Organ-specific autoimmunity induced by adult thymectomy and cyclophosphamide-induced lymphopenia

Naturally arising memory-phenotype CD4+ T lymphocytes contain an undifferentiated population that can generate TH1, TH17, and Treg cells

Memory-phenotype (MP) CD4+ T lymphocytes develop from naïve cells via self-recognition at homeostasis. While previous studies defined MP cells as a heterogeneous population that comprises T helper 1 (TH1)/17-like subsets, functional significance of the T-bet- Rorγt- subpopulation remains unknown. Here we show that MP lymphocytes as a whole population can differentiate into TH1/17/regulatory T (Treg) cells to mediate mild and persistent inflammation in lymphopenic environments, whereas naïve cells exhibit strong, TH1-dominated responses. Moreover, we demonstrate that MP lymphocytes comprise not only TH1/17-differentiated subsets but a polyclonal, transcriptomically immature "undifferentiated" subpopulation at homeostasis. Furthermore, our data argue that while the T-bet+ Rorγt- MP subset is terminally TH1-differentiated, its undifferentiated counterpart retains the capacity to rapidly proliferate to differentiate into TH1/17/Treg cells, with the latter response tonically constrained by preexisting Treg cells. Together, our results identify undifferentiated MP CD4+ T lymphocytes as a unique precursor that has a diverse differentiation potential to generate TH1/17/Treg cells to contribute to pathogenesis of inflammation.

Disruption of thymic central tolerance by infection with murine roseolovirus induces autoimmune gastritis

Infections with herpesviruses, including human roseoloviruses, have been proposed to cause autoimmune disease, but defining a causal relationship and mechanism has been difficult due to the ubiquitous nature of infection and development of autoimmunity long after acute infection. Murine roseolovirus (MRV) is highly related to human roseoloviruses. Herein we show that neonatal MRV infection induced autoimmune gastritis (AIG) in adult mice in the absence of ongoing infection. MRV-induced AIG was dependent on replication during the neonatal period and was CD4+ T cell and IL-17 dependent. Moreover, neonatal MRV infection was associated with development of a wide array of autoantibodies in adult mice. Finally, neonatal MRV infection reduced medullary thymic epithelial cell numbers, thymic dendritic cell numbers, and thymic expression of AIRE and tissue-restricted antigens, in addition to increasing thymocyte apoptosis at the stage of negative selection. These findings strongly suggest that infection with a roseolovirus early in life results in disruption of central tolerance and development of autoimmune disease.

Maintaining T cell tolerance of alloantigens: Lessons from animal studies

Achieving host immune tolerance of allogeneic transplants represents the ultimate challenge in clinical transplantation. It has become clear that different cells and mechanisms participate in acquisition versus maintenance of allograft tolerance. Indeed, manipulations which prevent tolerance induction often fail to abrogate tolerance once it has been established. Hence, elucidation of the immunological mechanisms underlying maintenance of T cell tolerance to alloantigens is essential for the development of novel interventions that preserve a robust and long lasting state of allograft tolerance that relies on T cell deletion in addition to intra-graft suppression of inflammatory immune responses. In this review, we discuss some essential elements of the mechanisms involved in the maintenance of naturally occurring or experimentally induced allograft tolerance, including the newly described role of antigen cross-dressing mediated by extracellular vesicles.

Glucocortiosteroid subsensitivity and asthma severity

PURPOSE OF REVIEW

Glucocorticosteroids (GCSs) remain the cornerstone of therapy for treating the inflammatory component of asthma. Clinical response to GCS is heterogeneous, varying both within asthma 'endotypes', as well as the same individual. Different factors and micro-environment can alter the canonical GCS-induced signalling pathways leading to reduced efficacy, collectively termed as GCS subsensitivity, which includes the entire spectrum of steroid insensitivity and steroid resistance.

RECENT FINDINGS

In the past, steroid subsensitivity has been associated with dysregulated expression of glucocorticoid-receptor isoforms, neutrophilic inflammation and Th17 cytokines, oxidative stress-inducing factors and their downstream effect on histone deacetylase activities and gene expression. The review highlights recent observations, such as GCS-induced dysregulation of key transcription factors involved in host defence, role of airway infections altering expression of critical regulatory elements like the noncoding microRNAs, and the importance of interleukin (IL)-10 in reinstating steroid response in key immune cells. Further, emerging concepts of autoimmunity triggered because of delayed resolution of eosinophilic inflammation (due to GCS subsensitivity) and observed lymphopenia (plausibly a side-effect of continued GCS use) are discussed.

SUMMARY

This review bridges concepts that have been known, and those under current investigation, providing both molecular and clinical insights to aid therapeutic strategies for optimal management of asthmatics with varying degree of steroid subsensitivity and disease severity, with particular emphasis on the PI3 kinase pathways.

Autoimmune Responses in Severe Asthma

Asthma and autoimmune diseases both result from a dysregulated immune system, and have been conventionally considered to have mutually exclusive pathogenesis. Autoimmunity is believed to be an exaggerated Th1 response, while asthma with a Th2 underpinning is congruent with the well-accepted Th1/Th2 paradigm. The hypothesis of autoimmune involvement in asthma has received much recent interest, particularly in the adult late-onset non-atopic patients (the “intrinsic asthma”). Over the past decades, circulating autoantibodies against diverse self-targets (beta-2-adrenergic receptors, epithelial antigens, nuclear antigens, etc.) have been reported and subsequently dismissed to be epiphenomena resulting from a chronic inflammatory condition, primarily due to lack of evidence of causality/pathomechanism. Recent evidence of ‘granulomas’ in the lung biopsies of severe asthmatics, detection of pathogenic sputum autoantibodies against autologous eosinophil proteins (e.g., eosinophil peroxidase) and inadequate response to monoclonal antibody therapies (e.g., subcutaneous mepolizumab) in patients with evidence of airway autoantibodies suggest that the role of autoimmune mechanisms be revisited. In this review, we have gathered available reports of autoimmune responses in the lungs, reviewed the evidence in the context of immunogenic tissue-response and danger-associated molecular patterns, and constructed the possibility of an autoimmune-associated pathomechanism that may contribute to the severity of asthma.

Sputum autoantibodies in patients with severe eosinophilic asthma

BACKGROUND

The persistence of eosinophils in sputum despite high doses of corticosteroids indicates disease severity in asthmatic patients. Chronic inflamed airways can lose tolerance over time to immunogenic entities released on frequent eosinophil degranulation, which further contributes to disease severity and necessitates an increase in maintenance corticosteroids.

OBJECTIVES

We sought to investigate the possibility of a polyclonal autoimmune event in the airways of asthmatic patients and to identify associated clinical and molecular characteristics.

METHODS

The presence of autoantibodies against eosinophil peroxidase (EPX) and anti-nuclear antibodies was investigated in patients with eosinophilic asthma maintained on high-dose corticosteroids, prednisone, or both. The ability of sputum immunoglobulins to induce eosinophil degranulation in vitro was assessed. In addition, the associated inflammatory microenvironment in patients with detectable autoantibodies was examined.

