Cryptdins: antimicrobial defensins of the murine small intestine

Structure, Function, and Physicochemical Properties of Pore-forming Antimicrobial Peptides

Antimicrobial peptides (AMPs), a class of antimicrobial agents, possess considerable potential to treat various microbial ailments. The broad range of activity and rare complete bacterial resistance to AMPs make them ideal candidates for commercial development. These peptides with widely varying compositions and sources share recurrent structural and functional features in mechanisms of action. Studying the mechanisms of AMP activity against bacteria may lead to the development of new antimicrobial agents that are more potent. Generally, AMPs are effective against bacteria by forming pores or disrupting membrane barriers. The important structural aspects of cytoplasmic membranes of pathogens and host cells will also be outlined to understand the selective antimicrobial actions. The antimicrobial activities of AMPs are related to multiple physicochemical properties, such as length, sequence, helicity, charge, hydrophobicity, amphipathicity, polar angle, and also self-association. These parameters are interrelated and need to be considered in combination. So, gathering the most relevant available information will help to design and choose the most effective AMPs.

Paneth cell dysfunction in radiation injury and radio-mitigation by human α-defensin 5

Introduction

The mechanism underlying radiation-induced gut microbiota dysbiosis is undefined. This study examined the effect of radiation on the intestinal Paneth cell α-defensin expression and its impact on microbiota composition and mucosal tissue injury and evaluated the radio-mitigative effect of human α-defensin 5 (HD5).

Methods

Adult mice were subjected to total body irradiation, and Paneth cell α-defensin expression was evaluated by measuring α-defensin mRNA by RT-PCR and α-defensin peptide levels by mass spectrometry. Vascular-to-luminal flux of FITC-inulin was measured to evaluate intestinal mucosal permeability and endotoxemia by measuring plasma lipopolysaccharide. HD5 was administered in a liquid diet 24 hours before or after irradiation. Gut microbiota was analyzed by 16S rRNA sequencing. Intestinal epithelial junctions were analyzed by immunofluorescence confocal microscopy and mucosal inflammatory response by cytokine expression. Systemic inflammation was evaluated by measuring plasma cytokine levels.

Results

Ionizing radiation reduced the Paneth cell α-defensin expression and depleted α-defensin peptides in the intestinal lumen. α-Defensin down-regulation was associated with the time-dependent alteration of gut microbiota composition, increased gut permeability, and endotoxemia. Administration of human α-defensin 5 (HD5) in the diet 24 hours before irradiation (prophylactic) significantly blocked radiation-induced gut microbiota dysbiosis, disruption of intestinal epithelial tight junction and adherens junction, mucosal barrier dysfunction, and mucosal inflammatory response. HD5, administered 24 hours after irradiation (treatment), reversed radiation-induced microbiota dysbiosis, tight junction and adherens junction disruption, and barrier dysfunction. Furthermore, HD5 treatment also prevents and reverses radiation-induced endotoxemia and systemic inflammation.

Conclusion

These data demonstrate that radiation induces Paneth cell dysfunction in the intestine, and HD5 feeding prevents and mitigates radiation-induced intestinal mucosal injury, endotoxemia, and systemic inflammation.

Keratinocyte-derived defensins activate neutrophil-specific receptors Mrgpra2a/b to prevent skin dysbiosis and bacterial infection

Healthy skin maintains a diverse microbiome and a potent immune system to fight off infections. Here, we discovered that the epithelial-cell-derived antimicrobial peptides defensins activated orphan G-protein-coupled receptors (GPCRs) Mrgpra2a/b on neutrophils. This signaling axis was required for effective neutrophil-mediated skin immunity and microbiome homeostasis. We generated mutant mouse lines lacking the entire Defensin (Def) gene cluster in keratinocytes or Mrgpra2a/b. Def and Mrgpra2 mutant animals both exhibited skin dysbiosis, with reduced microbial diversity and expansion of Staphylococcus species. Defensins and Mrgpra2 were critical for combating S. aureus infections and the formation of neutrophil abscesses, a hallmark of antibacterial immunity. Activation of Mrgpra2 by defensin triggered neutrophil release of IL-1β and CXCL2 which are vital for proper amplification and propagation of the antibacterial immune response. This study demonstrated the importance of epithelial-neutrophil signaling via the defensin-Mrgpra2 axis in maintaining healthy skin ecology and promoting antibacterial host defense.

In pursuit of next-generation therapeutics: Antimicrobial peptides against superbugs, their sources, mechanism of action, nanotechnology-based delivery, and clinical applications

Antimicrobial peptides (AMPs) attracted attention as potential source of novel antimicrobials. Multi-drug resistant (MDR) infections have emerged as a global threat to public health in recent years. Furthermore, due to rapid emergence of new diseases, there is pressing need for development of efficient antimicrobials. AMPs are essential part of the innate immunity in most living organisms, acting as the primary line of defense against foreign invasions. AMPs kill a wide range of microorganisms by primarily targeting cell membranes or intracellular components through a variety of ways. AMPs can be broadly categorized based on their physico-chemical properties, structure, function, target and source of origin. The synthetic analogues produced either with suitable chemical modifications or with the use of suitable delivery systems are projected to eliminate the constraints of toxicity and poor stability commonly linked with natural AMPs. The concept of peptidomimetics is gaining ground around the world nowadays. Among the delivery systems, nanoparticles are emerging as potential delivery tools for AMPs, amplifying their utility against a variety of pathogens. In the present review, the broad classification of various AMPs, their mechanism of action (MOA), challenges associated with AMPs, current applications, and novel strategies to overcome the limitations have been discussed.

Cross-Talk Between the Intestinal Epithelium and Salmonella Typhimurium

Salmonella enterica serovars are invasive gram-negative bacteria, causing a wide range of diseases from gastroenteritis to typhoid fever, representing a public health threat around the world. Salmonella gains access to the intestinal lumen after oral ingestion of contaminated food or water. The crucial initial step to establish infection is the interaction with the intestinal epithelium. Human-adapted serovars such as S. Typhi or S. Paratyphi disseminate to systemic organs and induce life-threatening disease known as typhoid fever, whereas broad-host serovars such as S. Typhimurium usually are limited to the intestine and responsible for gastroenteritis in humans. To overcome intestinal epithelial barrier, Salmonella developed mechanisms to induce cellular invasion, intracellular replication and to face host defence mechanisms. Depending on the serovar and the respective host organism, disease symptoms differ and are linked to the ability of the bacteria to manipulate the epithelial barrier for its own profit and cross the intestinal epithelium.

This review will focus on S. Typhimurium (STm). To better understand STm pathogenesis, it is crucial to characterize the crosstalk between STm and the intestinal epithelium and decipher the mechanisms and epithelial cell types involved. Thus, the purpose of this review is to summarize our current knowledge on the molecular dialogue between STm and the various cell types constituting the intestinal epithelium with a focus on the mechanisms developed by STm to cross the intestinal epithelium and access to subepithelial or systemic sites and survive host defense mechanisms.

The role of γδ T cells in the interaction between commensal and pathogenic bacteria in the intestinal mucosa

The intestinal mucosa is an important structure involved in resistance to pathogen infection. It is mainly composed of four barriers, which have different but interrelated functions. Pathogenic bacteria can damage these intestinal mucosal barriers. Here, we mainly review the mechanisms of pathogen damage to biological barriers. Most γδ T cells are located on the surface of the intestinal mucosa, with the ability to migrate and engage in crosstalk with microorganisms. Commensal bacteria are involved in the activation and migration of γδ T cells to monitor the invasion of pathogens. Pathogen invasion alters the migration pattern of γδ T cells. γδ T cells accelerate pathogen clearance and limit opportunistic invasion of commensal bacteria. By discussing these interactions among γδ T cells, commensal bacteria and pathogenic bacteria, we suggest that γδ T cells may link the interactions between commensal bacteria and pathogenic bacteria.

