Suppression of human mononuclear cell response by Helicobacter pylori: effects on isolated monocytes and lymphocytes

Historical and Molecular Perspectives on the Presence of Helicobacter pylori in Latin America: A Niche to Improve Gastric Cancer Risk Assessment

Helicobacter pylori (H. pylori) is responsible for causing chronic gastritis, which can cause peptic ulcer and premalignant lesions such as atrophic gastritis, intestinal metaplasia, and dysplasia, with the risk of developing gastric cancer. Recent data describe that H. pylori colonizes the gastric mucosa of more than 50% of the world's population; however, this bacterium has been described as infecting the human population since its prehistory. This review focuses on the populations and subpopulations of H. pylori, differentiated by the polymorphisms present in their constitutive and virulence genes. These genes have spread and associated with different human populations, showing variability depending on their geographical distribution, and have evolved together with the human being. The predominant genotypes worldwide, Latin America and Chile, are described to understand the genetic diversity and pathogenicity of H. pylori in different populations and geographic regions. The high similarity in the sequence of virulence genes between H. pylori strains present in Peruvian and Spanish natives in Latin America suggests a European influence. The presence of cagA-positive strains and vacA s1 m1 allelic variants is observed with greater prevalence in Chilean patients with more severe gastrointestinal diseases and is associated with its geographical distribution. These findings highlight the importance of understanding the genetic diversity of H. pylori in different regions of the world for a more accurate assessment of the risk of associated diseases and their potential impact on health.

Current status and future potential of predictive biomarkers for immune checkpoint inhibitors in gastric cancer

Immunotherapy is revolutionising cancer treatment and has already emerged as standard treatment for patients with recurrent or metastatic gastric cancer (GC). Recent research has been focused on identifying robust predictive biomarkers for GC treated with immune checkpoint inhibitors (ICIs). The expression of programmed cell death protein-ligand-1 (PD-L1) is considered a manifestation of immune response evasion, and several studies have already reported the potential of PD-L1 expression as a predictive parameter for various human malignancies. Meanwhile, based on comprehensive molecular characterisation of GC, testing for Epstein-Barr virus and microsatellite instability is a potential predictive biomarker. Culminating evidence suggests that novel biomarkers, such as the tumour mutational burden and gene expression signature, could indicate the success of treatment with ICIs. However, the exact roles of these biomarkers in GC treated with ICIs remain unclear. Therefore, this study reviews recent scientific data on current and emerging biomarkers for ICIs in GC, which have potential to improve treatment outcomes.

Current and Future Aspects of Immunotherapy for Esophageal and Gastric Malignancies

Esophagogastric (EG) cancer has a poor prognosis despite the use of standard therapies, such as chemotherapy and biologic agents. Recently, immune checkpoint inhibitors (ICIs) have been introduced as treatments for EG cancer; nivolumab and pembrolizumab have been approved in the United States and Europe to treat advanced EG cancer. Other ICIs, such as avelumab, durvalumab, ipilimumab, and tremelimumab, have been evaluated in several trials, although their roles are still not established in clinical practice. In addition, preclinical evidence suggests that combining an ICI with a tumor-targeting antibody can result in greater antitumor effects in metastatic EG cancer. There are not yet validated predictive biomarkers to identify which patients will respond best to ICI treatment. PD-L1 expression may predict intensity of response, although PD-L1-negative patients can still respond to ICIs. Despite differences in PD-L1 expression between Asian and non-Asian populations, no geographic differences in rates of treatment-related or immune-mediated/infusion-related adverse events have been reported. Also, several trials are currently evaluating combinations of ICIs, standard chemotherapy, and biologic agents as well as novel biomarkers to improve treatments and outcomes. Our review will address the current use of and evidence for ICIs for advanced EG cancer treatment and future trends in this area for clinical practice.

