Both CD4(+) T cells and CD8(+) T cells are required for iodine accelerated thyroiditis in NOD mice

Experimental rat models for Hashimoto's thyroiditis

PURPOSE

Hashimoto's thyroiditis (HT) is an autoimmune thyroid disease characterized by T lymphocyte-mediated destruction of thyroid follicles. To study the pathogenesis of HT and the efficacy of new substances for its treatment, an easily obtained and adequate to the human disease experimental model is needed. The aim of our study was to find out whether it is possible to induce experimental autoimmune thyroiditis (EAT) similar to Hashimoto's thyroiditis by injecting with thyroglobulin (Tg) without using agents that enhance its thyroiditogenicity and without taking into account the genetic sensitivity of animals.

METHODS

Wistar rats were immunized with freshly isolated rat Tg or porcine Tg. In 8 weeks, histological studies of the thyroid and parathyroid glands were performed. Thyroid function and total serum calcium level were also evaluated.

RESULTS

Immunization with both rat and porcine freshly isolated Tg caused T lymphocytic infiltration of the thyroid gland, thyroid follicle atrophy and degradation in Wistar rats. EAT caused by porcine Tg was characterized by greater severity than EAT induced with rat Tg. In 55% of rats with porcine Tg-induced EAT, oxyphilic metaplasia was detected in the parathyroid glands. In addition, low total serum calcium was observed in these rats.

CONCLUSION

Two rat models of autoimmune thyroiditis were obtained. EAT caused in Wistar rats by immunization with rat Tg is similar to Hashimoto's thyroiditis. EAT induced with porcine Tg was accompanied by oxyphil cell metaplasia in the parathyroids and hypocalcemia.

The NOD Mouse Beyond Autoimmune Diabetes

Autoimmune diabetes arises spontaneously in Non-Obese Diabetic (NOD) mice, and the pathophysiology of this disease shares many similarities with human type 1 diabetes. Since its generation in 1980, the NOD mouse, derived from the Cataract Shinogi strain, has represented the gold standard of spontaneous disease models, allowing to investigate autoimmune diabetes disease progression and susceptibility traits, as well as to test a wide array of potential treatments and therapies. Beyond autoimmune diabetes, NOD mice also exhibit polyautoimmunity, presenting with a low incidence of autoimmune thyroiditis and Sjögren's syndrome. Genetic manipulation of the NOD strain has led to the generation of new mouse models facilitating the study of these and other autoimmune pathologies. For instance, following deletion of specific genes or via insertion of resistance alleles at genetic loci, NOD mice can become fully resistant to autoimmune diabetes; yet the newly generated diabetes-resistant NOD strains often show a high incidence of other autoimmune diseases. This suggests that the NOD genetic background is highly autoimmune-prone and that genetic manipulations can shift the autoimmune response from the pancreas to other organs. Overall, multiple NOD variant strains have become invaluable tools for understanding the pathophysiology of and for dissecting the genetic susceptibility of organ-specific autoimmune diseases. An interesting commonality to all autoimmune diseases developing in variant strains of the NOD mice is the presence of autoantibodies. This review will present the NOD mouse as a model for studying autoimmune diseases beyond autoimmune diabetes.

The pathogenic role of IFN-α in thyroiditis mouse models

AIM

Patients with chronic hepatitis C are frequently treated with interferon (IFN)-α. Autoimmune thyroid disease occurs in 20% ~ 40% of IFN-α-treated patients. In this study, the effects of IFN-α administration on triggering and regulating autoimmune thyroiditis in various animal models were evaluated.

MAIN METHODS

Exogenous IFN-α was given to naive CBA mice, and both thyroglobulin (TG) immunization-induced (CBA) and spontaneous autoimmune thyroiditis (NOD·H-2 h4) models. Thyroid function, and anti-thyroglobulin antibody (ATA) and B-cell-activating factor (BAFF) levels were measured. Alterations in transcriptome profiles were analyzed.

KEY FINDINGS

In the TG-induced thyroiditis model, IFN-α administration reduced plasma free thyroxine levels but did not alter ATA titers, BAFF levels, or the severity of histological changes. Interestingly, even without changes in thyroid functions, four of eight mice in the IFN-α alone group exhibited thyroiditis compared to the control group. Immunologically, mice in the IFN-α group exhibited profound CD3⁺ cell infiltration in the thyroid and higher plasma BAFF levels compared to the control group. Meanwhile, pathological and serological alterations after IFN-α administration were not observed in the NOD·H-2 h4 model. An RNA sequencing analysis revealed that immunoregulatory signatures were not excited by IFN-α treatment in naive CBA mice. Meanwhile, innate and adaptive immunity, inflammatory cytokine, chemokine, and cell-killing signaling pathways were all stimulated by IFN-α administration after TG immunization of CBA mice.

SIGNIFICANCE

We confirmed the remarkable effects of IFN-α in both initiating thyroid immunity and modulating thyroid function and immunoregulatory signatures in established autoimmune thyroiditis. We suggest that IFN-α should be administered with caution in clinical settings.

A transgenic mouse that spontaneously develops pathogenic TSH receptor antibodies will facilitate study of antigen-specific immunotherapy for human Graves' disease

Graves' hyperthyroidism can be treated but not cured. Antigen-specific immunotherapy would accomplish this goal, for which purpose an animal model is an invaluable tool. Two types of animal models are available. First, pathogenic TSHR antibodies (TSHRAb) can be induced by injecting mice with fibroblasts co-expressing the human TSHR (hTSHR) and MHC class II, or in mammals using plasmid or adenovirus vectors encoding the hTSHR or its A-subunit. Second, a mouse model that spontaneously develops pathogenic TSHRAb resembling those in human disease was recently described. This outcome was accomplished by transgenic intrathyroidal expression of the hTSHR A-subunit in NOD.H2^h4 mice that are genetically predisposed to develop thyroiditis but, without the transgene, do not generate TSHRAb. Recently, novel approaches to antigen-specific immunotherapy have been tested, primarily in the induced model, by injecting TSHR A-subunit protein or cyclic TSHR peptides. T-cell tolerance has also been induced in "humanized" HLA-DR3 mice by injecting synthetic peptides predicted in silico to mimic naturally processed TSHR T-cell epitopes. Indeed, a phase 1 study based on the latter approach has been conducted in humans. In the spontaneous model (hTSHR/NOD.H2^h mice), injection of soluble or nanoparticle-bearing hTSHR A-subunits had the unwanted effect of exacerbating pathogenic TSHRAb levels. A promising avenue for tolerance induction, successful in other conditions and yet to be tested with the TSHR, involves encapsulating the antigen. In conclusion, these studies provide insight into the potential outcome of immunotherapeutic approaches and emphasize the importance of a spontaneous model to test future novel, antigen-specific immunotherapies for Graves' disease.

A Mouse Thyrotropin Receptor A-Subunit Transgene Expressed in Thyroiditis-Prone Mice May Provide Insight into Why Graves' Disease Only Occurs in Humans

Background: Graves' disease, caused by autoantibodies that activate the thyrotropin (TSH) receptor (TSHR), has only been reported in humans. Thyroiditis-prone NOD.H2^h4 mice develop autoantibodies to thyroglobulin (Tg) and thyroid peroxidase (TPO) but not to the TSHR. Evidence supports the importance of the shed TSHR A-subunit in the initiation and/or amplification of the autoimmune response to the holoreceptor. Cells expressing the gene for the isolated A-subunit secrete A-subunit protein, a surrogate for holoreceptor A-subunit shedding. NOD.H2^h4 mice with the human TSHR A-subunit targeted to the thyroid (a "self" antigen in such transgenic (Tgic) animals), unlike their wild-type (wt) siblings, spontaneously develop pathogenic TSHR antibodies to the human-TSH holoreceptor. These autoantibodies do not recognize the endogenous mouse-TSH holoreceptor and do not cause hyperthyroidism. Methods: We have now generated NOD.H2^h4 mice with the mouse-TSHR A-subunit transgene targeted to the thyroid. Tgic mice and wt littermates were compared for intrathyroidal expression of the mouse A-subunit. Sera from six-month-old mice were tested for the presence of autoantibodies to Tg and TPO as well as for pathogenic TSHR antibodies (TSH binding inhibition, bioassay for thyroid stimulating antibodies) and nonpathogenic TSHR antibodies (ELISA). Results: Expression of the mouse TSHR A-subunit transgene in the thyroid was confirmed by real-time polymerase chain reaction in the Tgics and had no effect on the spontaneous development of autoantibodies to Tg or TPO. However, unlike the same NOD.H2^h4 strain with the human-TSHR A-subunit target to the thyroid, mice expressing intrathyroidal mouse-TSHR A subunit failed to develop either pathogenic or nonpathogenic TSHR antibodies. The mouse TSHR A-subunit differs from the human TSHR A-subunit in terms of its amino acid sequence and has one less glycosylation site than the human TSHR A-subunit. Conclusions: Multiple genetic and environmental factors contribute to the pathogenesis of Graves' disease. The present study suggests that the TSHR A-subunit structure (possibly including posttranslational modification such as glycosylation) may explain, in part, why Graves' disease only develops in humans.