Multiomic analysis defines the first microRNA atlas across all small intestinal epithelial lineages and reveals novel markers of almost all major cell types

MicroRNA-mediated regulation is critical for the proper development and function of the small intestinal (SI) epithelium. However, it is not known which microRNAs are expressed in each of the cell types of the SI epithelium. To bridge this important knowledge gap, we performed comprehensive microRNA profiling in all major cell types of the mouse SI epithelium. We used flow cytometry and fluorescence-activated cell sorting with multiple reporter mouse models to isolate intestinal stem cells, enterocytes, goblet cells, Paneth cells, enteroendocrine cells, tuft cells, and secretory progenitors. We then subjected these cell populations to small RNA-sequencing. The resulting atlas revealed highly enriched microRNA markers for almost every major cell type (https://sethupathy-lab.shinyapps.io/SI_miRNA/). Several of these lineage-enriched microRNAs (LEMs) were observed to be embedded in annotated host genes. We used chromatin-run-on sequencing to determine which of these LEMs are likely cotranscribed with their host genes. We then performed single-cell RNA-sequencing to define the cell type specificity of the host genes and embedded LEMs. We observed that the two most enriched microRNAs in secretory progenitors are miR-1224 and miR-672, the latter of which we found is deleted in hominin species. Finally, using several in vivo models, we established that miR-152 is a Paneth cell-specific microRNA.NEW & NOTEWORTHY In this study, first, microRNA atlas (and searchable web server) across all major small intestinal epithelial cell types is presented. We have demonstrated microRNAs that uniquely mark several lineages, including enteroendocrine and tuft. Identification of a key marker of mouse secretory progenitor cells, miR-672, which we show is deleted in humans. We have used several in vivo models to establish miR-152 as a specific marker of Paneth cells, which are highly understudied in terms of microRNAs.

G.I. pros: Antimicrobial defense in the gastrointestinal tract

The gastrointestinal tract is a complex environment in which the host immune system interacts with a diverse array of microorganisms, both symbiotic and pathogenic. As such, mobilizing a rapid and appropriate antimicrobial response depending on the nature of each stimulus is crucial for maintaining the balance between homeostasis and inflammation in the gut. Here we focus on the mechanisms by which intestinal antimicrobial peptides regulate microbial communities during dysbiosis and infection. We also discuss classes of bacterial peptides that contribute to reducing enteric pathogen outgrowth. This review aims to provide a comprehensive overview on the interplay of diverse antimicrobial responses with enteric pathogens and the gut microbiota.

ATF4 Deficiency Promotes Intestinal Inflammation in Mice by Reducing Uptake of Glutamine and Expression of Antimicrobial Peptides

BACKGROUND & AIMS

Activating transcription factor 4 (ATF4) regulates genes involved in the inflammatory response, amino acid metabolism, autophagy, and endoplasmic reticulum stress. We investigated whether its activity is altered in patients with inflammatory bowel diseases (IBDs) and mice with enterocolitis.

METHODS

We obtained biopsy samples during endoscopy from inflamed and/or uninflamed regions of the colon from 21 patients with active Crohn's disease (CD), 22 patients with active ulcerative colitis (UC), and 38 control individuals without IBD and of the ileum from 19 patients with active CD and 8 individuals without IBD in China. Mice with disruption of Atf4 specifically in intestinal epithelial cells (Atf4ΔIEC mice) and Atf4-floxed mice (controls) were given dextran sodium sulfate (DSS) to induce colitis. Some mice were given injections of recombinant defensin α1 (DEFA1) and supplementation of l-alanyl-glutamine or glutamine in drinking water. Human and mouse ileal and colon tissues were analyzed by quantitative real-time polymerase chain reaction, immunoblots, and immunohistochemistry. Serum and intestinal epithelial cell (IEC) amino acids were measured by high-performance liquid chromatography-tandem mass spectrometry. Levels of ATF4 were knocked down in IEC-18 cells with small interfering RNAs. Microbiomes were analyzed in ileal feces from mice by using 16S ribosomal DNA sequencing.

RESULTS

Levels of ATF4 were significantly decreased in inflamed intestinal mucosa from patients with active CD or active UC compared with those from uninflamed regions or intestinal mucosa from control individuals. ATF4 was also decreased in colonic epithelia from mice with colitis vs mice without colitis. Atf4ΔIEC mice developed spontaneous enterocolitis and colitis of greater severity than control mice after administration of DSS. Atf4ΔIEC mice had decreased serum levels of glutamine and reduced levels of antimicrobial peptides, such as Defa1, Defa4, Defa5, Camp, and Lyz1, in ileal Paneth cells. Atf4ΔIEC mice had alterations in ileal microbiomes compared with control mice; these changes were reversed by administration of glutamine. Injections of DEFA1 reduced the severity of spontaneous enteritis and DSS-induced colitis in Atf4ΔIEC mice. We found that expression of solute carrier family 1 member 5 (SLC1A5), a glutamine transporter, was directly regulated by ATF4 in cell lines. Overexpression of SLC1A5 in IEC-18 or primary IEC cells increased glutamine uptake and expression of antimicrobial peptides. Knockdown of ATF4 in IEC-18 cells increased expression of inflammatory cytokines, whereas overexpression of SLC1A5 in the knockdown cells reduced cytokine expression. Levels of SLC1A5 were decreased in inflamed intestinal mucosa of patients with CD and UC and correlated with levels of ATF4.

CONCLUSIONS

Levels of ATF4 are decreased in inflamed intestinal mucosa from patients with active CD or UC. In mice, ATF4 deficiency reduces glutamine uptake by intestinal epithelial cells and expression of antimicrobial peptides by decreasing transcription of Slc1a5. ATF4 might therefore be a target for the treatment of IBD.

Modulation of ovine SBD-1 expression by Saccharomyces cerevisiae in ovine ruminal epithelial cells

Background

The ovine rumen is involved in host defense responses and acts as the immune interface with the environment. The ruminal mucosal epithelium plays an important role in innate immunity and secretes antimicrobial innate immune molecules that have bactericidal activity against a variety of pathogens. Defensins are cationic peptides that are produced by the mucosal epithelia and have broad-spectrum antimicrobial activity. Sheep β-defensin-1 (SBD-1) is one of the most important antibacterial peptides in the rumen. The expression of SBD-1 is regulated by the probiotic, Saccharomyces cerevisiae (S.c); however, the regulatory mechanism has not yet been elucidated. In the current study, the effects of S.c on the expression and secretion of SBD-1 in ovine ruminal epithelial cells were investigated using quantitative real-time PCR (qPCR) and enzyme-linked immunosorbent assay (ELISA). In addition, specific inhibitors were used to block the nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB), p38, JNK, and ERK1/2 signalling pathways separately or simultaneously, to determine the regulatory mechanism(s) governing S.c-induced SBD-1 upregulation.

Results

Incubation with S.c induced release of SBD-1 by ovine ruminal epithelial cells, with SBD-1 expression peaking after 12 h of incubation. The highest SBD-1 expression levels were achieved after treatment with 5.2 × 10⁷ CFU∙mL^− 1 S.c. Treatment with S.c resulted in significantly increased NF-κB, p38, JNK, ERK1/2, TLR2, and MyD88 mRNA expression. Whereas inhibition of mitogen-activated protein kinases (MAPKs) and NF-κB gene expression led to a decrease in SBD-1 expression.

Conclusions

S.c was induced SBD-1 expression and the S.c-induced up-regulation of SBD-1 expression may be related to TLR2 and MyD88 in ovine ruminal epithelial cells. This is likely simultaneously regulated by the MAPKs and NF-κB pathways with the p38 axis of the MAPKs pathway acting as the primary regulator. Thus, the pathways regulating S.c-induced SBD-1 expression may be related to TLR2-MyD88-NF-κB/MAPKs, with the TLR2-MyD88-p38 component of the TLR2-MyD88-MAPKs signalling acting as the main pathway.

