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

Discussion on the common controversies of Helicobacter pylori infection

BACKGROUND

Helicobacter pylori ( H. pylori ) can persistently colonize on the gastric mucosa after infection and cause gastritis, atrophy, metaplasia, and even gastric cancer (GC).

METHODS

Therefore, the detection and eradication of H. pylori are the prerequisite.

RESULTS

Clinically, there are some controversial issues, such as why H. pylori infection is persistent, why it translocases along with the lesser curvature of the stomach, why there is oxyntic antralization, what the immunological characteristic of gastric chronic inflammation caused by H. pylori is, whether H. pylori infection is associated with extra-gastric diseases, whether chronic atrophic gastritis (CAG) is reversible, and what the potential problems are after H. pylori eradication. What are the possible answers?

CONCLUSION

In the review, we will discuss these issues from the attachment to eradication in detail.

Role of Gastric Microorganisms Other than Helicobacter pylori in the Development and Treatment of Gastric Diseases

The microenvironment in the stomach is different from other digestive tracts, mainly because of the secretion of gastric acid and digestive enzymes, bile reflux, special mucus barrier, gastric peristalsis, and so on, which all contribute to the formation of antibacterial environment. Microecological disorders can lead to gastric immune disorders or lead to the decrease of dominant bacteria and the increase of the abundance and virulence of pathogenic microorganisms and then promote the occurrence of diseases. The body performs its immune function through innate and adaptive immunity and maintains microbial balance through the mechanism of immune homeostasis. Microecological imbalance can lead to the invasion of pathogenic microorganisms and damage mucosal barrier and immune system. The coexistence of gastric microorganisms (including viruses and fungi) may play a synergistic or antagonistic role in the pathogenesis of gastric diseases. Probiotics have the ability to compete with intestinal pathogens, increase the secretion of immunoglobulin A (IgA), stimulate the production of mucin, bacteriocin, and lactic acid, regulate the expression and secretion of cytokines, and regulate the growth of microbiota, which all have beneficial effects on the host microbial environment. At present, most studies focused on Helicobacter pylori, ignoring other stomach microbes and the overall stomach microecology. So, in this article, we reviewed advances in human gastric microecology, the relationship between gastric microecology and immunity or gastric diseases, and the treatment of probiotics in gastric diseases, in order to explore new area for further study of gastric microorganisms and treatment of gastric diseases.

Immunological Perspective: Helicobacter pylori Infection and Gastritis

Helicobacter pylori is a spiral-shaped gram-negative bacterium. Its infection is mainly transmitted via oral-oral and fecal-oral routes usually during early childhood. It can achieve persistent colonization by manipulating the host immune responses, which also causes mucosal damage and inflammation. H. pylori gastritis is an infectious disease and results in chronic gastritis of different severity in near all patients with infection. It may develop from acute/chronic inflammation, chronic atrophic gastritis, intestinal metaplasia, dysplasia, and intraepithelial neoplasia, eventually to gastric cancer. This review attempts to cover recent studies which provide important insights into how H. pylori causes chronic inflammation and what the characteristic is, which will immunologically explain H. pylori gastritis.

T Cell Cytokines Impact Epithelial Cell Responses during Helicobacter pylori Infection

The goal of this Brief Review is to highlight literature that demonstrates how cytokines made by T lymphocytes impact the gastric epithelium, especially during Helicobacter pylori infection. These cytokines effect many of the diverse functions of the epithelium and the epithelium's interactions with H. pylori The focal point of this Brief Review will be on how T cell cytokines impact antimicrobial function and barrier function and how T cell cytokines influence the development and progression of cancer. Furthermore, the modulation of epithelial-derived chemokines by H. pylori infection will be discussed.

H. pylori modulates DC functions via T4SS/TNFα/p38-dependent SOCS3 expression

Background

Helicobacter pylori (H. pylori) is a gram-negative bacterium that chronically infects approximately 50% of the world’s human population. While in most cases the infection remains asymptomatic, 10% of infected individuals develop gastric pathologies and 1–3% progress to gastric cancer. Although H. pylori induces severe inflammatory responses, the host’s immune system fails to clear the pathogen and H. pylori can persist in the human stomach for decades. As suppressor of cytokine signaling (SOCS) proteins are important feedback regulators limiting inflammatory responses, we hypothesized that H. pylori could modulate the host’s immune responses by inducing SOCS expression.

Methods

The phenotype of human monocyte-derived DCs (moDCs) infected with H. pylori was analyzed by flow cytometry and multiplex technology. SOCS expression levels were monitored by qPCR and signaling studies were conducted by means of Western blot. For functional studies, RNA interference-based silencing of SOCS1–3 and co-cultures with CD4⁺ T cells were performed.

Results

We show that H. pylori positive gastritis patients express significantly higher SOCS3, but not SOCS1 and SOCS2, levels compared to H. pylori negative patients. Moreover, infection of human moDCs with H. pylori rapidly induces SOCS3 expression, which requires the type IV secretion system (T4SS), release of TNFα, and signaling via the MAP kinase p38, but appears to be independent of TLR2, TLR4, MEK1/2 and STAT proteins. Silencing of SOCS3 expression in moDCs prior to H. pylori infection resulted in increased release of both pro- and anti-inflammatory cytokines, upregulation of PD-L1, and decreased T-cell proliferation.

Conclusions

This study shows that H. pylori induces SOCS3 via an autocrine loop involving the T4SS and TNFα and p38 signaling. Moreover, we demonstrate that high levels of SOCS3 in DCs dampen PD-L1 expression on DCs, which in turn drives T-cell proliferation.

The Role of Gastric Mucosal Immunity in Gastric Diseases

Gastric mucosa plays its immune function through innate and adaptive immunity by recruiting immune cells and releasing corresponding cytokines, which have an inseparable relationship with gastric diseases. Whether infective gastric diseases caused by Helicobacter pylori, Epstein-Barr virus or other microbe, noninfective gastric diseases, or gastric cancer, gastric mucosal immunity plays an important role in the occurrence and development of the disease. Understanding the unique immune-related tissue structure of the gastric mucosa and its role in immune responses can help prevent gastric diseases or treat them through immunotherapy. In this review, we summarize the basic feature of gastric mucosal immunity and its relationship with gastric diseases to track the latest progress of gastric mucosal immunity, update relevant knowledge and provide theoretical reference for the prevention and treatment of gastric diseases based on the gastric mucosal immunity.

Expression of Helicobacter pylori CagL gene in Lactococcus lactis MG1363 and evaluation of its immunogenicity as an oral vaccine in mice

Helicobacter pylori is a gram negative pathogen which commonly colonizes in the human gastric mucosa from early childhood and persists throughout life. CagL is a 27-kDa protein that is located at the tip of T4SS pili and highly conserved among pathogenic H. pylori strains. Lactic acid bacteria especially Lactococcus lactis (L. lactis) could serve as an antigen-delivering vehicle for the development of edible vaccine. In this study H. pylori CagL gene was cloned in pAMJ2008 vector and transferred to Lactococcus lactis MG1363 as the host for CagL antigen production. This recombinant bacterium was orally subjected to mice, and the immune response to CagL was evaluated by ELISA. Intracellular expression of CagL protein was confirmed by Western blot analysis. Mucosal immunization of mice with the recombinant L. lactis significantly stimulated CagL-Specific antibodies: IgA, IgG, cytokine IL-17 and IFN-γ. Moreover, the specific anti-CagL IgA response was detected in the feces of immunized mice. These results indicate that CagL of H. pylori was successfully expressed in L. lactis and the recombinant bacteria can be potentially used as an edible vaccine against H. pylori infection.