Nanoparticles Bearing TSH Receptor Protein and a Tolerogenic Molecule Do Not Induce Immune Tolerance but Exacerbate Thyroid Autoimmunity in hTSHR/NOD.H2h4 Mice

Transgenic NOD.H2h4 mice that express the human (h) TSHR A-subunit in the thyroid gland spontaneously develop pathogenic TSHR autoantibodies resembling those in patients with Graves disease. Nanoparticles coupled to recombinant hTSHR A-subunit protein and a tolerogenic molecule (ligand for the endogenous aryl-hydrocarbon receptor; ITE) were injected i.p. four times at weekly intervals into hTSHR/NOD.H2h4 mice with the goal of blocking TSHR Ab development. Unexpectedly, in transgenic mice, injecting TSHR A-subunit-ITE nanoparticles (not ITE-nanoparticles or buffer) accelerated and enhanced the development of pathogenic TSHR Abs measured by inhibition of TSH binding to the TSHR. Nonpathogenic TSHR Abs (ELISA) were enhanced in transgenics and induced in wild-type littermates. Serendipitously, these findings have important implications for disease pathogenesis: development of Graves TSHR Abs is limited by the availability of A-subunit protein, which is shed from membrane bound TSHR, expressed at low levels in the thyroid. The enhanced TSHR Ab response following injected TSHR A-subunit protein-nanoparticles is reminiscent of the transient increase in pathogenic TSHR Abs following the release of thyroid autoantigens after radio-iodine therapy in Graves patients. However, in the hTSHR/NOD.H2h4 model, enhancement is specific for TSHR Abs, with Abs to thyroglobulin and thyroid peroxidase remaining unchanged. In conclusion, despite the inclusion of a tolerogenic molecule, injected nanoparticles coated with TSHR A-subunit protein enhanced and accelerated development of pathogenic TSHR Abs in hTSHR/NOD. NOD.H2h4 These findings emphasize the need for sufficient TSHR A-subunit protein to activate the immune system and the generation of stimulatory TSHR Abs in genetically predisposed individuals.

MYMD-1, a Novel Immunometabolic Regulator, Ameliorates Autoimmune Thyroiditis via Suppression of Th1 Responses and TNF-α Release

MYMD-1 is a synthetic derivative of tobacco alkaloids, compounds that possess immunoregulatory properties and have been linked to the epidemiological observation that smoking reduces the odds of developing thyroid Abs and hypothyroidism. To assess the effect and mechanism(s) of the action of MYMD-1, we chose the NOD.H-2h4 mouse model of spontaneous thyroiditis. We began in vitro using T cells isolated from NOD.H-2h4 spleens and found that MYMD-1 suppressed TNF-α production by CD4+ T cells in a dose-dependent manner. We then treated 58 NOD.H-2h4 mice for 12 wk with either unsupplemented water that contained (10 mice) or did not contain (16 mice) MYMD-1 (185 mg/l) or water supplemented with sodium iodide (500 mg/l) that contained (16 mice) or did not contain (16 mice) MYMD-1. Mice were bled at baseline and then every 2 wk until sacrifice. MYMD-1 decreased the incidence and severity (p < 0.001) of thyroiditis, as assessed by histopathology. Similarly, the number of CD3+ T cells and CD19+ B cells infiltrating the thyroid was dampened by MYMD-1, as assessed by flow cytometry. Interestingly, the subset of thyroidal CD3+CD4+Tbet+RORγT- effector Th1 cells and the systemic levels of TNF-α were decreased by MYMD-1. Serum thyroglobulin Abs decreased in the MYMD-1 group. Thyroid hormones did not differ among the four groups, whereas thyroid-stimulating hormone increased upon iodine supplementation but remained normal in MYMD-1-treated mice. Overall, the study suggests that MYMD-1 ameliorates thyroiditis acting on specific lymphoid subsets. Further studies, including other models of autoimmunity, will confirm the potential clinical use of MYMD-1 as a novel immunometabolic regulator.

To reflect human autoimmune thyroiditis, thyroid peroxidase (not thyroglobulin) antibodies should be measured in female (not sex-independent) NOD.H2h4 mice

NOD.H2^h4 mice are the most commonly used model for human autoimmune thyroiditis. Because thyroid autoimmunity develops slowly (over months), NOD.H2^h4 mice are usually exposed to excess dietary iodide to accelerate and amplify the process. However, unlike the female bias in human thyroid autoimmunity, autoantibodies to thyroglobulin (TgAb) are reported to be similar in male and female NOD.H2^h4 . We sought evidence for sexual dimorphism in other parameters in this strain maintained on regular or iodized water. Without iodide, TgAb levels are higher in males than in females, the reverse of human disease. In humans, autoantibodies to thyroid peroxidase (TPOAb) are a better marker of disease than TgAb. In NOD.H2^h4 mice TPOAb develop more slowly than TgAb, being detectable at 6 months of age versus 4 months for the latter. Remarkably, unlike TgAb, TPOAb levels are higher in female than male NOD.H2^h4 mice on both regular and iodized water. As previously observed, serum T4 levels are similar in both sexes. However, thyroid-stimulating hormone (TSH) levels are significantly higher in males than females with or without iodide exposure. TSH levels correlate with TgAb levels in male NOD.H2^h4 mice, suggesting a possible role for TSH in TgAb development. However, there is no correlation between TSH and TPOAb levels, the latter more important than TgAb in human disease. In conclusion, if the goal of an animal model is to closely reflect human disease, TPOAb rather than TgAb should be measured in older female NOD.H2^h4 mice, an approach requiring patience and the use of mouse TPO protein.

Thyroid Hemiagenesis in a Thyroiditis Prone Mouse Strain

BACKGROUND

Thyroid hemiagenesis, a rare congenital condition detected by ultrasound screening of the neck, is usually not manifested clinically in humans. This condition has been reported in mice with hypothyroidism associated with induced deficiency in paired box 8 and NK2 homeobox 1, sonic hedgehog, or T-box 1. Unexpectedly, we observed thyroid hemiagenesis in NOD.H2^h4 mice, an unusual strain that spontaneously develops iodide enhanced thyroid autoimmunity but remains euthyroid.

OBJECTIVES AND METHODS

First, to compare mice with thyroid hemiagenesis versus bilobed littermates for serum T4, autoantibodies to thyroglobulin (ELISA) and thyroid peroxidase (TPO; flow cytometry with eukaryotic cells expressing mouse TPO), gross anatomy, and thyroid histology; second, to estimate the percentage of mice with thyroid hemiagenesis in the NOD.H2^h4 mice we have studied over 6 years.

RESULTS

Thyroid hemiagenesis was observed in 3 of 1,025 NOD.H2^h4 mice (2 females, 1 male; 0.3$). Two instances of hemiagenesis were in wild-type females and one in a transgenic male expressing the human TSHR A-subunit in the thyroid. Two mice had very large unilobed glands, as in some human cases with this condition. Thyroid lymphocytic infiltration, serum T4, and the levels of thyroid autoantibodies were similar in mice with thyroid hemiagenesis and bilobed littermates.

CONCLUSIONS

Unlike hypothyroidism associated with hemiagenesis in transcription factor knockout mice, hemiagenesis in euthyroid NOD.H2^h4 mice occurs spontaneously and is phenotypically similar to that occasionally observed in humans.

