Production of beta-defensins by human airway epithelia

AhR-Dependent Induction of β-Defensin 1 in Colonic Epithelial Cells Regulates Cross-Talk between Gut Microbiota and Immune Response Leading to Attenuation of Colitis

The aryl hydrocarbon receptor (AhR) acts as a critical signaling hub that connects immune cells, food and environmental cues, and microbiota to regulate intestinal homeostasis. In the current study, the role of AhR in the regulation of an antimicrobial peptide, β-defensin1 (BD-1) is investigated to control colitis. Human patients with ulcerative colitis (UC) and Crohn's disease (CD), and mice with three different models of colitis, express a significant decrease in the expression of BD-1 in colonic epithelial cells (CECs). Dietary and environmental AhR ligands induce the expression of BD-1 in CECs through the activation of two dioxin-responsive elements (DREs) expressed on its promoter. AhR ligands attenuate colitis in wild-type (WT) mice while inducing BD-1. However, AhR ligands fail to induce BD-1 and protect mice from colitis when there is an intestinal epithelial cell (IEC)-specific deletion of AhR. Blocking BD1 in vivo using antibodies prevents the ability of AhR ligands to ameliorate colitis, restore dysbiosis, and attenuate colonic inflammation. The current study identifies a novel pathway involving dietary, environmental, and endogenous AhR ligands to induce the antimicrobial peptide BD-1 in IECs, which in turn, plays a critical role in the regulation of intestinal homeostasis.

Incorporation of human β-defensin-1 into immunoliposomes to facilitate targeted autophagy therapy of colon carcinoma

Based on the discovery that human β-defensin-1 (hBD-1) triggers autophagy in colon cancer cells and inhibits proliferation, we proposed the consideration of its druggability. As a protein, its stability, targetability and bioavailability must be improved. Compared with the traditional medicinal chemistry technology, nanotechnology is more economical for increasing the druggability of hBD-1 and can be readily scaled up. Here, we propose an immunoliposome system containing hBD-1 to improve its stability and bioavailability. To enhance its targetability, anti-epidermal growth factor receptor (EGFR) antibodies were conjugated to the liposomal bilayer to produce immunoliposomes that can target EGFR, which is highly expressed in colon cancer cells. Although more studies are needed to support clinical trials and large-scale manufacturing, these immunoliposomes have great potential as therapeutics. Thus, immunoliposomes are suitable nanovesicles to improve the druggability of hBD-1; however, additional basic and translational research of these systems is warranted.

Gene expression responses of CF airway epithelial cells exposed to elexacaftor/tezacaftor/ivacaftor suggest benefits beyond improved CFTR channel function

The combination of elexacaftor/tezacaftor/ivacaftor (ETI, Trikafta) reverses the primary defect in cystic fibrosis (CF) by improving CFTR-mediated Cl- and HCO3- secretion by airway epithelial cells (AECs), leading to improved lung function and less frequent exacerbations and hospitalizations. However, studies have shown that CFTR modulators like ivacaftor, a component of ETI, have numerous effects on CF cells beyond improved CFTR channel function. Because little is known about the effect of ETI on CF AEC gene expression, we exposed primary human AEC to ETI for 48 h and interrogated the transcriptome by RNA-seq and qPCR. ETI increased CFTR Cl- secretion, and defensin gene expression (DEFB1), an observation consistent with reports of decreased bacterial burden in the lungs of people with CF (pwCF). ETI decreased MMP10 and MMP12 gene expression, suggesting that ETI may reduce proteolytic-induced lung destruction in CF. ETI also reduced the expression of the stress response gene heme oxygenase (HMOX1). qPCR analysis confirmed DEFB1, HMOX1, MMP10, and MMP12 gene expression results observed by RNA-seq. Gene pathway analysis revealed that ETI decreased inflammatory signaling, cellular proliferation, and MHC class II antigen presentation. Collectively, these findings suggest that the clinical observation that ETI reduces lung infections in pwCF is related in part to drug-induced increases in DEFB1 and that ETI may reduce lung damage by reducing MMP10 and MMP12 gene expression. Moreover, pathway analysis also identified several other genes responsible for the ETI-induced reduction in inflammation observed in pwCF.NEW & NOTEWORTHY Gene expression responses by CF AECs exposed to ETI suggest that in addition to improving CFTR channel function, ETI is likely to enhance resistance to bacterial infection by increasing levels of beta-defensin 1 (hBD-1). ETI may also reduce lung damage by suppressing MMP10 and MMP12 and reduce airway inflammation by repressing proinflammatory cytokine secretion by CF AECs.

Airway epithelium in lung transplantation: a potential actor for post-transplant complications?

Lung transplantation, a critical intervention for end-stage lung diseases, is frequently challenged by post-transplant complications. Indeed, primary graft dysfunction, anastomotic complications, infections and acute and chronic rejections pose significant hurdles in lung transplantation. While evidence regarding the role of airway epithelium after lung transplantation is still emerging, its importance is becoming increasingly recognised. This review looks at the complex involvement of airway epithelium in various post-transplant complications, while emphasising the utility of airway epithelial culture as a research model. In summary, by elucidating the involvement of airway epithelium in each post-transplant complication and explaining these intricate processes, the review aims to guide specific future research efforts and therapeutic strategies aimed at improving lung transplant outcomes and enhancing patient care.

IL-13 induces loss of CFTR in ionocytes and reduces airway epithelial fluid absorption

The airway surface liquid (ASL) plays a crucial role in lung defense mechanisms, and its composition and volume are regulated by the airway epithelium. The cystic fibrosis transmembrane conductance regulator (CFTR) is abundantly expressed in a rare airway epithelial cell type called an ionocyte. Recently, we demonstrated that ionocytes can increase liquid absorption through apical CFTR and basolateral barttin/chloride channels, while airway secretory cells mediate liquid secretion through apical CFTR channels and basolateral NKCC1 transporters. Th2-driven (IL-4/IL-13) airway diseases, such as asthma, cause goblet cell metaplasia, accompanied by increased mucus production and airway secretions. In this study, we investigate the effect of IL-13 on chloride and liquid transport performed by ionocytes. IL-13 treatment of human airway epithelia was associated with reduced epithelial liquid absorption rates and increased ASL volume. Additionally, IL-13 treatment reduced the abundance of CFTR-positive ionocytes and increased the abundance of CFTR-positive secretory cells. Increasing ionocyte abundance attenuated liquid secretion caused by IL-13. Finally, CFTR-positive ionocytes were less common in asthma and chronic obstructive pulmonary disease and were associated with airflow obstruction. Our findings suggest that loss of CFTR in ionocytes contributes to the liquid secretion observed in IL-13-mediated airway diseases.

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.

Gene expression responses of CF airway epithelial cells exposed to elexacaftor/tezacaftor/ivacaftor (ETI) suggest benefits beyond improved CFTR channel function

The combination of elexacaftor/tezacaftor/ivacaftor (ETI, Trikafta) reverses the primary defect in Cystic Fibrosis (CF) by improving CFTR mediated Cl - and HCO 3 - secretion by airway epithelial cells (AEC), leading to improved lung function and less frequent exacerbations and hospitalizations. However, studies have shown that CFTR modulators like ivacaftor, a component of ETI, has numerous effects on CF cells beyond improved CFTR channel function. Because little is known about the effect of ETI on CF AEC gene expression we exposed primary human AEC to ETI for 48 hours and interrogated the transcriptome by RNA-seq and qPCR. ETI increased defensin gene expression ( DEFB1 ) an observation consistent with reports of decreased bacterial burden in the lungs of people with CF (pwCF). ETI also decreased MMP10 and MMP12 gene expression, suggesting that ETI may reduce proteolytic induced lung destruction in CF. ETI also reduced the expression of the stress response gene heme oxygenase ( HMOX1 ). qPCR analysis confirmed DEFB1, HMOX1, MMP10 and MMP12 gene expression results observed by RNA-seq. Gene pathway analysis revealed that ETI decreased inflammatory signaling, cellular proliferation and MHC Class II antigen presentation. Collectively, these findings suggest that the clinical observation that ETI reduces lung infections in pwCF is related in part to drug induced increases in DEFB1 , and that ETI may reduce lung damage by reducing MMP10 and MMP12 gene expression, which is predicted to reduce matrix metalloprotease activity. Moreover, pathway analysis also identified several genes responsible for the ETI induced reduction in inflammation observed in people with CF.

