Myeloperoxidase associated with neutrophil extracellular traps is active and mediates bacterial killing in the presence of hydrogen peroxide

A versatile imaging platform with fluorescence and CT imaging capabilities that detects myeloperoxidase activity and inflammation at different scales

Aberrant innate immune response drives the pathophysiology of many diseases. Myeloperoxidase (MPO) is a highly oxidative enzyme secreted by activated myeloid pro-inflammatory immune cells such as neutrophils and macrophages, and is a key mediator of the damaging innate immune response. Current technologies for detecting MPO activity in living organisms are sparse and suffer from any combination of low specificity, low tissue penetration, or low spatial resolution. We describe a versatile imaging platform to detect MPO activity using an activatable construct conjugated to a biotin moiety (MPO-activatable biotinylated sensor, MABS) that allows monitoring the innate immune response and its modulation at different scales and settings.

Methods:We designed and synthesized MABS that contains MPO-specific and biotin moieties, and validated its specificity and sensitivity combining with streptavidin-labeled fluorescent agent and gold nanoparticles imaging in vitro and in vivo in multiple mouse models of inflammation and infection, including Matrigel implant, dermatitis, cellulitis, cerebritis and complete Fraud's adjuvant (CFA)-induced inflammation.

Results: MABS MPO imaging non-invasively detected varying MPO concentrations, MPO inhibition, and MPO deficiency in vivo with high sensitivity and specificity. MABS can be used to obtain not only a fluorescence imaging agent, but also a CT imaging agent, conferring molecular activity information to a structural imaging modality. Importantly, using this method on tissue-sections, we found that MPO enzymatic activity does not always co-localize with MPO protein detected with conventional techniques (e.g., immunohistochemistry), underscoring the importance of monitoring enzymatic activity.

Conclusion:By choosing from different available secondary probes, MABS can be used to create systems suitable to investigate and image MPO activity at different scales and settings.

Ochratoxin A-Triggered Chicken Heterophil Extracellular Traps Release through Reactive Oxygen Species Production Dependent on Activation of NADPH Oxidase, ERK, and p38 MAPK Signaling Pathways

Ochratoxin A (OTA) is a mycotoxin which could cause strong immunosuppressive toxicological effects in animals and humans. Heterophil extracellular traps (HETs) as a novel defense of chicken heterophils play an important role against pathogen infection. It has been reported that OTA can weaken the phagocytosis function of neutrophils. However, whether or not OTA shows immunosuppressive effects on HET release remains unclear. In the present study, we aim to first investigate the effects of OTA on HET release and then try to clarify the mechanisms in this process. OTA-induced HET structures were observed and analyzed by fluorescence confocal microscopy. The quantitative determination of OTA-induced HETs was measured by PicoGreen and a fluorescence microplate. The results clearly showed that OTA obviously induced the release of HET-like structures in heterophils, and these extracellular networks were composed by chromatin decorated with histones and neutrophil elastase. Reactive oxygen species (ROS) production was also increased in the process of OTA-induced HET formation. Furthermore, the inhibitors of NADPH oxidase, ERK [Formula: see text], and p38 MAPK signaling pathways significantly decreased OTA-induced HET formation. The abovementioned results suggest that OTA-induced HET formation is related to ROS production dependent on the activation of NADPH oxidase, ERK [Formula: see text], and p38 MAPK signaling pathways. Taken together, this study first shows that OTA possesses the ability to trigger HET formation, which provides our understanding of the host that continuously suffered OTA exposure leading to the hyporeactivity of the immune system against infection.

Neutrophil extracellular trap-microparticle complexes trigger neutrophil recruitment via high-mobility group protein 1 (HMGB1)-toll-like receptors(TLR2)/TLR4 signalling

BACKGROUND AND PURPOSE

Recent data suggest that neutrophil extracellular traps (NETs) form aggregates with microparticles (MPs) upon activation of neutrophils although the functional role of NET-MP complexes remain elusive. The objective of this study was to examine the role of NET-MP aggregates in leukocyte recruitment in vivo.

EXPERIMENTAL APPROACH

PMA stimulation of murine bone marrow neutrophils generated NET-MP complexes and pretreatment with caspase and calpain inhibitors resulted in the formation of NETs depleted of MPs. Leukocyte-endothelium interactions were studied by using intravital microscopy of the mouse cremaster microcirculation.

KEY RESULTS

Intrascrotal injection of NET-MP aggregates dose-dependently increased leukocyte recruitment. In contrast, leukocyte responses were markedly reduced after administration of NETs depleted of MPs. Neutrophil depletion abolished intravascular and extravascular leukocytes in response to challenge with NET-MP complexes. Electron microscopy revealed that NET-associated MPs express HMGB1. Notably, immunoneutralization of HMGB1 markedly decreased NET-MP complex-induced neutrophil accumulation. Moreover, inhibition of TLR2 and TLR4 significantly reduced neutrophil recruitment in response to NET-MP aggregates.

CONCLUSIONS AND IMPLICATIONS

These data show that NET-MP complexes are potent inducers of neutrophil recruitment, which is dependent on HMGB1 expressed on MPs and mediated via TLR2 and TLR4. Blocking MP binding to NETs or downstream inhibition of the HMGB1-TLR2/TLR4 axis might provide useful targets to attenuating NET-dependent tissue damage in acute inflammation.

Immunomodulatory and Antimicrobial Effects of Vitamin C

Humans have lost their vitamin C-synthesizing capacities during evolution. Therefore, the uptake of this essential compound from external sources is mandatory in order to prevent vitamin C-deficient conditions resulting in severe morbidities such as scurvy. The potent antioxidant, immunomodulatory, and antiinfectious effects of vitamin C are known since the 1930s. We here (i) review the impact of vitamin C on innate and adaptive immune functions, (ii) provide an overview of its antimicrobial, antibacterial, antiviral, antiparasitic, and antifungal properties, and finally, (iii) discuss vitamin C as an adjunct treatment option for the combat of human infections by bacteria, particularly by emerging multidrug-resistant species.

Regulation of Pseudomonas aeruginosa-Mediated Neutrophil Extracellular Traps

Pseudomonas aeruginosa is the most prevalent opportunistic pathogen in the airways of cystic fibrosis (CF) patients. The pulmonary disorder is characterized by recurrent microbial infections and an exaggerated host inflammatory immune response led primarily by influx of neutrophils. Under these conditions, chronic colonization with P. aeruginosa is associated with diminished pulmonary function and increased morbidity and mortality. P. aeruginosa has a wide array of genetic mechanisms that facilitate its persistent colonization of the airway despite extensive innate host immune responses. Loss of function mutations in the quorum sensing regulatory gene lasR have been shown to confer survival advantage and a more pathogenic character to P. aeruginosa in CF patients. However, the strategies used by LasR-deficient P. aeruginosa to modulate neutrophil-mediated bactericidal functions are unknown. We sought to understand the role of LasR in P. aeruginosa-mediated neutrophil extracellular trap (NET) formation, an important anti-microbial mechanism deployed by neutrophils, the first-line responder in the infected airway. We observe mechanistic and phenotypic differences between NETs triggered by LasR-sufficient and LasR-deficient P. aeruginosa strains. We uncover that LasR-deficient P. aeruginosa strains fail to induce robust NET formation in both human and murine neutrophils, independently of bacterial motility or LPS expression. LasR does not mediate NET release via downstream quorum sensing signaling pathways but rather via transcriptional regulation of virulence factors, including, but not restricted to, LasB elastase and LasA protease. Finally, our studies uncover the differential requirements for NADPH oxidase in NET formation triggered by different P. aeruginosa strains.

