Neutrophil Extracellular Traps Induction Research Articles

Targeting Neutrophil Extracellular Trap Formation: Exploring Promising Pharmacological Strategies for the Treatment of Preeclampsia

Neutrophils, which constitute the most abundant leukocytes in human blood, emerge as crucial players in the induction of endothelial cell death and the modulation of endothelial cell responses under both physiological and pathological conditions. The hallmark of preeclampsia is endothelial dysfunction induced by systemic inflammation, in which neutrophils, particularly through the formation of neutrophil extracellular traps (NETs), play a pivotal role in the development and perpetuation of endothelial dysfunction and the hypertensive state. Considering the potential of numerous pharmaceutical agents to attenuate NET formation (NETosis) in preeclampsia, a comprehensive assessment of the extensively studied candidates becomes imperative. This review aims to identify mechanisms associated with the induction and negative regulation of NETs in the context of preeclampsia. We discuss potential drugs to modulate NETosis, such as NF-κβ inhibitors, vitamin D, and aspirin, and their association with mutagenicity and genotoxicity. Strong evidence supports the notion that molecules involved in the activation of NETs could serve as promising targets for the treatment of preeclampsia.

Abstract 5329: Ovarian cancer predisposes neutrophils to form neutrophil extracellular traps(NETs)

Abstract Objective: Neutrophil extracellular trap (NETs) are neutrophil-derived extracellular DNA released in response to inflammation. In contrast to their primary host-defensive role, NETs have been recently reported to promote cancer progression. The aim of this study is to investigate the role of NETs in ovarian cancer progression. Method: The clinical data of ovarian cancer patients who underwent primary surgery at Osaka University Medical Hospital were retrospectively reviewed (n=340). The relationship between neutrophilia, peritoneal dissemination and prognosis were analyzed. Prior to initial treatment, peripheral blood was obtained from newly diagnosed ovarian cancer patients and examined for CBC and granulocyte-colony stimulating factor (G-CSF) concentration by ELISA. To evaluate NETs formation capacity, isolated neutrophils were stimulated with G-CSF and incubated in vitro to monitor NETs formation. The ascites was collected at the initial surgery and assessed for G-CSF concentration and for neutrophils population using flow cytometry. The omental tissues were pathologically examined for NETs using H&E-staining and immunostaining with anti-Citrullinated Histon3 (CitH3) antibody. To test NETs induction capacity, we treated human peripheral blood neutrophils with the conditioned media from 20 ovarian cancer cell lines and the serum from ovarian cancer patients. Then human ovarian cancer OVCAR8 cells were co-cultured with NETs to evaluate the effect of NETs on cancer cell adhesion. Results: Neutrophilia (neutrophils>7000/µl) was found in 39 patients (39/340,11.5%). Patients with neutrophilia were associated with advanced disease accompanied by peritoneal dissemination and compromised survival compared to patients without neutrophilia (5-year PFS 40.0 vs 59.9 %, p 0.0027). In these patients, serum G-CSF was upregulated. Neutrophils from ovarian cancer patients formed NETs significantly earlier than those from benign tumor patients. Ovarian cancer patients with neutrophilia showed elevated G-CSF concentration and increased neutrophils proportion in their ascites. Omental tissues from patients with neutrophilia showed NETs foci close to the disseminated lesions. G-CSF strongly induced neutrophils to form NETs in vitro, which was observed in some conditioned media from ovarian cancer cell lines and serum from ovarian cancer patients as well. The adhesion of ovarian cancer cell was increased by co-incubation with NETs. Conclusion: Neutrophilia is associated with peritoneal dissemination and poor prognosis in ovarian cancer. One of the underlying mechanism of neutrophilia is upregulated G-CSF, which stimulate neutrophils to form NETs. NETs may have a causative effect on ovarian cancer dissemination. Citation Format: Gaku Yamamoto, Mahiru Kawano, Michiko Bun, Koutaro Shimura, Aska Toda, Koji Nakamura, Yasuto Kinose, Michiko Kodama, Kae Hashimoto, Kenjiro Sawada, Tadashi Kimura. Ovarian cancer predisposes neutrophils to form neutrophil extracellular traps(NETs) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5329.