The role of Helicobacter pylori LPS in the pathogenesis of H. pylori-related gastropathy

Helicobacter pylori strains and/or their lipopolysaccharides (LPS) represent the trigger of different regional and systemic immune responses in the course of H. pylori-related gastropathy as indicated by the following: (i) in patients with chronic gastritis (CG) or duodenal ulcer (DU), eradication of H. pylori leads to a dramatic decrease of gastric mucosal content of various cytokines such as interleukin-1β and transforming growth factor-β1; (ii) gastric epithelial cells are activated by H. pylori organisms through tyrosine phosphorylation signaling events but H. pylori LPSs do not affect this signal transduction pathway; and (iii) in sera from patients with CG and DU, besides antibodies to S-form LPS, humoral IgG and IgA response against R-form LPS has been also detected. On the other hand, antibodies against synthetic polymeric Lewisx were found in a few patients with CG and in no patients with DU.

Vector-encoded Helicobacter pylori neutrophil-activating protein promotes maturation of dendritic cells with Th1 polarization and improved migration

Helicobacter pylori neutrophil-activating protein (HP-NAP) is a major virulence factor involved in H. pylori infection. Both HP-NAP protein and oncolytic viruses encoding HP-NAP have been suggested as immunotherapeutic anticancer agents and adjuvants for vaccination but with little known about its mode of action to activate adaptive immunity. Dendritic cells (DCs) are key players in bridging innate and adaptive immune responses, and in this study we aim to evaluate the effect of HP-NAP on DC maturation, migration, and induction of adaptive immune response. Maturation markers CD83, CD80, CD86, HLA-DR, CD40, and CCR7 were upregulated on human DCs after treatment with supernatants from HP-NAP adenovirus-infected cells. HP-NAP-activated DCs had a Th1 cytokine secretion profile, with high IL-12 and relatively low IL-10 secretion, and migrated toward CCL19. Ag-specific T cells were efficiently expanded by Ag-presenting HP-NAP-activated DCs, which is an important property of functionally mature DCs. Furthermore, intradermal injections of HP-NAP-encoding adenovirus in C57BL/6 mice enhanced resident DC migration to draining lymph nodes, which was verified by imaging lymph nodes by two-photon microscopy and by phenotyping migrating cells by flow cytometry. In conclusion, therapeutic effects of HP-NAP are mediated by maturation of DCs and subsequent activation of Ag-specific T cells in addition to provoking innate immunity.

Virulence factors of Helicobacter pylori vacA increase markedly gastric mucosal TGF-β1 mRNA expression in gastritis patients

OBJECTIVE

Helicobacter pylori (H. pylori) infection is the main cause of gastric inflammation. Regulatory T cells (Treg cells) suppress the activation and proliferation of antigen-specific T cells and mediate immunologic tolerance. TGF-β1 was shown to be secreted in a subset of Treg cells known as 'Th3 cells'. These cells have not been sufficiently studied in context to H. pylori-induced inflammation in human gastric mucosa. In this study we therefore, aimed to investigate the expression of TGF-β1 in the context of H. pylori colonization in chronic gastritis, to examine the relationship between it and histopathologic findings and to compare it with virulence factors.

PATIENTS AND METHODS

Total RNA was extracted from gastric biopsies of 48 H. pylori-infected patients and 38 H. pylori-negative patients with gastritis. Mucosal TGF-β1 mRNA expression in H. pylori-infected and uninfected gastric biopsies was determined by real-time PCR. Presence of vacA, cagA, iceA, babA2 and oipA virulence factors was evaluated using PCR.

RESULTS

TGF-β1 mRNA expression was significantly increased in biopsies of H. pylori-infected patients compared to H. pylori-uninfected patients. There was association between virulence factors and TGF-β1 mRNA expression. TGF-β1 mRNA expression in mucosa was significantly higher in patients with vacA s1 and s1m1.

CONCLUSIONS

TGF-β1 may play an important role in the inflammatory response and promote the chronic and persistent inflammatory changes in the gastric. This may ultimately influence the outcome of H. pylori-associated diseases that arise within the context of gastritis and vacA may suffice to induce expression of TGF-β1 mRNA.

