Resistance to experimental autoimmune thyroiditis induced by physiologic manipulation of thyroglobulin level

The Essential Role of Circulating Thyroglobulin in Maintaining Dominance of Natural Regulatory T Cell Function to Prevent Autoimmune Thyroiditis

Several key findings from the late 1960s to mid-1970s regarding thyroid hormone metabolism and circulating thyroglobulin composition converged with studies pertaining to the role of T lymphocytes in autoimmune thyroiditis. These studies cemented the foundation for subsequent investigations into the existence and antigenic specificity of thymus-derived natural regulatory T cells (nTregs). These nTregs prevented the development of autoimmune thyroiditis, despite the ever-present genetic predisposition, autoantigen (thyroglobulin), and thyroglobulin-reactive T cells. Guided by the hypothalamus-pituitary-thyroid axis as a fixed set-point regulator in thyroid hormone metabolism, we used a murine model and compared at key junctures the capacity of circulating thyroglobulin level (raised by thyroid-stimulating hormone or exogenous thyroglobulin administration) to strengthen self-tolerance and resist autoimmune thyroiditis. The findings clearly demonstrated an essential role for raised circulating thyroglobulin levels in maintaining the dominance of nTreg function and inhibiting thyroid autoimmunity. Subsequent identification of thyroglobulin-specific nTregs as CD4(+)CD25(+)Foxp3(+) in the early 2000s enabled the examination of probable mechanisms of nTreg function. We observed that whenever nTreg function was perturbed by immunotherapeutic measures, opportunistic autoimmune disorders invariably surfaced. This review highlights the step-wise progression of applying insights from endocrinologic and immunologic studies to advance our understanding of the clonal balance between natural regulatory and autoreactive T cells. Moreover, we focus on how tilting the balance in favor of maintaining peripheral tolerance could be achieved. Thus, murine autoimmune thyroiditis has served as a unique model capable of closely simulating natural physiologic conditions.

Opportunistic Autoimmune Disorders Potentiated by Immune-Checkpoint Inhibitors Anti-CTLA-4 and Anti-PD-1

To improve the efficacy of immunotherapy for cancer and autoimmune diseases, recent ongoing and completed clinical trials have focused on specific targets to redirect the immune network toward eradicating a variety of tumors and ameliorating the self-destructive process. In a previous review, both systemic immunomodulators and monoclonal antibodies (mAbs), anti-CTLA-4, and anti-CD52, were discussed regarding therapeutics and autoimmune sequelae, as well as predisposing factors known to exacerbate immune-related adverse events (irAEs). This review will focus on immune-checkpoint inhibitors, and the data from most clinical trials involve blockade with anti-CTLA-4 such as ipilimumab. However, despite the mild to severe irAEs observed with ipilimumab in ~60% of patients, overall survival (OS) averaged ~22-25% at 3-5 years. To boost OS, other mAbs targeting programed death-1 and its ligand are undergoing clinical trials as monotherapy or dual therapy with anti-CTLA-4. Therapeutic combinations may generate different spectrum of opportunistic autoimmune disorders. To simulate clinical scenarios, we have applied regulatory T cell perturbation to murine models combined to examine the balance between thyroid autoimmunity and tumor-specific immunity.

Breaking tolerance to thyroid antigens: changing concepts in thyroid autoimmunity

Thyroid autoimmunity involves loss of tolerance to thyroid proteins in genetically susceptible individuals in association with environmental factors. In central tolerance, intrathymic autoantigen presentation deletes immature T cells with high affinity for autoantigen-derived peptides. Regulatory T cells provide an alternative mechanism to silence autoimmune T cells in the periphery. The TSH receptor (TSHR), thyroid peroxidase (TPO), and thyroglobulin (Tg) have unusual properties ("immunogenicity") that contribute to breaking tolerance, including size, abundance, membrane association, glycosylation, and polymorphisms. Insight into loss of tolerance to thyroid proteins comes from spontaneous and induced animal models: 1) intrathymic expression controls self-tolerance to the TSHR, not TPO or Tg; 2) regulatory T cells are not involved in TSHR self-tolerance and instead control the balance between Graves' disease and thyroiditis; 3) breaking TSHR tolerance involves contributions from major histocompatibility complex molecules (humans and induced mouse models), TSHR polymorphism(s) (humans), and alternative splicing (mice); 4) loss of tolerance to Tg before TPO indicates that greater Tg immunogenicity vs TPO dominates central tolerance expectations; 5) tolerance is induced by thyroid autoantigen administration before autoimmunity is established; 6) interferon-α therapy for hepatitis C infection enhances thyroid autoimmunity in patients with intact immunity; Graves' disease developing after T-cell depletion reflects reconstitution autoimmunity; and 7) most environmental factors (including excess iodine) "reveal," but do not induce, thyroid autoimmunity. Micro-organisms likely exert their effects via bystander stimulation. Finally, no single mechanism explains the loss of tolerance to thyroid proteins. The goal of inducing self-tolerance to prevent autoimmune thyroid disease will require accurate prediction of at-risk individuals together with an antigen-specific, not blanket, therapeutic approach.

