Regulation of human beta-defensins by gastric epithelial cells in response to infection with Helicobacter pylori or stimulation with interleukin-1

Balancing Act of the Intestinal Antimicrobial Proteins on Gut Microbiota and Health

The human gut houses a diverse and dynamic microbiome critical for digestion, metabolism, and immune development, exerting profound effects on human health. However, these microorganisms pose a potential threat by breaching the gut barrier, entering host tissues, and triggering infections, uncontrolled inflammation, and even sepsis. The intestinal epithelial cells form the primary defense, acting as a frontline barrier against microbial invasion. Antimicrobial proteins (AMPs), produced by these cells, serve as innate immune effectors that regulate the gut microbiome by directly killing or inhibiting microbes. Abnormal AMP production, whether insufficient or excessive, can disturb the microbiome equilibrium, contributing to various intestinal diseases. This review delves into the complex interactions between AMPs and the gut microbiota and sheds light on the role of AMPs in governing host-microbiota interactions. We discuss the function and mechanisms of action of AMPs, their regulation by the gut microbiota, microbial evasion strategies, and the consequences of AMP dysregulation in disease. Understanding these complex interactions between AMPs and the gut microbiota is crucial for developing strategies to enhance immune responses and combat infections within the gut microbiota. Ongoing research continues to uncover novel aspects of this intricate relationship, deepening our understanding of the factors shaping gut health. This knowledge has the potential to revolutionize therapeutic interventions, offering enhanced treatments for a wide range of gut-related diseases.

Antimicrobial peptide production in response to gut microbiota imbalance

The gut microbiota presents essential functions in the immune response. The gut epithelium acts as a protective barrier and, therefore, can produce several antimicrobial peptides (AMPs) that can act against pathogenic microorganisms, including bacteria. Several factors cause a disturbance in gut microbiota, including the exacerbated and erroneous use of antibiotics. Antibiotic therapy has been closely related to bacterial resistance and is also correlated with undesired side-effects to the host, including the eradication of commensal bacteria. Consequently, this results in gut microbiota imbalance and inflammatory bowel diseases (IBD) development. In this context, AMPs in the gut epithelium play a restructuring role for gut microbiota. Some naturally occurring AMPs are selective for pathogenic bacteria, thus preserving the health microbiota. Therefore, AMPs produced by the host's epithelial cells represent effective molecules in treating gut bacterial infections. Bearing this in mind, this review focused on describing the importance of the host's AMPs in gut microbiota modulation and their role as anti-infective agents against pathogenic bacteria.

Host Cell Antimicrobial Responses against Helicobacter pylori Infection: From Biological Aspects to Therapeutic Strategies

The colonization of Helicobacter pylori (H. pylori) in human gastric mucosa is highly associated with the occurrence of gastritis, peptic ulcer, and gastric cancer. Antibiotics, including amoxicillin, clarithromycin, furazolidone, levofloxacin, metronidazole, and tetracycline, are commonly used and considered the major treatment regimens for H. pylori eradication, which is, however, becoming less effective by the increasing prevalence of H pylori resistance. Thus, it is urgent to understand the molecular mechanisms of H. pylori pathogenesis and develop alternative therapeutic strategies. In this review, we focus on the virulence factors for H. pylori colonization and survival within host gastric mucosa and the host antimicrobial responses against H. pylori infection. Moreover, we describe the current treatments for H. pylori eradication and provide some insights into new therapeutic strategies for H. pylori infection.

GM-CSF is key in the efficacy of vaccine-induced reduction of Helicobacter pylori infection

BACKGROUND

Helicobacter pylori (H. pylori) colonizes the human gastric mucosa with a high worldwide prevalence. Currently, H. pylori is eradicated by the use of antibiotics. However, elevated antibiotic resistance suggests new therapeutic strategies need to be envisioned: one approach being prophylactic vaccination. Pre-clinical and clinical data show that a urease-based vaccine is efficient in decreasing H. pylori infection through the mobilization of T helper (Th) cells, especially Th17 cells. Th17 cells produce interleukins such as IL-22 and IL-17, among others, and are key players in vaccine efficacy. Recently, granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing Th17 cells have been identified.

AIM

This study explores the possibility that GM-CSF plays a role in the reduction of H. pylori infection following vaccination.

RESULTS

We demonstrate that GM-CSF⁺ IL-17⁺ Th17 cells accumulate in the stomach mucosa of H. pylori infected mice during the vaccine-induced reduction of H. pylori infection. Secondly, we provide evidence that vaccinated GM-CSF deficient mice only modestly reduce H. pylori infection. Conversely, we observe that an increase in GM-CSF availability reduces H. pylori burden in chronically infected mice. Thirdly, we show that GM-CSF, by acting on gastric epithelial cells, promotes the production of βdefensin3, which exhibits H. pylori bactericidal activities.

CONCLUSION

Taken together, we demonstrate a key role of GM-CSF, most probably originating from Th17 cells, in the vaccine-induced reduction of H. pylori infection.

Sheep β-Defensin 2 Regulates Escherichia coli F17 Resistance via NF-κB and MAPK Signaling Pathways in Ovine Intestinal Epithelial Cells

Simple Summary

This study was conducted to explore the antibacterial ability of sheep β-defensin 2 (SBD-2) against E. coli F17 infection in ovine intestinal epithelial cells (OIECs). Our data revealed that E. coli F17 induces SBD-2 expression in OIECs in vitro, which appears to be mediated through the activation of the signaling pathways NF-κB and MAPK. Our results provide a novel insight for the functionality of SBD-2, which could be useful for developing anti-infective drugs and/or breeding for E. coli diarrhea disease-resistant sheep.

Abstract

Escherichia coli (E. coli) F17 is a member of enterotoxigenic Escherichia coli, which can cause massive diarrhea and high mortality in newborn lambs. β-defensin is mainly produced by the epithelial tissue of the gastrointestinal tract in response to microbial infection. However, the molecular mechanism of sheep β-defensin 2 (SBD-2) against E. coli F17 remains unclear. This study aims to reveal the antibacterial ability of SBD-2 against E. coli F17 infection in sheep. Firstly, we established the culture system of ovine intestinal epithelial cells (OIECs) in vitro, treated with different concentrations of E. coli F17 for an indicated time. Secondly, we performed RNA interference and overexpression to investigate the effect of SBD-2 expression on E. coli F17 adhesion to OIECs. Finally, inhibitors of NF-κB and MAPK pathways were pre-treated to explore the possible relationship involving in E. coli F17 infection regulating SBD-2 expression. The results showed that E. coli F17 markedly (p < 0.01) upregulated the expression levels of SBD-2 mRNA and protein in a concentration- and time-dependent manner. Overexpression of SBD-2 contributed to enhancing E. coli F17 resistance in OIECs, while silencing SBD-2 dramatically improved the adhesion of E. coli F17 to OIECs (p < 0.05 or p < 0.01). Furthermore, E. coli F17 stimulated SBD-2 expression was obviously decreased by pre-treatment with NF-κB inhibitor PDTC, p38 MAPK inhibitor SB202190 and ERK1/2 MAPK inhibitor PD98095 (p < 0.05 or p < 0.01). Interestingly, adhesion of E. coli F17 to OIECs were highly enhanced by pre-treated with PDTC, SB202190 and PD98095. Our data suggested that SBD-2 could inhibit E. coli F17 infection in OIECs, possibly through NF-κB and MAPK signaling pathways. Our results provide useful theoretical basis on developing anti-infective drug and breeding for E. coli diarrhea disease-resistant sheep.