Aberrant Iodine Autoregulation Induces Hypothyroidism in a Mouse Strain in the Absence of Thyroid Autoimmunity

We investigated factors underlying the varying effects of a high dietary iodide intake on serum T4 levels in a wide spectrum of mouse strains, including thyroiditis-susceptible NOD.H2h4, NOD.H2k, and NOD mice, as well as other strains (BALB/c, C57BL/6, NOD.Lc7, and B10.A4R) not previously investigated. Mice were maintained for up to 8 months on control or iodide-supplemented water (NaI 0.05%). On iodized water, serum T4 was reduced in BALB/c (males and females) in association with colloid goiters but was not significantly changed in mice that developed thyroiditis, namely NOD.H2h4 (males and females) or male NOD.H2k mice. Neither goiters nor decreased T4 developed in C57BL/6, NOD, NOD.Lc7, or B10.A4R female mice. In further studies, we focused on males in the BALB/c and NOD.H2h4 strains that demonstrated a large divergence in the T4 response to excess iodide. Excess iodide ingestion increased serum TSH levels to the same extent in both strains, yet thyroidal sodium iodide symporter (NIS) messenger RNA (mRNA) levels (quantitative polymerase chain reaction) revealed greatly divergent responses. NOD.H2h4 mice that remained euthyroid displayed a physiological NIS iodine autoregulatory response, whereas NIS mRNA was inappropriately elevated in BALB/c mice that became hypothyroid. Thus, autoimmune thyroiditis-prone NOD.H2h4 mice adapted normally to a high iodide intake, presumably by escape from the Wolff-Chaikoff block. In contrast, BALB/c mice that did not spontaneously develop thyroiditis failed to escape from this block and became hypothyroid. These data in mice may provide insight into the mechanism by which iodide-induced hypothyroidism occurs in some humans without an underlying thyroid disorder.

Thyroid Autoantibodies Display both "Original Antigenic Sin" and Epitope Spreading

Evidence for original antigenic sin in spontaneous thyroid autoimmunity is revealed by autoantibody interactions with immunodominant regions on thyroid autoantigens, thyroglobulin (Tg), thyroid peroxidase (TPO), and the thyrotropin receptor (TSHR) A-subunit. In contrast, antibodies induced by immunization of rabbits or mice recognize diverse epitopes. Recognition of immunodominant regions persists despite fluctuations in autoantibody levels following treatment or over time. The enhancement of spontaneously arising pathogenic TSHR antibodies in transgenic human thyrotropin receptor/NOD.H2^h4 mice by injecting a non-pathogenic form of TSHR A-subunit protein also provides evidence for original antigenic sin. From other studies, antigen presentation by B cells, not dendritic cells, is likely responsible for original antigenic sin. Recognition of restricted epitopes on the large glycosylated thyroid autoantigens (60-kDa A-subunit, 100-kDa TPO, and 600-kDa Tg) facilitates exploring the amino acid locations in the immunodominant regions. Epitope spreading has also been revealed by autoantibodies in thyroid autoimmunity. In humans, and in mice that spontaneously develop autoimmunity to all three thyroid autoantigens, autoantibodies develop first to Tg and later to TPO and the TSHR A-subunit. The pattern of intermolecular epitope spreading is related in part to the thyroidal content of Tg, TPO and TSHR A-subunit and to the molecular sizes of these proteins. Importantly, the epitope spreading pattern provides a rationale for future antigen-specific manipulation to block the development of all thyroid autoantibodies by inducing tolerance to Tg, first in the autoantigen cascade. Because of its abundance, Tg may be the autoantigen of choice to explore antigen-specific treatment, preventing the development of pathogenic TSHR antibodies.

Variable Effects of Dietary Selenium in Mice That Spontaneously Develop a Spectrum of Thyroid Autoantibodies

Selenium (Se) is a critical element in thyroid function, and variable dietary Se intake influences immunity. Consequently, dietary Se could influence development of thyroid autoimmunity and provide an adjunct to treat autoimmune thyroid dysfunction. Nonobese diabetic (NOD).H2h4 mice spontaneously develop autoantibodies to thyroglobulin (Tg) and thyroid peroxidase (TPO). This mouse strain expressing a human thyroid-stimulating hormone receptor (TSHR) A-subunit transgene in the thyroid also develops pathogenic TSHR autoantibodies. In this report, we investigated whether dietary Se influences these immune processes. Male and female wild-type and transgenic NOD.H2h4 mice were maintained on normal-, low-, or high-Se (0.1, 0, or 1.0 mg/kg) rodent diets. After 4 months, Se serum levels were extremely low or significantly increased on 0 or 1.0 mg/kg Se, respectively. Varying Se intake affected Tg antibody (TgAb) levels after 2 (but not 4) months; conversely, TPO antibody (TPOAb) levels were altered by dietary Se after 4 (but not 2) months. These data correspond to the earlier development of TgAb than TPOAb in NOD.H2h4 mice. In males, TgAb levels were enhanced by high Se and in females by low Se intake. Se intake had no effect on pathogenic TSHR autoantibodies in TSHR transgenic NOD.H2h4 females. In conclusion, in susceptible NOD.H2h4 mice, we found no evidence that a higher dietary Se intake ameliorates thyroid autoimmunity by reducing autoantibodies to Tg, TPO, or the TSHR. Instead, our finding that low dietary Se potentiates the development of autoantibodies to Tg and TPO in females is consistent with reports in humans of an increased prevalence of autoimmune thyroiditis in low-Se regions.

High-level intrathymic thyrotrophin receptor expression in thyroiditis-prone mice protects against the spontaneous generation of pathogenic thyrotrophin receptor autoantibodies

The thyrotrophin receptor (TSHR) A-subunit is the autoantigen targeted by pathogenic autoantibodies that cause Graves' hyperthyroidism, a common autoimmune disease in humans. Previously, we reported that pathogenic TSHR antibodies develop spontaneously in thyroiditis-susceptible non-obese diabetic (NOD).H2h4 mice bearing a human TSHR A-subunit transgene, which is expressed at low levels in both the thyroid and thymus (Lo-expressor transgene). The present study tested recent evidence that high intrathymic TSHR expression protects against the development of pathogenic TSHR antibodies in humans. By successive back-crossing, we transferred to the NOD.H2h4 background a human TSHR A-subunit transgene expressed at high levels in the thyroid and thymus (Hi-expressor transgene). In the sixth back-cross generation (> 98% NOD.H2h4 genome), only transgenic offspring produced spontaneously immunoglobulin (Ig)G class non-pathogenic human TSHR A-subunit antibodies. In contrast, both transgenic and non-transgenic offspring developed antibodies to thyroglobulin and thyroid peroxidase. However, non-pathogenic human TSHR antibody levels in Hi-expressor offspring were lower than in Lo-expressor transgenic mice. Moreover, pathogenic TSHR antibodies, detected by inhibition of TSH binding to the TSHR, only developed in back-cross offspring bearing the Lo-expressor, but not the Hi-expressor, transgene. High versus low expression human TSHR A-subunit in the NOD.H2h4 thymus was not explained by the transgene locations, namely chromosome 2 (127-147 Mb; Hi-expressor) and chromosome 1 (22.9-39.3 Mb; low expressor). Nevertheless, using thyroiditis-prone NOD.H2h4 mice and two transgenic lines, our data support the association from human studies that low intrathymic TSHR expression is associated with susceptibility to developing pathogenic TSHR antibodies, while high intrathymic TSHR expression is protective.

Genes Outside the Major Histocompatibility Complex Locus Are Linked to the Development of Thyroid Autoantibodies and Thyroiditis in NOD.H2h4 Mice

Thyroiditis and autoantibodies to thyroglobulin (TgAb) and thyroid peroxidase (TPOAb) develop spontaneously in NOD.H2h4 mice, a phenotype enhanced by dietary iodine. NOD.H2h4 mice were derived by introducing the major histocompatibility class (MHC) molecule I-Ak from B10.A(4R) mice to nonobese diabetic (NOD) mice. Apart from I-Ak, the genes responsible for the NOD.H2h4 phenotype are unknown. Extending serendipitous observations from crossing BALB/c to NOD.H2h4 mice, thyroid autoimmunity was investigated in both genders of the F1, F2, and the second-generation backcross of F1 to NOD.H2h4 (N2). Medium-density linkage analysis was performed on thyroid autoimmunity traits in F2 and N2 progeny. TgAb develop before TPOAb and were measured after 8 and 16 weeks of iodide exposure; TPOAb and thyroiditis were studied at 16 weeks. TgAb, TPOAb, and thyroiditis, absent in BALB/c and F1 mice, developed in most NOD.H2h4 and in more N2 than F2 progeny. No linkages were observed in F2 progeny, probably because of the small number of autoantibody-positive mice. In N2 progeny (equal numbers of males and females), a chromosome 17 locus is linked to thyroiditis and TgAb and is suggestively linked to TPOAb. This locus includes MHC region genes from B10.A(4R) mice (such as I-Ak and Tnf, the latter involved in thyrocyte apoptosis) and genes from NOD mice such as Satb1, which most likely plays a role in immune tolerance. In conclusion, MHC and non-MHC genes, encoded within the chromosome 17 locus from both B10.A(4R) and NOD strains, are most likely responsible for the Hashimoto disease-like phenotype of NOD.H2h4 mice.

