Isolation of mouse neutrophils

β-Lapachone promotes the recruitment and polarization of tumor-associated neutrophils (TANs) toward an antitumor (N1) phenotype in NQO1-positive cancers

NAD(P)H:quinone oxidoreductase 1 (NQO1) is overexpressed in most solid cancers, emerging as a promising target for tumor-selective killing. β-Lapachone (β-Lap), an NQO1 bioactivatable drug, exhibits significant antitumor effects on NQO1-positive cancer cells by inducing immunogenic cell death (ICD) and enhancing tumor immunogenicity. However, the interaction between β-Lap-mediated antitumor immune responses and neutrophils, novel antigen-presenting cells (APCs), remains unknown. This study demonstrates that β-Lap selectively kills NQO1-positive murine tumor cells by significantly increasing intracellular ROS formation and inducing DNA double strand breaks (DSBs), resulting in DNA damage. Treatment with β-Lap efficiently eradicates immunocompetent murine tumors and significantly increases the infiltration of tumor-associated neutrophils (TANs) into the tumor microenvironment (TME), which plays a crucial role in the drug's therapeutic efficacy. Further, the presence of β-Lap-induced antigen medium leads bone marrow-derived neutrophils (BMNs) to directly kill murine tumor cells, aiding in dendritic cells (DCs) recruitment and significantly enhancing CD8+ T cell proliferation. β-Lap treatment also drives the polarization of TANs toward an antitumor N1 phenotype, characterized by elevated IFN-β expression and reduced TGF-β cytokine expression, along with increased CD95 and CD54 surface markers. β-Lap treatment also induces N1 TAN-mediated T cell cross-priming. The HMGB1/TLR4/MyD88 signaling cascade influences neutrophil infiltration into β-Lap-treated tumors. Blocking this cascade or depleting neutrophil infiltration abolishes the antigen-specific T cell response induced by β-Lap treatment. Overall, this study provides comprehensive insights into the role of tumor-infiltrating neutrophils in the β-Lap-induced antitumor activity against NQO1-positive murine tumors.

Stimulus-responsive and dual-target DNA nanodrugs for rheumatoid arthritis treatment

Tumor necrosis factor receptor-1 (TNFR1) and DEK are closely associated with the development of rheumatoid arthritis (RA). Taking advantage of the high adenosine triphosphate (ATP) in RA microenvironment and the interactions of DNA aptamers with their targets, an ATP-responsive DNA nanodrug was constructed that simultaneously targets TNFR1 and DEK for RA therapy. To this end, DEK target aptamer DTA and TNFR1 target aptamer Apt1-67 were equipped with sticky ends to hybridize with ATP aptamer (Apt_ATP) and fabricated DNA nanodrug DAT. Our results showed that DAT was successfully prepared with good stability. In the presence of ATP, DAT was disassembled, resulting in the release of DTA and Apt1-67. In vitro studies demonstrated that DAT was superior to the non-responsive DNA nanodrug TD-3A3T in terms of anti-inflammation activity and ATP was inevitable to maximize the anti-inflammation ability of DAT. The superior efficacy of DAT is attributed to the more potent inhibition of caspase-3 and NETs formation. In vivo results further confirmed the anti-RA efficacy of DAT, whereas the administration routes (intravenous injection and transdermal administration via microneedles) did not cause significant differences. Overall, the present study supplies an intelligent strategy for RA therapy and explores a promising administration route for future clinical medication of RA patients.

Adjunctive Thymosin Beta-4 Treatment Influences PMN Effector Cell Function during Pseudomonas aeruginosa-Induced Corneal Infection

Previous work examining the therapeutic efficacy of adjunct thymosin beta 4 (Tβ4) to ciprofloxacin for ocular infectious disease has revealed markedly reduced inflammation (inflammatory mediators and innate immune cells) with increased activation of wound healing pathways. Understanding the therapeutic mechanisms of action have further revealed a synergistic effect with ciprofloxacin to enhance bacterial killing along with a regulatory influence over macrophage effector cell function. As a natural extension of the aforementioned work, the current study uses an experimental model of P. aeruginosa-induced keratitis to examine the influence of Tβ4 regarding polymorphonuclear leukocyte (PMN/neutrophil) cellular function, contributing to improved disease response. Flow cytometry was utilized to phenotypically profile infiltrating PMNs after infection. The generation of reactive oxygen species (ROS), neutrophil extracellular traps (NETs), and PMN apoptosis were investigated to assess the functional activities of PMNs in response to Tβ4 therapy. In vitro work using peritoneal-derived PMNs was similarly carried out to verify and extend our in vivo findings. The results indicate that the numbers of infiltrated PMNs into infected corneas were significantly reduced with adjunctive Tβ4 treatment. This was paired with the downregulated expression of proinflammatory markers on these cells, as well. Data generated from PMN functional studies suggested that the corneas of adjunctive Tβ4 treated B6 mice exhibit a well-regulated production of ROS, NETs, and limited PMN apoptosis. In addition to confirming the in vivo results, the in vitro findings also demonstrated that neutrophil elastase (NE) was unnecessary for NETosis. Collectively, these data provide additional evidence that adjunctive Tβ4 + ciprofloxacin treatment is a promising option for bacterial keratitis that addresses both the infectious pathogen and cellular-mediated immune response, as revealed by the current study.

Therapeutic ACPA inhibits NET formation: a potential therapy for neutrophil-mediated inflammatory diseases

Excessive release of neutrophil extracellular traps (NETs) is associated with disease severity and contributes to tissue injury, followed by severe organ damage. Pharmacological or genetic inhibition of NET release reduces pathology in multiple inflammatory disease models, indicating that NETs are potential therapeutic targets. Here, we demonstrate using a preclinical basket approach that our therapeutic anti-citrullinated protein antibody (tACPA) has broad therapeutic potential. Treatment with tACPA prevents disease symptoms in various mouse models with plausible NET-mediated pathology, including inflammatory arthritis (IA), pulmonary fibrosis, inflammatory bowel disease and sepsis. We show that citrulline residues in the N-termini of histones 2A and 4 are specific targets for therapeutic intervention, whereas antibodies against other N-terminal post-translational histone modifications have no therapeutic effects. Because citrullinated histones are generated during NET release, we investigated the ability of tACPA to inhibit NET formation. tACPA suppressed NET release from human neutrophils triggered with physiologically relevant human disease-related stimuli. Moreover, tACPA diminished NET release and potentially initiated NET uptake by macrophages in vivo, which was associated with reduced tissue damage in the joints of a chronic arthritis mouse model of IA. To our knowledge, we are the first to describe an antibody with NET-inhibiting properties and thereby propose tACPA as a drug candidate for NET-mediated inflammatory diseases, as it eliminates the noxious triggers that lead to continued inflammation and tissue damage in a multidimensional manner.

Bactericidal Permeability Increasing Protein Deficiency Aggravates Acute Colitis in Mice by Increasing the Serum Levels of Lipopolysaccharide

Objective

The objective of this study was to understand the role of bactericidal permeability increasing protein (BPI) in the pathogenesis of experimental murine colitis.

