Human beta-defensin-2 induction in Helicobacter pylori-infected gastric mucosal tissues: antimicrobial effect of overexpression

Development of a Novel Pan-Species Multi-Epitope Vaccine (PS-MEV) Targeting Nine Staphylococcus Species to Combat Antibiotic Resistance

The increasing prevalence of antibiotic-resistant Staphylococcus species, including methicillin-resistant strains, calls for innovative approaches like a pan-species multi-epitope vaccine (PS-MEV). In this study, Sortase A (SrtA) was selected as the target protein due to its conserved role in Staphylococcus pathogenesis, and the MEV was designed to target nine Staphylococcus species. After stringent filtration of epitopes to ensure antigenicity, non-toxicity, and non-allergenicity, structural models of the MEV construct were generated using I-TASSER, AlphaFold, and RoseTTAFold. Docking analyses confirmed strong binding interactions between the MEV and TLR-3, with the AlphaFold model exhibiting the lowest binding energy of - 1284.1 kcal/mol and a center energy of - 1066.5 kcal/mol. The I-TASSER and RoseTTAFold models showed slightly higher binding energies, with lowest binding energies of - 938.5 kcal/mol and - 950.9 kcal/mol, respectively, and center energies of - 842.2 kcal/mol and - 825.4 kcal/mol. These values demonstrate consistent receptor binding across the models. Molecular dynamics (MD) simulations confirmed the stability of the interactions with the immune receptor, and immune simulations showed notable cytokine peaks, memory cell production, and a sustained T-cell response, indicating the potential for long-lasting immunity. Physicochemical profiling indicated that the vaccine construct is stable, moderately thermostable, and hydrophilic, which can enhance bioavailability and immunogenic effectiveness. This pan-species MEV presents a promising avenue in Staphylococcus vaccine development, with implications for broader applications in combating antibiotic-resistant pathogens.

Human β-defensins: The multi-functional natural peptide

The increasing threat of antibiotic resistance among pathogenic microorganisms and the urgent demand for new antibiotics require immediate attention. Antimicrobial peptides exhibit effectiveness against microorganisms, fungi, viruses, and protozoa. The discovery of human β-defensins represents a major milestone in biomedical research, opening new avenues for scientific investigation into the innate immune system and its resistance mechanisms against pathogenic microorganisms. Multiple defensins present a promising alternative in the context of antibiotic abuse. However, obstacles to the practical application of defensins as anti-infective therapies persist due to the unique properties of human β-defensins themselves and serious pharmacological and technical challenges. To overcome these challenges, diverse delivery vehicles have been developed and progressively improved for the conjugation or encapsulation of human β-defensins. This review briefly introduces the biology of human β-defensins, focusing on their multistage structure and diverse functions. It also discusses several heterologous systems for producing human β-defensins, various delivery systems created for these peptides, and patent applications related to their utilization, concluding with a summary of current challenges and potential solutions.

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.

Gastric alarmin release: A warning signal in the development of gastric mucosal diseases

Alarmins exist outside cells and are early warning signals to the immune system; as such, alarmin receptors are widely distributed on various immune cells. Alarmins, proinflammatory molecular patterns associated with tissue damage, are usually released into the extracellular space, where they induce immune responses and participate in the damage and repair processes of mucosal diseases.In the stomach, gastric alarmin release has been shown to be involved in gastric mucosal inflammation, antibacterial defense, adaptive immunity, and wound healing; moreover, this release causes damage and results in the development of gastric mucosal diseases, including various types of gastritis, ulcers, and gastric cancer. Therefore, it is necessary to understand the role of alarmins in gastric mucosal diseases. This review focuses on the contribution of alarmins, including IL33, HMGB1, defensins and cathelicidins, to the gastric mucosal barrier and their role in gastric mucosal diseases. Here, we offer a new perspective on the prevention and treatment of gastric mucosal diseases.