Molecular Basis of Acute Cystitis Reveals Susceptibility Genes and Immunotherapeutic Targets

Tissue damage is usually regarded as a necessary price to pay for successful elimination of pathogens by the innate immune defense. Yet, it is possible to distinguish protective from destructive effects of innate immune activation and selectively attenuate molecular nodes that create pathology. Here, we identify acute cystitis as an Interleukin-1 beta (IL-1β)-driven, hyper-inflammatory condition of the infected urinary bladder and IL-1 receptor blockade as a novel therapeutic strategy. Disease severity was controlled by the mechanism of IL-1β processing and mice with intact inflammasome function developed a moderate, self-limiting form of cystitis. The most severe form of acute cystitis was detected in mice lacking the inflammasome constituents ASC or NLRP-3. IL-1β processing was hyperactive in these mice, due to a new, non-canonical mechanism involving the matrix metalloproteinase 7- (MMP-7). ASC and NLRP-3 served as transcriptional repressors of MMP7 and as a result, Mmp7 was markedly overexpressed in the bladder epithelium of Asc^-/- and Nlrp3^-/- mice. The resulting IL-1β hyper-activation loop included a large number of IL-1β-dependent pro-inflammatory genes and the IL-1 receptor antagonist Anakinra inhibited their expression and rescued susceptible Asc^-/- mice from bladder pathology. An MMP inhibitor had a similar therapeutic effect. Finally, elevated levels of IL-1β and MMP-7 were detected in patients with acute cystitis, suggesting a potential role as biomarkers and immunotherapeutic targets. The results reproduce important aspects of human acute cystitis in the murine model and provide a comprehensive molecular framework for the pathogenesis and immunotherapy of acute cystitis, one of the most common infections in man.

Infections continue to threaten human health as pathogenic organisms outsmart available therapies with remarkable genetic versatility. Fortunately, microbial versatility is matched by the flexibility of the host immune system which provide a rich source of novel therapeutic concepts. Emerging therapeutic solutions include substances that strengthen the immune system rather than killing the bacteria directly. Selectivity is a concern, however, as boosting of the antibacterial immune response may cause collateral tissue damage. This study addresses how the host response to urinary bladder infection causes acute cystitis and how this response can be attenuated in patients who suffer from this very common condition. We identify the cytokine Interleukin-1 beta (IL-1β) as a key immune response determinant in acute cystitis and successfully treat mice with severe acute cystitis by inhibiting IL-1β or the enzyme MMP-7 that processes IL-1β to its active form. Finally, we detect elevated levels of these molecules in urine samples from patients with cystitis, suggesting clinical relevance and a potential role of IL-1β and MMP-7 both as therapeutic targets and as biomarkers of infection. These findings provide a much needed, molecular framework for the pathogenesis and treatment of acute cystitis.

Increased alpha-defensin expression is associated with risk of coronary heart disease: a feasible predictive inflammatory biomarker of coronary heart disease in hyperlipidemia patients

Background

Atherosclerosis is a multifactorial disorder of the heart vessels that develops over decades, coupling inflammatory mechanisms and elevated total cholesterol levels under the influence of genetic and environmental factors. Without effective intervention, atherosclerosis consequently causes coronary heart disease (CHD), which leads to increased risk of sudden death.

Polymorphonuclear neutrophils play a pivotal role in inflammation and atherogenesis. Human neutrophil peptides (HNPs) or alpha (α)-defensins are cysteine-rich cation polypeptides that are produced and released from activated polymorphonuclear neutrophil granules during septic inflammation and acute coronary vascular disorders. HNPs cause endothelial cell dysfunction during early atherogenesis. In this cross-sectional study, control, hyperlipidemia and CHD groups were representative as atherosclerosis development and CHD complications. We aimed to assess the correlation between α-defensin expression and the development of CHD, and whether it was a useful predictive indicator for CHD risk.

Methods

First, DNA microarray analysis was performed on peripheral blood mononuclear cells (PBMCs) from Thai control, hyperlipidemia and CHD male patients (n = 7). Gene expression profiling revealed eight up-regulated genes common between hyperlipidemia and CHD patients, but not controls. We sought to verify and compare α-defensin expression among the groups using: 1) real-time quantitative RT-PCR (qRT-PCR) to determine α-defensin mRNA expression (n = 10), and 2) enzyme-linked immunosorbent assay to determine plasma HNP 1–3 levels (n = 17). Statistically significant differences and correlations between groups were determined by the Mann–Whitney U test or the Kruskal–Wallis test, and the Rho-Spearman correlation, respectively.

Results

We found that α-defensin mRNA expression increased (mean 2-fold change) in the hyperlipidemia (p = 0.043) and CHD patients (p = 0.05) compared with the controls. CHD development moderately correlated with α-defensin mRNA expression (r = 0.429, p = 0.023) and with plasma HNP 1–3 levels (r = 0.486, p = 0.000).

Conclusions

Increased α-defensin expression is a potential inflammatory marker that may predict the risk of CHD development in Thai hyperlipidemia patients.

Cell-autonomous responses in Listeria monocytogenes infection

ABSTRACT 

Listeria monocytogenes is a facultative intracellular bacterium causing listeriosis, a food-borne infection with a high mortality rate. The mechanisms and the role of cells and tissular components in generating protective adaptive immune responses are well studied, and cell biological studies provide a detailed understanding of the processes targeted by the bacterial products. Much less is known of the cellular responses activated to limit infection in individual cells when confronted with stress or infection. Eukaryotic cellular responses depend on multitiered homeostatic systems that ensure maintenance of proteostatis, organellar integrity, function and turnover, and overall cellular viability (‘the cell-autonomous response’). Here, we review the cell-autonomous responses induced during extracellular and intracellular L. monocytogenes growth and discuss their contribution to limiting infection.

Activation of intestinal epithelial Stat3 orchestrates tissue defense during gastrointestinal infection

Gastrointestinal infections with EHEC and EPEC are responsible for outbreaks of diarrheal diseases and represent a global health problem. Innate first-line-defense mechanisms such as production of mucus and antimicrobial peptides by intestinal epithelial cells are of utmost importance for host control of gastrointestinal infections. For the first time, we directly demonstrate a critical role for Stat3 activation in intestinal epithelial cells upon infection of mice with Citrobacter rodentium – a murine pathogen that mimics human infections with attaching and effacing Escherichia coli. C. rodentium induced transcription of IL-6 and IL-22 in gut samples of mice and was associated with activation of the transcription factor Stat3 in intestinal epithelial cells. C. rodentium infection induced expression of several antimicrobial peptides such as RegIIIγ and Pla2g2a in the intestine which was critically dependent on Stat3 activation. Consequently, mice with specific deletion of Stat3 in intestinal epithelial cells showed increased susceptibility to C. rodentium infection as indicated by high bacterial load, severe gut inflammation, pronounced intestinal epithelial cell death and dissemination of bacteria to distant organs. Together, our data implicate an essential role for Stat3 activation in intestinal epithelial cells during C. rodentium infection. Stat3 concerts the host response to bacterial infection by controlling bacterial growth and suppression of apoptosis to maintain intestinal epithelial barrier function.

Cationic antimicrobial peptides as potential new therapeutic agents in neonates and children: a review

PURPOSE OF REVIEW

Antimicrobial resistance towards conventional antibiotics is a serious problem for modern medicine and for our society. Multidrug-resistant bacteria are very difficult to treat and treatment options have begun to run out. Here, we summarize the newest studies of drug development using cationic antimicrobial peptides as lead molecules for novel antimicrobial drugs.