The number of Foxp3-positive regulatory T cells is increased in Helicobacter pylori gastritis and gastric cancer

Helicobacter pylori (H. pylori) colonization induces vigorous innate and specific immune responses; however, the infection is not removed, a state of chronic active gastritis persists for life if untreated. Recent studies have shown that CD4(+) CD25(+) Foxp3-positive regulatory T cells (Tregs) suppress the immune response to H. pylori. Persistent H. pylori-associated gastritis is closely associated with gastric carcinogenesis. We investigated the number of Tregs in the context of H. pylori colonization in chronic gastritis, examined the relationship between it and histopathological findings and compared it with that of gastric dysplasia and adenocarcinoma. This study was based on the analysis of gastric biopsy specimens from 126 cases of H. pylori-associated gastritis, 16 cases of H. pylori-negative gastritis, 17 cases of gastric dysplasia, and 25 cases of gastric adenocarcinoma. The number of Tregs was elevated in H. pylori-associated gastritis, where it was positively correlated with the grade of chronic inflammation and the number of lymphoid follicles. It was significantly elevated in adenocarcinomas compared to chronic gastritis and gastric dysplasia. In summary, the number of Tregs is increased in H. pylori-associated gastritis and gastric cancer.

A vaccine against Helicobacter pylori: towards understanding the mechanism of protection

Helicobacter pylori infection remains a significant global public health problem. Vaccine development against this infection appears to be feasible but has not yet delivered its promise in clinical trials. Efforts to improve current vaccination strategies would greatly benefit from a better molecular understanding of the mechanism of protection. Here, we review recent developments in this field.

Expression of the programmed death ligand 1, B7-H1, on gastric epithelial cells after Helicobacter pylori exposure promotes development of CD4+ CD25+ FoxP3+ regulatory T cells

During Helicobacter pylori infection, T cells are recruited to the gastric mucosa, but the host T-cell response is not sufficient to clear the infection. Some of the recruited T cells respond in a polarized manner to a Th1 response, while others become anergic. We have previously shown that T-cell anergy may be induced during infection by the interaction of T cells with B7-H1, which is up-regulated on the gastric epithelium during H. pylori infection. Recently, regulatory T (Treg) cells with a CD4(+) CD25(high) FoxP3(+) phenotype were found at an increased frequency in the gastric mucosa of biopsy specimens from H. pylori-infected patients. While Treg cells are important in maintaining tolerance, they can also suppress immune responses during infection. In this study, we examined the induction of the Treg phenotype when naïve T cells were incubated with gastric epithelial cells exposed to H. pylori. The frequency of this phenotype was markedly decreased when B7-H1 was blocked with monoclonal antibodies or its expression was blocked with small interfering RNA. The functional role of these Treg cells was assessed in proliferation assays when the cells were cocultured with activated T cells, which effectively decreased proliferation of the cells.

VacA-associated inhibition of T-cell function: reviewed and reconsidered

Chronic Helicobacter pylori infection is characterized by dense infiltration of the mucosa with neutrophilic granulocytes, lymphocytes, and monocytes/macrophages. Among these different cell types, T-lymphocytes are the most intriguing and crucial cells for the elimination of the bacteria. Previous studies have elucidated possible mechanisms on how bacteria could interfere with the human immune response and claimed that especially the secreted vacuolating toxin VacA may be responsible for the chronic persistence of the bacteria. Some of these results have to be interpreted with caution and may just describe in vitro phenomena; others may reveal promising facts.

Expression of B7-H1 on gastric epithelial cells: its potential role in regulating T cells during Helicobacter pylori infection

Helicobacter pylori infection is associated with gastritis, ulcers, and gastric cancer. The infection becomes chronic as the host response is unable to clear it. Gastric epithelial cells (GEC) play an important role during the host response, and their expression of class II MHC and costimulatory molecules such as CD80 and CD86 suggests their role in local Ag presentation. Although T cells are recruited to the infected gastric mucosa, they have been reported to be hyporesponsive. In this study, we detected the expression of B7-H1 (programmed death-1 ligand 1), a member of B7 family of proteins associated with T cell inhibition on GEC. Quantitative real-time RT-PCR revealed that B7-H1 expression increased significantly on GEC after H. pylori infection. Western blot analysis showed that B7-H1 expression was induced by various H. pylori strains and was independent of H. pylori virulence factors such as Cag, VacA, and Urease. The functional role of B7-H1 in the cross talk between GEC and T cells was assessed by coculturing GEC or H. pylori-infected GEC with CD4+ T cells isolated from peripheral blood. Using blocking Abs to B7-H1 revealed that B7-H1 was involved in the suppression of T cell proliferation and IL-2 synthesis, and thus suggested a role for B7-H1 on the epithelium as a contributor in the chronicity of H. pylori infection.

