Adenovirus encoding the thyrotropin receptor A-subunit improves the efficacy of dendritic cell-induced Graves' hyperthyroidism in mice

TSH Receptor Oligomers Associated With the TSH Receptor Antibody Reactome

The TSH receptor (TSHR) and its many forms are the primary antigens of Graves' disease as evidenced by the presence of TSHR antibodies of differing biological activity. The TSH holoreceptor undergoes complex posttranslational changes including cleavage of its ectodomain and oligomer formation. We have previously shown that the TSHR exists in both monomeric and dimeric structures in the thyroid cell membrane and have demonstrated, by modeling, that the transmembrane domains (TMD) can form stable dimeric structures. Based on these earlier simulations of the TSHR-TMD structure and our most recent model of the full-length TSHR, we have now built models of full-length TSHR multimers with and without TSH ligand in addition to multimers of the extracellular leucine-rich domain, the site of TSH and autoantibody binding. Starting from these models we ran molecular dynamics simulations of the receptor oligomers solvated with water and counterions; the full-length oligomers also were embedded in a dipalmitoylphosphatidylcholine bilayer. The full-length TSHR dimer and trimer models stayed in the same relative orientation and distance during 2000 ns (or longer) molecular dynamics simulation in keeping with our earlier report of TMD dimerization. Simulations were also performed to model oligomers of the leucine-rich domain alone; we found a trimeric complex to be even more stable than the dimers. These data provide further evidence that different forms of the TSHR add to the complexity of the immune response to this antigen that, in patients with autoimmune thyroid disease, generate an autoantibody reactome with multiple types of autoantibody to the TSHR.

CD11c+ B Cells Participate in the Pathogenesis of Graves’ Disease by Secreting Thyroid Autoantibodies and Cytokines

Graves’ disease (GD) is a common autoimmune disorder with an elevation in pathogenic autoantibodies, specifically anti-thyrotropin receptor antibodies (TRAbs), which are secreted by autoreactive B cells. To date, there has been little research on self-reactive B cells in GD. In the current study, we reported that a unique B-cell subset, CD11c+ B cells, was expanded in the peripheral blood (PB) of GD patients, as detected by flow cytometry. The frequency of CD11c+ B cells was positively correlated with serum TRAb levels. The flow cytometry data showed that CD11c expression was higher in a variety of B-cell subsets and that CD11c+ B cells presented a distinct immunophenotype compared to paired CD11c- B cells. Immunohistochemical and immunofluorescence staining indicated the presence of CD11c+CD19+ B cells in lymphocyte infiltration areas of the GD thyroid. Flow cytometric analysis of PB and fine-needle aspiration (FNA) samples showed that compared to PB CD11c+ B cells, CD11c+ B cells in the thyroid accumulated and further differentiated. We found that CD11c+ B cells from the PB of GD patients were induced to differentiate into autoreactive antibody-secreting cells (ASCs) capable of secreting TRAbs in vitro. Luminex liquid suspension chip detection data showed that CD11c+ B cells also secreted a variety of cytokines, including proinflammatory cytokines, anti-inflammatory cytokines, and chemokines, which might play roles in regulating the local inflammatory response and infiltration of lymphocytes in the thyroid. In addition, we performed a chemotaxis assay in a Transwell chamber to verify that CD11c+ B cells were recruited by thyroid follicular cells (TFCs) via the CXCR3-CXCL10 axis. In conclusion, our study determined that CD11c+ B cells were involved in the pathogenesis of GD in multiple ways and might represent a promising immunotherapeutic target in the future.

