An autoimmune disease with multiple molecular targets abrogated by the transgenic expression of a single autoantigen in the thymus

Reciprocal changes in trefoil 1 and 2 expression in stomachs of mice with gastric unit hypertrophy and inflammation

H+/K+-ATPase beta-subunit-deficient mice (129/Sv background) display numerous pathologies in the stomach. Expression of the mutation in BALB/cCrSlc mice results in the development of an aberrant 'mucus-rich' cell population. 'Mucus-rich' cells have been described in stomachs of mice with autoimmune gastritis, a disease mediated by CD4+ T cells. Other pathological features of autoimmune gastritis are similar to those in H+/K+ beta-deficient mice and include a mononuclear cell infiltrate in the gastric mucosa, non-functional or absent parietal cells, depletion of zymogenic cells, hypergastrinaemia, and gastric unit hypertrophy caused by immature cell hyperplasia. The present study investigates further the aberrant gastric 'mucus-rich' cell lineage and analyses the mRNA expression of mucus cell products TFF1 and TFF2. 'Mucus-rich' cells stained for both acidic and neutral mucins, and with a TFF2-specific antibody. Stomachs from both models expressed decreased TFF1 mRNA and reciprocally increased TFF2 mRNA. The involvement of gastrin in regulating trefoil mRNA expression was also investigated using gastrin-deficient mice. In contrast to previous findings, gastrin did not positively regulate TFF1 mRNA expression, but there was possible augmentation of TFF2. Additionally, a clear role for inflammation was established involving both polymorphonuclear and mononuclear cells in these models, and a link was found between mucosal hypertrophy and increased interleukin-11 (IL-11) expression.

Immunological and morphogenic basis of gastric mucosa atrophy and metaplasia

Chronic gastritis with gastric mucosa atrophy, intestinal metaplasia and endocrine cell hyperplasia are alterations with an increased risk for the development of gastric neoplasias. Immunological studies in autoimmune gastritis, in atrophic Helicobacter pylori gastritis and in studies with transgenic mice point to a central role of the parietal cell in the development of gastric mucosa atrophy. Destruction of gastric epithelial cells alone might not be sufficient for the loss of complete gastric glands. Gastric atrophy, endocrine cell hyperplasia and intestinal and pancreatic metaplasia can be regarded as the result of altered morphogenesis within the gastric mucosa. Impaired expression of the gastric morphogenic factor Sonic Hedgehog by parietal cells and increased expression of the transcriptional activators of intestinal and pancreatic differentiation, namely CDX2 and PDX1, seem to be crucial for the development of gastric atrophy and for intestinal, endocrine and pancreatic transdifferentiation processes. Altered expression of these morphogenic factors is partly caused by changes in the gastric milieu. Further studies concerning the normal and pathological morphogenesis of the gastric mucosa and related tissues might give new insight into the pathogenesis of gastric atrophy and metaplasia.

Growth factors associated with gastric mucosal hypertrophy in autoimmune gastritis

A prominent pathological feature of murine autoimmune gastritis is a pronounced mucosal hypertrophy. Here, we examined factors that may be responsible for inducing this hypertrophy. Because gastrin is known to be both an inducer of gastric mucosal cell proliferation and is elevated in autoimmune gastritis, mice deficient in gastrin were thymectomised at day 3 and assessed for autoimmune gastritis. Gastrin-deficient mice showed all the characteristic features of murine autoimmune gastritis, including gastric unit hypertrophy due to hyperproliferation and accumulation of immature epithelial cells, decreases in the number of zymogenic and parietal cells, and autoantibodies to the gastric H+/K+-ATPase. Hence, gastrin is not required for either the establishment of chronic gastritis or development of the typical pathological features of this disease. We also examined mRNA levels of a number of gastric mucosal growth factors in RNA samples from mice with hypertrophic autoimmune gastritis. Members of the Reg family, RegIIIbeta and RegIIIgamma, were greatly elevated in mice with hypertrophic gastritis, whereas RegI and amphiregulin (an EGF receptor ligand) were more modestly and/or inconsistently induced. These data demonstrate that induction of gastric mitogenic factors, such as members of the Reg family, can be achieved in inflammatory situations by gastrin-independent pathways. Members of the Reg family, in particular RegIIIbeta and RegIIIgamma, are good candidates to be involved in inducing the mucosal hyperproliferation in autoimmune gastritis. These findings are likely to be of relevance to other gastric inflammatory conditions.