Impact of Helicobacter pylori virulence factors and compounds on activation and maturation of human dendritic cells

Recently, we and others have shown that Helicobacter pylori induces dendritic cell (DC) activation and maturation. However, the impact of virulence factors on the interplay between DCs and H. pylori remains elusive. Therefore, we investigated the contribution of cag pathogenicity island (PAI) and VacA status on cytokine release and up-regulation of costimulatory molecules in H. pylori-treated DCs. In addition, to characterize the stimulatory capacity of H. pylori compounds in more detail, we studied the effect of formalin-inactivated and sonicated H. pylori, as well as secreted H. pylori molecules, on DCs. Incubation of DCs with viable or formalin-inactivated H. pylori induced comparable secretion of interleukin-6 (IL-6), IL-8, IL-10, IL-12, IL-1beta, and tumor necrosis factor (TNF). In contrast, IL-12 and IL-1beta release was significantly reduced in DCs treated with sonicated bacteria and secreted bacterial molecules. Treatment of sonicated H. pylori preparations with polymyxin B resulted in a significant reduction of IL-8 and IL-6 secretion, suggesting that H. pylori-derived lipopolysaccharide at least partially contributes to activation of immature DCs. In addition, the capacity of H. pylori-pulsed DCs to activate allogeneic T cells was not affected by cag PAI and VacA. Pretreatment of DC with cytochalasin D significantly inhibited secretion of IL-12, IL-1beta, and TNF, indicating that phagocytosis of H. pylori contributes to maximal activation of DCs. Taken together, our results suggest that DC activation and maturation, as well as DC-mediated T-cell activation, are independent of the cag PAI and VacA status of H. pylori.

A secreted low-molecular-weight protein from Helicobacter pylori induces cell-cycle arrest of T cells

BACKGROUND & AIMS

Although Helicobacter pylori is recognized by the human immune system, the bacteria are not eliminated and lead to a chronic inflammation of the gastric mucosa.

METHODS

We investigated the interaction of H. pylori with human lymphocytes. T and B lymphocytes were isolated from H. pylori-infected patients and stimulated with anti-CD3/CD28 or interleukin-6.

RESULTS

Proliferation of lymphocytes was abolished on co-incubation with different H. pylori strains (1-5 bacteria/cell) or with protein extracts of culture supernatants. Inhibition of proliferation was independent of known virulence factors. The factor is a protein or protein complex with an apparent molecular weight between 30 and 60 kilodaltons, clearly distinct from VacA. Although antigen-specific activation of T cells (as shown by nuclear factor of activated T cells [NFAT]-activation, interferon-gamma production, and CD25 or CD69 up-regulation) remained intact, cell-cycle analysis showed that S-phase entry of T cells was inhibited completely by H. pylori. Consequently, stimulated T cells arrested in the G1 phase of the cell cycle. Western blot analysis showed markedly reduced phosphorylation of the retinoblastoma protein (pRb), suggesting inhibition of G1 cyclin-dependent kinase activity. In line with this, activities of cyclin D3 and cyclin E were down-regulated, and levels of the cyclin-dependent kinase inhibitor p27Kip1 were increased. Mouse embryonic fibroblasts deficient in p27 showed a decrease in H. pylori-induced inhibition of cell proliferation, suggesting a central role for p27 in mediating H. pylori-induced G1 arrest.

CONCLUSIONS

Induction of cell-cycle arrest in lymphocytes may be of major significance for the chronic persistence of bacteria in the human stomach.

Persistent bacterial infections: the interface of the pathogen and the host immune system

Persistent bacterial infections involving Mycobacterium tuberculosis, Salmonella enterica serovar Typhi (S. typhi) and Helicobacter pylori pose significant public-health problems. Multidrug-resistant strains of M. tuberculosis and S. typhi are on the increase, and M. tuberculosis and S. typhi infections are often associated with HIV infection. This review discusses the strategies used by these bacteria during persistent infections that allow them to colonize specific sites in the host and evade immune surveillance. The nature of the host immune response to this type of infection and the balance between clearance of the pathogen and avoidance of damage to host tissues are also discussed.