Beta-defensins and analogs in Helicobacter pylori infections: mRNA expression levels, DNA methylation, and antibacterial activity

Antimicrobial peptides can protect the gastric mucosa from bacteria, but Helicobacter pylori (H. pylori) can equally colonize the gastric apparatus. To understand beta-defensin function in H. pylori-associated chronic gastritis, we investigated susceptibility, human beta-defensin mRNA expression, and DNA methylation changes to promoters in the gastric mucosa with or without H. pylori infection. We studied the expression of HBD2 (gene name DEFB4A), HBD3 (DEFB103A), and HBD4 (DEFB104) using real-time PCR in 15 control and 10 H. pylori infection patient gastric specimens. This study demonstrates that H. pylori infection is related to gastric enhancement of inducible HBD2, but inducible HBD3 and HBD4 expression levels remained unchanged. HBD2 gene methylation levels were overall higher in H. pylori-negative samples than in H. pylori-positive samples. We also assessed antimicrobial susceptibility using growth on blood agar. The H. pylori strain Tox+ was susceptible to all defensins tested and their analogs (3N, 3NI). These results show that HBD2 is involved in gastritis development driven by H. pylori, which facilitates the creation of an epigenetic field during H. pylori-associated gastric tumorigenesis.

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.

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.

Interleukin-17A (IL-17A) and IL-17F Are Critical for Antimicrobial Peptide Production and Clearance of Staphylococcus aureus Nasal Colonization

Approximately 20% of the population is persistently colonized by Staphylococcus aureus in the nares. Th17-like immune responses mediated by the interleukin-17 (IL-17) family of cytokines and neutrophils are becoming recognized as relevant host defense mechanisms for resolution of S. aureus mucocutaneous infections. Since antimicrobial peptides are regulated by the IL-17 cytokines, we sought to determine the role of IL-17 cytokines in production of antimicrobial peptides in a murine model of S. aureus nasal carriage. We discovered that nasal tissue supernatants have antistaphylococcal activity, and mice deficient in both IL-17A and IL-17F lost the ability to clear S. aureus nasal colonization. IL-17A was found to be sufficient for nasal mBD-3 production ex vivo and was required for CRAMP, mBD-3, and mBD-14 expression in response to S. aureus colonization in vivo These data were confirmed in a clinical study of nasal secretions in which elevated levels of the human forms of these antimicrobial peptides were found in nasal secretions from healthy human subjects when they were colonized with S. aureus but not in secretions from noncolonized subjects. Together, these data provide evidence for the importance of IL-17A regulation of antimicrobial peptides and IL-17F in the clearance of S. aureus nasal carriage.

Nontraditional therapies to treat Helicobacter pylori infection

The Gram-negative pathogen Helicobacter pylori is increasingly more resistant to the three major antibiotics (metronidazole, clarithromycin and amoxicillin) that are most commonly used to treat infection. As a result, there is an increased rate of treatment failure; this translates into an overall higher cost of treatment due to the need for increased length of treatment and/or the requirement for combination or sequential therapy. Given the rise in antibiotic resistance, the complicated treatment regime, and issues related to patient compliance that stem from the duration and complexity of treatment, there is clearly a pressing need for the development of novel therapeutic strategies to combat H. pylori infection. As such, researchers are actively investigating the utility of antimicrobial peptides, small molecule inhibitors and naturopathic therapies. Herein we review and discuss each of these novel approaches as a means to target this important gastric pathogen.

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.

Innate immunity and non-Hodgkin's lymphoma (NHL) related genes in a nested case-control study for gastric cancer risk

Objective

Genetic variants regulating the host immune system may contribute to the susceptibility for the development of gastric cancer. Little is known about the role of the innate immunity- and non-Hodgkin’s lymphoma (NHL)-related genes for gastric cancer risk. This nested case-control study was conducted to identify candidate genes for gastric cancer risk for future studies.