249. SARS-CoV-2 Spike Immune Complexes Induce NETosis in COVID-19

Abstract Background Disease severity in SARS-CoV-2 infection is associated with elevated levels of neutrophil extracellular traps (NETs) and antibodies. We previously demonstrated that plasma from patients with SARS-CoV-2 infection stimulates the release of NETs by healthy donor neutrophils and that this can be reversed by R406, a spleen tyrosine kinase (SYK) inhibitor. Immune complexes, stimulating through Fc receptors, induce robust NETosis through a SYK-mediated pathway. Therefore, we hypothesized that SARS-CoV-2 spike immune complexes can mediate the release of NETs from neutrophils and that this process can be reversed by R406. Methods To test this, we created spike specific immune complexes utilizing an optimized concentration of affixed spike-trimer and SARS-CoV-2 patient plasma and evaluated the ability of these complexes to stimulate NETosis from healthy neutrophils. We quantified both IgG and IgA spike specific immune complex formation by ELISA utilizing HRP conjugated secondary antibodies (Promega Glomax Plate Reader). Healthy donor neutrophils were isolated, added to wells containing the spike immune complexes with and without R406, and live cell imaging (Incucyte S3) was used to visualize and quantify NETs. Results Incubation of COVID-19 patient plasma with spike protein resulted in an average 7-fold and 9-fold increase in the formation of IgA and IgG spike specific immune complexes, respectively, compared to spike alone (Figure 1A). After stimulating healthy donor neutrophils with the spike immune complexes created from six SARS-CoV-2 patient plasma samples, we observed a mean 200% increase in the induction of NETs relative to spike alone (Figure 1B). There were positive correlations between immune complexes formation and NETs formed in cells exposed to those wells (IgA R2= 0.67, p=0.01 and IgG R2= 0.82, p=0.002). Preliminary data suggests that spike-immune complex NET formation can be reduced by R406 (n=3 COVID-19 plasma donors). Figure 1A-B A) Quantification of IgA and IgG spike immune complexes was measured through measurement of absorbance at 405 nm after exposure to ABTS for 15 minutes. Value normalized to the spike alone condition ran on each day, and data represents a fold change from that condition (Ordinary One-way ANOVA: ** indicates p < 0.01; *** indicates p < 0.001; **** indicates p <0.0001). B) Induction of NETs 6 hours after exposure, demonstrating percent increase in NETosis in plasma isolated from COVID-19 patients (n=6) and healthy patients (n=2) in the presence and absence of SARS-CoV-2 spike immune complexes. Area of NETs was quantified by calculating the area (µm2 ) of ecDNA, visualized by Incucyte® Cytotox Green Dye. Area of NETs at T0 was subtracted from all conditions, and the induction of NETs was calculated as percentage increase relative to NETosis induced by SARS-CoV spike alone condition run on each day (Ordinary One-way ANOVA: ** indicates p < 0.01; *** indicates p < 0.001; **** indicates p <0.0001). Conclusion Using our ELISA, we demonstrated that we can reliably generate spike-specific IgG and IgA immune complexes. Stimulation of healthy donor neutrophils by spike immune complexes increased NET-formation compared to spike alone providing evidence of immune complex mediated NET induction in SARS-CoV-2 infection. Disclosures All Authors: No reported disclosures

Neutrophil extracellular trap induction through peptidylarginine deiminase 4 activity is involved in 2,4,6-trinitrobenzenesulfonic acid-induced colitis.