The Dichotomous Responses Driven by β-Defensins

Defensins are short, rapidly evolving, cationic antimicrobial host defence peptides with a repertoire of functions, still incompletely realised, that extends beyond direct microbial killing. They are released or secreted at epithelial surfaces, and in some cases, from immune cells in response to infection and inflammation. Defensins have been described as endogenous alarmins, alerting the body to danger and responding to inflammatory signals by promoting both local innate and adaptive systemic immune responses. However, there is now increasing evidence that they exert variable control on the response to danger; creating a dichotomous response that can suppress inflammation in some circumstances but exacerbate the response to danger and damage in others and, at higher levels, lead to a cytotoxic effect. Focussing in this review on human β-defensins, we discuss the evidence for their functions as proinflammatory, immune activators amplifying the response to infection or damage signals and/or as mediators of resolution of damage, contributing to a return to homeostasis. Finally, we consider their involvement in the development of autoimmune diseases.

The Antimicrobial Peptide Human Beta-Defensin 2 Inhibits Biofilm Production of Pseudomonas aeruginosa Without Compromising Metabolic Activity

Biofilm production is a key virulence factor that facilitates bacterial colonization on host surfaces and is regulated by complex pathways, including quorum sensing, that also control pigment production, among others. To limit colonization, epithelial cells, as part of the first line of defense, utilize a variety of antimicrobial peptides (AMPs) including defensins. Pore formation is the best investigated mechanism for the bactericidal activity of AMPs. Considering the induction of human beta-defensin 2 (HBD2) secretion to the epithelial surface in response to bacteria and the importance of biofilm in microbial infection, we hypothesized that HBD2 has biofilm inhibitory activity. We assessed the viability and biofilm formation of a pyorubin-producing Pseudomonas aeruginosa strain in the presence and absence of HBD2 in comparison to the highly bactericidal HBD3. At nanomolar concentrations, HBD2 - independent of its chiral state - significantly reduced biofilm formation but not metabolic activity, unlike HBD3, which reduced biofilm and metabolic activity to the same degree. A similar discrepancy between biofilm inhibition and maintenance of metabolic activity was also observed in HBD2 treated Acinetobacter baumannii, another Gram-negative bacterium. There was no evidence for HBD2 interference with the regulation of biofilm production. The expression of biofilm-related genes and the extracellular accumulation of pyorubin pigment, another quorum sensing controlled product, did not differ significantly between HBD2 treated and control bacteria, and in silico modeling did not support direct binding of HBD2 to quorum sensing molecules. However, alterations in the outer membrane protein profile accompanied by surface topology changes, documented by atomic force microscopy, was observed after HBD2 treatment. This suggests that HBD2 induces structural changes that interfere with the transport of biofilm precursors into the extracellular space. Taken together, these data support a novel mechanism of biofilm inhibition by nanomolar concentrations of HBD2 that is independent of biofilm regulatory pathways.

Helicobacter pylori Exploits the NLRC4 Inflammasome to Dampen Host Defenses

Helicobacter pylori colonizes the stomach of around 50% of humans. This chronic infection can lead to gastric pathologic conditions such as gastric ulcers and gastric adenocarcinomas. The strong inflammatory response elicited by H. pylori is characterized by the induction of the expression of several cytokines. Among those, IL-18 is found highly upregulated in infected individuals, and its expression correlates with the severity of gastric inflammation. IL-18 is produced as inactive proform and has to be cleaved by the multiprotein complex inflammasome to be active. In immune cells, the NLRC4 inflammasome, which is activated by flagellin or bacterial secretion systems, was shown to be dispensable for H. pylori-induced inflammasome activation. However, apart from immune cells, gastric epithelial cells can also produce IL-18. In this study, we analyzed the role of the NLRC4 inflammasome during H. pylori infection. Our results indicate that NLRC4 and a functional type IV secretion system are crucial for the production of IL-18 from human and murine gastric epithelial cells. In vivo, Nlrc4^-/- mice failed to produce gastric IL-18 upon H. pylori infection. Compared with wild type mice, Nlrc4^-/- mice controlled H. pylori better without showing strong inflammation. Moreover, H. pylori-induced IL-18 inhibits β-defensin 1 expression in a NF-κB-dependent manner, resulting in higher bacterial colonization. At the same time, inflammasome activation enhances neutrophil infiltration, resulting in inflammation. Thus, NLRC4 inflammasome activation and subsequent IL-18 production favors bacterial persistence by inhibiting antimicrobial peptide production and, at the same time, contributes to gastric inflammation.

Carbohydrate-Dependent and Antimicrobial Peptide Defence Mechanisms Against Helicobacter pylori Infections

The human stomach is a harsh and fluctuating environment for bacteria with hazards such as gastric acid and flow through of gastric contents into the intestine. H. pylori gains admission to a stable niche with nutrient access from exudates when attached to the epithelial cells under the mucus layer, whereof adherence to glycolipids and other factors provides stable and intimate attachment. To reach this niche, H. pylori must overcome mucosal defence mechanisms including the continuously secreted mucus layer, which provides several layers of defence: (1) mucins in the mucus layer can bind H. pylori and transport it away from the gastric niche with the gastric emptying, (2) mucins can inhibit H. pylori growth, both via glycans that can have antibiotic like function and via an aggregation-dependent mechanism, (3) antimicrobial peptides (AMPs) have antimicrobial activity and are retained in a strategic position in the mucus layer and (4) underneath the mucus layer, the membrane-bound mucins provide a second barrier, and can function as releasable decoys. Many of these functions are dependent on H. pylori interactions with host glycan structures, and both the host glycosylation and concentration of antimicrobial peptides change with infection and inflammation, making these interactions dynamic. Here, we review our current understanding of mucin glycan and antimicrobial peptide-dependent host defence mechanisms against H. pylori infection.

How are the expression patterns of gut antimicrobial peptides modulated by human gastrointestinal diseases? A bridge between infectious, inflammatory, and malignant diseases

The human gut barrier is the tissue exposed to the highest load of microorganisms, harbouring 100 trillion bacteria. In addition, the gut's renewal rate outruns that of any other human tissue. Antimicrobial peptides (AMPs) are highly optimized defense molecules in the intestinal barrier optimized to maintain gastrointestinal homeostasis. Alterations in AMPs activity can lead to or result from human gastrointestinal diseases. In this review, unique, conserved, or otherwise regular alterations in the expression patterns of human AMPs across gastrointestinal inflammatory and infectious diseases were analyzed for pattern elucidation. Human gastrointestinal diseases are associated with alterations in gut AMPs' expression patterns in a peptide-specific, disease-specific, and pathogen-specific way, modulating human gastrointestinal functioning. Across diseases, there is a (i) marked reduction in otherwise constitutively expressed AMPs, leading to increased disease susceptibility, and a (ii) significant increase in the expression of inducible AMPs, leading to tissue damage and disease severity. Infections and inflammatory conditions are associated with altered gene expression in the gut, whose patterns may favour cellular metaplasia, mucosal dysfunction, and disease states. Altered expression of AMPs can thus thrive disease severity and evolution since its early stages. Nevertheless, the modulation of AMP expression patterns unveils promising therapeutic targets.