Induction of maturation and cytokine release of human dendritic cells by Helicobacter pylori

Helicobacter pylori causes a persistent infection in the human stomach, which can result in chronic gastritis and peptic ulcer disease. Despite an intensive proinflammatory response, the immune system is not able to clear the organism. However, the immune escape mechanisms of this common bacterium are not well understood. We investigated the interaction between H. pylori and human dendritic cells. Dendritic cells (DCs) are potent antigen-presenting cells and important mediators between the innate and acquired immune system. Stimulation of DCs with different concentrations of H. pylori for 8, 24, 48, and 72 h resulted in dose-dependent interleukin-6 (IL-6), IL-8, IL-10 and IL-12 production. Lipopolysaccharide (LPS) from Escherichia coli, a known DC maturation agent, was used as a positive control. The cytokine release after stimulation with LPS was comparable to that induced by H. pylori except for IL-12. After LPS stimulation IL-12 was only moderately released compared to the large amounts of IL-12 induced by H. pylori. We further investigated the potential of H. pylori to induce maturation of DCs. Fluorescence-activated cell sorting analysis of cell surface expression of maturation marker molecules such as CD80, CD83, CD86, and HLA-DR revealed equal upregulation after stimulation with H. pylori or LPS. We found no significant differences between H. pylori seropositive and seronegative donors of DCs with regard to cytokine release and upregulation of surface molecules. These data clearly demonstrate that H. pylori induces a strong activation and maturation of human immature DCs.

Helicobacter pylori arginase inhibits T cell proliferation and reduces the expression of the TCR zeta-chain (CD3zeta)

Helicobacter pylori infects approximately half the human population. The outcomes of the infection range from gastritis to gastric cancer and appear to be associated with the immunity to H. pylori. Patients developing nonatrophic gastritis present a Th1 response without developing protective immunity, suggesting that this bacterium may have mechanisms to evade the immune response of the host. Several H. pylori proteins can impair macrophage and T cell function in vitro through mechanisms that are poorly understood. We tested the effect of H. pylori extracts and live H. pylori on Jurkat cells and freshly isolated human normal T lymphocytes to identify possible mechanisms by which the bacteria might impair T cell function. Jurkat cells or activated T lymphocytes cultured with an H. pylori sonicate had a reduced proliferation that was not caused by T cell apoptosis or impairment in the early T cell signaling events. Instead, both the H. pylori sonicate and live H. pylori induced a decreased expression of the CD3zeta-chain of the TCR. Coculture of live H. pylori with T cells demonstrated that the wild-type strain, but not the arginase mutant rocF(-), depleted L-arginine and caused a decrease in CD3zeta expression. Furthermore, arginase inhibitors reversed these events. These results suggest that H. pylori arginase is not only important for urea production, but may also impair T cell function during infection.

Novel activities of the Helicobacter pylori vacuolating cytotoxin: from epithelial cells towards the immune system

H. pylori has developed a unique set of virulence factors, which allow its survival in a unique ecological niche, the human stomach. The vacuolating cytotoxin (VacA) and the cytotoxin-associated antigen (CagA) are major bacterial factors involved in modulating the host. VacA, so far mainly regarded as a cytotoxin for the gastric epithelial cell layer, apparently has profound effects in modulating the immune response. In this review we discuss some of the classical effects of VacA, such as cell vacuolation, and compare them with more recently identified mechanisms of VacA on immune cells.

The Helicobacter pylori vacuolating cytotoxin: from cellular vacuolation to immunosuppressive activities

Helicobacter pylori is a highly successful bacterial pathogen of humans, infecting the stomach of more than half of the world's population. The H. pylori infection results in chronic gastritis, eventually followed by peptic ulceration and, more rarely, gastric cancer. H. pylori has developed a unique set of virulence factors, actively supporting its survival in the special ecological niche of the human stomach. Vacuolating cytotoxin (VacA) and cytotoxin-associated antigen A (CagA) are two major bacterial virulence factors involved in host cell modulation. VacA, so far mainly regarded as a cytotoxin of the gastric epithelial cell layer, now turns out to be a potent immunomodulatory toxin, targeting the adapted immune system. Thus, in addition to the well-known vacuolating activity, VacA has been reported to induce apoptosis in epithelial cells, to affect B lymphocyte antigen presentation, to inhibit the activation and proliferation of T lymphocytes, and to modulate the T cell-mediated cytokine response.