The Spontaneous Autoimmune Neuromyopathy in ICOSL-/- NOD Mice Is CD4+ T-Cell and Interferon-γ Dependent

Abrogation of ICOS/ICOS ligand (ICOSL) costimulation prevents the onset of diabetes in the non-obese diabetic (NOD) mouse but, remarkably, yields to the development of a spontaneous autoimmune neuromyopathy. At the pathological level, ICOSL^−/− NOD mice show stronger protection from insulitis than their ICOS^−/− counterparts. Also, the ICOSL^−/− NOD model carries a limited C57BL/6 region containing the Icosl nul mutation, but, in contrast to ICOS^−/− NOD mice, no gene variant previously reported as associated to NOD diabetes. Therefore, we aimed at providing a detailed characterization of the ICOSL^−/− NOD model. The phenotype observed in ICOSL^−/− NOD mice is globally similar to that observed in ICOS^−/− and ICOS^−/−ICOSL^−/− double-knockout NOD mice, manifested by a progressive locomotor disability first affecting the front paws as observed by catwalk analysis and a decrease in grip test performance. The pathology remains limited to peripheral nerve and striated muscle. The muscle disease is characterized by myofiber necrosis/regeneration and an inflammatory infiltrate composed of CD4⁺ T-cells, CD8⁺ T-cells, and myeloid cells, resembling human myositis. Autoimmune neuromyopathy can be transferred to NOD.scid recipients by CD4⁺ but not by CD8⁺ T-cells isolated from 40-week-old female ICOSL^−/− NOD mice. The predominant role of CD4⁺ T-cells is further demonstrated by the observation that neuromyopathy does not develop in CIITA^−/−ICOSL^−/− NOD in contrast to β2microglobulin^−/−ICOSL^−/− NOD mice. Also, the cytokine profile of CD4⁺ T-cells infiltrating muscle and nerve of ICOSL^−/− NOD mice is biased toward a Th1 pattern. Finally, adoptive transfer experiments show that diabetes development requires expression of ICOSL, in contrast to neuromyopathy. Altogether, the deviation of autoimmunity from the pancreas to skeletal muscles in the absence of ICOS/ICOSL signaling in NOD mice is strictly dependent on CD4⁺ T-cells, leads to myofiber necrosis and regeneration. It provides the first mouse model of spontaneous autoimmune myopathy akin to human myositis.

Underlying Mechanisms of Pituitary-Thyroid Axis Function Disruption by Chronic Iodine Excess in Rats

BACKGROUND

Iodine is essential for thyroid hormone synthesis and is an important regulator of thyroid function. Chronic iodine deficiency leads to hypothyroidism, but iodine excess also impairs thyroid function causing hyperthyroidism, hypothyroidism, and/or thyroiditis. This study aimed to investigate the underlying mechanisms by which exposure to chronic iodine excess impairs pituitary-thyroid axis function.

METHODS

Male Wistar rats were treated for two months with NaI (0.05% and 0.005%) or NaI+NaClO₄ (0.05%) dissolved in drinking water. Hormone levels, gene expression, and thyroid morphology were analyzed later.

RESULTS

NaI-treated rats presented high levels of iodine in urine, increased serum thyrotropin levels, slightly decreased serum thyroxine/triiodothyronine levels, and a decreased expression of the sodium-iodide symporter, thyrotropin receptor, and thyroperoxidase mRNA and protein, suggesting a primary thyroid dysfunction. In contrast, thyroglobulin and pendrin mRNA and protein content were increased. Kidney and liver deiodinase type 1 mRNA expression was decreased in iodine-treated rats. Morphological studies showed larger thyroid follicles with higher amounts of colloid and increased amounts of connective tissue in the thyroid of iodine-treated animals. All these effects were prevented when perchlorate treatment was combined with iodine excess.

CONCLUSIONS

The present data reinforce and add novel findings about the disruption of thyroid gland function and the compensatory action of increased thyrotropin levels in iodine-exposed animals. Moreover, they draw attention to the fact that iodine intake should be carefully monitored, since both deficient and excessive ingestion of this trace element may induce pituitary-thyroid axis dysfunction.

CXCR4 antagonist AMD3100 ameliorates thyroid damage in autoimmune thyroiditis in NOD.H‑2h⁴ mice

CXC chemokine ligand 12 (CXCL12) and its receptor, CXC chemokine receptor 4 (CXCR4), are upregulated in mice with autoimmune thyroid diseases. However, whether this interaction is involved in the pathophysiology of autoimmune thyroiditis (AIT) remains to be elucidated. In the present study, the effects of the CXCR4 antagonist, AMD3100, in an iodine‑induced autoimmune thyroiditis model were investigated. NOD.H‑2h4 mice were randomly separated into a control, AIT and AIT+AMD3100 groups. The mice were fed with 0.05% sodium iodide water for 8 weeks to induce AIT. The AMD3100‑treated mice were administered with the CXCR4 antagonist at a dose of 10 mg/kg intraperitoneally three times a week during the experimental period. The percentages of CD19+interleukin (IL)10+ B cells and CD4+IL10+ T cells, and the mRNA expression levels of IL10 in the splenocytes were reduced in the AIT group, compared with the control group, however, they increased following AMD3100 treatment, compared with the untreated AIT group. The percentages of CD4+ T cells, CD8+ T cells, CD19+ B cells and CD8+ interferon (IFN)γ+ T cells, and the mRNA expression levels of IFNγ increased in the AIT group, compared with the control group, however, these were reduced in the AMD3100 group, compared with the AIT group. The AMD3100‑treated mice also had lower serum thyroglobulin antibody titers and reduced lymphocytic infiltration in the thyroid, compared with the untreated AIT mice. These results suggested that inhibition of this chemokine axis may offer potential as a therapeutic target for the treatment of AIT.

Genes and environment as predisposing factors in autoimmunity: acceleration of spontaneous thyroiditis by dietary iodide in NOD.H2(h4) mice

In the field of autoimmune thyroiditis, NOD.H2(h4) mice have attracted significant and increasing attention since they not only develop spontaneous disease but they present thyroiditis with accelerated incidence and severity if they ingest iodide through their drinking water. This animal model highlights the interplay between genetic and dietary factors in the triggering of autoimmune disease and offers new opportunities to study immunoregulatory parameters influenced by both genes and environment. Here, we review experimental findings with this mouse model of thyroiditis.

A unique mouse strain that develops spontaneous, iodine-accelerated, pathogenic antibodies to the human thyrotrophin receptor

Abs that stimulate the thyrotropin receptor (TSHR), the cause of Graves' hyperthyroidism, only develop in humans. TSHR Abs can be induced in mice by immunization, but studying pathogenesis and therapeutic intervention requires a model without immunization. Spontaneous, iodine-accelerated, thyroid autoimmunity develops in NOD.H2(h4) mice associated with thyroglobulin and thyroid-peroxidase, but not TSHR, Abs. We hypothesized that transferring the human TSHR A-subunit to NOD.H2(h4) mice would result in loss of tolerance to this protein. BALB/c human TSHR A-subunit mice were bred to NOD.H2(h4) mice, and transgenic offspring were repeatedly backcrossed to NOD.H2(h4) mice. All offspring developed Abs to thyroglobulin and thyroid-peroxidase. However, only TSHR-transgenic NOD.H2(h4) mice (TSHR/NOD.H2(h4)) developed pathogenic TSHR Abs as detected using clinical Graves' disease assays. As in humans, TSHR/NOD.H2(h4) female mice were more prone than male mice to developing pathogenic TSHR Abs. Fortunately, in view of the confounding effect of excess thyroid hormone on immune responses, spontaneously arising pathogenic human TSHR Abs cross-react poorly with the mouse TSHR and do not cause thyrotoxicosis. In summary, the TSHR/NOD.H2(h4) mouse strain develops spontaneous, iodine-accelerated, pathogenic TSHR Abs in female mice, providing a unique model to investigate disease pathogenesis and test novel TSHR Ag-specific immunotherapies aimed at curing Graves' disease in humans.