New and Noteworthy

Gene expression responses by CF AEC exposed to ETI suggest that in addition to improving CFTR channel function, ETI is likely to increase resistance to bacterial infection by increasing levels of beta defensin 1 (hBD-1). ETI may also reduce lung damage by suppressing MMP10, and reduce airway inflammation by repressing proinflammatory cytokine secretion by AEC cells.

Human β-defensins and their synthetic analogs: Natural defenders and prospective new drugs of oral health

As a family of cationic host defense peptides, human β-defensins (HBDs) are ubiquitous in the oral cavity and are mainly synthesized primarily by epithelial cells, serving as the primary barrier and aiming to prevent microbial invasion, inflammation, and disease while maintaining physiological homeostasis. In recent decades, there has been great interest in their biological functions, structure-activity relationships, mechanisms of action, and therapeutic potential in oral diseases. Meanwhile, researchers are dedicated to improving the properties of HBDs for clinical application. In this review, we first describe the classification, structural characteristics, functions, and mechanisms of HBDs. Next, we cover the role of HBDs and their synthetic analogs in oral diseases, including dental caries and pulp infections, periodontitis, peri-implantitis, fungal/viral infections and oral mucosal diseases, and oral squamous cell carcinoma. Finally, we discuss the limitations and challenges of clinical translation of HBDs and their synthetic analogs, including, but not limited to, stability, bioavailability, antimicrobial activity, resistance, and toxicity. Above all, this review summarizes the biological functions, mechanisms of action, and therapeutic potential of both natural HBDs and their synthetic analogs in oral diseases, as well as the challenges associated with clinical translation, thus providing substantial insights into the laboratory development and clinical application of HBDs in oral diseases.

CFTR dysfunction leads to defective bacterial eradication on cystic fibrosis airways

Dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel by genetic mutations causes the inherited disease cystic fibrosis (CF). CF lung disease that involves multiple disorders of epithelial function likely results from loss of CFTR function as an anion channel conducting chloride and bicarbonate ions and its function as a cellular regulator modulating the activity of membrane and cytosol proteins. In the absence of CFTR activity, abundant mucus accumulation, bacterial infection and inflammation characterize CF airways, in which inflammation-associated tissue remodeling and damage gradually destroys the lung. Deciphering the link between CFTR dysfunction and bacterial infection in CF airways may reveal the pathogenesis of CF lung disease and guide the development of new treatments. Research efforts towards this goal, including high salt, low volume, airway surface liquid acidosis and abnormal mucus hypotheses are critically reviewed.

Airway Epithelial-Derived Immune Mediators in COVID-19

The airway epithelium, which lines the conducting airways, is central to the defense of the lungs against inhaled particulate matter and pathogens such as SARS-CoV-2, the virus that causes COVID-19. Recognition of pathogens results in the activation of an innate and intermediate immune response which involves the release of cytokines and chemokines by the airway epithelium. This response can inhibit further viral invasion and influence adaptive immunity. However, severe COVID-19 is characterized by a hyper-inflammatory response which can give rise to clinical presentations including lung injury and lead to acute respiratory distress syndrome, viral pneumonia, coagulopathy, and multi-system organ failure. In response to SARS-CoV-2 infection, the airway epithelium can mount a maladaptive immune response which can delay viral clearance, perpetuate excessive inflammation, and contribute to the pathogenesis of severe COVID-19. In this article, we will review the barrier and immune functions of the airway epithelium, how SARS-CoV-2 can interact with the epithelium, and epithelial-derived cytokines and chemokines and their roles in COVID-19 and as biomarkers. Finally, we will discuss these immune mediators and their potential as therapeutic targets in COVID-19.

Serum β-Defensin 2, A Novel Biomarker for the Diagnosis of Acute Infections

BACKGROUND

Defensins are natural antimicrobial peptides that the human body secretes to protect itself from an infection. Thus, they are ideal molecules to serve as biomarkers for infection. This study was conducted to evaluate the levels of human β-defensins in patients with inflammation.

METHODS

CRP, hBD2 and procalcitonin were measured in 423 sera of 114 patients with inflammation and healthy individuals using nephelometry and commercial ELISA assays.

RESULTS

Levels of hBD2 in the serum of patients with an infection were markedly elevated compared to those of hBD2 in patients with inflammation of non-infectious etiology (p < 0.0001, t = 10.17) and healthy individuals. ROC analysis demonstrated that hBD2 showed the highest detection performance for infection (AUC 0.897; p < 0.001) followed by PCT (AUC 0.576; p = ns) and CRP (AUC 0.517; p = ns). In addition, analysis of hBD2 and CRP in patients' sera collected at different time points showed that hBD2 levels could help differentiate inflammation of infectious and non-infectious etiology during the first 5 days of hospitalization, while CRP levels could not.

CONCLUSIONS

hBD2 has the potential to serve as a diagnostic biomarker for infection. In addition, the levels of hBD2 may reflect the efficacy of antibiotic treatment.

β-defensinas como posibles indicadores de la actividad inflamatoria en la enfermedad periodontal

Periodontal disease (gingivitis and periodontitis) is an inflam-matory process caused by the activity of pathogenic bacteria and their products on the gingival sulcus, with the consequent activation of the immune response. Saliva and crevicular fluid contain a wide variety of enzymes and antimicrobial factors that are in contact with the supragingival and subgingival region, in-cluding β-defensins (hBDs). hHBDs are non-glycosylated, cysteine-rich cationic peptides produced by epithelial cells with antimicrobial and immunoregulatory effects, thus contributing to maintaining homeostasis in periodontal tissues. The changes in the microbiota and the immune response from a healthy peri-odontium to gingivitis and, finally, to periodontitis are complex. Their sever-ity depends on a dynamic balance between bacteria associated with plaque, genetic and environmental factors. Recent advances have made it possible to understand the implication of hBDs in the detection, diagnosis, and therapy of periodontal disease and the relationship between periodontitis and other inflammatory conditions. This review aims to describe the effect of hBDs on the immune response and its use as a possible marker of the inflammatory activity of the periodontal disease.

Recombinant human β-defensin 2 delivery improves smoking-associated lung neutrophilia and bacterial exacerbation

Treatment of the cigarette smoke-associated lung disease has largely focused on broad-spectrum anti-inflammatory therapies. However, these therapies, such as high-dose inhaled corticosteroids, enhance patient susceptibility to lung infection and exacerbation. Our objective was to assess whether the host-defense peptide, human beta-defensin 2 (hBD-2), can simultaneously reduce pulmonary inflammation in cigarette smoke-exposed mice while maintaining immune competence during bacterial exacerbation. Mice were exposed to cigarette smoke acutely (4 days) or chronically (5 days/week for 7 weeks) and administered hBD-2 intranasally or by gavage. In a separate model of acute exacerbation, chronically exposed mice treated with hBD-2 were infected with non-typeable Haemophilus influenzae prior to sacrifice. In the acute exposure model, cigarette smoke-associated pulmonary neutrophilia was significantly blunted by both local and systemic hBD-2 administration. Similarly, chronically exposed mice administered hBD-2 therapeutically exhibited reduced pulmonary neutrophil infiltration and downregulated pro-inflammatory signaling in the lungs compared to vehicle-treated mice. Finally, in a model of acute bacterial exacerbation, hBD-2 administration effectively limited neutrophil infiltration in the lungs while markedly reducing pulmonary bacterial load. This study shows that hBD-2 treatment can significantly attenuate lung neutrophilia induced by cigarette smoke exposure while preserving immune competence and promoting an appropriate host-defense response to bacterial stimuli.