RECENT FINDINGS

A new development is the use of antimicrobial peptides not only as direct antimicrobial lead structures but also using their ability to influence the immune system. Such approaches can be used to develop drugs that influence the immune system in a unique way, supporting specific branches of immune cells in order to clear infection. Applying such an 'immune boost' would also minimize the danger of new resistance emerging in bacteria. In addition, searching for and testing substances that trigger the production of host antimicrobial peptides is still ongoing and opens up a totally new avenue for the use of antimicrobial peptides against infections. Currently, more than 10 clinical trials, phase 2 or 3, using antimicrobial peptides are in progress or have been recently completed.

SUMMARY

Multidrug resistance is an urgent problem for modern medicine and novel antimicrobials are needed. Despite some drawbacks, antimicrobial peptides seem now to appear more numerous in clinical trials, indicating the success in developing peptides into novel therapeutics. This can be critical especially for neonates and children, as treatment options for infections with Gram-negatives in neonatal ICUs are becoming rare.

I-FABP as biomarker for the early diagnosis of acute mesenteric ischemia and resultant lung injury

Acute mesenteric ischemia (AMI) is a life-threatening condition that can result in multiple organ injury and death. A timely diagnosis and treatment would have a significant impact on the morbidity and mortality in high-risk patient population. The purpose of this study was to investigate if intestinal fatty acid binding protein (I-FABP) and α-defensins can be used as biomarkers for early AMI and resultant lung injury. C57BL/6 mice were subjected to intestinal ischemia by occlusion of the superior mesenteric artery. A time course of intestinal ischemia from 0.5 to 3 h was performed and followed by reperfusion for 2 h. Additional mice were treated with N-acetyl-cysteine (NAC) at 300 mg/kg given intraperitoneally prior to reperfusion. AMI resulted in severe intestinal injury characterized by neutrophil infiltrate, myeloperoxidase (MPO) levels, cytokine/chemokine levels, and tissue histopathology. Pathologic signs of ischemia were evident at 1 h, and by 3 h of ischemia, the full thickness of the intestine mucosa had areas of coagulative necrosis. It was noted that the levels of α-defensins in intestinal tissue peaked at 1 h and I-FABP in plasma peaked at 3 h after AMI. Intestinal ischemia also resulted in lung injury in a time-dependent manner. Pretreatment with NAC decreased the levels of intestinal α-defensins and plasma I-FABP, as well as lung MPO and cytokines. In summary, the concentrations of intestinal α-defensins and plasma I-FABP predicted intestinal ischemia prior to pathological evidence of ischemia and I-FABP directly correlated with resultant lung injury. The antioxidant NAC reduced intestinal and lung injury induced by AMI, suggesting a role for oxidants in the mechanism for distant organ injury. I-FABP and α-defensins are promising biomarkers, and may guide the treatment with antioxidant in early intestinal and distal organ injury.

Immunopathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a group of idiopathic, chronic and relapsing inflammatory conditions of the gastrointestinal tract. Familial and epidemiological studies have stressed the involvement of genetic factors and have also shown the critical role of environmental factors such as sanitation and hygiene in the development of IBD. However, the molecular mechanisms of intestinal inflammation in IBD have long remained unknown. In recent years, the study of susceptibility genes involved in the detection of bacterial components and in the regulation of the host immune response has shed light onto the potential role of intestinal pathogens and gut flora in IBD immunobiology. This review presents current knowledge on intestinal epithelial barrier alterations and on dysfunction of mucosal innate and acquired immune responses in IBD. The data support the etiological hypothesis which argues that pathogenic intestinal bacteria and/or infectious agents initiate and perpetuate the inflammation of the gut through disruption of tolerance towards the commensal microbiota in an individual with genetic vulnerability.

Black cobra (Naja naja karachiensis) lysates exhibit broad-spectrum antimicrobial activities

It is hypothesized that animals living in polluted environments possess antimicrobials to counter pathogenic microbes. The fact that snakes feed on germ-infested rodents suggests that they encounter pathogenic microbes and likely possess antimicrobials. The venom is used only to paralyze the rodent, but the ability of snakes to counter potential infections in the gut due to disease-ridden rodents requires robust action of the immune system against a broad range of pathogens. To test this hypothesis, crude lysates of different organs of Naja naja karachiensis (black cobra) were tested for antimicrobial properties. The antimicrobial activities of extracts were tested against selected bacterial pathogens (neuropathogenic Escherichia coli K1, methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, and Streptococcus pneumonia), protist (Acanthamoeba castellanii), and filamentous fungus (Fusarium solani). The findings revealed that plasma and various organ extracts of N. n. karachiensis exhibited antimicrobial activity against E. coli K1, MRSA, P. aeruginosa, S. pneumoniae, A. castellanii, and F. solani in a concentration-dependent manner. The results of this study are promising for the development of new antimicrobials.

Paneth cell-mediated multiorgan dysfunction after acute kidney injury

Acute kidney injury (AKI) is frequently complicated by extrarenal multiorgan injury, including intestinal and hepatic dysfunction. In this study, we hypothesized that a discrete intestinal source of proinflammatory mediators drives multiorgan injury in response to AKI. After induction of AKI in mice by renal ischemia-reperfusion or bilateral nephrectomy, small intestinal Paneth cells increased the synthesis and release of IL-17A in conjunction with severe intestinal apoptosis and inflammation. We also detected significantly increased IL-17A in portal and systemic circulation after AKI. Intestinal macrophages appear to transport released Paneth cell granule constituents induced by AKI, away from the base of the crypts into the liver. Genetic or pharmacologic depletion of Paneth cells decreased small intestinal IL-17A secretion and plasma IL-17A levels significantly and attenuated intestinal, hepatic, and renal injury after AKI. Similarly, portal delivery of IL-17A in macrophage-depleted mice decreased markedly. In addition, intestinal, hepatic, and renal injury following AKI was attenuated without affecting intestinal IL-17A generation. In conclusion, AKI induces IL-17A synthesis and secretion by Paneth cells to initiate intestinal and hepatic injury by hepatic and systemic delivery of IL-17A by macrophages. Modulation of Paneth cell dysregulation may have therapeutic implications by reducing systemic complications arising from AKI.

Characterization of low molecular weight antimicrobial peptide from human female reproductive tract

Background & objectives:

The mechanisms that protect female upper genital tract from ascending infection by microbes present in vagina are only partially understood. It is expected that epithelial cells in mucosal surfaces and their secretions directly interfere with microbial colonization and invasion. This study was aimed to demonstrate the expression of 2 kDa antimicrobial peptide which was identified and purified from female genital tract tissues using chromatographic techniques.

Methods:

Low molecular weight proteins were isolated from human female reproductive tract tissues obtained from premenopausal women. Antimicrobial activity of these LMW proteins was assessed against different reproductive tract pathogens viz., Neisseria gonorrhoeae, Group B streptococcus, Gardnerella vaginalis, Escherechia coli and Candida albicans. The expression of these peptides were also documented in reproductive tract tissues with the help of hyperimmune sera raised against the rabbits. The purified peptide was characterized by N-terminal sequencing.

Results:

Immunohistochemical and immunofluorescence studies demonstrated that 2 kDa peptide was expressed in the stratified squamous epithelial cells of the ectocervix while it was absent in columnar epithelial cells of upper genital tract. Upregulation of the expression of this peptide was observed in patients of chronic non-specific cervicitis and acute on chronic cervicitis. This purified antimicrobial peptide also showed broad spectrum antimicrobial activity against different reproductive tract pathogens.

Interpretation & conclusions:

Considering the emerging bacterial resistance against conventional antibiotics, isolation and understanding of the expression of antimicrobial peptides from female reproductive tissue extracts may provide some leads towards the development of strategies for the treatment of reproductive tract infections.