Thymic expression of a gastritogenic epitope results in positive selection of self-reactive pathogenic T cells

Intrathymic expression of tissue-specific self-Ags can mediate tolerance of self-reactive T cells. However, in this study we define circumstances by which thymic expression of a tissue-specific autoepitope enhances positive selection of disease-causing, self-reactive T cells. An immunodominant gastritogenic epitope, namely the gastric H/K ATPase beta subunit(253-277) (H/Kbeta(253-277)), was attached to the C terminus of the invariant chain (Ii) and the hybrid Ii (Ii-H/Kbeta(253-277)) expressed in mice under control of the Ii promoter. The Ii-H/Kbeta(253-277) fusion protein was localized to MHC class II-expressing cells in the thymus and periphery of Ii-H/Kbeta(253-277) transgenic mice. In one transgenic line the level of presentation in the periphery (spleen) was insufficient to activate naive, low affinity H/Kbeta(253-277)-specific transgenic T cells (1E4-TCR), whereas thymic presentation of H/Kbeta(253-277) enhanced positive selection of 1E4-TCR cells in Ii-H/Kbeta(253-277)/1E4-TCR double-transgenic mice. Furthermore, Ii-H/Kbeta(253-277)/1E4-TCR double-transgenic mice had an increased incidence of autoimmune gastritis compared with 1E4-TCR single-transgenic mice, demonstrating that the 1E4 T cells that seeded the periphery of Ii-H/Kbeta(253-277) mice were pathogenic. Therefore, low levels of tissue-specific Ags in the thymus can result in positive selection of low avidity, self-reactive T cells. These findings also suggest that the precise level of tissue-specific Ags in the thymus may be an important consideration in protection against autoimmune disease and that perturbation of the levels of self-Ags may be detrimental.

Tumor necrosis factor alpha is not implicated in the genesis of experimental autoimmune gastritis

Experimental autoimmune gastritis (EAG) characterised by mononuclear cell infiltrate, parietal and zymogenic cell destruction and circulating autoantibodies to gastric H(+)/K(+)ATPase is an animal model for human autoimmune gastritis, that leads to pernicious anaemia. We have previously shown that Fas has a role in initiating damage to target cells in EAG. Here we used three strategies to examine the role of TNFalpha in this disease. We administered neutralising anti-TNFalpha antibody either as a single injection or as twice weekly injections for 8 weeks to mice subjected to neonatal thymectomy-induced EAG. To address the role of apoptotic signals through TNFR1, TNFR1 deficient mice were either neonatally thymectomised or crossed to PC-GMCSF transgenic mice that spontaneously develop EAG. Neonatally thymectomised mice treated with anti-TNFalpha antibody developed destructive gastritis and autoantibodies to gastric H(+)/K(+)ATPase similar to control mice. Following either neonatal thymectomy or crossing to PC-GMCSF transgenic mice, TNFR1 deficient mice developed autoantibody-positive destructive gastritis at similar frequency compared with wild type and heterozygous littermates. Our observations that neutralisation of TNFalpha and absence of TNFR1 has no discernible effect on development of EAG suggest that TNFalpha is not required for mucosal cell damage or development of autoimmune gastritis. While blocking TNFalpha activity has therapeutic benefit in certain autoimmune diseases, this is not the case for EAG.

Chemokine receptor CCR5 is not required for development of experimental autoimmune gastritis

Experimental autoimmune gastritis (EAG) is a model of human autoimmune gastritis, the underlying cause of pernicious anaemia. It is characterised by gastric mononuclear cell infiltrates, destruction of parietal and zymogenic cells, and autoantibodies to parietal cell-associated H(+)/K(+) ATPase. Here, we have investigated the role of CCR5 in the development of EAG. We found that the development of EAG was not prevented in CCR5-deficient mice. Using reverse-transcriptase analysis of stomachs from normal and gastritic mice we found no difference in expression of CCR5 and its chemokine ligands MIP-1alpha, MIP-1beta, and RANTES. We also found that the CCR5 antagonist met-RANTES failed to prevent the development of EAG induced by neonatal thymectomy. These observations suggest that the CC chemokine receptor CCR5 is not essential for development of EAG.

HK-ATPase expression in the susceptible BALB/c and the resistant DBA/2 strains of mice to autoimmune gastritis

Neonatal thymectomy (NTx) in mice induces a group of alterations in the immune system homeostasis that results in the development of a variety of organ-specific autoimmune diseases such as gastritis, thyroiditis, oophoritis and orchitis. Given the importance of self-antigen expression in thymus for the control of autoreactive cells and generation of regulatory cells, we have compared the expression of parietal cell antigen in two strains of mice with the same H-2: BALB/c (susceptible to develop gastritis after NTx) and DBA/2 (resistant). We detected mRNA of HK-ATPase alpha and beta chains in day 1 thymi of both strains. Fifty percent of BALB/c mice presented mRNA levels similar to DBA/2. However, lower mRNA levels were found in the remaining BALB/c mice that may correspond to those that would develop AIG after NTx. Since the presence of the antigen in periphery is also necessary for the induction of regulatory cells, we have compared both strains observing in day 1 stomachs from resistant DBA/2 strain, a significantly higher content of positive cells for HK-ATPase subunits than stomachs from susceptible BALB/c strain. Also, the presence of antinuclear Abs in NTx BALB/c mice makes this model a useful experimental system for analyzing the responsible mechanisms breaking the non-specific self-tolerance.