Contribution of TLR2 pathway in the pathogenesis of vulvovaginal candidiasis

Candida albicans is the prevalent etiological agent in acute vulvovaginal infection and the most severe chronic condition known as recurrent vulvovaginal candidiasis (VVC). A critical role of local innate immunity in defense and pathogenesis of vaginal infection by Candida is proposed. The fungal recognition by the innate immune receptor is an essential step for the induction of local responses including cytokines and antimicrobial peptides (AMPs) production for host protection. Using TLR2-deficient mice, we characterized the early innate immune response during VVC. Intravaginal challenge of TLR2-/- mice with C. albicans demonstrated that in response to the initial massive penetration, a strong local inflammatory reaction with recruitment of polymorphonuclear neutrophils was developed. Both interleukin 1β (IL1β)-regarded as the hallmark of VVC immunopathogenesis-and IL6 were increased in vaginal lavage. Murine beta defensin 1 (mBD1), a constitutive AMP with fungicidal and chemotactic activity, was significantly upregulated in wild type (WT) animals in response to infection. Interestingly, in the absence of TLR2 recognition, levels of mBD1 RNA more than twice higher than those in WT infected animals were observed. Interestingly, our results demonstrate that TLR2 signaling is important to control the fungal burden in the vaginal tract. These finding provide new evidence about the role of this innate receptor during VVC.

β-Defensins in the Fight against Helicobacter pylori

Antimicrobial peptides (AMPs) play a pivotal role in the innate immune responses to Helicobacter pylori (Hp) in humans. β-Defensins, a class of cationic arginine-rich AMPs, are small peptides secreted by immune cells and epithelial cells that exert antimicrobial activity against a broad spectrum of microorganisms, including Gram-positive and Gram-negative bacteria and fungi. During Hp infections, AMP expression is able to eradicate the bacteria, thereby preventing Hp infections in gastrointestinal tract. It is likely that gastric β-defensins expression is increased during Hp infection. The aim of this review is to focus on increased knowledge of the role of β-defensins in response to Hp infection. We also briefly discuss the potential use of AMPs, either alone or in combination with conventional antibiotics, for the treatment of Hp infection.

β-Defensin-2 is overexpressed in human vocal cord polyps

The objective of the study is to investigate the expression of human β-defensin-1 (hBD-1) and human β-defensin-2 (hBD-2) in vocal cord polyps using tissue microarray. Tissue specimens from vocal cord polyps (N = 51), vocal cord nodules (N = 26), and healthy vocal cords (N = 8) were retrieved from the biobank of the Department of Pathology of Tianjin Tianhe Hospital between 2003 and 2006 and immunostained on tissue microarrays for the quantitative analysis of hBD-1 and hBD-2 expression. hBD-1 expression did not differ significantly between healthy vocal cords, vocal cord nodules, and vocal cord polyps (p = 0.904). In contrast, hBD-2 expression was significantly higher in vocal cord polyps compared to vocal cord nodules and healthy vocal cords (p < 0.001). The expression of hBD-2, but not hBD-1, is elevated in vocal cord polyp epithelium. This suggests that hBD-1 has a more constitutive role in host defense in the vocal cords, whereas hBD-2 expression may be a result of local inflammation or the presence of invading pathogens.

How host regulation of Helicobacter pylori-induced gastritis protects against peptic ulcer disease and gastric cancer

The bacterial pathogen Helicobacter pylori is the etiological agent of a range of gastrointestinal pathologies including peptic ulcer disease and the major killer, gastric adenocarcinoma. Infection with this bacterium induces a chronic inflammatory response in the gastric mucosa (gastritis). It is this gastritis that, over decades, eventually drives the development of H. pylori-associated disease in some individuals. The majority of studies investigating H. pylori pathogenesis have focused on factors that promote disease development in infected individuals. However, an estimated 85% of those infected with H. pylori remain completely asymptomatic, despite the presence of pathogenic bacteria that drive a chronic gastritis that lasts many decades. This indicates the presence of highly effective regulatory processes in the host that, in most cases, keeps a check on inflammation and protect against disease. In this minireview we discuss such known host factors and how they prevent the development of H. pylori-associated pathologies.

TFF2, a MUC6-binding lectin stabilizing the gastric mucus barrier and more (Review)

The peptide TFF2 (formerly 'spasmolytic polypeptide'), a member of the trefoil factor family (TFF) containing two TFF domains, is mainly expressed together with the mucin MUC6 in the gastric epithelium and duodenal Brunner's glands. Pathologically, TFF2 expression is observed ectopically during stone diseases, chronic inflammatory conditions and in several metaplastic and neoplastic epithelia; most prominent being the 'spasmolytic polypeptide-expressing metaplasia' (SPEM), which is an established gastric precancerous lesion. TFF2 plays a critical role in maintaining gastric mucosal integrity and appears to restrain tumorigenesis in the stomach. Recently, porcine TFF2 has been shown to interact with the gastric mucin MUC6 and thus stabilize the gastric mucus barrier. On the one hand, TFF2 binds to MUC6 via non-covalent lectin interactions with the glycotope GlcNAcα1→4Galβ1→R. On the other hand, TFF2 is probably also covalently bound to MUC6 via disulfide bridges. Thus, implications for the complex multimeric assembly, cross-linking, and packaging of MUC6 as well as the rheology of gastric mucus are discussed in detail in this review. Furthermore, TFF2 is also expressed in minor amounts in the immune and nervous systems. Thus, similar to galectins, its lectin activity would perfectly enable TFF2 to form multivalent complexes and cross-linked lattices with a plethora of transmembrane glycoproteins and thus modulate different signal transduction processes. This could explain the multiple and diverse biological effects of TFF2 [e.g., motogenic, (anti)apoptotic, and angiogenic effects]. Finally, a function during fertilization is also possible for TFF domains because they occur as shuffled modules in certain zona pellucida proteins.

Chromosome-8-coded proteome of Chinese Chromosome Proteome Data set (CCPD) 2.0 with partial immunohistochemical verifications

We upgraded the preliminary CCPD 1.0 to CCPD 2.0 using the latest deep-profiling proteome (CCPD 2013) of three hepatocellular carcinoma (HCC) cell lines, namely, Hep3B, MHCC97H, and HCCLM3 (ProteomeXchange identifiers: PXD000529, PXD000533, and PXD000535). CCPD 2.0 totally covered 63.6% (438/689) of Chr. 8-coded proteins and 62.6% (439/701) of Chr. 8-coded protein-coding genes. Interestingly, we found that the missing proteins exhibited a tendency to form a cluster region in chromosomes, such as two β-defensins clusters in Chr. 8, caused perhaps by their inflammation-related features. For the 41 Chr. 8-coded proteins being weakly or barely identified previously, we have performed an immunohistochemical (IHC) verification in 30 pairs of carcinoma/para-carcinoma HCC and 20 noncancerous liver tissues and confirmed their expressional evidence and occurrence proportions in tissue samples. We also verified 13 Chr. 8-coded HCC tumorigenesis-associated depleting or deficient proteins reported in CCPD 1.0 using IHC and screened 16 positive and 24 negative HCC metastatic potential-correlated proteins from large-scale label-free proteome quantitation data of CCPD 2013. Our results suggest that the selection of proper samples and the methodology to look for targeted missing proteins should be carefully considered in further verifications for the remaining Chr. 8-coded proteins.

Gastric antimicrobial peptides fail to eradicate Helicobacter pylori infection due to selective induction and resistance

Background

Although antimicrobial peptides protect mucus and mucosa from bacteria, Helicobacter pylori is able to colonize the gastric mucus. To clarify in which extend Helicobacter escapes the antimicrobial defense, we systematically assessed susceptibility and expression levels of different antimicrobial host factors in gastric mucosa with and without H. pylori infection.

Materials and Methods

We investigated the expression levels of HBD1 (gene name DEFB1), HBD2 (DEFB4A), HBD3 (DEFB103A), HBD4 (DEFB104A), LL37 (CAMP) and elafin (PI3) by real time PCR in gastric biopsy samples in a total of 20 controls versus 12 patients colonized with H. pylori. Immunostaining was performed for HBD2 and HBD3. We assessed antimicrobial susceptibility by flow cytometry, growth on blood agar, radial diffusion assay and electron microscopy.