Recombinant human β-defensin130 inhibited the growth of foodborne bacteria through membrane disruption and exerted anti-inflammatory activity

Foodborne pathogens causing food poisoning and infections are detrimental to human health, and the abuse of antibiotics induced severe antibiotic resistance in past decades. Thus, it is urgent to develop new antimicrobial agents. In the current study, human β-defensin 130 (hBD130), which is an antimicrobial peptide identified in human macrophages in 2017, was initially produced in Pichia pastoris. The purified hBD130 demonstrated broad bactericidal spectrum against foodborne pathogens through a membrane disruption, with concentrations ranging from 10 to 45 μg/mL. Moreover, hBD130 showed a low hemolytic effect and nearly no cytotoxicity to mammalian cells with a dosage of 400 μg/mL. In addition, the secretion amounts and mRNA levels of NO, IL-6, IL-1β, and TNF-α in LPS-induced mouse macrophage were significantly decreased with 1 mg/mL of hBD130. Taken together, these results showed that hBD130 is a promising antimicrobial agent to treat foodborne bacterial infections and inflammation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-022-01087-y.

HBD-2 binds SARS-CoV-2 RBD and blocks viral entry: Strategy to combat COVID-19

New approaches to complement vaccination are needed to combat the spread of SARS-CoV-2 and stop COVID-19-related deaths and medical complications. Human beta defensin 2 (hBD-2) is a naturally occurring epithelial cell-derived host defense peptide that has anti-viral properties. Our comprehensive in-silico studies demonstrate that hBD-2 binds the site on the CoV-2-RBD that docks with the ACE2 receptor. Biophysical measurements confirm that hBD-2 indeed binds to the CoV-2-receptor-binding domain (RBD) (KD ∼ 2μM by surface plasmon resonance), preventing it from binding to ACE2-expressing cells. Importantly, hBD-2 shows specificity by blocking CoV-2/spike pseudoviral infection, but not VSVG-mediated infection, of ACE2-expressing human cells with an IC50 of 2.8 ± 0.4 μM. These promising findings offer opportunities to develop hBD-2 and/or its derivatives and mimetics to safely and effectively use as agents to prevent SARS-CoV-2 infection.

In-Silico Tool for Predicting, Scanning, and Designing Defensins

Defensins are host defense peptides present in nearly all living species, which play a crucial role in innate immunity. These peptides provide protection to the host, either by killing microbes directly or indirectly by activating the immune system. In the era of antibiotic resistance, there is a need to develop a fast and accurate method for predicting defensins. In this study, a systematic attempt has been made to develop models for predicting defensins from available information on defensins. We created a dataset of defensins and non-defensins called the main dataset that contains 1,036 defensins and 1,035 AMPs (antimicrobial peptides, or non-defensins) to understand the difference between defensins and AMPs. Our analysis indicates that certain residues like Cys, Arg, and Tyr are more abundant in defensins in comparison to AMPs. We developed machine learning technique-based models on the main dataset using a wide range of peptide features. Our SVM (support vector machine)-based model discriminates defensins and AMPs with MCC of 0.88 and AUC of 0.98 on the validation set of the main dataset. In addition, we created an alternate dataset that consists of 1,036 defensins and 1,054 non-defensins obtained from Swiss-Prot. Models were also developed on the alternate dataset to predict defensins. Our SVM-based model achieved maximum MCC of 0.96 with AUC of 0.99 on the validation set of the alternate dataset. All models were trained, tested, and validated using standard protocols. Finally, we developed a web-based service "DefPred" to predict defensins, scan defensins in proteins, and design the best defensins from their analogs. The stand-alone software and web server of DefPred are available at https://webs.iiitd.edu.in/raghava/defpred.

Directed Expression of Tracheal Antimicrobial Peptide as a Treatment for Bovine-Associated Staphylococcus Aureus-Induced Mastitis in Mice

Bovine mastitis is perplexing the dairy industry since the initiation of intensive dairy farming, which has caused a reduction in the productivity of cows and an escalation in costs. The use of antibiotics causes a series of problems, especially the formation of bacterial antimicrobial resistance. However, there are limited antibiotic-free therapeutic strategies that can effectively relieve bacterial infection of bovine mammary glands. Hence, in this study, we constructed a mammary gland tissue-specific expression vector carrying the antimicrobial peptide of bovine-derived tracheal antimicrobial peptide (TAP) and evaluated it in both primary bovine mammary epithelial cells (pBMECs) and mice. The results showed that the vector driven by the β-lactoglobulin gene (BLG) promoter could efficiently direct the expression of TAP in pBMECs and the mammary gland tissue of mice. In addition, significant antibacterial effects were observed in both in vitro and in vivo experiments when introducing this vector to bovine-associated Staphylococcus aureus-treated pBMECs and mice, respectively. This study demonstrated that the mammary gland tissue-specific expression vector could be used to introduce antimicrobial peptide both in in vitro and in vivo and will provide a new therapeutic strategy in the treatment of bovine mastitis.

Antimicrobial peptides in hidradenitis suppurativa: a systematic review

BACKGROUND

Hidradenitis suppurativa (HS) is a chronic, inflammatory skin disease of the hair follicle defined by recurrent nodules, tunnels and scarring involving the intertriginous regions. HS is associated with microbial dysbiosis and immune dysregulation. In HS, an increasing number of studies have investigated antimicrobial peptides (AMPs).

OBJECTIVES

To provide an overview of the literature on AMPs in HS, and to discuss the potential role of AMPs in the pathogenesis of HS.

METHODS

PubMed, Embase and the Cochrane Library were searched. The titles, abstracts and full texts of all articles were manually screened. Additionally, the reference lists of the included articles were screened and hand searched for relevant studies.

RESULTS

The final literature sample comprised 18 retrospective and prospective studies (no reviews or commentaries) published between 2009 and 2020.

CONCLUSIONS

This review demonstrates the multitude of AMPs in HS. Although the methodology of the studies varied, the included studies indicate a consistent overexpression of human β-defensin (hBD)-2, S100A7, S100A8 and S100A9 at both the mRNA and protein levels, and a decreased expression of hBD-1. Overall, the studies point to a dysregulation of AMPs in both lesional and nonlesional HS skin.

Long-term exposure to particulate matter from air pollution alters airway β-defensin-3 and -4 and cathelicidin host defense peptides production in a murine model

Epidemiological studies have associated long-term exposure to environmental air pollution particulate matter (PM) with the development of diverse health problems. They include infectious respiratory diseases related to the deregulation of some innate immune response mechanisms, such as the host defense peptides' expression. Herein, we evaluated in BALB/c mice the effect of long-standing exposure (60 days) to urban-PM from the south of Mexico City, with aerodynamic diameters below 2.5 μm (PM_2.5) and 10 μm (PM₁₀) on the lung's gene expression and production of three host defense peptides (HDPs); murine beta-defensin-3, -4 (mBD-3, mBD-4) and cathelin-related antimicrobial peptide (CRAMP). We also evaluated mRNA levels of Il1b and Il10, two cytokines related to the expression of host defense peptides. Exposure to PM_2.5 and PM₁₀ differentially induced lung inflammation, being PM_2.5, which caused higher inflammation levels, probably associated with a differential deposition on the airways, that facilitate the interaction with alveolar macrophages. Inflammation levels were associated with an early upregulation of the three HDPs assessed and an increment in Il1b mRNA levels. Interestingly, after 28 days of exposure, Il10 mRNA upregulation was observed and was associated with the downregulation of HDPs and Il1b mRNA levels. The upregulation of Il10 mRNA and suppression of HDPs might facilitate microbial colonization and the development of diseases associated with long-term exposure to PM.

Chemically modified and conjugated antimicrobial peptides against superbugs

Antimicrobial resistance (AMR) is one of the greatest threats to human health that, by 2050, will lead to more deaths from bacterial infections than cancer. New antimicrobial agents, both broad-spectrum and selective, that do not induce AMR are urgently required. Antimicrobial peptides (AMPs) are a novel class of alternatives that possess potent activity against a wide range of Gram-negative and positive bacteria with little or no capacity to induce AMR. This has stimulated substantial chemical development of novel peptide-based antibiotics possessing improved therapeutic index. This review summarises recent synthetic efforts and their impact on analogue design as well as their various applications in AMP development. It includes modifications that have been reported to enhance antimicrobial activity including lipidation, glycosylation and multimerization through to the broad application of novel bio-orthogonal chemistry, as well as perspectives on the direction of future research. The subject area is primarily the development of next-generation antimicrobial agents through selective, rational chemical modification of AMPs. The review further serves as a guide toward the most promising directions in this field to stimulate broad scientific attention, and will lead to new, effective and selective solutions for the several biomedical challenges to which antimicrobial peptidomimetics are being applied.