Neutrophil extracellular traps (NETs) are induced in the innate immune response against infectious agents and are also implicated in the pathogenesis of various cancers and autoimmune diseases. Peptidylarginine deiminase 4 (PAD4), an enzyme that converts arginine to citrulline, is also involved in NET formation. In this study, we investigated the pathogenic effect of PAD4 on NETs in inflammatory bowel disease using a trinitrobenzene sulfonic acid (TNBS)-induced murine colitis model. PAD4-deficient (PAD4KO) mice were generated by CRISPR-Cas9-mediated genomic editing. NETs were triggered in peritoneal neutrophils obtained from wild-type mice by A23187 (a calcium ionophore), but these responses were completely abolished in the PAD4KO mice. Experimental colitis was induced in wild-type and PAD4KO mice via an intrarectal injection of TNBS. TNBS injection resulted in body weight loss, extensive colonic erosion, and ulceration in wildtype mice. However, these responses were significantly attenuated following the administration of Cl-amidine (an inhibitor of pan-PADs) and DNase I (an inhibitor of NET formation), in combination with PAD4KO in mice. TNBS-induced increases in myeloperoxidase activity, inflammatory cytokine expression, and NET formation in the colon were significantly reduced following the administration of Cl-amidine, DNase I injection, and PAD4KO. These findings suggest that NET formation contributes to the pathogenesis of TNBS-induced colitis via PAD4. Thus, PAD4 is a promising target for the treatment of inflammatory bowel disease.

Role and Therapeutic Targeting Strategies of Neutrophil Extracellular Traps in Inflammation.

Neutrophil extracellular traps (NETs) are large DNA reticular structures secreted by neutrophils and decorated with histones and antimicrobial proteins. As a key mechanism for neutrophils to resist microbial invasion, NETs play an important role in the killing of microorganisms (bacteria, fungi, and viruses). Although NETs are mostly known for mediating microbial killing, increasing evidence suggests that excessive NETs induced by stimulation of physical and chemical components, microorganisms, and pathological factors can exacerbate inflammation and organ damage. This review summarizes the induction and role of NETs in inflammation and focuses on the strategies of inhibiting NETosis and the mechanisms involved in pathogen evasion of NETs. Furthermore, herbal medicine inhibitors and nanodelivery strategies improve the efficiency of inhibition of excessive levels of NETs.

In vitro induction of neutrophil extracellular traps by SARS-CoV-2 is biased by extracellular mitochondria

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has a highly variable course that is dependent on the host immune system reaction. Lung tissue damage, endothelial dysfunction, and microthrombosis in severe COVID-19 is linked to neutrophilia and the production of neutrophil extracellular traps (NETs). Previous studies have shown that NETs are involved in the pathology of COVID-19 and that the virus itself induces NET formation, although the underlying mechanisms are not clear. In this study, we aimed to investigate the induction of NETs by SARS-CoV-2 in vitro. We have found that both, infectious and heat-inactivated virus induce NETs formation. Surprisingly, cell culture media derived from uninfected Vero cells exhibit similar potency. This suggests that NET inducers other than the virus might be involved. Mitochondria released from dying cells during SARS-CoV-2 infection acting as damage-associated molecular patterns (DAMPs) were identified as potential contributors to neutrophil activation and NET formation. Our findings point to an important source of bias when analyzing NETs induction by SARS-CoV-2 in vitro, but also the immune reaction to viruses in general. Further implications for the understanding of COVID-19 pathogenesis remain to be elucidated.

Mitochondria-induced formation of neutrophil extracellular traps is enhanced in the elderly via Toll-like receptor 9.

Neutrophil extracellular traps are potent antimicrobial weapons; however, their formation during sterile inflammation is detrimental, and the mechanism of induction is still unclear. Since advanced age is the primary clinical risk factor for poor outcomes in inflammatory diseases, we hypothesized that sterile stimuli, represented by mitochondria, would induce neutrophil extracellular trap formation in an age-dependent manner. Therefore, we analyzed induction of neutrophil extracellular traps in patients grouped according to age or immune status and observed that neutrophils from elderly patients responded to the presence of mitochondria with enhanced neutrophil extracellular trap formation. These neutrophil extracellular traps were also found to be more oxidized and exhibited higher resistance to DNase I degradation. Additionally, a higher concentration of residual neutrophil extracellular traps was detected in the plasma of the elderly. This plasma was capable of priming neutrophils through TLR9-mediated signaling, leading to further neutrophil extracellular trap formation, which was successfully inhibited with chloroquine. Finally, in a mouse model of mitochondria-induced acute lung injury, we observed that neutrophils from aged mice displayed impaired chemotactic activity but exhibited a trend of higher neutrophil extracellular trap formation. Thus, we propose that residual neutrophil extracellular traps circulating in the elderly preactivate neutrophils, making them more prone to enhanced neutrophil extracellular trap formation when exposed to mitochondria during sterile inflammation. Further investigation is needed to determine whether this vicious circle could be a suitable therapeutic target.

