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.

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.H2^h4 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.H2^h4 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.H2^h4 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.H2^h4 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.

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.

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.

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).H2^h4 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.H2^h4 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.H2^h4 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.H2^h4 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.H2^h4 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.

Critical Differences between Induced and Spontaneous Mouse Models of Graves' Disease with Implications for Antigen-Specific Immunotherapy in Humans

Graves' hyperthyroidism, a common autoimmune disease caused by pathogenic autoantibodies to the thyrotropin (TSH) receptor (TSHR), can be treated but not cured. This single autoantigenic target makes Graves' disease a prime candidate for Ag-specific immunotherapy. Previously, in an induced mouse model, injecting TSHR A-subunit protein attenuated hyperthyroidism by diverting pathogenic TSHR Abs to a nonfunctional variety. In this study, we explored the possibility of a similar diversion in a mouse model that spontaneously develops pathogenic TSHR autoantibodies, NOD.H2^h4 mice with the human (h) TSHR (hTSHR) A-subunit transgene expressed in the thyroid and (shown in this article) the thymus. We hypothesized that such diversion would occur after injection of "inactive" hTSHR A-subunit protein recognized only by nonpathogenic (not pathogenic) TSHR Abs. Surprisingly, rather than attenuating the pre-existing pathogenic TSHR level, in TSHR/NOD.H2^h4 mice inactive hTSHR Ag injected without adjuvant enhanced the levels of pathogenic TSH-binding inhibition and thyroid-stimulating Abs, as well as nonpathogenic Abs detected by ELISA. This effect was TSHR specific because spontaneously occurring autoantibodies to thyroglobulin and thyroid peroxidase were unaffected. As controls, nontransgenic NOD.H2^h4 mice similarly injected with inactive hTSHR A-subunit protein unexpectedly developed TSHR Abs, but only of the nonpathogenic variety detected by ELISA. Our observations highlight critical differences between induced and spontaneous mouse models of Graves' disease with implications for potential immunotherapy in humans. In hTSHR/NOD.H2^h4 mice with ongoing disease, injecting inactive hTSHR A-subunit protein fails to divert the autoantibody response to a nonpathogenic form. Indeed, such therapy is likely to enhance pathogenic Ab production and exacerbate Graves' disease in humans.

Evidence that TSH Receptor A-Subunit Multimers, Not Monomers, Drive Antibody Affinity Maturation in Graves' Disease

CONTEXT

The TSH receptor (TSHR) A-subunit shed from the cell surface contributes to the induction and/or affinity maturation of pathogenic TSHR autoantibodies in Graves' disease.

OBJECTIVE

This study aimed to determine whether the quaternary structure (multimerization) of shed A-subunits influences pathogenic TSHR autoantibody generation.

DESIGN

The isolated TSHR A-subunit generated by transfected mammalian cells exists in two forms; one (active) is recognized only by Graves' TSHR autoantibodies, the second (inactive) is recognized only by mouse monoclonal antibody (mAb) 3BD10. Recent evidence suggests that both Graves' TSHR autoantibodies and mAb 3BD10 recognize the A-subunit monomer. Therefore, if the A-subunit monomer is an immunogen, Graves' sera should have antibodies to both active and inactive A-subunits. Conversely, restriction of TSHR autoantibodies to active A-subunits would be evidence of a role for shed A-subunit multimers, not monomers, in the pathogenesis of Graves' disease. Therefore, we tested a panel of Graves' sera for their relative recognition of active and inactive A-subunits.

RESULTS

Of 34 sera from unselected Graves' patients, 28 were unequivocally positive in a clinical TSH binding inhibition assay. None of the latter sera, as well as 8/9 sera from control individuals, recognized inactive A-subunits on ELISA. In contrast to Graves' sera, antibodies induced in mice, not by shedding from the TSHR holoreceptor, but by immunization with adenovirus expressing the free human A-subunit, were directed to both the active and inactive A-subunit forms.