Results

H. pylori infection was associated with increased gastric levels of the inducible defensin HBD2 and of the antiprotease elafin, whereas the expression levels of the constitutive defensin HBD1, inducible HBD3 and LL37 remained unchanged. HBD4 was not expressed in significant levels in gastric mucosa. H. pylori strains were resistant to the defensins HBD1 as well as to elafin, and strain specific minimally susceptible to HBD2, whereas HBD3 and LL37 killed all H. pylori strains effectively. We demonstrated the binding of HBD2 and LL37 on the surface of H. pylori cells. Comparing the antibacterial activity of extracts from H. pylori negative and positive biopsies, we found only a minimal killing against H. pylori that was not increased by the induction of HBD2 in H. pylori positive samples.

Conclusion

These data support the hypothesis that gastric H. pylori evades the host defense shield to allow colonization.

Helicobacter pylori downregulates expression of human β-defensin 1 in the gastric mucosa in a type IV secretion-dependent fashion

Helicobacter pylori establishes a chronic lifelong infection in the human gastric mucosa, which may lead to peptic ulcer disease or gastric adenocarcinoma. The human beta-defensins (hβDs) are antimicrobial peptides, hβD1 being constitutively expressed in the human stomach. We hypothesized that H. pylori may persist, in part, by downregulating gastric hβD1 expression. We measured hβD1 and hβD2 expression in vivo in relation to the presence, density and severity of H. pylori infection, investigated differential effects of H. pylori virulence factors, and studied underlying signalling mechanisms in vitro. Significantly lower hβD1 and higher hβD2 mRNA and protein concentrations were present in gastric biopsies from infected patients. Those patients with higher-level bacterial colonization and inflammation had significantly lower hβD1 expression, but there were no differences in hβD2. H. pylori infection of human gastric epithelial cell lines also downregulated hβD1. Using wild-type strains and isogenic mutants, we showed that a functionalcag pathogenicity island-encoded type IV secretion system induced this downregulation. Treatment with chemical inhibitors or siRNA revealed that H. pylori usurped NF-κB signalling to modulate hβD1 expression. These data indicate that H. pylori downregulates hβD1 expression via NF-κB signalling, and suggest that this may promote bacterial survival and persistence in the gastric niche.

Differential expression of human beta defensin 2 and 3 in gastric mucosa of Helicobacter pylori-infected individuals

BACKGROUND

Antimicrobial peptides are key players of initial innate immune responses to human pathogens. Two major representatives, the human beta defensin 2 and 3 (hBD2 and hBD3), are both known to be regulated by, and to affect viability of, Helicobacter pylori. Previously, it was demonstrated in vitro that H. pylori actively abrogates hBD3 expression during prolonged infections. Here, we comprehensively assessed hBD2 and hBD3 expression ex vivo in the gastric mucosa of healthy individuals.

MATERIALS AND METHODS

Twenty volunteers (H. pylori positive and H. pylori negative: n = 10) were enrolled. Helicobacter pylori-positive subjects underwent eradication therapy and repeated the protocol. Expression of both defensins was assessed by quantitative RT-PCR and ELISA, and correlated with histopathologic degree of gastritis.

RESULTS

hBD2 and hBD3 were found to be ubiquitously expressed in all three groups. In general, hBD2 levels were elevated in relation to H. pylori infection (up to 40-fold). This upregulation correlated with degree of gastritis in corpus and antrum. In contrast, hBD3 protein levels were significantly decreased, while corresponding mRNA amounts remained unchanged. Eradication therapy led to normalization of mucosal hBD2 expression, while hBD3 expression demonstrated high interindividual variations among individuals.

CONCLUSIONS

Both defensins are ubiquitously but differentially expressed in gastric mucosa in relation to H. pylori infection. Ex vivo data support the notion that H. pylori infection is associated with reduced hBD3 expression in chronic active gastritis.

Antimicrobial peptide elicitors: New hope for the post-antibiotic era

Antimicrobial peptides or host defense peptides are fundamental components of human innate immunity. Recent and growing evidence suggests they have a role in a broad range of diseases, including cancer, allergies and susceptibility to infection, including HIV/AIDS. Antimicrobial peptide elicitors (APEs) are physical, biological or chemical agents that boost human antimicrobial peptide expression. The current knowledge of APEs and their potential use in the treatment of human infectious diseases are reviewed, and a classification system for APEs is proposed. The efficient use of APEs in clinical practice could mark the beginning of the urgently needed post-antibiotic era, but further trials assessing their efficacy and safety are required.

Recombinant human beta 2-defensin fusion proteins as a tool to investigate defensin structure and function in small human intestinal tissue samples

OBJECTIVE

Effects of immune cells on the beta 2 (β2)-defensin (HBD2) expression and its antibacterial activity in the intestinal mucosa of patients with inflammatory bowel diseases remains unclear. The small size of these proteins presents a major challenge in localizing antibacterial activities in human intestinal tissue. In this study, we evaluated the detection limits at mRNA and protein level by approaching HBD2 from small tissue samples.

METHODS

HT-29 colonic epithelial cells were incubated with proinflammatory cytokines before HBD2 mRNA was investigated by quantitative polymerase chain reaction. The HBD2 protein was assessed by Western blot analysis using HBD2 fused with enhanced green fluorescent protein (HBD2-EGFP). Purified HBD2 fused with the glutathione-S-transferase (GST-HBD2) was used to detect antibacterial activity in a densitometric assay.

RESULTS

Interleukin (IL)-1β induced HBD2 mRNA in HT-29 cells; however, tumor necrosis factor-α, IL-6 and IL-17 did not. The Western blot had a sensitivity of 1.5 pmol to detect recombinant HBD2, but did not detect HBD2 in either human intestinal or IL-1β-treated HT-29 cells. HBD2-EGFP was detected by HBD2-specific Western blot within cell lysates and culture supernants of transfected HT-29 and primary cells. In nanomolar ranges, GST-HBD2 reduced bacterial growth. The HBD2 bioactivity depended on solution conditions, but not on the size of the fusion partner.

CONCLUSION

The established fusion proteins provide excellent tools to evaluate expression patterns and antibacterial effects of HBD2 in human intestinal tissue samples.

Probiotics and small bowel mucosa: Molecular aspects of their interactions

Probiotics are described as "friendly bacteria" that could improve the intestine defense by interacting with the resident microflora. There is a large body of evidence suggesting that consumption of functional food containing probiotics exerts positive effects on human health. Several clinical trials have highlighted the efficiency of probiotics in the prevention and treatment of different gastrointestinal disorders including the prevention of antibiotic associated diarrhea, the remission in patients with inflammatory bowel disease, beneficial effects against Helicobacter pylori infection, positive effects in patients affected by allergies and atopic diseases. The clinical benefits of probiotics use are mainly attributed to their antimicrobial substances production and their positive interactions with the enterocytes to reinforce the intestinal epithelial barrier. Moreover, there is evidence suggesting that probiotics stimulate both specific and non-specific host immune responses. Recently, have been published some experiments performed with the DNA microarray technology which provided a global gene screening of the complex bacteria-host interplay. Nevertheless, the molecular mechanisms by which probiotics enhance the intestinal host defense are still not completely elucidated. Here, we review the experiments and clinical studies to date on the complex mechanisms regulating the communication between probiotics and their hosts.