N-chlorination mediates protective and immunomodulatory effects of oxidized human plasma proteins

Hypochlorous acid (HOCl), a powerful antimicrobial oxidant, is produced by neutrophils to fight infections. Here, we show that N-chlorination, induced by HOCl concentrations encountered at sites of inflammation, converts blood plasma proteins into chaperone-like holdases that protect other proteins from aggregation. This chaperone-like conversion was reversible by antioxidants and was abrogated by prior methylation of basic amino acids. Furthermore, reversible N-chlorination of basic amino acid side chains is the major factor that converts plasma proteins into efficient activators of immune cells. Finally, HOCl-modified serum albumin was found to act as a pro-survival molecule that protects neutrophils from cell death induced by highly immunogenic foreign antigens. We propose that activation and enhanced persistence of neutrophils mediated by HOCl-modified plasma proteins, resulting in the increased and prolonged generation of ROS, including HOCl, constitutes a potentially detrimental positive feedback loop that can only be attenuated through the reversible nature of the modification involved.

The Role of Physiological Vitamin C Concentrations on Key Functions of Neutrophils Isolated from Healthy Individuals

Vitamin C (ascorbate) is important for neutrophil function and immune health. Studies showing improved immune function have primarily used cells from scorbutic animals or from individuals with infectious conditions or immune cell disorders. Few studies have focused on the requirements of neutrophils from healthy adults. Therefore, we have investigated the role of vitamin C, at concentrations equivalent to those obtained in plasma from oral intakes (i.e., 50-200 µmol/L), on key functions of neutrophils isolated from healthy individuals. Cells were either pre-loaded with dehydroascorbic acid, which is rapidly reduced intracellularly to ascorbate, or the cells were activated in the presence of extracellular ascorbate. We measured the effects of enhanced ascorbate uptake on the essential functions of chemotaxis, oxidant production, programmed cell death and neutrophil extracellular trap (NET) formation. We found that neutrophils isolated from healthy individuals already had replete ascorbate status (0.35 nmol/106 cells), therefore they did not uptake additional ascorbate. However, they readily took up dehydroascorbic acid, thus significantly increasing their intracellular ascorbate concentrations, although this was found to have no additional effect on superoxide production or chemotaxis. Interestingly, extracellular ascorbate appeared to enhance directional mobilityin the presence of the chemoattractant formyl-methionyl-leucyl-phenylalanine (fMLP). Stimulation of the cells in the presence of ascorbate significantly increased intracellular ascorbate concentrations and, although this exhibited a non-significant increase in phosphatidylserine exposure, NET formation was significantly attenuated. Our findings demonstrate the ability of neutrophils to regulate their uptake of ascorbate from the plasma of healthy humans to maintain an optimal level within the cell for proper functioning. Higher oral intakes, however, may help reduce tissue damage and inflammatory pathologies associated with NET formation.

IL-1β Promotes Staphylococcus aureus Biofilms on Implants in vivo

Implant associated infections represent a serious health burden in clinics since some microorganisms are able to colonize biological surfaces or surfaces of indwelling medical devices and form biofilms. Biofilms represent communities of microorganisms attached to hydrated surfaces and enclosed in self-produced extracellular matrix. This renders them resistant to exogenous assaults like antibiotics or immune effector mechanisms. Little is known regarding the role of the immune system in the formation of biofilms during implant associated infections, largely due to the lack of suitable mouse models. Here we use colonized osmotic pumps in mice to study the interaction of an activated immune system with biofilm-forming Staphylococcus aureus encoding Gaussia luciferase. This approach permits biofilm formation on the osmotic pumps in living animals. It also allows the continuous supply of soluble immune cell activating agents, such as cytokines to study their effect on biofilm formation in vivo. Using non-invasive imaging of the bioluminescent signal emitted by the lux expressing bacteria for quantification of bacterial load in conjunction with light and electron microscopy, we observed that pump-supplied pro-inflammatory cytokine IL-1β strongly increased biofilm formation along with a massive influx of neutrophils adjacent to the biofilm-coated pumps. Thus, our data demonstrate that immune defense mechanisms can augment biofilm formation.

Peroxiredoxin expression and redox status in neutrophils and HL-60 cells

Peroxiredoxins (Prxs) are thiol peroxidases with a key role in antioxidant defense and redox signaling. They could be important in neutrophils for handling the large amount of oxidants that these cells produce. We investigated the redox state of Prx1 and Prx2 in HL-60 promyelocytic cells differentiated to neutrophil-like cells (dHL-60) and in human neutrophils. HL-60 cell differentiation with dimethyl sulfoxide caused a large decrease in expression of both Prxs, and all-trans retinoic acid also decreased Prx1 expression. Prx1 was mostly reduced in dHL-60 cells. NADPH oxidase activation by phorbol myristate acetate (PMA) or ingestion of Staphylococcus aureus induced rapid oxidation to disulfide-linked dimers, and eventually hyperoxidation. The NADPH oxidase inhibitor, diphenyleneiodonium, prevented Prx1 dimerization in stimulated dHL-60 cells, and decreased the extent of oxidation under resting conditions. In contrast, Prx1 and Prx2 were present in neutrophils from human blood as disulfides, and PMA or S. aureus caused no further oxidation. They remained oxidized on incubation with diphenyleneiodonium in media. Although this suggests that Prx redox cycling could be deficient in neutrophils, thioredoxin expression and thioredoxin reductase activity were similar in neutrophils and dHL-60 cells. Additionally, neutrophil thioredoxin was initially reduced and underwent oxidation after PMA activation. Thus, although the Prxs respond to oxidant generation in dHL-60 cells, in neutrophils they appear "locked" as disulfides. On this basis we propose that neutrophil Prxs are inefficient antioxidants and contribute little to peroxide removal during the oxidative burst, and speculate that they might be involved in other cell processes.

Oxidative cross-linking of calprotectin occurs in vivo, altering its structure and susceptibility to proteolysis

Calprotectin, the major neutrophil protein, is a critical alarmin that modulates inflammation and plays a role in host immunity by strongly binding trace metals essential for bacterial growth. It has two cysteine residues favourably positioned to act as a redox switch. Whether their oxidation occurs in vivo and affects the function of calprotectin has received little attention. Here we show that in saliva from healthy adults, and in lavage fluid from the lungs of patients with respiratory diseases, a substantial proportion of calprotectin was cross-linked via disulfide bonds between the cysteine residues on its S100A8 and S100A9 subunits. Stimulated human neutrophils released calprotectin and subsequently cross-linked it by myeloperoxidase-dependent production of hypochlorous acid. The myeloperoxidase-derived oxidants hypochlorous acid, taurine chloramine, hypobromous acid, and hypothiocyanous acid, all at 10 μM, cross-linked calprotectin (5 μM) via reversible disulfide bonds. Hypochlorous acid generated A9-A9 and A8-A9 cross links. Hydrogen peroxide (10 μM) did not cross-link the protein. Purified neutrophil calprotectin existed as a non-covalent heterodimer of A8/A9 which was converted to a heterotetramer - (A8/A9)₂ - with excess calcium ions. Low level oxidation of calprotectin with hypochlorous acid produced substantial proportions of high order oligomers, whether oxidation occurred before or after addition of calcium ions. At high levels of oxidation the heterodimer could not form tetramers with calcium ions, but prior addition of calcium ions afforded some protection for the heterotetramer. Oxidation and formation of the A8-A9 disulfide cross link enhanced calprotectin's susceptibility to proteolysis by neutrophil proteases. We propose that reversible disulfide cross-linking of calprotectin occurs during inflammation and affects its structure and function. Its increased susceptibility to proteolysis will ultimately result in a loss of function.