Immune Cell Signaling by Helicobacter pylori: Impact on Gastric Pathology

Helicobacter pylori represents a highly successful colonizer of the human stomach. Infections with this Gram-negative bacterium can persist lifelong, and although in the majority of cases colonization is asymptomatic, it can trigger pathologies ranging from chronic gastritis and peptic ulceration to gastric cancer. The interaction of the bacteria with the human host modulates immune responses in different ways to enable bacterial survival and persistence. H. pylori uses various pathogenicity-associated factors such as VacA, NapA, CGT, GGT, lipopolysaccharide, peptidoglycan, heptose 1,7-bisphosphate, ADP-heptose, cholesterol glucosides, urease and a type IV secretion system for controlling immune signaling and cellular functions. It appears that H. pylori manipulates multiple extracellular immune receptors such as integrin-β₂ (CD18), EGFR, CD74, CD300E, DC-SIGN, MINCLE, TRPM2, T-cell and Toll-like receptors as well as a number of intracellular receptors including NLRP3, NOD1, NOD2, TIFA and ALPK1. Consequently, downstream signaling pathways are hijacked, inducing tolerogenic dendritic cells, inhibiting effector T cell responses and changing the gastrointestinal microbiota. Here, we discuss in detail the interplay of bacterial factors with multiple immuno-regulatory cells and summarize the main immune evasion and persistence strategies employed by H. pylori.

Th17 activation by dendritic cells stimulated with gamma-irradiated Streptococcus pneumoniae

Dendritic cells (DCs) play an important role in antigen presentation, which is an essential step for the induction of antigen-specific adaptive immunity. Inactivated bacterial whole cell vaccines have been widely used to prevent many bacterial infections because they elicit good immunogenicity due to the presence of various antigens and are relatively inexpensive and easy to manufacture. Recently, gamma-irradiated whole cells of nonencapsulated Streptococcus pneumoniae were developed as a broad-spectrum and serotype-independent multivalent vaccine. In the present study, we generated gamma-irradiated S. pneumoniae (r-SP) and investigated its capacity to stimulate mouse bone marrow-derived DCs (BM-DCs) in comparison with heat-inactivated and formalin-inactivated S. pneumoniae (h-SP and f-SP, respectively). r-SP showed an attenuated binding and internalization level to BM-DCs when compared to h-SP or f-SP. r-SP weakly induced the expression of CD80, CD83, CD86, MHC class I, and PD-L2 compared with h-SP or f-SP. Furthermore, r-SP less potently induced IL-6, TNF-α, and IL-23 expression than h-SP or f-SP but more potently induced IL-1β expression than h-SP or f-SP in BM-DCs. Since Th17-mediated immune responses are known to be important for the protection against pneumococcal infections, r-SP-primed DCs were co-cultured with splenocytes or splenic CD4⁺ T cells. Interestingly, r-SP-sensitized BM-DCs markedly induced IL-17A⁺ CD4⁺ T cells whereas h-SP- or f-SP-sensitized BM-DCs weakly induced them. Collectively, these results suggest that r-SP could be an effective pneumococcal vaccine candidate eliciting Th17-mediated immune responses by stimulation of DCs.

Review: Impact of Helicobacter pylori on Alzheimer's disease: What do we know so far?

BACKGROUND

Helicobacter pylori has changed radically gastroenterologic world, offering a new concept in patients' management. Over time, more medical data gave rise to diverse distant, extragastric manifestations and interactions of the "new" discovered bacterium. Special interest appeared within the field of neurodegenerative diseases and particularly Alzheimer's disease, as the latter and Helicobacter pylori infection are associated with a large public health burden and Alzheimer's disease ranks as the leading cause of disability. However, the relationship between Helicobacter pylori infection and Alzheimer's disease remains uncertain.

METHODS

We performed a narrative review regarding a possible connection between Helicobacter pylori and Alzheimer's disease. All accessible relevant (pre)clinical studies written in English were included. Both affected pathologies were briefly analyzed, and relevant studies are discussed, trying to focus on the possible pathogenetic role of this bacterium in Alzheimer's disease.

RESULTS

Data stemming from both epidemiologic studies and animal experiments seem to be rather encouraging, tending to confirm the hypothesis that Helicobacter pylori infection might influence the course of Alzheimer's disease pleiotropically. Possible main mechanisms may include the bacterium's access to the brain via the oral-nasal-olfactory pathway or by circulating monocytes (infected with Helicobacter pylori due to defective autophagy) through disrupted blood-brain barrier, thereby possibly triggering neurodegeneration.

CONCLUSIONS

Current data suggest that Helicobacter pylori infection might influence the pathophysiology of Alzheimer's disease. However, further large-scale randomized controlled trials are mandatory to clarify a possible favorable effect of Helicobacter pylori eradication on Alzheimer's disease pathophysiology, before the recommendation of short-term and cost-effective therapeutic regimens against Helicobacter pylori-related Alzheimer's disease.

Autophagy impairment by Helicobacter pylori-induced methylation silencing of MAP1LC3Av1 promotes gastric carcinogenesis

Helicobacter pylori (H. pylori) infection induces methylation silencing of tumor suppressor genes causing gastric carcinogenesis. Impairment of autophagy induces DNA damage leading to genetic instability and carcinogenesis. We aimed to identify whether H. pylori infection induced methylation silencing of host autophagy-related (Atg) genes, impairing autophagy and enhancing gastric carcinogenesis. Gastric mucosae were obtained from 41 gastric cancer patients and 11 healthy volunteers (8 H. pylori-uninfected and 3 H. pylori-infected). Methylation status of Atg genes was analyzed by a methylation microarray and quantitative methylation-specific PCR (qMSP); mRNA expression was assessed by quantitative reverse transcription PCR (qRT-PCR). Cell proliferation, migration and invasion were assessed in normal rat gastric epithelial cells. Gene knock-down was performed by siRNA. Autophagy was assessed by western blotting. Of 34 Atg genes, MAP1LC3A variant 1 (MAP1LC3Av1) and ULK2 were identified by methylation microarray analysis as exhibiting specific methylation in H. pylori-infected mucosae and gastric cancer tissues. Methylation silencing of MAP1LC3Av1 was confirmed by qMSP, qRT-PCR and de-methylation treatment in two gastric cancer cell lines. Knock-down of map1lc3a, the rat homolog of the human MAP1LC3Av1, inhibited autophagy response and increased cell proliferation, migration and invasion in normal rat gastric epithelial cells, despite the presence of map1lc3b, the rat homolog of the human MAP1LC3B gene important for autophagy. Furthermore, MAP1LC3Av1 was methylation-silenced in 23.3% of gastric cancerous mucosae and 40% of non-cancerous mucosae with H. pylori infection. MAP1LC3Av1 is essential for autophagy and H. pylori-induced methylation silencing of MAP1LC3Av1 may impair autophagy, facilitating gastric carcinogenesis.

Wall teichoic acid is an essential component of Staphylococcus aureus for the induction of human dendritic cell maturation

Staphylococcus aureus is a Gram-positive pathogen that can cause chronic skin inflammation, pneumonia, and septic shock. The immunomodulatory functions of wall teichoic acid (WTA), a glycopolymer abundantly expressed on the Gram-positive bacterial cell wall, are poorly understood. Here, we investigated the role of WTA in the phenotypic and functional activation of human monocyte-derived dendritic cells (DCs) treated with ethanol-killed S. aureus. WTA-deficient S. aureus mutant (ΔtagO) exhibited attenuated binding and internalization to DCs compared to the wild-type. ΔtagO induced lower expression of maturation markers on and cytokines in DCs than the wild-type S. aureus. Furthermore, autologous human peripheral blood mononuclear cells cocultured with ΔtagO-treated DCs exhibited a marked reduction in T cell proliferative activity, the expression of activation markers, and the production of cytokines compared to the wild-type S. aureus-stimulated DCs. Collectively, these results suggest that WTA is an important cell wall component of S. aureus for the induction of DC maturation and activation.