Helicobacter pylori vacuolating cytotoxin inhibits T lymphocyte activation

Helicobacter pylori (Hp) vacuolating cytotoxin VacA induces cellular vacuolation in epithelial cells. We found that VacA could efficiently block proliferation of T cells by inducing a G1/S cell cycle arrest. It interfered with the T cell receptor/interleukin-2 (IL-2) signaling pathway at the level of the Ca2+-calmodulin-dependent phosphatase calcineurin. Nuclear translocation of nuclear factor of activated T cells (NFAT), a transcription factor acting as a global regulator of immune response genes, was abrogated, resulting in down-regulation of IL-2 transcription. VacA partially mimicked the activity of the immunosuppressive drug FK506 by possibly inducing a local immune suppression, explaining the extraordinary chronicity of Hp infections.

Helicobacter pylori organisms induce expression of activation and apoptotic surface markers on human lymphocytes and AGS cells: a cytofluorimetric evaluation

Human peripheral blood mononuclear cells (PBMCs) were treated with Helicobacter pylori (Hp) organisms alone or with Hp-stimulated AGS cells (a gastric adenocarcinoma cell line). Hp organisms were able per se to increase the percentage of CD8 +/- CD95 +/- cells, while number of CD25+ cells and HLA-DR molecule expression increased following pretreatment with Hp-stimulated AGS cells. A comparison was made with a test system in which PBMCs were stimulated with Escherichia coli (Ec) organisms and colo-cells (a colon carcinoma cell line). In this case, CD95+ cells and CD25+ cells increased when the combination Ec organisms/colo-cells was present in the culture. On the other hand, Hp bacteria in combination with colo-cells were not able to induce activation and/or apoptotic surface markers on PBMCs, while Ec-stimulated AGS cells increased the expression of CD95 on PBMC. Finally, the direct interaction of AGS cells with Hp was able to induce higher expression of CD95 on gastric epithelial cells than Hp-stimulated PBMCs. Taken together, these data support the interplay between bacteria and epithelial cells in the course of Hp-mediated gastropathy.

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.

Modulation of innate cytokine responses by products of Helicobacter pylori

The gastric inflammatory and immune response in Helicobacter pylori infection may be due to the effect of different H. pylori products on innate immune mechanisms. The aim of this study was to determine whether bacterial components could modulate cytokine production in vitro and thus contribute to Th1 polarization of the gastric immune response observed in vivo. The effect of H. pylori recombinant urease, bacterial lysate, intact bacteria, and bacterial DNA on proliferation and cytokine production by peripheral blood mononuclear cells (PBMCs) from H. pylori-negative donors was examined as a model for innate cytokine responses. Each of the different H. pylori preparations induced gamma interferon (IFN-gamma) and interleukin-12p40 (IL-12p40), but not IL-2 or IL-5, production, and all but H. pylori DNA stimulated release of IL-10. Addition of anti-IL-12 antibody to cultures partially inhibited IFN-gamma production. In addition, each bacterial product inhibited mitogen-stimulated IL-2 production by PBMCs and Jurkat T cells. The inhibitory effect of bacterial products on IL-2 production correlated with inhibition of mitogen-stimulated lymphocyte proliferation, although urease inhibited IL-2 production without inhibiting proliferation, suggesting that inhibition of IL-2 production alone is not sufficient to inhibit lymphocyte proliferation. The results of these studies demonstrate that Th1 polarization of the gastric immune response may be due in part to the direct effects of multiple different H. pylori components that enhance IFN-gamma and IL-12 production while inhibiting both IL-2 production and cell proliferation that may be necessary for Th2 responses.

Inhibition of mitogen-induced murine lymphocyte proliferation by Helicobacter pylori cell-free extract

BACKGROUND AND AIMS

Previous studies have shown that lysates of Helicobacter pylori inhibit mitogen-induced proliferation of human peripheral blood mononuclear cells. The objective of the present study was to determine whether H. pylori cell-free extract (HPCE) has similar effects on murine lymphoid cells and could, therefore, be used to further delineate the mechanisms of alteration of lymphocyte function by H. pylori.