RESULTS

We report a "polyclonal" autoimmune event occurring in the airways of prednisone-dependent asthmatic patients with increased eosinophil activity, recurrent pulmonary infections, or both, as evident by the concomitant presence of sputum anti-EPX and anti-nuclear antibodies of the IgG subtype. Extensive cytokine profiling of sputum revealed a T_H2-dominated microenvironment (eotaxin-2, IL-5, IL-18, and IL-13) and increased signalling molecules that support the formation of ectopic lymphoid structures (B-cell activating factor and B cell-attracting chemokine 1). Immunoprecipitated sputum immunoglobulins from patients with increased autoantibody levels triggered eosinophil degranulation in vitro, with release of extensive histone-rich extracellular traps, an event unsuppressed by dexamethasone and possibly contributing to the steroid-unresponsive nature of these eosinophilic patients.

CONCLUSION

This study identifies an autoimmune endotype of severe asthma that can be identified by the presence of sputum autoantibodies against EPX and autologous cellular components.

Impact of Human Mutant TGFβ1/Fc Protein on Memory and Regulatory T Cell Homeostasis Following Lymphodepletion in Nonhuman Primates

Transforming growth factor β1 (TGFβ1) plays a key role in T cell homeostasis and peripheral tolerance. We evaluated the influence of a novel human mutant TGFβ1/Fc (human IgG4 Fc) fusion protein on memory CD4⁺ and CD8⁺ T cell (Tmem) responses in vitro and their recovery following antithymocyte globulin (ATG)-mediated lymphodepletion in monkeys. TGFβ1/Fc induced Smad2/3 protein phosphorylation in rhesus and human peripheral blood mononuclear cells and augmented the suppressive effect of rapamycin on rhesus Tmem proliferation after either alloactivation or anti-CD3/CD28 stimulation. In combination with IL-2, the incidence of CD4⁺ CD25^hi Foxp3^hi regulatory T cells (Treg) and Treg:Th17 ratios were increased. In lymphodepleted monkeys, whole blood trough levels of infused TGFβ1/Fc were maintained between 2 and 7 μg/mL for 35 days. Following ATG administration, total T cell numbers were reduced markedly. In those given TGFβ1/Fc infusion, CD8⁺ T cell recovery to predepletion levels was delayed compared to controls. Additionally, numbers of CD4⁺ CD25^hi CD127^lo Treg increased at 4-6 weeks after depletion but subsequently declined to predepletion levels by 12 weeks. In all monkeys, CD4⁺ CD25^hi Foxp3^hi Treg/CD4⁺ IL-17⁺ cell ratios were reduced, particularly after stopping TGFβ1/Fc infusion. Thus, human TGFβ1/Fc infusion may delay Tmem recovery following lymphodepletion in nonhuman primates. Combined (low-dose) IL-2 infusion may be required to improve the Treg:Th17 ratio following lymphodepletion.

Potential role of bacterial lipopolysaccharides in the development of autoimmune gastritis induced by neonatal thymectomy

The role of LPS in the development of autoimmune gastritis (AIG) in BALB/c mice thymectomized on day 3 after birth (d3-Tx) was investigated in LPS-non-responder BALB/lpsdmice. The symptoms were classified into three types: (i) hypertrophic stomach (HS) and lymphocyte infiltration (LI)-double negative; (ii) HS-negative and LI-positive; and (iii) HS- and LI-double positive. The double positive type-3 was termed AIG. Following d3-Tx, LPS-responder BALB/c ( Lpsn) mice showed the following incidence: type-1 (14%), type-2 (14%) and type-3 (72%). In contrast, the incidence in BALB/lpsdmice was 67%, 22% and 11%, respectively. Thus the frequency of AIG development in BALB/lpsdmice was much lower than in BALB/c mice. A single administration of LPS on day 2 post-d3-Tx induced severe AIG incidence in all d3-Tx BALB/c mice but not in d3-Tx BALB/lpsdmice, suggesting that LPS influences the progression of AIG development. Formation of auto-antibodies against the proton pump (H+/K+-ATPase) seemed to be related to AIG incidence in d3-Tx BALB/c mice. In d3-Tx BALB/lpsdmice, however, higher levels of auto-antibodies were detected in the type-2 mice, whereas AIG incidence was much lower than that in d3-Tx BALB/c mice. Thus, formation of auto-antibodies against the proton pump in d3-Tx BALB/lpsdmice does not appear to correlate with AIG pathogenesis.

Can you rely on Treg cells on the rebound?

FoxP3(+) regulatory T (Treg) cells comprise a highly dynamic population that restrains autoreactivity. Although complete or long-term depletion of Foxp3(+) CD4(+) Treg cells in adult mice has been shown to result in chronic inflammation and autoimmune disease, the impact of transient Treg-cell depletion on self-reactive responses is poorly defined. A new study published in this issue of the European Journal of Immunology [Eur. J. Immunol. 2014. 44: 3621-3631] shows that, although transient depletion of Treg cells in mice is swiftly followed by recovery of Treg-cell numbers, the "rebounded" population fails to maintain tolerance, culminating in severe autoimmune gastritis. This commentary explores new questions about the quantitative and qualitative aspects of Treg-cell function in immunological tolerance raised by this study and others.

TGFβ in T cell biology and tumor immunity: Angel or devil?

The evolutionally conserved transforming growth factor β (TGFβ) affects multiple cell types in the immune system by either stimulating or inhibiting their differentiation and function. Studies using transgenic mice with ablation of TGFβ or its receptor have revealed the biological significance of TGFβ signaling in the control of T cells. However, it is now clear that TGFβ is more than an immunosuppressive cytokine. Disruption of TGFβ signaling pathway also leads to impaired generation of certain T cell populations. Therefore, in the normal physiological state, TGFβ actively maintains T cell homeostasis and regulates T cell function. However, in the tumor microenvironment, TGFβ creates an immunosuppressive milieu that inhibits antitumor immunity. Here, we review recent advances in our understanding of the roles of TGFβ in the regulation of T cells and tumor immunity.

Regulatory T cell ablation causes acute T cell lymphopenia

Regulatory T (Treg) cells enforce T cell homeostasis and maintain peripheral T cell tolerance. Here we report a previously unappreciated phenomenon of acute T cell lymphopenia in secondary lymphoid organs and non-lymphoid tissues triggered by Treg cell depletion that precedes the expansion of self-reactive T cells. Lymphopenia affects both neonates and adults indicating a dominant role of Treg cells in maintaining peripheral T cell numbers regardless of the developmental stage. The lymphopenia was neither triggered by caspase-dependent apoptosis nor macrophage-mediated clearance of T cells, nor diminished survival of naïve or recently activated T cells due to paucity of IL-7. It is possible that transient lymphopenia associated with congenital or acute Treg cell deficiency may contribute to the development of T cell mediated autoimmune disorders.