Caught in a Trap? Proteomic Analysis of Neutrophil Extracellular Traps in Rheumatoid Arthritis and Systemic Lupus Erythematosus

Neutrophil Extracellular Traps (NETs) are implicated in the development of auto-immunity in diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) through the externalization of intracellular neoepitopes e.g., dsDNA and nuclear proteins in SLE and citrullinated peptides in RA. The aim of this work was to use quantitative proteomics to identify and measure NET proteins produced by neutrophils from healthy controls, and from patients with RA and SLE to determine if NETs can be differentially-generated to expose different sets of neoepitopes. Ultra-pure neutrophils (>99%) from healthy individuals (n = 3) and patients with RA or SLE (n = 6 each) were incubated ± PMA (50 nM, PKC super-activator) or A23187 (3.8 μM, calcium ionophore) for 4 h. NETs were liberated by nuclease digestion and concentrated onto Strataclean beads prior to on-bead digestion with trypsin. Data-dependent LC-MS/MS analyses were conducted on a QExactive HF quadrupole-Orbitrap mass spectrometer, and label-free protein quantification was carried out using Progenesis QI. PMA-induced NETs were decorated with annexins, azurocidin and histone H3, whereas A23187-induced NETs were decorated with granule proteins including CAMP/LL37, CRISP3, lipocalin and MMP8, histones H1.0, H1.4, and H1.5, interleukin-8, protein-arginine deiminase-4 (PADI4), and α-enolase. Four proteins were significantly different between PMA-NETs from RA and SLE neutrophils (p < 0.05): RNASE2 was higher in RA, whereas MPO, leukocyte elastase inhibitor and thymidine phosphorylase were higher in SLE. For A23187-NETs, six NET proteins were higher in RA (p < 0.05), including CAMP/LL37, CRISP3, interleukin-8, MMP8; Thirteen proteins were higher in SLE, including histones H1.0, H2B, and H4. This work provides the first, direct comparison of NOX2-dependent (PMA) and NOX2-independent (A23187) NETs using quantitative proteomics, and the first direct comparison of RA and SLE NETs using quantitative proteomics. We show that it is the nature of the stimulant rather than neutrophil physiology that determines NET protein profiles in disease, since stimulation of NETosis in either a NOX2-dependent or a NOX2-independent manner generates broadly similar NET proteins irrespective of the disease background. We also use our proteomics pipeline to identify an extensive range of post-translationally modified proteins in RA and SLE, including histones and granule proteins, many of which are known targets of auto-antibodies in each disease.

Progression of Cystic Fibrosis Lung Disease from Childhood to Adulthood: Neutrophils, Neutrophil Extracellular Trap (NET) Formation, and NET Degradation

Genetic defects in cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene cause CF. Infants with CFTR mutations show a peribronchial neutrophil infiltration prior to the establishment of infection in their lung. The inflammatory response progressively increases in children that include both upper and lower airways. Infectious and inflammatory response leads to an increase in mucus viscosity and mucus plugging of small and medium-size bronchioles. Eventually, neutrophils chronically infiltrate the airways with biofilm or chronic bacterial infection. Perpetual infection and airway inflammation destroy the lungs, which leads to increased morbidity and eventual mortality in most of the patients with CF. Studies have now established that neutrophil cytotoxins, extracellular DNA, and neutrophil extracellular traps (NETs) are associated with increased mucus clogging and lung injury in CF. In addition to opportunistic pathogens, various aspects of the CF airway milieux (e.g., airway pH, salt concentration, and neutrophil phenotypes) influence the NETotic capacity of neutrophils. CF airway milieu may promote the survival of neutrophils and eventual pro-inflammatory aberrant NETosis, rather than the anti-inflammatory apoptotic death in these cells. Degrading NETs helps to manage CF airway disease; since DNAse treatment release cytotoxins from the NETs, further improvements are needed to degrade NETs with maximal positive effects. Neutrophil-T cell interactions may be important in regulating viral infection-mediated pulmonary exacerbations in patients with bacterial infections. Therefore, clarifying the role of neutrophils and NETs in CF lung disease and identifying therapies that preserve the positive effects of neutrophils, while reducing the detrimental effects of NETs and cytotoxic components, are essential in achieving innovative therapeutic advances.

Assessment of histopathology of wounds based on protein distribution detected by wound blotting

Background:

Shortening the duration of healing based on an accurate assessment is important in pressure ulcer management. This study focused on the peroxidase and alkaline phosphatase activity detected by wound blotting, a non-invasive method of collecting wound exudate, to establish a non-invasive and point-of-care assessment method for analyzing the histopathology of wounds using an animal model.

Methods:

Wounds were created on the dorsal skin of rats. Peroxidase and alkaline phosphatase activities in the wound exudate were detected by wound blotting on post-wounding days 1, 4, 7, and 10. Wound tissue was collected on the same sampling days. Peroxidase and alkaline phosphatase activity within the tissue and myeloperoxidase were visualized. Two types of peroxidase activities were detected by wound blotting: ring and non-ring signals. The histopathological features were compared between wounds with ring and non-ring signals.

Results:

The wounds with ring signals showed a high level of peroxidase activity, and histological analysis demonstrated that the secreted or deviated peroxidase activity originated from myeloperoxidase, indicating a strong inflammation reaction within the tissue. The histopathology of wounds related to the alkaline phosphatase signals was not identified.

Conclusion:

The results suggested that ring signals indicated a strong inflammatory reaction and that they could be used to assess non-visible inflammation.

Mechanisms and disease relevance of neutrophil extracellular trap formation

While the microscopic appearance of neutrophil extracellular traps (NETs) has fascinated basic researchers since its discovery, the (patho)physiological mechanisms triggering NET release, the disease relevance and clinical translatability of this unconventional cellular mechanism remained poorly understood. Here, we summarize and discuss current concepts of the mechanisms and disease relevance of NET formation.

Citrullinated Histone H3: Early Biomarker of Neutrophil Extracellular Traps in Septic Liver Damage

BACKGROUND

Neutrophil extracellular traps (NETs) play a crucial role in host defense, but excess and prolonged interaction of NETs with platelets can cause severe inflammation and host organ damage. Modification of histone H3 by citrullination is involved in in vitro NET formation. The phosphodiesterase III inhibitor, cilostazol (Ciz), which has a protective effect on liver sinusoidal endothelial cells and inhibits platelet aggregation, may prevent organ damage caused by excess NETosis. In this study, we investigated whether citrullinated histone H3 (H3Cit) could serve as a biomarker for the detection of critical liver damage in sepsis and the efficacy of phosphodiesterase-III inhibition for preventing the liver dysfunction induced by NETosis.

MATERIALS AND METHODS

Mice injected with lipopolysaccharide (LPS; 1 mg/kg) were used as a sepsis model with or without treatment with Ciz (200 mg/kg). H3Cit, myeloperoxidase, and neutrophil elastase levels were measured by immunohistochemistry. We evaluated H3Cit-positive neutrophils in the peripheral blood by flow cytometry.

RESULTS

Immunohistochemistry revealed that H3Cit-, neutrophil elastase-, and myeloperoxidase-positive cell numbers in the livers peaked at 12 h after LPS administration. However, flow cytometry showed a significant increase in H3Cit-positive neutrophils in the peripheral blood only 4 h after LPS injection. Treatment with Ciz significantly ameliorated all parameters.

CONCLUSIONS

H3Cit is a useful biomarker for early detection of NETosis or liver dysfunction, and Ciz may be an effective treatment for septic liver damage.

Characterization and comparison of neutrophil extracellular traps in gingival samples of periodontitis and gingivitis: A pilot study

BACKGROUND AND OBJECTIVE

Neutrophil extracellular traps (NETs) are a recently discovered antimicrobial mechanism used by neutrophils that have been proposed as an intervention in the pathogenesis of periodontitis. The objective of our study was to characterize the expression of NETs in gingival tissues with periodontitis and controls and to compare the expression of these traps in gingival tissue samples of patients with gingivitis and periodontitis.

MATERIAL AND METHODS

An observational cross-sectional study was conducted on patients with periodontitis, gingivitis, and controls that needed tooth extraction. Gingival tissue biopsies were gathered after clinical examination and tooth extraction. Electron microscopy and immunofluorescence were performed to characterize NETs, comparing periodontitis and control patients. Immunohistochemical analysis was performed to quantify neutrophil extracellular trap expression through extracellular citrullinated histone H3 and myeloperoxidase in biopsies from patients with gingivitis and periodontitis.

RESULTS

Thirteen biopsies were gathered from 13 patients: five gingivitis, six periodontitis, and two controls. Electron microscopy and immunofluorescence imaging showed greater expression of neutrophils present in periodontal inflamed tissue compared with controls. Release of nuclear content to the extracellular space was observed, compatible with the formation of NETs. The expression of citrullinated histone H3 was higher in gingivitis samples than periodontitis samples (P = 0.0106). Myeloperoxidase expression was higher in periodontitis than gingivitis, but without achieving statistical significance.