Methods

In the Discovery phase, 3,072 SNPs in 203 innate immunity- and 264 NHL-related genes using the Illumine GoldenGateTM OPA Panel were analyzed in 42 matched case-control sets selected from the Korean Multi-center Cancer Cohort (KMCC). Six significant SNPs in four innate immunity (DEFA6, DEFB1, JAK3, and ACAA1) and 11 SNPs in nine NHL-related genes (INSL3, CHMP7, BCL2L11, TNFRSF8, RAD50, CASP7, CHUK, CD79B, and CLDN9) with a permutated p-value <0.01 were re-genotyped in the Replication phase among 386 cases and 348 controls. Odds ratios (ORs) for gastric cancer risk were estimated adjusting for age, smoking status, and H. pylori and CagA sero-positivity. Summarized ORs in the total study population (428 cases and 390 controls) are presented using pooled- and meta-analyses.

Results

Four SNPs had no heterogeneity across the phases: in the meta-analysis, DEFA6 rs13275170 and DEFB1 rs2738169 had both a 1.3-fold increased odds ratio (OR) for gastric cancer (95% CIs = 1.1–1.6; and 1.1–1.5, respectively). INSL3 rs10421916 and rs11088680 had both a 0.8-fold decreased OR for gastric cancer (95% CIs = 0.7–0.97; and 0.7–0.9, respectively).

Conclusions

Our findings suggest that certain variants in the innate immunity and NHL-related genes affect the gastric cancer risk, perhaps by modulating infection-inflammation-immunity mechanisms that remain to be defined.

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.

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.

Role of virulence factors and host cell signaling in the recognition of Helicobacter pylori and the generation of immune responses

Helicobacter pylori colonizes a large proportion of the world's population, with infection invariably leading to chronic, lifelong gastritis. While the infection often persists undiagnosed and without causing severe pathology, there are a number of host, bacterial and environmental factors that can influence whether infection provokes a mild inflammatory response or results in significant morbidity. Intriguingly, the most virulent H. pylori strains appear to deliberately induce the epithelial signaling cascades responsible for activating the innate immune system. While the reason for this remains unclear, the resulting adaptive immune responses are largely ineffective in clearing the bacterium once infection has become established and, as a result, inflammation likely causes more damage to the host itself.

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.

Antibody-mediated protection against infection with Helicobacter pylori in a suckling mouse model of passive immunity

Studies of active immunization against Helicobacter pylori indicate that antibodies play a minor role in immunity. There is also evidence, however, that the translocation of antibodies in the stomach may be insufficient to achieve functional antibody levels in the gastric lumen. We have used a suckling mouse model of passive immunity to determine if perorally delivered antibodies can protect against infection with H. pylori. Female C57BL/6 mice were immunized parenterally with formalin-fixed cells of three clinical isolates of H. pylori (3HP) or the mouse-adapted H. pylori strain SS1 before mating. Their pups were challenged with the SS1 strain at 4 days of age and left to suckle before determination of bacterial loads 14 days later. Compared to age-matched controls, pups suckled by 3HP-vaccinated dams were significantly protected against infection (>95% reduction in median bacterial load; P<0.0001). Pups suckled by SS1-vaccinated dams were also significantly protected in terms of both median bacterial load (>99.5% reduction; P<0.0001) and the number of culture-negative pups (28% versus 2% for immune and nonimmune cohorts, respectively; P<0.0001). Similar results were obtained with pups suckled by dams immunized with a urease-deficient mutant of SS1. Fostering experiments demonstrated that protection was entirely attributable to suckling from an immunized dam, and antibody isotype analysis suggested that protection was mediated by the immunoglobulin G fraction of immune milk. Analysis of the bacterial loads in pups sampled before and after weaning confirmed that infection had been prevented in culture-negative animals. These data indicate that antibodies can prevent colonization by H. pylori and suppress the bacterial loads in animals that are colonized.