Cholesterol enhances Helicobacter pylori resistance to antibiotics and LL-37

The human gastric pathogen Helicobacter pylori steals host cholesterol, modifies it by glycosylation, and incorporates the glycosylated cholesterol onto its surface via a cholesterol glucosyltransferase, encoded by cgt. The impact of cholesterol on H. pylori antimicrobial resistance is unknown. H. pylori strain 26695 was cultured in Ham's F12 chemically defined medium in the presence or absence of cholesterol. The two cultures were subjected to overnight incubations with serial 2-fold dilutions of 12 antibiotics, six antifungals, and seven antimicrobial peptides (including LL-37 cathelicidin and human alpha and beta defensins). Of 25 agents tested, cholesterol-grown H. pylori cells were substantially more resistant (over 100-fold) to nine agents than were H. pylori cells grown without cholesterol. These nine agents included eight antibiotics and LL-37. H. pylori was susceptible to the antifungal drug pimaricin regardless of cholesterol presence in the culture medium. A cgt mutant retained cholesterol-dependent resistance to most antimicrobials but displayed increased susceptibility to colistin, suggesting an involvement of lipid A. Mutation of lpxE, encoding lipid A1-phosphatase, led to loss of cholesterol-dependent resistance to polymyxin B and colistin but not other antimicrobials tested. The cgt mutant was severely attenuated in gerbils, indicating that glycosylation is essential in vivo. These findings suggest that cholesterol plays a vital role in virulence and contributes to the intrinsic antibiotic resistance of H. pylori.

Differential localization of lingual antimicrobial peptide in the digestive tract mucosal epithelium of calves

Immunolocalization of lingual antimicrobial peptide (LAP), a member of the β-defensin family, in the digestive tract of calves was investigated to determine its distribution in the digestive tract of Holstein-Friesian calves. Various regions of the digestive tract were collected from slaughtered calves, and fixed in 10% formalin in PBS. Paraffin sections were stained with anti-LAP antibody, followed by visualization of immunoreactions products utilizing the avidin-biotin complex method. Expression of LAP mRNA was analyzed with reverse transcription-PCR. Immunoreactive LAP was localized in the stratum corneum of the stratified squamous epithelium of the tongue, esophagus, rumen, reticulum and omasum but not in their basal layer and lamina propria. In the gastric glands of the abomasum, only chief cells showed LAP positive reaction at the apical side of their cytoplasm. Lamina propria and Peyer's patch of the ileum had some leukocyte-like cells immunopositive for LAP. Weak immunoreaction of LAP was also detected in the mucosal epithelium of the intestinal gland of the cecum, colon and rectum. All regions of digestive tract showed LAP mRNA expression with PCR. These results indicate differential localization of LAP in the mucosal epithelium of digestive tracts in calves. The LAP expressed in stratum corneum of stratified squamous epithelium and chief cells of abomasum specifically may play role in the innate immune function in these tissues.

Implications of the innate immune response to adenovirus and adenoviral vectors

Adenovirus (AdV) is a common cause of respiratory illness in both children and adults. Respiratory symptoms can range from those of the common cold to severe pneumonia. Infection can also cause significant disease in the immunocompromised and among immunocompetent subjects in close quarters. Fortunately, infection with AdV in the normal host is generally mild. This is one reason why its initial use as a gene-therapy vector appeared to be so promising. Unfortunately, both innate and adaptive responses to the virus have limited the development of AdV vectors as a tool of gene therapy by increasing toxicity and limiting duration of transgene expression. This article will focus on the innate immune response to infection with wild-type AdV and exposure to AdV gene-therapy vectors. As much of the known information relates to the pulmonary inflammatory response, this organ system will be emphasized. This article will also discuss how that understanding has led to the creation of new vectors for use in gene therapy.

Defensin-mRNA expression in the upper gastrointestinal tract is modulated in children with celiac disease and Helicobacter pylori-positive gastritis

OBJECTIVES

Defensins are expressed in epithelial cells as cationic peptides with antimicrobial properties. Because of their role as immunologically important effector molecules, their contribution in maintaining a stable microenvironment in the gastrointestinal tract has recently received much attention. The present study was designed to further characterize expression patterns of defensins in diseases of the upper gastrointestinal tract in children, particularly in Helicobacter pylori (Hp)-associated gastritis or celiac disease (CD).

PATIENTS AND METHODS

Semiquantitative real-time reverse transcriptase-polymerase chain reaction (PCR) was carried out with gene-specific primers for human beta-defensin 1 to 6 (hBD1 to 6) and human alpha-defensin 5 and 6 (hD5 and 6) in mucosal biopsies of children diagnosed as having CD (n = 11; 4.2-16.2 years) or Hp gastritis (n = 18; 3.2-16.7 years). Levels of expression were compared with those of healthy individuals (n = 21; 2.8-14.6 years). Expression levels in Hp-infected specimens were furthermore compared with those with histologic inflammation not associated with Hp infection (n = 30; 3.6-15.7 years).

RESULTS

Expression of hBD2 was upregulated in the antrum and corpus of patients with Hp gastritis, whereas inflammation without detection of Hp was not associated with any change in defensin gene expression. In patients with CD, expression of hBD2 was upregulated in the antrum, whereas hBD1 and 4 were downregulated in duodenal biopsies.

CONCLUSIONS

Different pathological conditions of the upper gastrointestinal tract lead to specific modulations of defensin gene expression in children. Especially the pathophysiological role of hBD2 in Hp infection and hBD1 and 4 in CD warrant further attention.

The innate immune molecule, NOD1, regulates direct killing of Helicobacter pylori by antimicrobial peptides

The cytosolic innate immune molecule, NOD1, recognizes peptidoglycan (PG) delivered to epithelial cells via the Helicobacter pylori cag pathogenicity island (cagPAI), and has been implicated in host defence against cagPAI(+)H. pylori bacteria. To further clarify the role of NOD1 in host defence, we investigated NOD1-dependent regulation of human beta-defensins (DEFBs) in two epithelial cell lines. Our findings identify that NOD1 activation, via either cagPAI(+) bacteria or internalized PG, was required for DEFB4 and DEFB103 expression in HEK293 cells. To investigate cell type-specific induction of DEFB4 and DEFB103, we generated stable NOD1'knockdown' (KD) and control AGS cells. Reporter gene assay and RT-PCR analyses revealed that only DEFB4 was induced in an NOD1-/cagPAI-dependent fashion in AGS cells. Moreover, culture supernatants from AGS control, but not AGS NOD1 KD cells, stimulated with cagPAI(+)H. pylori, significantly reduced H. pylori bacterial numbers. siRNA studies confirmed that human beta-defensin 2 (hBD-2), but not hBD-3, contributes to the antimicrobial activity of AGS cell supernatants against H. pylori. This study demonstrates, for the first time, the involvement of NOD1 and hBD-2 in direct killing of H. pylori bacteria by epithelial cells and confirms the importance of NOD1 in host defence mechanisms against cagPAI(+)H. pylori infection.

Defensins are differentially expressed with respect to the anatomic region in the upper gastrointestinal tract of children

Defensins are antimicrobial peptides expressed on various epithelial surfaces. Although they are believed to contribute to intestinal homeostasis, their expression pattern in children is not well characterized. As determined by real-time polymerase chain reaction, amount of human alpha-defensins (hD)-5 and -6 mRNA in duodenal biopsies were significantly higher than in biopsies taken from the gastric mucosa. On the contrary, expression of human beta-defensins (hBD)-1 and -2 mRNA showed a significantly higher expression in the stomach. Expression of hBD3 to 6 was inconsistently detected. These results suggest a distinct role for various defensins in host defense in the upper gastrointestinal tract of children.