Mycobacterium tuberculosis PE/PPE proteins enhance the production of reactive oxygen species and formation of neutrophil extracellular traps.

Neutrophil granulocytes predominate in the lungs of patients infected with Mycobacterium tuberculosis (Mtb) in earlier stages of the disease. During infection, neutrophils release neutrophil extracellular traps (NETs), an antimicrobial mechanism by which a DNA-backbone spiked with antimicrobial components traps the mycobacteria. However, the specific mycobacterial factors driving NET formation remain unclear. Proteins from the proline-glutamic acid (PE)/proline-proline-glutamic acid (PPE) family are critical to Mtb pathophysiology and virulence. Here, we investigated NET induction by PE18, PPE26, and PE31 in primary human blood-derived neutrophils. Neutrophils were stimulated with the respective proteins for 3h, and NET formation was subsequently assessed using confocal fluorescence microscopy. Intracellular ROS levels and cell necrosis were estimated by flow cytometry. Additionally, the influence of phorbol-12-myristate-13-acetate (PMA), a known NADPH oxidase enhancer, on NET formation was examined. Neutrophil integrity following incubation with the PE/PPE proteins was evaluated using transmission electron microscopy. For the first time, we report that stimulation of primary human blood-derived neutrophils with Mtb proteins PE18, PPE26, and PE31 resulted in the formation of NETs, which correlated with an increase in intracellular ROS levels. Notably, the presence of PMA further amplified this effect. Following incubation with the PE/PPE proteins, neutrophils were found to remain viable and structurally intact, as verified through transmission electron microscopy, indicating the occurrence of vital NET formation. These findings offer valuable insights that contribute to a better understanding of host-pathogen interactions during Mtb infection. Moreover, they underscore the significance of these particular Mtb antigens in triggering NET formation, representing a distinctive and previously unrecognized function of PE/PPE antigens.

Neutrophil and NETosis Modulation in Traumatic Heterotopic Ossification.

To characterize the role of neutrophil extracellular traps (NETs) in heterotopic ossification (HO) formation and progression and to use mechanical and pharmacological methods to decrease NETosis and mitigate HO formation. Traumatic HO is the aberrant osteochondral differentiation of mesenchymal progenitor cells after traumatic injury, burns, or surgery. While the innate immune response has been shown to be necessary for HO formation, the specific immune cell phenotype and function remain unknown. Neutrophils, one of the earliest immune cells to respond after HO-inducing injuries, can extrude DNA, forming highly inflammatory NETs. We hypothesized that neutrophils and NETs would be diagnostic biomarkers and therapeutic targets for the detection and mitigation of HO. C57BL6J mice underwent burn/tenotomy (a well-established mouse model of HO) or a non-HO-forming sham injury. These mice were either (1) ambulated ad libitum, (2) ambulated ad libitum with daily intraperitoneal hydroxychloroquine, ODN-2088 (both known to affect NETosis pathways), or control injections, or (3) had the injured hind limb immobilized. Single-cell analysis was performed to analyze neutrophils, NETosis, and downstream signaling after the HO-forming injury. Immunofluorescence microscopy was used to visualize NETosis at the HO site and neutrophils were identified using flow cytometry. Serum and cell lysates from HO sites were analyzed using enzyme-linked immunosorbent assay for myeloperoxidase-DNA and ELA2-DNA complexes to identify NETosis. Micro-computerized tomography was performed on all groups to analyze the HO volume. Molecular and transcriptional analyses revealed the presence of NETs within the HO injury site, which peaked in the early phases after injury. These NETs were highly restricted to the HO site, with gene signatures derived from both in vitro NET induction and clinical neutrophil characterizations showing a high degree of NET "priming" at the site of injury, but not in neutrophils in the blood or bone marrow. Cell-cell communication analyses revealed that this localized NET formation coincided with high levels of toll-like receptor signaling specific to neutrophils at the injury site. Reducing the overall neutrophil abundance within the injury site, either pharmacologically through treatment with hydroxychloroquine, the toll-like receptor 9 inhibitor OPN-2088, or mechanical treatment with limb offloading, results in the mitigation of HO formation. These data provide a further understanding of the ability of neutrophils to form NETs at the injury site, clarify the role of neutrophils in HO, and identify potential diagnostic and therapeutic targets for HO mitigation.