CONCLUSION

Neutrophil extracellular traps were found in tissue samples of periodontitis as extracellular components of chromatin, along with neutrophil enzymes, that were not present in healthy controls. The comparison of NETs expression in periodontitis and gingivitis showed higher expression in gingivitis, associating them to acute phases of the periodontal inflammatory process.

Microbial communities and inflammatory response in the endometrium differ between normal and metritic dairy cows at 5-10 days post-partum

Post-partum metritis is among the most prevalent disease in dairy cows affecting animal welfare and inflicting considerable economic loses. While post-partum contamination of the uterus is rife in dairy cows, only a fraction of these animals will develop metritis. Our main objective was to compare the bacterial communities and the inflammatory response in the endometrium of healthy and metritic dairy cows. Holstein-Friesian cows (n = 35) were sampled immediately following clinical classification as healthy (n = 21), suffering from metritis (n = 13) or septic metritis (n = 1), based on veterinary examination at 5-10 days post-partum. Polymorphonuclear cells (PMN) percentage in endometrial cytology was significantly higher in cows with metritis. Full-thickness uterine biopsy analysis revealed that the luminal epithelium in inter-caruncle areas was preserved in healthy cows, but in metritis it was compromised, with marked PMN infiltration particularly in the apical endometrium. Gram staining revealed that bacterial load and spatial distribution was associated with disease severity. 16S-rDNA bacterial community analysis revealed unique endometrial bacterial community composition in metritic cows, as compared to more diverse communities among healthy cows. The most abundant phyla in healthy cows were Proteobacteria (31.8 ± 9.3%), Firmicutes (27.9 ± 8.4%) and Bacteroidetes (19.7 ± 7.2%), while Bacteroidetes (60.3 ± 10.3%), Fusobacteria (13.4 ± 5.9%) and Firmicutes (10.5 ± 3.3%) were most abundant in the endometrial mucosa of metritic cows. Relative abundance of Bacteroidetes (19.7 ± 7.2% vs. 60.3 ± 10.3%), Fusobacteria (7.5 ± 5.2% vs. 13.4 ± 5.9%) and Proteobacteria (31.8 ± 9.3% vs. 7.3 ± 5.6%) phyla differed significantly between healthy and metritic cows. In summary, endometrial PMN abundance, spatial distribution and bacterial communities differed between healthy and metritic dairy cows at early post-partum.

Thrombin and Plasmin Alter the Proteome of Neutrophil Extracellular Traps

Neutrophil extracellular traps (NETs) consist of a decondensed DNA scaffold decorated with neutrophil-derived proteins. The proteome of NETs, or "NETome," has been largely elucidated in vitro. However, components such as plasma and extracellular matrix proteins may affect the NETome under physiological conditions. Here, using a reductionistic approach, we explored the effects of two proteases active during injury and wounding, human thrombin and plasmin, on the NETome. Using high-resolution mass spectrometry, we identified a total of 164 proteins, including those previously not described in NETs. The serine proteases, particularly thrombin, were also found to interact with DNA and bound to NETs in vitro. Among the most abundant proteins were those identified previously, including histones, neutrophil elastase, and antimicrobial proteins. We observed reduced histone (H2B, H3, and H4) and neutrophil elastase levels upon the addition of the two proteases. Analyses of NET-derived tryptic peptides identified subtle changes upon protease treatments. Our results provide evidence that exogenous proteases, present during wounding and inflammation, influence the NETome. Taken together, regulation of NETs and their proteins under different physiological conditions may affect their roles in infection, inflammation, and the host response.

Entamoeba histolytica Induce Signaling via Raf/MEK/ERK for Neutrophil Extracellular Trap (NET) Formation

Amoebiasis, the disease caused by Entamoeba histolytica is the third leading cause of human deaths among parasite infections. E. histolytica was reported associated with around 100 million cases of amoebic dysentery, colitis and amoebic liver abscess that lead to almost 50,000 fatalities worldwide in 2010. E. histolytica infection is associated with the induction of inflammation characterized by a large number of infiltrating neutrophils. These neutrophils have been implicated in defense against this parasite, by mechanisms not completely described. The neutrophil antimicrobial mechanisms include phagocytosis, degranulation, and formation of neutrophil extracellular traps (NETs). Recently, our group reported that NETs are also produced in response to E. histolytica trophozoites. But, the mechanism for NETs induction remains unknown. In this report we explored the possibility that E. histolytica leads to NETs formation via a signaling pathway similar to the pathways activated by PMA or the Fc receptor FcγRIIIb. Neutrophils were stimulated by E. histolytica trophozoites and the effect of various pharmacological inhibitors on amoeba-induced NETs formation was assessed. Selective inhibitors of Raf, MEK, and NF-κB prevented E. histolytica-induced NET formation. In contrast, inhibitors of PKC, TAK1, and NADPH-oxidase did not block E. histolytica-induced NETs formation. E. histolytica induced phosphorylation of ERK in a Raf and MEK dependent manner. These data show that E. histolytica activates a signaling pathway to induce NETs formation, that involves Raf/MEK/ERK, but it is independent of PKC, TAK1, and reactive oxygen species (ROS). Thus, amoebas activate neutrophils via a different pathway from the pathways activated by PMA or the IgG receptor FcγRIIIb.

Recent advances in understanding the roles of blood platelets in the pathogenesis of allergic inflammation and bronchial asthma

Platelets play an essential role in hemostasis to minimize blood loss due to traumatic injury. In addition, they contain various immune-associated molecules and contribute to immunological barrier formation at sites of vascular injury, thereby protecting against invading pathogens. Platelets are also crucially involved in development of allergic diseases, including bronchial asthma. Platelets in asthmatics are more activated than those in healthy individuals. By using a murine asthma model, platelets were shown to be actively involved in progression of the disease, including in airway eosinophilia and airway remodeling. In the asthmatic airway, pathological microvascular angiogenesis, a component of airway remodeling, is commonly observed, and the degree of abnormality is significantly associated with disease severity. Therefore, in order to repair the newly formed and structurally fragile blood vessels under inflammatory conditions, platelets may be continuously activated in asthmatics. Importantly, platelets constitutively express IL-33 protein, an alarmin cytokine that is essential for development of bronchial asthma. Meanwhile, the concept of development of allergic diseases has recently changed dramatically, and allergy researchers now share a belief in the centrality of epithelial barrier functions. In particular, IL-33 released from epithelial barrier tissue at sites of eczema can activate the antigen-non-specific innate immune system as an alarmin that is believed to be necessary for subsequent antigen-specific acquired immunological responses. From this perspective, we propose in this review a possible mechanism for how activated platelets act as an alarmin in development of bronchial asthma.

2-Chlorofatty acids: lipid mediators of neutrophil extracellular trap formation

Neutrophils form neutrophil extracellular traps (NETs), which have been implicated in microcirculatory plugging. NET formation (NETosis) involves the fusion of granule and nuclear contents, which are then released in the extracellular space. Myeloperoxidase (MPO) plays a major role in NETosis leading to the dissociation of DNA from histones. During neutrophil activation, MPO is released and activated to convert hydrogen peroxide and chloride to hypochlorous acid (HOCl). HOCl targets plasmalogens leading to the production of the chlorinated lipids, 2-chlorofatty aldehyde and 2-chlorofatty acid (2-ClFA). Here, we tested the hypothesis that 2-ClFAs are important lipid mediators of NETosis. Human neutrophils treated with physiological levels of 2-ClFAs formed NETs, characterized by MPO association with DNA and neutrophil elastase (NE) redistribution to the perinuclear area. 2-ClFA-induced NETs reduced Escerichia coli colony forming units. 2-ClFA-induced NETosis is calcium- and protein arginine deiminase 4-dependent. Interestingly, unlike PMA, 2-ClFA initiates the NETosis process without neutrophil activation and degranulation. Furthermore, 2-ClFA elicits NETosis in bone-marrow derived neutrophils from MPO-deficient mice. Taken together, these findings suggest 2-ClFA as an MPO product that triggers the NETosis pathway following neutrophil activation.