Interaction between inflammatory mediators and miRNAs in Helicobacter pylori infection

Helicobacter pylori cause chronic inflammation favouring gastric carcinogenesis, and its eradication may prevent malignant transformation. We evaluated whether H. pylori infection and its eradication modify the expression of inflammatory mediators in patients with chronic gastritis. Furthermore, we assessed whether microRNAs modulate inflammatory pathways induced by H. pylori and identified miRNA–gene interaction networks. mRNA and protein expression of TNFA, IL6, IL1B, IL12A, IL2 and TGFBRII and miRNAs miR‐103a‐3p, miR‐181c‐5p, miR‐370‐3p, miR‐375 and miR‐223‐3p were evaluated in tissue samples from 20 patients with chronic gastritis H. pylori negative (Hp−) and 31 H. pylori positive (Hp+), before and three months after bacterium eradication therapy, in comparison with a pool of Hp− normal gastric mucosa. Our results showed that H. pylori infection leads to up‐regulation of TNFA, IL6, IL12A and IL2 and down‐regulation of miRNAs. Bacterium eradication reduces the expression of TNFA and IL6 and up‐regulates TGFBRII and all investigated miRNAs, except miR‐223‐3p. Moreover, transcriptional profiles of inflammatory mediators and miRNAs after eradication are different from the non‐infected group. Deregulated miRNA–mRNA interaction networks were observed in the Hp+ group before and after eradication. Therefore, miRNAs modulated cytokine expression in the presence of H. pylori and after its eradication, suggesting that miRNAs participate in the pathological process triggered by H. pylori in the gastric mucosa.

Helicobacter pylori vacuolating cytotoxin induces apoptosis via activation of endoplasmic reticulum stress in dendritic cells

BACKGROUND AND AIM

Dendritic cells (DCs) are observed on the Helicobacter pylori-infected gastric mucosa. DCs generally play an important role in the regulation of inflammation. Although stimulation of gastric epithelial cells with H. pylori vacuolating cytotoxin (VacA) has been reported to induce apoptosis and endoplasmic reticulum (ER) stress, the effects of VacA on the DC apoptotic response have not been well elucidated. This study was conducted to investigate the role of H. pylori VacA on the apoptotic process and ER stress in DCs.

METHODS

Murine and human DCs were generated from specific pathogen-free C57BL/6 mice and human peripheral blood mononuclear cells, respectively. DCs were incubated with purified VacA, after which Bax activation, cytochrome c release, and DNA fragmentation for apoptosis were measured by fluorescent microscopy, immunoblot, and ELISA. ER stress-related molecules such as GRP78 and CHOP were analyzed by immunoblot.

RESULTS

Treatment of DCs with purified H. pylori VacA resulted in the induction of apoptosis. DC stimulation with VacA led to the translocation of cytoplasmic Bax to mitochondria and cytochrome c release from mitochondria. H. pylori VacA induced signals for ER stress early during the stimulation process in DCs. Furthermore, suppression of ER stress resulted in a significant inhibition of the VacA-induced apoptosis in DCs.

CONCLUSION

These results suggest that ER stress is critical for regulation of DC apoptotic process in response to VacA stimulation.

Heme oxygenase-1 dysregulates macrophage polarization and the immune response to Helicobacter pylori

Helicobacter pylori incites a futile inflammatory response, which is the key feature of its immunopathogenesis. This leads to the ability of this bacterial pathogen to survive in the stomach and cause peptic ulcers and gastric cancer. Myeloid cells recruited to the gastric mucosa during H. pylori infection have been directly implicated in the modulation of host defense against the bacterium and gastric inflammation. Heme oxygenase-1 (HO-1) is an inducible enzyme that exhibits anti-inflammatory functions. Our aim was to analyze the induction and role of HO-1 in macrophages during H. pylori infection. We now show that phosphorylation of the H. pylori virulence factor cytotoxin-associated gene A (CagA) in macrophages results in expression of hmox-1, the gene encoding HO-1, through p38/NF (erythroid-derived 2)-like 2 signaling. Blocking phagocytosis prevented CagA phosphorylation and HO-1 induction. The expression of HO-1 was also increased in gastric mononuclear cells of human patients and macrophages of mice infected with cagA(+) H. pylori strains. Genetic ablation of hmox-1 in H. pylori-infected mice increased histologic gastritis, which was associated with enhanced M1/Th1/Th17 responses, decreased regulatory macrophage (Mreg) response, and reduced H. pylori colonization. Gastric macrophages of H. pylori-infected mice and macrophages infected in vitro with this bacterium showed an M1/Mreg mixed polarization type; deletion of hmox-1 or inhibition of HO-1 in macrophages caused an increased M1 and a decrease of Mreg phenotype. These data highlight a mechanism by which H. pylori impairs the immune response and favors its own survival via activation of macrophage HO-1.

Helicobacter pylori susceptible/resistant to antibiotic eradication therapy differ in the maturation and activation of dendritic cells

BACKGROUND

The natural course of Helicobacter pylori infection, as well as the success of antibiotic eradication is determined by the immune response to bacteria. The aim of the study is to investigate how different Helicobacter pylori isolates influence the dendritic cells maturation and antigen-presenting function in order to elucidate the differences between Helicobacter pylori strains, isolated from the patients with successful antibiotic eradication therapy or repeated eradication failure.

MATERIALS AND METHODS

Dendritic cells maturation and antigen presentation were monitored by flow cytometry analysis of the major histocompatibility complex class II (MHC-II), Toll-like receptor (TLR) and costimulatory molecules expression, and by determining cytokine secretion.

RESULTS

Dendritic cells stimulated with Helicobacter pylori isolated from patients with repeated antibiotic eradication failure expressed less human leukocyte antigen (HLA-DR), CD86, TLR-2, and interleukin-8 (IL-8) compared to Helicobacter pylori strains susceptible to antibiotic therapy; the latter expressed lower production of IL-10. Polymyxin B inhibition of lipopolysaccharide reduces IL-8 secretion in the group of Helicobacter pylori strains susceptible to antibiotic therapy. The differences in IL-8 secretion between both groups are lipopolysaccharide dependent, while the differences in secretion of IL-10 remain unchanged after lipopolysaccharide inhibition. Inhibitor of cathepsin X Mab 2F12 reduced the secretion of IL-6, and the secretion was significantly lower in the group of Helicobacter pylori strains isolated from patients with repeated antibiotic eradication failure.

CONCLUSION

Helicobacter pylori strains, susceptible/resistant to antibiotic eradication therapy, differ in their capability to induce DCs maturation and antigen-presenting function.

Interleukin polymorphisms and differential methylation status in gastric cancer: an association with Helicobacter pylori infection

AIM

Interleukin polymorphisms and Helicobacter pylori infection are believed to play critical roles in DNA methylation, a process frequently associated with carcinogenesis. The aim of this study was to determine the associations between interleukin polymorphisms and methylation status of three genes related to gastric cancer. Furthermore, the influence of the H. pylori strains was evaluated.

MATERIALS & METHODS

75 gastric tumor samples had the DNA extracted for interleukin polymorphisms genotyping by PCR-RFLP, promoter methylation by MS-PCR and detection and subtyping of H. pylori by PCR.

RESULTS

In the cardia tumors, methylation in the COX-2 promoter was associated with IL1RN*2 (p = 0.015), and the associated genotypes IL1B511T + IL1RN*2 seem to be important in the methylation of COX-2 (p = 0.013), especially in the presence of cagA(+) (p = 0.026) and vacAs1 (p = 0.025) H. pylori strains. The associated genotypes IL6 CC+TNF GG seem to be involved in the unmethylation of CDKN2A (p = 0.046), along with H. pylori cagA(+) infection.

CONCLUSION

DNA methylation in gastric cancer seems to be influenced by the presence of interleukin polymorphisms and by the H. pylori cagA/vacAs1m1 strains.

Lactic acid bacterial extracts as anti-Helicobacter pylori: a molecular approach

BACKGROUND

Helicobacter pylori (H. pylori) infection, the main cause of chronic gastritis, increases gastric cancer risk. Antibiotics-based H. pylori eradication treatment is 90% effective. However, it is expensive and causes side effects and antibiotic resistance. Lactic acid bacteria (LAB) could present a low-cost, large-scale alternative solution to prevent or decrease H. pylori colonization.

AIM

This work aimed to study the inhibitory effects of LAB strains on the growth and pathogenic activity of H. pylori stains. To this end, we have selected the most virulent H. pylori strains (out of 20 mucosal antral biopsies) regarding cellular vacuolization and induction of apoptosis/necrosis.

METHOD

The selection of H. pylori pathogenic strains (clinically pre-isolated) were based on their impact of VacA activities on Hep-2 cell line, induction of apoptosis and necrosis in Caco-2 cell line. The Inhibitory effect of LAB strains on the invasion was carried out using the Caco-2 and Hela cell lines, where, they were co-cultured with the pathogenic H. pylori in the presence or absence of LAB extracts. The effect of LAB extracts on TNF-α secretion which induced by H. pylori-LPS was carried out by RT-qPCR.