METHODS

The HPCE was prepared from a H. pylori reference strain and from five clinical strains with varying status of cagA and vacA. Mouse splenic and mesenteric lymph node cells were cultured in microwell plates in the presence or absence of varying concentrations of HPCE (0.625-12.5 microg/mL). T cell mitogens were added into the culture 2 h later and the cells were cultured at 37 degrees C in 5% CO2 for a further 72 h. Cell proliferation was determined by a non-radioactive rapid dye assay and the percentage inhibition caused by HPCE was calculated.

RESULTS

Pre-exposure to HPCE significantly inhibited concanavalin A-induced proliferation of murine spleen and mesenteric lymph node cells (up to 100% inhibition; P < or = 0.01). The HPCE also inhibited lymphocyte proliferation stimulated by mitogens phorbol-myristate-acetate and ionomycin and by the anti-CD3epsilon monoclonal antibody (P < or = 0.05). The inhibition was dose-dependent, but independent of the presence of virulence genes cagA or vacA. Treatment of HPCE at 80 degrees C for 30 min, but not at 55 degrees C for 60 min, completely abolished its inhibitory action. The HPCE, pretreated with pronase E, proteinase K, trypsin, acid or alkali also completely lost its inhibitory effect (P < or = 0.01), while in contrast, treatment with carboxypeptidase and leucine aminopeptidase had no effect.

CONCLUSION

Helicobacter pylori produces heat-labile proteins or peptides that suppress T cell mitogen-induced proliferation of murine lymphoid cells in a similar manner to that observed with human peripheral blood mononuclear cells. The mouse cell culture system can, therefore, be used as a model to further study the mechanisms of action and antigen specificity of these immunomodulatory factors.

Epstein-barr virus-associated malignancies: epidemiologic patterns and etiologic implications

Epstein-Barr virus (EBV), a ubiquitous B-lymphotrophic herpesvirus, has been found in the tumor cells of a heterogeneous group of malignancies (Burkitt's lymphoma, lymphomas associated with immunosuppression, other non-Hodgkin's lymphomas, Hodgkin's disease, nasopharyngeal carcinoma, gastric adenocarcinoma, lymphoepithelioma-like carcinomas, and immunodeficiency-related leiomyosarcoma). As the epidemiologic characteristics of these cancers have not been considered together, this review seeks to relate their incidence patterns and risk factors to EBV biology and virus-host interaction in an attempt to help elucidate factors involved in EBV-related carcinogenesis. We include a brief review of EBV virology and primary infection to provide a biologic context for considering the epidemiology, summarize the most salient epidemiologic features of each malignancy, synthesize epidemiologic data by risk factor to uncover commonalities and informative contrasts across the diseases, and propose hypotheses regarding etiologic mechanisms, based on the possible effect of the risk factors at various stages in the viral life cycle.

Flow cytometric analysis of lymphocytes in cerebrospinal fluid in patients with tick-borne encephalitis

INTRODUCTION

Cerebrospinal fluid (CSF) lymphocyte subsets were examined by flow cytometry in 33 patients with tick-borne encephalitis (TBE) in order to determine their values.

PATIENTS AND METHODS

Lymphocytes were isolated from CSF and lymphocyte subsets were determined: lymphocytes T (CD3+), lymphocytes B (CD19+), NK cells (CD3-CD56+), helper T cells (CD3+CD4+) and cytotoxic T cells (CD3+CD8+). The expression of IL-2 receptors (CD25+) and transferrin receptors (CD71+) on T cells and HLA-DR molecules on T cell subsets was examined. Furthermore, possible relationships among different TBE patient population variables (gender, age, severity of disease, duration of meningitis) were considered.

RESULTS

The analyses of the CSF lymphocyte population subsets are presented. Lymphocytes T (CD3+) were significantly higher in the CSF than in the peripheral blood as was the case with the T cells that expressed transferrin receptors (CD71). Lymphocytes B (CD19+) and NK cells (CD3-CD56+) prevailed in the peripheral blood. In the early course of the disease, a higher expression of HLA-DR molecules on T lymphocytes was observed, while later a higher expression of IL-2 receptors (CD25+) was observed.

