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Biomedical subjects

P B Ernst

Publications and source records attributed to P B Ernst.

At least 19 recordsLinked to original sources
PubMed2001

Negative selection of T cells by Helicobacter pylori as a model for bacterial strain selection by immune evasion.

The majority of humans infected with Helicobacter pylori maintain a lifelong infection with strains bearing the cag pathogenicity island (PAI). H. pylori inhibits T cell responses and evades immunity so the mechanism by which infection impairs responsiveness was investigated. H. pylori caused apoptotic T cell death, whereas Campylobacter jejuni did not. The induction of apoptosis by H. pylori was blocked by an anti-Fas Ab (ZB4) or a caspase 8 inhibitor. In addition, a T cell line with the Fas rendered nonfunctional by a frame shift mutation was resistant to H. pylori-induced death. H. pylori strains bearing the cag PAI preferentially induced the expression of Fas ligand (FasL) on T cells and T cell death, whereas isogenic mutants lacking these genes did not. Inhibiting protein synthesis blocked FasL expression and apoptosis of T cells. Preventing the cleavage of FasL with a metalloproteinase inhibitor increased H. pylori-mediated killing. Thus, H. pylori induced apoptosis in Fas-bearing T cells through the induction of FasL expression. Moreover, this effect was linked to bacterial products encoded by the cag PAI, suggesting that persistent infection with this strain may be favored through the negative selection of T cells encountering specific H. pylori Ags.

Antigens, Bacterial↗
PubMed2001

T-cell-mediated mucosal immunity in the absence of antibody: lessons from Helicobacter pylori infection.

Approximately 50% of humanity is infected with Helicobacter pylori. This lifelong infection elicits a marked host response, including a robust gastric IgA response. However, natural infection fails to yield protective immunity. Rather than providing protection, the chronic inflammatory response associated with natural infection can contribute to tissue damage and the pathogenesis of gastroduodenal disease, including atrophic gastritis, peptic ulcer, and gastric cancer. These immune responses are attributed to a subset of helper T cells, so-called Th1 cells, that enhance cell-mediated immunity and induce damage to the gastric epithelium. Thus, it is desirable to have effective vaccines that could prevent and cure infection and that may modify the host response in a manner that prevents immune-mediated disease. Using animal models as a tool to understand the immunobiology of Helicobacter infections, several investigators have shown that effective vaccines can be developed. Thus, prophylactic and even therapeutic vaccines have been described in various animal models. The basis for the effectiveness of these vaccines appears related to their ability to alter the gastric immune response, from a homogeneous Th1 response to a mixed Th1 and Th2 response. Interestingly, immunity can occur in the absence of B cells, suggesting that novel IgA-independent mechanisms exist that confer protection against a luminal infection. Thus, H. pylori infection provides a model with which new mechanisms of immunological protection can be identified and applied to other mucosal infections.

Animals↗
PubMed2001

Helicobacter pylori infection as a model for gastrointestinal immunity and chronic inflammatory diseases.

Approximately 50% of humanity is infected with Helicobacter pylori. It is a life-long infection that elicits a marked host inflammatory response; however, natural infection fails to yield protective immunity. Rather than providing protection, the chronic inflammatory response associated with natural infection contributes to tissue damage and the pathogenesis of gastroduodenal disease, including atrophic gastritis, peptic ulcer, and gastric cancer. While bacterial factors are important triggers of inflammation, many subjects infected with strains bearing putative virulence factors remain free from disease. Recent genetic studies have implicated the host's immune and inflammatory responses, suggesting that disease results from an interaction between bacterial and environmental factors in genetically susceptible hosts. Other digestive diseases, including celiac disease and inflammatory bowel disease, mimic this paradigm, where it appears that luminal triggers only manifest disease in subjects with the right combination of host and environmental factors. Since infection with H. pylori is relatively common, it is possible to study the impact of a specific etiologic agent on the pathogenesis of disease in humans. This approach has illuminated the complexity of the pathogenic mechanisms, but the advances achieved to date may provide some hints regarding the pathogenesis of chronic inflammatory diseases elsewhere in the digestive tract.