Regulatory T cells and other lymphocyte subpopulations in patients with melanoma developing interferon-induced thyroiditis during high-dose interferon-α2b treatment

CONTEXT

One of the side effects of interferon-alpha therapy is interferon-induced thyroiditis (IIT). The role of lymphocyte subpopulations in IIT melanoma patients remains to be defined.

OBJECTIVE

Our objective was to assess different peripheral blood lymphocyte subpopulations, mainly regulatory T cells (Tregs), in melanoma patients who developed IIT.

DESIGN, PATIENTS AND METHODS

From 30 melanoma patients receiving high-dose interferon (HDI)-alpha 2b (IFN-α2b) treatment, those who developed IIT (IIT patients) were selected and compared with patients who did not develop IIT (Co-MM) and healthy controls (Co-H). Peripheral blood mononuclear cells were obtained before treatment (BT), mid-treatment (MT), end of treatment (ET), 24 weeks post-treatment and at appearance of IIT (TT).

RESULTS

Nine patients developed IIT (30%): four Hashimoto's thyroiditis and five destructive thyroiditis. An increase in Tregs was observed in both melanoma groups during HDI treatment. A decrease in CD3(+) , NKT lymphocyte subpopulations and Bcl2 expression on B cells was also observed in both groups. However, no changes were observed in the percentage of CD4(+) , CD8(+) , CD3(+) γδ(+) , CD19(+) , transitional B cells (CD24(high) CD38(high) CD19(+) CD27(-) ), natural killer (NK), invariant NKT (iNKT) lymphocytes and Th1/Th2 balance when BT was compared with ET. At TT, IIT patients had a higher Tregs percentage than Co-MM (P = 0·012) and Co-H (P = 0·004), a higher iNKT percentage than Co-MM (P = 0·011), a higher transitional B cells percentage than Co-H (P = 0·015), a lower CD3(+) percentage than Co-H (P = 0·001) and a lower Bcl2 expression on B cells than Co-H (P < 0·001).

CONCLUSIONS

Our results point to the immunomodulatory effects of IFN-α on different lymphocyte subpopulations and a possible role of Tregs in melanoma patients who developed IIT.

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

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

Autoimmune thyroiditis as an indicator of autoimmune sequelae during cancer immunotherapy

Improving cancer immunotherapy by targeting T cell network also triggers autoimmunity. We disrupted regulatory T cell (Treg) function to probe the balance between breast cancer vaccination and autoimmune thyroiditis (EAT) in four models, with particular attention to MHC-associated susceptibility, EAT induction with mouse thyroglobulin (mTg) without adjuvant, and tolerance to Her-2/neu in transgenic mice. 1) In EAT-resistant BALB/c mice, Treg depletion enhanced tumor regression, and facilitated mild thyroiditis induction. 2) In Her-2 tolerant C57BL/6 mice expressing HLA-DR3, an EAT-susceptibility allele, Her-2 DNA vaccinations must follow Treg depletion for (Her-2xDR3)F(1) mice to resist tumor challenge; thyroiditis incidence was moderated by the EAT-resistant IA(b) allele. 3) In neu tolerant, EAT-resistant BALB/c mice, implanted neu(+) tumor also regressed only after Treg depletion and DNA vaccinations. Tumor immunity was long-term, providing protection from spontaneous tumorigenesis. In all three, immune stimuli from concurrent tumor regression and EAT development have a noticeable, mutually augmenting effect. 4) In Treg-depleted, EAT-susceptible CBA/J mice, strong tumor protection was established by immunization with a cell vaccine. mTg injections led to greater thyroiditis incidence and severity. Combination models with MHC class II diversity should facilitate autoimmunity risk assessment and management while generating tumor immunity.