DNA Blocks the Lethal Effect of Human Beta-Defensin 2 Against Neisseria meningitidis

Neisseria meningitidis is a gram-negative bacterium that often asymptomatically colonizes the human nasopharyngeal tract. These bacteria cross the epithelial barrier can cause life-threatening sepsis and/or meningitis. Antimicrobial peptides are one of the first lines of defense against invading bacterial pathogens. Human beta-defensin 2 (hBD2) is an antimicrobial peptide with broad antibacterial activity, although its mechanism of action is poorly understood. Here, we investigated the effect of hBD2 on N. meningitidis. We showed that hBD2 binds to and kills actively growing meningococcal cells. The lethal effect was evident after 2 h incubation with the peptide, which suggests a slow killing mechanism. Further, the membrane integrity was not changed during hBD2 treatment. Incubation with lethal doses of hBD2 decreased the presence of diplococci; the number and size of bacterial microcolonies/aggregates remained constant, indicating that planktonic bacteria may be more susceptible to the peptide. Meningococcal DNA bound hBD2 in mobility shift assays and inhibited the lethal effect of hBD2 in a dose-dependent manner both in suspension and biofilms, supporting the interaction between hBD2 and DNA. Taken together, the ability of meningococcal DNA to bind hBD2 opens the possibility that extracellular DNA due to bacterial lysis may be a means of N. meningitidis to evade immune defenses.

Promising role of defensins peptides as therapeutics to combat against viral infection

Antimicrobial peptides (AMPs) are ubiquitously present small peptides, which play a critical function in the innate immune system. The defensin class of AMPs represented an evolutionarily ancient family containing cationic cysteine residue and frequently expressed in epithelial or neutrophils cells. It plays myriad functions in host innate immune responses against various infection. Defensin has a broad spectrum of antimicrobial activities, including anti-bacteria, anti-viruses (AVPs), anti-fungi, anti-cancers, and also overcoming bacterial drug resistance. In this review, we compiled the progress on defensin, particularly incorporating the mechanism of action, their application as an antiviral agent, prospects in different areas, and limitations to be solved as an antiviral peptide. Defensins were explored, in particular, their capacity to stimulate innate and adaptive immunity by trigging as anti-coronavirus (COVID-19) peptides. The present review summarised its immunomodulatory and immunoenhancing properties and predominantly focused on its promising therapeutic adjuvant choices for combat against viral infection.

Supplementation with vitamin D in the COVID-19 pandemic?

The coronavirus disease 2019 (COVID-19) pandemic was declared a public health emergency of international concern by the World Health Organization. COVID-19 has high transmissibility and could result in acute lung injury in a fraction of patients. By counterbalancing the activity of the renin-angiotensin system, angiotensin-converting enzyme 2, which is the fusion receptor of the virus, plays a protective role against the development of complications of this viral infection. Vitamin D can induce the expression of angiotensin-converting enzyme 2 and regulate the immune system through different mechanisms. Epidemiologic studies of the relationship between vitamin D and various respiratory infections were reviewed and, here, the postulated mechanisms and clinical data supporting the protective role of vitamin D against COVID-19-mediated complications are discussed.

Molecular dynamics simulations and functional studies reveal that hBD-2 binds SARS-CoV-2 spike RBD and blocks viral entry into ACE2 expressing cells

New approaches to complement vaccination are needed to combat the spread of SARS-CoV-2 and stop COVID-19 related deaths and long-term medical complications. Human beta defensin 2 (hBD-2) is a naturally occurring epithelial cell derived host defense peptide that has antiviral properties. Our comprehensive in-silico studies demonstrate that hBD-2 binds the site on the CoV-2-RBD that docks with the ACE2 receptor. Biophysical and biochemical assays confirm that hBD-2 indeed binds to the CoV-2-receptor binding domain (RBD) (KD ~ 300 nM), preventing it from binding to ACE2 expressing cells. Importantly, hBD-2 shows specificity by blocking CoV-2/spike pseudoviral infection, but not VSV-G mediated infection, of ACE2 expressing human cells with an IC50 of 2.4± 0.1 μM. These promising findings offer opportunities to develop hBD-2 and/or its derivatives and mimetics to safely and effectively use as novel agents to prevent SARS-CoV-2 infection.

Selenium enriched Bacillus subtilis yb-1114246 activated the TLR2-NF-κB1 signaling pathway to regulate chicken intestinal β-defensin 1 expression

The aim of this study was to investigate the effects and potential signaling pathway of selenium-enriched Bacillus subtilis (SEBS) on beta defensin 1 (BD1) expression in chicken intestine. Chinese Huainan Partridge chickens (500 individuals) were randomly allocated into five groups, including control, inorganic Se, B. subtilis, SEBS, and a mixture of Se and B. subtilis (Se-BS). After 56 d of feeding, chicken ileal mucous membranes were harvested to detect differences in expression of BD1. The results indicated that BD1 was produced in intestinal crypt cells and secreted into the lumen through the villi brush border. BD1 was up-regulated in distal ileum segments colonized by SEBS and B. subtilis. Chicken primary intestinal crypt cells were cultured and grouped into control, inorganic Se, B. subtilis, SEBS, and Se-BS treatments to identify the receptor of B. subtilis. Results indicated that B. subtilis and SEBS were recognized by toll-like receptor 2 (TLR2), stimulating the NF-κB1 signaling pathway to increase expression of BD-1, which was further enhanced when combined with Se. Pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 were up-regulated with B. subtilis supplementation, and inhibited under the action of Se. In conclusion, B. subtilis and SEBS were recognized by the TLR2 receptor in the ileal mucous membrane, which activated the TLR2-MyD88-NF-κB1 signaling pathway to upregulate BD1 expression. In addition, Se enhanced recognition of B. subtilis and reduced levels of pro-inflammatory factors caused by estrogenic B. subtilis supplementation.

The Interplay Between Respiratory Microbiota and Innate Immunity in Flavor E-Cigarette Vaping Induced Lung Dysfunction

Global usage of electronic nicotine delivery systems (ENDS) has been increasing in the last decade. ENDS are non-combustible tobacco products that heat and aerosolize a liquid containing humectants, with added flavorings and often nicotine. Though ENDS are promoted as a less harmful alternative to smoking, current evidence links their use to a wide range of deleterious health effects including acute and chronic lung damage. ENDS can elicit an inflammatory response and impair the innate immune response in the lungs. Exposure to ENDS flavorings results in abnormal activation of the lung epithelial cells and β-defensins, dysfunction of the macrophage phagocytic activity, increased levels of mucin (MUC5AC) and abnormal activation of the neutrophilic response (NETosis). ENDS menthol flavorings disrupt innate immunity and might be associated with allergies and asthma through activation of transient receptor potential ankyrin 1 (TRAP1). Recent studies have expanded our understanding of the relationship between the homeostasis of lung innate immunity and the immunomodulatory effect of the host-microbiota interaction. Alterations of the normal respiratory microbiota have been associated with chronic obstructive pulmonary disease (COPD), asthma, atopy and cystic fibrosis complications which are strongly associated with smoking and potentially with ENDS use. Little is known about the short-and long-term effects of ENDS on the respiratory microbiota, their impact on the innate immune response and their link to pulmonary health and disease. Here we review the interaction between the innate immune system and the respiratory microbiota in the pathogenesis of ENDS-induced pulmonary dysfunction and identify future areas of research.

Host Defense Peptides as Templates for Antifungal Drug Development

Current treatment for invasive fungal diseases is limited to three classes of antifungal drugs: azoles, polyenes, and echinocandins. The most recently introduced antifungal class, the echinocandins, was first approved nearly 30 years ago. The limited antifungal drug portfolio is rapidly losing its clinical utility due to the inexorable rise in the incidence of invasive fungal infections and the emergence of multidrug resistant (MDR) fungal pathogens. New antifungal therapeutic agents and novel approaches are desperately needed. Here, we detail attempts to exploit the antifungal and immunoregulatory properties of host defense peptides (HDPs) in the design and evaluation of new antifungal therapeutics and discuss historical limitations and recent advances in this quest.