Inhibitory effects of Helicobacter pylori infection on murine autoimmune gastritis

BACKGROUND AND AIM

Long term Helicobacter pylori infection leads to atrophic gastritis but the relation between H pylori infection and autoimmune related atrophic gastritis (AIG) remains unclear. We studied the effects of H pylori infection on the pathophysiology of AIG in mice.

MATERIALS AND METHODS

BALB/c nu/nu mice (n=40) with or without H pylori infection received splenocytes from neonatally thymectomised mice to induce AIG. Half of the mice were orally infected with H pylori prior to AIG induction. Histological findings, and local and systemic immune responses were serially evaluated.

RESULTS

Two and six months after transfer, parietal cells in uninfected mice were depleted while those in infected mice were well preserved. The degree of gland atrophy (p<0.01), hyperplasia (p<0.01), gastric pH (p<0.05), and serum gastrin levels of infected mice were significantly lower than those of uninfected mice. Serum antiparietal cell antibody levels gradually decreased in infected mice, and were significantly lower than those of uninfected mice at six months (p<0.05). Real time polymerase chain reaction studies revealed significantly higher interleukin 4 (p<0.05) and transforming growth factor beta (p<0.05) gene expression in the gastric mucosa in infected mice than in uninfected mice at both two and six months after AIG induction.

CONCLUSIONS

H pylori infection inhibited the development of AIG in mice. Th2-type immune responses and transforming growth factor beta in the gastric microenvironment might be involved in the inhibitory effects of H pylori infection on the development of AIG, in which Th1-type responses have an important role.

Stem cells engineered to express self-antigen to treat autoimmunity

Autoimmune diseases are incurable. We propose a combination curative strategy using haematopoietic stem cells and gene therapy. The strategy should establish molecular chimerism with culprit antigen expressed by donor antigen-presenting cells in the thymus, resulting in immunological tolerance. Our strategy is based on the intrathymic tolerance and disease resistance established by transgenic expression of antigen in the thymus under control of an MHC class II promoter. We propose that transplantation with genetically engineered stem cells provides an advance over current autologous bone marrow transplantation, in that it should remove the significant risk of disease relapse.

Neonates support lymphopenia-induced proliferation

T cells expand without intentional antigen stimulation when transferred into adult lymphopenic environments. In this study, we show that the physiologic lymphopenic environment existing in neonatal mice also supports CD4 T cell proliferation. Strikingly, naive CD4 T cells that proliferate within neonates acquire the phenotypic and functional characteristics of memory cells. Such proliferation is inhibited by the presence of both memory and naive CD4 T cells, is enhanced by 3-day thymectomy, is independent of IL-7, and requires a class II MHC-TCR interaction and a CD28-mediated signal. CD44(bright) CD4 T cells in neonates have a wide repertoire as judged by the distribution of Vbeta expression. Thus, lymphopenia-induced T cell proliferation is a physiologic process that occurs during the early postnatal period.

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.

Fas/CD95 is required for gastric mucosal damage in autoimmune gastritis

BACKGROUND & AIMS

Experimental autoimmune gastritis (EAG), characterized by a gastric mononuclear cell infiltrate, mucosal cell damage, and autoantibodies to parietal cell-associated H(+)/K(+) adenosine triphosphatase, is a model for human autoimmune gastritis that leads to pernicious anemia. Previous in vitro studies have implicated Fas/CD95 in initiating damage to gastric mucosal cells in humans and an animal model of autoimmune gastritis. Here we used 2 in vivo animal models to examine the role of Fas in the development of mucosal cell damage in autoimmune gastritis.

METHODS

We initiated EAG in BALB/cCrSlc mice by neonatal thymectomy and examined for Fas expression in the gastric mucosa by immunohistochemistry. To address the in vivo relevance of Fas in mucosal injury, we examined the stomachs and sera of BALB/cCrSlc lpr/lpr mice subjected to neonatal thymectomy and BALB/cCrSlc nu/nu lpr/lpr mice transferred with lymphocytes from gastritic BALB/cCrSlc mice.

RESULTS

Fas expression was up-reguiated in parietal cells of mice with EAG. Neonatally thymectomized lpr/lpr mice were resistant to developing destructive gastritis compared with heterozygous and wild-type littermates. Nu/nu Fas-sufficient mice transferred with lymphocytes from thymectomized lpr/lpr mice developed destructive gastritis. Nu/nu lpr/lpr mice transferred with lymphocytes from gastritic mice developed a nondestructive gastritis.

CONCLUSIONS

The observations that Fas is up-regulated in gastric parietal cells of mice with EAG and that Fas-deficient mice are resistant to development of destructive gastritis provide compelling evidence that Fas is required in vivo for development of gastric mucosal cell damage in autoimmune gastritis.

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.