Chronic Disease↗
PubMed2000

Helicobacter pylori urease binds to class II MHC on gastric epithelial cells and induces their apoptosis.

Infection by Helicobacter pylori leads to injury of the gastric epithelium and a cellular infiltrate that includes CD4+ T cells. H. pylori binds to class II MHC molecules on gastric epithelial cells and induces their apoptosis. Because urease is an abundant protein expressed by H. pylori, we examined whether it had the ability to bind class II MHC and induce apoptosis in class II MHC-bearing cells. Flow cytometry revealed the binding of PE-conjugated urease to class II MHC+ gastric epithelial cell lines. The binding of urease to human gastric epithelial cells was reduced by anti-class II MHC Abs and by staphylococcal enterotoxin B. The binding of urease to class II MHC was confirmed when urease bound to HLA-DR1-transfected COS-1 (1D12) cells but not to untransfected COS-1 cells. Urease also bound to a panel of B cell lines expressing various class II MHC alleles. Recombinant urease induced apoptosis in gastric epithelial cells that express class II MHC molecules, but not in class II MHC- cells. Also, Fab from anti-class II MHC and not from isotype control Abs blocked the induction of apoptosis by urease in a concentration-dependent manner. The adhesin properties of urease might point to a novel and important role of H. pylori urease in the pathogenesis of H. pylori infection.

Alleles↗
PubMed2000

Staphylococcal enterotoxin B stimulates expansion of autoreactive T cells that induce apoptosis in intestinal epithelial cells: regulation of autoreactive responses by IL-10.

T cell responses to self Ags and normal microbial flora are carefully regulated to prevent autoreactivity. Because IL-10-deficient mice develop colitis, and this response is triggered by luminal flora, we investigated whether IL-10 regulates the ability of microbial Ags to induce autoreactive T cells that could contribute to intestinal inflammation. T cells from wild-type mice were primed with staphylococcal enterotoxin B (SEB) in vitro, which induced an autoreactive proliferative response to syngeneic feeder cells. The cells were predominately CD3+ and CD4+. T cells from IL-10-deficient mice were constitutively autoreactive, and SEB priming enhanced this further. The autoreactive, proliferative response of T cells from wild-type mice was suppressed by IL-10 in the primary or secondary culture, and this effect was inhibited by neutralizing Abs to the IL-10R. To confirm that an autoreactive repertoire was expanded after SEB priming, we used CBA/J mice (Mls-1a) in which autoreactive T cells recognizing the endogenous viral superantigen are depleted (Vbeta6, 7, 8.1 TCR-bearing cells). However, SEB rescued these autoreactive T cell repertoires. Adding anti-MHC class II Ab blocked the autoreactive response. SEB-primed splenic or colonic T cells also induced apoptosis in syngeneic intestinal epithelial cells that was blocked significantly by IL-10. Thus, microbial Ags have the potential to abrogate self tolerance by stimulating autoreactive T cells that become cytolytic to target cells. IL-10 plays a protective role in maintaining self tolerance after microbial stimulation by preventing the activation of T cells that contribute to epithelial cell damage.

Animals↗
PubMed2000

Expression of IL-10 receptors on epithelial cells from the murine small and large intestine.

The appearance of chronic intestinal inflammation in IL-10 knockout mice suggests IL-10 may inhibit adverse responses to luminal antigen. Moreover, this inflammation is associated with an increase in class II MHC molecule expression on intestinal epithelial cells. Thus, the role of IL-10 regulation in epithelial cell function was investigated. Using RT-PCR, it was shown that intestinal epithelial cells express mRNA for both subunits of the IL-10 receptor-signaling complex. In addition, biotinylated IL-10 was shown to bind to both cultured and freshly isolated intestinal epithelial cells prepared from the small or large intestine. This binding appeared specific as it was blocked by neutralizing antibodies to IL-10 but not the isotype control. Moreover, an excess of native IL-10 also inhibited the binding of radiolabeled IL-10. To evaluate whether IL-10 mediated any functions through this receptor, epithelial cells were cultured with IL-10 alone or with IFN-gamma plus IL-10. IL-10 alone had no detectable effects on epithelial cell growth or their expression of class II MHC molecules but it did antagonize the effect of IFN-gamma on the viability of cultured cells. In addition, IL-10 blocked the IFN-gamma-induced expression of class II MHC molecules on cultured epithelial cells. These results suggest that IL-10 binds to a specific receptor on intestinal epithelial cells and may regulate the contribution of epithelial cells to the inflammatory and immune response in the digestive tract.