An improved mouse model of Graves disease by once immunization with Ad-TSHR289

The novel Graves disease (GD) model was established in BALB/c mice with recombinant adenovirus expressing the full-length human TSHR (Ad-TSHR289) by three times immunizations for nearly three months. Reducing the frequency of immunizations may shorten the modeling time to improve the efficiency of the study. In this study, female BALB/c mice were immunized one time with an adenovirus expressing the autoantigen thyroid-stimulating hormone receptor (Ad-TSHR289). At the 3, 6, 12, 17 weeks after the immunization, mice were sacrificed. The blood was collected and thyroids were removed. T3, T4, TRAB and thyroid weight/body weight (TW/BW) were tested. Compared with the Normal control (NC) group, the incidence of hyperthyroidism at 3, 6, 12 and 17 weeks after immunization were about 66.67%, 100%, 100%, and 100%. Meanwhile, the incidences of goiter were nearly 50%, 83.33%, 100% and 100% at the same stages. Therefore, modeling rates of GD were about 50%, 83.33%, 100%, 100% at 3, 6, 12 and 17 weeks after immunization. T3 in serum continues to increase from 3 weeks to 17 weeks after immunization. Serum TRAb reached to peak at 6 weeks and remained from 12 weeks after immunization, while T4 and TW/BW had kept steady from 6 weeks. There are positive correlations between T3, T4 and TRAb, TRAb and TW/BW, as well as T3, T4 and TW/BW. GD model can be constructed by primary immunization with Ad-TSHR289, which could be detected at 3 weeks and at least until the 17 weeks after primary immunization. It would improve the efficiency of GD research.

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.

Modeling Graves' Orbitopathy in Experimental Graves' Disease

Graves' orbitopathy (GO), also known as thyroid eye disease is an inflammatory disease of the orbital tissue of the eye that arises as a consequence of autoimmune thyroid disease. The central feature of the disease is the production of antibodies to the thyrotropin hormone receptor (TSHR) that modulate the function of the receptor leading to autoimmune hyperthyroidism and GO. Over the years, all viable preclinical models of Graves' disease have been incomplete and singularly failed to progress in the treatment of orbital complications. A new mouse model of GO based upon immunogenic presentation of human TSHR A-subunit plasmid by close field electroporation is shown to lead to induction of prolonged functional antibodies to TSHR resulting in chronic disease with subsequent progression to GO. The stable preclinical GO model exhibited pathologies reminiscent of human disease characterized by orbital remodeling by inflammation and adipogenesis. Inflammatory lesions characterized by CD3+ T cells and macrophages were localized in the orbital muscle tissue. This was accompanied by extensive adipogenesis of orbital fat in some immune animals. Surprisingly, other signs of orbital involvement were reminiscent of eyelid inflammation involving chemosis, with dilated and congested orbital blood vessels. More recently, the model is replicated in the author's independent laboratories. The pre-clinical model will provide the basis to study the pathogenic and regulatory roles of immune T and B cells and their subpopulations to understand the initiation, pathophysiology, and progression of GO.

Current concepts in the molecular pathogenesis of thyroid-associated ophthalmopathy

Graves' disease (GD) is a common autoimmune condition. At its core, stimulatory autoantibodies are directed at the thyroid-stimulating hormone receptor (TSHR), resulting in dysregulated thyroid gland activity and growth. Closely associated with GD is the ocular condition known as thyroid-associated ophthalmopathy (TAO). The pathogenesis of TAO remains enigmatic as do the connections between the thyroid and orbit. This review highlights the putative molecular mechanisms involved in TAO and suggests how these insights provide future directions for identifying therapeutic targets. Genetic, epigenetic, and environmental factors have been suggested as contributory to the development of GD and TAO. Thyroid-stimulating hormone receptor and insulin-like growth factor receptor (IGF-1R) are expressed at higher levels in the orbital connective tissue from individuals with TAO than in healthy tissues. Together, they form a functional complex and appear to promote signaling relevant to GD and TAO. Orbital fibroblasts display an array of cell surface receptors and generate a host of inflammatory molecules that may participate in T and B cell infiltration. Recently, a population of orbital fibroblasts has been putatively traced to bone marrow-derived progenitor cells, known as fibrocytes, as they express CD45, CD34, CXCR4, collagen I, functional TSHR, and thyroglobulin (Tg). Fibrocytes become more numerous in GD and we believe traffic to the orbit in TAO. Numerous attempts at developing complete animal models of GD have been largely unsuccessful, because they lack fidelity with the ocular manifestations seen in TAO. Better understanding of the pathogenesis of TAO and development of improved animal models should greatly accelerate the identification of medical therapy for this vexing medical problem.