CONCLUSIONS

The present study supports the concept that pathogenic TSHR autoantibody affinity maturation in Graves' disease is driven by A-subunit multimers, not monomers.

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.

Genetic linkages for thyroxine released in response to thyrotropin stimulation in three sets of recombinant inbred mice provide evidence for shared and novel genes controlling thyroid function

BACKGROUND

Graves' hyperthyroidism is induced by immunizing mice with adenovirus expressing the human thyrotropin (TSH)-receptor. Using families of recombinant-inbred mice, we previously discovered that genetic susceptibility to induced thyroid-stimulating antibodies and hyperthyroidism are linked to loci on different chromosomes, indicating a fundamental genetic difference in thyroid sensitivity to ligand stimulation. An approach to assess thyroid sensitivity involves challenging genetically diverse lines of mice with TSH and measuring the genotype/strain-specific increase in serum thyroxine (T4).

METHODS

We investigated genetic susceptibility and genetic control of T4 stimulation by 10 mU bovine TSH in female mice of the CXB, BXH, and AXB/BXA strain families, all previously studied for induced Graves' hyperthyroidism.

RESULTS

Before TSH injection, T4 levels must be suppressed by inhibiting endogenous TSH secretion. Three daily intraperitoneal L-triiodothyronine injections efficiently suppressed serum T4 in females of 50 of 51 recombinant inbred strains. T4 stimulation by TSH was more strongly linked in CXB and BXH sets, derived from parental strains with divergent T4 stimulation, than in AXB/BXA strains generated from parents with similar TSH-induced responses. Genetic loci linked to the acute TSH-induced T4 response (hours) were not the same as those linked to induced hyperthyroidism (which develops over months).

CONCLUSIONS

Genetic susceptibility for thyroid sensitivity to TSH stimulation was distinct for three families of inbred mouse lines. These observations parallel the human situation with multiple genetic loci contributing to the same trait and different loci associated with the same trait in different ethnic groups. Of the genetic loci highlighted in mice, three overlap with, or are located up or downstream, of human TSH-controlling genes. Other studies show that human disease genes can be identified through cross-species gene mapping of evolutionary conserved processes. Consequently, our findings suggest that novel thyroid function genes may yet be revealed in humans.

Role of self-tolerance and chronic stimulation in the long-term persistence of adenovirus-induced thyrotropin receptor antibodies in wild-type and transgenic mice

BACKGROUND

Graves'-like disease, reflected by thyrotropin receptor (TSHR) antibodies and hyperthyroidism in some mouse strains, can be induced by immunization with adenovirus-expressing DNA for the human TSHR or its A-subunit. The conventional approach involves two or three adenovirus injections at 3-week intervals and euthanasia 10 weeks after the first injection. To investigate TSHR antibody persistence in mice with differing degrees of self-tolerance to the TSHR A-subunit, we studied the effect of delaying euthanasia until 20 weeks after the initial immunization.

METHODS

Wild-type (WT) mice and transgenic (tg) mice expressing low intrathyroidal levels of the human TSHR A-subunit were immunized with A-subunit-adenovirus on two occasions; a second group of mice was immunized on three occasions. Sera obtained 4, 10, and 20 weeks (euthanasia) after the initial immunization were tested for thyrotropin (TSH) binding inhibition (TBI), antibody binding to TSHR A-subunit protein-coated enzyme-linked immunosorbent assay (ELISA) plates, and thyroid stimulating antibody activity (TSAb; cyclic adenosine monophosphate [cAMP] generation). Serum thyroxine (T4) and thyroid histology were studied at euthanasia.

RESULTS

THE majority of WT mice retained high TSHR antibody levels measured by TBI or ELISA at euthanasia but only about 50% were TSAb positive. Low-expressor tgs exhibited self-tolerance, with fewer mice positive by TBI or ELISA and antibody levels were lower than in WT littermates. In WT mice, antibody persistence was similar after two or three immunizations; for tgs, only mice immunized three times had detectable TSAb at 20 weeks. Unlike our previous observations of hyperthyroidism in WT mice examined 4 or 10 weeks after immunization, all mice were euthyroid at 20 weeks.