Animals↗
PubMed2000

Helicobacter pylori modulates lymphoepithelial cell interactions leading to epithelial cell damage through Fas/Fas ligand interactions.

Helicobacter pylori causes a common chronic infection of humans that leads to epithelial cell damage. Studies have shown that apoptosis of the gastric epithelium is increased during infection and this response is associated with an expansion of gastric T-helper type 1 (Th1) cells. We report that gastric T cells contribute to apoptosis of the epithelium by a Fas/Fas ligand (FasL) interaction. Fas receptor expression was detected on freshly isolated gastric epithelial cells by flow cytometry and immunohistochemistry, and this level of expression was increased during infection with H. pylori. The expression of Fas receptor on three gastric epithelial cell lines was increased by H. pylori, either alone or in combination with gamma interferon or tumor necrosis factor alpha. The role of Fas in apoptosis of gastric epithelial cell lines was evidenced by DNA fragmentation after cross-linking of Fas with specific antibodies. FasL expression was detected by immunohistochemistry on mononuclear cells in gastric biopsy specimens of infected but not uninfected subjects. Gastric T-cell lines were also shown to express FasL, as evidenced by reverse transcription-PCR and killing of target cells expressing Fas receptor. Moreover, these T-cell lines were capable of killing cultured gastric epithelial target cells and antibodies that block the interaction between Fas receptor and FasL inhibited this cytotoxic activity. These observations demonstrate that local Th1 cells may contribute to the pathogenesis of gastric disease during H. pylori infection by increasing the expression of Fas on gastric epithelial cells and inducing apoptosis through Fas/FasL interactions.

Adult↗
PubMed2000

The disease spectrum of Helicobacter pylori: the immunopathogenesis of gastroduodenal ulcer and gastric cancer.

Helicobacter pylori is a gram-negative bacterium that resides under microaerobic conditions in a neutral microenvironment between the mucus and the superficial epithelium of the stomach. From this site, it stimulates cytokine production by epithelial cells that recruit and activate immune and inflammatory cells in the underlying lamina propria, causing chronic, active gastritis. Although epidemiological evidence shows that infection generally occurs in children, the inflammatory changes progress throughout life. H. pylori has also been recognized as a pathogen that causes gastroduodenal ulcers and gastric cancer. These more severe manifestations of the infection usually occur later in life and in a minority of infected subjects. To intervene and protect those who might be at greatest risk of the more severe disease outcomes, it is of great interest to determine whether bacterial, host, or environmental factors can be used to predict these events. To date, several epidemiological studies have attempted to define the factors affecting the transmission of H. pylori and the expression of gastroduodenal disease caused by this infection. Many other laboratories have focused on identifying bacterial factors that explain the variable expression of clinical disease associated with this infection. An alternative hypothesis is that microorganisms that cause lifelong infections can ill afford to express virulence factors that directly cause disease, because the risk of losing the host is too great. Rather, we propose that gastroduodenal disease associated with H. pylori infection is predominantly a result of inappropriately regulated gastric immune responses to the infection. In this model, the interactions between the immune/inflammatory response, gastric physiology, and host repair mechanisms would dictate the disease outcome in response to infection.

Adenocarcinoma↗
PubMed2000

Preventive and therapeutic vaccines against Helicobacter pylori: current status and future challenges.

