Experimental autoimmune thyroiditis. In vitro cytotoxic effects of T lymphocytes on thyroid monolayers

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.

The genetics of autoimmune thyroiditis: the first decade

Most of our current understanding of the genetic predisposition to autoimmune disease can be traced to experiments performed in the decade from 1971 to 1981. Chella David was a key contributor to this research. Many of these early steps came from studies of experimental autoimmune thyroiditis. This model has been especially valuable because essentially the same disease can occur spontaneously in selected strains of animals or can be induced by deliberate immunization. From a genetic point of view, the disease has been investigated in three different species: mice, rats and chickens. The same antigen, thyroglobulin, initiates the disease in all three species. Among the main discoveries were the relationship of autoimmune disease to the major histocompatibility complex (MHC), the interplay of different subregions within the MHC in promoting or retarding development of disease, the differing roles of MHC class II and MHC I class genes in induction and effector phases, respectively, and the cumulative effect of non-MHC genes, each of which represents a small addition to overall susceptibility. Other experiments revealed that genetic differences in thyroglobulin allotypes influence susceptibility to thyroiditis. Thyroid glands differed in different strains in vulnerability to passive transfer of antibody. The first evidence of modulatory genes on the sex-related X chromosome emerged. All of these genetic findings were concurrently translated to the human disease, Hashimoto's thyroiditis, where thyroglobulin is also the initiating antigen.

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.

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.

Navigating the passage between Charybdis and Scylla: recognizing the achievements of Noel Rose

This special edition of the Journal of Autoimmunity is dedicated to celebrate the enormous contributions of Dr. Noel Rose, a physician-scientist, someone that can be readily anointed as a gifted scientist who laid down the foundation and fundamental concepts of human autoimmunity. Dr. Rose performed a series of landmark studies that extend back more than 50 years and whose work is the cornerstone of the commonly used term "from the bench to the bedside." The studies included not only characterization of a normal immune response but, more importantly, defining the nature of not only the antigen, but also the aberrant response that results in organ, tissue specific reactions and immunopathology. These pioneering studies contributed to the biochemical nature of antigens, dissection of the immune repertoire, the recognition of the importance of genetics and environment, and the distinctions between a normal and an autoimmune response. Hence, this volume has been coined "Navigating the Passage Between Charybdis and Scylla: Recognizing the Achievements of Noel Rose."

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

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

The CD40, CTLA-4, thyroglobulin, TSH receptor, and PTPN22 gene quintet and its contribution to thyroid autoimmunity: back to the future

Autoimmune thyroid diseases (AITD) are common autoimmune diseases, affecting up to 5% of the general population. Thyroid-directed autoimmunity is manifested in two classical autoimmune conditions, Hashimoto's thyroiditis, resulting in hypothyroidism and Graves' disease resulting in hyperthyroidism. Autoimmune thyroid diseases arise due to an interplay between environmental and genetic factors. In the past decade significant progress has been made in our understanding of the genetic contribution to the etiology of AITD. Indeed, several AITD susceptibility genes have been identified. Some of these susceptibility genes are specific to either Graves' disease or Hashimoto's thyroiditis, while others confer susceptibility to both conditions. Both immunoregulatory genes and thyroid specific genes contribute to the pathogenesis of AITD. The time is now ripe to examine the mechanistic basis for the contribution of genetic factors to the etiology of AITD. In this review, we will focus on the contribution of non-MHC II genes.

Death ligand tumor necrosis factor-related apoptosis-inducing ligand inhibits experimental autoimmune thyroiditis

The role of TNF-related apoptosis-inducing ligand (TRAIL) in autoimmune thyroiditis is unclear. We used experimental autoimmune thyroiditis to clarify the contribution of TRAIL to the development of autoimmune thyroiditis. CBA/J mice were immunized with murine thyroglobulin, and spleen cells from these mice were subsequently injected into irradiated recipient CBA/J mice. One week later, the recipient mice were treated with recombinant TRAIL or a control protein. Compared with control animals, TRAIL-treated mice developed a milder form of the disease with a significant decrease in mononuclear cell infiltration in the thyroid and less thyroid follicular destruction. Furthermore, the number of apoptotic thyrocytes and also thyroglobulin-specific T helper-1 cell responses in TRAIL-treated mice was lower than that in the control animals. This study suggests that exogenous TRAIL suppresses the development of autoimmune thyroiditis via altering the function of cells involved in the immune response. These findings may contribute toward a novel treatment autoimmune thyroiditis.

HLA-DR and HLA-DQ polymorphism in human thyroglobulin-induced autoimmune thyroiditis: DR3 and DQ8 transgenic mice are susceptible

In contrast to H2-based susceptibility to experimental autoimmune thyroiditis (EAT) induced with thyroglobulin (Tg), human leukocyte antigen (HLA) association with Hashimoto's thyroiditis, the human counterpart, is less clear, and determining association is further complicated by DR/DQ linkage disequilibrium. Previously, we addressed the controversial implication of HLA-DR genes by introducing HLA-DRA/DRB1*0301 (DR3) transgene into endogenous class II negative H2Ab(0) mice. EAT induction with either human (h) or mouse (m) Tg demonstrated the permissiveness of DR3 molecules for shared Tg epitopes. Here, we examined the participation of HLA-DQ genes by introducing DQA1*0301/DQB1*0302 (DQ8) transgene into class II negative Ab(0) or class I and II negative beta(2)m((-/-)) Ab(0) mice. About 50% and 80% of HLA-DQ8(+) Ab(0) and beta(2)m(-) Ab(0) mice, respectively, developed moderate EAT after hTg immunization, but only minimal response to mTg. The hTg presentation to hTg-primed cells was blocked by anti-DQ mAb in vitro. By contrast, HLA-DRB1*1502 (DR2) and *0401 (DR4) transgenes contributed little to hTg induction. Similarly, DQA1*0103/DQB1*0601 or DQA1*0103/DQB1*0602 (DQ6) transgenic Ab(0) mice were unresponsive to hTg induction and carried no detectable influence in DQ8/DQ6 double transgenic mice. Thus, both HLA-DR and -DQ polymorphism exists for hTg in autoimmune thyroiditis. The use of defined single or double transgenic mice obviates the complications seen in polygenic human studies.