Methods

We used the Cre-LoxP system to generate BPI knockout (BPI KO) mice. Acute colitis was induced in BPI KO mice and wild-type (WT) mice by subjecting the mice to 5% dextran sulfate sodium (DSS). Mice were observed for symptoms of experimental colitis. The survival of BPI KO mice to infection with Acinetobacter baumannii, a gram-negative bacterium, was also assessed.

Results

Southern blot, RT-PCR, and western blot results showed that the 2nd and 3rd exons of the murine Bpi gene were knocked out systemically, confirming successful construction of the BPI KO mouse. BPI KO mice subjected to DSS showed increased symptoms of experimental colitis, increased colonic mucosal damage, increased epithelial permeability, elevated levels of serum LPS, and a disrupted fecal microbiome as compared with WT mice. Furthermore, BPI KO mice challenged intraperitoneally with A. baumannii died sooner than WT mice, and the total number of bacteria in the abdominal cavity, spleen, and liver was increased in BPI KO mice as compared to WT mice.

Conclusions

We successfully generated BPI KO mice. The BPI KO mice developed worse colitis than WT mice by increased colitis symptoms and colonic mucosal damage, elevated levels of serum LPS, and a disrupted microbiome. BPI could be a potential target for treatment of ulcerative colitis in humans.

Gut Microbiota Restricts NETosis in Acute Mesenteric Ischemia-Reperfusion Injury

OBJECTIVE

Recruitment of neutrophils and formation of neutrophil extracellular traps (NETs) contribute to lethality in acute mesenteric infarction. To study the impact of the gut microbiota in acute mesenteric infarction, we used gnotobiotic mouse models to investigate whether gut commensals prime the reactivity of neutrophils towards formation of neutrophil extracellular traps (NETosis). Approach and Results: We applied a mesenteric ischemia-reperfusion (I/R) injury model to germ-free (GF) and colonized C57BL/6J mice. By intravital imaging, we quantified leukocyte adherence and NET formation in I/R-injured mesenteric venules. Colonization with gut microbiota or monocolonization with Escherichia coli augmented the adhesion of leukocytes, which was dependent on the TLR4 (Toll-like receptor-4)/TRIF (TIR-domain-containing adapter-inducing interferon-β) pathway. Although neutrophil accumulation was decreased in I/R-injured venules of GF mice, NETosis following I/R injury was significantly enhanced compared with conventionally raised mice or mice colonized with the minimal microbial consortium altered Schaedler flora. Also ex vivo, neutrophils from GF and antibiotic-treated mice showed increased LPS (lipopolysaccharide)-induced NETosis. Enhanced TLR4 signaling in GF neutrophils was due to elevated TLR4 expression and augmented IRF3 (interferon regulatory factor-3) phosphorylation. Likewise, neutrophils from antibiotic-treated conventionally raised mice had increased NET formation before and after ischemia. Increased NETosis in I/R injury was abolished in conventionally raised mice deficient in the TLR adaptor TRIF. In support of the desensitizing influence of enteric LPS, treatment of GF mice with LPS via drinking water diminished LPS-induced NETosis in vitro and in the mesenteric I/R injury model.

CONCLUSIONS

Collectively, our results identified that the gut microbiota suppresses NETing neutrophil hyperreactivity in mesenteric I/R injury, while ensuring immunovigilance by enhancing neutrophil recruitment.

Application of a Flow-Based Hollow-Fiber Co-Culture System to Study Cellular Influences under Hyperglycemic Conditions

Elucidation of the basic mechanisms underlying human disease pathogenesis depends on the findings afforded to us through in vivo and in vitro approaches. While there are inherent limitations in any model system, 2D in vitro culture systems tend to be particularly restricted due to their static nature. Here, we adapted a flow-based hollow-fiber cartridge system to better understand the cellular influences of human retinal microvascular endothelial cells and mouse-derived neutrophils under high glucose conditions similar to those observed in diabetes. Analyses by western blot and flow cytometry indicate that pro-inflammatory molecules known to be associated with the pathogenesis of diabetic retinopathy were significantly elevated following high glucose exposure, including VEGF, ICAM-1, and ROS. Changes in mitochondrial potential were also observed. Further, we demonstrate that this innovative system allows for cross-species co-culture as well as long-term culturing conditions. This in vitro modeling system not only mimics the retinal microvasculature, it also allows for the examination of cellular interactions and mechanisms that contribute to diabetic retinopathy, a visually debilitating complication of diabetes.

VIP modulates the ALX/FPR2 receptor axis toward inflammation resolution in a mouse model of bacterial keratitis

Vasoactive intestinal peptide (VIP) has been shown to regulate corneal inflammation. Formyl peptide receptor 2 (FPR2) is a transmembrane protein belonging to the GPCR family. Ligands include pro-resolving lipids, lipoxin A4 (LXA4) and resolvin D1 (RvD1). The current study focuses on the effect of VIP regarding the FPR2 receptor axis in improving disease outcome in a mouse model of bacterial keratitis. Infection was induced in C57BL/6 (B6) mice using P. aeruginosa (PA) ATCC 19660. Mice received topical treatment (VIP or PBS) 3× daily after infection. Mean clinical scores, bacterial plate counts, Griess and myeloperoxidase (MPO) assays indicate that topical VIP effectively abrogates the disease response. Findings also reveal that VIP influences FPR2 pathway activation independent of archetypal VIP receptors. Exploring the immunoresolving role of FPR2, its ligand RvD1 and related enzymes (5-LOX, 12/15-LOX), our results suggest a mechanism by which VIP treatment influences the disease response in bacterial keratitis, which could offer a therapeutic point of intervention for enhancing this pro-resolving circuit.

Perforin-2 Breaches the Envelope of Phagocytosed Bacteria Allowing Antimicrobial Effectors Access to Intracellular Targets

Perforin-2, the product of the MPEG1 gene, limits the spread and dissemination of bacterial pathogens in vivo. It is highly expressed in murine and human phagocytes, and macrophages lacking Perforin-2 are compromised in their ability to kill phagocytosed bacteria. In this study, we used Salmonella enterica serovar Typhimurium as a model intracellular pathogen to elucidate the mechanism of Perforin-2's bactericidal activity. In vitro Perforin-2 was found to facilitate the degradation of Ags contained within the envelope of phagocytosed bacteria. In contrast, degradation of a representative surface Ag was found to be independent of Perforin-2. Consistent with our in vitro results, a protease-sensitive, periplasmic superoxide dismutase (SodCII) contributed to the virulence of S. Typhimurium in Perforin-2 knockout but not wild-type mice. In aggregate, our studies indicate that Perforin-2 breaches the envelope of phagocytosed bacteria, facilitating the delivery of proteases and other antimicrobial effectors to sites within the bacterial cell.