Requirements for two proximal NF-kappaB binding sites and IkappaB-zeta in IL-17A-induced human beta-defensin 2 expression by conducting airway epithelium

Among a panel of 21 cytokines (IL-1α, -1β, -2–13, and -15–18; interferon-γ; granulocyte-macrophage colony-stimulating factor; and tumor necrosis factor α), we have recently observed that IL-17A is the most potent inducer for human β-defensin 2 (hBD-2) in conducting airway epithelial cells (Kao, C. Y., Chen, Y., Thai, P., Wachi, S., Huang, F., Kim, C., Harper, R. W., and Wu, R. (2004) J. Immunol. 173, 3482–3491). The molecular basis of this regulation is not known. In this study, we demonstrated a coordinated degradation of inhibitory κB(IκB)-α followed by a nuclear translocation of p50 and p65 NF-κB subunits and their binding to NF-κB sites of hBD-2 promoter region. With site-directed mutagenesis, we demonstrated the requirement of two proximal NF-κB binding sites (pκB1, -205 to -186; pκB2, -596 to -572) but not the distal site (dκB, -2193 to -2182) in supporting IL-17A-induced hBD-2 promoter activity. These results are consistent with the data of the chromatin immunoprecipitation assay, which showed enhanced p50 binding to these pκB sites but not the dκB site in cells after IL-17A treatment. We also found that the NF-κB binding cofactor, IκB-ζ, was up-regulated by IL-17A, and the knockdown of IκB-ζ significantly diminished the IL-17A-induced hBD-2 expression. This is the first demonstration of the involvement of two proximal NF-κB sites and IκB-ζ in the regulation of hBD-2 by IL-17A, two important genes responsible for host defense.

Antimicrobial peptides: an essential component of the skin defensive barrier

The skin is positioned at the interface between an organism's internal milieu and an external environment characterized by constant assault with potential microbial pathogens. While the skin was formerly considered an inactive physical protective barrier that participates in host immune defense merely by blocking entry of microbial pathogens, it is now apparent that a major role of the skin is to defend the body by rapidly mounting an innate immune response to injury and microbial insult. In the skin, both resident and infiltrating cells synthesize and secrete small peptides that demonstrate broad-spectrum antimicrobial activity against bacteria, fungi, and enveloped viruses. Antimicrobial peptides also act as multifunctional immune effectors by stimulating cytokine and chemokine production, angiogenesis, and wound healing. Cathelicidins and defensins comprise two major families of skin-derived antimicrobial peptides, although numerous others have been described. Many such immune defense molecules are currently being developed therapeutically in an attempt to combat growing bacterial resistance to conventional antibiotics.

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.

Influence of polymorphisms in the NOD1/CARD4 and NOD2/CARD15 genes on the clinical outcome of Helicobacter pylori infection

Host immune response influences the clinical outcome of Helicobacter pylori infection leading to ulcer disease, gastric carcinoma and mucosa-associated lymphoid tissue (MALT) lymphoma. A genetic risk profile for gastric cancer has been identified, but genetic susceptibility to develop MALT lymphoma is still unclear. We investigated the role of NOD1 and NOD2 as intracellular recognition molecules for pathogen-associated molecules in H. pylori infection in vitro and analysed the influence of single nucleotide polymorphisms on susceptibility to ulcer disease and MALT lymphoma. Expression of NOD1 and NOD2 significantly sensitized HEK293 cells to H. pylori-induced NF-kappaB activation in a cag pathogenicity island (cagPAI)-dependent manner. In cells carrying the Crohn-associated NOD2 variant R702W the NF-kappaB response was significantly diminished. NOD1/NOD2 expression levels were induced in the gastric epithelium in H. pylori-positive patients. No mutations were found to be associated with gastritis or gastric ulcer development. However, the R702W mutation in the NOD2/CARD15 gene was significantly associated with gastric lymphoma. Carrier of the rare allele T had a more than doubled risk to develop lymphoma than controls [odds ratio (OR): 2.4, 95% confidence interval (CI): 1.2-4.6; P < 0.044]. H. pylori-induced upregulation of NOD1 and NOD2 in vivo may play a critical role in the recognition of this common pathogen. A missense mutation in the leucine-rich region of CARD15 is associated with gastric lymphoma.