Evidence that MHC I-E dampens thyroid autoantibodies and prevents spreading to a second thyroid autoantigen in I-A(k) NOD mice

NOD.H2^k and NOD.H2^h4 mice carry the MHC class II molecule I-A^k associated with susceptibility to experimentally-induced thyroiditis. Dietary iodine enhanced spontaneous thyroid autoimmunity, well known in NOD.H2^h4 mice, has not been investigated in NOD.H2^k mice. We compared NOD.H2^h4 and NOD.H2^k strains for thyroiditis and autoantibodies to thyroglobulin (TgAb) and thyroid peroxidase (TPOAb) without or with dietary sodium iodide (NaI) for up to 32 weeks. TgAb levels were significantly higher in NOD.H2^h4 than NOD.H2^k mice on NaI and TPOAb developed in NOD.H2^h4 but not NOD.H2^k mice. DNA exome analysis revealed, in addition to the differences in the chromosome (Chr) 17 MHC regions, that NOD.H2^k and particularly NOD.H2^h4 mice have substantial non-MHC parental DNA. KEGG pathway-analysis highlighted thyroid autoimmunity and immune-response genes on Chr 17 but not on Chr 7 and 15 parental B10.A4R DNA. Studies of parental strains provided no evidence for non-MHC gene contributions. The exon 10 thyroglobulin haplotype, associated with experimentally-induced thyroiditis, is absent in NOD.H2^h4 and NOD.H2^k mice and is not a marker for spontaneous murine thyroid autoimmunity. In conclusion, the absence of I-E is a likely explanation for the difference between NOD.H2^h4 and NOD.H2^k mice in TgAb levels and, as in humans, autoantibody spreading to TPO.

NOD.H-2h4 mice: an important and underutilized animal model of autoimmune thyroiditis and Sjogren's syndrome

NOD.H-2h4 mice express the K haplotype on the NOD genetic background. They spontaneously develop thyroiditis and Sjogren's syndrome, but they do not develop diabetes. Although autoimmune thyroid diseases and Sjogren's syndrome are highly prevalent autoimmune diseases in humans, there has been relatively little emphasis on the use of animal models of these diseases for understanding basic mechanisms involved in development and therapy of chronic organ-specific autoimmune diseases. The goal of this review is to highlight some of the advantages of NOD.H-2h4 mice for studying basic mechanisms involved in development of autoimmunity. NOD.H-2h4 mice are one of relatively few animal models that develop organ-specific autoimmune diseases spontaneously, i.e., without a requirement for immunization with antigen and adjuvant, and in both sexes in a relatively short period of time. Thyroiditis and Sjogren's syndrome in NOD.H-2h4 mice are chronic autoimmune diseases that develop relatively early in life and persist for the life of the animal. Because the animals do not become clinically ill, the NOD.H-2h4 mouse provides an excellent model to test therapeutic protocols over a long period of time. The availability of several mutant mice on this background provides a means to address the impact of particular cells and molecules on the autoimmune diseases. Moreover, to our knowledge, this is the only animal model in which the presence or absence of a single cytokine, IFN-γ, is sufficient to completely inhibit one autoimmune thyroid disease, with a completely distinct autoimmune thyroid disease developing when it is absent.

Apoptosis of NOD.H2 h4 thyrocytes by low concentrations of iodide is associated with impaired control of oxidative stress

BACKGROUND

Enhanced iodide intake in NOD.H2(h4) mice accelerates the incidence and severity of spontaneous autoimmune thyroiditis (SAT) via an unknown mechanism. A plausible hypothesis is that iodide-induced apoptosis of thyrocytes can create imbalances in antigenic load and/or disruption of immunoregulatory mechanisms that facilitate activation of autoreactive T cells in cervical lymph nodes draining the thyroid.

METHODS

We examined whether NOD.H2(h4) thyrocytes, exposed to low NaI concentrations in vitro, are more susceptible to apoptosis compared to thyrocytes from CBA/J mice, which are resistant to iodide-accelerated SAT (ISAT). We also looked, at the transcriptional level, for differential activation of genes involved in apoptosis or oxidative stress pathways that may account for potential differences in iodide-mediated apoptosis between NOD.H2(h4) and CBA/J thyrocytes.

RESULTS

We report that NOD.H2(h4) thyrocytes, cultured for 24 h at very low (4-8 μM) concentrations of NaI, exhibit high levels (40-55%) of apoptosis, as assessed microscopically following staining with fluorescent caspase inhibitors. Similar treatment of thyrocytes from CBA/J mice, which are resistant to ISAT, yielded significantly lower (10-20%) apoptotic rates. Expression analysis by real-time polymerase chain reaction using arrays of apoptosis- and oxidative stress-related genes showed that NaI intake upregulates the expression of 22 genes involved in ROS metabolism and/or antioxidant function in CBA/J thyrocytes, whereas only two of these genes were upregulated in NOD.H2(h4) thyrocytes. Among the set of overexpressed genes were those encoding thyroid peroxidase (Tpo; 5.77-fold), glutathione peroxidases (Gpx2, Gpx4, Gpx7; 2.03-3.14-fold), peroxiredoxins (Prdx1, Prdx2, Prdx5; 2.27-2.97-fold), superoxide dismutase 1 (Sod1; 3.57-fold), thioredoxin 1 (Txn1; 2.13-fold), and the uncoupling proteins 2 and 3 (Ucp2, Ucp3; 2.01-2.15-fold).

CONCLUSIONS

The results demonstrate that an impaired control of oxidative stress mechanisms is associated with the observed high susceptibility of NOD.H2(h4) thyrocytes to NaI-mediated apoptosis, and suggest a contributing factor for the development of ISAT in this strain.

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.

Defective expression of regulatory B cells in iodine-induced autoimmune thyroiditis in non-obese diabetic H-2(h4) mice

INTRODUCTION

The ability of B cells to negatively regulate cellular immune responses and inflammation has been described. The regulatory B (Breg) cells with the unique CD1d(hi)CD5(+)CD19(+) phenotype and the capacity to produce IL-10 are potent negative regulators of inflammation and autoimmunity in several in vivo mouse models of autoimmune disease.

AIM

To investigate whether Breg cell deficiency participates in autoimmune thyroiditis (AIT) in an animal model.

MATERIALS AND METHODS

Non-obese diabetic (NOD).H-2(h4) mice at 4 weeks of age were randomly divided into control and iodine-treated groups; the iodine-treated group received sterile water containing 0.005 % NaI for 10 or 20 weeks. The percentage of CD1d(hi)CD5(+)CD19(+) Bregs, CD4(+)CD25(+)FoxP3(+) regulatory T cells (Treg) and CD4(+)IL17(+) T helper 17 cells (Th17) in splenic mononuclear cells was detected by multicolor flow cytometry. The expression of IL-10 mRNA and TGF-β mRNA in splenocytes was measured by real-time RT-PCR.

RESULTS

NOD.H-2(h4) mice spontaneously develop anti-thyroglobulin autoantibodies and intrathyroidal lymphocyte infiltration when supplied with iodine in drinking water. Mice with AIT had a decreased CD1d(hi)CD5(+)CD19(+) Breg subset and reduced IL-10 mRNA expression in splenocytes compared with controls (p < 0.05) and maintained relatively low levels during the development of thyroiditis. The proportion of Breg cells was negatively correlated with the proportion of Th17 cells, but positively correlated with CD4(+)CD25(+)FoxP3(+) Treg cells in splenocytes (All p < 0.05).

CONCLUSIONS

The defective expression of Breg cells combined with impaired Treg cells and enhanced Th17 cells might play an important role in the development of iodine-induced AIT in NOD.H-2(h4) mice.

Inflammation and increased myxovirus resistance protein A expression in thyroid tissue in the early stages of Hashimoto's thyroiditis

BACKGROUND

The role of viruses as environmental triggers for Hashimoto's thyroiditis (HT) is controversial. Thyroid epithelial cells express a variety of molecules involved in antiviral responses. This study combined histological, immunological, and virological tests to describe changes in tissue from patients with newly diagnosed and untreated HT. To study the early events, patients with positive thyroid peroxidase antibodies (TPO-Ab) and normal thyroid function were also included. This stage was defined as "prethyroiditis."

METHODS

Thyroid tissue was collected from 47 patients with high titers of TPO-Ab and from 24 controls. Seventeen patients had prethyroiditis, 17 had subclinical hypothyroidism, and 13 had overt hypothyroidism. The interferon (IFN)-α/β-inducible myxovirus resistance protein 1 (myxovirus resistance protein A; MxA) was used as a surrogate marker for type I IFN expression. Inflammation, expression of MxA, and the presence of the enteroviralcapsid protein (VP1) were characterized by immunohistochemistry. The presence of enterovirus (EV) RNA was examined by in situ hybridization.