Flexibility of TCR repertoire and permissiveness of HLA-DR3 molecules in experimental autoimmune thyroiditis in nonobese diabetic mice

Experimental autoimmune thyroiditis (EAT) is inducible in genetically susceptible mice by immunization with mouse thyroglobulin (mTg). With susceptibility linked to MHC class II, EAT is useful in studying human leukocyte antigen (HLA) associations with Hashimoto's thyroiditis. In non-obese diabetic (NOD) mice, approximately 10% thyroiditis incidence occurs with aging. This potential was exploited to examine the T cell repertoire and HLA association in EAT. Similar to B10.K-Vbeta(c)mice with TCRBV genes reduced by approximately 70%, mTg-immunized NOD-Vbeta(c)mice developed thyroiditis comparable to controls, indicating plasticity of the TCR repertoire for pathogenic epitopes. HLA association was evaluated by introducing HLA-DRA/DRB1*0301 (DR3) transgene into class II-negative NOD mice (Ab(0)/NOD). Previously, this HLA-DR3 transgene rendered EAT-resistant B10.M and Ab(0)mice susceptible to both mTg- and hTg-induced EAT. These results are now confirmed. mTg-induced thyroiditis in DR3+ Ab(0)/NOD mice was comparable to that in NOD and DR3- NOD mice, and the proliferative response was stronger. By comparison, NOD mice were only moderately susceptible to hTg-induced EAT. However, thyroiditis was more severe in DR3+ Ab(0)/NOD than in DR3- NOD mice, with no difference in proliferative response to hTg harbouring heterologous epitopes. The confirmed permissiveness of HLA-DR3 molecules on an NOD background for EAT induction by both mTg and hTg supports the importance of this class II gene implicated in some patient studies.

New revelations in susceptibility to autoimmune thyroiditis by the use of H2 and HLA class II transgenic models

H2 and HLA transgenes were utilized to clarify the role of class II genes in susceptibility to experimental autoimmune thyroiditis (EAT), a model for Hashimoto's thyroiditis (HT). Susceptibility was transferred by H2 class II transgenes to a resistant haplotype and by HLA-DRA/DRB1*0301 (DR3) transgene into class II-negative Ab0 mice. Mice with a HLA-DRB1*1502 (DR2) transgene remain resistant to mouse thyroglobulin (mTg)-induced EAT, illustrating the role of HLA-DRB1 polymorphism. A role for HLA-DQ polymorphism was shown with hTg-induced EAT in HLA-DQ*0301/DQB1*0302 (DQ8), but not HLA-DQ*0103/DQB1*0601 (DQ6), transgenic mice. Yet, both DQ8+ and DQ6+ mice were unresponsive to mTg. Single transgenes obviate the problems from DR/DQ linkage disequilibrium and may distinguish the degree of susceptibility and the response to shared or specific epitopes. The introduction of conserved Eak transgene into Ab0 mice reveals a new role for H2E molecules in EAT. Without H2A molecules, EalphaEbetab molecules and T cells respond to hTg or pTg with severe thyroiditis, but not to mTg, thus distinguishing self from nonself. However, IAb genes in resistant mice ameliorate Eak transgene-mediated thyroiditis, similar to the effect of Eak transgene on IAs-mediated EAT. Studies in HLA DQ/DR double transgenic mice simulating human haplotypes could reveal HLA class II gene interactions in HT.

Pathogenic thyroglobulin peptides as model antigens: insights on the induction and maintenance of autoimmune thyroiditis

In recent years, the discovery of pathogenic thyroglobulin (Tg) peptides has given a new impetus to study, at the basic level, mechanisms of induction and immunoregulation of autoimmune thyroiditis. The genetic control of the immune response against defined Tg epitopes and the diversity of the T-cell receptor repertoire recruited for their recognition were among the first issues examined. Some of these epitopes contained hormonogenic sites, i.e. thyroxine residues, and thus offered an excellent opportunity to study how post-translational modifications such as iodination, can influence induction of thyroiditogenic cells. The delineation of pathogenic Tg determinants also enabled the search for "molecular mimics" i.e. peptides of microbial origin that may be involved in the pathogenesis of the disease. In addition, factors promoting the generation of pathogenic epitopes during Tg processing in antigen presenting cells could now be systematically investigated. This review summarizes recent findings in these areas.

Newer insights into the pathogenesis of experimental autoimmune thyroiditis

Experimental autoimmune thyroiditis (EAT), produced in the mouse by immunization with murine thyroglobulin plus complete Freund's adjuvant, represents a valuable model for studying the pathogenesis of human chronic (Hashimoto's) thyroiditis. A major issue requiring clarification is the difference between benign autoimmunity, characterized solely by production of autoantibodies to thyroglobulin, and pathogenic autoimmunity where injury occurs to the thyroid cells. In this article, we describe the role of two key cytokines, IL12 and IFNgamma, in modifying the pathogenic immune response. EAT, defined by cellular infiltration of the thyroid and the development of thyroglobulin-specific autoantibodies, is a dynamic process. Consequently, a cytokine may exert a different effect at different times during the disease process. For purposes of discussion, we propose that there are three stages in the development of EAT: priming; initiation; and progression. Administration of anti-IL12 during the priming stage and initiation dramatically decreases disease and lowers autoantibody levels. In contrast, injection of recombinant IL12 after disease was established significantly decreases the severity of disease and reduces autoantibody levels. Unlike IL-12, IFNgamma was not essential for the priming of EAT. However, the severity of disease in the anti-IFNgamma-treated initiation- and progression-treated animals was higher than in controls, implying a regulatory role for IFNgamma. These findings emphasize that EAT involves a complex array of pathogenic mechanisms. The balance of cytokines produced during the early phase of the autoimmune reaction probably determines the progression from a harmless autoimmune response to autoimmune disease.

