Oxygen-independent microbicidal mechanisms of phagocytes

Hyperglycemia Increases Severity of Staphylococcus aureus Osteomyelitis and Influences Bacterial Genes Required for Survival in Bone

Hyperglycemia, or elevated blood glucose, renders individuals more prone to developing severe Staphylococcus aureus infections. S. aureus is the most common etiological agent of musculoskeletal infection, which is a common manifestation of disease in hyperglycemic patients. However, the mechanisms by which S. aureus causes severe musculoskeletal infection during hyperglycemia are incompletely characterized. To examine the influence of hyperglycemia on S. aureus virulence during invasive infection, we used a murine model of osteomyelitis and induced hyperglycemia with streptozotocin. We discovered that hyperglycemic mice exhibited increased bacterial burdens in bone and enhanced dissemination compared to control mice. Furthermore, infected hyperglycemic mice sustained increased bone destruction relative to euglycemic controls, suggesting that hyperglycemia exacerbates infection-associated bone loss. To identify genes contributing to S. aureus pathogenesis during osteomyelitis in hyperglycemic animals relative to euglycemic controls, we used transposon sequencing (TnSeq). We identified 71 genes uniquely essential for S. aureus survival in osteomyelitis in hyperglycemic mice and another 61 mutants with compromised fitness. Among the genes essential for S. aureus survival in hyperglycemic mice was the gene encoding superoxide dismutase A (sodA), one of two S. aureus superoxide dismutases involved in detoxifying reactive oxygen species (ROS). We determined that a sodA mutant exhibits attenuated survival in vitro in high glucose and in vivo during osteomyelitis in hyperglycemic mice. SodA therefore plays an important role during growth in high glucose and promotes S. aureus survival in bone. Collectively, these studies demonstrate that hyperglycemia increases the severity of osteomyelitis and identify genes contributing to S. aureus survival during hyperglycemic infection.

Neutrophil elastase stimulates MUC5AC expression in human biliary epithelial cells: a possible pathway of PKC/Nox/ROS

INTRODUCTION

Bacterial infection and bile flow retardation form a vicious cycle which promotes stone formation and recurrence, and it seems that mucin overexpression plays an important role in this process. However, the mechanism of increased mucus secretion in the biliary tract by bacterial infection and its treatment remain unclear.

MATERIAL AND METHODS

Human biliary epithelial cells were induced by neutrophil elastase (NE), and H₂O₂ production in the cell supernatants was detected by a specific kit, and then cells were pretreated with a H₂O₂ inhibitor, and expression of MUC5AC was detected by real-time polymerase chain reaction (PCR), Western blot, and immunohistochemistry. Moreover, selective PKC and Nox inhibitors, apocynin and bisindolylmaleimide I, were used to pretreat cells and detect H₂O₂, MUC5AC mRNA and protein expression. Then, we pretreated cells with selective inhibitors or NE, and detected transforming growth factor α (TGF-α) using an ELISA kit.

RESULTS

H₂O₂ production increased in an NE dose-dependent manner (p < 0.001), and NE upregulated MUC5AC expression at both mRNA and protein levels, while DMTU, could reduce this high expression (p < 0.01 at mRNA level, p < 0.001 at grey analysis for western blot and p < 0.01 at mean density for immunohistochemical staining at protein level). Moreover, apocynin and bisindolylmaleimide I could reduce the H₂O₂ production stimulated by NE (p < 0.05), and reduce MUC5AC high expression (p < 0.01 at mRNA level, p < 0.001 at both grey analysis for western blot and mean density for immunohistochemical staining at protein level). In addition, NE induced TGF-α production, and any of the three selective inhibitors could reduce it (p < 0.05).

CONCLUSIONS

NE-induced reactive oxygen species participated in the upregulation of MUC5AC production. Moreover, protein kinase C and NADPH oxidase (Nox) regulate MUC5AC production in NE-challenged human biliary epithelial cells.