RESULTS

The density of CD4+ T cells was increased in all three patient groups, while CD8+ T cells were increased only in patients with overt hypothyroidism. The density of plasma cells increased as the disease progressed. The density of plasmacytoid dendritic cells and the expression of MxA were significantly increased in all patient groups compared with controls (p<0.01). EV RNA was present in 11% of HT patients, but in none of the control subjects, whereas the enteroviral protein was detected in 19% and 16%, respectively.

CONCLUSION

The inflammatory reaction in the thyroid gland is a very early event in the pathogenesis of HT. The increased expression of MxA in the inflamed tissue suggests that type I IFN plays a role in disease development. Whether this is virus-dependent needs to be explored in further studies.

Animal models used to examine the role of the environment in the development of autoimmune disease: findings from an NIEHS Expert Panel Workshop

Autoimmunity is thought to result from a combination of genetics, environmental triggers, and stochastic events. Environmental factors, such as chemicals, drugs or infectious agents, have been implicated in the expression of autoimmune disease, yet human studies are extremely limited in their ability to test isolated exposures to demonstrate causation or to assess pathogenic mechanisms. In this review we examine the research literature on the ability of chemical, physical and biological agents to induce and/or exacerbate autoimmunity in a variety of animal models. There is no single animal model capable of mimicking the features of human autoimmune disease, particularly as related to environmental exposures. An objective, therefore, was to assess the types of information that can be gleaned from the use of animal models, and how well that information can be used to translate back to human health. Our review notes the importance of genetic background to the types and severity of the autoimmune response following exposure to environmental factors, and emphasizes literature where animal model studies have led to increased confidence about environmental factors that affect expression of autoimmunity. A high level of confidence was reached if there were multiple studies from different laboratories confirming the same findings. Examples include mercury, pristane, and infection with Streptococcus or Coxsackie B virus. A second level of consensus identified those exposures likely to influence autoimmunity but requiring further confirmation. To fit into this category, there needed to be significant supporting data, perhaps by multiple studies from a single laboratory, or repetition of some but not all findings in multiple laboratories. Examples include silica, gold, TCE, TCDD, UV radiation, and Theiler's murine encephalomyelitis virus. With the caveat that researchers must keep in mind the limitations and appropriate applications of the various approaches, animal models are shown to be extremely valuable tools for studying the induction or exacerbation of autoimmunity by environmental conditions and exposures.

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.

Toxicology of autoimmune diseases

Susceptibility to most autoimmune diseases is dependent on polygenic inheritance, environmental factors, and poorly defined stochastic events. One of the significant challenges facing autoimmune disease research is in identifying the specific events that trigger loss of tolerance and autoimmunity. Although many intrinsic factors, including age, sex, and genetics, contribute to autoimmunity, extrinsic factors such as drugs, chemicals, microbes, or other environmental factors can also act as important initiators. This review explores how certain extrinsic factors, namely, drugs and chemicals, can promote the development of autoimmunity, focusing on a few better characterized agents that, in most instances, have been shown to produce autoimmune manifestations in human populations. Mechanisms of autoimmune disease induction are discussed in terms of research obtained using specific animal models. Although a number of different pathways have been delineated for drug/chemical-induced autoimmunity, some similarities do exist, and a working model is proposed.

Transgenic expression of TGF-beta on thyrocytes inhibits development of spontaneous autoimmune thyroiditis and increases regulatory T cells in thyroids of NOD.H-2h4 mice

Transgenic NOD.H-2h4 mice expressing TGF-beta under control of the thyroglobulin promoter were generated to assess the role of TGF-beta in the development of thyrocyte hyperplasia. In contrast to nontransgenic littermates, which develop lymphocytic spontaneous autoimmune thyroiditis (L-SAT), all TGF-beta transgenic (Tg) mice given NaI water for 2-7 mo developed thyroid lesions characterized by severe thyroid epithelial cell hyperplasia and proliferation, with fibrosis and less lymphocyte infiltration than in nontransgenic mice. Most Tg mice produced less anti-mouse thyroglobulin autoantibody than did wild type (WT) mice. T cells from Tg and WT mice were equivalent in their ability to induce L-SAT after transfer to SCID or TCRalpha(-/-) mice. WT lymphocytes could transfer experimental autoimmune thyroiditis or L-SAT to Tg mice, indicating that the transgenic environment did not prevent migration of lymphocytes to the thyroid. Thyroids of Tg mice had higher frequencies of Foxp3(+) regulatory T cells (Tregs) compared with nontransgenic WT mice. Transient depletion of Tregs by anti-CD25 resulted in increased infiltration of inflammatory cells into thyroids of transgenic mice. Treg depletion also resulted in increased anti-mouse thyroglobulin autoantibody responses and increased expression of IFN-gamma and IFN-gamma-inducible chemokines in thyroids of Tg mice. The results suggest that spontaneous autoimmune thyroiditis is inhibited in mice expressing transgenic TGF-beta on thyrocytes, at least in part, because there is an increased frequency of Tregs in their thyroids.

T helper type 17 immune response plays an indispensable role for development of iodine-induced autoimmune thyroiditis in nonobese diabetic-H2h4 mice

T helper type 1(Th1)/Th2 paradigm has been expanded by discovery of a novel effector T cell (T(eff)) subset, Th17 cells, which produce a proinflammatory cytokine IL-17. Th17 cells have recently been shown to play a major role in numerous autoimmune diseases that had previously been thought to be Th1-dominant diseases. We here studied the significance of Th17 cells in iodine-induced autoimmune thyroiditis in nonobese diabetic-H2(h4) mice, a mouse model of Hashimoto's thyroiditis in humans, which spontaneously develop antithyroglobulin autoantibodies and intrathyroidal lymphocyte infiltration when supplied with iodine in the drinking water. We observed increased numbers of Th1 and Th17 cells in spleen and accumulation of both types of T(eff) in the thyroid glands of iodine-fed wild-type mice, indicating that Th17 cells as well as Th1 cells constitute thyroid lesions. Furthermore, the incidence and severity of intrathyroidal lymphocyte infiltration, and the titers of antithyroglobulin autoantibodies were markedly reduced in iodine-treated IL-17(-/-) mice as compared with wild-type mice. Of interest, IL-17(+/-) mice showed an intermediate phenotype. Therefore, the present study, together with a previous report demonstrating the importance of Th1, not Th2, immune response for developing thyroiditis using mice deficient for interferon-gamma or IL-4, clearly indicates that both Th1 and Th17 cells are critical T(eff) subsets for the pathogenesis of spontaneous autoimmune thyroiditis in nonobese diabetic-H2(h4) mice.

Environmental triggers of autoimmune thyroiditis

Autoimmune thyroiditis is among the most prevalent of all the autoimmunities. Autoimmune thyroiditis is multifactorial with contributions from genetic and environmental factors. Much information has been published about the genetic predisposition to autoimmune thyroiditis both in experimental animals and humans. There is, in contrast, very little data on environmental agents that can serve as the trigger for autoimmunity in a genetically predisposed host. The best-established environmental factor is excess dietary iodine. Increased iodine consumption is strongly implicated as a trigger for thyroiditis, but only in genetically susceptible individuals. However, excess iodine is not the only environmental agent implicated as a trigger leading to autoimmune thyroiditis. There are a wide variety of other synthetic chemicals that affect the thyroid gland or have the ability to promote immune dysfunction in the host. These chemicals are released into the environment by design, such as in pesticides, or as a by-product of industry. Candidate pollutants include polyaromatic hydrocarbons, polybrominated biphenols, and polychlorinated biphenols, among others. Infections are also reputed to trigger autoimmunity and may act alone or in concert with environmental chemicals. We have utilized a unique animal model, the NOD.H2(h4) mouse to explore the influence of iodine and other environmental factors on autoimmune thyroiditis.