CONCLUSIONS

Our findings for induced TSHR antibodies in mice, similar to data for human thyroid autoantibodies, indicate that the parameters that contribute to the concentration of the antibody and thereby play a critical role in long-term persistence of TSHR antibodies are the degree of self-tolerance to the TSHR and chronic stimulation.

An attempt to induce "Graves' disease of the gonads" by immunizing mice with the luteinizing hormone receptor provides insight into breaking tolerance to self-antigens

BACKGROUND

Gonadotropin receptors, unlike the thyrotropin receptor (TSHR), are not cleaved into disulfide-linked A- and B-subunits, nor do they shed A-subunits. Heavily glycosylated TSHR A-subunits initiate or amplify responses leading to stimulating TSHR-autoantibodies and Graves' hyperthyroidism.

METHODS

To investigate the possibility that mice immunized with luteinizing hormone receptor (LHR) would develop functional antibodies, we constructed adenoviruses expressing the rat-LH holoreceptor (LHR-Ad) and an LHR A-subunit equivalent (LHR-289-Ad). Female BALB/c mice were immunized with high doses (10(11) particles) of LHR-Ad, LHR-289-Ad, or control (Con)-Ad. Sera were tested using LHR-expressing eukaryotic cells for antibody binding by flow cytometry and for bioactivity by measuring cyclic adenosine monophosphate (cAMP) stimulation.

RESULTS

Elevated serum binding to LHR cells in some LHR-Ad and LHR-289-Ad immunized mice was not specific for LHR-expressing cells. Moreover, sera lacked bioactivity, consistent with unchanged serum estradiol and ovary histology. The difference between rat and mouse LHR-ectodomains is relatively small (3% at the amino-acid level). In contrast, despite amino-acid identity, immunization of mice with adenovirus expressing membrane-bound mouse thyroid peroxidase (TPO), but not soluble mouse TPO ectodomain, elicited strong TPO-specific antibodies.

CONCLUSIONS

Our investigations provide insight into antibody responses to self-antigens. First, antibodies are induced to large self-antigens like mouse-TPO when membrane bound. Second, lesser amino acid homology between the immunogen and mouse protein (91% vs. 97% for the human-TSHR and rat-LHR, respectively) favors antibody induction. Finally, from previous studies demonstrating the immunogenicity of the highly glycosylated human TSHR A-subunit versus our present data for the nonimmunogenic less glycosylated rat LHR, we suggest that the extent of glycosylation contributes to breaking self-tolerance.

Distinct genetic signatures for variability in total and free serum thyroxine levels in four sets of recombinant inbred mice

C3H/He and BALB/c mice have elevated serum thyroxine levels associated with low deiodinase type-1 activity whereas C57BL/6 (B6) mice have low thyroxine levels and elevated deiodinase type-1 activity. High-resolution genetic maps are available for four sets of recombinant inbred (RI) mice derived from B6 parents bred to C3H/He, BALB/c, DBA/2, or A strains. Total and free T4 (T-T4 and F-T4) levels in females from these RI sets (BXH, CXB, BXD, and AXBXA) were analyzed to test two hypotheses: first, serum T4 variability is linked to the deiodinase type-1 gene; second, because of their shared B6 parent, the RI sets will share linkages responsible for T-T4 or F-T4 variability. A number of chromosomes (Chr) and loci were linked to T-T4 (Chr 1, 4, 13, 11) or F-T4 (Chr 1, 6, 13, 18, 19). Linkage between T-T4 and Chr 4 was limited to CXB and BXH strains, but the locus was distinct from the deiodinase type-1 gene. Surprisingly, many linkages were unique providing "genetic signatures" for T-T4 or F-T4 in each set of RI mice. Indeed, the strongest linkage between T-T4 (or F-T4) and a Chr 2 locus (logarithm of the odds scores >4.4) was only observed in AXBXA strains. Some loci corresponded to genes/Chr associated in humans with variable TSH or T-T4 levels. Unlike inbred mice, human populations are extremely diverse. Consequently, our data suggest that the contributions of unique chromosomes/loci controlling T-T4 and F-T4 in distinct human subgroups are likely to be "buried" in genetic analyses of heterogeneous human populations.