New possible biomarkers for diagnosis of infections and diagnostic distinction between bacterial and viral infections in children

Detailed information about patients with infections is required to ensure appropriate choice of treatment. Although white blood cell (WBC) counts, and C-reactive protein (CRP) levels are useful diagnostic indicators of infections, more rapid and easily assayed indicator(s) could improve diagnosis. Moreover, it is of pivotal importance to distinguish bacteria or viruses as causative pathogens. Overall, TLR2 and TLR4 expression levels in neutrophils derived from individuals (n = 118) with bacterial (n = 37) and viral (n = 34) infections were higher than those in control samples (n = 47). Significant higher levels of TNF-α in patients with both types of the infection were observed, and those of IL-4, IL-8, IL-10, and IL-12 also were observed in the present study. Levels of IL-2, IL-8, and IL-10 on day 1 post-viral infection were significantly higher than those on day 1 post-bacterial infection. Therefore, there is a possibility that IL-4, IL-8, IL-10, IL-12 and TNF-α might be biomarkers for infections, in addition to WBC counts and CRP levels, and that IL-2, IL-8 or IL-10 are potentially able to distinguish between bacterial and viral infections.

Neutrophil elastase cleaves epithelial cadherin in acutely injured lung epithelium

Background

In acutely injured lungs, massively recruited polymorphonuclear neutrophils (PMNs) secrete abnormally neutrophil elastase (NE). Active NE creates a localized proteolytic environment where various host molecules are degraded leading to impairment of tissue homeostasis. Among the hallmarks of neutrophil-rich pathologies is a disrupted epithelium characterized by the loss of cell-cell adhesion and integrity. Epithelial-cadherin (E-cad) represents one of the most important intercellular junction proteins. E-cad exhibits various functions including its role in maintenance of tissue integrity. While much interest has focused on the expression and role of E-cad in different physio- and physiopathological states, proteolytic degradation of this structural molecule and ensuing potential consequences on host lung tissue injury are not completely understood.

Methods

NE capacity to cleave E-cad was determined in cell-free and lung epithelial cell culture systems. The impact of such cleavage on epithelial monolayer integrity was then investigated. Using mice deficient in NE in a clinically relevant experimental model of acute pneumonia, we examined whether degraded E-cad is associated with lung inflammation and injury and whether NE contributes to E-cad cleavage. Finally, we checked for the presence of both degraded E-cad and NE in bronchoalveolar lavage samples obtained from patients with exacerbated COPD, a clinical manifestation characterised by a neutrophilic inflammatory response.

Results

We show that NE is capable of degrading E-cad in vitro and in cultured cells. NE-mediated degradation of E-cad was accompanied with loss of epithelial monolayer integrity. Our in vivo findings provide evidence that NE contributes to E-cad cleavage that is concomitant with lung inflammation and injury. Importantly, we observed that the presence of degraded E-cad coincided with the detection of NE in diseased human lungs.

Conclusions

Active NE has the capacity to cleave E-cad and interfere with its cell-cell adhesion function. These data suggest a mechanism by which unchecked NE participates potentially to the pathogenesis of neutrophil-rich lung inflammatory and tissue-destructive diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0449-x) contains supplementary material, which is available to authorized users.

Neutrophils extracellular traps damage Naegleria fowleri trophozoites opsonized with human IgG

Naegleria fowleri infects humans through the nasal mucosa causing a disease in the central nervous system known as primary amoebic meningoencephalitis (PAM). Polymorphonuclear cells (PMNs) play a critical role in the early phase of N. fowleri infection. Recently, a new biological defence mechanism called neutrophil extracellular traps (NETs) has been attracting attention. NETs are composed of nuclear DNA combined with histones and antibacterial proteins, and these structures are released from the cell to direct its antimicrobial attack. In this work, we evaluate the capacity of N. fowleri to induce the liberation of NETs by human PMN cells. Neutrophils were cocultured with unopsonized or IgG-opsonized N. fowleri trophozoites. DNA, histone, myeloperoxidase (MPO) and neutrophil elastase (NE) were stained, and the formation of NETs was evaluated by confocal microscopy and by quantifying the levels of extracellular DNA. Our results showed N. fowleri induce the liberation of NETs including release of MPO and NE by human PMN cells as exposure interaction time is increased, but N. fowleri trophozoites evaded killing. However, when trophozoites were opsonized, they were susceptible to the neutrophils activity. Therefore, our study suggests that antibody-mediated PMNs activation through NET formation may be crucial for antimicrobial responses against N. fowleri.