The front line of enteric host defense against unwelcome intrusion of harmful microorganisms: mucins, antimicrobial peptides, and microbiota

The intestinal tract is a complex ecosystem that combines resident microbiota and the cells of various phenotypes with complex metabolic activities that line the epithelial wall. The intestinal cells that make up the epithelium provide physical and chemical barriers that protect the host against the unwanted intrusion of microorganisms that hijack the cellular molecules and signaling pathways of the host and become pathogenic. Some of the organisms making up the intestinal microbiota also have microbicidal effects that contribute to the barrier against enteric pathogens. This review describes the two cell lineages present in the intestinal epithelium: the goblet cells and the Paneth cells, both of which play a pivotal role in the first line of enteric defense by producing mucus and antimicrobial peptides, respectively. We also analyze recent insights into the intestinal microbiota and the mechanisms by which some resident species act as a barrier to enteric pathogens. Moreover, this review examines whether the cells producing mucins or antimicrobial peptides and the resident microbiota act in partnership and whether they function individually and/or synergistically to provide the host with an effective front line of defense against harmful enteric pathogens.

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.

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.

Mechanisms of disease: defensins in gastrointestinal diseases

Defensins are endogenous antibiotics with microbicidal activity against Gram-negative and Gram-positive bacteria, fungi, viruses and protozoa. In the gastrointestinal tract, defensins help regulate the composition and number of colonizing microbes, and protect the host from food-borne and water-borne pathogens. In health, the normal host relationship with the commensal luminal microbiota is beneficial, but the same commensal bacteria could have a pathogenic role in inflammatory diseases. A disturbance in antimicrobial defense, as provided by Paneth cells of the small intestine, seems to be a critical factor in the pathogenesis of ileal Crohn's disease, an inflammatory disease of the intestinal tract. The disruption of the critical balance between antimicrobial peptides and luminal bacteria might also explain other gastrointestinal infections and diseases. Elucidating the underlying mechanisms involved in the regulation and biology of defensins could open up new therapeutic avenues.

High concentrations of human β-defensin 2 in gastric juice of patients with Helicobacter pylori infection

AIM: Human β-defensin (HBD)-1 and HBD-2 are endogenous antimicrobial peptides. Unlike HBD-1, the HBD-2 expression is augmented by Helicobacter pylori (H pylori). We sought to determine HBD-1 and HBD-2 concentrations in gastric juice during H pylori infection.

METHODS: HBD-1 and HBD-2 concentrations were measured by radioimmunoassay in plasma and gastric juice of 49 H pylori-infected and 33 uninfected subjects and before and after anti-H pylori treatment in 13 patients with H pylori-associated gastritis. Interleukin (IL)-1β and IL-8 concentrations in gastric juice were measured by enzyme-linked immunosorbent assay (ELISA). Histological grades of gastritis were determined using two biopsy specimens taken from the antrum and corpus. Reverse phase high performance liquid chromatography (RP-HPLC) was used to identify HBD-2.

RESULTS: HBD-2 concentrations in gastric juice, but not in plasma, were significantly higher in H pylori-positive than -negative subjects, albeit the post-treatment levels were unchanged. Immunoreactivity for HBD-2 was exclusively identified in H pylori-infected mucosa by RP-HPLC. HBD-2 concentrations in gastric juice correlated with histological degree of neutrophil and mononuclear cell infiltration in the corpus. IL-1β levels correlated with those of IL-8, but not HBD-2. Plasma and gastric juice HBD-1 concentrations were similar in H pylori-infected and uninfected subjects.