The role of natural killer cells in the induction of autoimmune gastritis

A number of experimental models of organ-specific autoimmunity involve a period of peripheral T cell lymphopenia prior to disease onset. In particular, experimental autoimmune gastritis, induced in susceptible mouse strains by neonatal thymectomy, is a CD4+ T cell mediated autoimmune disease. We have previously demonstrated that this disease displays the hallmarks of a Th1-mediated DTH inflammatory response with an essential role for IFN-gamma very early in the pathogenesis of disease. Given the interplay between the innate and adaptive immune responses, a potential source of early IFN-gamma production in these lymphopenic mice is the innate immune response. Here we have assessed the contribution of innate immunity to the induction of experimental autoimmune gastritis, in particular, the role of natural killer (NK) cells in production of IFN-gamma. Analysis of NK cells and macrophages revealed no difference in either the number or activation status between euthymic and neonatally thymectomised mice. Furthermore, in vivo depletion of NK cells immediately after neonatal thymectomy of (BALB/cCrSlcxC57BL/6) F1 mice demonstrated no reduction in disease incidence compared to control groups of neonatally thymectomised mice. Therefore, we conclude that NK cells are not the primary source of IFN-gamma required for the pathogenesis of autoimmune gastritis following neonatal thymectomy but rather the small cohort of T cells in the periphery of lymphopenic mice are likely to be responsible for the IFN-gamma production.

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.

In vivo tolerance breakdown with dendritic cells pulsed with U1A protein in non-autoimmune mice: the induction of a high level of autoantibodies but not renal pathological changes

One of the hallmarks of systemic autoimmune diseases, such as systemic lupus erythematosus (SLE), is the immune response to nuclear autoantigens. Several studies have proposed that dendritic cells may acquire the nuclear autoantigens from the apoptotic cells to initiate the systemic autoimmune responses. To examine the immune response to a nuclear autoantigen induced by dendritic cells, bone marrow-derived dendritic cells (BMDCs) pulsed with U1 small nuclear ribonucleoprotein (snRNP)-A protein (U1A) were intravenously injected into non-autoimmune mice. The results showed that BMDCs pulsed with U1A proteins by intravenous injection into BALB/c (H-2d) and DBA-2xNZW F1 (H-2d/u) mice were capable of activating the autoreactive T cells and inducing a high titre of immunoglobulin G (IgG) anti-U1A antibodies. Both groups of mice with a high anti-U1A autoantibody titre also transiently developed IgG against double-stranded (ds) DNA. However, unlike NZBxNZW F1 (BWF1) (H-2d/u) mice, no obviously histopathological changes to the glomeruli were noted in the mice treated either with BMDCs or with U1A-pulsed BMDCs. Several months after immunization, all mice treated with U1A-pulsed BMDCs did develop IgG, but not the complement C3 deposit in the glomeruli. The cytokine profile produced by the U1A-specific T cells of primed DBA-2xNZW F1 mice was skewed toward the T helper type 1 phenotype compared with that of BWF1 mice. The model we describe here adds to the further understanding of the pathogenic mechanisms, such as self-antigen shifting, and the mechanisms that account for the different responses to self-antigens when in a normal or an autoimmune state.

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.

Requirements for autoimmune responses to mouse gastric autoantigens

Autoimmune gastritis, in which the H+/K(+)-ATPase of parietal cells is the major antigen, is one of the most common autoimmune diseases. Here we examined if specific properties of the H+/K(+)-ATPase or parietal cells are involved in rendering them autoimmune targets. The model antigens beta-galactosidase and ovalbumin (OVA) were expressed in parietal cells of transgenic mice. On experimental induction of autoimmune gastritis by neonatal thymectomy, autoantibodies to beta-galactosidase developed in mice expressing beta-galactosidase in parietal cells, a response that was independent of either the response to the gastric H+/K(+)-ATPase or gastric inflammation. In contrast, mice that expressed OVA in parietal cells did not exhibit an antibody response to OVA after thymectomy. However, increasing the frequency of anti-OVA T lymphocytes in OVA-expressing mice resulted in autoantibodies to OVA and gastritis. These studies indicate that parietal cells can present a variety of antigens to the immune system. Factors such as the identity and expression level of the autoantigen and the frequency of autoreactive T cells play a role in determining the prevalence and outcome of the particular immune response. In addition, as not all mice of a particular genotype displayed autoimmunity, random events are involved in determining the target of autoimmune recognition.

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.