Neuromyelitis optica spectrum disorders in patients with myasthenia gravis: ten new aquaporin-4 antibody positive cases and a review of the literature

BACKGROUND

Neuromyelitis optica (NMO, Devic syndrome) and myasthenia gravis (MG) are rare antibody-mediated autoimmune disorders. Concurrent incidence has been reported in only few patients, mostly non-Caucasians.

OBJECTIVE

To report on ten Caucasian patients with NMO spectrum disorders (NMOSD) and MG and to provide a comprehensive review of the literature.

METHOD

Retrospective study.

RESULTS

In total, 26 patients (m:f = 1:12; Caucasian in 12) with MG (generalized in 17) and NMOSD (NMO in 21, longitudinally extensive transverse myelitis in five) were identified from the authors' own files (n = 10) and the previous literature (n = 16). MG preceded NMOSD in 24/25 cases (96%). AQP4-Ab were tested in 20 patients and were positive in 17 (85%). Twenty out of 25 patients (80%) had been treated with thymectomy or thymic irradiation, which preceded NMOSD in all cases (median latency, 12 years; range, 0.3-32). At last follow-up, complete remission of MG was reported in 15/22 (68%), and MG was well controlled with pyridostigmine in three. Co-existing autoimmune disorders or autoimmune antibodies were reported in 17 patients.

CONCLUSION

Our study demonstrates that i) AQP4-Ab-positive NMOSD are more commonly associated with MG in Caucasians than previously thought; ii) MG precedes NMOSD in most cases, often by more than a decade; iii) NMOSD almost exclusively occur in females with juvenile or early-onset MG; and iv) MG frequently takes an unusually mild course in patients with NMOSD. A history of thymectomy could be a possible risk factor for the later development of NMOSD. We recommend testing for AQP4-Ab in MG patients presenting with atypical motor or optic symptoms.

A convenient model of severe, high incidence autoimmune gastritis caused by polyclonal effector T cells and without perturbation of regulatory T cells

Autoimmune gastritis results from the breakdown of T cell tolerance to the gastric H(+)/K(+) ATPase. The gastric H(+)/K(+) ATPase is responsible for the acidification of gastric juice and consists of an α subunit (H/Kα) and a β subunit (H/Kβ). Here we show that CD4(+) T cells from H/Kα-deficient mice (H/Kα(-/-)) are highly pathogenic and autoimmune gastritis can be induced in sublethally irradiated wildtype mice by adoptive transfer of unfractionated CD4(+) T cells from H/Kα(-/-) mice. All recipient mice consistently developed the most severe form of autoimmune gastritis 8 weeks after the transfer, featuring hypertrophy of the gastric mucosa, complete depletion of the parietal and zymogenic cells, and presence of autoantibodies to H(+)/K(+) ATPase in the serum. Furthermore, we demonstrated that the disease significantly affected stomach weight and stomach pH of recipient mice. Depletion of parietal cells in this disease model required the presence of both H/Kα and H/Kβ since transfer of H/Kα(-/-) CD4(+) T cells did not result in depletion of parietal cells in H/Kα(-/-) or H/Kβ(-/-) recipient mice. The consistency of disease severity, the use of polyclonal T cells and a specific T cell response to the gastric autoantigen make this an ideal disease model for the study of many aspects of organ-specific autoimmunity including prevention and treatment of the disease.

Reversing the Autoimmune Condition: Experience with Experimental Autoimmune Gastritis

Autoimmune diseases remain a significant health problem in our society, despite the best efforts to understand and treat these conditions. Current clinical treatments are aimed at alleviating the consequences of these diseases, with limited prospects for cure. Our studies with the experimental model of autoimmune gastritis have led us to explore potential curative strategies that can reverse the autoimmune condition. Using mouse models, we have shown that expression of the known gastric autoantigen in the thymus results in immunological tolerance and resistance to the induction of autoimmune gastritis. Also, induced tolerance in donor mice can be transferred to syngeneic recipient mice by bone marrow cells. Strategies based on these observations could lead to reversal of established disease. Transfer of ensuing knowledge to the cure of serious human autoimmune diseases is our ultimate goal.

Experimental Autoimmune Gastritis: Mouse Models Of Human Organ-specific Autoimmune Disease

Experimental autoimmune gastritis (EAG) is an excellent model of human autoimmune gastritis, the underlying cause of pernicious anaemia. Murine autoimmune gastritis replicates human gastritis in being characterized by a chronic inflammatory mononuclear cell infiltrate in the gastric mucosa, destruction of parietal and zymogenic cells, and autoantibodies to the alpha-and beta-subunits of the gastric H+/K+ ATPase. Disease is induced strain specifically in gastritis-susceptible BALB/c mice by methods with a greater variety than those for most other experimental autoimmune diseases. The disease is induced in the regional gastric lymph node in which pathogenic CD4+ T cells are recruited. The model provides an excellent illustration of regulation by CD4+CD25+T cells, and, indeed, the removal of such regulatory cells, e.g., by neonatal thymectomy, is thought to be a major mechanism by which disease can develop. The culprit T helper type 1 (Th1) CD4+ T cells recognize either the alpha- or beta-subunits of the gastric H+/K+ ATPase, but the beta-subunit appears to be the initiating autoantigen, while the alpha-subunit may have a role in perpetuating disease. Since no specific environmental modifiers are identifiable, the origins of the disease are intrinsic; this is illustrated by the capacity of a cytokine (GM-CSF)-dependent inflammatory stimulus in the stomach to initiate EAG, according to a transgenic model in which thymectomy is dispensible. Thus, EAG is an exquisite model for a reductionist analysis of the multiple elements that in combination induce autoimmunity in humans.

Autoimmune Gastritis: Historical Antecedents, Outstanding Discoveries, and Unresolved Problems

The earliest recorded history of autoimmune gastritis can be traced to 1849 in London, when Thomas Addison described "a very remarkable form of anemia" later called pernicious (fatal) anemia (PA). This was followed by the recognition of a gastric mucosal defect suspected to have a nutritional basis, the discovery of the megaloblast that characterized the anemia, the insufficiency of a dietary extrinsic factor characterized as vitamin B12 (cobalamin), and a gastric-secreted intrinsic factor. Treatment with vitamin B12 proved curative. The link between PA and gastritis and atrophy was first confirmed histologically after immediate fixation of the stomach postmortem and later, in the 1940s, by peroral tube biopsy. The causes of gastritis remained enigmatic until the era of autoimmunity, when autoantibodies were detected first to gastric intrinsic factor and then to gastric parietal cells. Hints of a dichotomy in pathogenesis of gastritis were crystallized by the description in 1973 of Type A (Autoimmune) and Type B (later, Bacterial) gastritis. Clarification was enhanced by identification in Type A gastritis of the autoantigen of the parietal cell antibody, by the alpha and beta subunits of gastric H+/K+ ATPase, and by the highly informative experimental murine model of postneonatal thymectomy autoimmune gastritis, and in Type B of the causative role of gastric infection with Helicobacter pylori (H. pylori). A denouement will require a full understanding of (1) the origin and pathogenetic contribution of antibody to intrinsic factor; (2) the connection, if any, between H. pylori infection and Type A autoimmune gastritis; and (3) the genetic contributions to gastritis, whether due to autoimmunity or to H. pylori infection.