CONCLUSION: Our results place the β-defensins, especially HBD-2, in the front line of innate immune defence. Moreover, HBD-2 may be involved in the pathogenesis of H pylori-associated gastritis, possibly through its function as immune and inflammatory mediator.

Enhanced human beta-defensin-2 (hBD-2) expression by corticosteroids is independent of NF-kappaB in colonic epithelial cells (CaCo2)

Beta-defensins are small cationic peptides with antimicrobial properties that contribute to innate host defense. Unlike human beta-defensin-1 (hBD-1), which is produced constitutively, human beta-defensin-2 (hBD-2) is expressed after adequate stimulation by cytokines and/or bacterial endotoxins in epithelial tissue and mononuclear phagocytes but may be deficient in patients with Crohn's disease. To further elucidate the role of the intestinal epithelium in antimicrobial host defense, gene regulation of hBD-2 and the interaction with NF-kappaB were analyzed in a cell culture model. Human colonic epithelial cells (CaCo2) were stimulated by pro-inflammatory cytokines (IL-1beta, TNF-alpha, IF-gamma) to induce hBD-2 mRNA transcription. Interactions with NF-kappaB were analyzed using specific inhibitors (sulfasalazine, gliotoxine, dexamethasone) at different concentrations. Defensin mRNA expression was quantified by competitive RT-PCR and antibacterial capacity of supernatants was determined by an antimicrobial assay. HBD-2 mRNA transcription and antimicrobial activity of CaCo2 cells were induced by stimulation with pro-inflammatory cytokines. Induction was not inhibited by sulfasalazine or gliotoxine, whereas dexamethasone further enhanced both gene transcription and antimicrobial capacity. The lack of inhibition of induced hBD-2 expression by specific NF-kappaB antagonists suggests an additional pathway of activation, independent of NF-kappaB. The induction of hBD-2 expression in cytokine-stimulated CaCo2 cells by corticosteroids indicates further immunomodulatory ability of steroid hormones not yet understood.

Concentrations of α- and β-defensins in gastric juice of patients with various gastroduodenal diseases

AIM: To determine the concentration of α- and β-defensins in gastric juice of patients with various gastroduodenal diseases.

METHODS: Concentrations of human neutrophil peptides (HNPs) 1-3, the major forms of α-defensins, and human β-defensin (HBD)-1 and HBD-2 were measured by radioimmunoassay in plasma and gastric juice of 84 subjects, consisting of 54 Helicobacter pylori-infected and 30 uninfected subjects. They included 33 patients with chronic gastritis (CG), 12 with gastric ulcer (GU), 11 with duodenal ulcer (DU), 11 with benign gastric polyp (BGP) and 16 with normal mucosa (N group) on upper endoscopy. Plasma pepsinogen I and II levels, biomarkers for gastric mucosal inflammation and atrophy, were also measured.

RESULTS: Gastric juice HNPs 1-3 levels in patients with CG, GU and BGP were significantly higher than those in patients with DU and N. Gastric juice HBD-2 concentrations in patients with CG and GU were significantly higher than those in the N group, but were significantly lower in DU patients than in GU patients. Gastric juice HBD-1 levels and plasma levels of these peptides were similar in the patient groups. Concentrations of gastric juice HNPs 1-3 and HBD-2 of in H pylori-infected patients were significantly different from those in uninfected subjects. HNPs 1-3 concentrations in gastric juice correlated negatively with plasma pepsinogen I levels and I/II ratios. HBD-2 levels in gastric juice correlated positively and negatively with plasma pepsinogen II concentrations and I/II ratios, respectively.

CONCLUSION: HNPs 1-3 and HBD-2 levels in gastric juice are diverse among various gastrointestinal diseases, reflecting the inflammatory and atrophic events of the background gastric mucosa affected by H pylori.

Elevated concentrations of alpha-defensins in gastric juice of patients with Helicobacter pylori infection

OBJECTIVE

Defensins (alpha- and beta-defensins) are endogenous antimicrobial peptides. Little is known about alpha-defensins during Helicobacter pylori infection.

