EAT. In this study, we have employed fine epitope mapping to examine whether this property of p2340 is the result of recognition of distinct or shared minimal T-cell epitopes in the context of HR or LR MHC class II molecules. Use of overlapping peptides showed that a core minimal 9-mer epitope (LTWVQTHIR, amino acids 2344-2352) was recognized by p2340-primed T cells from both HR (H2(k,s) ) and LR (H2(b,d) ) strains, whereas a second 9-mer epitope (HIRGFGGDP, amino acids 2350-2358) was antigenic only in H2(s) hosts. Truncation analysis of LTWVQTHIR and HIRGFGGDP peptides delineated them as the minimal epitopes recognized by p2340-primed T cells from the above strains. Subcutaneous challenge of all mouse strains with the 9-mer core peptide LTWVQTHIR in adjuvant elicited specific lymph node cell proliferative responses and mild EAT only in HR hosts, highlighting this sequence as a minimal pathogenic Tg peptide in EAT. The 9-mer peptide HIRGFGGDP was not found to be immunogenic in H2(s) hosts. These data demonstrate that minimal T-cell epitopes, defined as autoantigenic in hosts of various MHC haplotypes, are not intrinsically immunogenic. Activation of naive autoreactive T cells may require contributions from flanking residues within longer peptide sequences encompassing these epitopes.

Efficacy of HLA-DRB1∗03:01 and H2E transgenic mouse strains to correlate pathogenic thyroglobulin epitopes for autoimmune thyroiditis

Thyroglobulin (Tg), a homodimer of 660 kD comprising 2748 amino acids, is the largest autoantigen known. The prevalence of autoimmune thyroid disease, including Hashimoto's thyroiditis and Graves' disease, has provided the impetus for identifying pathogenic T cell epitopes from human Tg over two decades. With no known dominant epitopes, the search has long been a challenge for investigators. After identifying HLA-DRB1∗03:01 (HLA-DR3) and H2E(b) as susceptibility alleles for Tg-induced experimental autoimmune thyroiditis in transgenic mouse strains, we searched for naturally processed T cell epitopes with MHC class II-binding motif anchors and tested the selected peptides for pathogenicity in these mice. The thyroiditogenicity of one peptide, hTg2079, was confirmed in DR3 transgenic mice and corroborated in clinical studies. In H2E(b)-expressing transgenic mice, we identified three T cell epitopes from mouse Tg, mTg179, mTg409 and mTg2342, based on homology to epitopes hTg179, hTg410 and hTg2344, respectively, which we and others have found stimulatory or pathogenic in both DR3- and H2E-expressing mice. The high homology among these peptides with shared presentation by DR3, H2E(b) and H2E(k) molecules led us to examine the binding pocket residues of these class II molecules. Their similar binding characteristics help explain the pathogenic capacity of these T cell epitopes. Our approach of using appropriate human and murine MHC class II transgenic mice, combined with the synthesis and testing of potential pathogenic Tg peptides predicted from computational models of MHC-binding motifs, should continue to provide insights into human autoimmune thyroid disease.

Autoimmune thyroiditis: a model uniquely suited to probe regulatory T cell function

Murine experimental autoimmune thyroiditis (EAT) is a model for Hashimoto's thyroiditis that has served as a prototype of T cell-mediated autoimmunity for more than three decades. Key roles for MHC restriction and autoantigen influence on susceptibility to autoimmunity have been demonstrated in EAT. Moreover, it has served a unique role in investigations of self tolerance. In the early 1980s, self tolerance and resistance to EAT induction could be enhanced by increasing circulating levels of the autoantigen, thyroglobulin (Tg), by exogenous addition as well as endogenous release. This observation, directly linking circulating self antigen to self tolerance, led to subsequent investigations of the role of regulatory T cells (Tregs) in self tolerance. These studies revealed that protection against autoimmunity, in both naive and tolerized mice, was mediated by thymically-derived CD4(+)CD25(+)Foxp3(+) Tregs. Moreover, these naturally-existing Tregs required proper costimulation, in context with autoantigen presentation, to maintain and enhance self tolerance. In particular was the selected use of MHC- and heterologous Tg-restricted models from both conventional and transgenic mice. These models helped to elucidate the complex interplay between autoantigen presentation and MHC class II-mediated T cell selection in the development of Treg and autoreactive T cell repertoires determining susceptibility to autoimmunity. Here we describe these investigations in further detail, providing a context for how EAT has helped shape our understanding of self tolerance and autoimmunity.