Naturally-existing CD4(+)CD25(+)Foxp3(+) regulatory T cells are required for tolerance to experimental autoimmune thyroiditis induced by either exogenous or endogenous autoantigen

Murine experimental autoimmune thyroiditis (EAT) is a model for Hashimoto's thyroiditis, an organ-specific autoimmune disease characterized by mononuclear cell infiltration and destruction of the thyroid gland. Susceptibility to EAT is MHC-linked, and influenced by CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs). Treg depletion enables thyroiditis induction with mouse thyroglobulin (mTg) in traditionally-resistant mice and mTg-induced, Treg-mediated tolerance protects against EAT induction in genetically-susceptible mice. Here, we demonstrate the existence of naturally-existing CD4(+)CD25(+)Foxp3(+) Tregs (nTregs) influencing thyroiditis development in naive susceptible mice and that induction of thyroiditis in these mice involves overcoming peripheral homeostatic immune suppression by nTregs. Additionally we demonstrate that nTregs are required for induction of antigen-specific tolerance, indicating that induced EAT tolerance is a result of activation of naturally-existing nTregs rather than de novo generation of induced Tregs (iTregs). Examination of several potential costimulatory molecules previously described as involved in peripheral activation of Tregs demonstrates a critical role indeed for CTLA-4 in the activation of nTregs leading to development of EAT tolerance and providing a mechanism for mTg-induced Treg activation during tolerance induction. Together, these data reinforce the important role of Tregs in mediating self-tolerance, and illuminate a potential mechanism for their therapeutic expansion in induced tolerance.

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.

Chronic exposure in vivo to thyrotropin receptor stimulating monoclonal antibodies sustains high thyroxine levels and thyroid hyperplasia in thyroid autoimmunity-prone HLA-DRB1*0301 transgenic mice

We have examined the induction of autoimmunity and the maintenance of sustained hyperthyroidism in autoimmunity-prone human leucocyte antigen (HLA) DR3 transgenic non-obese diabetic (NOD) mice following chronic stimulation of the thyrotropin receptor (TSHR) by monoclonal thyroid-stimulating autoantibodies (TSAbs). Animals received weekly injections over the course of 9 weeks of monoclonal antibodies (mAbs) with strong thyroid-stimulating properties. Administration of the mAbs KSAb1 (IgG2b) or KSAb2 (IgG2a), which have similar stimulating properties but different TSH-binding blocking activity, resulted in significantly elevated serum thyroxine (T(4)) levels and thyroid hyperplasia. After the first injection, an initial surge then fall in serum T(4) levels was followed by sustained elevated levels with subsequent injections for at least 63 days. Examination of KSAb1 and KSAb2 serum bioactivity showed that the accumulation of the TSAbs in serum was related to their subclass half-lives. The thyroid glands were enlarged and histological examination showed hyperplastic follicles, with minimal accompanying thyroid inflammation. Our results show that chronic in vivo administration of mAbs with strong thyroid-stimulating activity resulted in elevated T(4) levels, suggesting persistent stimulation without receptor desensitization, giving a potential explanation for the sustained hyperthyroid status in patients with Graves' disease. Moreover, despite the presence of HLA disease susceptibility alleles and the autoimmune prone NOD background genes, chronic stimulation of the thyroid gland did not lead to immune cell-mediated follicular destruction, suggesting the persistence of immunoregulatory influences to suppress autoimmunity.

Recognition of thyroglobulin by T cells: the role of iodine

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

Experimental autoimmune thyroiditis in the mouse

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

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

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

Interference with CD4+CD25+ T-cell-mediated tolerance to experimental autoimmune thyroiditis by glucocorticoid-induced tumor necrosis factor receptor monoclonal antibody

Experimental autoimmune thyroiditis (EAT), a murine model for Hashimoto's thyroiditis, is inducible with mouse thyroglobulin (mTg), and characterized by mononuclear cell infiltration and destruction of the thyroid gland. Pretreatment with mTg leads to CD4+CD25+ T-cell-mediated resistance to subsequent EAT induction. We have recently demonstrated that in vivo administration of a monoclonal antibody (mAb) to CD137, a member of the tumor necrosis factor receptor (TNFR) family, interferes with both the development and mediation of induced EAT tolerance. Here, we examined the influence of another TNFR family member, glucocorticoid-induced TNFR (GITR), which has been reported to modulate the function of CD4+CD25+ T cells in other models. We found that in vivo administration of GITR mAb inhibited EAT tolerance induction and abrogated established tolerance, enabling thyroiditis induction. In in vitro assays, GITR mAb inhibited suppression of mTg-primed T cells by CD4+CD25+ T cells isolated from mTg-pretreated mice. The target of GITR mAb appears to be CD4+CD25- T cells, rather than CD4+CD25+ T cells from tolerized mice, suggesting that GITR signaling likely interferes with EAT tolerance by enabling thyroiditogenic T cells to circumvent suppression by CD4+CD25+ regulatory T cells.