Resistance to antimicrobial peptides in Gram-negative bacteria

Antimicrobial peptides (AMPs) are present in virtually all organisms and are an ancient and critical component of innate immunity. In mammals, AMPs are present in phagocytic cells, on body surfaces such as skin and mucosa, and in secretions and body fluids such as sweat, saliva, urine, and breast milk, consistent with their role as part of the first line of defense against a wide range of pathogenic microorganisms including bacteria, viruses, and fungi. AMPs are microbicidal and have also been shown to act as immunomodulators with chemoattractant and signaling activities. During the co-evolution of hosts and bacterial pathogens, bacteria have developed the ability to sense and initiate an adaptive response to AMPs to resist their bactericidal activity. Here, we review the various mechanisms used by Gram-negative bacteria to sense and resist AMP-mediated killing. These mechanisms play an important role in bacterial resistance to host-derived AMPs that are encountered during the course of infection. Bacterial resistance to AMPs should also be taken into consideration in the development and use of AMPs as anti-infective agents, for which there is currently a great deal of academic and commercial interest.

Activation of the unfolded protein response by Listeria monocytogenes

The endoplasmic reticulum (ER) responds to perturbation of homeostasis with stress. To maintain ER function, a signalling-circuitry has evolved which, when engaged, attempts to reduce a surplus of unfolded proteins by triggering the unfolded protein response (UPR). Several studies have implicated UPR in viral infections, neurodegenerative disorders and metabolic diseases but UPR has not yet been widely linked to bacterial infections. Here we demonstrate that the facultative intracellular pathogen Listeria monocytogenes (Lm) induces ER expansion and UPR prior to host cell entry. Lm activated protein kinase RNA-like ER kinase (PERK) evidenced by the phosphorylation of the α-subunit of eukaryotic translation initiation factor-2 (eIF2α), inositol-requiring protein-1 (IRE1) as shown by detection of spliced X-box binding protein-1 (XBP1) and activating transcription factor-6 (ATF6) as demonstrated by depletion of its inactive form. A mutant LmΔhly strain that did not produce listeriolysin (LLO) lacked the UPR response. Conversely purified LLO activated UPR. Sustained infection with Lm resulted in apoptosis. Induction of ER stress by thapsigargin or tunicamycin reduced intracellular bacterial number. Our findings suggest that UPR plays an important role in the cell autonomous defence responses to bacterial infection.

Evaluation of amoebicidal potential of Paneth cell cryptdin-2 against Entamoeba histolytica

BACKGROUND

Amoebiasis is a major public health problem in tropical and subtropical countries. Currently, metronidazole is the gold choice medication for the treatment of this disease. However, reports have indicated towards the possibility of development of metronidazole-resistance in Entamoeba strains in near future. In view of the emergence of this possibility, in addition to the associated side effects and mutagenic ability of the currently available anti-amoebic drugs, there is a need to explore newer therapeutics against this disease. In this context, the present study evaluated the amoebicidal potential of cryptdin-2 against E. histolytica.

METHODS/PRINCIPAL FINDINGS

In the present study, cryptdin-2 exhibited potent in-vitro amoebicidal activity against E. histolytica in a concentration dependent manner at a minimum amoebicidal concentration (MAC) of 4 mg/L. Scanning electron microscopy as well as phase contrast microscopic investigations of cryptdin-2 treated trophozoites revealed that the peptide was able to induce significant morphological alterations in terms of membrane wrinkling, leakage of the cytoplasmic contents and damaged plasma membrane suggesting a possible membrane dependent amoebicidal activity. N-phenyl napthylamine (NPN) uptake assay in presence of sulethal, lethal as well as twice the lethal concentrations further confirmed the membrane-dependent mode of action of cryptdin-2 and suggested that the peptide could permeabilize the plasma membrane of E. histolytica. It was also found that cryptdin-2 interfered with DNA, RNA as well as protein synthesis of E. histolytica exerting the highest effect against DNA synthesis. Thus, the macromolecular synthesis studies correlated well with the observations of membrane permeabilization studies.

SIGNIFICANCE/CONCLUSIONS

The amoebicidal efficacy of cryptdin-2 suggests that it may be exploited as a promising option to combat amoebiasis or, at least, may act as an adjunct to metronidazole and/or other available anti-amoebic drugs.

Biosynthesis and antimicrobial evaluation of backbone-cyclized α-defensins

Defensins are antimicrobial peptides that are important in the innate immune defense of mammals. Upon stimulation by bacterial antigens, enteric α-defensins are secreted into the intestinal lumen where they have potent microbicidal activities. Cryptdin-4 (Crp4) is an α-defensin expressed in Paneth cells of the mouse small intestine and the most bactericidal of the known cryptdin isoforms. The structure of Crp4 consists of a triple-stranded antiparallel β-sheet but lacks three amino acids between the fourth and fifth cysteine residues, making them distinct from other α-defensins. The structure also reveals that the α-amino and C-terminal carboxylic groups are in the proximity of each other (d ≈ 3 Å) in the folded structure. We present here the biosynthesis of backbone-cyclized Crp4 using a modified protein splicing unit or intein. Our data show that cyclized Crp4 can be biosynthesized by using this approach both in vitro and in vivo, although the expression yield was significantly lower when the protein was produced inside the cell. The resulting cyclic defensins retained the native α-defensin fold and showed equivalent or better microbicidal activities against several Gram-positive and Gram-negative bacteria when compared to native Crp4. No detectable hemolytic activity against human red blood cells was observed for either native Crp4 or its cyclized variants. Moreover, both forms of Crp4 also showed high stability to degradation when incubated with human serum. Altogether, these results indicate the potential for backbone-cyclized defensins in the development of novel peptide-based antimicrobial compounds.

Antimicrobial peptides and proteins of the horse--insights into a well-armed organism

Antimicrobial peptides play a pivotal role as key effectors of the innate immune system in plants and animals and act as endogenous antibiotics. The molecules exhibit an antimicrobial activity against bacteria, viruses, and eukaryotic pathogens with different specificities and potencies depending on the structure and amino-acid composition of the peptides. Several antimicrobial peptides were comprehensively investigated in the last three decades and some molecules with remarkable antimicrobial properties have reached the third phase of clinical studies. Next to the peptides themselves, numerous organisms were examined and analyzed regarding their repertoire of antimicrobial peptides revealing a huge number of candidates with potencies and properties for future medical applications. One of these organisms is the horse, which possesses numerous peptides that are interesting candidates for therapeutical applications in veterinary medicine. Here we summarize investigations and knowledge on equine antimicrobial peptides, point to interesting candidates, and discuss prospects for therapeutical applications.

In vitro and in vivo synergistic effects of cryptdin 2 and ampicillin against Salmonella

In view of the emergence of multidrug-resistant Salmonella strains, there is a need for therapeutic alternatives. To reduce the dose of antibiotic required in order to decrease the associated side effects, the present study was aimed at evaluating the synergism between cryptdin 2 (a Paneth cell antimicrobial peptide) and ampicillin (Amp) against Salmonella enterica serovar Typhimurium. The synergy was evaluated in terms of the fractional bactericidal concentration (FBC) index, time-kill assay results (in vitro), macrophage functions, i.e., intracellular killing, lipid peroxidation, superoxide dismutase activity, and generation of nitrite (ex vivo), and decreases in CFU of salmonellae in livers, spleens, and small intestines of infected mice treated with cryptdin 2 and/or Amp (in vivo). In vitro synergism between the two agents was observed on the basis of the FBC index and time-kill assays. When the agents were used in combination, ex vivo studies revealed an enhanced effect on macrophage functions, particularly exhibiting a synergetic effect in terms of SOD levels. In vivo synergy was indicated by larger log unit decreases in all target organs of mice treated with the combination than those for the drugs used alone. These results point toward the possible use of cryptdin 2 as an adjunct to ampicillin and may help in developing alternate strategies to combat Salmonella infections.