Dual antiplatelet therapy inhibits neutrophil extracellular traps to reduce liver micrometastases of intrahepatic cholangiocarcinoma

The involvement of neutrophil extracellular traps (NETs) in cancer metastasis is being clarified, but the relationship between intrahepatic cholangiocarcinoma (iCCA) and NETs remains unclear. The presence of NETs was verified by multiple fluorescence staining in clinically resected specimens of iCCA. Human neutrophils were co-cultured with iCCA cells to observe NET induction and changes in cellular characteristics. Binding of platelets to iCCA cells and its mechanism were also examined, and their effects on NETs were analyzed in vitro and in in vivo mouse models. NETs were present in the tumor periphery of resected iCCAs. NETs promoted the motility and migration ability of iCCA cells in vitro. Although iCCA cells alone had a weak NET-inducing ability, the binding of platelets to iCCA cells via P-selectin promoted NET induction. Based on these results, antiplatelet drugs were applied to these cocultures in vitro and inhibited the binding of platelets to iCCA cells and the induction of NETs. Fluorescently labeled iCCA cells were injected into the spleen of mice, resulting in the formation of liver micrometastases coexisting with platelets and NETs. These mice were treated with dual antiplatelet therapy (DAPT) consisting of aspirin and ticagrelor, which dramatically reduced micrometastases. These results suggest that potent antiplatelet therapy prevents micrometastases of iCCA cells by inhibiting platelet activation and NET production, and it may contribute to a novel therapeutic strategy.

Neutrophil intrinsic and extrinsic regulation of NETosis in health and disease.

Neutrophil extracellular traps (NETs) evolved to protect the host against microbial infections and are formed by a web-like structure of DNA that is decorated with antimicrobial effectors. Due to their potent inflammatory functions, NETs also cause tissue damage and can favor and/or aggravate inflammatory diseases. This multipronged activity of NETs requires that the induction, release, and degradation of NETs are tightly regulated. Here we describe the key pathways that are intrinsic to neutrophils and regulate NETosis, and we review the most recent findings on how neutrophil extrinsic factors participate in the formation of NETs. In particular, we emphasize how bystander cells contribute to modifying the capacity of neutrophils to undergo NETosis. Finally, we discuss how these neutrophil extrinsic processes can be harnessed to protect the host against the excessive inflammation elicited by uncontrolled NET release.

Spontaneous NETosis in diabetes: A role of hyperglycemia mediated ROS and autophagy.

Type 2-diabetes, particularly poorly controlled diabetes, is a risk factor for several infections such as lower respiratory tract and skin infections. Hyperglycemia, a characteristic downstream effect of poorly controlled diabetes, has been shown to impair the function of immune cells, in particular neutrophils. Several studies have demonstrated that hyperglycemia-mediated priming of NADPH oxidase results in subsequent elevated levels of reactive oxygen species (ROS). In healthy neutrophils, ROS plays an important role in pathogen killing by phagocytosis and by induction of Neutrophil Extracellular Traps (NETs). Given the key role of ROS in autophagy, phagocytosis and NETosis, the relationship between these pathways and the role of diabetes in the modulation of these pathways has not been explored previously. Therefore, our study aimed to understand the relationship between autophagy, phagocytosis and NETosis in diabetes. We hypothesized that hyperglycemia-associated oxidative stress alters the balance between phagocytosis and NETosis by modulating autophagy. Using whole blood samples from individuals with and without type 2-diabetes (in the presence and absence of hyperglycemia), we demonstrated that (i) hyperglycemia results in elevated levels of ROS in neutrophils from those with diabetes, (ii) elevated levels of ROS increase LCIII (a marker for autophagy) and downstream NETosis. (iii) Diabetes was also found to be associated with low levels of phagocytosis and phagocytic killing of S. pneumoniae. (iv) Blocking either NADPH oxidase or cellular pathways upstream of autophagy led to a significant reduction in NETosis. This study is the first to demonstrate the role of ROS in altering NETosis and phagocytosis by modulating autophagy in type 2-diabetes. GRAPHICAL ABSTRACT.