RESULTS

L. bulgaricus DSMZ 20080, L. acidophilus and L. plantarum (studied previously and reported as high antioxidant candidate strains) showed the highest anti-pylori activities with inhibition ranged from 51.46 to 88.19%, they preventing the adhesion, invasion and DNA fragmentation of cell lines. In addition, they could reduce the TNF-α expression by 62.13%.

CONCLUSION

LAB extracts could inhibit the bacterial adhesion and invasion, gastric inflammation and DNA fragmentation induced by Helicobacter pylori.

Inflammatory cytokine and microRNA responses of primary human dendritic cells cultured with Helicobacter pylori strains

Primary human dendritic cells (DC) were used to explore the inflammatory effectors, including cytokines and microRNAs, regulated by Helicobacter pylori. In a 48 h ex-vivo co-culture system, both H. pylori B38 and B45 strains activated human DCs and promoted a strong inflammatory response characterized by the early production of pro-inflammatory TNFα and IL-6 cytokines, followed by IL-10, IL-1β, and IL-23 secretion. IL-23 was the only cytokine dependent on the cag pathogenicity island status of the bacterial strains. DC activation and cytokine production were accompanied by an early miR-146a upregulation followed by a strong miR-155 induction, which mainly controlled TNFα production. These results pave the way for further investigations into the nature of H. pylori antigens and the subsequently activated signaling pathways involved in the inflammatory response to H. pylori infection, the deregulation of which may likely contribute to gastric lymphomagenesis.

Helicobacter pylori infection inhibits phagocyte clearance of apoptotic gastric epithelial cells

Increased apoptotic death of gastric epithelial cells is a hallmark of Helicobacter pylori infection, and altered epithelial cell turnover is an important contributor to gastric carcinogenesis. To address the fate of apoptotic gastric epithelial cells and their role in H. pylori mucosal disease, we investigated phagocyte clearance of apoptotic gastric epithelial cells in H. pylori infection. Human gastric mononuclear phagocytes were analyzed for their ability to take up apoptotic epithelial cells (AECs) in vivo using immunofluorescence analysis. We then used primary human gastric epithelial cells induced to undergo apoptosis by exposure to live H. pylori to study apoptotic cell uptake by autologous monocyte-derived macrophages. We show that HLA-DR(+) mononuclear phagocytes in human gastric mucosa contain cytokeratin-positive and TUNEL-positive AEC material, indicating that gastric phagocytes are involved in AEC clearance. We further show that H. pylori both increased apoptosis in primary gastric epithelial cells and decreased phagocytosis of the AECs by autologous monocyte-derived macrophages. Reduced macrophage clearance of apoptotic cells was mediated in part by H. pylori-induced macrophage TNF-α, which was expressed at higher levels in H. pylori-infected, compared with uninfected, gastric mucosa. Importantly, we show that H. pylori-infected gastric mucosa contained significantly higher numbers of AECs and higher levels of nonphagocytosed TUNEL-positive apoptotic material, consistent with a defect in apoptotic cell clearance. Thus, as shown in other autoimmune and chronic inflammatory diseases, insufficient phagocyte clearance may contribute to the chronic and self-perpetuating inflammation in human H. pylori infection.

Periodontal disease immunology: 'double indemnity' in protecting the host

During the last two to three decades our understanding of the immunobiology of periodontal disease has increased exponentially, both with respect to the microbial agents triggering the disease process and the molecular mechanisms of the host engagement maintaining homeostasis or leading to collateral tissue damage. These foundational scientific findings have laid the groundwork for translating cell phenotype, receptor engagement, intracellular signaling pathways and effector functions into a 'picture' of the periodontium as the host responds to the 'danger signals' of the microbial ecology to maintain homeostasis or succumb to a disease process. These findings implicate the chronicity of the local response in attempting to manage the microbial challenge, creating a 'Double Indemnity' in some patients that does not 'insure' health for the periodontium. As importantly, in reflecting the title of this volume of Periodontology 2000, this review attempts to inform the community of how the science of periodontal immunology gestated, how continual probing of the biology of the disease has led to an evolution in our knowledge base and how more recent studies in the postgenomic era are revolutionizing our understanding of disease initiation, progression and resolution. Thus, there has been substantial progress in our understanding of the molecular mechanisms of host-bacteria interactions that result in the clinical presentation and outcomes of destructive periodontitis. The science has embarked from observations of variations in responses related to disease expression with a focus for utilization of the responses in diagnosis and therapeutic outcomes, to current investigations using cutting-edge fundamental biological processes to attempt to model the initiation and progression of soft- and hard-tissue destruction of the periodontium. As importantly, the next era in the immunobiology of periodontal disease will need to engage more sophisticated experimental designs for clinical studies to enable robust translation of basic biologic processes that are in action early in the transition from health to disease, those which stimulate microenvironmental changes that select for a more pathogenic microbial ecology and those that represent a rebalancing of the complex host responses and a resolution of inflammatory tissue destruction.

Lower circulating levels of chemokine CXCL10 in Helicobacter pylori-infected patients with peptic ulcer: Influence of the bacterial virulence factor CagA

BACKGROUND AND OBJECTIVES

Alterations in CXCL10 (a Th1 chemokine) expression have been associated with various diseases. The aim of this study was to evaluate the serum CXCL10 levels in H. pylori-infected patients with peptic ulcer (PU), H. pylori-infected asymptomatic (AS) subjects and healthy H. pylori-negative subjects, and also to determine its association with bacterial virulence factor cytotoxin-associated gene A (CagA).

MATERIALS AND METHODS

Serum samples from 90 H. pylori infected patients with PU (70 were anti-CagA(+), 20 were anti-CagA(-)), 65 AS carriers (40 were anti-CagA(+), 25 were anti-CagA(-)) and 30 healthy H. pylori-negative subjects (as a control group) were tested for concentrations of CXCL10 by using the ELISA method.

RESULTS

The mean serum levels of CXCL10 in PU patients (96.64 ± 20.85 pg/mL) were significantly lower than those observed in AS subjects (162.16 ± 53.31 pg/mL, P < 0.01) and the control group (193.93 ± 42.14 pg/mL, P < 0.02). In the PU group, the serum levels of CXCL10 in anti-CagA(+) subjects was significantly higher in comparison to anti-CagA(-) patients (P < 0.04).

CONCLUSION

These results showed that the mean concentrations of CXCL10 in H. pylori-infected-PU patients was lower than AS carriers and control group. In the PU group, the serum levels of CXCL10 were associated with bacterial factor CagA.

Dendritic cell function in the host response to Helicobacter pylori infection of the gastric mucosa

Dendritic cells (DCs) play an important role as antigen-presenting cells that direct the nature of the adaptive immune response. Subtypes are differentiated by lineage, tissue, marker expression and function. Their function in promoting regulatory T cells in the gut to maintain immunologic homeostasis is well documented, but their role in the Helicobacter pylori-infected stomach is less clear. Some analyses of bone marrow-derived DCs stimulated with H. pylori have demonstrated proinflammatory potential based on secretion of IL-12 or IL-23 or activation of Th1 and Th17 cells. Other analyses indicate that H. pylori-activated DCs are less responsive compared with other gastrointestinal bacteria and activate DCs to promote Treg development. DC depletion in mice supports a role for DCs in down-regulating H. pylori-induced gastritis. These data indicate that gastric DCs recognize H. pylori much like DCs in the gut that recognize commensal organisms and promote a regulatory T-cell response. This is consistent with a growing body of literature documenting the prevalence and function of Treg cells in the host response to H. pylori. Research is now focused on characterizing how H. pylori induces such activity in DCs and identifying the mechanisms by which H. pylori-activated DCs activate Treg cells.