Spontaneous autoimmune thyroiditis in NOD.H-2h4 mice

NOD.H-2h4 mice, which express I-Ak on the NOD genetic background, spontaneously develop autoimmune thyroiditis (SAT) and anti-mouse thyroglobulin (MTg) autoantibodies. The incidence of SAT is nearly 100% in mice of both sexes 6-8 weeks after administration of 0.05% NaI in the drinking water. After reaching maximum severity, inflammation is chronic over the next 3-4 months. All mice that develop thyroid lesions also produce MTg-specific IgG1 and IgG2b autoantibodies. Thyroid lesions and anti-MTg autoantibodies did not develop in CBA/J (H-2(k)) or NOD.SWR(H-2(q)) mice after administration of NaI water. Both CD4(+)and CD8(+)T cells are involved in the initial development of SAT. Depletion of CD4(+), but not CD8(+), T cells after thyroid lesions have developed also markedly reduced SAT severity, indicating that CD4(+)T cells are required for both developing and maintaining SAT. Analysis of cytokine gene expression indicated that both Th1 and Th2 cytokines were expressed in thyroids of NOD.H-2h4 mice with SAT. Th1 and proinflammatory cytokines were maximally expressed 4-6 weeks after mice began receiving NaI water, while Th2 cytokine gene expression was greatest at 8-15 weeks, when lesions had reached maximal severity and were in the chronic phase. TGF-beta was highly expressed in NOD.H-2h4 thyroids, irrespective of whether the mice had received NaI water or had thyroid lesions.

Induction of experimental autoimmune thyroiditis by heat-denatured porcine thyroglobulin: a Tc1-mediated disease

Recent studies have shown that denatured exogenous antigens can prime cytotoxic T lymphocytes (CTL). To assess the contribution of CTL to experimental autoimmune thyroiditis (EAT), porcine thyroglobulin (pTg) was heat-denatured (hdpTg) and injected i.v. into CBA/J mice, without the aid of adjuvants. Both lymphocytic infiltrations of the thyroid glands and levels of Tg-specific CTL were similar to those found in conventional EAT induced by Tg and adjuvants. In contrast, proliferative responses could not be detected, and titers of antibodies to pTg were 20 times lower. These EAT-inducer CTL belong to the CD8+ cell subset and exerted their thyroiditogenic potential through release of IFN-gamma. We conclude that hdpTg-induced EAT is mediated by type 1 cytotoxic T cells (Tc1).

Flexibility of the thyroiditogenic T cell repertoire for murine autoimmune thyroiditis in CD8-deficient (beta2m -/-) and T cell receptor Vbeta(c) congenic mice

In murine experimental autoimmune thyroiditis (EAT), previous studies have revealed a highly adaptable thyroiditogenic T cell repertoire which involves both CD4+ and CD8+ T cells in the susceptible H2k strain. To further test this flexibility, congenic B10.K mice lacking CD8+ T cells (B2m -/-) or harboring 70% T cell receptor (TCR) Vbeta gene deletions (Vbeta(c)) were immunized with mouse thyroglobulin (MTg) and evaluated for EAT 28 days later. All B2m -/- mice developed moderate antibodies to MTg, and thyroidal inflammation was comparable to B10.K mice, averaging 35-40%. Spleen cells (SC) from MTg-immunized mice were then injected into syngeneic recipients after stimulation in vitro with MTg or with conserved, thyroxine (T4)- or thyronine (T0)- containing 12mer peptides, hT4(5), hT0(2553), or hT4(2553), derived from the primary hormonogenic sites at position 5 or 2553 of human Tg. As previously shown in another H2k strain (CBA/J), all three peptides activated MTg-primed SC to transfer EAT in B10.K mice. hT4(5) and hT4(2553) were further tested in B10.K-Vbeta(c) and beta2m- B10.K mice. Both peptides expanded thyroiditogenic T cells in either strain, resulting in severe thyroiditis in syngeneic recipients. That EAT can develop in the absence of CD8+ T cells or in the presence of a severely restricted TCR repertoire underscores the remarkable flexibility of the thyroiditogenic T cell profile in the susceptible k haplotype.

Apoptosis and thyroiditis

The origin of the various forms of autoimmune thyroiditis remains unclear. Most investigations into the pathogenesis of these disorders have focused on immune abnormalities that might lead to an autoimmune response. However, no unique immune response to thyroid autoantigens has been identified that either is limited to patients with thyroiditis or is absolutely correlated with clinical disease expression. CD8 T-cell-mediated cytotoxicity is thought to be a major cause of thyroid follicular cell damage in thyroiditis. This damage is produced in part through the induction of apoptosis in thyroid cells. Recent studies have demonstrated that programmed cell death is regulated in thyroid cells and that a major pathway for immune-mediated apoptosis, the Fas pathway, is blocked by labile inhibitors in a manner that could prevent cytotoxicity. This review also examines several other types of regulation of apoptotic pathways in thyrocytes. We hypothesize that the regulation of programmed cell death pathways in the thyroid may alter the expression of autoimmune thyroid diseases by modifying the susceptibility of thyroid cells to immune-mediated apoptosis.

Inhibition of the development of spontaneous autoimmune thyroiditis in the obese strain (OS) chickens by in vivo treatment with anti-CD4 or anti-CD8 antibodies

The involvement of CD4+ and CD8+ T cells in pathogenesis of spontaneous autoimmune thyroiditis (SAT) in obese strain (OS) chickens has not been studied in depth until now. We depleted CD4+ or CD8+ T cells in OS chickens by treatment with murine monoclonal anti-CD4 or anti-CD8 antibodies at 3 day intervals beginning at hatching. The birds were killed at 19-25 days of age. Treatment with anti-CD4 antibody completely prevented SAT development, while treatment with anti-CD8 antibody partially inhibited SAT. These results show the critical role of CD4+ T cells in the development of SAT in OS chickens, and indicate that CD8+ T cells are also involved in SAT pathogenesis.