CD137 signaling interferes with activation and function of CD4+CD25+ regulatory T cells in induced tolerance to experimental autoimmune thyroiditis

Experimental autoimmune thyroiditis (EAT), a model for Hashimoto's thyroiditis, is a T cell-mediated disease inducible with mouse thyroglobulin (mTg). Pretreatment with mTg, however, can induce CD4+ T cell-mediated tolerance to EAT. We demonstrate that CD4+CD25+ regulatory cells are critical for the tolerance induction, as in vivo depletion of CD25+ cells abrogated established tolerance, and CD4+CD25+ cells from tolerized mice suppressed mTg-responsive cells in vitro. Importantly, administration of an agonistic CD137 monoclonal antibody (mAb) inhibited tolerance development, and the mediation of established tolerance. CD137 mAb also inhibited the suppression of mTg-responsive cells by CD4+CD25+ cells in vitro. Signaling through CD137 likely resulted in enhancement of the responding inflammatory T cells, as anti-CD137 did not enable CD4+CD25+ T cells to proliferate in response to mTg in vitro.

Development of a murine model of autoimmune thyroiditis induced with homologous mouse thyroid peroxidase

Autoimmune thyroid disease (AITD) is a common autoimmune disease. Thyroid peroxidase (TPO) is a well characterized autoantigen in AITD. Autoantibodies and autoreactive T lymphocytes to TPO are believed to play a major role in the pathogenesis of lymphocytic thyroiditis. To understand the pathogenic mechanisms of AITD and the role of TPO, we have established a mouse model of lymphocytic thyroiditis by immunizing C57Bl/6 (H-2(b)), CBA (H-2(k)), and C57Bl/6 x CBA F1 mice with recombinant murine TPO (rmTPO) ectodomain comprising amino acid residue 1-837 produced in Escherichia coli. Mice were immunized with 30 microg purified ectodomain in complete Freund's adjuvant. Antibodies against rmTPO were detected in the serum of all mice from day 21 onward. Draining lymph node cells from rmTPO-immunized animals showed dose-dependent proliferation to TPO stimulation. Mice killed at d 50 and 90 revealed variable degrees of thyroiditis with infiltration of mononuclear cells and destruction of thyroid follicles. C57Bl/6 and the F1 mice, in comparison with CBA mice, showed a greater degree of thyroiditis. There was a lack of correction between the intensity of thyroiditis and the anti-TPO response. Immunotyping of the thyroid cellular infiltrates showed predominantly CD4+ T cells and B220+ B cells but scanty CD8+ T cells. None of the control mice injected with the purified fusion partner developed anti-TPO antibodies and thyroiditis. In conclusion, a genuine autoimmune mouse model of lymphocytic thyroiditis was established using autologous mouse TPO. This new model induced with autologous TPO will lead to a better understanding of the mechanisms in destructive thyroiditis and will assist in the development of new strategies for modulating the pathogenic immune response.

IL-12 prevents tolerance induction with mouse thyroglobulin by priming pathogenic T cells in experimental autoimmune thyroiditis: role of IFN-gamma and the costimulatory molecules CD40l and CD28

Deaggregated mouse thyroglobulin (dMTg) induces tolerance to experimental autoimmune thyroiditis (EAT), a Th1-cell-mediated disease. To test whether IL-12, a potent activator of Th1 cells, can overcome tolerance induction, different doses of IL-12 were given to CBA/J mice during the critical interval of 2--3 days after dMTg administration. After challenge with MTg/LPS, dMTg/IL-12-pretreated mice showed more extensive thyroiditis than immunized controls, but comparable levels of anti-MTg and T cell proliferation. Without challenge, few MTg antibodies were produced. In contrast, pretreatment with dMTg/poly A:U or dMTg/IL-1, two other T cell activators which also interfere with tolerance induction, induced antibodies before challenge, but not more severe thyroiditis. Mice pretreated with IL-12 without dMTg developed thyroiditis comparable to immunized controls, but less severe thyroiditis than dMTg/IL-12-pretreated mice. Clearly, IL-12 not only blocked tolerance induction, but also primed antigen-specific T cells during the tolerogenic period of dMTg pretreatment, resulting in stronger thyroiditis than immunization only. Neither treatment with anti-IFN-gamma nor the use of IFN-gamma knockout mice altered the capacity of IL-12 to prevent tolerance induction. However, both anti-CD28 and anti-CD40L antibodies diminished the priming effect by dMTg/IL-12. The mechanisms of IL-12 action include priming of MTg-specific T cells and the involvement of T cell costimulatory molecules.