Copy number variation, gene expression and histological localization of human beta-defensin 2 in patients with adeno-tonsillar hypertrophy

Both bacterial infections and innate oral immunity response participate in development of adeno-tonsillar hypertrophy (ATH). ATH can lead to obstructive sleep apnea. We investigated the beta-defensin 2 (hBD-2) encoding gene, DEFB4, by analyzing the copy number variations (CNVs) of the defensin gene cluster in patients with ATH and by correlating CNV with DEFB4 gene expression. We enrolled 79 patients with ATH, 21 of whom presented with only adenoid hypertrophy, while 58 exhibited hypertrophy of both adenoid and tonsil. CNVs of the defensin gene cluster, DEFB4 mRNA, and hBD-2 protein expression were assessed. Also, beta-defensin 2 was localized histologically using immunohistochemistry. The distribution of defensin gene cluster CNV was similar among the 79 subjects. DEFB4 expression analysis exhibited considerable inter-individual variability, but with neither specific differences among subjects nor correlation with the CNV number. Immunohistochemistry enabled localization of hBD-2 in the tonsil and adenoid epithelium. No differences in localization between the two ATH presentations were found. Inducible antimicrobial defensin peptides exhibited great inter-individual variability in terms of both CNV and gene expression, but no correlation with presentation of ATH was found.

An Alphaherpesvirus Exploits Antimicrobial β-Defensins To Initiate Respiratory Tract Infection

How herpesviruses circumvent mucosal defenses to promote infection of new hosts through the respiratory tract remains unknown due to a lack of host-specific model systems. We used the alphaherpesvirus equine herpesvirus type 1 (EHV1) and equine respiratory tissues to decipher this key event in general alphaherpesvirus pathogenesis. In contrast to several respiratory viruses and bacteria, EHV1 resisted potent antimicrobial equine β-defensins (eBDs) eBD2 and eBD3 by the action of glycoprotein M. Instead, eBD2 and -3 facilitated EHV1 particle aggregation and infection of rabbit kidney (RK13) cells. In addition, virion binding to and subsequent infection of respiratory epithelial cells were increased upon preincubation of these cells with eBD1, -2, and -3. Infected cells synthesized eBD2 and -3, promoting further host cell invasion by EHV1. Finally, eBD1, -2, and -3 recruited leukocytes, which are well-known EHV1 dissemination and latency vessels. The exploitation of host innate defenses by herpesviruses during the early phase of host colonization indicates that highly specialized strategies have developed during host-pathogen coevolution.

β-Defensins protect the respiratory tract against the myriad of microbial pathogens entering the airways with each breath. However, this potentially hostile environment is known to serve as a portal of entry for herpesviruses. The lack of suitable respiratory model systems has precluded understanding of how herpesvirus virions overcome the abundant mucosal β-defensins during host invasion. We demonstrate how a central alphaherpesvirus, equine herpesvirus type 1 (EHV1), actually exploits β-defensins to invade its host and initiate viral spread. The equine β-defensins (eBDs) eBD1, -2, and -3 were produced and secreted along the upper respiratory tract. Despite the marked antimicrobial action of eBD2 and -3 against many bacterial and viral pathogens, EHV1 virions were resistant to eBDs through the action of the viral glycoprotein M envelope protein. Pretreatment of EHV1 virions with eBD2 and -3 increased the subsequent infection of rabbit kidney (RK13) cells, which was dependent on viral N-linked glycans. eBD2 and -3 also caused the aggregation of EHV1 virions on the cell surface of RK13 cells. Pretreatment of primary equine respiratory epithelial cells (EREC) with eBD1, -2, and -3 resulted in increased EHV1 virion binding to and infection of these cells. EHV1-infected EREC, in turn, showed an increased production of eBD2 and -3 compared to that seen in mock- and influenza virus-infected EREC. In addition, these eBDs attracted leukocytes, which are essential for EHV1 dissemination and which serve as latent infection reservoirs. These novel mechanisms provide new insights into herpesvirus respiratory tract infection and pathogenesis.

IMPORTANCE How herpesviruses circumvent mucosal defenses to promote infection of new hosts through the respiratory tract remains unknown due to a lack of host-specific model systems. We used the alphaherpesvirus equine herpesvirus type 1 (EHV1) and equine respiratory tissues to decipher this key event in general alphaherpesvirus pathogenesis. In contrast to several respiratory viruses and bacteria, EHV1 resisted potent antimicrobial equine β-defensins (eBDs) eBD2 and eBD3 by the action of glycoprotein M. Instead, eBD2 and -3 facilitated EHV1 particle aggregation and infection of rabbit kidney (RK13) cells. In addition, virion binding to and subsequent infection of respiratory epithelial cells were increased upon preincubation of these cells with eBD1, -2, and -3. Infected cells synthesized eBD2 and -3, promoting further host cell invasion by EHV1. Finally, eBD1, -2, and -3 recruited leukocytes, which are well-known EHV1 dissemination and latency vessels. The exploitation of host innate defenses by herpesviruses during the early phase of host colonization indicates that highly specialized strategies have developed during host-pathogen coevolution.

Mechanisms of Epithelial Immunity Evasion by Respiratory Bacterial Pathogens

Bacterial lung infections are major healthcare challenges killing millions of people worldwide and resulting in a huge economic burden. Both basic and clinical research have elucidated host mechanisms that contribute to the bacterial clearance where an indispensable role of immune cells has been established. However, the role of respiratory epithelial cells in bacterial clearance has garnered limited attention due to their weak inflammatory or phagocytic ability compared to immune cells such as macrophages and neutrophils. These studies often underappreciate the fact that epithelial cells are the most abundant cells in the lung, not only serving as building blocks but also providing immune protection throughout the lung. Epithelial cells function either independently to eradicate the pathogen or communicate with immune cells to orchestrate pathogen clearance. The epithelial cells have multiple mechanisms that include mucus production, antimicrobial peptide production, muco-ciliary clearance, and phagocytosis, all of which contribute to their direct antibacterial function. Secretion of cytokines to recruit immune cells and potentiate their antimicrobial activities is a pathway by which the epithelium contributes to bacterial clearance. Successful pathogens outsmart epithelial resistance and find a way to replicate in sufficient numbers to establish infections in the airway or lung epithelial surfaces. In this mini-review, we discuss evidences that establish important roles for epithelial host defense against invading respiratory bacterial pathogens and demonstrate how pathogens outsmart these epithelial immune mechanisms to successfully establish infection. Finally, we discuss briefly how to boost epithelial immunity to improve outcomes in bacterial lung infections.

Mechanisms of Epithelial Immunity Evasion by Respiratory Bacterial Pathogens

Bacterial lung infections are major healthcare challenges killing millions of people worldwide and resulting in a huge economic burden. Both basic and clinical research have elucidated host mechanisms that contribute to the bacterial clearance where an indispensable role of immune cells has been established. However, the role of respiratory epithelial cells in bacterial clearance has garnered limited attention due to their weak inflammatory or phagocytic ability compared to immune cells such as macrophages and neutrophils. These studies often underappreciate the fact that epithelial cells are the most abundant cells in the lung, not only serving as building blocks but also providing immune protection throughout the lung. Epithelial cells function either independently to eradicate the pathogen or communicate with immune cells to orchestrate pathogen clearance. The epithelial cells have multiple mechanisms that include mucus production, antimicrobial peptide production, muco-ciliary clearance, and phagocytosis, all of which contribute to their direct antibacterial function. Secretion of cytokines to recruit immune cells and potentiate their antimicrobial activities is a pathway by which the epithelium contributes to bacterial clearance. Successful pathogens outsmart epithelial resistance and find a way to replicate in sufficient numbers to establish infections in the airway or lung epithelial surfaces. In this mini-review, we discuss evidences that establish important roles for epithelial host defense against invading respiratory bacterial pathogens and demonstrate how pathogens outsmart these epithelial immune mechanisms to successfully establish infection. Finally, we discuss briefly how to boost epithelial immunity to improve outcomes in bacterial lung infections.