Local transgenic expression of granulocyte macrophage-colony stimulating factor initiates autoimmunity

Mechanisms leading to breakdown of immunological tolerance and initiation of autoimmunity are poorly understood. Experimental autoimmune gastritis is a paradigm of organ-specific autoimmunity arising from a pathogenic autoimmune response to gastric H/K ATPase. The gastritis is accompanied by autoantibodies to the gastric H/K ATPase. The best characterized model of experimental autoimmune gastritis requires neonatal thymectomy. This procedure disrupts the immune repertoire, limiting its usefulness in understanding how autoimmunity arises in animals with intact immune systems. Here we tested whether local production of GM-CSF, a pro-inflammatory cytokine, is sufficient to break tolerance and initiate autoimmunity. We generated transgenic mice expressing GM-CSF in the stomach. These transgenic mice spontaneously developed gastritis with an incidence of about 80% after six backcrosses to gastritis-susceptible BALBc/CrSlc mice. The gastritis is accompanied by mucosal hypertrophy, enlargement of draining lymph nodes and autoantibodies to gastric H/K ATPase. An infiltrate of dendritic cells and macrophages preceded CD4 T cells into the gastric mucosa. T cells from draining lymph nodes specifically proliferated to the gastric H/K ATPase. CD4 but not CD8 T cells transferred gastritis to nude mouse recipients. CD4(+) CD25(+) T cells from the spleen retained anergic suppressive properties that were reversed by IL-2. We conclude that local expression of GM-CSF is sufficient to break tolerance and initiate autoimmunity mediated by CD4 T cells. This new mouse model should be useful for studies of organ-specific autoimmunity.

H(+),K(+)-atpase (proton pump) is the target autoantigen of Th1-type cytotoxic T cells in autoimmune gastritis

BACKGROUND & AIMS

The proton pump H(+),K(+)-adenosine triphosphatase (H(+),K(+)-ATPase) of parietal cells is the major humoral autoantigen in both human and experimental autoimmune gastritis (AIG) characterized by an inflammatory infiltrate in the gastric mucosa and loss of parietal cells. The aim of this study was to detect H(+),K(+)-ATPase-specific T cells in the gastric mucosa of patients with AIG and to define their functional properties.

METHODS

In vivo-activated T cells from the infiltrates of the gastric mucosa of 5 patients with AIG were isolated and cloned. The ability of gastric T-cell clones to proliferate and to produce cytokines in response to H(+),K(+)-ATPase, as well as their expression of B-cell help, perforin-mediated cytotoxicity, and Fas-Fas ligand-mediated apoptosis in target cells, were assessed.

RESULTS

A proportion (25%) of the CD4(+) clones from the gastric corpus of AIG patients proliferated in response to porcine H(+),K(+)-ATPase. Most of these clones (88%) showed a Th1 profile, whereas a few secreted both Th1 and Th2 cytokines. Virtually all of the H(+),K(+)-ATPase-specific clones produced tumor necrosis factor alpha and provided substantial help for B-cell immunoglobulin production, and most of them expressed perforin-mediated cytotoxicity against antigen-presenting cells and induced Fas-Fas ligand-mediated apoptosis in target cells.

CONCLUSIONS

Activation of proton pump-specific Th1 cytotoxic/proapoptotic T cells in the gastric mucosa can represent an effector mechanism for the target cell destruction in AIG.

Prevention of autoimmunity by induction of cutaneous tolerance

Autoimmune gastritis develops in 20-60% of BALB/c mice following thymectomy at 3 days after birth (3dnTx). Previously we identified the gastric H+/K+ ATPase as the causative autoantigen and mapped the immunoreactive T cell epitope to a carboxyl-terminal peptide on the gastric H+/K+ ATPase beta subunit. Here we show that autoimmune gastritis can be suppressed by immunizing 3dnTx mice through neonatal skin with the beta subunit peptide, in combination with the contact sensitizer TNCB. When spleen cells were transferred from suppressed mice to nude mice a proportion of recipient mice developed gastritis. These results indicate that pathogenic T cells were still present in the 3dnTx mice but the absence of gastritis indicates that their activity can be regulated following induction of cutaneous tolerance by immunizing through neonatal skin. We propose that cutaneous tolerance is induced through mediation of immature Langerhans cells in neonatal skin and that this tolerance prevented the autoreactivity of pathogenic T cells. This procedure will have implications for strategies to suppress autoimmunity.

Antigen-specific therapy for autoimmune disease

The application of self-antigens as therapeutic tools is validated in inbred animal models of autoimmune disease. Mechanisms of antigen-induced tolerance (apoptosis, anergy, regulatory T cells and immune deviation) are being clarified in relation to the properties of antigens and the modes and routes of their delivery. Mucosa-mediated tolerance remains the predominant mode of antigen-specific therapy but awaits demonstration of clinical efficacy in human autoimmune disease.

Peripheral T cell expansion in lymphopenic mice results in a restricted T cell repertoire

In the absence of thymic contribution, the peripheral T cell pool is maintained by division of mature lymphocytes. Recent studies suggest that peripheral T cell expansion may be driven by low-affinity interactions with self ligands. Here we have investigated the consequence of homeostatic proliferation on the T cell repertoire. Following day 3 thymectomy of mice, there is a subsequent 30-fold expansion of the peripheral T cell population. Significantly, expansion of the T cell population results in skewed TCR Vbeta complementarity-determining region (CDR)3 length distributions and, in some cases, a marked bias toward one or two CDR3 lengths. TCR sequence analysis showed that these biases were a consequence of (oligo)clonal T cell expansion. Neonatally thymectomized adult mice have reduced antibody responses to primary challenge with T-dependent antigens. These data demonstrate that peripheral expansion of the T cell pool can result in a limited T cell repertoire, indicating that the array of stimulating ligands that drives homeostatic expansion is restricted.