Steroid treatments in mice do not alter the number and function of regulatory T cells, but amplify cyclophosphamide-induced autoimmune disease

Corticosteroids are commonly used in the therapy of autoimmune disease (AID), although they are rarely, if ever, curative. This failure may result from their deleterious effects on regulatory T cells (Treg). In this work, we directly tested the effects of hydrocortisone (HC) administration on Treg number and function in established mouse models of multiple sclerosis and colitis. Treatment with pertussis toxin (Ptx) or Cyclophosphamide (Cyp), two compounds known to affect Treg function served as controls. We first show that contrarily to Ptx, HC administration to mice transgenic for a TCR specific to myelin basic protein induces a mild lymphopenia, without selective depletion of Treg, nor induction of experimental autoimmune encephalomyelitis (EAE). We next report that HC administration to normal mice has no effect on Treg suppressive function tested in vitro. Moreover, we document that Treg isolated from HC-treated animals maintain their capacity to prevent T cell-induced colitis. In contrast, the combined administration of HC and Cyp, as is frequently used in the therapy of severe AID, dramatically enhanced the deleterious effect of Cyp on Treg number and function. Our analysis indicates that while a short course of corticosteroids alone is not deleterious to immune regulation, combined therapies, notably with Cyp, should be avoided.

Foxp3+CD25+CD4+ natural regulatory T cells in dominant self-tolerance and autoimmune disease

Naturally arising CD25+ CD4+ regulatory T (Treg) cells, most of which are produced by the normal thymus as a functionally mature T-cell subpopulation, play key roles in the maintenance of immunologic self-tolerance and negative control of a variety of physiological and pathological immune responses. Natural Tregs specifically express Foxp3, a transcription factor that plays a critical role in their development and function. Complete depletion of Foxp3-expressing natural Tregs, whether they are CD25+ or CD25-, activates even weak or rare self-reactive T-cell clones, inducing severe and widespread autoimmune/inflammatory diseases. Natural Tregs are highly dependent on exogenously provided interleukin (IL)-2 for their survival in the periphery. In addition to Foxp3 and IL-2/IL-2 receptor, deficiency or functional alteration of other molecules, expressed by T cells or non-T cells, may affect the development/function of Tregs or self-reactive T cells, or both, and consequently tip the peripheral balance between the two populations toward autoimmunity. Elucidation of the molecular and cellular basis of this Treg-mediated active maintenance of self-tolerance will facilitate both our understanding of the pathogenetic mechanism of autoimmune disease and the development of novel methods of autoimmune disease prevention and treatment via enhancing and re-establishing Treg-mediated dominant control over self-reactive T cells.

Self-recognition is crucial for maintaining the peripheral CD4+ T-cell pool in a nonlymphopenic environment

The role of self-recognition in the maintenance of the peripheral CD4+ T-cell pool has been extensively studied, but no clear answer has so far emerged. Indeed, in studies of the role of self-major histocompatibility complex (MHC) molecules in CD4+ T-cell survival, several parameters must be taken into account when interpreting the results: (1) in a lymphopenic environment, observations are biased by concomitant proliferation of T cells arising in MHC-expressing mice; (2) the peripheral T-cell compartment is qualitatively and quantitatively different in nonlymphopenic, normal, and MHC class II-deficient mice; and (3) in C57BL/6 Aβ-/- mice (traditionally considered MHC class II-deficient), the Aα chain and the Eβ chain associate to form a hybrid AαEβ MHC class II molecule. In light of these considerations, we revisited the role of interactions with MHC class II molecules in the survival of peripheral CD4+ T cells. We found that the answer to the question “is self-recognition required for CD4+ T cells to survive?” is not a simple yes or no. Indeed, although long-term survival of CD4+ T cells does not depend on self-recognition in lymphopenic mice, interactions with MHC class II molecules are required for maintaining the peripheral CD4+ T-cell pool in a nonlymphopenic environment. (Blood. 2006;108:270-277)

CD4+CD25+ Regulatory T Cells Inhibit the Antigen-Dependent Expansion of Self-Reactive T Cells In Vivo

A deficiency of CD4+CD25+ regulatory T cells (CD25+ Tregs) in lymphopenic mice can result in the onset of autoimmune gastritis. The gastric H/K ATPase alpha (H/Kalpha) and beta (H/Kbeta) subunits are the immunodominant autoantigens recognized by effector CD4+ T cells in autoimmune gastritis. The mechanism by which CD25+ Tregs suppress autoimmune gastritis in lymphopenic mice is poorly understood. To investigate the antigenic requirements for the genesis and survival of gastritis-protecting CD25+ Tregs, we analyzed mice deficient in H/Kbeta and H/Kalpha, as well as a transgenic mouse line (H/Kbeta-tsA58 Tg line 224) that lacks differentiated gastric epithelial cells. By adoptive transfer of purified T cell populations to athymic mice, we show that the CD25+ Treg population from mice deficient in either one or both of H/Kalpha and H/Kbeta, or from the H/Kbeta-tsA58 Tg line 224 mice, is equally effective in suppressing the ability of polyclonal populations of effector CD4+ T cells to induce autoimmune gastritis. Furthermore, CD25+ Tregs, from either wild-type or H/Kalpha-deficient mice, dramatically reduced the expansion of pathogenic H/Kalpha-specific TCR transgenic T cells and the induction of autoimmune gastritis in athymic recipient mice. Proliferation of H/Kalpha-specific T cells in lymphopenic hosts occurs predominantly in the paragastric lymph node and was dependent on the presence of the cognate H/Kalpha Ag. Collectively, these studies demonstrate that the gastritis-protecting CD25+ Tregs do not depend on the major gastric Ags for their thymic development or their survival in the periphery, and that CD25+ Tregs inhibit the Ag-specific expansion of pathogenic T cells in vivo.