Immunoregulatory role of 15-lipoxygenase in the pathogenesis of bacterial keratitis

Although autacoids primarily derived from the cyclooxygenase-2 and 5-lipoxygenase (LOX) pathways are essential mediators of inflammation, endogenous specialized proresolving mediators (SPMs) act as robust agonists of resolution. SPM biosynthesis is initiated by the conversion of arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid primarily via the 12/15-LOX pathway. Although 12/15-LOX activity is prominent in the cornea, the role of SPM pathway activation during infection remains largely unknown and is the focus of the current study. Pseudomonas keratitis was induced in resistant BALB/c and susceptible C57BL/6 (B6) mice. Biosynthetic pathways for proinflammatory autacoids and SPMs were assessed. Divergent lipid mediator profiles demonstrate the importance of 15-LOX pathways in the pathogenesis of ocular infectious disease. Results indicate that an imbalance of LOX enzymatic pathways contributes to susceptibility observed in B6 mice where deficient activation of SPM circuits, as indicated by reduced 15-hydroxy-eicosatetraenoic acid and 17-hydroxydocosahexaenoic acid levels, prevented transition toward resolution and led to chronic inflammation. In sharp contrast, BALB/c mice demonstrated a well-balanced axis of 5-LOX/12-LOX/15-LOX pathways, resulting in sufficient proresolving bioactive metabolite formation and immune homeostasis. Furthermore, a novel immunoregulatory role for 15-LOX was revealed in inflammatory cells (polymorphonuclear leukocytes and macrophages), which influenced phagocytic activity. These data provide evidence that SPM circuits are essential for host defense during bacterial keratitis.-Carion, T. W., Greenwood, M., Ebrahim, A. S., Jerome, A., Suvas, S., Gronert, K., Berger, E. A. Immunoregulatory role of 15-lipoxygenase in the pathogenesis of bacterial keratitis.

Enhancement of glycolysis by inhibition of oxygen-sensing prolyl hydroxylases protects alveolar epithelial cells from acute lung injury

Cellular bioenergetic failure caused by mitochondrial dysfunction is a key process of alveolar epithelial injury during acute respiratory distress syndrome (ARDS). Prolyl hydroxylases (PHDs) act as cellular oxygen sensors, and their inhibition activates hypoxia-inducible factor (HIF), resulting in enhanced cellular glycolytic activity, which could compensate for impaired mitochondrial function and protect alveolar epithelial cells from ARDS. Here, we evaluated the effects of pharmacological PHD inhibition with dimethyloxalylglycine (DMOG) on alveolar epithelial cell injury using in vitro and in vivo ARDS models. We established an in vitro model of alveolar epithelial injury mimicking ARDS by adding isolated neutrophils and LPS to cultured MLE12 alveolar epithelial cells. DMOG treatment protected MLE12 cells from neutrophil-LPS-induced ATP decline and cell death. Knockdown of HIF-1α or inhibition of glycolysis abolished the protective effect of DMOG, suggesting that it was exerted by HIF-1-dependent enhancement of glycolysis. Additionally, intratracheal DMOG administration to mice protected the alveolar epithelial barrier and improved arterial oxygenation, preventing ATP decline during LPS-induced lung injury. In summary, enhancement of glycolysis by PHD inhibition is a potential therapeutic approach for ARDS, protecting alveolar epithelial cells from bioenergetic failure and cell death.- Tojo, K., Tamada, N., Nagamine, Y., Yazawa, T., Ota, S., Goto, T. Enhancement of glycolysis by inhibition of oxygen-sensing prolyl hydroxylases protects alveolar epithelial cells from acute lung injury. FASEB J. 32, 2258-2268 (2018). www.fasebj.org.

Twin Attributes of Tyrosyl-tRNA Synthetase of Leishmania donovani: A HOUSEKEEPING PROTEIN TRANSLATION ENZYME AND A MIMIC OF HOST CHEMOKINE

Aminoacyl-tRNA synthetases (aaRSs) are housekeeping enzymes essential for protein synthesis. Apart from their parent aminoacylation activity, several aaRSs perform non-canonical functions in diverse biological processes. The present study explores the twin attributes of Leishmania tyrosyl-tRNA synthetase (LdTyrRS) namely, aminoacylation, and as a mimic of host CXC chemokine. Leishmania donovani is a protozoan parasite. Its genome encodes a single copy of tyrosyl-tRNA synthetase. We first tested the canonical aminoacylation role of LdTyrRS. The recombinant protein was expressed, and its kinetic parameters were determined by aminoacylation assay. To study the physiological role of LdTyrRS in Leishmania, gene deletion mutations were attempted via targeted gene replacement. The heterozygous mutants showed slower growth kinetics and exhibited attenuated virulence. LdTyrRS appears to be an essential gene as the chromosomal null mutants did not survive. Our data also highlights the non-canonical function of L. donovani tyrosyl-tRNA synthetase. We show that LdTyrRS protein is present in the cytoplasm and exits from the parasite cytoplasm into the extracellular medium. The released LdTyrRS functions as a neutrophil chemoattractant. We further show that LdTyrRS specifically binds to host macrophages with its ELR (Glu-Leu-Arg) peptide motif. The ELR-CXCR2 receptor interaction mediates this binding. This interaction triggers enhanced secretion of the proinflammatory cytokines TNF-α and IL-6 by host macrophages. Our data indicates a possible immunomodulating role of LdTyrRS in Leishmania infection. This study provides a platform to explore LdTyrRS as a potential target for drug development.

Sepsis-induced expansion of granulocytic myeloid-derived suppressor cells promotes tumour growth through Toll-like receptor 4

Severe sepsis remains a frequent and dreaded complication in cancer patients. Beyond the often fatal short-term outcome, the long-term sequelae of severe sepsis may also impact directly on the prognosis of the underlying malignancy in survivors. The immune system is involved in all stages of tumour development, in the detection of transforming and dying cells and in the prevention of tumour growth and dissemination. In fact, the profound and sustained immune defects induced by sepsis may constitute a privileged environment likely to favour tumour growth. We investigated the impact of sepsis on malignant tumour growth in a double-hit animal model of polymicrobial peritonitis, followed by subcutaneous inoculation of MCA205 fibrosarcoma cells. As compared to their sham-operated counterparts, post-septic mice exhibited accelerated tumour growth. This was associated with intratumoural accumulation of CD11b(+) Ly6G(high) polymorphonuclear cells (PMNs) that could be characterized as granulocytic myeloid-derived suppressor cells (G-MDSCs). Depletion of granulocytic cells in post-septic mice inhibited the sepsis-enhanced tumour growth. Toll-like receptor (TLR)-4 (Tlr4) and Myd88 deficiencies prevented sepsis-induced expansion of G-MDSCs and tumour growth. Our results demonstrate that the myelosuppressive environment induced by severe bacterial infections promotes malignant tumour growth, and highlight a critical role of CD11b(+) Ly6G(high) G-MDSCs under the control of TLR-dependent signalling. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Enteric pathogens deploy cell cycle inhibiting factors to block the bactericidal activity of Perforin-2

Perforin-2 (MPEG1) is an effector of the innate immune system that limits the proliferation and spread of medically relevant Gram-negative, -positive, and acid fast bacteria. We show here that a cullin-RING E3 ubiquitin ligase (CRL) complex containing cullin-1 and βTrCP monoubiquitylates Perforin-2 in response to pathogen associated molecular patterns such as LPS. Ubiquitylation triggers a rapid redistribution of Perforin-2 and is essential for its bactericidal activity. Enteric pathogens such as Yersinia pseudotuberculosis and enteropathogenic Escherichia coli disarm host cells by injecting cell cycle inhibiting factors (Cifs) into mammalian cells to deamidate the ubiquitin-like protein NEDD8. Because CRL activity is dependent upon NEDD8, Cif blocks ubiquitin dependent trafficking of Perforin-2 and thus, its bactericidal activity. Collectively, these studies further underscore the biological significance of Perforin-2 and elucidate critical molecular events that culminate in Perforin-2-dependent killing of both intracellular and extracellular, cell-adherent bacteria.