Helicobacter pylori colonization ameliorates glucose homeostasis in mice through a PPAR γ-dependent mechanism

Background

There is an inverse secular trend between the incidence of obesity and gastric colonization with Helicobacter pylori, a bacterium that can affect the secretion of gastric hormones that relate to energy homeostasis. H. pylori strains that carry the cag pathogenicity island (PAI) interact more intimately with gastric epithelial cells and trigger more extensive host responses than cag⁻ strains. We hypothesized that gastric colonization with H. pylori strains differing in cag PAI status exert distinct effects on metabolic and inflammatory phenotypes.

Methodology/Principal Findings

To test this hypothesis, we examined metabolic and inflammatory markers in db/db mice and mice with diet-induced obesity experimentally infected with isogenic forms of H. pylori strain 26695: the cag PAI wild-type and its cag PAI mutant strain 99–305. H. pylori colonization decreased fasting blood glucose levels, increased levels of leptin, improved glucose tolerance, and suppressed weight gain. A response found in both wild-type and mutant H. pylori strain-infected mice included decreased white adipose tissue macrophages (ATM) and increased adipose tissue regulatory T cells (Treg) cells. Gene expression analyses demonstrated upregulation of gastric PPAR γ-responsive genes (i.e., CD36 and FABP4) in H. pylori-infected mice. The loss of PPAR γ in immune and epithelial cells in mice impaired the ability of H. pylori to favorably modulate glucose homeostasis and ATM infiltration during high fat feeding.

Conclusions/Significance

Gastric infection with some commensal strains of H. pylori ameliorates glucose homeostasis in mice through a PPAR γ-dependent mechanism and modulates macrophage and Treg cell infiltration into the abdominal white adipose tissue.

Comparative analysis of the interaction of Helicobacter pylori with human dendritic cells, macrophages, and monocytes

Helicobacter pylori may cause chronic gastritis, gastric cancer, or lymphoma. Myeloid antigen-presenting cells (APCs) are most likely involved in the induction and expression of the underlying inflammatory responses. To study the interaction of human APC subsets with H. pylori, we infected monocytes, monocyte-derived dendritic cells (DCs), and monocyte-derived (classically activated; M1) macrophages with H. pylori and analyzed phenotypic alterations, cytokine secretion, phagocytosis, and immunostimulation. Since we detected CD163(+) (alternatively activated; M2) macrophages in gastric biopsy specimens from H. pylori-positive patients, we also included monocyte-derived M2 macrophages in the study. Upon H. pylori infection, monocytes secreted interleukin-1β (IL-1β), IL-6, IL-10, and IL-12p40 (partially secreted as IL-23) but not IL-12p70. Infected DCs became activated, as shown by the enhanced expression of CD25, CD80, CD83, PDL-1, and CCR7, and secreted IL-1β, IL-6, IL-10, IL-12p40, IL-12p70, and IL-23. However, infection led to significantly downregulated CD209 and suppressed the constitutive secretion of macrophage migration inhibitory factor (MIF). H. pylori-infected M1 macrophages upregulated CD14 and CD32, downregulated CD11b and HLA-DR, and secreted mainly IL-1β, IL-6, IL-10, IL-12p40, and IL-23. Activation of DCs and M1 macrophages correlated with increased capacity to induce T-cell proliferation and decreased phagocytosis of dextran. M2 macrophages upregulated CD14 and CD206 and secreted IL-10 but produced less of the proinflammatory cytokines than M1 macrophages. Thus, H. pylori affects the functions of human APC subsets differently, which may influence the course and the outcome of H. pylori infection. The suppression of MIF in DCs constitutes a novel immune evasion mechanism exploited by H. pylori.

A role for altered phagosome maturation in the long-term persistence of Helicobacter pylori infection

The vigorous host immune response that is mounted against Helicobacter pylori is unable to eliminate this pathogenic bacterium from its niche in the human gastric mucosa. This results in chronic inflammation, which can develop into gastric or duodenal ulcers in 10% of infected individuals and gastric cancer in 1% of infections. The determinants for these more severe pathologies include host (e.g., high IL-1β expression polymorphisms), bacterial [e.g., cytotoxicity-associated gene (cag) pathogenicity island], and environmental (e.g., dietary nitrites) factors. However, it is the failure of host immune effector cells to eliminate H. pylori that underlies its persistence and the subsequent H. pylori-associated disease. Here we discuss the mechanisms used by H. pylori to survive the host immune response and, in particular, the role played by altered phagosome maturation.

Stimulation of dendritic cells with Helicobacter pylori vacuolating cytotoxin negatively regulates their maturation via the restoration of E2F1

Helicobacter pylori induces an infiltration of dendritic cells (DCs) into the infected gastric mucosa. Although DCs play an important role in the regulation of inflammation, the effects of H. pylori vacuolating cytotoxin (VacA) on DC maturation process have not yet been elucidated. The role of VacA in DC maturation following co-exposure to Escherichia coli lipopolysaccharide (LPS) was investigated. The treatment of immature DCs with LPS up-regulated the expression of surface molecules [e.g. CD40, CD80, CD86 and major histocompatibility complex (MHC) class II], as well as the production of cytokines [e.g. interleukin (IL)-1β, IL-12p70 and tumour necrosis gactor (TNF)-α] compared with those of unstimulated controls. Co-stimulation with H. pylori VacA significantly reduced the up-regulated DC maturation markers induced by LPS. In addition, VacA sustained the immature state of DCs with high endocytosis and low migratory capacity. The LPS-induced down-regulation of E2F1 expression in DCs was recovered by co-stimulation with VacA. Moreover, suppression of E2F1 by small interfering RNA resulted in a significant recovery of the inhibited DC maturation by VacA. In contrast, VacA did not affect nuclear factor (NF)-κB responses to LPS and the NF-κB signal was not associated with VacA-induced inhibition of DC maturation. These results suggest that the exposure of DCs to H. pylori VacA negatively regulates DC maturation via the restoration of E2F1. The immunomodulatory action of VacA on DCs may contribute to the ability of VacA-producing H. pylori to establish a persistent infection in the gastric mucosa.

Stromal regulation of human gastric dendritic cells restricts the Th1 response to Helicobacter pylori

BACKGROUND & AIMS

Mucosal dendritic cells (DCs) play a key role in initiating the T-helper (Th)1 response to Helicobacter pylori. To further elucidate the mucosal response to H pylori, we examined whether gastric stromal factors condition DCs to support tolerance to H pylori, analogous to intestinal stromal factor-driven macrophage tolerance to commensal bacteria.

METHODS

To model mucosal DC development, we isolated and cultured cell-depleted human stroma/extracellular matrix from fresh gastric and intestinal mucosa to generate stroma-conditioned media. We then analyzed the capacity of stroma-conditioned media-treated monocyte-derived DCs and primary human gastric and intestinal DCs pulsed in vitro with H pylori to induce T-cell proliferation and interferon gamma secretion.

RESULTS

Stromal factors in gastric mucosa suppressed H pylori-stimulated DC activation and the ability of DCs to drive a Th1 proliferative and cytokine response to H pylori. The ability of gastric stromal factors to down-regulate DC function was similar to that of intestinal stromal factors and was independent of transforming growth factor β, prostaglandin E₂, interleukin (IL)-10, and thymic stromal lymphopoietin. Stroma-conditioned media-induced reduction in DC-stimulated Th1 responses was associated with reduced DC release of IL-12.

CONCLUSIONS

Gastric stromal factors down-regulate DC responsiveness to H pylori, resulting in a dampened gastric Th1 response. We speculate that stroma-induced down-regulation of DC function contributes to the permissiveness of both gastric and intestinal mucosa to colonization by persistent residential microbes.

Circulating interleukin-27 levels in Helicobacter pylori-infected patients with gastric or duodenal ulcers, independent of the bacterial cytotoxin-associated gene A virulence factor

OBJECTIVE

The aim was to evaluate the interleukin (IL)-27 levels in Helicobacter pylori (H. pylori)-infected patients with gastric ulcer (GU) or duodenal ulcer (DU) and to determine its association with H. pylori virulence factor cytotoxin-associated gene A (CagA).

METHODS

In all, 127 H. pylori infected patients (including 96 DU patients, of whom 61 were anti-CagA(+) and 35 were anti-CagA(-)) and 31 GU patients (of whom 15 were anti-CagA(+) and 16 were anti-CagA(-)), 60 asymptomatic (AS) carriers (of whom 30 were anti-CagA(+) and 30 were anti-CagA(-)) and 30 healthy H. pylori-negative participants (as a control) were enrolled in the study. Serum concentrations of IL-27 were measured by the enzyme-linked immunosorbent assay method.