Approximately 50% of humanity is infected with Helicobacter pylori. Normally, this is a life-long infection indicating that the host response to natural infection fails to yield protective immunity. Moreover, the chronic inflammatory response associated with this infection can contribute to tissue damage and the pathogenesis of gastroduodenal disease including atrophic gastritis, peptic ulcer and gastric cancer. These damaging immune responses are attributed to a subset of helper T cells, so-called Th1 cells, that enhance cell-mediated immunity and induce damage to the gastric epithelium. Thus, it is desirable to have effective vaccines that could prevent and cure infection or at least, modify the host response in a manner that prevents immune-mediated disease. Using animal models as a tool to understand the immunobiology of Helicobacter infections, several investigators have shown that effective vaccines can be developed. Thus, prophylactic and even therapeutic vaccines have been described in various animal models. The basis for the effectiveness of these vaccines seems to be found in their ability to alter the gastric immune response, perhaps away from a homogeneous Th1 response towards a mixed Th1 and Th2 response. Using these encouraging approaches, vaccines are being developed for use in humans for the treatment and prevention of H. pylori infection and the gastroduodenal diseases associated with this infection.

Autoimmunity↗
PubMed1999

Antigen-specific T cell activation and proliferation during oral tolerance induction.

One of several routes of achieving immunologic tolerance is through functional inactivation of Ag-specific T cells. Oral administration of Ag can allow survival of the Ag-specific T cells that are functionally anergic. The aim of this study was to investigate whether functional inactivation of Ag-specific T cells is directed through an activation process and to further define the differentiative pathways and functional characteristics of anergic T cells. Mice were transplanted with OVA-specific TCR-transgenic T cells and either fed OVA or immunized s.c. with the OVA peptide 323-339 in CFA. OVA-specific T cells from OVA-fed mice were unresponsive to restimulation in vitro within 48-72 h after treatment. In vivo, however, T cell proliferation was detected by 5, 6-carboxy-succinimidyl-fluoresceine-ester intensity changes in OVA-specific T cells. The mesenteric lymph nodes (LNs) from OVA-fed mice more frequently contained OVA-specific dividing cells in vivo than those in the peripheral LNs, and the reciprocal was observed following s.c. immunization of the OVA peptide in CFA. The induction of anergy in OVA-fed mice was accompanied by rapid up-regulation of CD69 and CTLA-4, later down-regulation of CD45RB on OVA-specific T cells, and a marked decrease in T cell secretion of IL-2, IL-10, and IFN-gamma after OVA restimulation in vitro. Results from this study indicate that the inductive phase of oral tolerance is preceded by Ag-specific T cell activation in vivo, proliferation in the regional draining LNs, and differentiation into a memory-like state. These results indicate that Ag-directed differentiation occurs as a part of T cell tolerance through anergy.

Administration, Oral↗
PubMed1999

Expression of the neutrophil chemokine KC in the colon of mice with enterocolitis and by intestinal epithelial cell lines: effects of flora and proinflammatory cytokines.

IL-10 plays an important role in preventing excessive inflammation to the normal flora in the intestinal lumen. The purpose of this study was to compare the effect of normal flora on inflammation in mice in which the IL-10 gene was disrupted. IL-10 knock-out mice housed in germfree conditions remained healthy while those housed in conventional conditions developed colitis after weaning, suggesting that IL-10 inhibits the adverse responses to luminal Ag. Crypt abscesses were present in virtually all of the diseased animals as evidenced by flattening of the epithelial cells and a large number of neutrophils in the lumen of the crypt. Since KC is a chemokine that is capable of recruiting neutrophils in mice, mRNA and protein for KC was measured. Increased levels of both KC mRNA and protein were detected in the colon of diseased mice. To determine whether the epithelial cells were capable of synthesizing KC and contributing to neutrophil accumulation in the crypts, a murine intestinal epithelial cell line (Mode-K) was shown to express mRNA and protein for KC. Two cytokines induced in association with colitis in these mice, TNF-alpha and IFN-gamma, increased the expression of KC mRNA and protein in murine epithelial cells. However, IL-10 was incapable of decreasing the induction of KC, even though the cells expressed the IL-10 receptor. These results suggest that the neutrophil chemokine KC is produced by gastrointestinal epithelial cells in response to inflammatory mediators that are expressed following exposure to normal flora in animals lacking IL-10.

Age Factors↗
PubMed1999

Regulation of the mucosal immune response.