H2E-derived Ealpha52-68 peptide presented by H2Ab interferes with clonal deletion of autoreactive T cells in autoimmune thyroiditis

Susceptibility and resistance to experimental autoimmune thyroiditis is encoded by MHC H2A genes. We reported that traditionally resistant B10 (H2(b)) mice permit thyroiditis induction with mouse thyroglobulin (mTg) after depleting regulatory T cells (Tregs), supporting A(b) presentation to thyroiditogenic T cells. Yet, Ea(k) transgenic mice, expressing A(b) and normally absent E(b) molecules (E(+)B10 mice), are susceptible to thyroiditis induction without Treg depletion. To explore the effect of E(b) expression on mTg presentation by A(b), seven putative A(b)-binding, 15-16-mer peptides were synthesized. Five were immunogenic for both B10 and E(+)B10 mice. The effect of E(b) expression was tested by competition with an Ealpha52-68 peptide, because Ealpha52-68 occupies approximately 15% of A(b) molecules in E(+)B10 mice, binding with high affinity. Ealpha52-68 competitively reduced the proliferative response to mTg, mTg1677, and mTg2342 of lymph node cells primed to each Ag. Moreover, mTg1677 induced mild thyroiditis in Treg-depleted B10 mice, and in E(+)B10 mice without the need for Treg depletion. Ealpha52-68 competition with mTg-derived peptides may impede clonal deletion of pathogenic, mTg-specific T cells in the thymus.

A novel H2A-E+ transgenic model susceptible to human but not mouse thyroglobulin-induced autoimmune thyroiditis: identification of mouse pathogenic epitopes

The A-E+ transgenic mouse is highly susceptible to human thyroglobulin (hTg)-induced thyroiditis, but strongly tolerant to a challenge by mouse thyroglobulin (mTg), in stark contrast to traditionally susceptible strains, wherein mTg induces stronger thyroiditis. To identify mouse thyroid epitopes recognized by destructive, hTg-primed T cells, we selected the three hTg epitopes known to be presented by H2E(b), as the basis for synthesizing potential mTg epitopes. One 15-mer peptide, mTg409, did prime T cells, elicit Ab, and induce thyroiditis. Moreover, cells primed with corresponding, pathogenic hTg410 cross-reacted with mTg409, and vice versa. mTg409 contained 4/4 anchor residues, similar to the corresponding hTg peptide. Based on this finding, a second mTg epitope, mTg179, was subsequently identified. These mTg autoepitopes, identified by using thyroiditogenic hTg epitopes, help to explain the severe thyroiditis seen in this novel A-E+ transgenic model.

Evaluating the role of HLA-DQ polymorphisms on immune response to bacterial superantigens using transgenic mice

Bacterial superantigens bind directly to human leukocyte antigen (HLA) class II molecules and vigorously activate T cells expressing certain T-cell receptor variable region families. As interaction with HLA class II molecules is the primary step in this process, polymorphic variations in HLA class II can determine the extent of superantigen binding to HLA class II molecules, govern the magnitude of immune activation induced by given superantigens and determine the outcome of superantigen-mediated diseases. As direct assessment of the influence of HLA class II polymorphism in humans is impossible because of expression of more than one HLA class II alleles in a given individual and toxicity of superantigens, transgenic mice expressing HLA-DQ6 (HLA-DQA1*0103 and HLA-DQB1*0601) and HLA-DQ8 (HLA-DQA1*0301 and HLA-DQB1*0302) were used to achieve this goal. HLA-DQ6 and HLA-DQ8 elicited comparable in vitro and in vivo immune response to staphylococcal enterotoxins (SE) A, SEB, SEH and SEK, toxic shock syndrome toxin-1, streptococcal pyrogenic exotoxin (SPE) A and SPEC and streptococcal mitogenic exotoxin Z (SMEZ). However, each superantigen had a unique T-cell receptor activation profile. In vivo challenge with Streptococcus pyogenes, H305, capable of elaborating SPEA and SMEZ, yielded a similar clinical outcome in HLA-DQ6 and HLA-DQ8 transgenic mice. In conclusion, HLA-DQ6 and HLA-DQ8 elicited comparable response to certain bacterial superantigens. Our report highlights the advantages of HLA class II transgenic mice in such studies.

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.

Experimental autoimmune thyroiditis in the mouse

Experimental autoimmune thyroiditis (EAT) in mice is an excellent model for Hashimoto's thyroiditis (HT). It is induced with thyroglobulin (Tg), a known thyroid autoantigen that is common to both mouse and human and for which several conserved, thyroiditogenic epitopes have been identified. This unit describes induction and evaluation of EAT using thyroid histology and in vitro proliferative response assays. An ELISA is presented to detect the level of antibody to mouse thyroglobulin (MTg). To induce EAT, either bacterial lipopolysaccharide (LPS) or supplemented complete Freund's adjuvant (CFA) can be used as adjuvant. A support protocol for preparing MTg is included. The T cell proliferation assay can be used to examine the antigenicity of synthetic peptides derived from MTg or heterologous Tg. EAT can be adoptively transferred utilizing cells that have been expanded in vitro, as described. A protocol is provided for inducing tolerance using deaggregated MTg; induction of tolerance requires larger amounts of MTg but efficiently suppresses EAT development. Also included is a protocol to demonstrate the role of regulatory T cells in mediating tolerance. A protocol to delineate HLA association with HT is illustrated using HLA class II transgenic mice.