Paneth cell hyperplasia and metaplasia in necrotizing enterocolitis

Paneth cell dysfunction has been suggested in necrotizing enterocolitis (NEC). The aim of this study was to i) study Paneth cell presence, protein expression, and developmental changes in preterm infants with NEC and ii) determine Paneth cell products and antimicrobial capacity in ileostomy outflow fluid. Intestinal tissue from NEC patients (n = 55), preterm control infants (n = 22), and term controls (n = 7) was obtained during surgical resection and at stoma closure after recovery. Paneth cell abundance and protein expression were analyzed by immunohistochemistry. RNA levels of Paneth cell proteins were determined by real-time quantitative RT-PCR. In ileostomy outflow fluid, Paneth cell products were quantified, and antimicrobial activity was measured in vitro. In acute NEC, Paneth cell abundance in small intestinal tissue was not significantly different from preterm controls. After recovery from NEC, Paneth cell hyperplasia was observed in the small intestine concomitant with elevated human alpha-defensin 5 mRNA levels. In the colon, metaplastic Paneth cells were observed. Ileostomy fluid contained Paneth cell proteins and inhibited bacterial growth. In conjunction, these data suggest an important role of Paneth cells and their products in various phases of NEC.

Strain-specific polymorphisms in Paneth cell α-defensins of C57BL/6 mice and evidence of vestigial myeloid α-defensin pseudogenes

Paneth cells at the base of small intestinal crypts secrete microbicidal α-defensins, termed cryptdins (Crps) in mice, as mediators of innate immunity. Proteomic studies show that five abundant Paneth cell α-defensins in C57BL/6 mice are strain specific in that they have not been identified in other inbred strains of mice. Two C57BL/6-specific peptides are coded for by the Defcr20 and -21 genes evident in the NIH C57BL/6 genome but absent from the Celera mixed-strain assembly, which excludes C57BL/6 data and differs from the NIH build with respect to the organization of the α-defensin gene locus. Conversely, C57BL/6 mice lack the Crp1, -2, -4, and -6 peptides and their corresponding Defcr1, -2, -4, and -6 genes, which are common to several mouse strains, including those of the Celera assembly. In C57BL/6 mice, α-defensin gene diversification appears to have occurred by tandem duplication of a multigene cassette that was not found in the mixed-strain assembly. Both mouse genome assemblies contain conserved α-defensin pseudogenes that are closely related to functional myeloid α-defensin genes in the rat, suggesting that the neutrophil α-defensin defect in mice resulted from progressive gene loss. Given the role of α-defensins in shaping the composition of the enteric microflora, such polymorphisms may influence outcomes in mouse models of disease or infection.

Defensins attenuate cytokine responses yet enhance antibody responses to Porphyromonas gingivalis adhesins in mice

AIM

Our aim is to assess the ability of human neutrophil peptide alpha-defensins (HNPs) and human beta-defensins (HBDs) to attenuate proinflammatory cytokine responses and enhance antibody responses to recombinant hemagglutinin B (rHagB) or recombinant fimbrillin A (rFimA) from Porphyromonas gingivalis 381 in mice.

MATERIALS & METHODS

In the first study, C57BL/6 mice were given 10 microg rHagB or rFimA without and with 1 microg HNP1, HNP2, HBD1, HBD2 or HBD3. At 24 h, mice were euthanized and cytokine concentrations were determined in nasal wash fluid (NWF), bronchoalveolar lavage fluids, saliva and serum. In the second study, C57BL/6 mice were given 10 microg rHagB or rFimA without and with 1 microg HNPs or HBDs similarly on days 0, 7 and 14. At 21 days, mice were euthanized and rHagB- and rFimA-specific antibody responses were determined in NWF, bronchoalveolar lavage fluids, saliva and serum.

RESULTS

Mice given rHagB + HNP2, rHagB + HBD1 and rHagB + HBD3 produced significantly lower (p < 0.05) IL-6 responses than mice given rHagB alone. Mice given rHagB + HNP1, rHagB + HNP2, rHagB + HBD1 and rHagB + HBD3 produced significantly lower (p < 0.05) keratinocyte-derived chemokine responses than mice given rHagB alone. Mice given rFimA produced very low levels of IL-6 and only moderate levels of keratinocyte-derived chemokine in NWF that were not attenuated by prior incubation of rFimA with any defensin. Mice given rHagB + HNP1 produced a significantly higher (p < 0.05) serum IgG antibody response than mice given rHagB alone and mice given rFimA + HNP2 produced a higher, but not significant, antibody response.

CONCLUSION

The ability of HNPs and HBDs to attenuate proinflammatory cytokine responses in murine NWF and enhance IgG antibody responses in serum was dependent upon both the defensin and antigen of P. gingivalis.

Polymyxin B resistance in El Tor Vibrio cholerae requires lipid acylation catalyzed by MsbB

Antimicrobial peptides are critical for innate antibacterial defense. Both Gram-negative and Gram-positive microbes have mechanisms to alter their surfaces and resist killing by antimicrobial peptides. In Vibrio cholerae, two natural epidemic biotypes, classical and El Tor, exhibit distinct phenotypes with respect to sensitivity to the peptide antibiotic polymyxin B: classical strains are sensitive and El Tor strains are relatively resistant. We carried out mutant screens of both biotypes, aiming to identify classical V. cholerae mutants resistant to polymyxin B and El Tor V. cholerae mutants sensitive to polymyxin B. Insertions in a gene annotated msbB (encoding a predicted lipid A secondary acyltransferase) answered both screens, implicating its activity in antimicrobial peptide resistance of V. cholerae. Analysis of a defined mutation in the El Tor biotype demonstrated that msbB is required for resistance to all antimicrobial peptides tested. Mutation of msbB in a classical strain resulted in reduced resistance to several antimicrobial peptides but in no significant change in resistance to polymyxin B. msbB mutants of both biotypes showed decreased colonization of infant mice, with a more pronounced defect observed for the El Tor mutant. Mass spectrometry analysis showed that lipid A of the msbB mutant for both biotypes was underacylated compared to lipid A of the wild-type isolates, confirming that MsbB is a functional acyltransferase in V. cholerae.

The repertoire of equine intestinal alpha-defensins

Background

Defensins represent an important class of antimicrobial peptides. These effector molecules of the innate immune system act as endogenous antibiotics to protect the organism against infections with pathogenic microorganisms. Mammalian defensins are classified into three distinct sub-families (α-, β- and θ-defensins) according to their specific intramolecular disulfide-bond pattern. The peptides exhibit an antimicrobial activity against a broad spectrum of microorganisms including bacteria and fungi. Alpha-Defensins are primarily synthesised in neutrophils and intestinal Paneth cells. They play a role in the pathogenesis of intestinal diseases and may regulate the flora of the intestinal tract. An equine intestinal α-defensin (DEFA1), the first characterised in the Laurasiatheria, shows a broad antimicrobial spectrum against human and equine pathogens. Here we report a first investigation of the repertoire of equine intestinal α-defensins. The equine genome was screened for putative α-defensin genes by using known α-defensin sequences as matrices. Based on the obtained sequence information, a set of oligonucleotides specific to the α-defensin gene-family was designed. The products generated by reverse-transcriptase PCR with cDNA from the small intestine as template were sub-cloned and numerous clones were sequenced.

Results

Thirty-eight equine intestinal α-defensin transcripts were determined. After translation it became evident that at least 20 of them may code for functional peptides. Ten transcripts lacked matching genomic sequences and for 14 α-defensin genes apparently present in the genome no appropriate transcript could be verified. In other cases the same genomic exons were found in different transcripts.

Conclusions

The large repertoire of equine α-defensins found in this study points to a particular importance of these peptides regarding animal health and protection from infectious diseases. Moreover, these findings make the horse an excellent species to study biological properties of α-defensins. Interestingly, the peptides were not found in other species of the Laurasiatheria to date. Comparison of the obtained transcripts with the genomic sequences in the current assembly of the horse (EquCab2.0) indicates that it is yet not complete and/or to some extent falsely assembled.