METHODS

The concentrations of human neutrophil peptides (HNP-1, -2, and -3), the major components of neutrophils-derived alpha-defensins, were measured by radioimmunoassay (RIA) in plasma and gastric juice of 61 H. pylori-infected and 33 uninfected subjects, and before and after anti-H. pylori treatment in 12 patients with H. pylori-associated gastritis. Interleukin (IL)-8 concentrations in gastric juice were measured by enzyme-linked immunosorbent assay. Histological grades of gastritis and neutrophil counts (/mm(2)) infiltrating in the gastric mucosa were determined using two biopsy specimens taken from the antrum and corpus. Immunohistochemistry and reverse-phase high performance liquid chromatography (RP-HPLC) were used to identify HNPs 1-3.

RESULTS

HNP 1-3 concentrations in gastric juice were significantly higher in H. pylori-positive than in H. pylori-negative patients and significantly decreased after cure. HNP 1-3 concentrations in gastric juice correlated with IL-8 levels and neutrophil densities in the gastric mucosa and were associated with histological degree of gastritis, especially the grades of activity. Intense immunoreactivity for anti-HNPs 1-3 antiserum was noted in infiltrating neutrophils in H. pylori-infected mucosa. In RP-HPLC analysis, all of the HNP 1-3 molecules were identified as their mature forms. Plasma HNP 1-3 concentrations were similar in H. pylori-infected and non-infected groups and showed no correlations with other parameters.

CONCLUSIONS

We demonstrated significantly elevated levels of HNPs 1-3 in gastric juice during H. pylori infection. The elevation of HNPs is presumably secondary to H.pylori-associated gastric inflammation involving neutrophil infiltration.

Gastric transcription profile of Helicobacter pylori infection in the rhesus macaque

Infection with Helicobacter pylori is usually asymptomatic but sometimes progresses to peptic ulcer disease or gastric adenocarcinoma. The development of disease involves both host and bacterial factors. In order to better understand host factors in pathogenesis, we studied the gastric transcription profile of H. pylori infection in the rhesus macaque by using DNA microarrays. Significant changes were found in the expression of genes important for innate immunity, chemokines and cytokines, cell growth and differentiation, apoptosis, structural proteins, and signal transduction and transcription factors. This broad transcription profile demonstrated expected up-regulation of cell structural elements and the host inflammatory and immune response, as well as the novel finding of down-regulation of heat shock proteins. These results provide a unique view of acute H. pylori infection in a relevant animal model system and will direct future studies regarding the host response to H. pylori infection.

IL-17 markedly up-regulates beta-defensin-2 expression in human airway epithelium via JAK and NF-kappaB signaling pathways

Using microarray gene expression analysis, we first observed a profound elevation of human beta-defensin-2 (hBD-2) message in IL-17-treated primary human airway epithelial cells. Further comparison of this stimulation with a panel of cytokines (IL-1alpha, 1beta, 2-13, and 15-18; IFN-gamma; GM-CSF; and TNF-alpha) demonstrated that IL-17 was the most potent cytokine to induce hBD-2 message (>75-fold). IL-17-induced stimulation of hBD-2 was time and dose dependent, and this stimulation also occurred at the protein level. Further studies demonstrated that hBD-2 stimulation was attenuated by IL-17R-specific Ab, but not by IL-1R antagonist or the neutralizing anti-IL-6 Ab. This suggests an IL-17R-mediated signaling pathway rather than an IL-17-induced IL-1alphabeta and/or IL-6 autocrine/paracrine loop. hBD-2 stimulation was sensitive to the inhibition of the JAK pathway, and to the inhibitors that affect NF-kappaB translocation and the DNA-binding activity of its p65 NF-kappaB subunit. Transient transfection of airway epithelial cells with an hBD-2 promoter-luciferase reporter gene expression construct demonstrated that IL-17 stimulated promoter-reporter gene activity, suggesting a transcriptional mechanism for hBD-2 induction. These results support an IL-17R-mediated signaling pathway involving JAK and NF-kappaB in the transcriptional stimulation of hBD-2 gene expression in airway epithelium. Because IL-17 has been identified in a number of airway diseases, especially diseases related to microbial infection, these findings provide a new insight into how IL-17 may play an important link between innate and adaptive immunity, thereby combating infection locally within the airway epithelium.