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.

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.

NKT cells are phenotypically and functionally diverse

NK1.1(+)alpha betaTCR(+) (NKT) cells have several important roles including tumor rejection and prevention of autoimmune disease. Although both CD4(+) and CD4(-)CD8(-) double-negative (DN) subsets of NKT cells have been identified, they are usually described as one population. Here, we show that NKT cells are phenotypically, functionally and developmentally heterogeneous, and that three distinct subsets (CD4(+), DN and CD8(+)) are differentially distributed in a tissue-specific fashion. CD8(+) NKT cells are present in all tissues but the thymus, and are highly enriched for CD8alpha(+)beta(-) cells. These subsets differ in their expression of a range of cell surface molecules (Vbeta8, DX5, CD69, CD45RB, Ly6C) and in their ability to produce IL-4 and IFN-gamma, with splenic NKT cell subsets producing lower levels than thymic NKT cells. Developmentally, most CD4(+) and DN NKT cells are thymus dependent, in contrast to CD8(+) NKT cells, and are also present amongst recent thymic emigrants in spleen and liver. TCR Jalpha281-deficient mice show a dramatic deficiency in thymic NKT cells, whereas a significant NKT cell population (enriched for the DN and CD8(+) subsets) is still present in the periphery. Taken together, this study reveals a far greater level of complexity within the NKT cell population than previously recognized.

A mouse gene encoding an oocyte antigen associated with autoimmune premature ovarian failure

Autoimmune premature ovarian failure causes young women to develop menopausal symptoms and infertility. A similar syndrome appears in mice with postthymectomy autoimmune premature ovarian failure. We demonstrate that these mice develop antibodies against a 125-kDa protein located in the oocyte cytoplasm (ooplasm). By screening a mouse ovarian complementary DNA expression library with autoimmune serum, we have identified a novel mouse gene with a 3.75-kb ovarian transcript, the expression of which is restricted to the oocyte. The longest open reading frame (3333 bp) encodes an oocyte-specific protein, designated OP1 (ooplasm-specific protein 1). The protein is composed of 1111 amino acids with a predicted molecular mass of 125,502 Da. Based on its primary structure, it appears to be novel and has no motifs to suggest a localization other than in the cytoplasm. The ability of immune serum from mice with ovarian autoimmunity to react specifically with recombinant OP1 raises the possibility that OP1 as an antigen may play a role in murine autoimmune premature ovarian failure.

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.

A Major Linkage Region on Distal Chromosome 4 Confers Susceptibility to Mouse Autoimmune Gastritis

Although much is known about the pathology of human chronic atrophic (type A, autoimmune) gastritis, its cause is poorly understood. Mouse experimental autoimmune gastritis (EAG) is a CD4+ T cell-mediated organ-specific autoimmune disease of the stomach that is induced by neonatal thymectomy of BALB/c mice. It has many features similar to human autoimmune gastritis. To obtain a greater understanding of the genetic components predisposing to autoimmune gastritis, a linkage analysis study was performed on (BALB/cCrSlc × C57BL/6)F2 intercross mice using 126 microsatellite markers covering 95% of the autosomal genome. Two regions with linkage to EAG were identified on distal chromosome 4 and were designated Gasa1 and Gasa2. The Gasa1 gene maps within the same chromosomal segment as the type 1 diabetes and systemic lupus erythematosus susceptibility genes Idd11 and Nba1, respectively. Gasa2 is the more telomeric of the two genes and was mapped within the same chromosomal segment as the type 1 diabetes susceptibility gene Idd9. In addition, there was evidence of quantitative trait locus controlling autoantibody titer within the telomeric segment of chromosome 4. The clustering of genes conferring susceptibility to EAG with those conferring susceptibility to type 1 diabetes is consistent with the coinheritance of gastritis and diabetes within human families. This is the first linkage analysis study of autoimmune gastritis in any organism and as such makes an important and novel contribution to our understanding of the etiology of this disease.