Regulatory SNP rs5743417 impairs constitutive expression of human β-defensin 1 and has high frequency in Africans and Afro-Americans

The prediction of regulatory single nucleotide polymorphisms (rSNPs) in proximal promoters of disease-related genes could be a useful tool for personalized medicine in both patient stratification and customized therapy. Using our previously reported method of rSNPs prediction (currently a software called SNPClinic v.1.0) as well as with PredictSNP tool, we performed in silico prediction of regulatory SNPs in the antimicrobial peptide human β-defensin 1 gene in three human cell lines from 1,000 Genomes Project (1kGP), namely A549 (epithelial cell line), HL-60 (neutrophils) and T_H 1 (lymphocytes). These predictions were run in a proximal pseudo-promoter comprising all common alleles on each polymorphic site according to the 1,000 Genomes Project data (1kGP: ALL). Plasmid vectors containing either the major or the minor allele of a putative rSNP rs5743417 (categorized as regulatory by SNPClinic and confirmed by PredictSNP) and a non-rSNP negative control were transfected to lung A549 human epithelial cell line. We assessed functionality of rSNPs by qPCR using the Pfaffl method. In A549 cells, minor allele of the SNP rs5743417 G→A showed a significant reduction in gene expression, diminishing DEFB1 transcription by 33% when compared with the G major allele (p-value = .03). SNP rs5743417 minor allele has high frequency in Gambians (8%, 1kGP population: GWD) and Afro-Americans (3.3%, 1kGP population: ASW). This SNP alters three transcription factors binding sites (TFBSs) comprising SREBP2 (sterols and haematopoietic pathways), CREB1 (cAMP, insulin and TNF pathways) and JUND (apoptosis, senescence and stress pathways) in the proximal promoter of DEFB1. Further in silico analysis reveals that this SNP also overlaps with GS1-24F4.2, a lincRNA gene complementary to the X Kell blood group related 5 (XKR5) mRNA. The potential clinical impact of the altered constitutive expression of DEFB1 caused by rSNP rs5743417 in DEFB1-associated diseases as tuberculosis, COPD, asthma, cystic fibrosis and cancer in African and Afro-American populations deserves further research.

Indoor Particulate Matter From Smoker Homes Induces Bacterial Growth, Biofilm Formation, and Impairs Airway Antimicrobial Activity. A Pilot Study

Background: Particulate matter (PM) air pollution causes deleterious health effects; however, less is known about health effects of indoor air particulate matter (IAP). Objective: To understand whether IAP influences distinct mechanisms in the development of respiratory tract infections, including bacterial growth, biofilm formation, and innate immunity. Additionally, we tested whether IAP from Iowa houses of subjects with and without recent respiratory exacerbations recapitulated the National Institute of Standards and Technology (NIST) IAP findings. Methods: To test the effect of NIST and Iowa IAP on bacterial growth and biofilm formation, we assessed Staphylococcus aureus growth and Pseudomonas aeruginosa biofilm formation with and without the presence of IAP. To assess the effect of IAP on innate immunity, we exposed primary human airway surface liquid (ASL) to NIST, and Iowa IAP. Lastly, we tested whether specific metals may be responsible for effects on airway innate immunity. Results: NIST and Iowa IAP significantly enhanced bacterial growth and biofilm formation. NIST IAP (whole particle and the soluble portion) impaired ASL antimicrobial activity. IAP from one Iowa home significantly impaired ASL antimicrobial activity (p < 0.05), and five other homes demonstrated a trend (p ≤ 0.18) of impaired ASL antimicrobial activity. IAP from homes of subjects with a recent history of respiratory exacerbation tended (p = 0.09) to impair ASL antimicrobial activity more than IAP from homes of those without a history respiratory exacerbation. Aluminum and Magnesium impaired ASL antimicrobial activity, while copper was bactericidal. Combining metals varied their effect on ASL antimicrobial activity. Conclusions: NIST IAP and Iowa IAP enhanced bacterial growth and biofilm formation. ASL antimicrobial activity was impaired by NIST IAP, and Iowa house IAP from subjects with recent respiratory exacerbation tended to impair ASL antimicrobial activity. Individual metals may explain impaired ASL antimicrobial activity; however, antimicrobial activity in the presence of multiple metals warrants further study.

Tryptophan promoted β-defensin-2 expressionviathe mTOR pathway and its metabolites: kynurenine banding to aryl hydrocarbon receptor in rat intestine

In this study, we investigated the signalling pathways mediating tryptophan (Trp)-promoted β-defensin-2 (BD-2) expression in rat intestinal mucosa. Sprague Dawley rats were administered with l-Trp and treated with rapamycin (RAPA), 1-methyltryptophan (1-MT), or para-chlorophenyl-amine (PCPA) to inhibit mammalian target of rapamycin (mTOR), indoleamine-2,3-dioxygenase (IDO), or tryptophan hydroxylase (TPH), respectively. The mRNA and protein levels of BD-2 in the jejunal and ileal mucosa of rats increased with administration of l-Trp. Intraperitoneal injection of RAPA significantly decreased the mRNA level of BD-2 and the concentrations of p-mTORC1 and BD-2 in the jejunal and ileal mucosa of rats with administration of l-Trp (P < 0.05). Oral administration of 1-MT decreased the IDO activity and the mRNA and protein levels of BD-2, and increased the concentrations of tumour necrosis factor (TNF-α), interleukin (IL)-17, and IL-22 in the jejunal and ileal mucosa of rats with administration of l-Trp (P < 0.05). Intraperitoneal injection of PCPA decreased the TPH activity and increased the mRNA and protein levels of BD-2, but did not change the concentrations of TNF-α, IL-17, or IL-22 in the jejunal and ileal mucosa of rats with administration of l-Trp. The results indicate the Trp-promoted BD-2 expression in the jejunum and ileum via the mTOR pathway and its metabolites: kynurenine banding to aryl hydrocarbon receptor in rat intestine.

In this study, we investigated the signalling pathways mediating tryptophan (Trp)-promoted β-defensin-2 (BD-2) expression in rat intestinal mucosa.

Molecular characterization of pulmonary defenses against bacterial invasion in allergic asthma: The role of Foxa2 in regulation of β-defensin 1

Allergic asthma, characterized by chronic airway Th2-dominated inflammation, is associated with an increased risk of infection; however, the underlying mechanisms are unclear. Forkhead box protein A2 (Foxa2) plays a critical role in Th2 inflammation and is associated with pulmonary defenses. To determining the role of Foxa2 in Th2-dominated lung inflammation against the invading bacteria, we established a mouse OVA-sensitized model, an Escherichia coli lung invasion model, and mice with conditional deletion of Foxa2 in respiratory epithelial cells. The number of bacteria in the lung tissue was counted to assess clearance ability of lung. Lung inflammation and histopathology was evaluated using HE and PAS staining. It was found that OVA-sensitized mice had decreased E. coli clearance, reduced Foxa2 expression, and decreased DEFB1 secretion. Conditional deletion of Foxa2 in respiratory epithelial cells led to decreased clearance of E. coli and impaired secretion of DEFB1, similar to the OVA-induced allergic condition. The impaired secretion of DEFB1 may be responsible for the increased risk of infection in the Th2-dominated airway inflammation. Dual luciferase assay demonstrated that Foxa2 regulates DEFB1 expression by affecting its promoter activity in HBE cells. Our study indicated that Foxa2 plays an important role in Th2-dominated airway inflammation against invading bacteria. Conditional deletion of Foxa2 in respiratory epithelial cells can reduce pulmonary's defense against bacterial invasion by inhibiting DEFB1expression.