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.

Attenuation of induced hyperthyroidism in mice by pretreatment with thyrotropin receptor protein: deviation of thyroid-stimulating to nonfunctional antibodies

Graves'-like hyperthyroidism is induced by immunizing BALB/c mice with adenovirus expressing the thyrotropin receptor (TSHR) or its A-subunit. Nonantigen-specific immune strategies can block disease development and some reduce established hyperthyroidism, but these approaches may have unforeseen side effects. Without immune stimulation, antigens targeted to the mannose receptor induce tolerance. TSHR A-subunit protein generated in eukaryotic cells binds to the mannose receptor. We tested the hypothesis that eukaryotic A-subunit injected into BALB/c mice without immune stimulation would generate tolerance and protect against hyperthyroidism induced by subsequent immunization with A-subunit adenovirus. Indeed, one sc injection of eukaryotic, glycosylated A-subunit protein 1 wk before im A-subunit-adenovirus immunization reduced serum T(4) levels and the proportion of thyrotoxic mice decreased from 77 to 22%. Prokaryotic A-subunit and other thyroid proteins (thyroglobulin and thyroid peroxidase) were ineffective. A-subunit pretreatment reduced thyroid-stimulating and TSH-binding inhibiting antibodies, but, surprisingly, TSHR-ELISA antibodies were increased. Rather than inducing tolerance, A-subunit pretreatment likely expanded B cells that secrete nonfunctional antibodies. Follow-up studies supported this possibility and also showed that eukaryotic A-subunit administration could not reverse hyperthyroidism in mice with established disease. In conclusion, glycosylated TSHR A-subunit is a valuable immune modulator when used before immunization. It acts by deviating responses away from pathogenic toward nonfunctional antibodies, thereby attenuating induction of hyperthyroidism. However, this protein treatment does not reverse established hyperthyroidism. Our findings suggest that prophylactic TSHR A-subunit protein administration in genetically susceptible individuals may deviate the autoantibody response away from pathogenic epitopes and provide protection against future development of Graves' disease.

Studies in mice deficient for the autoimmune regulator (Aire) and transgenic for the thyrotropin receptor reveal a role for Aire in tolerance for thyroid autoantigens

The autoimmune regulator (Aire) mediates central tolerance for many autoantigens, and autoimmunity occurs spontaneously in Aire-deficient humans and mice. Using a mouse model of Graves' disease, we investigated the role of Aire in tolerance to the TSH receptor (TSHR) in Aire-deficient and wild-type mice (hyperthyroid-susceptible BALB/c background). Mice were immunized three times with TSHR A-subunit expressing adenovirus. The lack of Aire did not influence T-cell responses to TSHR protein or TSHR peptides. However, antibody levels were higher in Aire-deficient than wild-type mice after the second (but not the third) immunization. After the third immunization, hyperthyroidism persisted in a higher proportion of Aire-deficient than wild-type mice. Aire-deficient mice were crossed with transgenic strains expressing high or low-intrathyroidal levels of human TSHR A subunits. In the low-expressor transgenics, Aire deficiency had the same effect on the pattern of the TSHR antibody response to immunization as in nontransgenics, although the amplitude of the response was lower in the transgenics. High-expressor A-subunit transgenics were unresponsive to immunization. We examined intrathymic expression of murine TSHR, thyroglobulin, and thyroid peroxidase (TPO), the latter two being the dominant autoantigens in Hashimoto's thyroiditis (particularly TPO). Expression of the TSHR and thyroglobulin were reduced in the absence of Aire. Dramatically, thymic expression of TPO was nearly abolished. In contrast, the human A-subunit transgene, lacking a potential Aire-binding motif, was unaffected. Our findings provide insight into how varying intrathymic autoantigen expression may modulate thyroid autoimmunity and suggest that Aire deficiency may contribute more to developing Hashimoto's thyroiditis than Graves' disease.