Thyroglobulin peptides of specific primary hormonogenic sites can generate cytotoxic T cells and serve as target autoantigens in experimental autoimmune thyroiditis

Previously we demonstrated that thyroxine (T4)-containing, 12-mer peptides from positions 5 (1-12) and 2553 (2549-2560), as well as thyronine (T0)-substituted 2553 peptide, derived from human (H) thyroglobulin (Tg) are capable of activating T cells that infiltrate the thyroid (thyroiditogenic). In contrast, peptides T4(2567) and T0(2567) (2559-2570) are not. To determine if these thyroiditogenic peptides, T4(5), T4(2553), and T0(2553), activated cytotoxic T cells (Tc) and served as target autoantigens when loaded onto indicator cells (BW5147 lymphoma, H2k), lymph node cells from CBA mice immunized with mouse (M) Tg were cultured in vitro with MTg, HTg, or Tg peptide. After MTg or HTg activation, Tc were detected for both MTg- and HTg-loaded target cells in an 18-h, 51Cr-release assay at an effector:target cell ratio of 50:1. These Tc also killed target cells labeled with T4(5), T4(2553), or T0(2553), but not the control peptide T4(2567). When MTg-primed lymphocytes were cultured with T4(5), T4(2553), or T0(2553), specific Tc were also generated against target cells labeled with the respective peptide. The data suggest that one of the thyroiditogenic properties of these peptides previously shown by adoptive transfer of thyroiditis is related to the generation of Tc. In addition, these conserved autoepitopes of Tg also serve as target antigens for Tc.

Expression of thyroid peroxidase in EBV-transformed B cell lines using adenovirus

Thyroid peroxidase (TPO) is thought to be one of the pathological antigens in Hashimoto's thyroiditis. Epstein-Barr virus-transformed B cell lines (EBVL) can be used for antigen-presenting cells and target cells of cytotoxic T cells. To develop a model for endogenous TPO presentation in EBVL, we constructed a recombinant adenovirus carrying the TPO gene driven by the cytomegalovirus promoter (Ad5-TPO). Enzymatically active human TPO could be expressed in COS cells using Ad5-TPO. the peroxidase activity of the membrane extract from Ad5-TPO-infected COS cells was approximately 6 times higher than that from stably transfected TPO expressing CHO cells. TPO protein expression in the EBVL was analyzed by Western blotting technique. A band at approximately 110 kDa characteristic of hTPO was detected in EBVL infected with Ad5-TPO. hTPO expression in EBVL induced with adenovirus should facilitate understanding of T cell immunity to TPO in patients with autoimmune thyroid diseases.

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.

Depletion of CD4+ and CD8+ cells eliminates immunologic memory of thyroiditogenicity in murine experimental autoimmune thyroiditis

Experimental autoimmune thyroiditis (EAT) develops in genetically susceptible mice after immunization with mouse thyroglobulin (MTg), and is mediated by T cells, both CD4+ and CD8+, infiltrating the thyroid. Previous work showed that depletion of CD4+, but not CD8+, cells with rat monoclonal antibodies (mAbs) interfered with EAT induction. To test if concomitant CD4+ cell depletion and immunization led to EAT resistance, mice were reimmunized at an interval of 15 or 43 days after injection of CD4 mAbs. No resistance had been established; disease severity and anti-MTg titers were comparable to mice with primary immunization. Previous work also showed that treatment during advancing EAT with only CD4 mAbs on days 21, 25 led to long-lasting, reduced severity in EAT, whereas administration of CD8 mAbs alone reduced the smaller CD8+ subset only. However, therapy with both mAbs was most efficacious; > 50% of thyroids were purged of all cellular infiltrate after only two doses. Moreover, T cells emerging subsequent to depletion were not retained in the thyroid, despite ongoing antibody production. To test if nondepleting CD4 and CD8 mAbs were similarly effective for therapy, mAbs of the IgG2a isotype were administered during advancing EAT. No effect on thyroidal infiltration was observed, indicating that modulation of the CD4 and CD8 antigen without depletion was insufficient for efficacious therapy. To determine if combined therapy with depleting mAbs reestablished self tolerance, treated mice were reimmunized on days 70, 77, when T cell recovery was nearly complete. Thyroiditis was comparable to controls given primary immunization, despite high antibody levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Adhesion molecule monoclonal antibodies inhibit experimental autoimmune thyroiditis

To examine the role played by adhesion molecules in thyroid autoimmunity, we have assessed the effect of administering monoclonal antibodies (mAb) against intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-1 (LFA-1) in experimental autoimmune thyroiditis, induced by immunizing rats with thyroglobulin in complete Freund's adjuvant. The antibody against LFA-1, but not against ICAM-1, reduced thyroglobulin antibody production (P < 0.01) and both antibodies caused a significant reduction (P < 0.002) in the severity of the thyroidal lymphocytic infiltration. In vitro, both mAb impaired the proliferative response of splenic and lymph node T cells to thyroglobulin, but only the antibody against LFA-1 reduced thyroid cell killing assessed using splenic lymphocytes as effectors. Monoclonal antibodies against both these adhesion molecules appear to inhibit cell-mediated autoimmunity in vivo, but only the LFA-1 mAb reduced the autoantibody response.

Cellular basis of T-cell autoreactivity in autoimmune diseases

There is no doubt that T cells play a key role in the pathogenesis of autoimmune diseases (AD) both as effector and regulatory cells. Despite spectacular progress in the understanding of natural tolerance to self, owing particularly to transgenic technology, important questions remain open regarding the pathogenesis of AD, the conditions favoring the transition from benign or 'physiological' autoimmunity to deleterious autoimmunity, and the precise effector mechanisms. This review on the cellular basis of T-cell-mediated AD begins with an enumeration of the main arguments in favor of direct T-cell involvement, special emphasis being given to two animal models which have been most extensively investigated: experimental allergic encephalomyelitis, and the nonobese diabetic mouse. The question as to whether pathogenic T cells use a restricted repertoire of V beta genes is examined in the context of these two models. From here we proceed to an evaluation of the mechanisms of onset of AD, discussing both extrinsic and intrinsic factors responsible for the breakdown in T-cell tolerance and reviewing the arguments in favor of suppressor T cells being actively involved in the prevention of autoimmunity. The last two sections are devoted to the effector mechanisms responsible for tissue injury in organ-specific AD and to T-cell-directed therapeutic interventions, respectively. We discuss the two main pathogenic hypotheses based on direct intervention of cytotoxic T cells or indirect involvement of inflammatory cytokines and macrophages, and evaluate the importance of ecotaxis in leading autoreactive T cells to the site of injury. We conclude on a brief and nonexhaustive list of strategies aimed at selectively neutralizing potentially harmful T cells.