DOI:http://dx.doi.org/10.7554/eLife.06505.001

A wide range of bacteria and other microbes can infect animals and cause disease. Throughout evolution, these microbes and their hosts have been fighting never ending arms races in which the microbes deploy ever more elaborate weapons, while the hosts adapt to defend themselves. An animal's first line of defense is provided by its ‘innate’ immune system. This system is activated by the general features of microbial cells; for example, the molecules that make up the walls surrounding most bacteria. Microbes must defeat the innate immune system in order to cause disease, and ultimately to spread from one host to the next.

One component of innate immunity is a protein called Perforin-2 that is present in most, if not all, animal cells. This protein forms pores on bacterial cells, causing them to split open and die. However, it was not clear how Perforin-2 is switched on and what, if anything, bacteria do to counteract it. To address these questions, McCormack et al. infected human and mice cells with bacteria that cause serious diseases of the digestive tract.

The experiments show that when animal cells detect bacteria, or merely a fragment of their cell wall, a specific group of proteins, called the CRL complex, attaches a molecule called ubiquitin to Perforin-2. Ubiquitin works much like the shipping label of a package, enabling the efficient targeting of Perforin-2 to the invading bacteria. McCormack et al. also show that some bacteria use a protein called a cell cycle inhibiting factor (or Cif for short) to inhibit the CRL complex. This blocks the ubiquitin labeling of Perforin-2, which renders it a useless weapon that can no longer be directed towards bacteria.

Mice that are infected with a bacterium called Yersinia pseudotuberculosis become seriously unwell and often die. However, McCormack et al. found that mice infected with mutant Y. pseudotuberculosis that lacked Cif remained healthy. Also, mice that lacked Perforin-2 are highly susceptible to infectious diseases. McCormack et al.'s findings reveal how Perforin-2 is activated during the innate immune response and how some bacteria can defeat this pivotal defense. In the current age of antibiotic resistant bacteria, these studies may spur the development of new drugs that restore or increase the activity of Perforin-2.

DOI:http://dx.doi.org/10.7554/eLife.06505.002

Perforin-2 is essential for intracellular defense of parenchymal cells and phagocytes against pathogenic bacteria

Perforin-2 (MPEG1) is a pore-forming, antibacterial protein with broad-spectrum activity. Perforin-2 is expressed constitutively in phagocytes and inducibly in parenchymal, tissue-forming cells. In vitro, Perforin-2 prevents the intracellular replication and proliferation of bacterial pathogens in these cells. Perforin-2 knockout mice are unable to control the systemic dissemination of methicillin-resistant Staphylococcus aureus (MRSA) or Salmonella typhimurium and perish shortly after epicutaneous or orogastric infection respectively. In contrast, Perforin-2-sufficient littermates clear the infection. Perforin-2 is a transmembrane protein of cytosolic vesicles -derived from multiple organelles- that translocate to and fuse with bacterium containing vesicles. Subsequently, Perforin-2 polymerizes and forms large clusters of 100 Å pores in the bacterial surface with Perforin-2 cleavage products present in bacteria. Perforin-2 is also required for the bactericidal activity of reactive oxygen and nitrogen species and hydrolytic enzymes. Perforin-2 constitutes a novel and apparently essential bactericidal effector molecule of the innate immune system.

Unexpected Roles for Toll-Like Receptor 4 and TRIF in Intraocular Infection with Gram-Positive Bacteria

Inflammation caused by infection with Gram-positive bacteria is typically initiated by interactions with Toll-like receptor 2 (TLR2). Endophthalmitis, an infection and inflammation of the posterior segment of the eye, can lead to vision loss when initiated by a virulent microbial pathogen. Endophthalmitis caused by Bacillus cereus develops as acute inflammation with infiltrating neutrophils, and vision loss is potentially catastrophic. Residual inflammation observed during B. cereus endophthalmitis in TLR2(-/-) mice led us to investigate additional innate pathways that may trigger intraocular inflammation. We first hypothesized that intraocular inflammation during B. cereus endophthalmitis would be controlled by MyD88- and TRIF-mediated signaling, since MyD88 and TRIF are the major adaptor molecules for all bacterial TLRs. In MyD88(-/-) and TRIF(-/-) mice, we observed significantly less intraocular inflammation than in eyes from infected C57BL/6J mice, suggesting an important role for these TLR adaptors in B. cereus endophthalmitis. These results led to a second hypothesis, that TLR4, the only TLR that signals through both MyD88 and TRIF signaling pathways, contributed to inflammation during B. cereus endophthalmitis. Surprisingly, B. cereus-infected TLR4(-/-) eyes also had significantly less intraocular inflammation than infected C57BL/6J eyes, indicating an important role for TLR4 in B. cereus endophthalmitis. Taken together, our results suggest that TLR4, TRIF, and MyD88 are important components of the intraocular inflammatory response observed in experimental B. cereus endophthalmitis, identifying a novel innate immune interaction for B. cereus and for this disease.

Neutrophil-mediated phagocytic host defense defect in myeloid Cftr-inactivated mice

Cystic fibrosis (CF) is a common and deadly inherited disease, caused by mutations in the CFTR gene that encodes a cAMP-activated chloride channel. One outstanding manifestation of the disease is the persistent bacterial infection and inflammation in the lung, which claims over 90% of CF mortality. It has been debated whether neutrophil-mediated phagocytic innate immunity has any intrinsic defect that contributes to the host lung defense failure. Here we compared phagosomal CFTR targeting, hypochlorous acid (HOCl) production, and microbial killing of the neutrophils from myeloid Cftr-inactivated (Myeloid-Cftr-/-) mice and the non-inactivated control (Cftrfl10) mice. We found that the mutant CFTR that lacked Exon-10 failed to target to the neutrophil phagosomes. This dysfunction resulted in impaired intraphagosomal HOCl production and neutrophil microbial killing. In vivo lung infection with a lethal dose of Pseudomonas aeruginosa caused significantly higher mortality in the myeloid CF mice than in the controls. The myeloid-Cftr-/- lungs were deficient in bacterial clearance, and had sustained neutrophilic inflammation and stalled transition from early to late immunity. These manifestations recapitulated the symptoms of human CF lungs. The data altogether suggest that myeloid CFTR expression is critical to normal host lung defense. CFTR dysfunction in neutrophils compromises the phagocytic innate immunity, which may predispose CF lungs to infection.