Post-thymectomy autoimmune gastritis: fine specificity and pathogenicity of anti-H/K ATPase-reactive T cells

Thymectomy at day 3 of life (d3Tx) results in the development of organ-specific autoimmunity. We have recently shown that d3Tx BALB/c mice which develop autoimmune gastritis contain CD4+ T cells specific for the gastric parietal cell proton pump, H/K ATPase. Here, we demonstrate that freshly explanted gastric lymph node (LN) cells from d3Tx mice react significantly to the H/K ATPase alpha chain, but only marginally to the beta chain. Two H/K ATPase-reactive T cell lines were derived from the gastric LN of d3Tx mice. Both are CD4+, TCR alpha/beta-, and I-Ad restricted, and recognize distinct peptides from the H/K ATPase alpha chain. One cell line secretes Th1 and the other Th2 cytokines, but both are equally potent in inducing gastritis with distinct profiles of cellular infiltration in nu/nu recipient animals. Neither of the cell lines induced disease in normal BALB/c recipients and transfer of disease to nu/nu recipients was blocked by co-transfer of normal BALB/c spleen cells containing CD4+ CD25+ cells. Although CD4+ CD25+ T cells are thought to emigrate from the thymus after day 3 of life, they could be identified in LN of 2-day-old animals. The capacity of CD4+ CD25+ T cells to abrogate the pathogenic activity in vivo of both activated Th1/Th2 lines strongly suggests that this suppressor T cell population may have a therapeutic role in other models of established autoimmunity. The availability of well-characterized lines of autoantigen-specific T cells should greatly facilitate the analysis of the mechanism of action and target of the CD4+ CD25+ immunoregulatory cells.

Identification of a gastritogenic epitope of the H/K ATPase beta-subunit

We have previously shown that autoimmune gastritis can be elicited in mice by immunization with the gastric parietal cell H/K ATPase alpha beta heterodimer and that tolerance specifically induced to the H/K ATPase beta-subunit protects mice from the development of gastritis. Here we have identified the immunodominant gastritogenic epitope of the H/K ATPase beta-subunit (H/Kbeta). Epitope mapping was carried out with a panel of 21 overlapping peptides that spanned the entire sequence of the gastric H/K ATPase beta-subunit. T cells from gastric H/K ATPase-immunized mice responded to only one of the overlapping peptides, namely H/Kbeta253-277. Furthermore, a single subcutaneous immunization of 6-week-old BALB/c mice with the ATPase beta-subunit peptides resulted in a T-cell response to only H/Kbeta253-277. Multiple immunization with the overlapping H/K ATPase peptides demonstrated that H/Kbeta253-277 was capable of inducing a mononuclear infiltrate specifically within the gastric mucosa. We conclude that H/Kbeta253-277 is the dominant gastritogenic epitope of the gastric H/K ATPase.

Induction of peripheral tolerance in neonatally thymectomized mice by immunization through chemical carcinogen-altered skin

BALB/c mice thymectomized 3 days after birth (3dnTx) are prone to the development of autoimmune gastritis. As this outcome may be a consequence of altered immunoregulatory mechanisms, we set out to determine the immunological status of these mice and their capacity to acquire antigen-specific peripheral tolerance. The latter was assessed by the capacity of these mice to suppress a contact sensitivity response to 2,4,6-trinitrochlorobenzene (TNCB) following treatment of the skin by the carcinogen, DMBA. The 3dnTx mice had a reduced number of CD4(+) and CD8(+) T cells and a reduced lymphocyte proliferative response to PHA, but a normal contact sensitivity response to TNCB. After treatment of the skin with DMBA these mice failed to develop contact sensitivity to TNCB. Adoptive transfer of splenocytes from these mice to naive mice transfered antigen-specific suppression, irrespective of whether the 3dnTx mice had developed autoimmune gastritis. We conclude that despite thymectomy at day 3 and the attendant immunosuppression, the capacity of BALB/c mice to generate antigen-specific peripheral tolerance to TNCB was retained. These results suggest that precursor T cells which mediate suppression to antigens such as TNCB are present in 3dnTx mice and that these cells are likely to have developed in the thymus and exported to the periphery before 3 days after birth.

T lymphocyte-mediated control of autoimmunity

Autoreactive T cells can be readily identified in the peripheral lymphocyte pool of both humans and experimental animals. Peripheral tolerance may be maintained by regulatory/suppressor T cells which prevent the activation of autoantigen-specific cells. Mice thymectomized on day 3 of life (d3Tx) develop a wide spectrum of organ-specific autoimmune diseases. Reconstitution of d3Tx mice with CD4+ CD25+ T cells from normal mice prevents the development of disease. Similarly, CD4+ CD25+ T cells prevent the transfer of disease by autoantigen-specific cloned T cells derived from d3Tx mice. Thus, regulatory T cells can prevent both the induction and effector function of autoreactive T cells. In vitro, the CD4+ CD25+ population is anergic to stimulation through the T cell receptor (TCR) and suppresses the proliferative responses of normal CD4+ CD25- cells by a contract-dependent mechanism. Suppression is not MHC-dependent, but requires activation of the CD4+ CD25+ population. The mechanism of suppression in vivo and the target antigen(s) of this unique regulatory population remain to be characterized.

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.

Are there unique autoantigens triggering autoimmune diseases?