RESULTS

The mean levels of IL-27 in the GU (44.26 ± 7.12 pg/mL) and DU patients (40.84 ± 3.90 pg/mL) was significantly higher than those observed in the AS carriers (22.06 ± 1.90 pg/mL, P < 0.001) and the control group (18.12 ± 1.68 pg/mL, P < 0.001 and P < 0.002, respectively). In the GU, DU and AS groups the levels of IL-27 in anti-CagA(+) participants were not significantly differ from that in the anti-CagA(-) participants.

CONCLUSIONS

These results showed that the mean concentration of IL-27 in H. pylori-infected peptic ulcer (PU) patients was higher than in AS carriers and the healthy control group. The serum concentrations of IL-27 were not affected by the CagA factor.

Helicobacter pylori and gastric cancer: factors that modulate disease risk

Helicobacter pylori is a gastric pathogen that colonizes approximately 50% of the world's population. Infection with H. pylori causes chronic inflammation and significantly increases the risk of developing duodenal and gastric ulcer disease and gastric cancer. Infection with H. pylori is the strongest known risk factor for gastric cancer, which is the second leading cause of cancer-related deaths worldwide. Once H. pylori colonizes the gastric environment, it persists for the lifetime of the host, suggesting that the host immune response is ineffective in clearing this bacterium. In this review, we discuss the host immune response and examine other host factors that increase the pathogenic potential of this bacterium, including host polymorphisms, alterations to the apical-junctional complex, and the effects of environmental factors. In addition to host effects and responses, H. pylori strains are genetically diverse. We discuss the main virulence determinants in H. pylori strains and the correlation between these and the diverse clinical outcomes following H. pylori infection. Since H. pylori inhibits the gastric epithelium of half of the world, it is crucial that we continue to gain understanding of host and microbial factors that increase the risk of developing more severe clinical outcomes.

Helicobacter pylori defines local immune response through interaction with dendritic cells

The bacterial pathogen Helicobacter pylori colonizes the human gastric and duodenal mucosa, evades clearance by the host response and is associated with peptic ulcer disease and an increased risk of gastric adenocarcinoma. Dendritic cells (DCs) are initiators of the immune response to H. pylori. The aim of the current study was to investigate the interaction between H. pylori with DCs. To determine the impact of H. pylori on the maturation and the activation of monocyte-derived DCs, the effect of 20 clinical H. pylori strains with different inflammatory backgrounds on adenocarcinoma gastric epithelial cells was investigated. The inflammatory background was defined according to the degree of lymphocyte and granulocyte infiltration and the bacterial density at the site of infection. DC maturation and activation varied after exposure to the different strains. While maturation appeared to be independent of any virulence factor tested, a significant increase in the average level of cytokine production was observed for the proinflammatory cytokines interleukin-12 (IL-12), tumour necrosis factor-α, IL-6 and IL-1β when comparing strains with low inflammatory backgrounds with those of the medium or high backgrounds. In conclusion, the DC response towards different strains in vitro was associated with the clinical outcome of the individual host, suggesting a major role of this cell type in modulating strain-specific H. pylori infection.

Comparison of Helicobacter pylori and Escherichia coli in induction of TNF-alpha mRNA from human peripheral blood mononuclear cells

PURPOSE

To investigate the difference between the abilities of Helicobacter pylori and Escherichia coli to induce expression of TNF-alpha in human peripheral blood mononuclear cells (PBMC).

MATERIALS AND METHODS

H pylori was isolated from gastric biopsy specimens. The mononuclear cells were isolated from human blood, cultured, and treated with either intact or sonicated E coli or H pylori, and mRNA expression for TNF-alpha was detected using semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

TNF-alpha mRNA expression levels were significantly higher in PBMCs stimulated with E coli compared to those stimulated with H pylori at the same number and identical conditions (P < .001). The results also suggest that sonicated bacteria were significantly (P < .001) less stimulatory for PBMCs than intact bacteria for both E coli and H pylori.

CONCLUSIONS

The ability of different H pylori strains isolated from biopsy samples to stimulate TNF-alpha from PBMCs was significantly lower than that of E coli. Sonicated bacteria, as compared to intact bacteria, was a very poor inducer of TNF-alpha mRNA expression, suggesting that the conformation of lipopolysaccharides (LPS) on the outer leaflet of the outer membrane is not totally conserved in sonicated bacteria.

Role of innate immunity in Helicobacter pylori-induced gastric malignancy

Helicobacter pylori colonizes the majority of persons worldwide, and the ensuing gastric inflammatory response is the strongest singular risk factor for peptic ulceration and gastric cancer. However, only a fraction of colonized individuals ever develop clinically significant outcomes. Disease risk is combinatorial and can be modified by bacterial factors, host responses, and/or specific interactions between host and microbe. Several H. pylori constituents that are required for colonization or virulence have been identified, and their ability to manipulate the host innate immune response will be the focus of this review. Identification of bacterial and host mediators that augment disease risk has profound ramifications for both biomedical researchers and clinicians as such findings will not only provide mechanistic insights into inflammatory carcinogenesis but may also serve to identify high-risk populations of H. pylori-infected individuals who can then be targeted for therapeutic intervention.

Cytotoxic T cells in H. pylori-related gastric autoimmunity and gastric lymphoma

Helicobacter pylori infection is the major cause of gastroduodenal pathologies, but only a minority of infected patients develop gastric B-cell lymphoma, gastric autoimmunity, or other life threatening diseases, as gastric cancer or peptic ulcer. The type of host immune response against H. pylori, particularly the cytolytic effector functions of T cells, is crucial for the outcome of the infection. T cells are potentially able to kill a target via different mechanisms, such as perforins or Fas-Fas ligand interaction. In H. pylori-infected patients with gastric autoimmunity cytolytic T cells, that cross-recognize different epitopes of H. pylori proteins and H(+)K(+)-ATPase autoantigen, infiltrate the gastric mucosa and lead to gastric atrophy via long-lasting activation of Fas ligand-mediated appotosis and perforin-induced cytotoxicity. On the other hand, gastric T cells from MALT lymphoma exhibit defective perforin- and Fas-Fas ligand-mediated killing of B cells, with consequent abnormal help for B-cell proliferation, suggesting that deregulated and exhaustive H. pylori-induced T cell-dependent B-cell activation can support both the onset and the promotion of low-grade B-cell lymphoma.

Human primary gastric dendritic cells induce a Th1 response to H. pylori

Adaptive CD4 T-cell responses are important in the pathogenesis of chronic Helicobacter pylori gastritis. However, the gastric antigen-presenting cells that induce these responses have not yet been identified. Here we show that dendritic cells (DCs) are present in the gastric mucosa of healthy subjects and are more prevalent and more activated in the gastric mucosa of H. pylori-infected subjects. H. pylori induced gastric DCs isolated from noninfected subjects to express increased levels of CD11c, CD86 and CD83, and to secrete proinflammatory cytokines, particularly interleukin (IL)-6 and IL-8. Importantly, gastric DCs pulsed with live H. pylori, but not control DCs, mediated T-cell secretion of interferon-gamma. The ability of H. pylori to induce gastric DC maturation and stimulate gastric DC activation of Th1 cells implicates gastric DCs as initiators of the immune response to H. pylori.

The CagA protein of Helicobacter pylori suppresses the functions of dendritic cell in mice

CagA protein is the most assessed effecter molecule of Helicobacter pylori. In this report, we demonstrate how CagA protein regulates the functions of dendritic cells (DC) against H. pylori infection. In addition, we found that CagA protein was tyrosine-phosphorylated in DC. The responses to cagA-positive H. pylori in DC were reduced in comparison to those induced by cagA-negative H. pylori. CagA-overexpressing DC also exhibited a decline in the responses against LPS stimulation and the differentiation of CD4(+) T cells toward Th1 type cells compared to wild type DC. In addition, the level of phosphorylated IRF3 decreased in CagA-overexpressing DC stimulated with LPS, indicating that activated SHP-2 suppressed the enzymatic activity of TBK1 and consequently IRF3 phosphorylation. These data suggest that CagA protein negatively regulates the functions of DC via CagA phosphorylation and that cagA-positive H. pylori strains suppress host immune responses resulting in their chronic colonization of the stomach.