Phosphoinositol 3-kinase-driven NET formation involves different isoforms and signaling partners depending on the stimulus.

Neutrophil extracellular traps (NETs) serve to immobilize and kill pathogens, but also can contribute to the progression of several inflammatory and auto-immune diseases, as well as cancer. Whence the importance of elucidating the mechanisms underlying NET formation. In this regard, the PI3K signaling pathway has been shown to be crucial; yet little is known about which of its components are involved. Here, we identified the PI3K isoforms and associated signaling partners that are mobilized in response to different classes of physiological NET inducers (inflammatory cytokines, growth factors, chemoattractants). NET generation was assessed by microscopy and signalling molecule activation by immunoblot using phospho-antibodies. Across the various stimuli, PI3Kα and PI3Kγ isoforms clearly contributed to NET induction, while the participation of other isoforms was stimulus-dependent. Some PI3K isoforms were also found to signal through Akt, the canonical downstream effector of PI3K, while others did not. Downstream of PI3K, mTOR and PLCγ2 were used by all stimuli to control NET generation. Conversely, the involvement of other kinases depended on the stimulus - both TNFα and GM-CSF relied on PDK1 and Akt; and both TNFα and fMLP additionally used S6K. We further established that all PI3K isoforms and downstream effectors act belatedly in NET generation, as reported previously for PI3K. Finally, we revisited the PI3K-PDK1-Akt signaling hierarchy in human neutrophils and again found stimulus-dependent differences. Our data uncover unsuspected complexity and redundancy in the signaling machinery controlling NET formation through the all-important PI3K pathway. Conserved signaling molecules represent therapeutic targets for pathologies involving NETs and in this regard, the existence of drugs currently used in the clinic or undergoing clinical trials (which target PI3K isoforms, mTOR or Akt), underscores the translational potential of our findings.

Morphological and Compositional Analysis of Neutrophil Extracellular Traps Induced by Microbial and Chemical Stimuli.

Neutrophils function as the first line of cellular defense in an innate immune response by employing diverse mechanisms, such as the formation of neutrophil extracellular traps (NETs). This study analyzes the morphological and compositional changes in NETs induced by microbial and chemical stimuli using standardized in vitro methodologies for NET induction and characterization with human cells. The procedures described here allow the analysis of NET morphology (lytic or non-lytic) and composition (DNA-protein structures and enzymatic activity), and the effect of soluble factors or cellular contact on such characteristics. Additionally, the techniques described here could be modified to evaluate the effect of exogenous soluble factors or cellular contact on NET composition. The applied techniques include the purification of polymorphonuclear cells from human peripheral blood using a double density gradient (1.079-1.098 g/mL), guaranteeing optimal purity and viability (≥ 95%) as demonstrated by Wright's staining, trypan blue exclusion, and flow cytometry, including FSC versus SSC analysis and 7AAD staining. NET formation is induced with microbial (Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans) and chemical (phorbol myristate acetate, HOCl) stimuli, and the NETs are characterized by DNA-DAPI staining, immunostaining for the antimicrobial peptide cathelicidin (LL37), and quantification of enzymatic activity (neutrophil elastase, cathepsin G, and myeloperoxidase). The images are acquired through fluorescence microscopy and analyzed with ImageJ.

Biomarker of neutrophil extracellular traps is associated with deep-seated infections and predicts mortality and cardiovascular morbidity in commensal streptococcal bacteremia.