Using three reference disease models--insulin-dependent diabetes mellitus (IDDM) as a prototype of T-cell mediated organ-specific autoimmune disease, myasthenia gravis (MG) as a prototype of autoantibody-mediated organ-specific autoimmune disease and systemic lupus erythematosus (SLE) as a prototype of non-organ-specific autoimmune disease--we have reached several conclusions: 1) All three diseases are associated with the presence of multiple autoantibodies and/or autoreactive T cells that recognize a large number of antigenic molecules. The apparent predominant role of certain antibodies in some diseases could relate to their functional properties such as acetylcholine receptor (AChR) blockade for anti-AChR autoantibodies in MG or anti-dsDNA in SLE. 2) Major target antigens are clustered in the target cell affected by organ-specific autoimmune diseases: beta cells in IDDM, striated-muscle cells in MG, or apoptotic cells in the case of SLE. 3) Antibodies and T cells recognize multiple epitopes in these molecules. 4) The most evident explanation for the observed clustering and diversity is autoantigen spreading. Spreading probably involves T cells secreting proinflammatory cytokines but also possibly antibodies as in the case of nucleosome autoantibodies in SLE. 5) The counterpart of antigen spreading is bystander suppression in which regulatory cytokines deviate the immune response towards a protective response. 6) The mechanisms underlying the initiation of the autoimmune response and antigen spreading are still undetermined. They could imply a direct abnormality of the target cell in the case of organ-specific autoimmune diseases (e.g. infection with a virus showing a selective tropism for the target cell in organ-specific autoimmune diseases, or loss of physiological regulation of major histocompatibility complex molecule expression) or could be consequence of a ubiquitous cell abnormality such as increased apoptosis in SLE. The respective roles of genetic and environmental factors in these triggering events remain to be determined.

Determinant spreading: lessons from animal models and human disease

Spreading of the immune response is a common theme in organ-specific and systemic autoimmune diseases. We evaluated whether some of the mixed antinuclear antibody patterns characteristic of systemic autoimmunity might be the result of determinant spreading from a single initiating event. Immunisation of healthy mice with individual protein components of the La/Ro ribonucleoprotein (RNP) targeted in systemic lupus erythematosus and primary Sjögren's syndrome induced autoantibodies recognising Ro60 (SS-A), Ro52 (SS-A) and La (SS-B) and in some cases the molecular chaperones calreticulin and Grp78. The endogenous antigen(s) driving determinant spreading might be derived from physiological apoptosis which could explain the involvement of some chaperone proteins in the autoimmune response. Diversified anti-La/Ro antibody responses were initiated by challenge with a single subdominant T epitope of La even though some self epitopes of La were efficiently tolerised. The pattern of autoantibody responses in primary Sjögren's syndrome was strongly influenced by HLA class II phenotype which we speculate controls activation of T cells recognising defined peptides from the La/Ro RNP. In this way, HLA class II alleles may be critical in influencing initiation and spreading of systemic autoimmune reactions. Molecular mimicry of such determinants by exogenous agents might readily initiate spreading of an autoimmune response in genetically susceptible hosts.

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.

Atrophic gastric changes in both Helicobacter felis and Helicobacter pylori infected mice are host dependent and separate from antral gastritis

BACKGROUND/AIMS

The role of host factors has been neglected in studies of the pathogenesis of Helicobacter associated disease. The aim of this study was to assess the response of different mouse strains to infection with a single strain of Helicobacter felis.

METHOD

Six strains of inbred mice were infected with the identical H felis culture and were killed at one month, two months, and six months after infection to assess histopathological changes. In addition, two strains of mice were infected with a mouse adapted strain of H pylori and examined at six months after infection.

RESULTS

In SJL, C3H/He, DBA/2, and C57BL/6 infected mice, severe to moderate chronic active gastritis was observed only in the body of the stomach, which increased in severity over time with specialised cells in the body glands being replaced. As the severity of this damage in the body increased and atrophic changes were seen, the level of bacterial colonisation of the antrum decreased. In contrast, in BALB/c and CBA mice, there was only mild gastritis in the antrum, no remarkable changes were detected in their body mucosa, and no atrophy was seen over time. In both these strains of mice, heavy bacterial colonisation was seen, which tended to increase over the period of the experiment. Of particular importance in this experiment was that bacterial colonisation was mainly restricted to the antrum yet the atrophy, when present, was only observed in the body of the stomach. H pylori infected C3H/He mice showed moderate colonisation of the antrum, which persisted up to six months with little development of atrophy. In contrast, H pylori in C57BL/6 mice showed excellent colonisation of the antrum at two months but six months after infection there was moderate to severe body atrophy, which was associated with a loss of bacteria from the antrum.

CONCLUSIONS

These findings challenge current concepts of the development of Helicobacter induced atrophy in that active chronic gastritis of antrum or the body mucosa, or both, is not a prerequisite. They also suggest an autoimmune basis for the pathology although no autoantibody or antibody to the H+/K+ ATPase was detected. Loss of infecting helicobacters from the stomach together with development of an atrophic gastritis in the body of the stomach is similar to the pattern found in certain H pylori infected human subjects.