Noninvolvement of IL-4 and IL-10 in tolerance induction to experimental autoimmune thyroiditis

The mechanisms of tolerance induced with deaggregated mouse thyroglobulin (dMTg) in experimental autoimmune thyroiditis (EAT) is not yet well defined. As shown previously, the induction and maintenance of tolerance require CD4+ T cells exerting active regulatory function to prevent EAT induction. To examine whether Th2 cells are responsible for resistance we injected anti-IL-4 and anti-IL-10, separately or together, into CBA (H2k) mice at the time of MTg pretreatment to study the role of IL-4 and IL-10 in tolerance induction. Our results show that tolerance can be well established without involving IL-4 or IL-10. To determine whether IL-4 was involved in tolerance induction in another EAT-susceptible strain, IL-4 knockout mice on B10.Q background were similarly pretreated with dMTg and immunized. These IL-4 knockout mice exhibited very good tolerance. The lack of response to EAT induction was not due to IL-4 deficiency, since immunized IL-4 knock-out control mice developed severe EAT. Moreover, resistance was strong in IL-4 knock-out mice also given anti-IL-10. The data in both susceptible strains show that IL-4 and IL-10 play a small role in induced resistance to EAT.

Tolerance induction as a therapeutic strategy for the control of autoimmune endocrine disease in mouse models

This chapter aims to describe ways in which autoimmunity can be prevented or reversed and 'self-tolerance' re-established. To this end we have largely restricted our overview to the two main autoimmune disease models with which we are involved, i.e. IDDM in NOD mice and EAT in H-2k mice although, where appropriate and to demonstrate a particular point, other models are mentioned. The chapter has been divided into sections covering protection afforded by 1) transgenes, 2) autoantigen and 3) by reagents targetting T-cell surface molecules. Where established, the mechanism by which protection or tolerance is achieved is described but where, as in most cases, it is unknown the possibilities are discussed. Investigations using T-cell lines and clones and on islet regeneration which are currently being followed as part of a comprehensive approach to the study of autoimmunity are included as separate sections and their relevance discussed.

Animal models of autoimmune endocrine disease and their uses in developing new methods of intervention

This review provides basic information concerning the major animal models in use for the study of autoimmune endocrine diseases (AEDs). Although several other models exist which parallel human AEDs such as autoimmune orchitis, most research in this area has centred on animal models of insulin-dependent diabetes mellitus (IDDM) and thyroiditis. These models, between them, appear to exhibit most of the disease manifestations of their human counterparts and thereby permit the study of possible methods of intervention in the disease process. While no one model represents a perfect correlation with the human disease it represents, common characteristics are recognizable between them. For instance, the central role of activated T cells in controlling the disease process. The chapter continues by examining the various ways in which models of autoimmunity, specifically IDDM and experimental allergic thyroiditis (EAT), have been used to investigate the possibility of preventing or arresting autoimmune destruction. Several different approaches are described that illustrate the variety of techniques that have proven both potentially, or in reality, effective and those that have proven less efficacious than first hoped.

Autoreactive IgG elicited in mice by the non-dominant but pathogenic thyroglobulin peptide (2495-2511): implications for thyroid autoimmunity

We have previously shown that mice challenged with the rat thyroglobulin (Tg) peptide TgP1 (corresponding to aa 2495-2511 of human Tg) develop experimental autoimmune thyroiditis (EAT) and produce IgG antibodies that cross-react with Tg from various species. It was not clear, however, whether such antibodies were TgP1-specific or were induced secondarily--i.e. by autologous Tg released from the destroyed gland--and therefore directed to determinants other than TgP1. In this study we describe that, 5 weeks after priming with TgP1, the binding of serum IgG on native Tg is completely inhibited by free peptide, suggesting lack of recognition of other determinants on mouse Tg (mTg). In addition, TgP1-induced but not mTg-induced IgG bound better to heat-denatured than intact mTg, a result compatible with the recognition of a linear epitope by the peptide-induced antibodies. Comparison of the IgG subclass distribution among mTg-induced versus TgP1-induced IgG did not reveal qualitative differences, since all subclasses were represented in the order IgG1 > IgG2b > IgG2a > IgG3. Finally, TgP1-specific IgG reacted strongly with the follicular colloid in sections of normal thyroids, indicating the potential to bind to native Tg in vivo. These data: (i) highlight TgP1 as the only, so far, Tg sequence known to generate both EAT and Tg-reactive IgG in mice; and (ii) do not provide evidence for an amplification of the Tg-specific IgG response through the involvement of endogenous autoantigen in EAT.