Warifteine, an alkaloid purified from Cissampelos sympodialis, inhibits neutrophil migration in vitro and in vivo

Cissampelos sympodialis Eichl is a plant from the Northeast and Southeast of Brazil. Its root infusion is popularly used for treatment of inflammatory and allergic diseases. We investigated whether warifteine, its main alkaloid, would have anti-inflammatory effect due to a blockage of neutrophil function. In vivo warifteine treatment inhibited casein-induced neutrophil migration to the peritoneal cavity but did not inhibit neutrophil mobilization from the bone marrow. Analysis of the direct effect of warifteine upon neutrophil adherence and migration in vitro demonstrated that the alkaloid decreased cell adhesion to P and E-selectin-transfected cells. In addition, fLMP-induced neutrophil migration in a transwell system was blocked by warifteine; this effect was mimicked by cAMP mimetic/inducing substances, and warifteine increased intracellular cAMP levels in neutrophils. The production of DNA extracellular traps (NETs) was also blocked by warifteine but there was no alteration on PMA-induced oxidative burst or LPS-stimulated TNFα secretion. Taken together, our data indicate that the alkaloid warifteine is a potent anti-inflammatory substance and that it has an effect on neutrophil migration through a decrease in both cell adhesion and migration.

TLR4 contributes to the host response to Klebsiella intraocular infection

PURPOSE/AIM

Klebsiella pneumoniae causes a blinding infection called endogenous endophthalmitis. The role of innate immune recognition of K. pneumoniae in the eye during infection is not known. We hypothesized that intraocular recognition of K. pneumoniae was mediated by Toll-like receptor (TLR)-4 and may be dependent on MagA-regulated hypermucoviscosity.

MATERIALS AND METHODS

Experimental endophthalmitis was induced in C57BL/6J or TLR4(-/-) mice by intravitreal injection of 100 CFU of wild type or ΔmagA K. pneumoniae. Infection and inflammation were quantified by determining viable K. pneumoniae per eye, retinal responses via electroretinography, myeloperoxidase activity of infiltrating neutrophils and the proinflammatory cytokine and chemokine response.

RESULTS

C57BL/6J and TLR4(-/-) mice could not control intraocular wild-type K. pneumoniae growth. TLR4(-/-) mice were less able than C57BL/6J to control the intraocular growth of ΔmagA K. pneumoniae. Retinal function testing suggested that infection with ΔmagA K. pneumoniae resulted in less retinal function loss. There was a TLR4-dependent delay in initial neutrophil recruitment, regardless of the infecting organism. The proinflammatory cytokine/chemokine data supported these results. These findings were not due to an inability of TLR4(-/-) neutrophils to recognize or kill K. pneumoniae.

CONCLUSIONS

These studies suggest that TLR4 is important in the early intraocular recognition and host response to K. pneumoniae. However, the role of MagA in TLR4-mediated intraocular recognition and subsequent inflammation is less clear.

The nitrated fatty acid 10-nitro-oleate attenuates allergic airway disease

Asthma is a serious, growing problem worldwide. Inhaled steroids, the current standard therapy, are not always effective in this chronic inflammatory disease and can cause adverse effects. We tested the hypothesis that nitrated fatty acids (NFAs) may provide an effective alternative treatment. NFAs are endogenously produced by nonenzymatic reaction of NO with unsaturated fatty acids and exert anti-inflammatory actions both by activating the nuclear hormone receptor peroxisome proliferator-activated receptor (PPAR)γ and via PPAR-independent mechanisms, but whether they might ameliorate allergic airway disease was previously untested. We found that pulmonary delivery of the NFA 10-nitro-oleic acid (OA-NO2) reduced the severity of murine allergic airway disease, as assessed by various pathological and molecular markers. Fluticasone, an inhaled steroid commonly used to treat asthma, produced similar effects on most end points, but only OA-NO2 induced robust apoptosis of neutrophils and their phagocytosis by alveolar macrophages. This suggests that OA-NO2 may be particularly effective in neutrophil-rich, steroid-resistant severe asthma. In primary human bronchial epithelial cells, OA-NO2 blocked phosphorylation and degradation of IκB and enhanced inhibitory binding of PPARγ to NF-κB. Our results indicate that the NFA OA-NO2 is efficacious in preclinical models of allergic airway disease and may have potential for treating asthma patients.

HIF-1α is essential for effective PMN bacterial killing, antimicrobial peptide production and apoptosis in Pseudomonas aeruginosa keratitis

Hypoxia-inducible factor (HIF)-1α, is a transcription factor that controls energy metabolism and angiogenesis under hypoxic conditions, and a potent regulator of innate immunity. The studies described herein examined the role of HIF-1α in disease resolution in BALB/c (resistant, cornea heals) mice after ocular infection with Pseudomonas (P.) aeruginosa. Furthermore, the current studies focused on the neutrophil (PMN), the predominant cell infiltrate in keratitis. Using both siRNA and an antagonist (17-DMAG), the role of HIF-1α was assessed in P. aeruginosa-infected BALB/c mice. Clinical score and slit lamp photography indicated HIF-1α inhibition exacerbated disease and corneal destruction. Real time RT-PCR, immunohistochemistry, ELISA, Greiss and MPO assays, bacterial load, intracellular killing, phagocytosis and apoptosis assays further tested the regulatory role of HIF-1α. Despite increased pro-inflammatory cytokine expression and increased MPO levels after knocking down HIF-1α expression, in vivo studies revealed a decrease in NO production and higher bacterial load. In vitro studies using PMN provided evidence that although inhibition of HIF-1α did not affect phagocytosis, both bacterial killing and apoptosis were significantly affected, as was production of antimicrobial peptides. Overall, data provide evidence that inhibition of HIF-1α converts a normally resistant disease response to susceptible (corneal thinning and perforation) after induction of bacterial keratitis. Although this inhibition does not appear to affect PMN transmigration or phagocytosis, both in vivo and in vitro approaches indicate that the transcriptional factor is essential for effective bacterial killing, apoptosis and antimicrobial peptide production.

Absence of CXCL10 aggravates herpes stromal keratitis with reduced primary neutrophil influx in mice

Herpes simplex virus 1 (HSV-1) replication initiates inflammation and angiogenesis responses in the cornea to result in herpetic stromal keratitis (HSK), which is a leading cause of infection-induced vision impairment. Chemokines are secreted to modulate HSK by recruiting leukocytes, which affect virus growth, and by influencing angiogenesis. The present study used a murine infection model to investigate the significance of the chemokine CXC chemokine ligand 10 (CXCL10; gamma interferon-inducible protein 10 [IP-10]) in HSK. Here, we show that HSV-1 infection of the cornea induced CXCL10 protein expression in epithelial cells. The corneas of mice with a targeted disruption of the gene encoding CXCL10 displayed decreases in levels of neutrophil-attracting cytokine (interleukin-6), primary neutrophil influx, and viral clearance 2 or 3 days postinfection. Subsequently, absence of CXCL10 aggravated HSK with elevated levels of interleukin-6, chemokines for CD4(+) T cells and/or neutrophils (macrophage inflammatory protein-1α and macrophage inflammatory protein-2), angiogenic factor (vascular endothelial growth factor A), and secondary neutrophil influx, as well as infiltration of CD4(+) T cells to exacerbate opacity and angiogenesis in the cornea at 14 and up to 28 days postinfection. Our results collectively show that endogenous CXCL10 contributes to recruit the primary neutrophil influx and to affect the expression of cytokines, chemokines, and angiogenic factors as well as to reduce the viral titer and HSK severity.