Carp neutrophilic granulocytes form extracellular traps via ROS-dependent and independent pathways

Neutrophil extracellular traps (NETs) have recently been described as an important innate defense mechanism that leads to immobilization and killing of invading pathogens. NETs have been identified in several species, but the mechanisms involved in NET formation and their role in infection have not been well determined yet. Here we show that upon in vitro stimulation with different immunostimulants of bacterial, fungal or viral origin, carp neutrophilic granulocytes rapidly release NET structures. We analyzed the composition of these structures and the kinetics of their formation by confocal microscopy, by quantifying the levels of extracellular DNA and the release of enzymes originating from neutrophilic granules: myeloperoxidase, neutrophil elastase and matrix metalloproteinase 9 (MMP-9). Profiles of NET release by carp neutrophils as well as their enzyme composition are stimulus- and time-dependent. This study moreover provides evidence for a stimulus-dependent selective requirement of reactive oxygen species in the process of NET formation. Collectively the results support an evolutionary conserved and strictly regulated mechanism of NET formation in teleost fish.

Neutrophil elastase modulates cytokine expression: contribution to host defense against Pseudomonas aeruginosa-induced pneumonia

There is accumulating evidence that following bacterial infection, the massive recruitment and activation of the phagocytes, neutrophils, is accompanied with the extracellular release of active neutrophil elastase (NE), a potent serine protease. Using NE-deficient mice in a clinically relevant model of Pseudomonas aeruginosa-induced pneumonia, we provide compelling in vivo evidence that the absence of NE was associated with decreased protein and transcript levels of the proinflammatory cytokines TNF-α, MIP-2, and IL-6 in the lungs, coinciding with increased mortality of mutant mice to infection. The implication of NE in the induction of cytokine expression involved at least in part Toll-like receptor 4 (TLR-4). These findings were further confirmed following exposure of cultured macrophages to purified NE. Together, our data suggest strongly for the first time that NE not only plays a direct antibacterial role as it has been previously reported, but released active enzyme can also modulate cytokine expression, which contributes to host protection against P. aeruginosa. In light of our findings, the long held view that considers NE as a prime suspect in P. aeruginosa-associated diseases will need to be carefully reassessed. Also, therapeutic strategies aiming at NE inhibition should take into account the physiologic roles of the enzyme.

Inhibition of lung serine proteases in mice: a potentially new approach to control influenza infection

BACKGROUND

Host serine proteases are essential for the influenza virus life cycle because the viral haemagglutinin is synthesized as a precursor which requires proteolytic maturation. Therefore, we studied the activity and expression of serine proteases in lungs from mice infected with influenza and evaluated the effect of serine protease inhibitors on virus replication both in cell culture and in infected mice.

RESULTS

Two different inbred mouse strains were investigated: DBA/2J as a highly susceptible and C57Bl/6J as a more resistant strain to influenza virus infection. The serine proteases from lung homogenates of mice exhibited pH optima of 10.00. Using the substrate Bz-Val-Gly-Arg-p-nitroanilide or in zymograms, the intensities of proteolysis increased in homogenates from both mouse strains with time post infection (p.i.) with the mouse-adapted influenza virus A/Puerto Rico/8/34 (H1N1; PR8). In zymograms at day 7 p.i., proteolytic bands were stronger and numerous in lung homogenates from DBA/2J than C57Bl/6J mice. Real-time PCR results confirmed differential expression of several lung proteases before and after infecting mice with the H1N1 virus. The most strongly up-regulated proteases were Gzma, Tmprss4, Elane, Ctrl, Gzmc and Gzmb. Pretreatment of mouse and human lung cell lines with the serine protease inhibitors AEBSF or pAB or a cocktail of both prior to infection with the H1N1 or the A/Seal/Massachusetts/1/80 (H7N7; SC35M) virus resulted in a decrease in virus replication. Pretreatment of C57Bl/6J mice with either AEBSF or a cocktail of AEBSF and pAB prior to infection with the H1N1 virus significantly reduced weight loss and led to a faster recovery of treated versus untreated mice while pAB alone exerted a very poor effect. After infection with the H7N7 virus, the most significant reduction of weight loss was obtained upon pretreatment with either the protease inhibitor cocktail or pAB. Furthermore, pretreatment of C57BL/6J mice with AEBSF prior to infection resulted in a significant reduction in the levels of both the H1N1 and H7N7 nucleoproteins in mice lungs and also a significant reduction in the levels of the HA transcript in the lungs of the H1N1--but not the H7N7-infected mice.

CONCLUSION

Multiple serine protease activities might be implicated in mediating influenza infection. Blocking influenza A virus infection in cultured lung epithelia and in mice by the used serine protease inhibitors may provide an alternative approach for treatment of influenza infection.