Arginase II restricts host defense to Helicobacter pylori by attenuating inducible nitric oxide synthase translation in macrophages

Helicobacter pylori infection of the stomach causes peptic ulcer disease and gastric cancer. Despite eliciting a vigorous immune response, the bacterium persists for the life of the host. An important antimicrobial mechanism is the production of NO derived from inducible NO synthase (iNOS). We have reported that macrophages can kill H. pylori in vitro by an NO-dependent mechanism, but supraphysiologic levels of the iNOS substrate l-arginine are required. Because H. pylori induces arginase activity in macrophages, we determined if this restricts NO generation by reducing l-arginine availability. Inhibition of arginase with S-(2-boronoethyl)-l-cysteine (BEC) significantly enhanced NO generation in H. pylori-stimulated RAW 264.7 macrophages by enhancing iNOS protein translation but not iNOS mRNA levels. This effect resulted in increased killing of H. pylori that was attenuated with an NO scavenger. In contrast, inhibition of arginase in macrophages activated by the colitis-inducing bacterium Citrobacter rodentium increased NO without affecting iNOS levels. H. pylori upregulated levels of arginase II (Arg2) mRNA and protein, which localized to mitochondria, whereas arginase I was not induced. Increased iNOS protein and NO levels were also demonstrated by small interfering RNA knockdown of Arg2 and in peritoneal macrophages from C57BL/6 Arg2(-/-) mice. In H. pylori-infected mice, treatment with BEC or deletion of Arg2 increased iNOS protein levels and NO generation in gastric macrophages, but treatment of Arg2(-/-) mice with BEC had no additional effect. These studies implicate Arg2 in the immune evasion of H. pylori by causing intracellular depletion of l-arginine and thus reduction of NO-dependent bactericidal activity.

Serum levels of high-sensitivity C-reactive protein (hs-CRP)in Helicobacter pylori-infected peptic ulcer patients and its association with bacterial CagA virulence factor

OBJECTIVE

CRP is a marker of inflammation and infection of the gastric mucosa with Helicobacter pylori, which causes an inflammatory reaction. It has been reported that CagA(+) H. pylori strains induce more severe gastric inflammation and are also associated with higher risks of peptic ulcer and gastric cancer. The purpose of this study was to compare serum concentrations of hs-CRP in H. pylori-infected peptic ulcer (PU) patients, H. pylori infected asymptomatic (AS) carriers, and a healthy control group, and their association with bacterial virulence factor CagA.

MATERIAL AND METHODS

A total of 60 H. pylori infected PU patients (30 patients were positive for anti-CagA antibody and 30 were negative for anti-CagA antibody), 53 H. pylori-infected AS carriers (25 subjects were positive for anti-CagA antibody and 28 were negative for anti-CagA antibody), and 22 healthy H. pylori-negative subjects (as a control group) were enrolled in the study. Serum concentrations of hs-CRP were measured by use of an ELISA method.

RESULTS

The mean serum level of hs-CRP in all PU patients (124.9±32.4 μg/dl) was significantly higher than that in all AS subjects (18.6±2.6 μg/dl; P<0.001) and the healthy uninfected control group (10.7±2.9 μg/dl; P<0.0001). Moreover, the mean serum level of hs-CRP in the AS group was significantly higher than that observed in the uninfected control group (P<0.04). No significant difference was observed between mean serum levels of hs-CRP of PU patients with positive test for anti-CagA antibody (132.6±49.4 μg/dl) and PU patients with negative test for anti-CagA antibody (117.1±42.9 μg/dl). Moreover, mean serum levels of hs-CRP were similar in AS subjects with positive test for anti-CagA (18.4±3.1 μg/dl) and in those who were negative for anti-CagA antibody (18.9±4.1 μg/dl).

CONCLUSION

The results of this study showed that mean serum concentrations of hs-CRP in PU patients and in H. pylori infected AS carriers were higher than in a healthy control group. Although H. pylori infection is associated with higher serum levels of hs-CRP, serum concentrations of this inflammatory marker were not affected by expression of bacterial CagA virulence factor.

Helicobacter pylori stimulates dendritic cells to induce interleukin-17 expression from CD4+ T lymphocytes

Helicobacter pylori is a human gastroduodenal pathogen that leads to active chronic inflammation characterized by T-cell responses biased toward a Th1 phenotype. It has been accepted that H. pylori infection induces a Th17 response. At mucosal sites, dendritic cells (DCs) have the capacity to induce effector T cells. Here, we evaluate the role of DCs in the H. pylori-induced interleukin-17 (IL-17) response. Immunohistochemistry and immunofluorescence were performed on human gastric mucosal biopsy samples and showed that myeloid DCs in H. pylori-infected patients colocalized with IL-23- and that IL-17-producing lymphocytes were present in H. pylori-infected antral biopsy samples. In parallel, human monocyte-derived DCs stimulated in vitro with live H. pylori cells produced significant levels of IL-23 in the absence of IL-12 release. The subsequent incubation of H. pylori-infected DCs with autologous CD4(+) T cells led to gamma interferon (IFN-gamma) and IL-17 expression. The inhibition of IL-1 and, to a lesser extent, IL-23 inhibited IL-17 production by T cells. Finally, isogenic H. pylori mutant strains not expressing major virulence factors were less effective in inducing IL-1 and IL-23 release by DCs and IL-17 release by T cells than parental strains. Altogether, we can conclude that DCs are potent inducers of IL-23/IL-17 expression following H. pylori stimulation. IL-1/IL-23 as well as H. pylori virulence factors seem to play an important role in mediating this response.

Evidence for transepithelial dendritic cells in human H. pylori active gastritis

BACKGROUND

Despite extensive experimental investigation stressing the importance of bacterial interaction with dendritic cells (DCs), evidence regarding direct interaction of Helicobacter pylori or its virulence products with DCs in the human gastric mucosa is lacking.

METHODS

Human gastric mucosa biopsies, with or without H. pylori infection and active inflammation, were investigated at light and electron microscopy level with immunocytochemical tests for bacterial products (VacA, urease, outer membrane proteins) and DC markers (DC-SIGN, CD11c, CD83) or with the DC-labeling ZnI(2)-OsO(4 )technique. Parallel tests with cultured DCs were carried out.

RESULTS

Cells reproducing ultrastructural and cytochemical patterns of DCs were detected in the lamina propria and epithelium of heavily infected and inflamed (but not of normal) mucosa, where DC luminal endings directly contact H. pylori and take up their virulence products. Cytotoxic changes (mitochondrial swelling, cytoplasmic vacuolation, autophagy) were observed in intraepithelial DCs and reproduced in cultured DCs incubated with H. pylori broth culture filtrates to obtain intracellular accumulation of VacA and urease. Granulocytes were also seen to contact and heavily phagocytose luminal H. pylori, while macrophages remained confined to basal epithelium, though taking up bacteria and bacterial products.

CONCLUSION

Human DCs can enter H. pylori-infected gastric epithelium, in association with other innate immunity cells, to take up bacteria and their virulence products. This process is likely to be important for bacterial sensing and pertinent immune response; however, it may also generate DC cytotoxic changes potentially hampering their function.

Smooth muscle cells, dendritic cells and mast cells are sources of TNFalpha and nitric oxide in human carotid artery atherosclerosis

INTRODUCTION

In atherogenesis, dendritic cells, beside presenting antigens, may be sources of tumour necrosis factor (TNF)alpha and nitric oxide (NO), together with mast cells and smooth muscle cells.

MATERIAL AND METHODS

We have looked at the expression of TNFalpha and inducible NO synthase (iNOs) by these cells by affinity cytochemistry in autoptical specimens from normal carotid arteries and not ruptured, hemorrhagic or calcified atheromata.