TGF-beta promotes thyroid epithelial cell hyperplasia and fibrosis in IFN-gamma-deficient NOD.H-2h4 mice

IFN-gamma(-/-)NOD.H-2h4 mice given 0.05% NaI in their water develop severe thyroid epithelial cell (thyrocyte) hyperplasia and proliferation (TEC H/P) and fibrosis. Proliferating thyrocytes of IFN-gamma(-/-) mice with TEC H/P produce TGF-beta as demonstrated by immunohistochemical staining and in situ hybridization. Strong expression of activating phosphorylated Smad-2/3 and weak expression of inhibitory Smad-7 by proliferating thyrocytes correlate with the severity of TEC H/P. Splenocytes from IFN-gamma(-/-) mice with severe TEC H/P transfer severe TEC H/P to IFN-gamma(-/-)NOD.H-2h4.SCID mice. Mice given anti-TGF-beta had markedly reduced thyrocyte proliferation and decreased fibrosis compared with mouse Ig-treated controls, suggesting that TGF-beta plays an important role in development of TEC H/P induced by activated splenocytes. Moreover, transgenic IFN-gamma(-/-)NOD.H-2h4 mice expressing TGF-beta on thyrocytes all develop fibrosis and moderate to severe TEC H/P with accelerated kinetics, directly demonstrating a role for TGF-beta in severe TEC H/P and fibrosis.

B cell depletion inhibits spontaneous autoimmune thyroiditis in NOD.H-2h4 mice

B cells are important for the development of most autoimmune diseases. B cell depletion immunotherapy has emerged as an effective treatment for several human autoimmune diseases, although it is unclear whether B cells are necessary for disease induction, autoantibody production, or disease progression. To address the role of B cells in a murine model of spontaneous autoimmune thyroiditis (SAT), B cells were depleted from adult NOD.H-2h4 mice using anti-mouse CD20 mAb. Anti-CD20 depleted most B cells in peripheral blood and cervical lymph nodes and 50-80% of splenic B cells. Flow cytometry analysis showed that marginal zone B cells in the spleen were relatively resistant to depletion by anti-CD20, whereas most follicular and transitional (T2) B cells were depleted after anti-CD20 treatment. When anti-CD20 was administered before development of SAT, development of SAT and anti-mouse thyroglobulin autoantibody responses were reduced. Anti-CD20 also reduced SAT severity and inhibited further increases in anti-mouse thyroglobulin autoantibodies when administered to mice that already had autoantibodies and thyroid inflammation. The results suggest that B cells are necessary for initiation as well as progression or maintenance of SAT in NOD.H-2h4 mice.

Recognition of thyroglobulin by T cells: the role of iodine

Among known autoantigens, thyroglobulin (Tg) is unique in its capacity to store iodine, an element provided in our daily diet. Evolutionary pressure has sculpted Tg into a large molecular scaffolding to allow organification of iodide and its incorporation into thyroid hormones. The increase in molecular size and the posttranslational modification by iodine had to exact immunological consequences. Over the last 15 years, numerous Tg peptides-targets of thyroiditogenic T cells-have been mapped, raising questions regarding the mechanisms that maintain or abrogate immune tolerance against this large autoantigen. This review summarizes the work in this area and discusses the role iodine may play in these processes.

Contrasting roles of IFN-gamma in murine models of autoimmune thyroid diseases

Interferon-gamma (IFN-gamma), a prototypic proinflammatory cytokine produced by several different cell types, including the Th1 subset of CD4(+) T cells, plays an important role in inflammation and autoimmune diseases. This review focuses on the varied and often contrasting roles of IFN-gamma in three murine models of autoimmune thyroid disease, experimentally induced autoimmune thyroiditis, the model of iodine-induced spontaneous autoimmune thyroiditis in NOD.H-2h4 mice and several different murine models of Graves' disease.

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.

Induction of goitrous hypothyroidism by dietary iodide in SJL mice

Prolonged intake of large amounts of iodide has been reported to increase the incidence of goiter and/or hypothyroidism in humans as well as animals prone to spontaneous autoimmune thyroiditis. In the current study, we investigated the role of dietary iodide on the development of hypothyroidism, as well as thyroiditis, in strains of mice that do not develop spontaneous autoimmune thyroiditis. Intake of 0.05% NaI via drinking water for 10 wk induced hypothyroidism in SJL/J mice as indicated by elevated TSH and depressed total T(4) values in serum and formation of colloidal goiter with an inactive flattened thyroid epithelium. Hypothyroidism did not appear to have an autoimmune basis because only focal mononuclear cell infiltrates were found intrathyroidally, and antithyroglobulin antibodies or increased organification of iodide were not detected. These phenomena were not observed in similarly treated CBA/J mice, suggesting polymorphisms in genes controlling events downstream of iodide uptake by thyrocytes. Interestingly, RT-PCR analysis indicated that unlike CBA/J, SJL/J mice could not down-regulate Na/I symporter gene expression during the NaI treatment. No significant temporal or strain differences were observed regarding the expression of thyroglobulin, pendrin, thyroid peroxidase, and DUOX1 and DUOX2 genes after NaI intake. Our results point to the generation of a mouse model for the study of iodine-induced hypothyroidism, which does not seem to have an autoimmune basis.

Depletion of CD4+CD25+ regulatory T cells exacerbates sodium iodide-induced experimental autoimmune thyroiditis in human leucocyte antigen DR3 (DRB1*0301) transgenic class II-knock-out non-obese diabetic mice

Both genetic and environmental factors contribute to autoimmune disease development. Previously, we evaluated genetic factors in a humanized mouse model of Hashimoto's thyroiditis (HT) by immunizing human leucocyte antigen DR3 (HLA-DR3) and HLA-DQ8 transgenic class II-knock-out non-obese diabetic (NOD) mice. DR3+ mice were susceptible to experimental autoimmune thyroiditis (EAT) induction by both mouse thyroglobulin (mTg) and human (h) Tg, while DQ8+ mice were weakly susceptible only to hTg. As one environmental factor associated with HT and tested in non-transgenic models is increased sodium iodide (NaI) intake, we examined the susceptibility of DR3+ and/or DQ8+ mice to NaI-induced disease. Mice were treated for 8 weeks with NaI in the drinking water. At 0 x 05% NaI, 23% of DR3+, 0% of DQ8+ and 20% of DR3+DQ8+ mice had thyroid destruction. No spleen cell proliferation to mTg was observed. Most mice had undetectable anti-mTg antibodies, but those with low antibody levels usually had thyroiditis. At 0.3% NaI, a higher percentage of DR3+ and DR3+DQ8+ mice developed destructive thyroiditis, but it was not statistically significant. However, when DR3+ mice had been depleted of CD4+CD25+ regulatory T cells prior to NaI treatment, destructive thyroiditis (68%) and serum anti-mTg antibodies were exacerbated further. The presence of DQ8 molecules does not alter the susceptibility of DR3+DQ8+ mice to NaI-induced thyroiditis, similar to earlier findings with mTg-induced EAT. Susceptibility of DR3+ mice to NaI-induced EAT, in both the presence and absence of regulatory T cells, demonstrates the usefulness of HLA class II transgenic mice in evaluating the roles of environmental factors and immune dysregulation in autoimmune thyroid disease.

Identification of nuclear spliceosomal antigens targeted by NOD mouse antibodies following sodium iodide intake

The non-obese diabetic (NOD) mouse spontaneously develops a range of autoreactive responses including an autoantibody response to nuclear antigens. As elevated dietary iodine has been shown to increase thyroid autoimmune pathology in NOD mice, the effect of sodium iodide (NaI) on the development of anti-nuclear antibodies (ANA) was assessed. Interestingly, the NaI symporter is expressed in both thyroid and salivary glands. Elevated dietary iodine was found to increase the percentage of male NOD mice developing autoantibodies. Specifically, the nuclear autoantibodies that develop in NOD mice were shown to target specific spliceosomal components. The target specificity of the autoantibodies was determined using recombinant spliceosomal proteins and shown to include U1A, U170K, U2B'', U2A', as well as the Sm proteins D1, D2, and B. The autoantibody isotypes most consistently represented were IgG2a and IgG2b.