Vitamin D deficiency modulates Graves' hyperthyroidism induced in BALB/c mice by thyrotropin receptor immunization

TSH receptor (TSHR) antibodies and hyperthyroidism are induced by immunizing mice with adenovirus encoding the TSHR or its A-subunit. Depleting regulatory T cells (Treg) exacerbates thyrotoxicosis in susceptible BALB/c mice and induces hyperthyroidism in normally resistant C57BL/6 mice. Vitamin D plays an important role in immunity; high dietary vitamin D intake suppresses (and low intake enhances) adaptive immune responses. Vitamin D-induced immunosuppression may enhance Treg. Therefore, we hypothesized that decreased vitamin D intake would mimic Treg depletion and enhance hyperthyroidism induced by A-subunit adenovirus immunization. BALB/c mice had a reduced ability vs. C57BL/6 mice to generate the active metabolite of vitamin D (1,25-dihydroxyvitamin D3). Vitamin D deficiency induced subtle immune changes in BALB/c (not C57BL/6) mice. Compared with mice fed regular chow, vitamin D-deprived BALB/c mice had fewer splenic B cells and decreased interferon-gamma responses to mitogen and lacked memory T-cell responses to A-subunit protein. However, vitamin D deficiency did not alter TSHR antibody responses measured by ELISA, TSH binding inhibition, or cAMP generation from TSHR-expressing cells. Unexpectedly, compared with vitamin D-sufficient mice, vitamin D-deficient BALB/c mice had lower preimmunization T(4) levels and developed persistent hyperthyroidism. This difference was unrelated to the immunological changes between vitamin D-deficient or -sufficient animals. Previously, we found that different chromosomes or loci confer susceptibility to TSHR antibody induction vs. thyroid function. Our present studies provide evidence that an environmental factor, vitamin D, has only minor effects on induced immunity to the TSHR but directly affects thyroid function in mice.

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

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

Shared and unique susceptibility genes in a mouse model of Graves' disease determined in BXH and CXB recombinant inbred mice

Susceptibility genes for TSH receptor (TSHR) antibodies and hyperthyroidism can be probed in recombinant inbred (RI) mice immunized with adenovirus expressing the TSHR A-subunit. The RI set of CXB strains, derived from susceptible BALB/c and resistant C57BL/6 (B6) mice, were studied previously. High-resolution genetic maps are also available for RI BXH strains, derived from B6 and C3H/He parents. We found that C3H/He mice develop TSHR antibodies, and some animals become hyperthyroid after A-subunit immunization. In contrast, the responses of the F1 progeny of C3H/He x B6 mice, as well as most BXH RI strains, are dominated by the B6 resistance to hyperthyroidism. As in the CXB set, linkage analysis of BXH strains implicates different chromosomes (Chr) or loci in the susceptibility to induced TSHR antibodies vs. hyperthyroidism. Importantly, BXH and CXB mice share genetic loci controlling the generation of TSHR antibodies (Chr 17, major histocompatibility complex region, and Chr X) and development of hyperthyroidism (Chr 1 and 3). Moreover, some chromosomal linkages are unique to either BXH or CXB strains. An interesting candidate gene linked to thyroid-stimulating antibody generation in BXH mice is the Ig heavy chain locus, suggesting a role for particular germline region genes as precursors for these antibodies. In conclusion, our findings reinforce the importance of major histocompatibility complex region genes in controlling the generation of TSHR antibodies measured by TSH binding inhibition. Moreover, these data emphasize the value of RI strains to dissect the genetic basis for induced TSHR antibodies vs. their effects on thyroid function in Graves' disease.