The other myeloperoxidase: Emerging functions

Myeloperoxidase (MPO) is a member of the mammalian peroxidase family. It is mainly expressed in neutrophils, monocytes and macrophages. As a catalyzer of reactive oxidative species and radical species formation, it contributes to neutrophil bactericidal activity. Nevertheless MPO invalidation does not seem to have major health consequences in affected individuals. This suggests that MPO might have alternative functions supporting its conservation during evolution. We will review the available data supporting these non-canonical functions in terms of tissue specific expression, function and enzymatic activity. Thus, we discuss its cell type specific expression. We review in between others its roles in angiogenesis, endothelial (dys-) function, immune reaction, and inflammation. We summarize its pathological actions in clinical conditions such as cardiovascular disease and cancer.

Relative antibacterial functions of complement and NETs: NETs trap and complement effectively kills bacteria

Neutrophil extracellular traps (NETs) are web-like DNA structures released by activated neutrophils. These structures are decorated with antimicrobial proteins, and considered to trap and kill bacteria extracellularly. However, the exact functions of NETs remain elusive, and contradictory observations have been made with NETs functioning as an antimicrobial or a pathogentrapping mechanism. There is a disconnect in the interpretation of the involvement of other major immune mechanisms, such as the complement system, as effectors of the function of NETs. We have recently shown that NETs activate complement. In this study, we aimed to elucidate the relative antimicrobial roles of NETs in the absence and presence of complement. Using primary human neutrophils, human serum (normal, heat inactivated, and C5-depleted), P. aeruginosa (at multiplicity of infection, MOI, of 1 or 10), S. aureus (MOI of 1), colony-counting assays and confocal microscopy, we demonstrate that most bacteria trapped by NETs remain viable, indicating that NETs have limited bactericidal properties. By contrast, complement effectively killed bacteria, but NETs decreased the bactericidal ability of complement and degrading NETs by DNases restored complement-mediated killing. Experiments with conditions allowing for specific pathway activation showed that the complement classical and lectin, but not the alternative, pathway lead to bacterial killing. NETs under static conditions showed limited killing of bacteria while NETs under dynamic conditions showed enhanced bacteria trapping and reduced killing. Furthermore, NETs incubated with normal human serum depleted complement and reduced the hemolytic capacity of the serum. This report, for the first time, clarifies the relative bactericidal contributions of NETs and complement. We propose that - while NETs can ensnare bacteria such as P. aeruginosa - complement is necessary for efficient bacterial killing.

Quantification of NETs-associated markers by flow cytometry and serum assays in patients with thrombosis and sepsis

INTRODUCTION

Neutrophil extracellular traps (NETs) are networks of extracellular fibres produced from neutrophil DNA with a pathogenic role in infection, thrombosis and other conditions. Reliable assays for measuring NETs are desirable as novel treatments targeting NETs are being explored for the treatment of these conditions. We compare a whole blood flow cytometry method with serum assays to measure NETs-associated markers in patients with sepsis and thrombosis.

METHODS

Patients with deep venous thrombosis (n = 25), sepsis (n = 21) and healthy controls (n = 23) were included in the study. Neutrophil surface NETs markers were determined by flow cytometry on whole blood samples by gating of neutrophils stained for surface citrullinated histone (H3cit) and myeloperoxidase (MPO). Serum double-stranded (ds) DNA, MPO, myeloid-related protein, nucleosomes, DNAse, elastase, human high-mobility group box 1 and MPO-DNA complexes were quantified as circulating markers of NETs.

RESULTS

Neutrophil NETs markers by flow cytometry and serum NETs markers were significantly higher in patients with thrombosis and sepsis compared with healthy controls. Neutrophil NETs markers significantly correlated with the serum marker dsDNA.

CONCLUSION

Flow cytometry detection of neutrophil NETs markers is feasible in whole blood and correlates with serum markers of NETs. We propose the flow cytometry detection of MPO/H3cit positive neutrophils and serum dsDNA as simple methods to quantify cellular and extracellular NET markers in patients with thrombosis and sepsis.

Development and Application of High-Content Biological Screening for Modulators of NET Production

Neutrophil extracellular traps (NETs) are DNA-based antimicrobial web-like structures whose release is predominantly mediated by reactive oxygen species (ROS); their purpose is to combat infections. However, unbalanced NET production and clearance is involved in tissue injury, circulation of auto-antibodies and development of several chronic diseases. Currently, there is lack of agreement regarding the high-throughput methods available for NET investigation. This study, therefore, aimed to develop and optimize a high-content analysis (HCA) approach, which can be applied for the assay of NET production and for the screening of compounds involved in the modulation of NET release. A suitable paraformaldehyde fixation protocol was established to enable HCA of neutrophils and NETs. Bespoke and in-built bioinformatics algorithms were validated by comparison with standard low-throughput approaches for application in HCA of NETs. Subsequently, the optimized protocol was applied to high-content screening (HCS) of a pharmaceutically derived compound library to identify modulators of NETosis. Of 56 compounds assessed, 8 were identified from HCS for further characterization of their effects on NET formation as being either inducers, inhibitors or biphasic modulators. The effects of these compounds on naïve neutrophils were evaluated by using specific assays for the induction of ROS and NET production, while their modulatory activity was validated in phorbol 12-myristate 13-acetate-stimulated neutrophils. Results indicated the involvement of glutathione reductase, Src family kinases, molecular-target-of-Rapamycin, and mitogen-activated-protein-kinase pathways in NET release. The compounds and pathways identified may provide targets for novel therapeutic approaches for treating NET-associated pathologies.

A Novel Biological Role for Peptidyl-Arginine Deiminases: Citrullination of Cathelicidin LL-37 Controls the Immunostimulatory Potential of Cell-Free DNA

LL-37, the only human cathelicidin that is released during inflammation, is a potent regulator of immune responses by facilitating delivery of oligonucleotides to intracellular TLR-9, thereby enhancing the response of human plasmacytoid dendritic cells (pDCs) to extracellular DNA. Although important for pathogen recognition, this mechanism may facilitate development of autoimmune diseases. In this article, we show that citrullination of LL-37 by peptidyl-arginine deiminases (PADs) hindered peptide-dependent DNA uptake and sensing by pDCs. In contrast, carbamylation of the peptide (homocitrullination of Lys residues) had no effect. The efficiency of LL-37 binding to oligonucleotides and activation of pDCs was found to be inversely proportional to the number of citrullinated residues in the peptide. Similarly, preincubation of carbamylated LL-37 with PAD2 abrogated the peptide's ability to bind DNA. Conversely, LL-37 with Arg residues substituted by homoarginine, which cannot be deiminated, elicited full activity of native LL-37 regardless of PAD2 treatment. Taken together, the data showed that citrullination abolished LL-37 ability to bind DNA and altered the immunomodulatory function of the peptide. Both activities were dependent on the proper distribution of guanidinium side chains in the native peptide sequence. Moreover, our data suggest that cathelicidin/LL-37 is citrullinated by PADs during NET formation, thus affecting the inflammatory potential of NETs. Together this may represent a novel mechanism for preventing the breakdown of immunotolerance, which is dependent on the response of APCs to self-molecules (including cell-free DNA); overactivation may facilitate development of autoimmunity.

Graphene oxide is degraded by neutrophils and the degradation products are non-genotoxic

Neutrophils were previously shown to digest oxidized carbon nanotubes through a myeloperoxidase (MPO)-dependent mechanism, and graphene oxide (GO) was found to undergo degradation when incubated with purified MPO, but there are no studies to date showing degradation of GO by neutrophils. Here we produced endotoxin-free GO by a modified Hummers' method and asked whether primary human neutrophils stimulated to produce neutrophil extracellular traps or activated to undergo degranulation are capable of digesting GO. Biodegradation was assessed using a range of techniques including Raman spectroscopy, transmission electron microscopy, atomic force microscopy, and mass spectrometry. GO sheets of differing lateral dimensions were effectively degraded by neutrophils. As the degradation products could have toxicological implications, we also evaluated the impact of degraded GO on the bronchial epithelial cell line BEAS-2B. MPO-degraded GO was found to be non-cytotoxic and did not elicit any DNA damage. Taken together, these studies have shown that neutrophils can digest GO and that the biodegraded GO is non-toxic for human lung cells.