Adenosine-5'-triphosphate (ATP) protects mice against bacterial infection by activation of the NLRP3 inflammasome

It has been established that Adenosine-5'-triphosphate (ATP) can activate the NLRP3 inflammasome. However, the physiological effect of extracellular ATP on NLRP3 inflammasome activation has not yet been investigated. In the present study, we found that ATP was indeed released during bacterial infection. By using a murine peritonitis model, we also found that ATP promotes the fight against bacterial infection in mice. ATP induced the secretion of IL-1β and chemokines by murine bone marrow-derived macrophages in vitro. Furthermore, the intraperitoneal injection of ATP elevated the levels of IL-1β and chemokines in the mouse peritoneal lavage. Neutrophils were rapidly recruited to the peritoneum after ATP injection. In addition, the effects on cytokine and chemokine secretion and neutrophil recruitment were markedly attenuated by the pre-administration of the caspase-1 inhibitor Ac-YVAD-cho. Ac-YVAD-cho also significantly attenuated the protective effect of ATP against bacterial infection. In the present study, we demonstrated a protective role for ATP during bacterial infection and this effect was related to NLRP3 inflammasome activation. Together, these results suggest a role for ATP in initiating the immune response in hosts suffering from infections.

HP0197 contributes to CPS synthesis and the virulence of Streptococcus suis via CcpA

Streptococcus suis serotype 2 (SS2), a major swine pathogen and an emerging zoonotic agent, has greatly challenged global public health. The encoding proteins with unknown functions the bacterium encodes are an obstruction to studies of the pathogenesis. A novel surface protective antigen HP0197 is one of these proteins which have no sequence homology to any known protein. In the present study, the protein was determined to be involved in bacterial virulence through an evaluation of the isogenic mutant (Δhp0197) in both mice and pigs. The experimental infection also indicated that Δhp0197 could be cleared easily during infection, which could be attributed to the reduced thickness of the capsular polysaccharides (CPS) and the significantly reduced phagocytotic resistance. Microarrays-based comparative transcriptome analysis suggested that the suppressed expression of the operon responsible for CPS synthesis might be reversed by CcpA activity, which controlled global regulation of carbon catabolite through the binding of the CcpA and HPr-Ser-46-P to the catabolite-responsive elements (cre) of the target operons. The hypothesis was approved by the fact that the purified FLAG-tagged HPr from WT stain exhibited a higher binding activity to cre with CcpA compared to the Δhp0197 by the Electrophoretic Mobility Shift Assay, suggesting lower level of phosphorylation of the phosphocarrier protein HPr at residue Ser-46 (HPr-Ser-46P) in Δhp0197. These indicated that HP0197 could enhance CcpA activity to control the expression of genes involved in carbohydrate utilization and CPS synthesis, thus contributing to the virulence of S. suis.

Silencing α1,3-fucosyltransferases in human leukocytes reveals a role for FUT9 enzyme during E-selectin-mediated cell adhesion

Leukocyte adhesion during inflammation is initiated by the binding of sialofucosylated carbohydrates expressed on leukocytes to endothelial E/P-selectin. Although the glycosyltransferases (glycoTs) constructing selectin-ligands have largely been identified using knock-out mice, important differences may exist between humans and mice. To address this, we developed a systematic lentivirus-based shRNA delivery workflow to create human leukocytic HL-60 cell lines that lack up to three glycoTs. Using this, the contributions of all three myeloid α1,3-fucosyltransferases (FUT4, FUT7, and FUT9) to selectin-ligand biosynthesis were evaluated. The cell adhesion properties of these modified cells to L-, E-, and P-selectin under hydrodynamic shear were compared with bone marrow-derived neutrophils from Fut4(-/-)Fut7(-/-) dual knock-out mice. Results demonstrate that predominantly FUT7, and to a lesser extent FUT4, forms the selectin-ligand at the N terminus of leukocyte P-selectin glycoprotein ligand-1 (PSGL-1) in humans and mice. Here, 85% reduction in leukocyte interaction was observed in human FUT4(-)7(-) dual knockdowns on P/L-selectin substrates. Unlike Fut4(-/-)Fut7(-/-) mouse neutrophils, however, human knockdowns lacking FUT4 and FUT7 only exhibited partial reduction in rolling interaction on E-selectin. In this case, the third α1,3-fucosyltransferase FUT9 played an important role because leukocyte adhesion was reduced by 50-60% in FUT9-HL-60, 70-80% in dual knockdown FUT7(-)9(-) cells, and ∼85% in FUT4(-)7(-)9(-) triple knockdowns. Gene silencing results are in agreement with gain-of-function experiments where all three fucosyltransferases conferred E-selectin-mediated rolling in HEK293T cells. This study advances new tools to study human glycoT function. It suggests a species-specific role for FUT9 during the biosynthesis of human E-selectin ligands.

ADAMTS-12 metalloprotease is necessary for normal inflammatory response

ADAMTSs (a disintegrin and metalloprotease with thrombospondin domains) are a family of enzymes with both proteolytic and protein interaction functions, which have been implicated in distinct pathologies. In this work, we have investigated the putative role of ADAMTS-12 in inflammation by using a mouse model deficient in this metalloprotease. Control and mutant mice were subjected to different experimental conditions to induce colitis, endotoxic sepsis, and pancreatitis. We have observed that Adamts12-deficient mice exhibit more severe inflammation and a delayed recovery from these challenges compared with their wild-type littermates. These changes are accompanied by an increase in inflammatory markers including several cytokines, as assessed by microarray expression analysis and proteomic-based approaches. Interestingly, the clinical symptoms observed in Adamts12-deficient mice are also concomitant with an elevation in the number of neutrophils in affected tissues. Finally, isolation and in vitro culture of human neutrophils demonstrate that the presence of ADAMTS-12 induces neutrophil apoptosis. On the basis of these results, we propose that ADAMTS-12 is implicated in the inflammatory response by modulating normal neutrophil apoptosis.

Human anti-CCR4 minibody gene transfer for the treatment of cutaneous T-cell lymphoma

Background

Although several therapeutic options have become available for patients with Cutaneous T-cell Lymphoma (CTCL), no therapy has been curative. Recent studies have demonstrated that CTCL cells overexpress the CC chemokine receptor 4 (CCR4).