Gastritis in Neonatal BALB/cCrSlc Mice Induced by Immunization Without Adjuvant can be Transferred to Syngeneic nu/nu Recipients

The popularly exploited murine neonatal thymectomy experimental autoimmune gastritis (nTx:EAG) model requires the animal to be in a state of lymphopenia. Here we report on a novel murine immunization (without adjuvant) model that can establish a lasting gastritis. We demonstrate that the immunization model (imm:EAG) results in a bona fide autoimmune disease and define the resulting pathology and serology observed and compare it with that reported for human autoimmune gastritis. Immune cells present in the stomachs of imm:EAG gastritic mice include CD8 T cells, CD11b and Gr1 (granulocytes/monocytes) and B cells. We detected circulating antibodies of immunoglobulin G1 (IgG1) subclass, with some IgG(2a) and IgG(2b) reactive to stomach membranes and the parietal cell proton pump. The class and subclass of autoreactive antibodies resulting from imm:EAG suggest a T helper 1 (Th1)/Th2 immune response. We establish that both self-reactive T and B cells from BALB/cCrSlc imm:EAG gastritic mice have the potential to induce a gastritis in BALB/c syngeneic nu/nu recipients. We conclude that this model is likely to be superior to the currently popularly exploited nTx:EAG and provide insight into and an understanding of the mechanisms of and remedies for autoimmunity in an intact immune system.

Control of autoimmunity by naturally arising regulatory CD4+ T cells

Naturally acquired immunological self-tolerance is not entirely accounted for by clonal deletion, anergy, and ignorance. It is now well established that the T cell-repertoire of healthy individuals harbors self-reactive lymphocytes with a potential to cause autoimmune disease and these lymphocytes are under dominant control by a unique subpopulation of CD4+ T cells now called regulatory T cells. Efforts to delineate these Treg cells naturally present in normal individuals have revealed that they are enriched in the CD25+ CD4+ population. The identification of the CD25 molecule as a useful marker for naturally arising CD4+ regulatory T cells has made it possible to investigate many key aspects of their immunobiology, including their antigen specificities and the cellular/molecular pathways involved in their development and their mechanisms of action. Furthermore, reduction or dysfunction of the CD25+ CD4+ regulatory T cell population can be responsible for certain autoimmune diseases in humans.

The role of regulatory T cells in controlling immunologic self-tolerance

Accumulating evidence indicates that T cell-mediated dominant control of self-reactive T cells contributes to the maintenance of immunologic self-tolerance and its alternation may lead to development of autoimmune disease. Efforts to delineate such a regulatory T cell population have revealed that CD25+ cells within the CD4+ population in normal naive animals including humans possess the regulatory activity. The CD25+CD4+ regulatory T cells are produced by the normal thymus as a functionally distinct subpopulation of T cells. They play critical roles not only in preventing autoimmunity but also in controlling various immune reactions.

On the role of MHC class II molecules in the survival and lymphopenia-induced proliferation of peripheral CD4+ T cells

CD4(+) T cells expand after transfer into lymphopenic H-2(b) A(beta)-/- mice (I-A(beta)-, I-E(alpha)-deficient mice) but not after transfer into lymphopenic MHC II(Delta/Delta) mice (I-A(alpha)-, I-A(beta)-, I-E(alpha)-, and I-E(beta)-deficient mice), implying that in H-2(b) A(beta)-/- mice, A(alpha) chain and E(beta) chain associate to form a hybrid A(alpha)E(beta) MHC class II molecule. In light of this unexpected result, we reexamined the MHC class II requirement in the survival and lymphopenia-induced proliferation of CD4(+) T cells. Here we show that expansion, but not short-term survival, of CD4(+) T cells depends on interactions with MHC class II molecules in lymphopenic mice. Nevertheless, interactions with classical MHC class II molecules are required for CD4(+) T cells to survive in CD8(+) T-cell-containing mice.

The role of CD4+CD25+ immunoregulatory T cells in the induction of autoimmune gastritis

A number of experimental models of organ-specific autoimmunity involve a period of peripheral lymphopenia prior to disease onset. There is now considerable evidence that the development of autoimmune disease in these models is due to the absence of CD4+CD25+ regulatory T cells. However, the role of CD4+CD25+ regulatory T cells in the prevention of autoimmune disease in normal individuals has not been defined. Here we have assessed the affect of depletion of CD4+CD25+ regulatory T cells in BALB/c mice on the induction of autoimmune gastritis. The CD4+CD25+ T cell population was reduced to 95% of the original population in adult thymectomized mice by treatment with anti-CD25 mAb. By 48 days after the anti-CD25 treatment, the CD4+CD25+ regulatory T cell population had returned to a normal level. Treatment of thymectomized adult mice for up to 4 weeks with anti-CD25 mAb did not result in the development of autoimmune gastritis. Furthermore, we have demonstrated that depletion of CD4+CD25+ regulatory T cells, together with transient CD4+ T lymphopenia, also did not result in the development of autoimmune gastritis, indicating that peripheral expansion of the CD4+ T cell population, per se, does not result in autoimmunity in adult mice. On the other hand, depletion of CD4+CD25+ T cells in 10-day-old euthymic mice resulted in a 30% incidence of autoimmune gastritis. These data suggest that CD4+CD25+ regulatory T cells may be important in protection against autoimmunity while the immune system is being established in young animals, but subsequently other factors are required to initiate autoimmunity.

Endogenous H/K ATPase beta-subunit promotes T cell tolerance to the immunodominant gastritogenic determinant

A CD4(+) T cell response to the gastric H/K ATPase beta-subunit (H/Kbeta) is required for the onset of experimental autoimmune gastritis in BALB/c mice. The extent to which endogenous H/Kbeta contributes toward the tolerance of the H/Kbeta-specific T cell repertoire in normal individuals is not known. By comparison of T cell responses in H/Kbeta-deficient (o/o) and H/Kbeta-expressing BALB/c mice, in this work we show that the endogenous H/Kbeta autoantigen plays a major role in the tolerance of pathogenic H/Kbeta-specific T cells. First, T cell-dependent Ab responses to the H/Kbeta Ag were enhanced in H/K ATPase-immunized H/Kbeta-deficient mice compared with wild-type mice. Second, peptide immunization experiments indicated that immune responses to the major gastritogenic epitope of the H/K ATPase, namely H/Kbeta(253-277), were significantly more vigorous in H/Kbeta-deficient mice compared with wild-type mice. Third, unfractionated splenocytes from H/Kbeta-deficient mice, but not H/Kbeta-expressing mice, induced autoimmune gastritis after adoptive transfer to BALB/c nude mice. The enhanced responses to H/Kbeta in H/Kbeta-deficient mice were shown to be intrinsic to CD4(+)CD25(-) T cells rather than a change in status of CD4(+)CD25(+) regulatory T cells. We conclude from these studies that the H/Kbeta-specific T cells in wild-type mice represent the residue of a T cell repertoire, directed toward a single determinant, that has been subjected to partial tolerance induction.