B cell-deficient NOD.H-2h4 mice have CD4+CD25+ T regulatory cells that inhibit the development of spontaneous autoimmune thyroiditis

Wild-type (WT) NOD.H-2h4 mice develop spontaneous autoimmune thyroiditis (SAT) when given 0.05% NaI in their drinking water, whereas B cell-deficient NOD.H-2h4 mice are SAT resistant. To test the hypothesis that resistance of B cell-deficient mice to SAT was due to the activity of regulatory CD4+CD25+ T (T reg) cells activated if autoantigen was initially presented on non-B cells, CD25+ T reg cells were transiently depleted in vivo using anti-CD25. B cell-deficient NOD.H-2h4 mice given three weekly injections of anti-CD25 developed SAT 8 wk after NaI water. Thyroid lesions were similar to those in WT mice except there were no B cells in thyroid infiltrates. WT and B cell-deficient mice had similar numbers of CD4+CD25+Foxp3+ cells. Mice with transgenic nitrophenyl-specific B cells unable to secrete immunoglobulin were also resistant to SAT, and transient depletion of T reg cells resulted in severe SAT with both T and B cells in thyroid infiltrates. T reg cells that inhibit SAT were eliminated by day 3 thymectomy, indicating they belong to the subset of naturally occurring T reg cells. However, T reg cell depletion did not increase SAT severity in WT mice, suggesting that T reg cells may be nonfunctional when effector T cells are activated; i.e., by autoantigen-presenting B cells.

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.

Spontaneous lymphocyt ic thyroiditis in interferon regulatory factor-1 deficient non-obese diabetic mice

Interferon regulatory factor-1 (IRF-1) is a transcription factor involved in interferon-mediated immune reaction, CD8+ T cell differentiation and development of T helper 1 immune reaction. We have recently demonstrated that IRF-1 is pivotal in iodine-induced lymphocytic thyroiditis (LT) in non-obese diabetic (NOD) mice. However, it remains unclear whether the mechanism involved in spontaneous LT is identical with iodine-induced LT in NOD mice. To determine the role of IRF-1 in spontaneous LT, we used IRF-1 deficient NOD mice as well as IRF-1 +/+ and +/- mice which were free from treatments for LT induction, and LT was evaluated at 24 weeks of age. IRF-1 +/+, +/- and -/- mice developed LT spontaneously, and there were no differences among the 3 IRF-1 genotypes in the incidence and severity of LT. Whereas both CD4+ and CD8+ T cells were present in the diseased thyroid of IRF-1 +/+ mice, CD8+ T cells were absent in the thyroid of IRF-1 -/- mice. MHC class II antigen expression was induced in the inflamed thyroid of IRF-1 -/- mice comparable to IRF-1 +/+ mice. There was a selective reduction in the number of CD8+ T cells in the spleen of IRF-1 -/- mice. IFNgamma production, but not IL-10, by concanavalin A-stimulated splenocytes was significantly reduced in IRF-1 deficient mice. These results suggest that IRF-1 plays only a minor role in spontaneous LT in NOD mice and, furthermore, the mechanism involved in spontaneous LT is different from that of iodine-induced LT in NOD mice.

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

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

Characterization of rat CD8+ uveitogenic T cells specific for interphotoreceptor retinal-binding protein 1177-1191

The uveitogenic T cells that mediate experimental autoimmune uveitis are commonly assumed to be exclusively CD4(+). In the present study, we showed that, although a panel of long-term cultured rat uveitogenic T cell lines specific for the interphotoreceptor retinal-binding protein peptide, R16, all expressed CD4, approximately 40% of the R16-specific uveitogenic T cells freshly prepared from Ag-immunized rats were CD8(+)alphabetaTCR(+), as demonstrated by CFSE staining. We showed that the expansion of these CD8(+)alphabetaTCR(+) T cells was Ag-specific and that highly purified CD8(+) R16-specific T cells were able to induce uveitis on transfusion into naive rats. Moreover, CD8(+) uveitogenic T cells more readily switched phenotype from, and to, TCR(-)CD8(-)CD4(-) during in vivo or in vitro activation compared with their CD4(+) counterparts. In a previous study, we showed that highly purified CD8(+) myelin oligodendrocyte glycoprotein-specific T cells induced more severe autoimmune encephalomyelitis than the corresponding CD4(+) T cells. In this study, we show that an interphotoreceptor retinal-binding protein peptide consistently activated a high proportion of CD8(+)alphabetaTCR(+) T cells, which were uveitogenic in Lewis rats.

FLIP and FasL expression by inflammatory cells vs thyrocytes can be predictive of chronic inflammation or resolution of autoimmune thyroiditis

Spontaneous autoimmune thyroiditis (SAT) in NOD.H-2h4 mice is a model of chronic inflammation of the thyroid, while granulomatous experimental autoimmune thyroiditis (G-EAT) is a model with spontaneous resolution of inflammation. In chronic inflammation (SAT), Fas, FasL, and FLIP were upregulated and predominant in inflammatory cells. There were few apoptotic cells, and low expression of active caspase-8 and -3. In resolving G-EAT in CBA/J and NOD.H-2h4 mice, FasL and FLIP were predominantly expressed by thyrocytes. There were many apoptotic inflammatory cells, and increased expression of active caspase-8 and -3. Depletion of CD8+ T cells inhibited G-EAT resolution and resulted in chronic inflammation. FLIP was expressed predominantly by inflammatory cells, and apoptosis of inflammatory cells and expression of active caspase-3 was reduced as in chronic SAT. Thus, differences in expression of pro- or antiapoptotic molecules in SAT or G-EAT were apparently related to the acute vs chronic nature of the inflammatory response rather than the method of disease induction. Upregulation of FLIP by inflammatory cells may block Fas-mediated apoptosis, contributing to chronic inflammation, whereas increased FLIP expression by thyrocytes in resolving G-EAT may protect thyrocytes from apoptosis, and FasL expression by thyrocytes may induce apoptosis of inflammatory cells, contributing to resolution.

Chemokines determine local lymphoneogenesis and a reduction of circulating CXCR4+ T and CCR7 B and T lymphocytes in thyroid autoimmune diseases

Chemokines and their corresponding receptors are crucial for the recruitment of lymphocytes into the lymphoid organs and for its organization acting in a multistep process. Tissues affected by autoimmune disease often contain ectopic lymphoid follicles which, in the case of autoimmune thyroid disorders, are highly active and specific for thyroid Ags although its pathogenic role remains unclear. To understand the genesis of these lymphoid follicles, the expression of relevant cytokines and chemokines was assessed by real time PCR, immunohistochemistry and by in vitro assays in autoimmune and nonautoimmune thyroid glands. Lymphotoxin alpha, lymphotoxin beta, C-C chemokine ligand (CCL) 21, CXC chemokine ligand (CXCL) 12, CXCL13, and CCL22 were increased in thyroids from autoimmune patients, whereas CXCL12, CXCL13, and CCL22 levels were significantly higher in autoimmune glands with ectopic secondary lymphoid follicles than in those without follicles. Interestingly, thyroid epithelium produced CXCL12 in response to proinflammatory cytokines providing a possible clue for the understanding of how tissue stress may lead to ectopic follicle formation. The finding of a correlation between chemokines and thyroid autoantibodies further suggests that intrathyroidal germinal centers play a significant role in the autoimmune response. Unexpectedly, the percentage of circulating CXCR4(+) T cells and CCR7(+) B and T cells (but not of CXCR5) was significantly reduced in PBMCs of patients with autoimmune thyroid disease when they were compared with their intrathyroidal lymphocytes. This systemic effect of active intrathyroidal lymphoid tissue emerges as a possible new marker of thyroid autoimmune disease activity.

Kinetics of mononuclear cell infiltration and cytokine expression in iodine-induced thyroiditis in the NOD-H2h4 mouse

Mononuclear cell infiltration of the thyroid gland is a common histologic feature of chronic lymphocytic thyroiditis. Although the infiltrating mononuclear cells have been implicated in the destruction of the thyroid, information concerning the progression of infiltration into the thyroid is limited. In this report, we examine the composition and kinetics of mononuclear cell infiltration in the thyroid and the expression of major histocompatibility complex class II (I-Ak), IL-12, and IFN-gamma in the thyroid of the NOD-H2h4 mouse, a model of spontaneous autoimmune thyroiditis accelerated by the administration of excess dietary iodine. Mice were given a low dose of 0.015% NaI in their drinking water for 2, 4, 6, 8, and 16 weeks, and thyroids were removed, serially sectioned, and stained in an avidin-biotin peroxidase assay. The thyroid infiltrate included CD4+ and CD8+ T cells, F4/80+ macrophages, and B220+ B cells. After 2 weeks of iodine treatment, CD4+ T cells were the first seen in the thyroid, followed by CD8+ T cells and F4/80+ macrophages. B220+ B cells entered the thyroid after 4 weeks of iodine treatment. IL-12 and IFN-gamma positive cells were located in the thyroid early in disease and were up-regulated in the focal accumulations of infiltrating cells. Thyrocytes clearly expressed I-Ak after 4 weeks of iodine treatment near the location of mononuclear cell infiltration.