Autoantigens in thyroid diseases

The autoantigens involved in autoimmune thyroid disease have now been extensively characterised, and the autoantibodies they evoke provide important aids to diagnosis, leading to early treatment of thyroid autoimmunity. The next stage in the puzzle is to determine towards which epitopes on the autoantigens the immune response is directed. We have already come a long way in the identification of immunodominant epitopes and have been able to identify one T cell epitope which has pathogenic capabilities. Identification of other T cell and B cell epitopes will help us understand the cell-mediated and humoral responses in greater detail and in time lead to more specific therapeutic intervention. A greater understanding of the mechanisms underlying one particular autoimmune disease will give us insights into other diseases, due to the belief that there may well be common underlying defects that, due to a multitude of factors, manifest as different diseases. The susceptibility factors in autoimmune thyroidits and autoimmune disease in general are very complex. A greater understanding is required of HLA associations and how particular peptides are presented in vivo. Are susceptible MHC types the ones capable of presenting the pathogenic peptides? Our major T cell thyroiditogenic epitope contains a T4 residue which accounts for over half the molecular weight of the peptide. Its structure is large and consists of a double benzene ring structure with four iodine atoms. It will be interesting to see how such a peptide can be presented and which residues bind T cell receptor or MHC. In summary we can say that autoimmune disease is due to a cocktail of factors which all contrive to tip the delicate balance of the immune system into an autoimmune state. HLA association may play a role in conferring an enhanced ability to select from a restricted repertoire of pathogenic epitopes, those epitopes perhaps only becoming available for presentation after interaction with environmental agents, whatever they may be. Following this, the normal regulation of self presentation and tolerance mechanisms break down and autoimmunity supervenes.

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.

Antigen-specific immunoregulation and autoimmune thyroiditis

1. Large Thy1+, CD8+ immunoregulatory cells were found in the thymus of mice 9-16 days after injection of soluble mouse thyroglobulin (without adjuvant). 2. Similar immunoregulatory cells appeared in the spleen 14-21 days after antigen administration suggesting that they were generated in the thymus and later migrated to the spleen. 3. The immunoregulatory cells were antigen-specific and attached to cognate antigen. 4. The degree of inhibition by the immunoregulatory cells differed among various inbred strains of mice and were virtually absent from SJL mice. 5. The regulatory function of the cells was strain specific in vitro and in vivo, and was restricted by both H-2 and non-H-2 haplotype. 6. By panning on antigen-coated plates, immunoregulatory cells were isolated and cell lines and clones with inhibitory function established.

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.

Thyroid-specific T cells in the normal Wistar rat. II. T cell clones interact with cloned wistar rat thyroid cells and provide direct evidence for autoantigen presentation by thyroid epithelial cells

Strains of rat differ in their susceptibility to experimental autoimmune thyroiditis (EAT). We recently observed that the normal Wistar rat has lymph node (LN) T cells which recognize the newly available cloned Wistar thyroid cell line (WRT) and/or rat thyroglobulin (rTg). We have now cloned thyroid-specific T cells and characterized their interaction with the WRT target cell. Twenty-three T cell clones were tested for their reactivity to syngeneic thymocytes, WRT cells alone, or WRT cells with thymocytes. All the clones were of the CD4+CD8- phenotype. Seven of 23 T cell clones proliferated in the presence of WRT cells alone or with the combination of WRT cells and thymocytes, exhibiting stimulation indices of 1.5 to 5. In all but one of the T cell clones responding to WRT cells alone was there no evidence that the additional presence of thymocytes supplied a stronger "second" proliferative signal than the WRT cells. These WRT-reactive clones which were able to be more extensively characterized were MHC class II restricted, secreted rat interferon (IFN)-gamma in response to WRT cell exposure, and one clone showed cross-reactivity with rTg antigen. Induction of WRT cell MHC class II antigen by prior treatment with IFN-gamma failed to further enhance the WRT cell-induced T cell proliferation. These data provide the first evidence for direct antigen presentation by thyroid epithelial cells (TECs) in the absence of other antigen-presenting cells. Furthermore, they provide evidence that TECs are able to provide the appropriate "second" signals required for T cell activation and successful autoantigen presentation.

Thyroid-specific T cells in the normal Wistar rat. I. Characterization of lymph node T cell reactivity to syngeneic thyroid cells and thyroglobulin

Wistar rats are susceptible to the induction of experimental autoimmune thyroiditis (EAT) and recently a cloned Wistar thyroid epithelial cell line (WRT) has become available. In this study we have examined the in vitro proliferative response of Wistar rat lymphoid cells to the WRT cells as a model for better understanding thyroid cell-T cell interactions. Lymph node (LN) cells from normal Wistar rats showed an early and vigorous response to syngeneic thyroid cells (WRT). Further examination of the Wistar phenomenon revealed that unpurified lymphoid cells were also able to mount a proliferative response to rat thyroglobulin. The Wistar LN cell response to WRT cells consisted of T cell proliferation that was both MHC class I and class II restricted. There was a greater proliferation of CD8+ than CD4+ T cells, but WRT-stimulated lymphoblast cells were not cytotoxic to 51Cr-labeled WRT cell targets. These data suggest that normal Wistar rats have circulating thyroid-specific T cells that may be related to their known susceptibility to EAT. Furthermore, the interaction between such thyroid-specific T cells and cloned syngeneic thyroid cells offers a unique model for the further investigation of thyroid-immune interactions and the escape from tolerance induction.