Serum amyloid A3 confers protection against acute lung injury in Pseudomonas aeruginosa-infected mice

Pseudomonas aeruginosa is a gram-negative bacterium associated with serious illnesses, including ventilator-associated pneumonia and various sepsis syndromes in humans. Understanding the host immune mechanisms against P. aeruginosa is, therefore, of clinical importance. The present study identified serum amyloid A3 (SAA3) as being highly inducible in mouse bronchial epithelium following P. aeruginosa infection. Genetic deletion of Saa3 rendered mice more susceptible to P. aeruginosa infection with decreased neutrophil superoxide anion production, and ex vivo treatment of mouse neutrophils with recombinant SAA3 restored the ability of neutrophils to produce superoxide anions. The SAA3-deficient mice showed exacerbated inflammatory responses, which was characterized by pronounced neutrophil infiltration, elevated expression of TNF-α, KC/CXCL1, and MIP-2/CXCL2 in bronchoalveolar lavage fluid (BALF), and increased lung microvascular permeability compared with their wild-type littermates. BALF neutrophils from Saa3 knockout mice exhibited reduced superoxide anion production compared with neutrophils from wild-type mice. Adoptive transfer of SAA3-treated neutrophils to Saa3 knockout mice ameliorated P. aeruginosa-induced acute lung injury. These findings demonstrate that SAA3 not only serves as a biomarker for infection and inflammation, but also plays a protective role against P. aeruginosa infection-induced lung injury in part through augmentation of neutrophil bactericidal functions.

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.

Antibacterial spectrum of human omentum and differential expression of beta defensins

BACKGROUND

Human β defensins (hBD1 and hBD2) are cationic, cysteine-rich peptides and form an integral part of the mammalian innate immune system. hBD1 is constitutively expressed in epithelial cells, whereas hBD2 increases in response to bacterial infection. Human omentum is known for its anti-inflammatory properties and also possesses an antibacterial activity of its own. We hypothesized that antimicrobial peptides, β defensins, may govern host defense mechanism in the microbe-rich environment of the peritoneal cavity. Therefore, we analyzed the expression of hBD1 and hBD2 in omentum tissue in vivo and also studied the antibacterial activity of omentum against common pathogens.

METHODOLOGY

Omentum tissues were obtained from 30 patients (15 cases and 15 controls). Real-time polymerase chain reaction (PCR) was used to evaluate the mRNA expression of hBD1 and hBD2. Protein quantification was done using Western blotting technique. Antibacterial susceptibility was performed to check the antibacterial activity of omentum.

RESULT

Significantly higher expression of hBD2 was observed in cases compared to controls at both the transcriptional and translational levels. In comparison with an array of antibiotics, activated omentum also showed antibacterial property even at lower concentration of its extract.

CONCLUSION

Omentum directly responds to bacterial infection, which may be due to differential expression of hBD1 and hBD2 in human omental tissue. These peptides (hBD1 and hBD2) may be an ideal candidate for novel antibiotic class with a broad-spectrum activity.

Randomized controlled study of aerosolized hypertonic xylitol versus hypertonic saline in hospitalized patients with pulmonary exacerbation of cystic fibrosis

BACKGROUND

Cystic fibrosis (CF) lung disease is characterized by chronic bacterial infection and recurrent pulmonary exacerbations. Xylitol is a 5-carbon sugar that can lower the airway surface salt concentration and augment innate immunity. We examined the safety and efficacy of aerosolized xylitol use for 2 weeks in subjects hospitalized with a pulmonary exacerbation of CF.

METHODS

In a 2-week study, 60 subjects with cystic fibrosis and FEV₁ > 30% predicted were enrolled to receive aerosolized 7% hypertonic saline (4 ml) or 15% xylitol (5 ml) twice a day for 14 days. Outcomes assessed included change from baseline in FEV₁% predicted, change in sputum microbial density, revised CF quality of life questionnaire including the respiratory symptom score, time to next hospitalization for a pulmonary exacerbation, and frequency of adverse events.

RESULTS

59 subjects completed the study (one subject in the saline group withdrew before any study product administration). No significant differences were noted between the 2 arms in mean changes in lung function, sputum microbial density for Pseudomonas aeruginosa and Staphylococcus aureus, body weight, quality of life, and frequency of adverse events.

CONCLUSIONS

Aerosolized hypertonic xylitol was well-tolerated among subjects hospitalized for CF pulmonary exacerbation. Future studies examining efficacy for long term use in patients with CF lung disease would be worthwhile. The clinical trial registration number for this study is NCT00928135.

A β-defensin gene of Trachinotus ovatus might be involved in the antimicrobial and antiviral immune response

Defensins are a group of small cationic and cysteine-rich peptides that are important components of the innate immune system. However, studies on defensins in teleosts are very limited, particularly studies on defensin functions through in vivo assays. In this study, we cloned and identified one β-defensin (TroBD) the golden pompano, Trachinotus ovatus, and analyzed the functions of TroBD in both in vivo and in vitro assays. TroBD is composed of 63 amino acids and shares high sequence identities (27.27-98.41%) with known β-defensins of other teleosts. The protein has a signature motif of six conserved cysteine residues within the mature peptide. The expression of TroBD was most abundant in the head kidney and spleen and was significantly upregulated following infection by Vibrio harveyi and viral nervous necrosis virus (VNNV). Purified recombinant TroBD (rTroBD) inhibited the growth of V. harveyi, and its antimicrobial activity was influenced by salt concentration. TroBD was found to have a chemotactic effect on macrophages in vitro. The results of an in vivo study demonstrated that TroBD overexpression/knockdown in T. ovatus significantly reduced/increased bacterial colonization or viral copy numbers in tissues. Taken together, these results indicate that TroBD plays a significant role in both antibacterial and antiviral immunity and provide new avenues for protection against pathogen infection in the aquaculture industry.

β-Defensins Coordinate In Vivo to Inhibit Bacterial Infections of the Trachea

β-defensins are predicted to play an important role in innate immunity against bacterial infections in the airway. We previously observed that a type III-secretion product of Bordetella bronchiseptica inhibits the NF-κB-mediated induction of a β-defensin in airway epithelial cells in vitro. To confirm this in vivo and to examine the relative roles of other β-defensins in the airway, we infected wild-type C57BL/6 mice and mice with a deletion of the mBD-1 gene with B. bronchiseptica wild-type strain, RB50 and its mutant strain lacking the type III-secretion system, WD3. The bacteria were quantified in the trachea and the nasal tissue and mRNA levels of mouse β-defensin-3 (mBD-3) were assessed after 24 h. Infection with the wild-type bacterial strain resulted in lower mBD-3 mRNA levels in the trachea than in mice infected with the type III-deficient strain. Furthermore, we observed an increase in bacterial numbers of RB50 only in the tracheas of mBD-1-deficient mice. Neutrophils were also more abundant on the trachea in RB50 infected WT mice but not in the bronchiolar lavage fluid (BAL), compared with WD3 infected WT and mBD-1^−/− mice, indicating that the coordination of β-defensin chemotactic effects may be confined to tracheal epithelial cells (TEC). RB50 decreased the ability of mice to mount an early specific antibody response, seven days after infection in both WT and mBD-1^−/− mice but there were no differences in titers between RB50-infected WT and mBD-1^−/− mice or between WD3-infected WT and mBD-1^−/− mice, indicating mBD-1 was not involved in induction of the humoral immune response to the B. bronchiseptica. Challenge of primary mouse TEC in vitro with RB50 and WD3, along with IL-1β, further corroborated the in vivo studies. The results demonstrate that at least two β-defensins can coordinate early in an infection to limit the growth of bacteria in the trachea.

Neuropeptides SP and CGRP Diminish the Moraxella catarrhalis Outer Membrane Vesicle- (OMV-) Triggered Inflammatory Response of Human A549 Epithelial Cells and Neutrophils

Neuropeptides such as substance P (SP) and calcitonin gene-related peptide (CGRP) play both pro- and anti-inflammatory activities and are produced during infection and inflammation. Moraxella catarrhalis is one of the leading infectious agents responsible for inflammatory exacerbation in chronic obstructive pulmonary disease (COPD). Since the airway inflammation in COPD is connected with activation of both epithelial cells and accumulated neutrophils, in this study we determined the in vitro effects of neuropeptides on the inflammatory potential of these cells in response to M. catarrhalis outer membrane vesicle (OMV) stimulant. The various OMV-mediated proinflammatory effects were demonstrated. Next, using hBD-2-pGL4[luc2] plasmid with luciferase reporter gene, SP and CGRP were shown to inhibit the IL-1β-dependent expression of potent neutrophil chemoattractant, hBD-2 defensin, in transfected A549 epithelial cells (type II alveolar cells) upon OMV stimulation. Both neuropeptides exerted antiapoptotic activity through rescuing a significant fraction of A549 cells from OMV-induced cell death and apoptosis. Finally, CGRP caused an impairment of specific but not azurophilic granule exocytosis from neutrophils as shown by evaluation of gelatinase-associated lipocalin (NGAL) or CD66b expression and elastase release, respectively. Concluding, these findings suggest that SP and CGRP mediate the dampening of proinflammatory action triggered by M. catarrhalis OMVs towards cells engaged in lung inflammation in vitro.