Nanoparticle effect on neutrophil produced myeloperoxidase

Nanoparticles affect the immune system as they may interact directly with immune cells and activate them. However, it is possible that nanoparticles also interact with released cytokines and immunologically active enzymes. To test this hypothesis, the activity of myeloperoxidase released from activated neutrophils was measured in the presence of nanoparticles with different chemistry and size. In high concentrations of nanoparticles, myeloperoxidase activity is decreased whereas in low concentrations of nanoparticles the activity is increased. The effect of the nanoparticles on myeloperoxidase is dependent on the total protein concentration as low concentrations of bovine serum albumin together with nanoparticles further increase the myeloperoxidase activity. The results herein show that nanoparticles affect the immune response not only at the cellular level but also on released immune effectors. In particular, they show that the nanoparticle effect on myeloperoxidase activity in the neutrophil degranulation environment is the result of an intricate interplay between the enzyme and protein concentrations in the environment and the available surface area on the nanoparticle.

Measuring Neutrophil Bactericidal Activity

The best-known role of neutrophils is control of pathogen growth. Neutrophils contain and kill pathogens through a variety of antimicrobial activities. Regardless of the mechanism, the ability to kill pathogens is a vital outcome. This chapter describes a method to measure the in vitro bactericidal activity of isolated neutrophils as the endpoint of converging innate immune functions.

Neutrophils and PMN-MDSC: Their biological role and interaction with stromal cells

Neutrophils and polymorphonucler myeloid-derived suppressor cells (PMN-MDSC) share origin and many morphological and phenotypic features. However, they have different biological role. Neutrophils are one of the major mechanisms of protection against invading pathogens, whereas PMN-MDSC have immune suppressive activity and restrict immune responses in cancer, chronic infectious disease, trauma, sepsis, and many other pathological conditions. Although in healthy adult individuals, PMN-MDSC are not or barely detectable, in patients with cancer and many other diseases they accumulate at various degree and co-exist with neutrophils. Recent advances allow for better distinction of these cells and better understanding of their biological role. Accumulating evidence indicates PMN-MDSC as pathologically activated neutrophils, with important role in regulation of immune responses. In this review, we provide an overview on the definition and characterization of PMN-MDSC and neutrophils, their pathological significance in a variety of diseases, and their interaction with other stromal components.

Evidence for multiple modes of neutrophil serine protease recognition by the EAP family of Staphylococcal innate immune evasion proteins

Neutrophils contain high levels of chymotrypsin-like serine proteases (NSPs) within their azurophilic granules that have a multitude of functions within the immune system. In response, the pathogen Staphylococcus aureus has evolved three potent inhibitors (Eap, EapH1, and EapH2) that protect the bacterium as well as several of its secreted virulence factors from the degradative action of NSPs. We previously showed that these so-called EAP domain proteins represent a novel class of NSP inhibitors characterized by a non-covalent inhibitory mechanism and a distinct target specificity profile. Based upon high levels of structural homology amongst the EAP proteins and the NSPs, as well as supporting biochemical data, we predicted that the inhibited complex would be similar for all EAP/NSP pairs. However, we present here evidence that EapH1 and EapH2 bind the canonical NSP, Neutrophil Elastase (NE), in distinct orientations. We discovered that alteration of EapH1 residues at the EapH1/NE interface caused a dramatic loss of affinity and inhibition of NE, while mutation of equivalent positions in EapH2 had no effect on NE binding or inhibition. Surprisingly, mutation of residues in an altogether different region of EapH2 severely impacted both the NE binding and inhibitory properties of EapH2. Even though EapH1 and EapH2 bind and inhibit NE and a second NSP, Cathepsin G, equally well, neither of these proteins interacts with the structurally related, but non-proteolytic granule protein, azurocidin. These studies expand our understanding of EAP/NSP interactions and suggest that members of this immune evasion protein family are capable of diverse target recognition modes.

Vitamin C and Immune Function

Vitamin C is an essential micronutrient for humans, with pleiotropic functions related to its ability to donate electrons. It is a potent antioxidant and a cofactor for a family of biosynthetic and gene regulatory enzymes. Vitamin C contributes to immune defense by supporting various cellular functions of both the innate and adaptive immune system. Vitamin C supports epithelial barrier function against pathogens and promotes the oxidant scavenging activity of the skin, thereby potentially protecting against environmental oxidative stress. Vitamin C accumulates in phagocytic cells, such as neutrophils, and can enhance chemotaxis, phagocytosis, generation of reactive oxygen species, and ultimately microbial killing. It is also needed for apoptosis and clearance of the spent neutrophils from sites of infection by macrophages, thereby decreasing necrosis/NETosis and potential tissue damage. The role of vitamin C in lymphocytes is less clear, but it has been shown to enhance differentiation and proliferation of B- and T-cells, likely due to its gene regulating effects. Vitamin C deficiency results in impaired immunity and higher susceptibility to infections. In turn, infections significantly impact on vitamin C levels due to enhanced inflammation and metabolic requirements. Furthermore, supplementation with vitamin C appears to be able to both prevent and treat respiratory and systemic infections. Prophylactic prevention of infection requires dietary vitamin C intakes that provide at least adequate, if not saturating plasma levels (i.e., 100–200 mg/day), which optimize cell and tissue levels. In contrast, treatment of established infections requires significantly higher (gram) doses of the vitamin to compensate for the increased inflammatory response and metabolic demand.

Reactive nitrogen species (RNS)-resistant microbes: adaptation and medical implications

Nitrosative stress results from an increase in reactive nitrogen species (RNS) within the cell. Though the RNS - nitric oxide (·NO) and peroxynitrite (ONOO-) - play pivotal physiological roles, at elevated concentrations, these moieties can be poisonous to both prokaryotic and eukaryotic cells alike due to their capacity to disrupt a variety of essential biological processes. Numerous microbes are known to adapt to nitrosative stress by elaborating intricate strategies aimed at neutralizing RNS. In this review, we will discuss both the enzymatic systems dedicated to the elimination of RNS as well as the metabolic networks that are tailored to generate RNS-detoxifying metabolites - α-keto-acids. The latter has been demonstrated to nullify RNS via non-enzymatic decarboxylation resulting in the production of a carboxylic acid, many of which are potent signaling molecules. Furthermore, as aerobic energy production is severely impeded during nitrosative stress, alternative ATP-generating modules will be explored. To that end, a holistic understanding of the molecular adaptation to nitrosative stress, reinforces the notion that neutralization of toxicants necessitates significant metabolic reconfiguration to facilitate cell survival. As the alarming rise in antimicrobial resistant pathogens continues unabated, this review will also discuss the potential for developing therapies that target the alternative ATP-generating machinery of bacteria.

Redox Regulation of Inflammatory Processes Is Enzymatically Controlled

Redox regulation depends on the enzymatically controlled production and decay of redox active molecules. NADPH oxidases, superoxide dismutases, nitric oxide synthases, and others produce the redox active molecules superoxide, hydrogen peroxide, nitric oxide, and hydrogen sulfide. These react with target proteins inducing spatiotemporal modifications of cysteine residues within different signaling cascades. Thioredoxin family proteins are key regulators of the redox state of proteins. They regulate the formation and removal of oxidative modifications by specific thiol reduction and oxidation. All of these redox enzymes affect inflammatory processes and the innate and adaptive immune response. Interestingly, this regulation involves different mechanisms in different biological compartments and specialized cell types. The localization and activity of distinct proteins including, for instance, the transcription factor NFκB and the immune mediator HMGB1 are redox-regulated. The transmembrane protein ADAM17 releases proinflammatory mediators, such as TNFα, and is itself regulated by a thiol switch. Moreover, extracellular redox enzymes were shown to modulate the activity and migration behavior of various types of immune cells by acting as cytokines and/or chemokines. Within this review article, we will address the concept of redox signaling and the functions of both redox enzymes and redox active molecules in innate and adaptive immune responses.