Expression of intercellular adhesion molecule-1 (ICAM-1) on thyroid epithelial cells in Hashimoto's thyroiditis but not in Graves' disease or papillary thyroid cancer

In order to study the possible role of antigen-independent adhesion systems in thyroid autoimmunity, we evaluated by indirect immunofluorescence the expression of lymphocyte functional antigen-1 (LFA-1) and its ligand ICAM-1 on mononuclear cell infiltrates (when present) and thyroid follicular cells of four patients with Hashimoto's thyroiditis, 30 with Graves' disease, five with papillary cancer, two with follicular adenoma, and two normal thyroid specimens. The expression of MHC class I and class II antigens was also evaluated. Most mononuclear infiltrates were LFA-1 positive, as expected. A positivity for ICAM-1 on follicular cells was observed in three out of four Hashimoto's thyroiditis specimens; such a phenomenon was totally absent in Graves' disease or any other pathological condition, or in normal tissue. MHC class II expression on thyrocytes was observed in all the patients with Hashimoto's thyroiditis, in 27 out of 30 with Graves' disease and in three out of five papillary cancer specimens.

Activation of cytotoxic cells by syngeneic prostate antigens in experimental autoimmune vesiculo-prostatitis

In our experimental model of autoimmune vesiculo-prostatitis, obtained by immunization with syngeneic male accessory glands (MAG) and complete Freund's adjuvant, the presence of specific autoreactive cells with cytotoxic activity against prostate antigens was studied. The specific cytotoxicity generated in MAG immunized rats was tested using 51Cr labelled syngeneic prostate cells or labelled chicken erythrocytes coated with specific antigens (MAG homogenate or chromatographic fractions from prostate homogenate) which were used as target cells in a medium free of complement. The addition of spleen sensitized cells to prostate cells suspension produced a significant release of 51Cr in regard to normal effector cells (11.87 +/- SE 1.12 versus 1.5 +/- 0.75). Similar results were obtained when MAG-coated erythrocytes were used as target cells (10.87 +/- SE 0.62 versus 1.50 +/- 0.25). Depletion of T but no B or adherent-cells was shown to abolish the lytic effect indicating that MAG immunization provides determinants which are recognized by sensitized T-cells on cells of the prostate gland where the most severe tissue alterations were previously observed. Erythrocytes coated with chromatographic fractions obtained from prostate homogenate were used to identify the antigens triggering the lytic effect. It was demonstrated that two fractions (FI and FII) functioned as in vivo sensitizing antigens as well as in vitro activating antigens for themselves. The restimulation in vitro of sensitized cells with purified prostate fractions induces an additional lytic effect suggesting that an expansion of effector cells may take place after contacting the antigens at the prostate site.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunogenetic aspects of human thyroglobulin-reactive T cell lines and hybridomas

The in vitro proliferative response to T cells primed with human thyroglobulin (Tg) was compared in 11 independent haplotypes on B10 background. B10.K and B10.S mice were the most responsive, whereas, with the exception of B10.PL (H-2u), all other B10 congenics were intermediate responders. The two best responders to in vitro challenge with human Tg, of the k and s haplotype, are the same as those showing H-2-linked susceptibility to induction of experimental autoimmune thyroiditis (EAT) with mouse Tg. Since shared epitopes on human and mouse Tgs have been shown to be thyroiditogenic by adoptive transfer studies in CBA (H2k) mice, the findings indicate that shared epitopes may be studied in appropriate (i.e. EAT-susceptible) strains of mice. Therefore, we proceeded to develop methods to produce T-cell lines and hybridomas to human Tg in B10.K and B10.S mice, test their cross-reactivity to heterologous Tgs and their Ia restriction patterns. By using antigen-presenting cells from recombinant strains, we identified restriction elements encoded by the I-A subregion alone and a combinatorial molecule from the I-A/I-E subregions.

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.

Experimental murine thyroiditis induced by porcine thyroid peroxidase and its transfer by the antigen-specific T cell line

Thyroid peroxidase purified from porcine thyroid (pTPO) was found to induce an experimental murine thyroiditis with genetic restriction which was very different from that induced by mouse thyroglobulin (mTg). C57BL/6 and C57BL/10 (both H-2b) were good responders for thyroiditis, whereas A/J (H-2a), BALB/c (H-2d), DBA/2 (H-2d), CBA (H-2k), C3H/He (H-2k), and SJL/J (H-2s) were poor responders. Genetic analyses using congenic or recombinant strains revealed the following results: The H-2-linked gene (probably the I-A subregion) had a weak association with the induction of thyroiditis, and at least one non-H-2-linked gene controlled the development of thyroid lesions; antibody production to pTPO, porcine thyroglobulin (pTg) and mTg did not correlate with the incidence of thyroiditis in any strain. None of the murine thyroid microsome-specific antibodies tested by the indirect immunofluorescent technique was detected. The T cell line specific for pTPO was successfully transferred to produce thyroid lesions in C57BL/6 mice. Thyroiditis appeared 3 days after the transfer of T cell blasts, and a low concentration of anti-pTPO antibodies was detected concurrently. Thyroid lesions remained up to 48 days with almost the same extent of thyroiditis, but anti-pTPO antibodies gradually increased. In the vaccination experiments using either 0.645 C/kg (2500 rad)-irradiated or 0.3% glutaraldehyde-fixed T cell blasts, the induction of thyroid lesions by transfer was strongly suppressed. Glutaraldehyde fixation was more effective than X-irradiation in preventing thyroiditis after the transfer of T cell blasts. Vaccination also suppressed significantly the development of thyroid lesions after pTPO administration.

Thyroid peroxidase and the induction of autoimmune thyroid disease

Animal models of autoimmune thyroid disease are associated with thyroglobulin (Tg) as autoantigen whereas in man the autoimmune response to microsomal antigen/thyroid peroxidase (TPO) appears to play a major role in thyroiditis. Consequently, we have compared the ability of TPO and Tg to induce thyroid autoantibodies and thyroid damage in mice known to be susceptible (CBA/J) or resistant (BALB/c) to thyroiditis induced using murine Tg. Groups of three to five mice were immunized twice using Freund's complete adjuvant with 80-100 micrograms highly purified porcine (p) TPO, pTg, rat (r) Tg, human Tg, bovine serum albumin (BSA) or BSA + 0.2 micrograms pTg (the level of Tg contamination of TPO). Four weeks after immunization with TPO, plasma from CBA/J (but not BALB/c) mice contained IgG class antibodies which bound to TPO-coated tubes in the presence or absence of excess Tg (and could therefore be clearly distinguished from Tg antibodies) but there was no evidence of thyroiditis in either strain of mice. In contrast, in CBA/J mice immunized with rTg and, to a lesser extent in mice that had received pTg, thyroid tissue was infiltrated with lymphoid cells and/or neutrophils and antibodies to pTg (but not pTPO) were present. Our observations demonstrate that induction of TPO antibody alone is insufficient to lead to thyroiditis in CBA/J mice. Further, these studies emphasize the complex interactions between MHC and different thyroid antigens in the processes leading to thyroid destruction.