Alpha-defensins in enteric innate immunity: functional Paneth cell alpha-defensins in mouse colonic lumen

Paneth cells are a secretory epithelial lineage that release dense core granules rich in host defense peptides and proteins from the base of small intestinal crypts. Enteric alpha-defensins, termed cryptdins (Crps) in mice, are highly abundant in Paneth cell secretions and inherently resistant to proteolysis. Accordingly, we tested the hypothesis that enteric alpha-defensins of Paneth cell origin persist in a functional state in the mouse large bowel lumen. To test this idea, putative Crps purified from mouse distal colonic lumen were characterized biochemically and assayed in vitro for bactericidal peptide activities. The peptides comigrated with cryptdin control peptides in acid-urea-PAGE and SDS-PAGE, providing identification as putative Crps. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry experiments showed that the molecular masses of the putative alpha-defensins matched those of the six most abundant known Crps, as well as N-terminally truncated forms of each, and that the peptides contain six Cys residues, consistent with identities as alpha-defensins. N-terminal sequencing definitively revealed peptides with N termini corresponding to full-length, (des-Leu)-truncated, and (des-Leu-Arg)-truncated N termini of Crps 1-4 and 6. Crps from mouse large bowel lumen were bactericidal in the low micromolar range. Thus, Paneth cell alpha-defensins secreted into the small intestinal lumen persist as intact and functional forms throughout the intestinal tract, suggesting that the peptides may mediate enteric innate immunity in the colonic lumen, far from their upstream point of secretion in small intestinal crypts.

Chicken intestine defensins activated murine peripheral blood mononuclear cells through the TLR4-NF-kappaB pathway

Defensins serve as alarm signals in mobilizing the immune system and activating the innate and adaptive immune responses. In order to investigate whether avian defensins could activate monocytes of another species, and whether chicken defensins could modulate or amplify the adaptive immune responses of murine through the TLR-NF-kappaB pathway, the relationship between the chicken intestinal defensin AvBD13 and TLR4 in murine peripheral blood mononuclear cells (PBMCs) was explored in vitro. Monocytes were stimulated with AvBD13 (1 microg/mL). The levels of NF-kappaB p65, CD80, CD86, IL-12 and IFN-alpha were measured by immunohistochemical analysis of the cells or enzyme-linked immunosorbent assay (ELISA), and the TLR4 levels in monocytes were measured by flow-cytometry. We found that AvBD13 can activate NF-kappaB, induce the inflammatory cytokines IL-12 and IFN-alpha, and upregulate costimulatory molecules like CD80 and monocyte proliferation, which was clearly inhibited by the anti-TLR4 antibody. TLR4 expression was rapidly downregulated in the presence of AvBD13. AvBD13 could modulate monocytes directly and serve as an endogenous ligand for TLR4 and upregulate costimulatory molecules and monocyte proliferation. Thus, TLR4 is involved in AvBD13-mediated activation of adaptive immune responses.

Molecular cloning and characterization of β-defensin cDNA expressed in distal ileum of buffalo (Bubalus bubalis)

Defensins play a prominent role in protection of various epithelial surfaces. In this study, we have cloned and characterized the mRNA from the distal ileum of Bubalus bubalis. Total RNA after isolation from ileal epithelium was reverse transcribed to synthesize cDNA using primers designed by taking conserved region of cattle enteric beta-defensin (EBD) mRNA, goat beta-defensin 2 (BD 2) and cattle lingual antimicrobial peptide (LAP) mRNA sequences. The PCR amplified cDNA of 254 bp was ligated to pDrive cloning vector and transformed into XL-blue strain of E coli. The sequence analysis indicated 29 nucleotide substitutions with reported cattle EBD mRNA sequence sharing 86.2% homology, 92.1% with cattle LAP, 81.6% with cattle tracheal antimicrobial peptide and 84.6% with goat BD 2. The deduced amino acid sequence encodes for a 64 amino acid precursor peptide. Both nucleotide and amino acid sequence homology shows that the cloned sequence is closer to cattle LAP.

Subversion of antimicrobial calprotectin (S100A8/S100A9 complex) in the cytoplasm of TR146 epithelial cells after invasion by Listeria monocytogenes

Expressed by squamous mucosal keratinocytes, calprotectin is a complex of two EF-hand calcium-binding proteins of the S100 subfamily (S100A8 and S100A9) with significant antimicrobial activity. Calprotectin-expressing cells resist invasion by Porphyromonas gingivalis, Listeria monocytogenes, and Salmonella enterica serovar Typhimurium (S. typhimurium). To understand the interactions between calprotectin and invasive bacteria, we studied the distribution of calprotectin in the cytoplasm of TR146 epithelial cells. In response to L. monocytogenes, calprotectin mobilized from a diffuse cytoplasmic distribution to a filamentous pattern and colocalized with the microtubule network. Listeria more frequently invaded cells with mobilized calprotectin. Calprotectin mobilization was listeriolysin O-dependent and required calcium (extracellular and intracellular) and an intact microtubule network. In the presence of preformed microtubules in vitro, the anti-Listeria activity of calprotectin was abrogated. To facilitate intraepithelial survival, therefore, Listeria mobilizes calprotectin to colocalize with cytoplasmic microtubules, subverting anti-Listeria activity and autonomous cellular immunity.

A novel horse alpha-defensin: gene transcription, recombinant expression and characterization of the structure and function

Defensins are a predominant class of antimicrobial peptides, which act as endogenous antibiotics. Defensins are classified into three distinct sub-families: theta-, beta-, and alpha-defensins. Synthesis of alpha-defensin has been confirmed only in primates and glires to date and is presumably unique for a few tissues, including neutrophils and Paneth cells of the small intestine. Antimicrobial activities of these peptides were shown against a wide variety of microbes including bacteria, fungi, viruses and protozoan parasites. In the present study, we report the characterization of the equine alpha-defensin DEFA (defensin alpha) 1. Transcription analysis revealed that the transcript of the gene is present in the small intestine only. An alignment with known alpha-defensins from primates and glires displayed a homology with Paneth-cell-specific alpha-defensins. DEFA1 was recombinantly expressed in Escherichia coli and subsequently analysed structurally by CD and molecular modelling. To examine the antimicrobial properties, a radial diffusion assay was performed with 12 different micro-organisms and the LD90 (lethal dose killing > or =90% of target organism) and MBC (minimal bactericidal concentration) values were examined. DEFA1 showed an antimicrobial activity against different Gram-positive and Gram-negative bacteria and against the yeast Candida albicans. Using viable bacteria in combination with a membrane-impermeable fluorescent dye, as well as depolarization of liposomes as a minimalistic system, it became evident that membrane permeabilization is at least an essential part of the peptide's mode of action.

Antimicrobial peptides from amphibian skin: an overview

Over the past three decades, numerous peptides have been isolated from amphibian skin secretions. Many of these peptides were shown to be homologous to hormones and neurotransmitters of mammals. In recent years it has been shown that these secretions also contain a multitude of antimicrobial peptides. Most of these peptides are positively charged and have a propensity for forming an amphipathic helix. Other types of peptides have been detected as well, including one group which contain D-allo-isoleucine in their sequences. This work has mainly been done with three species from different families, Xenopus laevis, Bombina variegata and Rana esculenta. Each of these frogs produces distinct sets of peptides which are not related to those of other species. It can therefore be expected that many additional peptides with antimicrobial activity are present in amphibian species from other families.