Resistance to experimental autoimmune thyroiditis is correlated with the duration of raised thyroglobulin levels

We have used the mouse model of experimental autoimmune thyroiditis (EAT) to examine the hypothesis that the strengthening of self-tolerance to thyroglobulin by exogenous mouse thyroglobulin (MTg) or stimulation of endogenous MTg secretion by thyroid-stimulating hormone (TSH) is correlated with the length of time MTg rises above the normal range. Bacterial lipopolysaccharide (LPS) treatment increases the initial half-life of MTg from about 3 hr to about 5 hr, probably interfering with its clearance by the mononuclear phagocytic (reticuloendothelial) system. By pretreating mice with LPS, a subtolerogenic MTg dose is rendered tolerogenic. Similarly the effect of TSH infusion by osmotic minipumps, which stimulates MTg secretion and also strengthens tolerance to MTg, can be enhanced by injecting LPS shortly after pump implantation. The resulting increase in MTg level (due to delayed clearance of MTg) is greater than that from TSH alone and suppresses further the animals' susceptibility to disease induction by MTg and adjuvant. Moreover, resistance following pretreatment with LPS and subtolerogenic MTg is mediated by CD4+ suppressor T cells, as shown recently for the suppression in mice given high doses of tolerogenic MTg. These experiments are in full agreement with the hypothesis and confirm that small increases in circulating MTg concentrations, which could occur physiologically, can be effective in protecting against EAT induction.

Suppression in murine experimental autoimmune thyroiditis: in vivo inhibition of CD4+ T cell-mediated resistance by a nondepleting rat CD4 monoclonal antibody

Genetically susceptible mice become resistant to experimental autoimmune thyroiditis (EAT) induction with mouse thyroglobulin (MTg) and lipopolysaccharide after pretreatment with deaggregated MTg (dMTg). Recent work showed this suppression to be mediated by CD4+ suppressor T cells (Ts). To study Ts action in vivo, we used a rat IgG2a monoclonal antibody (mAb), YTS 177.9, which modulates CD4 antigen in vivo without depleting CD4+ cells. Initial studies showed that after two 1-mg doses of mAb 7 days apart, extensive CD4 antigen modulation of peripheral blood leukocytes occurred within 4 days. Mice given CD4 mAb 24 hr before dMTg (2 doses, 7 days apart) were resistant to EAT induction when immunized with MTg and LPS 20 days later. Also, anti-rat IgG2a titers were reduced following challenge with heat-aggregated rat IgG2a compared to controls. Subsequent analysis of serum in CD4 mAb-treated animals revealed that mAb was present in the circulation for 14 days. Moreover, mice given CD4 mAb and dMTg, then challenged after only 10 days, when CD4 mAb was still circulating, developed a significantly higher incidence of thyroid damage than controls. These findings suggest that modulation of CD4 antigen does not interfere with Ts activation, but the presence of CD4 mAb, at the time of autoantigenic challenge, can interfere with tolerance to EAT induction. Thus, the direct relationship between the presence of CD4 mAb and inhibition of EAT suppression implicates a role for CD4 molecules in the mediation of suppression.

Synergism between mouse thyroglobulin- and vaccination-induced suppressor mechanisms in murine experimental autoimmune thyroiditis

Previous studies have shown that genetically susceptible mice can be rendered resistant to the induction of experimental autoimmune thyroiditis (EAT) by pretreatment with deaggregated mouse thyroglobulin (dMTg). This resistance is mediated by CD4+ suppressor T cells (Ts) which suppress the afferent/inductive phase of EAT. Recent work has also shown that resistance to EAT can be achieved by vaccination with irradiated spleen cells previously primed in vivo with MTg and cultured in vitro with MTg (gamma SC). The gamma SC-induced resistance also inhibits the afferent phase of EAT but is mediated by both CD4+ and CD8+ Ts. To determine if dMTg- and gamma SC-induced suppression can cooperate to prevent EAT, we pretreated mice with suboptimal doses of dMTg and gamma SC before challenge with MTg and adjuvant. Mice receiving dMTg or gamma SC only showed suppressed in vitro response to MTg, but the development of thyroid lesions was unaltered. However, mice given one or two subtolerogenic doses of dMTg followed by gamma SC not only showed suppressed in vitro response to MTg, but also little or no thyroiditis, indicating cooperation between these two mechanisms. The cooperation was not reciprocal since reversing the order, giving gamma SC first followed by dMTg, was not effective in suppressing EAT. Thus, suppressor mechanisms activated by pretreatment with dMTg and gamma SC can act synergistically to suppress EAT induction; the two mechanisms may cooperate in vivo to maintain self-tolerance provided that MTg-specific CD4+ Ts are initially activated.