Neutrophil extracellular traps (NETs) play important roles in sepsis and deep-seated infections, but whether NET formation correlates with clinical outcomes of patients with streptococcal bloodstream infections (BSIs) is unclear. We analyzed serum levels of complexes of myeloperoxidase and DNA (MPO-DNA) in patients with streptococcal-BSIs. Invitro assay of NET induction by serum from BSI patients was performed. MPO-DNA values for the Streptococci-BSI group (n=59) were significantly higher than those for healthy controls (p<0.00001) and matched control groups (n=59, p=0.004). The rate of higher MPO-DNA levels (>1.87μg/mL) were higher in abscess-prone streptococcal groups (streptococcus milleri group) (72.2% vs. 52.5%, p=0.02). For patients with BSIs due to highly infective endocarditis (IE)-prone pathogens, the values of serum MPO-DNA were also higher in patients diagnosed of IE compared to their counterparts (p=0.009). Notably, serum from patients with leukopenia could induce higher amounts of invitro NET formation, despite having low MPO-DNA levels, suggesting that NET formation could be influenced by WBC counts. Therefore, we combined WBC counts with MPO-DNA to predict all-cause 30-day mortality in patients with commensal streptococcal-BSIs. The mortality risk was lowest among patients who had neither high MPO-DNA levels nor abnormal WBC counts (p=0.058). Furthermore, this group of patients also had a favorable composite outcome consisting of major adverse cardiovascular events (MACE) and all-cause mortality (p=0.026). Together, these study data suggested that serum MPO-DNA can be a biomarker for predicting a composite outcome consisting of MACE and all-cause mortality in patients with commensal streptococcal-BSIs.

Neutrophil extracellular traps in fungal infections: A seesaw battle in hosts.

Fungal infections are a growing health care challenge. Neutrophils play a key role in defense against fungal infections. There are many effective ways for neutrophils to eliminate fungal invaders, such as phagocytosis, oxidative bursts, and the formation of extracellular traps. This process has received considerable attention and has made rapid progress since neutrophil extracellular traps (NETs) formation was described. Here, we describe the formation, induction, and function of NETs, as well as fungal strategies against NETs hunting. We highlight the effects of NETs on common fungal pathogens and how these pathogens survive.

New Insights into Neutrophil Extracellular Trap (NETs) Formation from Porcine Neutrophils in Response to Bacterial Infections.

Actinobacillus pleuropneumoniae (A.pp, Gram negative) and Streptococcus (S.) suis (Gram positive) can cause severe diseases in pigs. During infection, neutrophils infiltrate to counteract these pathogens with phagocytosis and/or neutrophil extracellular traps (NETs). NETs consist of a DNA-backbone spiked with antimicrobial components. The NET formation mechanisms in porcine neutrophils as a response to both of the pathogens are not entirely clear. The aim of this study was to investigate whether A.pp (serotype 2, C3656/0271/11) and S. suis (serotype 2, strain 10) induce NETs by NADPH oxidase- or CD18-dependent mechanisms and to characterize phenotypes of NETs in porcine neutrophils. Therefore, we investigated NET induction in porcine neutrophils in the presence and absence of NET inhibitors and quantified NETs after 3 h. Furthermore, NETosis and phagocytosis were investigated by transmission electron microscopy after 30 min to characterize different phenotypes. A.pp and S. suis induce NETs that are mainly ROS-dependent. A.pp induces NETs that are partially CD18-dependent. Thirty minutes after infection, both of the pathogens induced a vesicular NET formation with only slight differences. Interestingly, some neutrophils showed only NET-marker positive phagolysosomes, but no NET-marker positive vesicles. Other neutrophils showed vesicular NETs and only NET-marker negative phagolysosomes. In conclusion, both of the pathogens induce ROS-dependent NETs. Vesicular NETosis and phagocytosis occur in parallel in porcine neutrophils in response to S. suis serotype 2 and A.pp serotype 2.

Neutrophil Extracellular Traps and Pancreatic Cancer Development: A Vicious Cycle.