Methodology/Principal Findings

In this study, a xenograft model of CTCL was established and a recombinant adeno-associated viral serotype 8 (AAV8) vector expressing a humanized single-chain variable fragment (scFv)-Fc fusion (scFvFc or “minibody”) of anti-CCR4 monoclonal antibody (mAb) h1567 was evaluated for curative treatment. Human CCR4⁺ tumor-bearing mice treated once with intravenous infusion of AAV8 virions encoding the h1567 (AAV8-h1567) minibody showed anti-tumor activity in vivo and increased survival. The AAV8-h1567 minibody notably increased the number of tumor-infiltrating Ly-6G⁺ FcγRIIIa(CD16A)⁺ murine neutrophils in the tumor xenografts over that of AAV8-control minibody treated mice. Furthermore, in CCR4⁺ tumor-bearing mice co-treated with AAV8-h1567 minibody and infused with human peripheral blood mononuclear cells (PBMCs), marked tumor infiltration of human CD16A⁺ CD56⁺ NK cells was observed. The h1567 minibody also induced in vitro ADCC activity through both mouse neutrophils and human NK cells.

Conclusions/Significance

Overall, our data demonstrate that the in vivo anti-tumor activity of h1567 minibody is mediated, at least in part, through CD16A⁺ immune effector cell ADCC mechanisms. These data further demonstrate the utility of the AAV-minibody gene transfer system in the rapid evaluation of candidate anti-tumor mAbs and the potency of h1567 as a potential novel therapy for CTCL.

Anaplasma phagocytophilum dihydrolipoamide dehydrogenase 1 affects host-derived immunopathology during microbial colonization

Anaplasma phagocytophilum is a tick-borne rickettsial pathogen that provokes an acute inflammatory response during mammalian infection. The illness caused by A. phagocytophilum, human granulocytic anaplasmosis, occurs irrespective of pathogen load and results instead from host-derived immunopathology. Thus, characterizing A. phagocytophilum genes that affect the inflammatory process is critical for understanding disease etiology. By using an A. phagocytophilum Himar1 transposon mutant library, we showed that a single transposon insertion into the A. phagocytophilum dihydrolipoamide dehydrogenase 1 gene (lpda1 [APH_0065]) affects inflammation during infection. A. phagocytophilum lacking lpda1 revealed enlargement of the spleen, increased splenic extramedullary hematopoiesis, and altered clinicopathological abnormalities during mammalian colonization. Furthermore, LPDA1-derived immunopathology was independent of neutrophil infection and correlated with enhanced reactive oxygen species from NADPH oxidase and nuclear factor (NF)-κB signaling in macrophages. Taken together, these findings suggest the presence of different signaling pathways in neutrophils and macrophages during A. phagocytophilum invasion and highlight the importance of LPDA1 as an immunopathological molecule.

Optimized protocol for the isolation of spleen-resident murine neutrophils

Neutrophils are an important cellular component of the innate immune system that provides immediate protection to the host from infection. Neutrophil infiltration into inflamed peripheral tissues during infection is beneficial for immunity through phagocytosis of microbes, the release of antimicrobial factors, and secretion of proinflammatory cytokines. Recent reports further suggest that spleen-infiltrating neutrophils play a role in the adaptive immune response by providing survival signals to B cells. However, neutrophils may have detrimental effects on immunity in inflammatory diseases where their recruitment to lymphoid tissues and activation occur abnormally. To determine the contribution of neutrophils that reside in secondary lymphoid tissues to adaptive immunity, direct evaluation of the functional properties of tissue-resident neutrophils is required. We have developed a modified magnetic bead isolation approach for purifying neutrophils from inflamed spleens of autoimmune-prone mice by negative selection. Using this approach, we yielded neutrophils with greater than 90% purity without compromising cell viability. Equally important, the isolation procedure had little effect on the activation of neutrophils and did not impair phagocytic function. Thus, isolation of spleen-resident neutrophils by this optimized approach could be useful for interrogating the functional role of murine neutrophils in normal and abnormal immune responses.

Naloxone inhibits immune cell function by suppressing superoxide production through a direct interaction with gp91phox subunit of NADPH oxidase

BACKGROUND

Both (-) and (+)-naloxone attenuate inflammation-mediated neurodegeneration by inhibition of microglial activation through superoxide reduction in an opioid receptor-independent manner. Multiple lines of evidence have documented a pivotal role of overactivated NADPH oxidase (NOX2) in inflammation-mediated neurodegeneration. We hypothesized that NOX2 might be a novel action site of naloxone to mediate its anti-inflammatory actions.

METHODS

Inhibition of NOX-2-derived superoxide by (-) and (+)-naloxone was measured in lipopolysaccharide (LPS)-treated midbrain neuron-glia cultures and phorbol myristate acetate (PMA)-stimulated neutrophil membranes by measuring the superoxide dismutase (SOD)-inhibitable reduction of tetrazolium salt (WST-1) or ferricytochrome c. Further, various ligand (3H-naloxone) binding assays were performed in wild type and gp91phox-/- neutrophils and transfected COS-7 and HEK293 cells. The translocation of cytosolic subunit p47phox to plasma membrane was assessed by western blot.

RESULTS

Both (-) and (+)-naloxone equally inhibited LPS- and PMA-induced superoxide production with an IC50 of 1.96 and 2.52 μM, respectively. Competitive binding of 3H-naloxone with cold (-) and (+)-naloxone in microglia showed equal potency with an IC50 of 2.73 and 1.57 μM, respectively. 3H-Naloxone binding was elevated in COS-7 and HEK293 cells transfected with gp91phox; in contrast, reduced 3H-naloxone binding was found in neutrophils deficient in gp91phox or in the presence of a NOX2 inhibitor. The specificity and an increase in binding capacity of 3H-naloxone were further demonstrated by 1) an immunoprecipitation study using gp91phox antibody, and 2) activation of NOX2 by PMA. Finally, western blot studies showed that naloxone suppressed translocation of the cytosolic subunit p47phox to the membrane, leading to NOX2 inactivation.

CONCLUSIONS

Strong evidence is provided indicating that NOX2 is a non-opioid novel binding site for naloxone, which is critical in mediating its inhibitory effect on microglia overactivation and superoxide production.

Nonhematopoietic toll-like receptor 2 contributes to neutrophil and cardiac function impairment during polymicrobial sepsis

Toll-like receptor 2 (TLR2) has been implicated in neutrophil and cardiac dysfunction during sepsis. Here we tested the hypothesis that nonhematopoietic (parenchymal) and hematopoietic TLR2 play distinct roles in sepsis pathogenesis. To achieve this, we generated two groups of chimeric mice with TLR2 deletions either in nonhematopoietic cells (knockout [KO] mice with wild-type [WT] bone marrow [BM]) or in BM cells (WT mice with KO-BM). Polymicrobial sepsis was created by cecal ligation and puncture (CLP). Neutrophil functions, cytokine production, and bacterial clearance were investigated following CLP or sham procedures. Cardiac contractile function was measured in a Langendorff apparatus. Intracellular reactive oxygen species (ROS) were measured using redox-sensitive dye and flow cytometry. Cecal ligation and puncture mice had markedly increased peritoneal neutrophil recruitment compared with the sham-operated mice. Toll-like receptor 2 KO mice, regardless their TLR2 phenotypes (WT vs. KO) in their BM-derived hematopoietic cells, had markedly increased neutrophil migration as well as phagocytosis and reduced cytokine productions compared with TLR2 WT mice following polymicrobial peritonitis. These changes in the chimeric TLR2 KO mice were associated with enhanced blood bacterial clearance and markedly improved cardiac contractile function. Moreover, CLP induced a robust ROS production in the peritoneal leukocytes isolated from WT mice but not from TLR2 KO mice. Taken together, these data indicate that TLR2, particularly that of nonhematopoietic cells, plays a major role in sepsis pathogenesis by impairing neutrophil migratory and phagocytic function, promoting cytokine production, and mediating cardiac contractile dysfunction during polymicrobial sepsis. Toll-like receptor 2 also mediates critical ROS production during polymicrobial sepsis.