In vivo evidence for CD4+ and CD8+ suppressor T cells in vaccination-induced suppression of murine experimental autoimmune thyroiditis

In several experimental autoimmune diseases, including experimental autoimmune thyroiditis (EAT), vaccination with attenuated autoantigen-specific T cells has provided protection against subsequent induction of disease. However, the mechanism(s) of vaccination-induced suppression remains to be clarified. Since we have previously shown that suppression generated by pretreatment with mouse thyroglobulin (MTg) or thyroid-stimulating hormone in EAT is mediated by CD4+, not CD8+, suppressor T cells, we examined the role of T cell subsets in vaccination-induced suppression of EAT. Mice were vaccinated with irradiated, MTg-primed, and MTg-activated spleen cells and then challenged. Pretreatment with these cells suppressed EAT induced by immunization with MTg and adjuvant, but not by adoptive transfer of thyroiditogenic cells, suggesting a mechanism of afferent suppression. The activation of suppressor mechanisms did not require CD8+ cells, since mice depleted of CD8+ cells before vaccination showed reduced EAT comparable to control vaccinated mice. Furthermore, depletion of either the CD4+ or the CD8+ subset after vaccination did not significantly abrogate suppression. However, suppression was eliminated by the depletion of both CD4+ and CD8+ cells in vaccinated mice. These results provide evidence for the cooperative effects of CD4+ and CD8+ T cells in vaccination-induced suppression of EAT.

Identification of a thyroxine-containing self-epitope of thyroglobulin which triggers thyroid autoreactive T cells

Although thyroglobulin (Tg), the thyroid prohormone, is well known as a T cell dependent autoantigen in human and experimental autoimmune thyroid disease, very little is known about the molecular basis of Tg recognition by T cells. In this paper, we have characterized the epitopes recognized by two clonotypically distinct, murine Tg autoreactive T cell hybridomas, CH9 and ADA2. In vitro iodination of a Tg preparation which was deficient in in vivo organified iodine was first used to confirm our previous observation that these T cells recognize iodination-related epitopes in the Tg molecule. Affinity chromatography of tryptic peptides derived from normally iodinated human Tg revealed that these epitopes were exclusively located in thyroxine (T4) containing peptides. Through the use of synthetic T4-containing peptides, representing the four major hormonogenic sites in Tg, we demonstrated that both CH9 and ADA2 recognize an epitope containing the T4 at position 2553 in human Tg. Sets of overlapping 5mer to 12mer peptides around this T4 showed that the most potent peptide was a 9mer beginning at Asp 2551. The T4 was shown to be a critical residue, since its replacement with any of the 20 naturally occurring amino acids produced only nonstimulatory peptides. Since the T cell hybridomas could also be stimulated by major histocompatibility complex class II positive (interferon-gamma-treated) thyroid epithelial cells in vitro, and their parent T cell lines can induce thyroiditis on adoptive transfer, the T4-containing Tg sequence described here is implicated as a pathogenic epitope in murine thyroid autoimmunity.

Suppression in experimental autoimmune thyroiditis: the role of unique and shared determinants on mouse thyroglobulin in self-tolerance

Previous studies have shown that T cells from mice genetically susceptible to experimental autoimmune thyroiditis (EAT) recognize determinants shared between mouse thyroglobulin (Tg) and heterologous Tgs. Some shared determinants are thyroiditogenic; lymphocytes from mice immunized with mouse Tg (MTg) or human Tg (HTg) and reciprocally restimulated in vitro with either Tg can transfer EAT. Studies on the mechanisms of self-tolerance have shown that pretreatment with soluble MTg suppresses in vitro proliferation to MTg and EAT induction with MTg. To determine the role of share epitopes in maintaining tolerance, mice were pretreated with soluble HTg and immunized with HTg or MTg and adjuvant. Cells from HTg-pretreated. HTg-immunized mice showed suppressed in vitro proliferative response to HTg. Following MTg immunization, the cells showed suppressed in vitro response to MTg. However, in contrast to MTg pretreatment, the subsequent development of EAT in vivo was unaltered in severity following HTg pretreatment. Thus, determinants shared between HTg and MTg can induce suppression of in vitro responses to HTg and MTg, but not inhibit the onset of thyroiditis, suggesting that T cells recognizing MTg-unique epitopes expanded to mediate thyroiditis. We conclude that recognition of both unique epitopes expanded to mediate thyroiditis. We conclude that recognition of both unique and shared epitopes on MTg are essential for the overall maintenance of self-tolerance.