Potential role of human beta-defensin 1 in Helicobacter pylori-induced gastritis

OBJECTIVE

Helicobacter pylori-induced gastric inflammation is dependent on the persistence of the microorganism in the gastric epithelium. Modulation of the host epithelial antimicrobial responses may be a critical determinant in H. pylori-induced gastritis. Human beta-defensins (hBDs) are important components of the host defence at mucosal surfaces. The aim of the present study was to investigate the relevance of three single nucleotide polymorphisms (SNPs) of the human beta defensin-1 (hBD-1) gene in H. pylori-induced gastritis and to assess the mRNA expression of hBD-1 in H. pylori-infected AGS cells.

MATERIAL AND METHODS

Three SNPs of the beta defensin DEFB1 gene, DEFB1 G-20A (rs11362), DEFB1 C-44G (rs1800972) and DEFB1 G-52A (rs1799946), were genotyped either by Custom TaqMan SNP genotyping assays or by restriction fragment length polymorphism (RFLP) in 150 patients with chronic active gastritis; 100 serologically H. pylori-positive subjects without gastric or duodenal symptoms served as controls. hBD-1 mRNA expression in AGS cells was measured by quantitative reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Significant differences in frequencies of the GA and AA genotypes of G-52A SNPs were observed between patients with chronic active gastritis and healthy controls. The maximum level of hBD-1 mRNA expression in AGS cells was observed at 24 h after infection with H. pylori, this not being dependent on the presence of the cag pathogenicity island (PAI).

CONCLUSIONS

The results of these genetic and in vitro experiments suggest that not only the inducible, but also the constitutive form of hBD may be important in the pathogenesis of H. pylori-induced gastritis.

Rhamnolipid-induced shedding of flagellin from Pseudomonas aeruginosa provokes hBD-2 and IL-8 response in human keratinocytes

Several 'pathogen-associated molecular pattern' (PAMP) of the opportunistic pathogen Pseudomonas aeruginosa activate the innate immune system in epithelial cells. Particularly the production of antimicrobial peptides such as the human beta-defensin-2 (hBD-2) and proinflammatory cytokines as the interleukin (IL)-8 is boosted. In the present study culture supernatants of static grown P. aeruginosa were found to be potent hBD-2 and IL-8 inducers, indicating a soluble or shedded PAMP, comparable to that of heat-killed bacterial supernatants. In subsequent analyses this PAMP was identified as flagellin, the major structural protein of the flagella. Flagellin is known to be an immunostimulatory potent factor, but the mechanisms by which P. aeruginosa is able to remove flagellin from the flagella remain unknown. Here we provide evidence for the presence of a factor responsible for release of flagellin from the flagella. Purification of this factor and subsequent mass spectrometry analyses identified rhamnolipids as responsible agents. Our findings indicate that maybe upon adhesion to surfaces P. aeruginosa alters the outer membrane composition in a rhamnolipid-depending manner, thereby shedding flagellin from the flagella. In turn epithelial cells recognize flagellin and cause the synthesis of antimicrobial peptides as well as recruitment of inflammatory cells by induction of proinflammatory cytokines.

Expression of beta-defensin 4 is increased in human gastritis

BACKGROUND

Infection with Helicobacter pylori (H. pylori) leads to the initiation of innate immune responses with increased antimicrobial peptide (AMP) expression in the gastric epithelium. This study aimed to determine the expression of the novel peptides beta-defensin 4 (hBD-4) and RNase 7 in infectious and non-infectious gastritis. Furthermore, pattern recognition receptors and mechanisms of regulation were characterized.

MATERIALS AND METHODS

Expression of AMPs was quantified by real-time PCR in biopsies obtained from healthy individuals and patients with infectious and non-infectious gastritis as well as in AGS gastric epithelial cells infected with H. pylori. Distribution of hBD-4 in the gastric mucosa was characterized by in-situ hybridisation and immunohistochemistry. The role of Toll-like receptors (TLRs) 2 and 4 and associated signalling pathways was addressed.

RESULTS

hBD-4 was expressed at low levels in gastric epithelial cells and was significantly upregulated in infectious and non-infectious gastritis. Standard eradication but not acid suppression therapy significantly decreased hBD-4 expression. Cytotoxin associated gene (cag)A positive H. pylori significantly increased the expression of hBD-4 whereas cagA negative organisms, non-viable bacteria or culture supernatants had no significant effect. Overexpression and downregulation of TLRs was not associated with an altered hBD-4 expression. However, blocking experiments revealed an essential role for the p38 mitogen-activated protein kinase. RNase7 was inconsistently expressed in biopsies and not significantly upregulated by H. pylori.

CONCLUSIONS

hBD-4 may play a significant role in H. pylori associated gastritis. Inconsistent expression of RNase 7 does not support a pivotal role for this peptide in response to infection with H. pylori.

Human antimicrobial proteins effectors of innate immunity

We live in a world populated by an enormous number of micro-organisms. This necessitates the existence of highly effective mechanisms to control microbial growth. Through many research efforts, a chemical defense system based on the production of antimicrobial proteins (AMPs) has been identified. AMPs are endogenous, small proteins exhibiting antimicrobial activity against a wide variety of micro-organisms. The wide distribution of these molecules in the plant and animal kingdom reflects their biological significance. Various human AMPs show a potent effect on pathogenic micro-organisms including antibiotic-resistant bacteria. Thus, there is great interest in understanding the role of AMPs within innate immunity and evaluating their use and/or specific induction to fend off infections. In this review, we provide an overview of the characteristics of human AMPs and discuss examples where AMPs may be involved in the pathogenesis of infectious and inflammatory diseases.

Helicobacter pylori induces an antimicrobial response in rhesus macaques in a cag pathogenicity island-dependent manner

BACKGROUND & AIMS

We used the rhesus macaque model to study the effects of the cag pathogenicity island (cag PAI) on the H pylori host-pathogen interaction.

METHODS

H pylori-specific pathogen-free (SPF) monkeys were experimentally challenged with wild-type (WT) H pylori strain J166 (J166WT, n = 4) or its cag PAI isogenic knockout (J166Deltacag PAI, n = 4). Animals underwent endoscopy before and 1, 4, 8, and 13 weeks after challenge. Gastric biopsies were collected for quantitative culture, histopathology, and host gene expression analysis.

RESULTS

Quantitative cultures showed that all experimentally challenged animals were infected with J166WT or its isogenic J166Deltacag PAI. Histopathology demonstrated that inflammation and expansion of the lamina propria were attenuated in animals infected with J166Deltacag PAI compared with J166WT. Microarray analysis showed that of the 119 up-regulated genes in the J166WT-infected animals, several encode innate antimicrobial effector proteins, including elafin, siderocalin, DMBT1, DUOX2, and several novel paralogues of human-beta defensin-2. Quantitative RT-PCR confirmed that high-level induction of each of these genes depended on the presence of the cag PAI. Immunohistochemistry confirmed increased human-beta defensin-2 epithelial cell staining in animals challenged with J166WT compared with either J166Deltacag PAI-challenged or uninfected control animals.

CONCLUSIONS

We propose that one function of the cag PAI is to induce an antimicrobial host response that may serve to increase the competitive advantage of H pylori in the gastric niche and could even provide a protective benefit to the host.

Alpha-defensin expression in the gastric tissue of children with Helicobacter pylori-associated chronic gastritis: an immunohistochemical study

In this study, we evaluated the expression of alpha-defensin and its correlation with histological criteria in children with and without Helicobacter pylori-associated gastritis. Forty-five children were included. Immunohistochemical staining was performed and the relationship between alpha-defensin immunoscoring and H. pylori status and histological criteria was evaluated. Expression of alpha-defensin was significantly higher in the H. pylori-positive group (P < 0.001) and it was significantly associated with higher grades of chronic inflammation and neutrophil density (P < 0.001 for both). Our data show that alpha-defensin expression is increased in H. pylori infection in childhood and is associated with inflammatory tissue damage.