Pathogenicity of a human thyroglobulin peptide (2340-2359) in mice with high or low genetic susceptibility to thyroiditis

We have previously identified a 20-mer peptide of human thyroglobulin (hTg), p2340 (aa2340-2359), which induced experimental autoimmune thyroiditis (EAT) in AKR/J (H-2(k)) and HLA-DR3 transgenic mice. In this study, we investigated the thyroiditogenic potential of p2340 in 'high responder' CBA/J (H-2(k)) and SJL/J (H-2(s)) or 'low responder' C57BL/6 (H-2(b)) and BALB/c (H-2(d)) mice. Mice were immunized subcutaneously with 100 nmol of p2340 in complete Freund's adjuvant (CFA) and both the proliferative capacity of their lymph node cells in the presence of p2340 or intact Tg and the production of peptide-specific antibodies were investigated. The p2340 peptide was found to contain B-cell and non-dominant T-cell epitope(s) in all strains tested. Moreover, it elicited EAT in CBA/J (2/6, infiltration index (I.I.) 1) and SJL/J (5/5, I.I. 1-3) mice after direct challenge and in BALB/c (4/7, I.I. 1) and C57BL/6 (1/5, I.I. 1) after adoptive transfer of p2340-primed lymph node cells. P2340 is the first Tg peptide found to be pathogenic in low as well as high responder mouse strains and thus will allow us to investigate mechanisms of EAT induction in a genetically resistant host.

The association between HLA class II haplotype with Graves' disease in Thai population

The distribution of HLA-DRB1, -DQA1 and -DQB1 alleles were analysed in 124 Graves' disease (GD) patients compared to 124 normal controls in order to identify the alleles/haplotypes associated with GD in Thai population. The DRB1*1602-DQA1*0102-DQB1*0502 haplotype was significantly increased in GD patients (P = 0.0209, OR = 2.55). DRB1*07-DQA1*0201-DQB1*0201 haplotype (P = 0.039, OR = 0.32) and HLA-DRB1*12-DQA1*0601-DQB1*0301 haplotype (P = 0.0025, OR = 0.28) were significantly decreased in GD patients. Interestingly, a protective DRB1*07 allele in Thai population lacks an arginine at position 74 similar to DRB1*0311 (a protective allele in Caucasians). A significant association of DRB1*1602-DQA1*0102-DQB1*0502 and HLA-DRB1*12-DQA1*0601-DQB1*0301 alleles and haplotypes with GD was recently reported in Korean but not in any Caucasian studies. Thus, DRB1*1602 allele and closely linked haplotype, DRB1*1602-DQA1*0102-DQB1*0502, might serve as a marker for genetic susceptibility to GD in Asian population.

Human thyroglobulin peptide p2340 induces autoimmune thyroiditis in HLA-DR3 transgenic mice

In a previous study we demonstrated that the human thyroglobulin (hTg) peptide p2340 (aa 2340-2359) can stimulate a T cell response and elicit experimental autoimmune thyroiditis (EAT) in AKR/J (H-2(k)) mice. In the present study we examined whether p2340 can induce EAT in single HLA class II DR3 transgenic mice. This peptide was found to be immunogenic at the T cell level in DR3 mice, since it induced specific proliferative responses, as well as IL-2 and IFN-gamma secretion in secondary cultures of peptide-primed lymph node cells (LNC). Immunization of HLA-DR3 mice with p2340 in CFA elicited EAT (infiltration index of 1 to 2) in eight of nine mice. Peptide-primed LNC responded to intact hTg, whereas, hTg-primed LNC did not respond to p2340 in culture, suggesting that p2340 contains subdominant T cell epitope(s). P2340 was also found to be immunogenic at the B cell level, since strong p2340-specific IgG response was detected in all transgenic mice tested. Thus, we provide evidence for a pathogenic role of an hTg peptide in HLA-DR3 transgenic mice. Therefore, p2340 could be presented by DR3 molecule in patients with Hashimoto's thyroiditis and participate in the development of the disease.

Degenerate self-reactive human T-cell receptor causes spontaneous autoimmune disease in mice

Thyroid autoimmune disorders comprise more than 30% of all organ-specific autoimmune diseases and are characterized by autoantibodies and infiltrating T cells. The pathologic role of infiltrating T cells is not well defined. To address this issue, we generated transgenic mice expressing a human T-cell receptor derived from the thyroid-infiltrating T cell of a patient with thyroiditis and specific for a cryptic thyroid-peroxidase epitope. Here we show that mouse major histocompatibility complex molecules sustain selection and activation of the transgenic T cells, as coexpression of histocompatibility leukocyte antigen molecules was not needed. Furthermore, the transgenic T cells had an activated phenotype in vivo, and mice spontaneously developed destructive thyroiditis with histological, clinical and hormonal signs comparable with human autoimmune hypothyroidism. These results highlight the pathogenic role of human T cells specific for cryptic self epitopes. This new 'humanized' model will provide a unique tool to investigate how human pathogenic self-reactive T cells initiate autoimmune diseases and to determine how autoimmunity can be modulated in vivo.