Resistance to experimental autoimmune thyroiditis: L3T4+ cells as mediators of both thyroglobulin-activated and TSH-induced suppression

Mechanisms suppressive to induction of murine experimental autoimmune thyroiditis (EAT) can be activated by pretreatment with tolerogenic doses of mouse thyroglobulin (MTg) or prior TSH infusion to raise circulatory MTg levels. MTg-activated suppressor T cells (Ts), shown earlier to be Thy-1+ and probably I-J+, were further characterized by in vivo administration of paired rat monoclonal antibodies to distinct epitopes on the L3T4 or Lyt-2 molecule, either on the day of, or subsequent to, initiation of the tolerogenic regimes. The cells required at the time of MTg pretreatment were L3T4+, Lyt-2- and low anti-L3T4 doses had no effect on their activation. The cells that mediated the strong MTg-induced resistance following pretreatment were also L3T4+; their suppressor function could only be abrogated by depletion of L3T4+, but not Lyt-2+, cells. Injection of cyclophosphamide (20-100 mg/kg) either prior to EAT induction or after Ts activation did not affect the severity of disease. Similarly, the suppressor state evoked by TSH infusion could only be abrogated by anti-L3T4 treatment. These findings indicate that both MTg-activated and TSH-induced suppression are mediated by L3T4+ cells. We hypothesize that MTg-specific Ts are present in normal, EAT-susceptible mice in low numbers to contribute to the maintenance of self-tolerance and that they are stimulated by increased levels of circulatory MTg to expand/differentiate and mediate the marked resistance to EAT induction.

Variability in production and immunoreactivity of in-vitro secreted human thyroglobulin

We examined basal and bTSH-stimulated human thyroglobulin (hTg) secretion by autologous normal and abnormal (benign and malignant) human thyroid cell monolayers. Basal and bTSH-stimulated hTg secretion was highly variable and ranged from 50-700 ng/ml/10(5) cells over a 6 day period. All normal and benign 'non-functioning' adenoma cells demonstrated a dose and time related stimulation of hTg secretion in response to bTSH. Comparison of hTG secretion by autologous normal and abnormal cells showed that in six of eight pairs, the normal thyroid cells had a greater output of hTg than the benign adenoma cells in contrast to our previous studies using non-autologous cells. Malignant thyroid cell hTg production was less predictable than that obtained with normal and benign thyroid cells varying from absent to normal responses to bTSH. Characterization studies of the secreted hTg showed no difference between normal, benign and malignant thyroid cell hTg with reference to molecular weight. However, hTg secreted in vitro was non-iodinated and had a marked reduction (up to 200-fold) in immunoreactivity assessed by both polyclonal and monoclonal antibodies to hTg when compared to hTg standard prepared from intact thyroid tissue (which had 4.58 micrograms iodine/mg). This reduction in hTg immunoreactivity was greatest for hTg secreted by malignant thyroid cells. These data demonstrate the wide variability in the hTg secretory capacity of human thyroid cell monolayers and indicate, when compared to autologous normal cells, that abnormal human thyroid epithelial cells may be relatively deficient in their ability to secrete hTg in vitro. There were also qualitative differences in the immunoreactivity, and iodine content, of in-vitro secreted hTg. These observations suggest that there may be much greater heterogeneity in hTg secreted in vitro than previously realized, perhaps secondary to differences in iodine content and/or degree of glycosylation. Human thyroglobulin (hTg) is the major secretory protein of the thyroid cell (Van Herle et al., 1979). Intracellular hTg is the site of thyroid hormone iodination yet its extrathyroidal role, if any, remains unclear. While hTg is usually present in the peripheral circulation of normal individuals, in species of differing molecular weight (Feldt-Rasmussen et al., 1978), there have been few studies of in-vitro production of hTg by isolated human thyroid cells. Our interest in hTg is in its role as an antigen in thyroid autoimmune disease (De Bernardo et al., 1983; 1986).(ABSTRACT TRUNCATED AT 400 WORDS)