RESULTS

Round to dendritic, major histocompatibility complex class II molecules (MHC-II+) cells and avidin-labeled mast cells were rare in normal arteries and significantly more numerous in atheromata. Many MHC-II+ cells expressed S-100 antigen; while a few were positive for phalloidin; appreciable fractions of these cells were immunoreactive for TNFalpha and iNOs, both in control specimens and atheromata. The fraction of mast cells labeled for iNOs was significantly lower in atheromata than in controls. Phalloidin positive cells were the most abundant cell type in the normal intima and atheromata; the fractions of these cells labeled for TNFalpha and iNOs were significantly higher in atheromata than in controls. Very few of these cells were also labeled for MHC-II. Computerized image analysis confirmed that the amounts of iNOs and TNFalpha were higher in atheromata than in controls. The increase in TNFalpha in atheromata was also confirmed by western blot.

CONCLUSIONS

Dendritic cells and mast cells can participate to the generation of TNFalpha and NO in the normal arterial wall and in atheromata, but myointimal cells are candidates as major sources of these molecules.

Conventional, regulatory, and unconventional T cells in the immunologic response to Helicobacter pylori

Infection by the gastroduodenal pathogen Helicobacter pylori elicits a complex immunologic response in the mucosa involving neutrophils, plasma cells, eosinophils, and lymphocytes, of which T cells are the principal orchestrators of immunity. While so-called classical T cells (e.g. T-helper cells) that are activated by peptide fragments presented on antigen-presenting cells have received much attention in H. pylori infection, there exists a diverse array of other T cell populations that are potentially important for the outcome of the ensuing immune response, some of which have not been extensively studied in H. pylori infection. Pathogen-specific regulatory T cells that control and prevent the development of immunopathology associated with H. pylori infection have been investigated, but these cells can also benefit the bacterium in helping to prolong the chronicity of the infection by suppressing protective immune responses. An overlooked T cell population, the more recently described Th17 cells, may play a role in H. pylori-induced inflammation, due to triggering responses that ultimately lead to the recruitment of polymorphs, including neutrophils. The so-called innate or unconventional T cells, that include two conserved T cell subsets expressing invariant antigen-specific receptors, the CD1d-restricted natural killer T cells which are activated by glycolipids, and the mucosal-associated invariant T cells which play a role in defense against orally acquired pathogens in the intestinal mucosa, have only begun to receive attention. A greater knowledge of the range of T cell responses induced by H. pylori is required for a deeper understanding of the pathogenesis of this bacterium and its ability to perpetuate chronic infection, and could reveal new strategies for therapeutic exploitation.

Helicobacter pylori induces CCL20 expression

CCL20 attracts immature dendritic cells and memory T cells and plays a role on mucosal surfaces in inflammation. However, whether Helicobacter pylori infection induces CCL20 in human gastric epithelial cells remains to be determined. The aim of this study was to analyze the molecular mechanism of H. pylori-induced CCL20 expression. Expression of CCL20 mRNA was assessed by reverse transcription-PCR. Five normal and five H. pylori-infected gastric tissue samples were stained immunohistochemically for CCL20. A luciferase assay was used to monitor activation of the CCL20 gene promoter, and an electrophoretic mobility shift assay was used to explore the binding of transcription factors to this promoter. The CCL20 expression in epithelial cells of H. pylori-positive tissues was higher than that in H. pylori-negative tissues. H. pylori induced CCL20 expression in gastric epithelial cell lines, and the induction was dependent on an intact cag pathogenicity island. Activation of the CCL20 promoter by H. pylori occurred through the action of NF-kappaB. Transfection of IkappaB kinase and NF-kappaB-inducing kinase dominant negative mutants inhibited H. pylori-mediated activation of CCL20. Treatment with an inhibitor of Hsp90 suppressed H. pylori-induced CCL20 mRNA due to deactivation of NF-kappaB. Collectively, these results suggest that H. pylori activates NF-kappaB through an intracellular signaling pathway that involves IkappaB kinase and NF-kappaB-inducing kinase, leading to CCL20 gene transcription, and that Hsp90 is a crucial regulator of H. pylori-induced CCL20 expression, presumably contributing to the immune response in H. pylori.

Helicobacter pylori vaccine development: optimisation of strategies and importance of challenging strain and animal model

Gastric infection with the gram-negative bacterial pathogen Helicobacter pylori is widespread (approximately 50% of the human population is affected) and is associated with the induction of specific gastroduodenal disease. Although extensive studies in the H. pylori mouse model have demonstrated the feasibility of both therapeutic and prophylactic immunisations, the mechanism of vaccine-induced protection is still poorly understood. We report here on novel strategies to optimise the generation of H. pylori ghosts as vaccine candidates and highlight the need to concentrate on alternative animal models and the use of fully virulent H. pylori type I strains for vaccination. An effective vaccine strategy against H. pylori has the potential to significantly improve population health worldwide.

Expression of Helicobacter pylori virulence factors and associated expression profiles of inflammatory genes in the human gastric mucosa

Helicobacter pylori virulence factors have been suggested to be important in determining the outcome of infection. The H. pylori adhesion protein BabA2 is thought to play a crucial role in bacterial colonization and in induction of severe gastric inflammation, particularly in combination with expression of CagA and VacA. However, the influence of these virulence factors on the pathogenesis of H. pylori infection is still poorly understood. To address this question, the inflammatory gene expression profiles for two groups of patients infected with triple-negative strains (lacking expression of cagA, babA2, and vacAs1 but expressing vacAs2) and triple-positive strains (expressing cagA, vacAs1, and babA2 but lacking expression of vacAs2) were investigated. The gene expression patterns in the antrum gastric mucosa from patients infected with different H. pylori strains were very similar, and no differentially expressed genes could be identified by pairwise comparisons. Our data thus suggest that there is a lack of correlation between the host inflammatory responses in the gastric mucosa and expression of the babA2, cagA, and vacAs1 genes.

Immunology of Helicobacter pylori: insights into the failure of the immune response and perspectives on vaccine studies

Helicobacter pylori infects the stomach of half of the human population worldwide and causes chronic active gastritis, which can lead to peptic ulcer disease, gastric adenocarcinoma, and mucosa-associated lymphoid tissue lymphoma. The host immune response to the infection is ineffective, because the bacterium persists and the inflammation continues for decades. Bacterial activation of epithelial cells, dendritic cells, monocytes, macrophages, and neutrophils leads to a T helper cell 1 type of adaptive response, but this remains inadequate. The host inflammatory response has a key functional role in disrupting acid homeostasis, which impacts directly on the colonization patterns of H pylori and thus the extent of gastritis. Many potential mechanisms for the failure of the host response have been postulated, and these include apoptosis of epithelial cells and macrophages, inadequate effector functions of macrophages and dendritic cells, VacA inhibition of T-cell function, and suppressive effects of regulatory T cells. Because of the extent of the disease burden, many strategies for prophylactic or therapeutic vaccines have been investigated. The goal of enhancing the host's ability to generate protective immunity has met with some success in animal models, but the efficacy of potential vaccines in humans remains to be demonstrated. Aspects of H pylori immunopathogenesis are reviewed and perspectives on the failure of the host immune response are discussed. Understanding the mechanisms of immune evasion could lead to new opportunities for enhancing eradication and prevention of infection and associated disease.

The neutrophil-activating protein of Helicobacter pylori (HP-NAP) as an immune modulating agent

During evolution microorganisms have developed several immune modulating strategies. The Helicobacter pylori neutrophil-activating protein (HP-NAP) is a virulence factor that attracts and activates neutrophils, and promotes their endothelial adhesion and the production of oxygen radicals and chemokines, including CXCL8, CCL3 and CCL4. HP-NAP, a TLR2 agonist, is an immune modulator able to induce the expression of interleukin-12 (IL-12) and IL-23 by human neutrophils and monocytes. In fact, HP-NAP has the potential to shift antigen-specific T-cell responses from a predominant Th2 to a polarized Th1 cytotoxic phenotype, characterized by high levels of interferon-gamma and tumor necrosis factor-alpha production. Thus, HP-NAP is a key factor driving Th1 inflammation in H. pylori infection and may be a new tool for future therapeutic strategies aimed at redirecting Th2 into Th1 responses, for example in atopy, vaccinology and cancer immunotherapy.