Hyperthyroid monkeys: a nonhuman primate model of experimental Graves' disease

Graves' disease (GD) is a common organ-specific autoimmune disease with the prevalence between 0.5 and 2% in women. Several lines of evidence indicate that the shed A-subunit rather than the full-length thyrotropin receptor (TSHR) is the autoantigen that triggers autoimmunity and leads to hyperthyroidism. We have for the first time induced GD in female rhesus monkeys, which exhibit greater similarity to patients with GD than previous rodent models. After final immunization, the monkeys injected with adenovirus expressing the A-subunit of TSHR (A-sub-Ad) showed some characteristics of GD. When compared with controls, all the test monkeys had significantly higher TSHR antibody levels, half of them had increased total thyroxine (T₄) and free T₄, and 50% developed goiter. To better understand the underlying mechanisms, quantitative studies on subpopulations of CD4+T helper cells were carried out. The data indicated that this GD model involved a mixed Th1 and Th2 response. Declined Treg proportions and increased Th17:Treg ratio are also observed. Our rhesus monkey model successfully mimicked GD in humans in many aspects. It would be a useful tool for furthering our understanding of the pathogenesis of GD and would potentially shorten the distance toward the prevention and treatment of this disease in human.

The significance of immune-related molecule expression profiles in an animal model of Graves' disease

BACKGROUND

The thyrotropin receptor (TSHR) A-subunit has been reported to be a critical autoantigen in the generation of thyroid-stimulating antibodies, thereby causing Graves' disease (GD). However, immune mechanisms associated with GD animal models induced by TSHR A-subunit are poorly understood until now.

METHODS

Female BALB/c mice (n = 23) were randomly divided into two groups, and GD presentation was monitored following injection with either 50 μl phosphate-buffered saline containing 10(9) particles of adenovirus expressing the human TSHR A-subunit (Ad-TSHR289) or the Ad-LacZ control. Expressions of CD40, CD40L, CD80, CD86, CD28, CTLA-4, FOXP3 and IL-17A in various tissues were assessed by quantitative RT-PCR and immunohistochemical assays.

RESULTS

Compared with control group, mice of the hyperthyroid group showed significant elevation of expression in the thyroid of CD40 and CD86, expression in the heart of CD28, CD40 and CD40L and expression in the liver of CD28, CD40 and CD86. Conversely, there was significantly diminished expression of CTLA-4 in the thymus of mice in the hyperthyroid group. Expression of all genes examined was not significantly different in the spleens of mice from either of the groups and CD40L and FOXP3 expression was not detected in the thyroids of hyperthyroid mice.

CONCLUSIONS

The expression profile of multiple immune-related molecules differed in mice in the GD group following Ad-TSHR289 immunization, suggesting that these molecules played a potential role in GD pathogenesis.

Orbital fibrosis in a mouse model of Graves' disease induced by genetic immunization of thyrotropin receptor cDNA

The TSH receptor (TSHR) is the critical target for antibody production in Graves' disease (GD). Insulin-like growth factor 1 receptor (IGF1R) has been proposed as a second autoantigen in complications of GD such as orbitopathy. We attempted to induce orbital tissue remodeling in mice undergoing immunizations with plasmids encoding TSHR and IGF1R delivered by in vivo skeletal muscle electroporation, a procedure known to give a sustained, long-term antibody response. Female BALB/c mice were challenged with TSHR A-subunit or IGF1Rα subunit plasmid by injection and electroporation. Mice challenged with TSHR A-subunit plasmid resulted in high frequency (75%) of hyperthyroidism and thyroid-stimulating antibodies. But strikingly, immunization with TSHR A-subunit plasmid also elicited antibody to IGF1Rα subunit. Mice challenged in the same manner with IGF1Rα subunit plasmid produced strong antibody responses to IGF1R, but did not undergo any changes in phenotype. Simultaneous challenge by double antigen immunization with the two plasmids in distant anatomical sites reduced the incidence of hyperthyroidism, potentially as a consequence of antigenic competition. Thyroid glands from the TSHR A-subunit plasmid-challenged group were enlarged with patchy microscopic infiltrates. Histological analysis of the orbital tissues demonstrated moderate connective tissue fibrosis and deposition of Masson's trichrome staining material. Our findings imply that immunization with TSHR A-subunit plasmid leads to generation of IGF1R antibodies, which together with thyroid-stimulating antibodies may precipitate remodeling of orbital tissue, raising our understanding of its close association with GD.