Mechanism of Development of Atherosclerosis and Cardiovascular Disease in Diabetes Mellitus

Diabetic macroangiopathy, atherosclerosis secondary to diabetes mellitus (DM), causes cerebro-cardiovascular diseases, which are major causes of death in patients with DM and significantly reduce their quality of life. The alterations in vascular homeostasis due to endothelial and vascular smooth muscle cell dysfunction are the main features of diabetic macroangiopathy. Although multiple metabolic abnormalities that characterize diabetes are involved in the progression of atherosclerosis in patients with DM, it may be said that prolonged exposure to hyperglycemia and insulin resistance clustering with other risk factors such as obesity, arterial hypertension, and dyslipidemia play crucial roles. Laboratory and clinical researches in the past decades have revealed that major biochemical pathways involved in the development of diabetic macroangiopathy are as follows: overproduction of reactive oxygen species, increased formation of advanced glycation end-products (AGEs) and activation of the AGEs-receptor for AGE axis, polyol and hexosamine flux, protein kinase C activation, and chronic vascular inflammation. Among them, oxidative stress is considered to be a key factor.

Molecular analyses on Neospora caninum-triggered NETosis in the caprine system

Neospora caninum is an obligate intracellular protozoan parasite causing serious reproductive disorders in large and small ruminants worldwide. Polymorphonuclear neutrophils (PMN) react against multiple invading pathogens through different mechanisms including the release of neutrophil extracellular traps (NETs). Here, in vitro interactions of caprine PMN and N. caninum tachyzoites were studied. Scanning electron microscopic- and immunofluorescence-analyses demonstrated that caprine PMN undergo NETosis upon contact with tachyzoites of N. caninum, extruding filaments that entrap parasites. Detailed co-localization studies of N. caninum tachyzoite-induced NETs revealed the presence of PMN-derived DNA being decorated with histones (H1, H2A/H2B, H3,H4) and neutrophil elastase (NE) corroborating the molecular characteristics of classical mammalian NETs. As a new result for parasite-induced NETosis, we identified pentraxin and cathepsin B in N. caninum-triggered NETs. Nonetheless, functional inhibition assays revealed that during caprine NET formation triggered by N. caninum different molecular signaling pathways are induced, when compared to other apicomplexan parasites or host species. As such, N. caninum-induced NETosis appears to be influenced by MPO but independent of NADPH oxidase, SOCE, ERK1/2 and p38 MAPK activities. Furthermore, the inhibition of PMN autophagy via blockage of the PI3K-mediated signaling pathway failed to influence tachyzoite-induced NETosis. Since N. caninum-tachyzoites induced caprine NETosis, this effector mechanism should be considered as an early host immune response during acute caprine neosporosis.

Shedding of Syndecan-1/CXCL1 Complexes by Matrix Metalloproteinase 7 Functions as an Epithelial Checkpoint of Neutrophil Activation

Although neutrophils play critical roles in innate immunity, in excess these cells cause severe tissue damage. Thus, neutrophil activation must be tightly regulated to prevent indiscriminant damage. Previously, we reported that mice lacking matrix metalloproteinase (MMP) 7 are protected from lung injury owing to markedly impaired neutrophil movement from the interstitium into mucosal lumenal spaces. This phenotype resulted from a lack of MMP7 shedding of syndecan-1, a heparan sulfate proteoglycan that carries the neutrophil chemokine CXCL1 as cargo. Here, we assessed if shedding syndecan-1/CXCL1 complexes affects neutrophil activation. Whereas injured monolayers of wild-type alveolar type II cells potently stimulated neutrophil activation, as gauged by release of myeloperoxidase, cells from Mmp7(-/-) or syndecan-1-null (Sdc1(-/-)) mice or human cells with MMP7 knockdown did not. In vivo, we observed reduced myeloperoxidase release relative to neutrophil numbers in bleomycin-injured Mmp7(-/-) and Sdc1(-/-) mice. Furthermore, we determined that soluble syndecan-1 directly stimulated neutrophil activation in the absence of cellular damage. These data indicate that MMP7 shedding of syndecan-1/CXCL1 complexes functions as a checkpoint that restricts neutrophil activation at sites of epithelial injury.

Oxygen atoms are critical in rendering THP-1 leukaemia cells susceptible to cold physical plasma-induced apoptosis

Cold physical plasma has been suggested as a powerful new tool in oncology. However, some cancer cells such as THP-1 leukaemia cells have been shown to be resistant towards plasma-induced cell death, thereby serving as a good model for optimizing plasmas in order to foster pro-apoptotic anticancer effects. A helium/oxygen radio frequency driven atmospheric plasma profoundly induced apoptosis in THP-1 cells whereas helium, humidified helium, and humidified helium/oxygen plasmas were inefficient. Hydrogen peroxide – previously shown as central plasma-derived agent – did not participate in the killing reaction but our results suggest hypochlorous acid to be responsible for the effect observed. Proteomic analysis of THP-1 cells exposed to He/O₂ plasma emphasized a prominent growth retardation, cell stress, apoptosis, and a pro-immunogenic profile. Altogether, a plasma setting that inactivates previously unresponsive leukaemia cells is presented. Crucial reactive species in the plasma and liquid environment were identified and discussed, deciphering the complexity of plasma from the gas phase into the liquid down to the cellular response mechanism. These results may help tailoring plasmas for clinical applications such as oxidation-insensitive types of cancer.

Bovine Polymorphonuclear Neutrophils Cast Neutrophil Extracellular Traps against the Abortive Parasite Neospora caninum

Neospora caninum represents a relevant apicomplexan parasite causing severe reproductive disorders in cattle worldwide. Neutrophil extracellular trap (NET) generation was recently described as an efficient defense mechanism of polymorphonuclear neutrophils (PMN) acting against different parasites. In vitro interactions of bovine PMN with N. caninum were analyzed at different ratios and time spans. Extracellular DNA staining was used to illustrate the typical molecules of NETs [i.e., histones (H3), neutrophil elastase (NE), myeloperoxidase (MPO), pentraxin] via antibody-based immunofluorescence analyses. Functional inhibitor treatments were applied to reveal the role of several enzymes [NADPH oxidase (NOX), NE, MPO, PAD4], ATP-dependent P2Y2 receptor, store-operated Ca⁺⁺entry (SOCE), CD11b receptor, ERK1/2- and p38 MAPK-mediated signaling pathway in tachyzoite-triggered NETosis. N. caninum tachyzoites triggered NETosis in a time- and dose-dependent manner. Scanning electron microscopy analyses revealed NET structures being released by bovine PMN and entrapping tachyzoites. N. caninum-induced NET formation was found not to be NOX-, NE-, MPO-, PAD4-, ERK1/2-, and p38 MAP kinase-dependent process since inhibition of these enzymes led to a slight decrease of NET formation. CD11b was also identified as a neutrophil receptor being involved in NETosis. Furthermore, N. caninum-triggered NETosis depends on Ca⁺⁺ influx as well as neutrophil metabolism since both the inhibition of SOCE and of P2Y2-mediated ATP uptake diminished NET formation. Host cell invasion assays indicated that PMN-derived NETosis hampered tachyzoites from active host cell invasion, thereby inhibiting further intracellular replication. NET formation represents an early and effective mechanism of response of the innate immune system, which might reduce initial infection rates during the acute phase of cattle neosporosis.

In vitro induction of NETosis: Comprehensive live imaging comparison and systematic review

BACKGROUND

Multiple inducers of in vitro Neutrophil Extracellular Trap (NET) formation (NETosis) have been described. Since there is much variation in study design and results, our aim was to create a systematic review of NETosis inducers and perform a standardized in vitro study of NETosis inducers important in (cardiac) wound healing.