Intestinal manipulation affects mucosal antimicrobial defense in a mouse model of postoperative ileus

Aim

To explore the effects of abdominal surgery and interleukin-1 signaling on antimicrobial defense in a model of postoperative ileus.

Methods

C57BL/6 and Interleukin-1 receptor type I (IL-1R1) deficient mice underwent intestinal manipulation to induce POI. Expression of mucosal IL-1α, IL-1β and IL-1R1 and several antimicrobial peptides and enzymes were measured by quantitative PCR or ELISA, western blotting or immunohistochemistry. Bacterial overgrowth was determined by fluorescent in-situ hybridization and counting of jejunal luminal bacteria. Translocation of aerobic and anaerobic bacteria into the intestinal wall, mesenteric lymph nodes, liver and spleen was determined by counting bacterial colonies on agar plates 48h after plating of tissue homogenates. Antimicrobial activity against E. coli and B. vulgatus was analyzed in total and cationic fractions of small bowel mucosal tissue homogenates by a flow cytometry-based bacterial depolarization assay.

Results

Jejunal bacterial overgrowth was detected 24h after surgery. At the same time point, but not in the early phase 3h after surgery, bacterial translocation into the liver and mesenteric lymph nodes was observed. Increased antimicrobial activity against E. coli was induced within early phase of POI. Basal antimicrobial peptide and enzyme gene expression was higher in the ileal compared to the jejunal mucosa. The expression of lysozyme 1, cryptdin 1, cryptdin 4 and mucin 2 were reduced 24h after surgery in the ileal mucosa and mucin 2 was also reduced in the jejunum. Postoperative IL-1α and IL-1β were increased in the postoperative mucosa. Deficiency of IL-1R1 affected the expression of antimicrobial peptides during homeostasis and POI.

Conclusion

Small bowel antimicrobial capacity is disturbed during POI which is accompanied by bacterial overgrowth and translocation. IL-1R1 is partially involved in the gene expression of mucosal antimicrobial peptides. Altered small bowel antimicrobial activity may contribute also to POI development and manifestation in patients undergoing abdominal surgery.

Human beta defensin (HBD) gene copy number affects HBD2 protein levels: impact on cervical bactericidal immunity in pregnancy

Human beta defensin 2 (HBD2) is an endogenous mucosal antimicrobial peptide (AMP) upregulated during infection and inflammation. HBD2 is encoded by the DEFB4 gene, which exhibits extensive copy number variation. Previous studies have demonstrated a relationship between HBD copy number and serum HBD2 protein levels; however, our current understanding of the influence of copy number on mucosal AMP function remains limited. This study explores the relationship between HBD copy number, cervicovaginal HBD2 protein levels and antimicrobial activity in 203 women with risk factors for preterm birth. We provide evidence that suggests HBD copy number modulates cervical antimicrobial immunity.

Overview of Innate Lung Immunity and Inflammation

The nasal passages, conducting airways and gas-exchange surfaces of the lung, are constantly exposed to substances contained in the air that we breathe. While many of these suspended substances are relatively harmless, some, for example, pathogenic microbes, noxious pollutants, and aspirated gastric contents can be harmful. The innate immune system, lungs and conducting airways have evolved specialized mechanisms to protect the respiratory system not only from these harmful inhaled substances but also from the overly exuberant innate immune activation that can arise during the host response to harmful inhaled substances. Herein, we discuss the cell types that contribute to lung innate immunity and inflammation and how their activities are coordinated to promote lung health.

Immunohistochemical study on the distribution of β-defensin 1 and β-defensin 2 throughout the respiratory tract of healthy rats

The distributions of β-defensin 1 and 2 in secretory host defense system throughout respiratory tract of healthy rats were immunohistochemically investigated. In the nasal epithelium, a large number of non-ciliated and non-microvillous cells (NCs) were immunopositive for both β-defensin 1 and 2, whereas a small number of goblet cells (GCs) were immunopositive only for β-defensin 1. Beta-defensin 2-immunopositive GCs were few. In the nasal glands, a small number of acinar cells and a large number of ductal epithelial cells were immunopositive for both β-defensins. In the laryngeal and tracheal epithelia, a very few NCs and GCs were immunopositive for both β-defensins. In laryngeal and tracheal glands, a very few acinar cells and a large number of ductal epithelial cells were immunopositive for both β-defensins. In the extra-pulmonary bronchus, a small number of NCs were immunopositive for both β-defensins. A small number of GCs were immunopositive for β-defensin 1, whereas few GCs were immunopositive for β-defensin 2. From the intra-pulmonary bronchus to alveoli, a very few or no epithelial cells were immunopositive for both β-defensins. In the mucus and periciliary layers, β-defensin 1 was detected from the nose to the extra-pulmonary bronchus, whereas β-defensin 2 was weakly detected only in the nose and the larynx. These findings suggest that the secretory sources of β-defensin 1 and 2 are mainly distributed in the nasal mucosa and gradually decrease toward the caudal airway in healthy rats.

Soy isoflavones enhance β-defensin synthesis and secretion in endometrial epithelial cells with exposure to TLR3 agonist polyinosinic-polycytidylic acid

PROBLEM

β-defensins are important innate chemical barriers that protect the endometrium from pathogen invasion. The effects of soy isoflavones, genistein and daidzein, on the expression and secretion of porcine β-defensins (PBD) in endometrial epithelial cells were investigated under normal or poly I:C-stimulated conditions.

METHOD OF STUDY

Primary cultured porcine endometrial epithelial (PE) cells were pretreated with genistein or daidzein followed by poly I:C inoculation. During treatment, the culture media were analyzed for PBD 1-4 secretion by ELISA and the total RNA for PBD gene expression by quantitative RT-PCR.

RESULTS

Porcine endometrial epithelial cells constitutively expressed PBD 1-4 and secreted PBD-1, PBD-2, and PBD-4. Genistein and daidzein enhanced PBD-2 expression and PBD-2 and PBD-3 secretion. These compounds also potentiated PBD-2 and PBD-3 expression and secretion which were upregulated by poly I:C.

CONCLUSION

Soy isoflavones, genistein and daidzein, could be potentially used for promoting the innate host defense of endometrium against infection.

Plant flavones enhance antimicrobial activity of respiratory epithelial cell secretions against Pseudomonas aeruginosa

Flavones are a class of natural plant secondary metabolites that have anti-inflammatory and anti-bacterial effects. Some flavones also activate the T2R14 bitter taste receptor, which is expressed in motile cilia of the sinonasal epithelium and activates innate immune nitric oxide (NO) production. Flavones may thus be potential therapeutics for respiratory infections. Our objective was to examine the anti-microbial effects of flavones on the common sinonasal pathogens Candida albicans, Staphylococcus aureus, and Pseudomonas aeruginosa, evaluating both planktonic and biofilm growth. Flavones had only very low-level antibacterial activity alone. They did not reduce biofilm formation, but did reduce production of the important P. aeruginosa inflammatory mediator and ciliotoxin pyocyanin. However, flavones exhibited synergy against P. aeruginosa in the presence of antibiotics or recombinant human lysozyme. They also enhanced the efficacy of antimicrobials secreted by cultured and primary human airway cells grown at air-liquid interface. This suggests that flavones may have anti-gram-negative potential as topical therapeutics when combined with antibiotics or in the context of innate antimicrobials secreted by the respiratory or other epithelia. This may have an additive effect when combined with T2R14-activated NO production. Additional studies are necessary to understand which flavone compounds or mixtures are the most efficacious.