Characterisation of proton pump antibodies and stomach pathology in gastritis induced by neonatal immunisation without adjuvant

It has previously been reported that neonatal BALB.D2 mice injected with native proton pump antigens without adjuvant develop an irreversible gastritis (Claeys et al, 1997). The ease of inititating gastritis in the neonate stands in contrast with the difficulty in initiating gastritis in adult mice that require repeated immunisation in adjuvant that is reversible following cessation of immunisation (Scarff et al, 1997). In view of these contrasting observations, we set out to ascertain whether we could confirm the observations in neonatal mice as well as further characterise the pathology and the autoantibody response. We found that neonatal gastritis-susceptible BALB/c mice (n=12), immunised with either pig or mouse gastric membranes in the absence of adjuvant, develop gastritis without circulating antibody to parietal cells detected by immunofluorescence, a hallmark of murine and human gastritis (Toh et al, 1997). However, mice immunized with pig gastric membranes (n=6) had circulating antibodies reactive by immunofluorescence to recombinant alpha and/or beta subunit of gastric H+/K+-ATPase expressed by insect cells (Sfalpha and Sfbeta). Four mice from this cohort with antibodies to Sfbeta also had reactivity to gastric H+/K+-ATPase by ELISA, and 3 immunoblotted the beta but not the alpha subunit of the ATPase. In the cohort of mice immunised with mouse gastric membranes (n=6), four produced antibodies reactive by immunofluorescence to Sfalpha, two of which were also reactive to Sfbeta and one developed antibodies detected by ELISA to gastric H+/K+-ATPase. However, no members of this cohort had antibodies reactive by immunoblotting to either the beta or alpha subunit of the ATPase. In all cases gastritic stomachs were characterised by areas deficient in ribosome-rich zymogenic cells and marked reductions in H+/K+-ATPase-positive parietal cells. Metaplasia detected by Maxwell stain, as clusters of mucus-producing cells throughout gastric units, were non-reactive to stomach mucin autoantibody suggesting the mucins comprise other and/or aberrant form(s). Compared to our previous observations in adult mice, our present data confirms that gastric autoimmunity is more readily induced in the neonate than the adult. Our data also affirms that while the neonatal immune system can mount a damaging inflammatory cellular immune response to gastric antigens, it develops an altered antibody response.

Animal models of human disease: experimental autoimmune gastritis--a model for autoimmune gastritis and pernicious anemia

Human autoimmune gastritis is an organ-specific autoimmune disease of the stomach. It is characterized by the development of disease-specific autoantibodies and a pathology that specifically targets specialized cells within the gastric environment. The autoantigens associated with this disease have been defined as the gastric H+/K+ ATPase and intrinsic factor. The development of experimental disease models has been pivotal in our contemporary understanding of autoimmunity. Here we review mouse models of autoimmune gastritis and their relevance to human autoimmune gastritis associated with pernicious anemia. We appraise some historical as well as recent studies of experimental autoimmune gastritis (EAG), highlighting key findings that have formed the basis of our current understanding of the etiology and mechanism(s) associated with autoimmune gastritis. A precise understanding of the pathogenesis of autoimmune gastritis will permit the design of innovative and rational therapeutic strategies to prevent, arrest, ameliorate or reverse the disease.

Non-Th2 regulatory T-cell control of Th1 autoimmunity

The Th1/Th2 concept brought an attractive explanation of the active self tolerance which appears to control the onset of pathogenic autoimmunity. New data coming from various independent horizons indicate that self immunoregulation could also depend to a large extent on non-Th2 cells. Original data derived from the day-3-thymectomy model, selective T-cell lymphocytopenia and nonobese diabetic mice are discussed in an effort to analyze similarities and differences in phenotype (CD25, CD62L and CD45RB) and cytokine pattern (notably interleukin (IL)-4, IL-10 and transforming growth factor (TGF)beta) of regulatory cells involved in these models. The relationship of these cells with Th3, Tr1 and natural killer (NK) T cells are also discussed. The hypothesis is proposed that CD25 CD62L T cells mediate the physiologic regulation of self regulation whereas Th2 and Th3 cells are essentially induced following sensitization against autoantigens.

Defining T cell receptors which recognise the immunodominant epitope of the gastric autoantigen, the H/K ATPase beta-subunit

We have previously shown that autoimmune gastritis can be elicited in mice by immunisation with the gastric parietal cell H/K ATPase alphabeta heterodimer, and, furthermore, have identified the H/K ATPase beta-subunit epitope, H/Kbeta253-277 as the dominant epitope of the gastric H/K ATPase. Using gastric H/K ATPase-immunised mice, here we have generated two T cell hybridomas specific for the H/Kbeta253-277 peptide, namely 4B11.F4.5 and 1E4.C1. Hybridoma 4B11.F4.5 uses Valpha8 and Vbeta8.2 TCR chains and 1E4.C1 uses Valpha9 and V1beta8.3 chains. Although both hybridomas are specific for H/Kbeta253-277, T cell assays using overlapping 14-mers of the 25-mer epitope showed that the two autoreactive TCRs recognise different regions of the 25-mer. The TCR from 1E4.C1 has been used to generate a TCR beta-chain transgenic mouse. >80% of peripheral CD4+ T cells utilise the Vbeta8.3 transgene. As expected, 1E4-TCR beta-chain transgenic mice are susceptible to neonatal thymectomy induced autoimmune gastritis. While none of the 1E4-TCR beta chain transgenic mice spontaneously developed a destructive gastritis, a minority (20%) of the transgenic mice developed a non-invasive and non-destructive gastritis. This suggests that the pathogenic T cells are maintained in a tolerant state in the periphery of the transgenic mice.

Animal models of autoimmunity and their relevance to human diseases

T cells mediate various autoimmune diseases. Pathologic autoimmunity can be induced by manipulating thymic or peripheral control of self-reactive T cells. There is, for example, accumulating evidence that elimination or dysfunction of regulatory T cells can elicit T cell mediated, destructive autoimmune disease in otherwise normal animals and enhance autoimmunity in spontaneous models.

Regulatory T cells in autoimmmunity*

Clonal deletion of autoreactive T cells in the thymus is not the sole mechanism for the induction of tolerance to self-antigens since partial depletion of peripheral CD4(+) T cells from neonatal and adult animals results in the development of organ-specific autoimmunity. Reconstitution of these immunodeficient animals with populations of regulatory CD4(+)T cells prevents the development of autoimmunity. The lineage of regulatory CD4(+) T cells is generated in the thymus and can be distinguished from effector cells by the expression of unique membrane antigens. The target antigens for these suppressor populations and their mechanisms of action remain poorly defined. Depletion of regulatory T cells may be useful in the induction of immunity to weak antigens, such as tumor-specific antigens. Conversely, enhancement of regulatory T cell function may be a useful adjunct to the therapy of autoimmune diseases and for prevention of allograft rejection.

The causative H+/K+ ATPase antigen in the pathogenesis of autoimmune gastritis

The gastric H+/K+ ATPase is the causative autoantigen recognized by CD4+ T cells that mediate autoimmune gastritis. Pathogenic CD4+ T cells are regulated by CD25+CD4+ T cells. Here, it is proposed that waves of activation and migration of antigen presenting cells and CD4+ T cells to and from the target organ and draining lymph node result in tissue damage.