In situ analysis of T cell subset composition in experimental autoimmune thyroiditis after adoptive transfer of activated spleen cells

T cells from genetically susceptible mice developing experimental autoimmune thyroiditis (EAT) proliferate in response to restimulation with mouse thyroglobulin (MTg) in vitro. The in vitro-activated cells adoptively transfer EAT as well as differentiate into cells cytotoxic for syngeneic thyroid monolayers. To examine the kinetics of T cell subset infiltration and distribution in situ after adoptive transfer, we applied the avidin-biotin-peroxidase labeling technique to thyroid sections, utilizing rat monoclonal antibodies followed by a biotinylated rabbit anti-rat antibody. Female CBA donor mice were immunized with MTg and lipopolysaccharide. Their spleen cells were obtained 7 days later, cultured with MTg, and transferred into recipient mice. The thyroids were removed on Days 7, 10, and 14 after transfer and serially sectioned. The early phase of transferred EAT showed a higher percentage of L3T4+ cells compared to Lyt-2+ cells, yielding a ratio of 2.3 and total T cells of about 35%. By Day 10, both T cell subsets had increased to a total of about 56%. However, the relative increase was greater in the Lyt-2+ subset; the nearly doubled percentage was statistically significant, resulting in a downward shift in the subset ratio to 1.7. Little change in the in situ distribution was seen on Day 14. The percentages of F4/80+ (macrophage) population in lesions examined on Days 10 and 14 were fairly constant and B cell involvement was minimal. These findings illustrate the pathogenic role of both T cell subsets in adoptively transferred EAT and the time-dependent changes in their relative proportions leading to thyroid gland destruction.

Long-term observation and effect of age on induction of experimental autoimmune thyroiditis in susceptible and resistant mice

After induction of experimental autoimmune thyroiditis (EAT) in mice, long-term observation on both the severity of thyroiditis and antibody formation against mouse thyroglobulin (MTg) was carried out over a period of 18 months. In EAT-susceptible strains (CBA, C3H/Anf), both the severity of thyroiditis and MTg antibody production continued for a long term. In EAT-resistant mice (BALB/c), thyroiditis remained minimal, if present, and the low antibody response to MTg became negligible. On the other hand, aging had a prominent effect on the EAT induction in susceptible mice; both MTg antibody response and thyroid infiltration were markedly reduced. These data were well correlated with reduced antibody formation against sheep red blood cells. Young and old mice were further compared as donors or recipients in adoptive transfer of concanavalin A-stimulated cells. Lymph node cells from either young or old MTg-immunized mice transferred appreciable thyroiditis to normal young and old recipient mice. However, similarly treated spleen cells from MTg-immunized old mice responded more poorly to in vitro stimulation with mitogens or MTg and transferred thyroiditis to very few normal young or old mice.

In situ kinetic analysis of thyroid lymphocyte infiltrate in mice developing experimental autoimmune thyroiditis

L3T4+ T cells from genetically susceptible mice developing experimental autoimmune thyroiditis (EAT) were shown earlier to proliferate in response to restimulation with mouse thyroglobulin (MTg) in vitro and to mediate the adoptive transfer of EAT, whereas Lyt-2+ cells differentiated in vitro into cells cytotoxic for thyroid monolayers. Leukocyte suspensions from disrupted thyroid glands examined on Days 13-21 after immunization revealed the accumulation of both T cell subsets in the infiltrate at varying ratios. To characterize the in situ kinetics of cellular infiltration in chronic EAT, we extended the observation intervals after immunization to include Days 21 to 42. The leukocytes in thyroid sections were labeled immunohistochemically first with rat monoclonal antibodies to L3T4, Lyt-2, Thy-1, k light chain, or F4/80 macrophage antigen, then with biotinylated anti-rat IgG, utilizing the avidin-biotin-peroxidase technique. Throughout the 21- to 42-day interval, no significant variations were detected in the percentages of L3T4+ subset, but those of Lyt-2+ cells increased and then declined. The shift in the L3T4+:Lyt-2+ ratio, down from 2.4 to 1.6 and then up to 3.0, was directly related to changes in the Lyt-2+ subpopulation. The F4/80+ and B cell populations changed little during this period. These findings illustrate the changing kinetics of T cell subsets in situ in the development and perpetuation of EAT and MTg-immunized mice.

Pathogenic mechanisms in autoimmune diseases

Autoimmunity may be initiated by a variety of mechanisms involving changes in autologous antigens or alterations in immune regulation. Autoimmune disease, the pathological consequence of an autoimmune response, depends principally upon the stimulation of helper/inducer T cells reactive with self-antigens. Such T cells direct the quantity and quality of the immune response by influencing the mixture of interleukins produced. Autoantibodies react with accessible cells and mediate injury directly or indirectly. Delayed hypersensitivity reactions indirectly damage tissues through the agency of lymphokines. Cytotoxic T cells penetrate tissue spaces and attack cells bearing requisite surface antigens complexed with the appropriate major histocompatibility complex product. Macrophages and NK cells, activated by lymphokines, have potential to augment tissue damage. These several mechanisms do not operate in isolation; rather, multiple processes act in unison in most autoimmune diseases.