Antimicrobial peptides as agents of mucosal immunity

Mucosal surfaces are continually exposed to a wide range of potentially pathogenic organisms, yet the incidence of infectious disease resulting from these encounters is relatively low. This suggests the presence of highly effective defence mechanisms in these tissues. Antimicrobial peptides have recently been discovered in mucosal tissues and may play a significant role in host defence. Several mucosal peptides (andropin, magainin, tracheal antimicrobial peptide, enteric defensins and PR-39) all fulfil minimal criteria for a role in mucosal host defence, including potent in vitro antimicrobial activity and accumulation at the mucosal surface. Most of these mucosal peptides are encoded by members of large gene families that contain members found in other biological contexts more classically associated with antimicrobial defence. The abundance, activity and evolutionary history of several epithelial peptides suggest that antimicrobial peptides play a key role in host defence at mucosal surfaces.

Structure-dependent functional properties of human defensin 5

The mucosal epithelium secretes a variety of antimicrobial peptides that act as part of the innate immune system to protect against invading microbes. Here, we describe the functional properties of human defensin (HD) 5, the major antimicrobial peptide produced by Paneth cells in the ileum, in relation to its structure. The antimicrobial activity of HD-5 against Escherichia coli proved to be independent of its structure, whereas the unstructured peptide showed greatly reduced antimicrobial activity against Staphylococcus aureus. We find that HD-5 binds to the cell membrane of intestinal epithelial cells and induced secretion of the chemokine interleukin (IL)-8 in a concentration- and structure-dependent fashion. Incubation of HD-5 in the presence of tumor necrosis factor alpha further increased IL-8 secretion synergistically, suggesting that HD-5 may act as a regulator of the intestinal inflammatory response.

Penicillin-binding protein 1a promotes resistance of group B streptococcus to antimicrobial peptides

Evasion of host immune defenses is critical for the progression of invasive infections caused by the leading neonatal pathogen, group B streptococcus (GBS). Upon characterizing the factors required for virulence in a neonatal rat sepsis model, we found that a surface-associated penicillin-binding protein (PBP1a), encoded by ponA, played an essential role in resistance of GBS to phagocytic clearance. In order to elucidate how PBP1a promotes resistance to innate immunity, we compared the susceptibility of wild-type GBS and an isogenic ponA mutant to the bactericidal components of human neutrophils. The isogenic strains were found to be equally capable of blocking complement activation on the bacterial surface and equally associated with phagocytes and susceptible to oxidative killing. In contrast, the ponA mutant was significantly more susceptible to killing by cationic antimicrobial peptides (AMPs) of the cathelicidin and defensin families, which are now recognized as integral components of innate host defense against invasive bacterial infection. These observations may help explain the sensitivity to phagocytic killing and attenuated virulence of the ponA mutant. This novel function for PBP1a in promoting resistance of GBS to AMP did not involve an alteration in bacterial surface charge or peptidoglycan cross-linking. While the peptidoglycan polymerization and cross-linking activity of PBPs are essential for bacterial survival, our study is the first to identify a role for a PBP in resistance to host AMPs.

Paneth cell α-defensins: peptide mediators of innate immunity in the small intestine

Epithelial cells contribute to innate immunity by releasing antimicrobial peptides (AMPs) onto mucosal surfaces. In the small bowel, Paneth cells at the base of the crypts of Lieberkühn secrete alpha-defensins and additional AMPs at high levels in response to cholinergic stimulation and when exposed to bacterial antigens. The release of Paneth cell products into the crypt lumen is inferred to protect mitotically active crypt cells that renew the epithelial cell monolayer from colonization by potentially pathogenic microbes and to confer protection from enteric infection. The most compelling evidence for a Paneth cell role in enteric resistance to infection is evident from studies of mice transgenic for a human Paneth cell alpha-defensin, HD-5, which are completely immune to infection and systemic disease from orally administered Salmonella enterica serovar typhimurium. Cystic fibrosis mice are subject to small bowel bacterial overgrowth that is associated with impaired dissolution of released Paneth cell granules in the crypt lumen. Mutations that cause defects in the activation, secretion, dissolution, and bactericidal effects of Paneth cell AMPs may alter crypt innate immunity and contribute to immunopathology.

Nod2-Dependent Regulation of Innate and Adaptive Immunity in the Intestinal Tract

The gene encoding the Nod2 protein is frequently mutated in Crohn's disease (CD) patients, although the physiological function of Nod2 in the intestine remains elusive. Here we show that protective immunity mediated by Nod2 recognition of bacterial muramyl dipeptide is abolished in Nod2-deficient mice. These animals are susceptible to bacterial infection via the oral route but not through intravenous or peritoneal delivery. Nod2 is required for the expression of a subgroup of intestinal anti-microbial peptides, known as cryptdins. The Nod2 protein is thus a critical regulator of bacterial immunity within the intestine, providing a possible mechanism for Nod2 mutations in CD.

Primate defensins

Defensins are endogenous, cysteine-rich antimicrobial peptides that contribute to host defence against bacterial, fungal and viral infections. There are three subfamilies of defensins in primates: alpha-defensins are most common in neutrophils and Paneth cells of the small intestine; beta-defensins protect the skin and the mucous membranes of the respiratory, genitourinary and gastrointestinal tracts; and theta-defensins, which are expressed only in Old World monkeys, lesser apes and orangutans, are lectins with broad-spectrum antiviral efficacy. Here, their discovery and recent advances in understanding their properties and functions are described.

Defensin-mediated innate immunity in the small intestine

Epithelial cells contribute to innate immunity by releasing antimicrobial peptides (AMPs) onto mucosal surfaces. In the small bowel, Paneth cells at the base of the crypts of Lieberkühn secrete alpha-defensins and additional AMPs at high levels in response to cholinergic stimulation and when exposed to bacterial antigens. The release of Paneth cell products into the crypt lumen is inferred to protect mitotically active crypt cells that renew the epithelial cell monolayer from colonization by potentially pathogenic microbes and to confer protection from enteric infection. The most compelling evidence for a Paneth cell role in enteric resistance to infection is evident from studies of mice transgenic for a human Paneth cell alpha-defensin, HD-5, which are completely immune to infection and systemic disease from orally administered Salmonella typhimurium. Alpha-defensins in Paneth cell secretions may also interact with bacteria in the intestinal lumen above the crypt-villus boundary and influence the composition of the enteric microbial flora, but that remains to be demonstrated.

Identification of GM-CSF in Paneth cells using single-cell RT-PCR

Paneth cells, granule-containing cells located at the bottom of the intestinal crypts, have a role in innate mucosal immunity. We identified the exclusive expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) in Paneth cells using single-cell reverse transcription-polymerase chain reaction and cDNA array. Cytosolic total RNA was aspirated from single Paneth cells and other villous epithelial cells (non-Paneth cells) of rats using capillary micropipettes. In addition to lysozyme, secretory phospholipase A2, defensin, TNF-alpha, and xanthine dehydrogenase genes, cDNA array analysis revealed that the GM-CSF gene is specifically present in Paneth cells, whereas GM-CSF receptor beta-chain mRNA is expressed in Paneth cells and other epithelial cells. There was intense immunohistochemical staining of GM-CSF in Paneth cells but not in other epithelial cells. Treatment of IEC6 cells with GM-CSF enhanced expression of CD80 and CD86. Thus, GM-CSF in Paneth cells might have an important role in mucosal immunity through increasing the expression of costimulatory molecules in epithelial cells.

Defensins in granules of phagocytic and non-phagocytic cells

Antimicrobial proteins stored in lysosome-like granules of neutrophils and macrophages probably play an important role in killing phagocytosed microbes after delivery to the phagolysosome. Among the granules' antimicrobial armamentarium are defensins, peptides that kill a broad spectrum of microorganisms in vitro. Antimicrobial defensins were recently also isolated from non-phagocytic granulocytes of the mouse small intestinal epithelium, from where they are secreted into the lumen to function extracellularly. Clarification of the antimicrobial mechanisms of defensins in intracellular and extracellular environments will provide a key to understanding peptide-mediated host defence.