Regulatory CD4 T cells control the size of the peripheral activated/memory CD4 T cell compartment

The mechanisms leading to stable T cell numbers in the periphery of a healthy animal are, to date, not well understood. We followed the expansion of CD45RBhigh (naive) and CD45RBlow (activated/memory) CD4 T cells transferred from normal mice into syngeneic Rag-20/0 recipients and the dynamics of peripheral reconstitution when both populations were coinjected. Naive cells acquired an activated phenotype and showed a high proliferative capacity that was dependent on the environment in which the recipients were kept (specific pathogen-free vs conventional housing conditions), the age of the recipients, and the presence of CD45RBlow T cells in the injected cohort. CD45RBlow CD4 T cells protected the host from CD45RBhigh CD4 T cell-induced inflammatory bowel disease and showed a limited degree of expansion. CD45RBlow CD4 T cells isolated from GF mice also showed the ability to prevent inflammatory bowel disease, indicating that at least part of the natural regulatory T cells are self-reactive. The results indicate that 1) peripheral T cell expansion in lymphocyte-deficient recipients represent classical immune responses, which are mainly promoted by exogenous Ags and 2) natural regulatory T cells control the size of the activated/memory peripheral CD4 T cell compartment.

Tumor-specific immunotherapy based on dominant models of natural tolerance

The assumption that cancer immunotherapy may be based on the existence of autoreactive lymphocytes recognizing self-antigens on cancer cells, obviously opens a new opportunity. Nevertheless this analysis, relying on a recessive model of natural tolerance, limits the approach to try to activate peripheral lymphocytes, by increasing co-stimulatory signals or using modified self-antigens for immunization. Here we hypothesize that, based on emerging dominant tolerance notions in autoimmunity, it would be possible to induce a specific autoimmunity against tumor cells and arrest their growth following the removal of regulatory T cells. These immunoregulatory cells suppress available immunocompetent autoreactive cells capable of destroying tumor cells. Therefore, in order to reach a complete tumor-specific autoimmunity it is necessary to combine the T cell immunosuppression which abrogates the regulatory cells, with the cancer vaccines, which induces extensive proliferation of lymphoid cells directed towards specificities on tumor cells.

Tolerance and autoimmunity to a gastritogenic peptide in TCR transgenic mice

The catalytic alpha and glycoprotein beta subunits of the gastric H/K ATPase are major molecular targets in human and mouse autoimmune gastritis. We have previously shown that the H/K ATPase beta subunit is required for the initiation of mouse gastritis and identified a gastritogenic H/K ATPase beta subunit peptide (H/Kbeta253-277). Here we report the generation of MHC class II-restricted TCR transgenic mice using V(alpha)9 and V(beta)8.3 TCR chains with specificity for the gastritogenic H/Kbeta253-277 peptide. We found an 8-fold reduction in CD4(+) T cells in the thymus of the transgenic mice. Despite the reduction in intrathymic CD4(+) T cells, V(beta)8. 3-expressing T cells comprised the majority (>90%) of peripheral spleen and lymph node T cells. These peripheral T cells retained their capacity to proliferate in vitro to the H/Kbeta253-277 peptide. Using the responsive T cells, we have restricted the gastritogenic T cell epitope to H/Kbeta261-274. Despite the capacity of the peripheral T cells to proliferate in vitro to the peptide, the majority ( approximately 80%, 13 of 16) of transgenic mice remained free of gastritis while a minority (20%, three of 16) spontaneously developed an invasive and destructive gastritis. Our results confirm that H/Kbeta261-274 is a gastritogenic peptide. The data also suggest that CD4 T cell tolerance to the gastritogenic peptide in the transgenic mice is maintained by a combination of intrathymic and peripheral tolerance mechanisms.

Autoimmune gastritis results in disruption of gastric epithelial cell development

We have investigated the underlying basis of the lesion in murine autoimmune gastritis, a model of the human disease pernicious anemia. The disease is mediated by T lymphocytes and characterized by selective depletion of parietal and zymogenic cells from the gastric unit (gland) together with gastric epithelial cell hyperplasia. The gastric units of gastritic stomachs contained 2.3-fold more cells than normal and accumulated rapidly dividing, short-lived gastric epithelial stem cells and mucous neck cells. Most of these immature cells failed to differentiate into end-stage cells but rather appeared to die by apoptosis. We also found no correlation between anti-parietal cell autoantibody titers and the degree of gastric pathology, providing further evidence that autoantibodies do not play a direct role in the pathogenesis of gastritis. Taken together, the normal developmental pathways of the gastric mucosa are disrupted in autoimmune gastritis, resulting in an amplification of immature cell types. The differentiation of these immature cells appears to be blocked, contributing to depletion of end-stage cells. This scenario provides an explanation for depletion of not only parietal cells but also zymogenic cells even though they are not directly targeted by the immune system.

Tolerization of Mice to Schistosoma mansoni Egg Antigens Causes Elevated Type 1 and Diminished Type 2 Cytokine Responses and Increased Mortality in Acute Infection

The granuloma that surrounds the Schistosoma mansoni egg is the cause of pathology in murine schistosomiasis, and its formation is driven by egg Ag-stimulated type 1 and type 2 cytokines. To determine the role of egg-driven immune responses during schistosome infection we rendered CBA/Ca mice unresponsive to schistosome eggs by combined cyclophosphamide treatment and thymectomy. In the early acute stages of schistosome infection, egg-tolerized mice suffered high mortalities. Granuloma size and deposition of collagen in the liver were significantly reduced in egg-tolerized mice. Similarly, limited granuloma responses were detected in the intestines of these mice, and this was associated with a >90% reduction in egg excretion. Histologically, egg-tolerized mice had exacerbated hepatocyte damage, with extensive microvesicular steatosis. Elevated plasma transaminase levels confirmed the damage to hepatocytes. Infected egg-tolerized mice had impaired proliferation responses to egg Ag but intact responses to worm Ag. Tolerized mice had diminished Ab responses to egg Ag and had a type 1 cytokine isotype pattern to worm Ag, with elevated IgG2a and diminished IgG1 and IgE. Egg-tolerized mice failed to down-regulate type 1 cytokines that are normally elicited during early schistosome infection. Hepatic granuloma cells from egg-tolerized mice were also type 1 cytokine dominated, with elevated frequencies of Tc1/Th1 and reduced Tc2/Th2 cells. This study demonstrates that mice tolerized to schistosome eggs have elevated type 1 cytokine responses with diminished type 2 responses and reduced anti-egg Ab during schistosome infection, and these effects are detrimental to the host.