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

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

Distinct role of T helper Type 17 immune response for Graves' hyperthyroidism in mice with different genetic backgrounds

T helper type 17 (Th17) cells, a newly identified effector T-cell subset, have recently been shown to play a role in numerous autoimmune diseases, including iodine-induced autoimmune thyroiditis in non-obese diabetic (NOD)-H2(h4) mice, which had previously been thought Th1-dominant. We here studied the role of Th17 in Graves' hyperthyroidism, another thyroid-specific autoimmune disease, in a mouse model. Two genetically distinct BALB/c and NOD-H2(h4) strains with intact or disrupted IL-17 genes (IL-17(+/+) or IL-17(-/-)) were immunized with adenovirus (Ad) expressing the thyrotropin receptor (TSHR) A-subunit (Ad-TSHR289). Both IL-17(+/+) and IL-17(-/-) mice developed anti-TSHR antibodies and hyperthyroidism at equally high frequencies on the BALB/c genetic background. In contrast, some IL-17(+/+), but none of IL-17(-/-), mice became hyperthyroid on the NOD-H2(h4) genetic background, indicating the crucial role of IL-17 for development of Graves' hyperthyroidism in non-susceptible NOD-H2(h4), but not in susceptible BALB/c mice. In the T-cell recall assay, splenocytes and lymphocytes from the draining lymph nodes from either mouse strains, irrespective of IL-17 gene status, produced IFN-γ and IL-10 but not other cytokines including IL-17 in response to TSHR antigen. Thus, the functional significance of Th17 may not necessarily be predictable from cytokine expression patterns in splenocytes or inflammatory lesions. In conclusion, this is, to our knowledge, the first report showing that the role of Th17 cells for the pathogenesis of a certain autoimmune disease depends on the mouse genetic backgrounds.

Autoimmune thyroid disease: unlocking a complex puzzle

PURPOSE OF REVIEW

The autoimmune thyroid diseases (AITD), Graves' disease and chronic lymphocytic thyroiditis (CLT) are amongst the most common endocrine diseases in childhood and adolescence. The application of molecular biology has permitted an unparalleled insight into susceptibility genes that predispose to their development and has allowed enhanced understanding of their complex immune pathophysiology.

RECENT FINDINGS

The susceptibility genes that predispose to AITD can be subdivided into those that affect the immune response in general and thyroid-specific antigens. Both known and new susceptibility genes have been the focus of recent attention. Although there is no known human leukocyte antigen (HLA) association in CLT, recent work has demonstrated an association with a specific amino acid pocket signature irrespective of the HLA-DR class. In Graves' disease a specific combination of polymorphisms for thyroglobulin and HLA-DR markedly increases the odds ratio for developing disease. The availability of recombinant antigen [particularly thyroid peroxidase and thyrotropin (TSH) receptor] and of high affinity monoclonal antibodies has provided insight into the specific epitopes recognized by antibodies in AITD and has confirmed the increased affinity of stimulating TSH receptor antibodies for the shed A subunit rather than the holoreceptor.

SUMMARY

Powerful molecular tools have been developed that have shed light on the nature of the susceptibility genes for and the pathophysiology of AITD. These have already led to improved diagnostic tools and, hopefully, will permit the development of more specific immune therapy in the future.

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.

Lack of effect of methimazole on dendritic cell (DC) function and DC-induced Graves' hyperthyroidism in mice

In addition to the biochemical inhibition of thyroid hormone synthesis, antithyroid drugs including methimazole (MMI) may have immunosuppressive effect through inhibition of major histocompatibility complex (MHC) class I and II expressions on non-professional (thyrocytes) and professional (macrophages and B cells) antigen presenting cells (APCs). Dendritic cells (DCs) are another professional APCs and very likely play the most important role in the primary immune response. Therefore, we focused in this study on evaluating the effect of MMI on DC function in mice. Bone marrow cells cultured with granulocyte macrophage colony stimulating factor and interleukin (IL)-4 expressed high levels of CD11c and moderate levels of MHC class II, both of which are widely used markers for DCs. In vitro incubation of this DC-containing cell population with 10(- 6)-10(- 4) M MMI for 2 days did not change basal- and maturation signal (adenoviral infection and lipopolysaccharide)-induced levels of the cell surface marker expressions such as MHC class I and II, CD86, CD40 and DEC205, and of proinflammatory cytokine IL-6 release. Further we found that treatment of the DC-containing cell population with MMI did not influence the incidence of Graves' hyperthyroidism and anti-thyrotropin receptor (TSHR) antibody titers in a mouse Graves' model we have recently established with DCs infected with adenovirus expressing the TSHR A subunit. Although we cannot completely exclude immunosuppressive effect of MMI on other immune cells, our data indicate that DCs do not appear to be the primary target for the immunosuppressive effect of MMI.

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.