Structural characterization of mouse neutrophil serine proteases and identification of their substrate specificities: relevance to mouse models of human inflammatory diseases

It is widely accepted that neutrophil serine proteases (NSPs) play a critical role in neutrophil-associated lung inflammatory and tissue-destructive diseases. To investigate NSP pathogenic role(s), various mouse experimental models have been developed that mimic acutely or chronically injured human lungs. We and others are using mouse exposure to cigarette smoke as a model for chronic obstructive pulmonary disease with or without exacerbation. However, the relative contribution of NSPs to lung disease processes as well as their underlying mechanisms remains still poorly understood. And the lack of purified mouse NSPs and their specific substrates have hampered advances in these studies. In this work, we compared mouse and human NSPs and generated three-dimensional models of murine NSPs based on three-dimensional structures of their human homologs. Analyses of these models provided compelling evidence that peptide substrate specificities of human and mouse NSPs are different despite their conserved cleft and close structural resemblance. These studies allowed us to synthesize for the first time novel sensitive fluorescence resonance energy transfer substrates for individual mouse NSPs. Our findings and the newly identified substrates should better our understanding about the role of NSPs in the pathogenesis of cigarette-associated chronic obstructive pulmonary disease as well as other neutrophils-associated inflammatory diseases.

Macrophage elastase kills bacteria within murine macrophages

Macrophages are aptly positioned to function as the primary line of defence against invading pathogens in many organs, including the lung and peritoneum. Their ability to phagocytose and clear microorganisms has been well documented. Macrophages possess several substances with which they can kill bacteria, including reactive oxygen species, nitric oxide, and antimicrobial proteins. We proposed that macrophage-derived proteinases may contribute to the antimicrobial properties of macrophages. Macrophage elastase (also known as matrix metalloproteinase 12 or MMP12) is an enzyme predominantly expressed in mature tissue macrophages and is implicated in several disease processes, including emphysema. Physiological functions for MMP12 have not been described. Here we show that Mmp12(-/-) mice exhibit impaired bacterial clearance and increased mortality when challenged with both gram-negative and gram-positive bacteria at macrophage-rich portals of entry, such as the peritoneum and lung. Intracellular stores of MMP12 are mobilized to macrophage phagolysosomes after the ingestion of bacterial pathogens. Once inside phagolysosomes, MMP12 adheres to bacterial cell walls where it disrupts cellular membranes resulting in bacterial death. The antimicrobial properties of MMP12 do not reside within its catalytic domain, but rather within the carboxy-terminal domain. This domain contains a unique four amino acid sequence on an exposed beta loop of the protein that is required for the observed antimicrobial activity. The present study represents, to our knowledge, the first report of direct antimicrobial activity by a matrix metallopeptidase, and describes a new antimicrobial peptide that is sequentially and structurally unique in nature.

Neutrophil elastase mediates innate host protection against Pseudomonas aeruginosa

According to the widely accepted view, neutrophil elastase (NE), a neutrophil-specific serine protease, is a major contributor to Pseudomonas aeruginosa infection-associated host tissue inflammation and damage, which in severe cases can lead to death. Herein, we provide for the first time compelling evidence that the host rather employs NE to protect itself against P. aeruginosa infection. Using a clinically relevant model of pneumonia, targeted deficiency in NE increased the susceptibility of mice to P. aeruginosa. We found that NE was required for maximal intracellular killing of P. aeruginosa by neutrophils. In investigating the mechanism of NE-mediated killing of P. aeruginosa, we found that NE degraded the major outer membrane protein F, a protein with important functions, including porin activity, maintenance of structural integrity, and sensing of host immune system activation. Consistent with this, the use of an isogenic mutant deficient in outer membrane protein F negated the role of NE in host defense against P. aeruginosa infection.