Spontaneous autoimmune gastritis in C3H/He mice: a new mouse model for gastric autoimmunity

Autoimmune gastritis is the underlying pathological lesion of pernicious anemia in humans. The lesion is characterized by a chronic inflammatory infiltrate in the gastric mucosa with loss of parietal and zymogenic cells. It is associated with circulating autoantibodies to the gastric H/K-ATPase, the enzyme responsible for acidification of gastric juice. Experimental models of autoimmune gastritis have previously been produced in mice after a variety of manipulations, including thymectomy. Here we report for the first time a spontaneous mouse model of autoimmune gastritis in C3H/He mice. The spontaneous gastritis is also accompanied by circulating autoantibodies to the gastric H/K-ATPase. The spontaneous mouse model should be useful for studies directed toward the immunopathogenesis and treatment of autoimmune gastritis.

Protection against diabetes by MHC heterozygosity and reversal by cyclophosphamide

In type I diabetes in both rodents and humans, genetic susceptibility to disease is strongly linked to MHC class II alleles. In some cases, however, certain class II alleles provide resistance to disease. To examine this effect in a well-defined system, we studied double transgenic mice expressing influenza hemagglutinin (HA) on pancreatic islet beta cells and an HA-specific TCR on CD4 T cells. On a susceptible B10.D2 background, 70% of double transgenic mice develop an early-onset spontaneous autoimmune diabetes. MHC heterozygosity induced variable protection from diabetes, depending on the specific nonpermissive allele, but insulitis was invariably present. Autoreactive T cells retained the ability to induce diabetes because cyclophosphamide treatment induced diabetes in 81% of young MHC(d/b) transgenic mice, although the effect was diminished in older mice. Most importantly, treatment induced higher IFN-gamma/IL-4 ratios among CD4 T cells, suggesting a strong shift toward Th1 development, perhaps through direct effects on patterns of gene expression in CD4 T cells.

CD4+ T cells, but not CD8+ T cells, are required for the development of experimental autoimmune gastritis

Murine autoimmune gastritis, induced by neonatal thymectomy, is characterized by a mononuclear infiltrate within the gastric mucosa, loss of parietal and zymogenic cells and circulating autoantibodies to the gastric H/K ATPase. The infiltrate contains both CD4+ and CD8+ T cells. Here we have investigated the roles of CD4+ and CD8+ T cells in the development of gastritis by in vivo treatment with depleting rat anti-CD4 and anti-CD8 monoclonal antibodies. Depletion of CD4+ T cells decreased the incidence of gastric mononuclear infiltrates from 63% (5/8), observed in normal rat immunoglobulin G (IgG)-injected mice, to 8% (1/12) and also abolished the production of antigastric autoantibodies. In contrast, depletion of CD8+ T cells did not reduce the incidence of gastritis. The absence of CD8+ T cells in the infiltrate of the stomach of anti-CD8(+)-treated mice was confirmed by immunocytochemistry. These results argue that neonatal thymectomy-induced autoimmune gastritis is mediated by CD4+ T cells and that CD8+ T cells do not play a significant role in the development of the gastric lesion.

CD4+CD25+ T Cells Inhibit Both the Induction and Effector Function of Autoreactive T Cells and Represent a Unique Lineage of Immunoregulatory Cells

Thymectomy of susceptible strains of mice on day 3 of life results in a spectrum of organ-specific autoimmunity that can be prevented by reconstitution of the thymectomized animals early in life with normal adult lymphocytes. The effectors and suppressors of autoimmunity in this model have been convincingly shown to be CD4+ T cells. It has been demonstrated recently that the regulatory CD4+ T cells that prevent disease coexpress CD25. We have further characterized the population of CD4+CD25+ immunoregulatory cells and demonstrated that they can suppress not only the induction of disease post-thymectomy, but can also efficiently suppress disease induced by cloned autoantigen-specific effector cells. Furthermore, the CD4+CD25+ T cells appear to be members of a unique lineage of regulatory T cells, as the induction of CD25 expression on a monospecific population of T cells derived from TCR transgenic SCID mice did not result in suppression of post-thymectomy autoimmunity. In addition, the TCR transgenic SCID mice were highly susceptible to autoimmune disease induced by the cloned line of autoantigen-specific effectors, while normal mice were relatively resistant. The capacity of the cloned line to transfer disease to nu/nu recipients could be inhibited by normal spleen cell populations containing CD4+CD25+ cells and by purified CD4+CD25+ cells. Although the target Ag(s) and mechanism of action of the CD4+CD25+ T cells remain to be determined, it is likely that they also play an important role in modulating other autoimmune diseases that are mediated by activation of “ignorant” self-reactive T cells present in the normal peripheral lymphocyte pool.

Immunization with gastric H+/K(+)-ATPase induces a reversible autoimmune gastritis

The gastric H+/K(+)-ATPase has been implicated as a major autoantigen in pernicious anaemia in humans and in thymectomy-induced autoimmune gastritis in mice. Here we have shown that autoimmune gastritis can be generated by direct immunization of non-thymectomized BALB/c mice with mouse gastric H+/K(+)-ATPase in complete Freund's adjuvant. The gastritis was characterized by infiltration of the gastric submucosa and mucosa with macrophages, CD4+ and CD8+ T cells, and B cells and by circulating autoantibodies to the H+/K(+)-ATPase. The mononuclear infiltrate within the gastric mucosa was accompanied by loss of parietal and zymogenic cells and accumulation of small immature epithelial cells. Splenocytes from gastritic mice adoptively transferred gastritis to naive recipients. Cessation of immunization resulted in decrease in autoantibody titre and regeneration of parietal and zymogenic cells. The results directly confirm that the gastric H+/K(+)-ATPase is the causative autoantigen in the genesis of autoimmune gastritis. Recovery of the lesion following cessation of immunization suggests that homeostatic mechanisms can reverse a destructive autoimmune process.

Expression of the gastric H/K-ATPase alpha-subunit in the thymus may explain the dominant role of the beta-subunit in the pathogenesis of autoimmune gastritis

The two subunits of the gastric H/K ATPase, namely the catalytic alpha-subunit and the glycoprotein beta-subunit, are the major targets of parietal cell autoantibodies associated with human and murine autoimmune gastritis. The murine disease induced by neonatal thymectomy is T cell-mediated. We have previously shown that transgenic expression of the H/K ATPase beta-subunit gene in the thymus prevented the development of autoimmune gastritis induced by thymectomy. However, little is known of the contribution of the H/K ATPase alpha-subunit in disease development. Here, we show that (1) in contrast to the gastric H/K ATPase beta-subunit, the alpha-subunit gene is expressed in normal BALB/c thymus. (2) transgenic expression of the gastric H/K ATPase alpha-subunit gene in the thymus failed to prevent the development of autoimmune gastritis and (3) normal BALB/c and transgenic mice expressing the alpha-subunit in the thymus develop autoimmune gastritis following immunisation with purified murine gastric H/K ATPase, whereas transgenic mice expressing the beta-subunit in the thymus do not. We propose that the expression of the H/K ATPase alpha-subunit in the normal thymus may account for the predominant role of the beta-subunit in the development of autoimmune gastritis induced either by thymectomy or by immunisation with the ATPase.