The link between Graves' disease and Hashimoto's thyroiditis: a role for regulatory T cells

Hyperthyroidism in Graves' disease is caused by thyroid-stimulating autoantibodies to the TSH receptor (TSHR), whereas hypothyroidism in Hashimoto's thyroiditis is associated with thyroid peroxidase and thyroglobulin autoantibodies. In some Graves' patients, thyroiditis becomes sufficiently extensive to cure the hyperthyroidism with resultant hypothyroidism. Factors determining the balance between these two diseases, the commonest organ-specific autoimmune diseases affecting humans, are unknown. Serendipitous findings in transgenic BALB/c mice, with the human TSHR A-subunit targeted to the thyroid, shed light on this relationship. Of three transgenic lines, two expressed high levels and one expressed low intrathyroidal A-subunit levels (Hi- and Lo-transgenics, respectively). Transgenics and wild-type littermates were depleted of T regulatory cells (Treg) using antibodies to CD25 (CD4(+) T cells) or CD122 (CD8(+) T cells) before TSHR-adenovirus immunization. Regardless of Treg depletion, high-expressor transgenics remained tolerant to A-subunit-adenovirus immunization (no TSHR antibodies and no hyperthyroidism). Tolerance was broken in low-transgenics, although TSHR antibody levels were lower than in wild-type littermates and no mice became hyperthyroid. Treg depletion before immunization did not significantly alter the TSHR antibody response. However, Treg depletion (particularly CD25) induced thyroid lymphocytic infiltrates in Lo-transgenics with transient or permanent hypothyroidism (low T(4), elevated TSH). Neither thyroid lymphocytic infiltration nor hypothyroidism developed in similarly treated wild-type littermates. Remarkably, lymphocytic infiltration was associated with intermolecular spreading of the TSHR antibody response to other self thyroid antigens, murine thyroid peroxidase and thyroglobulin. These data suggest a role for Treg in the natural progression of hyperthyroid Graves' disease to Hashimoto's thyroiditis and hypothyroidism in humans.

Probing the genetic basis for thyrotropin receptor antibodies and hyperthyroidism in immunized CXB recombinant inbred mice

Immunization with adenovirus encoding the TSH receptor (TSHR) or its A-subunit induces Graves' hyperthyroidism in BALB/c and BALB/c x C57BL/6 offspring but not C57BL/6 mice. High-resolution genetic maps are available for 13 recombinant inbred CXB strains generated from BALB/c x C57BL/6 progeny by repeated brother x sister matings to establish fully inbred lines. CXB strains were studied before and after A-subunit adenovirus immunization for TSHR antibodies (TBI, inhibition of TSH binding), serum T4, and thyroid histology. All strains developed TBI activity (at variable levels), six strains became hyperthyroid, and one was overtly thyrotoxic. No low TBI responders became hyperthyroid, but high TBI did not predict hyperthyroidism. Preimmunization T4 levels varied in different CXB strains and was unrelated to subsequent T4 elevation. Linkage analysis indicated that different chromosomes were involved in generating TSHR antibodies and serum T4 before and after immunization. TBI activity was linked in part with major histocompatibility (MHC) genes on chromosome 17 (Chr 17) but induced Graves' disease involved non-MHC genes (Chr 19 and 10). The Chr 10 locus is close to the Trhde gene that encodes TSH-releasing hormone degrading enzyme. Expression of Trhde is controlled by thyroid hormones and linkage with a thyroid function-related gene is intriguing. Our data, the first genome scan in murine Graves' disease, provides insight into the role of MHC and non-MHC genes in human and murine Graves' disease. Finally, our study demonstrates the potential of recombinant inbred mice for discriminating between immune-response genes and thyroid function susceptibility genes in Graves' disease.