Clinical potential of Spirulina as a source of phycocyanobilin

Recent research reveals that free bilirubin functions physiologically as a potent inhibitor of NADPH oxidase activity. The chromophore phycocyanobilin (PCB), found in blue-green algae and cyanobacteria such as Spirulina, also has been found to be a potent inhibitor of this enzyme complex, likely because in mammalian cells it is rapidly reduced to phycocyanorubin, a close homolog of bilirubin. In light of the protean roles of NADPH oxidase activation in pathology, it thus appears likely that PCB supplementation may have versatile potential in prevention and therapy -- particularly in light of rodent studies demonstrating that orally administered Spirulina or phycocyanin (the Spirulina holoprotein that contains PCB) can exert a wide range of anti-inflammatory effects. Until PCB-enriched Spirulina extracts or synthetically produced PCB are commercially available, the most feasible and least expensive way to administer PCB is by ingestion of whole Spirulina. A heaping tablespoon (about 15 g) of Spirulina can be expected to provide about 100 mg of PCB. By extrapolating from rodent studies, it can be concluded that an intake of 2 heaping tablespoons daily would be likely to have important antioxidant activity in humans -- assuming that humans and rodents digest and absorb Spirulina-bound PCB in a comparable manner. An intake of this magnitude can be clinically feasible if Spirulina is incorporated into "smoothies" featuring such ingredients as soy milk, fruit juices, and whole fruits. Such a regimen should be evaluated in clinical syndromes characterized and in part mediated by NADPH oxidase overactivity in affected tissues.

Myeloperoxidase plays critical roles in killing Klebsiella pneumoniae and inactivating neutrophil elastase: effects on host defense

Activated neutrophils use myeloperoxidase (MPO) to generate an array of potent toxic oxidants. In the current studies we used genetically altered mice deficient in MPO to investigate the role of the enzyme in host defense against the Gram-negative bacterium Klebsiella pneumoniae, an important human pathogen. For comparison, we used mice deficient in the antimicrobial molecule, neutrophil elastase (NE). When challenged i.p., mice deficient in either MPO or NE were markedly more susceptible to bacterial infection and death. In vitro studies suggested that MPO impairs the morphology of bacteria in a distinctive way. Of importance, our in vitro studies found that MPO mediated oxidative inactivation of NE, an enzyme that has been widely implicated in the pathogenesis of various tissue-destructive diseases. This pathway of oxidative inactivation may be physiologically relevant, because activated neutrophils isolated from MPO-deficient mice exhibited increased elastase activity. Our observations provide strong evidence that MPO, like NE, is a key player in the killing of K. pneumoniae bacteria. They also suggest that MPO may modulate NE to protect the host from the tissue-degrading activity of this proteinase.

Neutrophil Serine Proteinases Inactivate Surfactant Protein D by Cleaving within a Conserved Subregion of the Carbohydrate Recognition Domain

Surfactant protein D (SP-D) plays important roles in innate immunity including the defense against bacteria, fungi, and respiratory viruses. Because SP-D specifically interacts with neutrophils that infiltrate the lung in response to acute inflammation and infection, we examined the hypothesis that the neutrophil-derived serine proteinases (NSPs): neutrophil elastase, proteinase-3, and cathepsin G degrade SP-D. All three human NSPs specifically cleaved recombinant rat and natural human SP-D dodecamers in a time- and dose-dependent manner, which was reciprocally dependent on calcium concentration. The NSPs generated similar, relatively stable, disulfide cross-linked immunoreactive fragments of approximately 35 kDa (reduced), and sequencing of a major catheptic fragment definitively localized the major sites of cleavage to a highly conserved subregion of the carbohydrate recognition domain. Cleavage markedly reduced the ability of SP-D to promote bacterial aggregation and to bind to yeast mannan in vitro. Incubation of SP-D with isolated murine neutrophils led to the generation of similar fragments, and cleavage was inhibited with synthetic and natural serine proteinase inhibitors. In addition, neutrophils genetically deficient in neutrophil elastase and/or cathepsin G were impaired in their ability to degrade SP-D. Using a mouse model of acute bacterial pneumonia, we observed the accumulation of SP-D at sites of neutrophil infiltration coinciding with the appearance of approximately 35-kDa SP-D fragments in bronchoalveolar lavage fluids. Together, our data suggest that neutrophil-derived serine proteinases cleave SP-D at sites of inflammation with potential deleterious effects on its biological functions.

Neutrophil elastase-mediated killing of bacteria: lessons from targeted mutagenesis

Engineering of mice deficient in neutrophil elastase (NE) has allowed us to demonstrate the role of this protease in host defense against bacteria and to begin to understand its killing mechanism. Strategies to inhibit NE because of its involvement in tissue-destructive diseases should be reconsidered, while preserving its beneficial properties.

Differential role of neutrophil Fcgamma receptor IIIB (CD16) in phagocytosis, bacterial killing, and responses to immune complexes

OBJECTIVE

To determine the roles played by the neutrophil Fcgamma receptor type II (FcgammaRII) (CD32) and FcgammaRIIIb (CD16) in phagocytosis, bacterial killing, and activation by immune complexes (ICs) and to test the hypothesis that inhibition of pathologic effector neutrophil function is possible without compromising host defense.