Host anti-microbial response to Helicobacter pylori infection

beta-Defensin peptides are known to be potent anti-bacterials with a wide spectrum of activity. They, therefore, represent an important aspect of innate immunity. In the present study, we have extended our understanding of the regulation of the beta-defensins in response to Helicobacter pylori (H. pylori) infection. We found elevated levels of hBD2 and hBD3 transcripts within gastric cells following infection. This was reflected by increased secretion of the corresponding peptide. The relative bactericidal potency of the beta-defensins was also assessed. Our findings show that hBD3 was the most potent peptide tested followed by hBD2 and hBD1. Relatively modest synergy between hBD1 and hBD2 was also noted. More importantly, we observed endogenous production of putative anti-microbial factors by infected gastric epithelial cells. Our study highlights the active participation of the epithelium in protection against potential pathogens.

Expression of LL-37 by human gastric epithelial cells as a potential host defense mechanism against Helicobacter pylori

BACKGROUND & AIMS

LL-37/human cationic antimicrobial peptide 18 (hCAP18) is a human cathelicidin with broad-spectrum antimicrobial, lipopolysaccharide binding, and chemotactic activities. This study examined the role of LL-37/hCAP18 in gastric innate immune defense by characterizing its constitutive and regulated expression by human gastric mucosa and its bactericidal activity against the gastric pathogen Helicobacter pylori.

METHODS

LL-37/hCAP18 messenger RNA expression in normal and H. pylori -infected gastric mucosa and gastric epithelial cells was determined by in situ hybridization, real-time polymerase chain reaction, immunostaining, and immunoblot analysis. Bactericidal activity was measured by using a colony-forming unit assay.

RESULTS

LL-37/hCAP18 messenger RNA and protein were expressed in a distinct distribution by surface epithelial cells as well as chief and parietal cells in the fundic glands of normal gastric mucosa. LL-37/hCAP18 was significantly increased in the epithelium and gastric secretions of H. pylori -infected patients, but not in individuals with non-H. pylori -induced gastric inflammation. Infection of cultured gastric epithelial cells with a wild-type but not an isogenic Delta cagE mutant strain of H. pylori increased LL-37/hCAP18 expression, indicating that H. pylori -induced regulation of LL-37/hCAP18 production required an intact type IV secretion system. LL-37, the C-terminal peptide of LL-37/hCAP18, alone or in synergy with human beta-defensin 1, was bactericidal for several H. pylori strains.

CONCLUSIONS

These data indicate that H. pylori up-regulates production of LL-37/hCAP18 by gastric epithelium and suggest this cathelicidin contributes to determining the balance between host mucosal defense and H. pylori survival mechanisms that govern chronic infection with this gastric pathogen.

Endogenous production of antimicrobial peptides in innate immunity and human disease

Antimicrobial peptides are diverse and evolutionarily ancient molecules produced by all living organisms. Peptides belonging to the cathelicidin and defensin gene families exhibit an immune strategy as they defend against infection by inhibiting microbial survival, and modify hosts through triggering tissue-specific defense and repair events. A variety of processes have evolved in microbes to evade the action of antimicrobial peptides, including the ability to degrade or inactivate antimicrobial peptides, or suppress host production of the peptide in response to infection. Animal models and clinical investigations have shown that an absence of cathelicidin or defensin antimicrobials can lead to disease. In this article, we review important recent advances in understanding the biology of antimicrobial peptides and their role in normal immunity and human disease.