Cloning and identification of a novel sperm binding protein, HEL-75, with antibacterial activity and expressed in the human epididymis

BACKGROUND

The HEL-75 protein is a beta-defensin that was identified by analyzing a human epididymis cDNA library. Studying its function may not only elucidate the mechanisms of host defense, but may also provide new alternatives for novel therapeutic drugs for reproductive tract infections.

METHODS

The HEL-75 gene was amplified by PCR, and its structure and function were predicted and analyzed with bioinformatics tools. Polyclonal serum was raised against recombinant HEL (rHEL)-75 protein. The gene expression pattern was analyzed with RT-PCR and immunofluorescent staining. Finally, the antimicrobial activity and function during fertilization of HEL-75 were analyzed using a colony-forming unit assay and IVF, respectively.

RESULTS

The human HEL-75 gene is located on chromosome 20p13 and encodes a 95 amino acid protein with a predicted N-terminal signal peptide of 22 amino acids. The protein has six conserved cysteine residues, characteristic of members of the beta-defensin superfamily, as well as several potential post-translational modification sites. At the transcriptional level, HEL-75 was expressed in the epididymis and lung, but only in the epididymis at the translational level. Immunofluorescent staining showed that HEL-75 protein bound spermatozoa in the epididymis. RHEL-75 protein could kill Escherichia coli in vitro in a dose- and time-dependent fashion. However, no effect was observed on sperm motility nor fertilization when spermatozoa were blocked with anti-rHEL-75 polyclonal serum.

CONCLUSION

HEL-75 is a new beta-defensin expressed in the epididymis and on sperm; it may play an important role in host defense.

Avian defensins

Modulation of defensin expression may be one way to improve animal health and to reduce zoonotic diseases. Defensins are small, cationic, and amphipathic cysteine-rich antibiotic peptides found in plants, insects, mammals and birds. Whereas α- and θ-defensins appear to be absent in birds, several β-defensins have been isolated from avian heterophils. In addition, β-defensins were found to be constitutively or inducibly expressed at mucosal surfaces of the respiratory, intestinal and urogenital tracts. In this review the current knowledge of the defensin repertoire of birds, their tissue-specific expression, regulation and corresponding biological functions are described.

Nuclear localization of HBD-1 in human keratinocytes

OBJECTIVE

Human defensins and cathelicidins are a family of cationic antimicrobial peptides (AMPs), which play multiple roles in both innate and adaptive immune systems. They have direct antimicrobial activity against several microorganisms including burn pathogens. The majority of components of innate and adaptive immunity either express naturally occurring defensins or are otherwise chemoattracted or functionally affected by them. They also enhance adaptive immunity and wound healing and alter antibody production. All mechanisms to explain multiple functions of AMPs are not clearly understood. Prior studies to localize defensins in normal and burned skin using deconvolution fluorescence scanning microscopy indicate localization of defensins in the nucleus, perinuclear regions, and cytoplasm. The objective of this study is to further confirm the identification of HBD-1 in the nucleus by deconvolution microscopic studies involving image reconstruction and wire frame modeling.

RESULTS

Our study demonstrated the presence of intranuclear HBD-1 in keratinocytes throughout the stratum spinosum by costaining with the nuclear probe DAPI. In addition, HBD-1 sequence does show some homology with known cationic nuclear localization signal sequences.

CONCLUSION

To our knowledge, this is the first report to localize HBD-1 in the nuclear region, suggesting a role for this peptide in gene expression and providing new data that may help determine mechanisms of defensin functions.

Host antimicrobial defence peptides in human disease

Antimicrobial peptides or host defence peptides are endogenous peptide antibiotics, which have been confirmed as an essential part of the immune system. Apart from direct killing of bacteria, a role for the peptides in antiviral and immunomodulatory functions has recently been claimed. In this chapter we have focused on the host contact with microbes, where these host defence peptides are key players. The interplay with commensals and pathogens in relation to antimicrobial peptide expression is discussed, with specific emphasis on the respiratory and the alimentary systems. A possible novel difference in epithelial interactions between commensals and pathogens is considered in relation to disease.

Human β-defensin-3 induction in H pylori-infected gastric mucosal tissues

AIM: To examine human β-defensin-3 (hBD-3) expression in inflamed gastric mucosal tissues or MKN45 gastric cancer cells with or without H pylori infection for better understanding the innate immune response to H pylori.

METHODS: We used reverse transcription-polymerase chain reactions and immunohistochemistry to examine hBD-3 expression in inflamed gastric mucosal tissues or MKN45 gastric cancer cells with or without H pylori. Effects of hBD-3 against H pylori were also evaluated.

RESULTS: The mean mRNA expression of hBD-3 in H pylori-positive specimens was significantly higher than that in H pylori-negative specimens (P = 0.0002, Mann-Whitney). In addition, unlike uninfected samples, 8 of 15 (53.33%) infected mucosal samples expressed hBD-3 protein. H pylori dose-dependently induced mRNA expression of hBD-3 in MKN45 cells, an effect inhibited by adding anti-toll-like receptor (TLR)-4 antibody. HBD-3 protein completely inhibited H pylori growth.

CONCLUSION: Our results suggest that like hBD-2, hBD-3 may be involved in the pathophysiology of H pylori-induced gastritis.

Localization of antimicrobial peptides in normal and burned skin

Severe burn causes immunosuppression, and the eschar remains a perfect culture medium for microbial growth. The resulting sepsis is a common complication of burns with a high mortality. The skin produces a number of molecules including antimicrobial peptides (AMPs) that act in the first line of host defense. Previous studies from our laboratory suggested decreased expression of human beta-defensin-2 (HBD-2) in burned wounds. Here, we have expanded our work by identifying HBD-1, HBD-2, HBD-3 and human neutrophil peptide (HNP) in normal and burn skin samples using fluorescence deconvolution microscopy. In normal skin, HBD-1 was localized to the perinuclear region of keratinocytes, while HBD-2 was seen primarily in the stratum basale of the epidermis. HBD-3 was found in dendritic cells of the stratum spinosum. HNP was distributed in a somewhat random pattern in the papillary dermis. In burned skin, in which the epidermis had been destroyed or disrupted, the presence of HBD-1 was localized to dermal glandular structures and hair shafts. HBD-2 was found in both the upper portions of the remaining keratin layers, and localized to lower, f-actin containing, acini-like structures, a pattern also evident with HBD-3. We conclude that although the upper layers of skin are destroyed and disrupted by burn, cells in the lower portions of the skin demonstrate an ability to synthesize most of the AMPs, thereby maintaining some barrier against infection. The results of these studies further contribute to an understanding of the role of AMPs in the pathophysiology of cutaneous burn and the possibility of using these sites for upregulation of AMP synthesis in the prevention of burn sepsis.