Infectious diseases continue to exact an extensive toll on populations living closest to the equatorial regions of the globe. A substantial proportion of these infections gain access to the host via the mucosal tissues. Thus, the development of new vaccines that enhance mucosal immunity is considered to be of paramount importance in order to prevent or limit the impact of these infections. Mucosal immune responses must discriminate between commensal flora within the lumen and potential pathogens. These responses are highly adapted to induce protection without excessive amounts of inflammation. The balances that regulate mucosal immune and inflammatory responses have to be understood if effective mucosal immunity is to be induced through local immunization. This review will summarize some of the unique properties of mucosal immune responses and focus on recent advances that have significantly influenced our understanding of the regulation of immune and inflammatory responses following infection.

Animals↗
PubMed1998

The effect of class II major histocompatibility complex expression on adherence of Helicobacter pylori and induction of apoptosis in gastric epithelial cells: a mechanism for T helper cell type 1-mediated damage.

Helicobacter pylori infection is associated with gastric epithelial damage, including apoptosis, ulceration, and cancer. Although bacterial factors and the host response are believed to contribute to gastric disease, no receptor has been identified that explains how the bacteria attach and signal the host cell to undergo apoptosis. Using H. pylori as "bait" to capture receptor proteins in solubilized membranes of gastric epithelial cells, class II major histocompatibility complex (MHC) molecules were identified as a possible receptor. Signaling through class II MHC molecules leading to the induction of apoptosis was confirmed using cross-linking IgM antibodies to surface class II MHC molecules. Moreover, binding of H. pylori and the induction of apoptosis were inhibited by antibodies recognizing class II MHC. Since type 1 T helper cells are present during infection and produce interferon (IFN)-gamma, which increases class II MHC expression, gastric epithelial cell lines were exposed to H. pylori in the presence or absence of IFN-gamma. IFN-gamma increased the attachment of the bacteria as well as the induction of apoptosis in gastric epithelial cells. In contrast to MHC II-negative cell lines, H. pylori induced apoptosis in cells expressing class II MHC molecules constitutively or after gene transfection. These data describe a novel receptor for H. pylori and provide a mechanism by which bacteria and the host response interact in the pathogenesis of gastric epithelial cell damage.

Animals↗
PubMed1998

Cytokine modulation of human corneal epithelial cell ICAM-1 (CD54) expression.

To determine whether pro-inflammatory cytokines modulate intercellular adhesion molecule-1 (ICAM-1; CD54) expression on cultured primary human corneal epithelial cells (HCEs), confluent HCEs were treated with various concentrations of interferon-gamma(IFN-gamma), interleukin-1alpha(IL-1alpha), IL-1beta, IL-4, tumor necrosis factor-alpha (TNF-alpha), or combinations over time. ICAM-1 expression was measured by flow cytometry and/or a cell-based ELISA using a monoclonal mouse anti-human CD54 antibody. The apparent MW of ICAM-1 protein was determined by immunoprecipitation of biotinylated HCEs. RT-PCR was used to detect ICAM-1 RNA. The mature cell surface form of HCE ICAM-1 was approximately 110 kDa as determined by immunoprecipitation. IFN-gammaand TNF-alpha induced both dose- and time-dependent increases in ICAM-1 expression. An approximately 20-fold increase in ICAM-1 was seen at 50-100 U IFN-gamma ml-1. ICAM-1 specific mRNA accumulated approximately 4.5-fold after IFN-gammatreatment. TNF-alpha(100 U ml-1) induced a consistent approximately 6.0-fold increase in ICAM-1 expression. When IFN-gammaand TNF-alpha were mixed, at sub-optimal concentrations of each, a synergistic effect on ICAM-1 expression was not detected. Neither IL-4, IL-1alpha nor IL-1beta affected ICAM-1 expression in a consistent fashion. In summary, ICAM-1 was modulated on primary human corneal epithelial cells by the cytokines IFN-gamma and TNF-alpha in a dose- and time-dependent fashion. Cytokine modulation of corneal epithelial cell ICAM-1 during inflammation may contribute to corneal epithelial cell injury by aiding the attachment of inflammatory cells such as eosinophils which express the receptor for ICAM-1, the beta2 integrins (CD11a,b,c/CD18).