Toward better models of hyperthyroid Graves' disease

Graves' disease affects only humans. Although it is a treatable illness, medical therapy with antithyroid drugs is imperfect, showing high rates of recurrence. Furthermore, the etiology and treatment of the associated ophthalmopathy still represent problematic issues. Animal models could contribute to the solution of such problems by providing a better understanding of the underlying pathogenesis and could be used for evaluating novel therapeutic strategies. This article discusses the pursuit of a better experimental model for hyperthyroid Graves' disease and outlines how this research has clarified the immunology of the disease.

Evidence that shed thyrotropin receptor A subunits drive affinity maturation of autoantibodies causing Graves' disease

CONTEXT

In Graves' disease, thyroid-stimulating antibodies (TSAb) activate the TSH receptor (TSHR) causing hyperthyroidism. Serum polyclonal TSAb are difficult to study because of their extremely low serum levels.

OBJECTIVE

Our objective was to determine whether monoclonal TSAb possess characteristics previously reported for polyclonal autoantibodies in Graves' sera.

DESIGN

We studied monoclonal TSAb from three laboratories: six generated from mice with induced hyperthyroidism; and one, M22, a human autoantibody obtained from Graves' B cells.

RESULTS

All TSAb with one exception were potent activators of TSHR-mediated cAMP generation, with relatively similar half-maximal stimulatory concentrations. Like polyclonal autoantibodies, monoclonal TSAb were largely neutralized by conformationally "active" (but not "inactive") recombinant TSHR A subunits (the N-terminal cleavage product of the TSHR). Chimeric substitutions of TSHR amino acids 25-30 (the extreme N terminus after removal of the 21 residue signal peptide) abrogated the binding and function of all monoclonal TSAb but with one antibody (TSAb4) revealing a nonidentical epitope. Remarkably, these residues are uninvolved in the M22 epitope determined by x-ray analysis. Finally, flow-cytometric dose-response analyses, not previously possible with polyclonal TSAb, revealed that all monoclonal TSAb, human and murine, bound with lower affinity to their in vivo target, the TSH-holoreceptor, than to the isolated TSHR ectodomain.

CONCLUSIONS

TSAb function does not require antibodies with identical epitopes, and human autoantibody M22 may, therefore, not represent the full epitopic repertoire of polyclonal TSAb in Graves' disease. Most important, we provide strong evidence that the shed ectodomain (primarily the A subunit) is the primary antigen driving affinity maturation of TSAb producing B cells.

Exacerbation of autoimmune thyroiditis by a single low dose of whole-body irradiation in non-obese diabetic-H2h4 mice

PURPOSE

To evaluate how irradiation affects thyroid autoimmunity in mouse models of Hashimoto's thyroiditis and Graves' hyperthyroidism.

MATERIALS AND METHODS

Non-obese diabetic (NOD)-H2(h4) mice spontaneously develop anti-thyroglobulin (Tg) antibodies and thyroiditis when supplied with sodium iodine (NaI) in the drinking water. BALB/c mice develop anti-thyrotropin receptor (TSHR) antibodies and hyperthyroidism following immunization with adenovirus expressing TSHR (Ad-TSHR). Mice were irradiated as follows: A single whole-body irradiation with 0.05, 0.5 or 3 Gy one week before or after the beginning of NaI or immunization with Ad-TSHR, fractionated whole-body irradiations with 0.05 Gy twice a week or 0.5 Gy once a week from one week before NaI or Ad-TSHR immunization, or a single regional irradiation to the thyroid gland with 0.5 Gy one week before NaI. The effect of a single irradiation with 0.05, 0.5 or 3 Gy on splenocytes was also evaluated.

RESULTS

A single whole-body irradiation with 0.5 Gy one week before NaI exacerbated thyroiditis and increased anti-Tg antibody titers in NOD-H2(h4) mice. In contrast, any irradiation protocols employed did not affect incidence of hyperthyroidism or anti-TSHR antibody titers in BALB/c mice. High-dose irradiation increased the relative ratios of effector T cells to regulatory T cells (an indication of enhanced immune status) but kills most of T cells.

CONCLUSIONS

These results indicate that a single whole-body low-dose irradiation with 0.5 Gy exacerbates thyroiditis in NOD-H2(h4) mice, data consistent with some clinical evidence for increased incidence of thyroid autoimmunity by environmental irradiation.