Simple SummaryCancer-associated thrombosis is a significant complication in cancer patients with various clinical consequences. Neutrophil extracellular traps (NETs), are associated with cancer development and hypercoagulability in various cancers, including pancreatic cancer. On the other hand, pancreatic cancer development is associated with increased NETs formation. This feedback mechanism suggests the existence of a vicious cycle between NETs and the tumor microenvironment in pancreatic cancer, that supports tumor development and may lead to cancer-associated thrombosis.Neutrophil extracellular traps (NETs) are a neutrophil-generated extracellular network of chromatin and chromatin-bound molecules with antimicrobial potency. Recent data suggest that NETs are associated with cancer progression and cancer-associated hypercoagulability. Pancreatic adenocarcinoma (PDAC) is a lethal type of cancer in which hypercoagulability and cancer-related thrombosis are among the main complications. In the current report, we summarize the available data on the interplay between NET formation and PDAC development. We conclude that NETs support a dual role during PDAC progression and metastasis. Their formation is on the one hand an important event that shapes the cancer microenvironment to support cancer cell proliferation, invasion and metastasis. On the other hand, NETs may lead to cancer-associated thrombosis. Both mechanisms seem to be dependent on distinct molecular mechanisms that link inflammation to cancer progression. Collectively, NET formation may contribute to the pathogenesis of PDAC, while during cancer development, the proinflammatory environment enables the induction of new NETs and thrombi, forming a vicious cycle. We suggest that targeting NET formation may be an effective mechanism to inhibit both PDAC development and the accompanying hypercoagulability.

Neutrophil Extracellular Traps in Candida albicans Infection.

Candida albicans is the most common pathogen causing clinical Candida infections. Neutrophils are a key member of the host innate immunity that plays an essential role in clearing invading C. albicans. In addition to the well-known defensive approaches such as phagocytosis, degranulation, and reactive oxygen species production, the formation of neutrophil extracellular traps (NETs) has also become an important way for neutrophils to defend against various pathogens. C. albicans has been reported to be capable of activating neutrophils to release NETs that subsequently kill fungi. The induction of NETs is affected by both the morphology and virulence factors of C. albicans, which also develops specific strategies to respond to the attack by NETs. Our review specifically focuses on the mechanisms by which C. albicans triggers NET formation and their subsequent interactions, which might provide meaningful insight into the innate immunity against C. albicans infection.

Lipofundin mediates major inhibition of intravenous propofol on phorbol myristate acetate and Escherichia coli-induced neutrophil extracellular traps.

Neutrophil extracellular traps (NETs) consist of chromatin DNA networks that are studded with cytosolic and granular antimicrobial proteins to trap or kill an infected microorganism. A lipid emulsion, the solvent of pure propofol for intravenous application, is given to clinical patients who require intravenous feeding of fatty acids and fat for energy. Intravenous propofol is widely used to sedate critically ill patients. Both intravenous propofol and its lipid emulsion have immunomodulatory activity. However, the role of lipid emulsion of intravenous propofol on NET induction remains unclear. In this study, neutrophils were stimulated with phorbol myristate acetate (PMA) or Escherichia coli (E. coli) in the absence or presence of intravenous propofol (Propofol-Lipuro®), its solvent lipid emulsion (Lipofundin) or pure propofol, and NETs were stained with SYTOX Green for visualization and quantification. Total HOCl was determined by measuring the taurine-chloramine complex, and intracellular HOCl was evaluated with BioTracker™ TP-HOCl 1 dye. PMA-induced NETs were not efficiently inhibited whenPropofol-Lipuro® was addedafter PMA stimulation. Clinically relevant concentrations of Lipofundin exerted a significant reduction in PMA-induced NETs and total reactive oxidative species (ROS), which was comparable to that observed for Propofol-Lipuro®. Lipofundin transiently reduced intracellular HOCl production and thephosphorylation level of extracellular regulated kinase (p-ERK) but did not scavenge HOCl. Moreover, Lipofundin decreased E. coli-induced NETs in a ROS-independent pathway, similar to Propofol-Lipuro®. All data agree that Lipofundin, the major component of Propofol-Lipuro®, inhibits intracellular HOCl and p-ERK to suppress PMA-induced NET formation but reduces E.coli-induced NETs in a ROS-independent pathway.