PAD4-mediated neutrophil extracellular trap formation is not required for immunity against influenza infection

During an inflammatory response, neutrophils migrate to the site of infection where they can kill invading pathogens by phagocytosis, secretion of anti-microbicidal mediators or the release of neutrophil extracellular traps (NETs). NETs are specialized anti-microbial structures comprised of decondensed chromatin decorated with microbicidal agents. Increased amount of NETs have been found in patients suffering from the chronic lung inflammatory disease cystic fibrosis, correlating with increased severity of pulmonary obstruction. Furthermore, acute lung inflammation during influenza A infection is characterized by a massive influx of neutrophils into the lung. The role of NETs during virus-mediated lung inflammation is unknown. Peptidylarginine deiminase 4 (PAD4)-mediated deimination of histone H3 and H4 is required for NET formation. Therefore, we generated a PAD4-deficient mouse strain that has a striking inability to form NETs. These mice were infected with influenza A/WSN, and the disease was monitored at the level of leukocytic lung infiltration, lung pathology, viral replication, weight loss and mortality. PAD4 KO fared comparable to WT mice in all the parameters tested, but they displayed slight but statistically different weight loss kinetics during infection that was not reflected in enhanced survival. Overall, we conclude that PAD4-mediated NET formation is dispensable in a mouse model of influenza A infection.

Dual protective mechanisms of matrix metalloproteinases 2 and 9 in immune defense against Streptococcus pneumoniae

A localized and effective innate immune response to pathogenic bacterial invasion is central to host survival. Identification of the critical local innate mediators of lung defense against such pathogens is essential for a complete understanding of the mechanism(s) underlying effective host defense. In an acute model of Streptococcus pneumoniae lung infection, deficiency in matrix metalloproteinase (MMP)2 and MMP9 (Mmp2/9(-/-)) conferred a survival disadvantage relative to wild-type mice treated under the same conditions. S. pneumoniae-infected Mmp2/9(-/-) mice recruited more polymorphonuclear leukocytes to the lung but had higher bacterial burdens. Mmp2/9(-/-) mice showed significantly higher levels of IL-17A, IP-10, and RANTES in the lung. Although MMP2-dependent cleavage partially inactivated IL-17A, MMP9 was critical for effective bacterial phagocytosis and reactive oxygen species generation in polymorphonuclear neutrophils. These data demonstrate critical nonredundant and protective roles for MMP2 and MMP9 in the early host immune response against S. pneumoniae infection.

IL-10 administration reduces PGE-2 levels and promotes CR3-mediated clearance of Escherichia coli K1 by phagocytes in meningitis

Ineffectiveness of antibiotics in treating neonatal Escherichia coli K1 meningitis and the emergence of antibiotic-resistant strains evidently warrants new prevention strategies. We observed that administration of interleukin (IL)-10 during high-grade bacteremia clears antibiotic-sensitive and -resistant E. coli from blood of infected mice. Micro-CT studies of brains from infected animals displayed gross morphological changes similar to those observed in infected human neonates. In mice, IL-10, but not antibiotic or anti-TNF antibody treatment prevented brain damage caused by E. coli. IL-10 administration elevated CR3 expression in neutrophils and macrophages of infected mice, whereas infected and untreated mice displayed increased expression of FcγRI and TLR2. Neutrophils or macrophages pretreated with IL-10 ex vivo exhibited a significantly greater microbicidal activity against E. coli compared with cells isolated from wild-type or IL-10^−/− mice. The protective effect of IL-10 was abrogated when CR3 was knocked-down in vivo by siRNA. The increased expression of CR3 in phagocytes was caused by inhibition of prostaglandin E-2 (PGE-2) levels, which were significantly increased in neutrophils and macrophages upon E. coli infection. These findings describe a novel modality of IL-10–mediated E. coli clearance by diverting the entry of bacteria via CR3 and preventing PGE-2 formation in neonatal meningitis.

Inhibition of inducible nitric oxide controls pathogen load and brain damage by enhancing phagocytosis of Escherichia coli K1 in neonatal meningitis

Escherichia coli K1 is a leading cause of neonatal meningitis in humans. In this study, we sought to determine the pathophysiologic relevance of inducible nitric oxide (iNOS) in experimental E. coli K1 meningitis. By using a newborn mouse model of meningitis, we demonstrate that E. coli infection triggered the expression of iNOS in the brains of mice. Additionally, iNOS-/- mice were resistant to E. coli K1 infection, displaying normal brain histology, no bacteremia, no disruption of the blood-brain barrier, and reduced inflammatory response. Treatment with an iNOS specific inhibitor, aminoguanidine (AG), of wild-type animals before infection prevented the development of bacteremia and the occurrence of meningitis. The infected animals treated with AG after the development of bacteremia also completely cleared the pathogen from circulation and prevented brain damage. Histopathological and micro-CT analysis of brains revealed significant damage in E. coli K1-infected mice, which was completely abrogated by AG administration. Peritoneal macrophages and polymorphonuclear leukocytes isolated from iNOS-/- mice or pretreated with AG demonstrated enhanced uptake and killing of the bacteria compared with macrophages and polymorphonuclear leukocytes from wild-type mice in which E. coli K1 survive and multiply. Thus, NO produced by iNOS may be beneficial for E. coli to survive inside the macrophages, and prevention of iNOS could be a therapeutic strategy to treat neonatal E. coli meningitis.

Nod1 signaling overcomes resistance of S. pneumoniae to opsonophagocytic killing

Airway infection by the Gram-positive pathogen Streptococcus pneumoniae (Sp) leads to recruitment of neutrophils but limited bacterial killing by these cells. Co-colonization by Sp and a Gram-negative species, Haemophilus influenzae (Hi), provides sufficient stimulus to induce neutrophil and complement-mediated clearance of Sp from the mucosal surface in a murine model. Products from Hi, but not Sp, also promote killing of Sp by ex vivo neutrophil-enriched peritoneal exudate cells. Here we identify the stimulus from Hi as its peptidoglycan. Enhancement of opsonophagocytic killing was facilitated by signaling through nucleotide-binding oligomerization domain-1 (Nod1), which is involved in recognition of gamma-D-glutamyl-meso-diaminopimelic acid (meso-DAP) contained in cell walls of Hi but not Sp. Neutrophils from mice treated with Hi or compounds containing meso-DAP, including synthetic peptidoglycan fragments, showed increased Sp killing in a Nod1-dependent manner. Moreover, Nod1(-/-) mice showed reduced Hi-induced clearance of Sp during co-colonization. These observations offer insight into mechanisms of microbial competition and demonstrate the importance of Nod1 in neutrophil-mediated clearance of bacteria in vivo.