Cell damage and autoimmunity: a critical appraisal

In April 2007, an international Colloquium bridging scientific and clinical disciplines was held to discuss the role of cellular and tissue damage in the initiation, development and persistence of autoimmune disease. Five potential etiologic and pathophysiologic processes fundamental to autoimmune disease (i.e. inflammation, infection, apoptosis, environmental exposure and genetics) were the focus of the presentations and integrative discussions at the Colloquium. The information presented on these topics is condensed in this review. Inflammation has close clinico-pathologic associations with autoimmunity, but future analyses will require better definition and metrics of inflammation, particularly for the earliest cellular and molecular components dependent on recruitment of elements of innate immunity. Although infection may be associated with increased levels of autoantibodies, most infections and virtually all vaccinations in humans lack well-established links to autoimmune diseases. Further application of well-designed, long-term epidemiologic and population-based studies is urgently needed to relate antecedent exposures with later occurring stigmata of autoimmunity with a goal of discerning potentially susceptible individuals or subpopulations. Suspect infections requiring closer interrogation include EB virus (SLE and other diseases), HCV (autoimmune hepatitis), beta hemolytic streptococci (rheumatic carditis) and Helicobacter pylori (autoimmune gastritis) among others. And even if a micro-organism was to be incriminated, mechanisms of initiation/perpetuation of autoimmunity continue to challenge investigators. Plausible mechanisms include potentiation and diversion of innate immunity; exposure or spillage of intracellular autoantigens; or provision of autoantigenic mimics. Integrity of apoptosis as a critical safeguard against autoimmunity was discussed in the contexts of over-reactivity causing autoantigens to gain enhanced exposure to the immune system, or under-reactivity producing insufficient elimination of autoreactive clones of lymphocytes. Although environmental agents are widely believed to serve as necessary "triggers" of autoimmune disease in genetically predisposed individuals, only a few such agents (mainly drugs and some nutrients) have been clearly identified and their mechanism of action defined. Finally an essential genetic foundation underlies all these hazards for autoimmunity in the form of risk-associated polymorphisms in immunoregulatory genes. They may be predictive of future or impending disease.

A novel method of bone marrow transplantation (BMT) for intractable autoimmune diseases

We have previously proposed that autoimmune diseases are hemopoietic stem cell (HSC) disorders. In this review article, we provide evidence that most age-associated diseases such as osteoporosis are mesenchymal stem cell (MSC) disorders and, based on this evidence, we propose a new concept of "stem cell disorders (SCDs)", including HSC and MSC disorders. To treat SCDs, we have recently developed a new strategy (intra-bone marrow-bone marrow transplantation: IBM-BMT) for replacing the abnormal stem cells of recipients with donor-derived normal stem cells (both HSCs and MSCs). We here show that this strategy not only can be used to treat SCDs but is also applicable to organ transplantation, since IBM-BMT can induce tolerance (full chimerism) without the need for immunosuppressants even when radiation doses as the conditioning regimen of BMT are reduced to less than 5.0 Gy x 2, which is equivalent to one shot of 8 Gy (a sublethal dose). We believe that this strategy heralds a revolution in the field of transplantation (BMT and organ transplantation) and regeneration therapy.

CD8+CD122+ T cells, a newly identified regulatory T subset, negatively regulate Graves' hyperthyroidism in a murine model

Graves' disease is a thyroid-specific autoimmune disease mediated by stimulatory autoantibodies against the TSH receptor (TSHR). We have previously shown in our mouse model with adenovirus expressing the TSHR that antibody mediated depletion of CD4(+)CD25(+) regulatory T cells (Tregs) enhances incidence and severity of hyperthyroidism in resistant and susceptible mouse strains, respectively. These data indicate that balance between effector T cells and Tregs is critical for disease development. This study was designed to evaluate the role played by another recently identified type of Treg, CD8(+)CD122(+) T cells, in our mouse model to delineate the significance of different types of Tregs in Graves' disease. Flow cytometry analysis showed that CD4(+)CD25(+) and CD8(+)CD122(+) T cells are distinct cell types, and anti-CD122 antibody effectively and selectively depleted CD8(+)CD122(+) T cells. As for CD4(+)CD25(+) Treg, CD8(+)CD122(+) T cell depletion increased the incidence of hyperthyroidism both in resistant and susceptible mice. Of interest, intrathyroidal lymphocytic infiltration was observed in some CD8(+)CD122(+) T cell-depleted, hyperthyroid resistant mice. These results indicate that in addition to CD4(+)CD25(+) T cells, CD8(+)CD122(+) T cells also play a crucial role in disease susceptibility in mouse Graves' disease. Thus, different types of Tregs appear to be involved in tolerance to a self-antigen, the TSHR.