Blockade of costimulation between T cells and antigen-presenting cells: an approach to suppress murine Graves' disease induced using thyrotropin receptor-expressing adenovirus

OBJECTIVE

Immune responses require costimulatory interactions between molecules on antigen-presenting cells and T cells: CD40 binding to CD40 ligand and B7 binding to CD28. Graves' hyperthyroidism is induced in BALB/c mice by immunization with thyrotropin receptor (TSHR) A-subunit adenovirus (Ad-A-subunit). We attempted to modulate Ad-A-subunit-induced Graves' disease using adenoviruses expressing costimulation "decoys": CD40-IgG-Fc (CD40-Ig) to block CD40:CD40-ligand interactions and CTLA4-Fc (CTLA4-Ig) to prevent B7:CD28 binding.

OUTCOME

Unexpectedly, coimmunizing mice with Ad-A-subunit and excess control adenovirus (1:10 Ad-A-subunit:Ad-control) reduced TSHR antibody levels (thyrotropin binding inhibition [TBI]). Furthermore, only 15% of mice developed hyperthyroidism versus 75% using the same Ad-A-subunit dose (10(8) particles) without Ad-control. This effect was related to the dose of control adenovirus but not to the adenovirus insert, the timing or immunization site. Increasing the Ad-subunit dose (10(9) particles) and decreasing the control adenovirus dose (10:1 Ad-A-subunit:Ad-control) induced high TBI levels and 80% of mice were hyperthyroid. Coimmunization with Ad-CD40-Ig (but not Ad-CTLA4-Ig) reduced the incidence of hyperthyroidism to 40%.

CONCLUSIONS

Using appropriate controls and adenovirus ratios, our data suggest the importance of CD40:CD40-ligand interactions for inducing Graves' hyperthyroidism by Ad-A-subunit. Furthermore, our observations emphasize the potential pitfalls of non-specific inhibition by coimmunization with two adenovirus species.

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

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

Optimization of biotinyl-tyramide-based in situ hybridization for sensitive background-free applications on formalin-fixed, paraffin-embedded tissue specimens

BACKGROUND: Over the past five years in situ hybridization techniques employing tyramide amplification reagents have been developed and promise the potential detection of low/single-copy nucleic acid sequences. However the increased sensitivity that tyramide amplification brings about may also lead to problems of background staining that confound data interpretation. METHODS: In this study those factors enabling background-free biotinyl-tyramide based in situ hybridization assay of formalin-fixed paraffin-embedded tissues have been examined. SiHa, HeLa and CaSki cell lines known to contain HPV integrated into the cell genome, and archival cervical pre-invasive lesions and carcinomas have been successfully assessed using biotinylated HPV and centromeric probes. RESULTS: The single most important factor both for sensitivity and clean background was a tissue unmasking regimen that included treatment with 10 mM sodium citrate pH 6.0 at 95 degrees C followed by digestion with pepsin/0.2 M HCl. Concentrations both of probe and primary streptavidin-peroxidase conjugate and pH of hybridization mix and stringency washes were also critical for sensitivity. Certain probes were more associated with background staining than others. This problem was not related to probe purity or size. In these instances composition of hybridization mix solution was especially critical to avoid background. 3-amino-9-ethylcarbazole was preferred over 3,3'-diaminobenzidene as a chromogen because background was cleaner and the 1-2 copies of HPV16 integrated in SiHa cells were readily demonstrable. HPV detection on metaphase spreads prepared from SiHa cells was only successful when a fluorescent detection method was combined with tyramide reagent. 'Punctate' and 'diffuse' signal patterns were identified amongst tissues consistent with the former representing integration and 'diffuse' representing episomal HPV. Only punctate signals were detected amongst the cell lines and were common amongst high-grade pre-invasive lesions and carcinomas. However it remains to be determined why single/low-copy episomal HPV in basal/parabasal cells of low-grade lesions is not also detectable using tyramide-based techniques and whether every punctate signal represents integration. CONCLUSIONS: A tyramide-based in situ hybridization methodology has been established that enables sensitive, background-free assay of clinical specimens. As punctate signals characterize HPV in high-grade cervical lesions the method may have potential for clinical applications.