METHODS

Receptor function was probed by enzymic removal of FcgammaRIIIb from the cell surface and by use of Fab/F(ab')(2) fragments of monoclonal antibodies to block receptor-ligand binding. Cells were challenged with (a) serum-opsonized Staphylococcus aureus, (b) serum- and IgG-opsonized latex particles, and (c) synthetic soluble and insoluble ICs to mimic bacterial and inflammatory stimuli.

RESULTS

Phosphatidylinositol-phospholipase C treatment removed >97% of surface FcgammaRIIIb from neutrophils previously treated with tumor necrosis factor alpha to mobilize intracellular stores of receptor. This treatment profoundly inhibited activation of primed neutrophils by soluble ICs of the type found in diseased rheumatoid joints, but had no effect on phagocytosis and killing of serum-opsonized S aureus.

CONCLUSION

FcgammaRIIIb plays a major role in the secretion of toxic products in response to ICs, but little or no role in the phagocytosis and killing of serum-opsonized bacteria. The selective suppression of effector neutrophil function is therefore possible. FcgammaRIIIb, or its intracellular signaling pathway, is a potential therapeutic target in inflammatory diseases such as rheumatoid arthritis, because disruption of its function should decrease inflammatory tissue damage, but not jeopardize host protection against infection.

Membrane-permeabilizing polypeptides of amoebae – constituents of an archaic antimicrobial system

Amoebae may be viewed as primitive, actively phagocytosing eukaryotic cells, many of which use bacteria as a major nutrient source. At a very archaic level, amoebae exert mechanisms which kill bacteria comparable to those found in phagocytic cells of higher organisms. Accordingly, it is tempting to suggest that the ancestors of effector cells of the innate immune system were bacteria-feeding amoebae and that their molecular armament is ancient. Here, we summarize the characteristics of antimicrobial and cytolytic 77-residue polypeptides from the protozoon Entamoeba histolytica for which correlates were found in effector cells of the mammalian immune systems. Based on the current knowledge about these small membrane-destabilizing proteins of phylogenetically extremely diverse origin, we discuss similarities and differences in their structure and activities.

Host defense function in neutrophils from the American bison (Bison bison)

Selected host defense functions of neutrophils isolated from American bison (Bison bison) were characterized and compared with those of cattle (Bos taurus). Bison neutrophils had a robust chemotactic response to both IL-8 and LTB(4), with maximal responses occurring at 10(-7) M (IL-8) and 10(-8) M (LTB(4)). The magnitude of the chemotactic response to IL-8 was similar in bison and bovine neutrophils (except at 10(-7) M IL-8, where bison had a stronger response). In response to LTB(4), bison neutrophils had a much stronger chemotaxis at both 10(-8) and 10(-7) M than did bovine cells. Production of reactive oxygen species (ROS) in response to phorbol myristate acetate (PMA) and opsonized zymosan (OpZ) was similar between bison and bovine neutrophils. However, the production of ROS in bison neutrophils stimulated with OpZ was primarily intracellular, while extracellular release of ROS was evident in bovine neutrophils stimulated with OpZ. Like bovine neutrophils, bison neutrophils did not generate a respiratory burst in response to fMLF. Granules prepared from bison neutrophils had potent direct killing action on the Gram-negative bacteria Escherichia coli but failed to kill the Gram-positive bacteria Staphylococcus aureus and, at intermediate doses, actually had a permissive effect for this bacteria. Thus, bison neutrophils have potent host defense capabilities similar in quality to those of bovine neutrophils; however, unique differences are present, which may allow bison neutrophils to respond to the distinct immunological challenges that bison encounter.

Degradation of outer membrane protein A in Escherichia coli killing by neutrophil elastase

In determining the mechanism of neutrophil elastase (NE)-mediated killing of Escherichia coli, we found that NE degraded outer membrane protein A (OmpA), localized on the surface of Gram-negative bacteria. NE killed wild-type, but not OmpA-deficient, E. coli. Also, whereas NE-deficient mice had impaired survival in response to E. coli sepsis, as compared to wild-type mice, the presence or absence of NE had no influence on survival in response to sepsis that had been induced with OmpA-deficient E. coli. These findings define a mechanism of nonoxidative bacterial killing by NE and point to OmpA as a bacterial target in host defense.