Graves' animal models of Graves' hyperthyroidism

Fifty years after the discovery of thyroid autoimmunity, several animal models of Graves' hyperthyroidism are now available. All are inducible types, and diseases are elicited by injecting living cells (professional or nonprofessional antigen-presenting cells) expressing the recombinant thyrotropin receptor (TSHR) or by DNA vaccination with TSHR cDNA in plasmid or adenovirus vectors. Thus most Graves' models are attributed to the cloning of the TSHR cDNA and involve in vivo expression of the TSHR. These breakthroughs have provided us important insights into our understanding of the pathogenesis of Graves' disease, and also indispensable means to exploring the possibility of development of novel therapeutic modalities. In particular, recent studies have begun to scrutinize the genetic factors contributing to the susceptibility to this ailment, and to delineate the roles for central and peripheral tolerance and also for fine balance between autoreactive effector T cells and regulatory T cells in the pathophysiology of anti-TSHR autoimmunity and Graves' hyperthyroidism. Moreover, preliminary, but novel, therapeutic approaches have also been started to treat experimental hyperthyroidism.

The thyrotropin receptor in Graves' disease

The application of molecular biology to the study of the thyrotropin receptor (TSHR) has led to major advances in our understanding of its structure, function, and relationship to the pathogenesis of Graves' disease. This review summarizes many of these features and also provides a personal perspective, questioning some assumptions and general concepts, as well as describing remaining challenges. Among the issues raised are the limits in our understanding of the spatial orientation of the structural domains of the TSHR, including the enigmatic hinge region. We review the phenomenon of TSHR intramolecular cleavage, the shedding of the A-subunit component of the ectodomain, and the importance of the latter in generating thyroid-stimulating antibodies. The epitopes of thyroid-stimulating and -blocking autoantibodies have been a confusing and controversial subject that requires review and evaluation of available data. Finally, we address the potential physiological or pathophysiological significance of TSHR multimerization in TSHR. Taken together, this review will, hopefully, convey the fascination and excitement that molecular biology has contributed to the study of the TSHR, especially as it relates to the pathogenesis of Graves' disease.

CD4+CD25+ naturally occurring regulatory T cells and not lymphopenia play a role in the pathogenesis of iodide-induced autoimmune thyroiditis in NOD-H2h4 mice

NOD-H2(h4) mice, which express I-A(k) on the NOD background, spontaneously develop autoimmune thyroiditis, a model of Hashimoto thyroiditis in humans, by adding iodide in the drinking water. Parental NOD mice have previously been shown to have intrinsic numerical abnormalities in peripheral lymphocytes and lymphocyte subpopulations such as CD4(+)CD25(+) naturally occurring regulatory T cells (Treg). Therefore we first investigated whether the similar abnormalities exist in NOD-H2(h4) mice. We observed that, compared with other non-autoimmune disease prone BALB/c and C57BL/6 mice, NOD-H2(h4) mice have lower numbers of splenocytes, CD3(+)T, CD4(+)T and CD8(+)T cells but the ratios of Treg to CD4(+)T cells were comparable. Increasing the numbers of peripheral lymphocytes by Complete Freund's Adjuvant immunization or splenocyte transfer did not affect development of thyroiditis, indicating that lymphopenia does not play a critical role in the pathogenesis of thyroiditis. We next examined the significance of Treg by depleting this lymphocyte subset with anti-CD25 antibody. Treg depletion, performed 4days before the administration of NaI water for 8 weeks, significantly exacerbated thyroiditis (p<0.01). Anti-thyroglobulin antibody titers also increased by Treg depletion (p<0.01) without changing the IgG2b to IgG1 ratios. In addition, expression levels of mRNA for IFN-gamma and IL-4 were enhanced in parallel. However, T(4) levels were similar between antibody-treated and untreated groups. Additional anti-CD25 administration at 3 weekly intervals did not influence these results. These data, together with previous studies on other mouse models of inducible thyroiditis and Graves' disease, indicate the role played by Treg in keeping anti-thyroid autoimmune reaction in check in experimental autoimmune thyroid diseases.