METHODS

In vitro NETosis was studied by incubating neutrophils with PMA, living and dead bacteria (S. aureus and E. coli), LPS, (activated) platelets (supernatant), glucose and calcium ionophore Ionomycin using 3-hour periods of time-lapse confocal imaging.

RESULTS

PMA is a consistent and potent inducer of NETosis. Ionomycin also consistently resulted in extrusion of DNA, albeit with a process that differs from the NETosis process induced by PMA. In our standardized experiments, living bacteria were also potent inducers of NETosis, but dead bacteria, LPS, (activated) platelets (supernatant) and glucose did not induce NETosis.

CONCLUSION

Our systematic review confirms that there is much variation in study design and results of NETosis induction. Our experimental results confirm that under standardized conditions, PMA, living bacteria and Ionomycin all strongly induce NETosis, but real-time confocal imaging reveal different courses of events.

LL37:DNA complexes provide antimicrobial activity against intracellular bacteria in human macrophages

As part of the innate host response neutrophils release neutrophil extracellular traps (NETs), protein:DNA complexes that contain a number of antimicrobial peptides (AMPs), such as cathelicidin. Human cathelicidin in its active form, LL37, has potent antimicrobial activity against bacteria. However, whether LL37 derived from NETs contributes to antimicrobial activity against intracellular pathogens remains unclear. Here, we report that NETs induced by mycobacteria contain cathelicidin. Human macrophages internalized NET-bound cathelicidin, which is transported to lysosomal compartments. Furthermore, using a model of in vitro-generated LL37:DNA complexes we found that LL37 derived from such complexes attacks mycobacteria in macrophage phagolysosomes resulting in antimicrobial activity. Taken together, our results suggest a mechanism by which LL37 in complex with DNA contributes to host defence against intracellular bacteria in human macrophages.

Hypercoagulability in patients with Cushing disease detected by thrombin generation assay is associated with increased levels of neutrophil extracellular trap-related factors

Patients with Cushing disease (CD) are at increased risk of venous thromboembolism (VTE). It was surmised, but not conclusively shown that the risk is related to plasma hypercoagulability secondary to the glucocorticoids effect. This study is aimed at detecting hypercoagulability in patients with CD. Case-control study of 48 CD patients and controls enrolled at two Italian clinics for whom we assessed the thrombin-forming-potential in the presence of optimal activation of protein C obtained by adding into the assay system its main endothelial activator, thrombomodulin. These experimental conditions mimic more closely than any other test the in vivo situation. We observed enhanced thrombin-generation in CD patients, as shown by the modification of thrombin-generation parameters [i.e., shortened lag-time and time-to-peak, increased thrombin peak and endogenous thrombin potential (ETP)]. Moreover, the ETP ratio (with/without thrombomodulin), recognized as an index of hypercoagulability, was increased in patients as compared to controls. We attempted to explain such hypercoagulability by measuring both procoagulant and anticoagulant factors, and some other non-coagulation parameters (i.e., neutrophil extracellular traps (NET), recently associated with the VTE risk and/or increased hypercoagulability. We showed that the hypercoagulability in patients with CD is associated with increased levels of factor VIII and NET-related variables. We detected plasma hypercoagulability in patients with CD and found experimental explanation for its occurrence. Whether this hypercoagulability can entirely explain the occurrence of VTE in patients with CD should be investigated by ad-hoc clinical trials. However, until these studies will be available the evidence supports the concept that patients with CD are candidates for antithrombotic prophylaxis.

In vitro and in vivo generation of heterophil extracellular traps after Salmonella exposure

The release of extracellular traps (ETs) by granulocytes is a unique strategy to stop the dissemination of microbial pathogens. This study was undertaken to elucidate the potential of avian granulocytes (heterophils) to form ETs that can arrest and kill Salmonella organisms. After in vitro exposure of isolated heterophils and in vivo infection of day-old chicks with Salmonella enterica subsp. enterica serovars Infantis (SI) or Enteritidis (SE), the generation of ETs as well as the trapping and survivability of Salmonella organisms in the ET meshwork were determined by means of microscopy and spectrophotometry. In vitro, heterophils were able to form ETs within 15min after SE and SI inoculation. At 120min and with a multiplicity of infection of 1 and 5, SI induced significantly more ETs and DNA release than SE. Both SE and SI were found to be associated with the ET structures. Live-dead staining showed most of the microorganisms within the extracellular scaffold alive. In vivo, heterophils were detected in cecal lumen of SE-, but not SI-infected chicks. In cecum of the SE-exposed chicks, ET formations were scarcely detected whereas intact heterophils with phagocytosed bacteria were frequently found. The results evidence the capability of heterophils to generate ETs after SE and SI exposure in vitro. However, an infection of chicks with Salmonella did not significantly induce the formation of ET structures in cecum. Thus, the process to form ETs (ETosis) seems not to be of special relevance for Salmonella defense within the cecal lumen of young chicks.

Parecoxib reduced ventilation induced lung injury in acute respiratory distress syndrome

Background

Cyclooxygenase-2 (COX-2) contributes to ventilation induced lung injury (VILI) and acute respiratory distress syndrome (ARDS). The objective of present study was to observe the therapeutic effect of parecoxib on VILI in ARDS.

Methods

In this parallel controlled study performed at Harbin Medical University, China between January 2016 and March 2016, 24 rats were randomly allocated into sham group (S), volume ventilation group/ARDS (VA), parecoxib/volume ventilation group/ARDS (PVA). Rats in the S group only received anesthesia; rats in the VA and PVA group received intravenous injection of endotoxin to induce ARDS, and then received ventilation. Rats in the VA and PVA groups were treated with intravenous injection of saline or parecoxib. The ratio of arterial oxygen pressure to fractional inspired oxygen (PaO₂/FiO₂), the wet to dry weight ratio of lung tissue, inflammatory factors in serum and bronchoalveolar lavage fluid (BALF), and histopathologic analyses of lung tissue were examined. In addition, survival was calculated at 24 h after VILI.

Results

Compared to the VA group, in the PVA group, PaO₂/FiO₂ was significantly increased; lung tissue wet to dry weight ratio; macrophage and neutrophil counts, total protein and neutrophil elastase levels in BALF; tumor necrosis factor-α, interleukin-1β, and prostaglandin E₂ levels in BALF and serum; and myeloperoxidase (MPO) activity, malondialdehyde levels, and Bax and COX-2 protein levels in lung tissue were significantly decreased, while Bcl-2 protein levels were significantly increased. Lung histopathogical changes and apoptosis were reduced by parecpxib in the PVA group. Survival was increased in the PVA group.

Conclusions

Parecoxib improves gas exchange and epithelial permeability, decreases edema, reduces local and systemic inflammation, ameliorates lung injury and apoptosis, and increases survival in a rat model of VILI.

Interactions between Neutrophils and Pseudomonas aeruginosa in Cystic Fibrosis

Cystic fibrosis (CF) affects 70,000 patients worldwide. Morbidity and mortality in CF is largely caused by lung complications due to the triad of impaired mucociliary clearance, microbial infections and chronic inflammation. Cystic fibrosis airway inflammation is mediated by robust infiltration of polymorphonuclear neutrophil granulocytes (PMNs, neutrophils). Neutrophils are not capable of clearing lung infections and contribute to tissue damage by releasing their dangerous cargo. Pseudomonas aeruginosa is an opportunistic pathogen causing infections in immunocompromised individuals. P. aeruginosa is a main respiratory pathogen in CF infecting most patients. Although PMNs are key to attack and clear P. aeruginosa in immunocompetent individuals, PMNs fail to do so in CF. Understanding why neutrophils cannot clear P. aeruginosa in CF is essential to design novel therapies. This review provides an overview of the antimicrobial mechanisms by which PMNs attack and eliminate P. aeruginosa. It also summarizes current advances in our understanding of why PMNs are incapable of clearing P. aeruginosa and how this bacterium adapts to and resists PMN-mediated killing in the airways of CF patients chronically infected with P. aeruginosa.