DISCUSSION

Significant differences in lymphocyte subsets between the CSF and the peripheral blood were found. Significant time-dependent changes of CSF lymphocyte subsets during course of infection were observed. The results of the present study give us deeper insight into CNS cellular immunopathogenic mechanisms in patients with TBE.

Partial characterization of a cell proliferation-inhibiting protein produced by Helicobacter pylori

Despite the induction of an immunological reaction, Helicobacter pylori-associated gastritis is a chronic disease, suggesting that this microbe can evade the host immune defense. Previous studies by our group showed that H. pylori suppresses the in vitro proliferative response of human mononuclear cells to mitogens and antigens. Here we demonstrate that the antiproliferative activity of H. pylori also affects the proliferation of various mammalian cell lines (U937, Jurkat, AGS, Kato-3, HEP-2, and P388D1). This effect is detectable in the first 16 h of incubation and maximal between 24 and 48 h. In addition, the presence of H. pylori significantly diminished the protein synthesis of cells in the first 6 h of incubation, comparable to the results with cycloheximide and diphtheria toxin. The urease enzyme, the cagA gene product, and the vacuolizing cytotoxin of H. pylori were excluded as causative agents of the antiproliferative effect by using isogenic knockout mutant strains. The inhibitory effect was not due to a lytic activity of this bacterium. The results reported here indicate that the responsible factor is a protein with an apparent native molecular mass of 100 +/- 10 kDa. Our work implicates the presence of a protein factor in H. pylori (termed PIP [for proliferation-inhibiting protein]) with antiproliferative activity for mammalian cells, including immunocompetent and epithelial cells. Thus, it is reasonable to presume that this property may contribute to the pathogenesis of H. pylori-induced diseases. It may be involved on the one hand in immune response evasion and on the other hand in the suppression of epithelial repair mechanisms.

Immune and inflammatory responses to Helicobacter pylori infection

The gastroduodenal response to chronic Helicobacter pylori infection is characterized by the infiltration of plasma cells, lymphocytes, neutrophils and monocytes into the mucosa. Eradication studies have shown that this inflammatory response represents a specific reaction to the presence of H. pylori. As well as stimulating specific local T and B cell responses and a systemic antibody response, H. pylori infection also induces a local pro-inflammatory cytokine response. Interleukin-8 (IL-8), which is expressed and secreted by gastric epithelial cells, may be an important host mediator inducing neutrophil migration and activation. IL-8 mRNA and protein secretion in gastric epithelial cell lines can be up-regulated by the cytokines tumour necrosis factor-alpha and IL-1 and also by type I strains of H. pylori (expressing the vacuolating toxin and cytotoxin-associated protein, CagA). The gastric epithelium thus plays an active role in mucosal defence. Neutrophil activation and the production of reactive oxygen metabolites will be induced directly by bacterial factors and indirectly via host-derived cytokines, products of complement activation and bioactive lipids. Strain variation in the induction of both IL-8 from epithelial cells and the oxidative burst in neutrophils may be an important factor determining the extent of mucosal injury. There is now increasing evidence from both in vivo and in vitro studies that type I strains induce an enhanced inflammatory response and mucosal damage. An understanding of the bacterial mediators of mucosal inflammation is important in elucidating the role of chronic H. pylori infection in the pathogenesis of gastroduodenal disease.

HLA-DR expression on CD8 lymphocytes from gastric mucosa in urease-positive and urease-negative gastritis

We isolated lymphocytes from chronically inflamed gastric mucosa. We analysed the expression of IL-2 receptors (CD25), transferin receptors (CD71) and HLA-DR molecules on T lymphocytes by flow cytometric analysis in 16 patients with urease-positive and in 7 patients with urease-negative chronic gastritis. In G0, G1 and G2 histological type (Sydney classification) of gastritis the number of lymphocytes obtained from the gastric mucosa biopsies was too low for the flow cytometric analysis. However, in G3 histological type of chronic gastritis we obtained enough cells for the flow cytometric analysis in 75%. We demonstrated a significant increase in HLA-DR expression on CD8 cells from patients with urease-positive gastritis compared to urease-negative gastritis. We also observed a statistically non-significant increase in HLA-DR expression on CD3 cells, and in CD71 expression on both CD3 and CD8 cells in urease-positive gastritis. However, no difference in CD25 expression was found between the two types of gastritis.