Cell Culture Techniques↗
PubMed1998

Rotavirus infection of cultured intestinal epithelial cells induces secretion of CXC and CC chemokines.

BACKGROUND & AIMS: Rotaviruses are the major cause of pediatric gastroenteritis worldwide. The target cell of rotavirus infection is the mature enterocyte of the small intestine. Recently, intestinal epithelial cells have been shown to produce chemoattractant mediators in response to cytokine stimulation and bacterial infection, suggesting a potentially important role of epithelial cells in initiating immune responses. In this study, the production of chemokines by cultured intestinal epithelial cells after rotavirus infection was investigated. METHODS: Two human intestinal epithelial cell lines (HT29 and Caco-2) were infected with sucrose-purified rotavirus (strain SA114F) and assayed by reverse-transcription polymerase chain reaction and enzyme-linked immunosorbent assay for chemokine expression. Virus-like particles and inactivated rotavirus were used to test the importance of viral attachment and replication. RESULTS: Increased messenger RNA expression and secretion of immunoreactive interleukin 8, growth-related peptide alpha, and RANTES (regulated upon activation, normal T cell expressed and secreted) were detected in rotavirus-infected cells. Chemokine production was time and dose dependent and required viral replication. CONCLUSIONS: Rotavirus infection induces the expression of a subset of chemokines in intestinal epithelial cells. These data support the hypothesis that chemokine secretion by enterocytes may play a role in the initiation and modulation of the immune response to rotavirus infection.

Chemokine CCL5↗
PubMed1998

Lymphocytes in the human gastric mucosa during Helicobacter pylori have a T helper cell 1 phenotype.

BACKGROUND & AIMS: Studies have shown that gastric T cells are increased during Helicobacter pylori infection. The purpose of this study was to characterize the human gastric T-cell responses in the presence or absence of H. pylori. METHODS: T-cell surface antigens were examined by immunohistochemistry or after isolation for evaluation of surface antigens and cytoplasmic cytokines using flow cytometry. RESULTS: CD4+ and CD8+ T cells were increased in situ during infection with H. pylori. Freshly isolated gastric T cells expressed cytoplasmic interferon gamma (IFN-gamma) and interleukin (IL)-2 after a brief stimulation. Simultaneous four-color flow cytometry demonstrated that both CD8+ and CD4+ T cells expressed IFN-gamma. Because stimulation through CD30 favors the induction of IL-5 and Th2 cells, gastric and colonic T cells were examined for CD30 expression. Consistent with the notion that Th2 cells are found in the intestine, CD30 was evident throughout the lamina propria of the colon but was virtually absent in the stomach. Furthermore, freshly isolated gastric T cells produced little IL-4 and virtually no IL-5 or tumor necrosis factor beta. CONCLUSIONS: These observations show that gastric T cells resemble the Th1 type, which may explain their failure to induce immunity to H. pylori and their ability to contribute to the pathogenesis of gastric disease.

Adult↗
PubMed1998

Recombinant Helicobacter pylori urease activates primary mucosal macrophages.

Helicobacter pylori urease is absorbed into the gastric mucosa at sites of inflammation, but whether the enzyme activates mucosal macrophages is not known. Because mucosal macrophages differ phenotypically and functionally from blood monocytes, whether recombinant H. pylori urease (rUrease) activated purified lamina propria macrophages in vitro was investigated. rUrease (1-10 microgram/mL) induced primary mucosal macrophages to produce interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha but not IL-8 proteins in a dose-dependent manner (P<.05 to P<.001). Quantitative reverse transcriptase-polymerase chain reaction using capillary electrophoresis laser-induced fluorescence showed that rUrease (0.1-10 microgram/mL) also induced dose-dependent expression of IL-1beta, IL-6, and TNF-alpha but not IL-8 mRNA (P<.05), suggesting that rUrease-induced production of certain cytokines is regulated at the level of gene transcription. These findings indicate that the ability of H. pylori urease to activate mucosal macrophages, resulting in production of proinflammatory cytokines, may be involved in the pathogenesis of H. pylori-associated mucosal inflammation.

Helicobacter pylori↗