Nucleotide-binding oligomerization domain-1 and epidermal growth factor receptor: critical regulators of beta-defensins during Helicobacter pylori infection

Host-pathogen interactions that allow Helicobacter pylori to survive and persist in the stomach of susceptible individuals remain unclear. Human beta-defensins (hBDs), epithelial-derived antimicrobial peptides are critical components of host-defense at mucosal surfaces. The role of H. pylori-mediated NF-kappaB and epidermal growth factor receptor (EGFR) activation on beta-defensin expression was investigated. Transient transfection studies utilizing beta-defensin promoter constructs were conducted in gastric cells with contribution of individual signaling events evaluated by the addition of specific inhibitors, small interference nucleotide-binding oligomerization domain 1 (NOD1) RNA or plasmids encoding Vaccinia virus proteins that interrupt interleukin-1 and Toll-like receptor signaling. The role of individual MAPK pathways was further delineated in HEK-293 cells expressing conditional MAPK mutants. We found hBD2 expression exclusively dependent on the presence of the bacterial cag pathogenicity island, with NOD1 a critical host sensor. Impairment of murinebeta-defensin 4 (an orthologue of hBD2) expression in NOD1-deficient mice 7-days post-infection further confirmed the role of this cytoplasmic pattern-recognition receptor in eliciting host innate immunity. In contrast to hBD2, hBD3 expression was NOD1-independent but EGFR and ERK pathway-dependent. Importantly, Toll-like receptor signaling was not implicated in H. pylori-mediated hBD2 and hBD3 gene expression. The divergent signaling events governing hBD2 and hBD3 expression suggest temporal functional variation, such that hBD2 may contribute to antimicrobial barrier function during the inflammatory phase with hBD3 playing a greater role during the repair, wound healing phase of infection.

Expression of nuclear factor-kappa B and β-defensin-2 in patients with Helicobacter pylori-positive peptic ulcer and their relations with antral gastritis

AIM: To investigate the roles of nuclear factor kappa B (NF-κB), human β-defensin-2 (HBD-2) and antral gastritis in H. pylori-positive peptic ulcer (PU).

METHODS: Patients with H. pylori-positive (n = 40) or H. pylori-negative (n = 17) PU were included in this study. Eight individual were selected as normal controls. Antral histopathology was observed in the patients and controls. The expression of NF-κBp65 and β-denfensin-2 were measured by immunohistochemistry, and then compared between H. pylori-positive and negative patients and normal group as well as between patients with different stages of PU by One-Way ANOVA. Nonparametric statistics was used to analyze the correlations of H. pylori infection, NF-κBp65, HBD-2 expression with the degree of antral gastritis. Meanwhile, the relationship between expression of NF-κBp65 and HBD-2 was also analyzed in H. pylori-positive PU.

RESULTS: The histological severities of both active and chronic inflammation were correlated with H. pylori density (active: r = 0.374, P < 0.01; chronic: r = 0.333, P < 0.05). NF-κBp65 was expressed mainly in the nucleus of gastric epithelial and mesenchymal cells in lamina propria while HBD-2 was expressed mainly in the cytoplasm of the surface cells of gastric mucosal epithelium. The expression of NF-κBp65 and HBD-2 were significantly higher in H. pylori-positive patients than those in H. pylori-negative ones (6.4 ± 3.28 vs 3.78 ± 2.16, P < 0.01; 12.96 ± 5.03 vs 4.69 ± 2.05, P < 0.01), and both expression of NF-κBp65 and HBD-2 were correlated with histological severity of active and chronic inflammation (active: r = 0.744, 0.524, P < 0.01; chronic: r = 0.650, 0.606, P < 0.01). There was a positive correlation between the expression of NF-κBp65 and HBD-2 (r = 0.438, P < 0.01). The expression of NF-κBp65 (4.28 ± 2.11, 3.65 ± 2.27) and HBD-2 (8.15 ± 4.28, 6.24 ± 3.71) in PU patients at the stage of healing and scaring were lower significantly than those (7.14 ± 3.24, 13.56 ± 5.43) of PU patients at active stage (P < 0.05 or P < 0.01).

CONCLUSION: H. pylori infection leads to the over-expression of NF-κB and HBD-2 and enhancement of active and chronic inflammation. NF-κB activation may contribute to the induction of HBD-2 expression, and play an important role in the pathogenesis of H. pylori-positive PU.

The translation of Helicobacter pylori basic research to patient care

In 1984, Barry Marshall and Robin Warren proposed a role for bacterial infections in the pathogenesis of gastroduodenal disease, which triggered an avalanche of research intended to prove or disprove their theory. The result has been a series of advances that have enhanced our understanding of these diseases and completely modernized the clinical approach to their management. In just over 20 years, many aspects of the immunopathogenesis of these diseases have been dissected at the molecular level, with key pathogenic mechanisms being validated by the identification of genes that are associated with the development of gastric cancer. There has been particular emphasis on understanding the molecular structures associated with Helicobacter pylori and their role in modifying the host responses. Gastric immune and inflammatory responses have emerged as key elements in the pathogenesis of gastritis and epithelial cell damage. This review summarizes important findings emanating from basic research primarily related to the immunopathogenesis of H pylori that have advanced the practice of medicine or our understanding of gastroduodenal disease.

Regulation of mammalian defensin expression by Toll-like receptor-dependent and independent signalling pathways

The immune system consists of innate and adaptive immune responses. The innate immune system confers non-specific protection against a large number of pathogens, hence, serving as the first line of defence. The innate immune system utilizes Toll-like receptors (TLRs) to recognize and bind pathogen-associated molecular patterns (PAMPs). Binding of PAMPs leads to TLR activation, which, in turn, initiates MAPK- or NF-kappaB-dependent cascades that culminate in a proinflammatory response. This response involves the secretion of cytokines, chemokines and broad-spectrum antibacterial substances, such as defensins. Increased defensin synthesis is also mediated by the activation of receptors other than TLRs, such as NOD2, IL-17R and PAR-2. This review summarizes the recently characterized signalling pathways leading to increased defensin synthesis as well as the pathway by which defensins activate TLRs on immature dendritic and memory T cells. Thus, not only do defensins eliminate pathogens, but they also recruit the adaptive immune system in instances of infection and/or inflammation.

NOD2/CARD15 mediates induction of the antimicrobial peptide human beta-defensin-2

Production of inducible antimicrobial peptides offers a first and rapid defense response of epithelial cells against invading microbes. Human beta-defensin-2 (hBD-2) is an antimicrobial peptide induced in various epithelia upon extracellular as well as intracellular bacterial challenge. Nucleotide-binding oligomerization domain protein 2 (NOD2/CARD15) is a cytosolic protein involved in intracellular recognition of microbes by sensing peptidoglycan fragments (e.g. muramyl dipeptide). We used luciferase as a reporter gene for a 2.3-kb hBD-2 promoter to test the hypothesis that NOD2 mediates the induction of hBD-2. Activation of NOD2 in NOD2-overexpressing human embryonic kidney 293 cells through its ligand muramyl dipeptide (MDP) induced hBD-2 expression. In contrast, overexpression of NOD2 containing the 3020insC frame-shift mutation, the most frequent NOD2 variant associated with Crohn disease, resulted in defective induction of hBD-2 through MDP. Luciferase gene reporter analyses and site-directed mutagenesis experiments demonstrated that functional binding sites for NF-kappaB and AP-1 in the hBD-2 promoter are required for NOD2-mediated induction of hBD-2 through MDP. Moreover, the NF-kappaB inhibitor Helenalin as well as a super-repressor form of the NF-kappaB inhibitor IkappaB strongly inhibited NOD2-mediated hBD-2 promoter activation. Expression of NOD2 was detected in primary keratinocytes, and stimulation of these cells with MDP induced hBD-2 peptide release. In contrast, small interference RNA-mediated down-regulation of NOD2 expression in primary keratinocytes resulted in a defective induction of hBD-2 upon MDP treatment. Together, these data suggest that NOD2 serves as an intracellular pattern recognition receptor to enhance host defense by inducing the production of antimicrobial peptides such as hBD-2.