Depletion of L3T4+ and Lyt-2+ cells by rat monoclonal antibodies alters the development of adoptively transferred experimental autoimmune thyroiditis

To delineate the contribution of L3T4+ and Lyt-2+ cells in the pathogenesis of experimental autoimmune thyroiditis (EAT), synergistic pairs of monoclonal antibodies (mAb) to the T cell subsets were used in conjunction with the adoptive transfer of mouse thyroglobulin (MTg)-activated cells from immunized mice. Initial experiments verified the important role of L3T4+ cells in the transfer of EAT. Subsequent experiments pointed to the relative contribution of both L3T4+ and Lyt-2+ cells, depending on the stage and extent of disease development. Treatment during disease with L3T4, but not Lyt-2, mAb alone significantly reduced thyroiditis. However, in situ analysis of the cellular infiltrate in thyroid sections revealed that, after treatment with mAb, the appropriate subset was eliminated without altering the amount of the other subset in the remaining lesion. In addition, treatment during severe thyroiditis following the transfer of MTg-activated lymph node cells showed that Lyt-2 mAb alone also reduced thyroid infiltration. When the recipients were pretreated with either pair of mAb before transfer, disease development was only moderately affected. We conclude that (i) donor L3T4+ cells are the primary cells responsible for the initial transfer and development of thyroiditis; and (ii) previous in vitro cytotoxicity data, plus current monoclonal antibody treatment of disease and in situ analysis, further implicate a role for Lyt-2+ cells in EAT pathogenesis.

Pathogenic mechanisms in murine autoimmune thyroiditis: short- and long-term effects of in vivo depletion of CD4+ and CD8+ cells

Both murine CD4+ and CD8+ cells are found in the thyroid infiltrate in experimental autoimmune thyroiditis (EAT) induced with mouse thyroglobulin (MTg). MTg activation of immune cells in vitro enables CD4+ cells to transfer thyroiditis adoptively and to aid the cytotoxic capacity of CD8+ cells for thyroid monolayers. To dissect their relative contribution to pathogenesis in vivo, depleting doses of paired rat monoclonal antibodies (MoAb) recognizing two distinct CD4 or CD8 epitopes were injected alone or in combination. Early treatment with CD4 MoAb interfered with the induction and development of EAT, whereas similar treatment with CD8 MoAb reduced infiltration moderately and did not enhance antibody response. To examine the long-term effect of therapy on advancing EAT, administration of MoAb was delayed to days 21 and 25, and thyroids were analysed immunohistochemically on days 28 and 70. Whereas control mice showed about 30% CD4+ and CD8+ cells at a 2:1 ratio (the remainder being mostly macrophages) on both days 28 and 70, the CD4 therapy regime led to reduced severity and the lesions on day 70 contained very low percentage of CD4+ cells, but elevated percentage of CD8+ cells (ratio 1:3.5). The CD8 therapy regime led to reduced CD8+ cells without changing the range of CD4+ cells (ratio 4:1). Thus, subset involvement may be influenced by the MoAb used. When CD4 and CD8 MoAb were combined, greater than 50% of the thyroids were cleared of all inflammatory cells; lesions when found were very small and contained less than 10% T cells (ratio 1:1). Since emerging T cells were not retained in the thyroid despite ongoing antigenic stimulus leading to increased antibody titres, the therapeutic effect of MoAb, even at an advanced stage of disease, was long lasting.

Experimental autoimmune thyroiditis in mice chronically treated from birth with anti-IgM antibodies

The role of T lymphocytes in the pathogenesis of experimental autoimmune thyroiditis in mice is well established while the role of B lymphocytes is unclear. Mice with thyroid lesions have thyroglobulin antibodies whereas these antibodies can occur in mice immunized with Tg that do not develop thyroid lesions. To determine whether thyroglobulin antibodies are necessary for the development of the thyroid infiltrates with mononuclear cells, which are characteristic for experimental autoimmune thyroiditis, AKR mice chronically treated from birth with goat anti-mouse IgM antibodies were immunized with mouse thyroglobulin in Freund's complete adjuvant when they were 7 weeks old. Control mice, similarly immunized, were chronically injected from birth with normal goat gamma-globulin. Three weeks after immunization, all mice were sacrificed, thyroglobulin antibodies in the serum were measured by hemagglutination assay and enzyme-linked immunosorbent assay, and thyroid pathology was assessed. The serum concentration of IgG and IgM, the percentage of B and T lymphocytes in the spleen (flow cytometry), and the in vitro proliferative response of spleen lymphocytes to stimulation by PHA, LPS, and Tg were also measured. All mice treated with anti-IgM antibodies did not have detectable thyroglobulin antibodies but 63% of these mice and 88% of control mice (all of which had thyroglobulin antibodies) had thyroid lesions. Mice treated with anti-IgM antibodies that did not have thyroid lesions had a more pronounced depression of B lymphocytes than similarly treated mice that had thyroid lesions. These experiments suggest that thyroglobulin antibodies are not necessary for the development of thyroid infiltrates with mononuclear cells. B lymphocytes could still participate in the production of experimental autoimmune thyroiditis by presenting thyroglobulin to helper T lymphocytes.

Graves' disease: phenotypic and functional analysis at the clonal level of the T-cell repertoire in peripheral blood and in thyroid

We have investigated at the clonal level the repertoire of intrathyroid and peripheral T lymphocytes in three patients with Graves' disease using a high efficiency cloning technique. Clonal efficiencies ranged from 10 to 31% for intrathyroid, and from 19 to 100% for peripheral T cells. In Graves' disease the phenotypic analysis showed similar percentages of CD3+ CD4+ CD8- and CD3+ CD4- CD8+ clones in thyroid infiltrates and peripheral blood. The functional evaluation showed similar or lower proportions of cytolytic clones in thyroid infiltrates with respect to peripheral blood. Furthermore, the proportions of intrathyroid and peripheral T-cell clones capable of releasing interleukin-2 and/or gamma-interferon in response to mitogen stimulation were similar. Finally, 44% of intrathyroid clones were neither cytolytic nor able to release IL-2 and gamma-interferon. These results are strikingly different from those obtained in Hashimoto's thyroiditis, where the large majority of intrathyroid T-cell clones are cytolytic and the proportions of clones able to release gamma-IFN are remarkably increased in thyroid infiltrates when compared to those obtained from peripheral blood. Taken together, these data suggest a different role for T lymphocytes in the pathogenesis of the two major human autoimmune thyroid diseases.