Healthy Neutrophils Research Articles

Classification of chronic myeloid leukemia neutrophils by hyperspectral imaging using Euclidean and Mahalanobis distances

Chronic Myeloid Leukemia (CML) is a type of blood cancer which needs to be diagnosed in early stages to facilitate effective treatment. This necessitates quick, error free and automated diagnostic techniques. In this study, hyperspectral images have been analyzed using statistical distances to classify neutrophils from CML versus healthy blood samples. The statistical distances were used in multidimensional space offered by hyperspectral images. For computational efficiency, principal component analysis was used to achieve dimensionality reduction. The Euclidean distance method, and Mahalanobis distance method which compensates the variance of the target data distribution were used to classify CML neutrophils. The effectiveness of the proposed methods were tested and compared using experimental results. The Euclidean distance was found to be superior when it came to sensitivity in detecting CML neutrophils whereas the Mahalanobis distance was better at detecting healthy neutrophils and distinguishing CML neutrophils from healthy neutrophils.

A Novel Microfluidic Device for the Neutrophil Functional Phenotype Analysis: Effects of Glucose and Its Derivatives AGEs.

Neutrophil dysfunction is closely related to the pathophysiology of patients with diabetes mellitus, but existing immunoassays are difficult to implement in clinical applications, and neutrophil’s chemotaxis as a functional biomarker for diabetes mellitus prognostic remains largely unexplored. Herein, a novel microfluidic device consisted of four independent test units with four cell docking structures was developed to study the neutrophil chemotaxis, which allowed multiple cell migration observations under a single field of view (FOV) and guaranteed more reliable results. In vitro studies, the chemotaxis of healthy neutrophils to N-Formyl-Met-Leu-Phe (fMLP) gradient (0, 10, 100, and 1000 nM) was concentration-dependent. The distinct promotion or suppression in the chemotaxis of metformin or pravastatin pretreated cells were observed after exposure to 100 nM fMLP gradient, indicating the feasibility and efficiency of this novel microfluidic device for clinically relevant evaluation of neutrophil functional phenotype. Further, the chemotaxis of neutrophils pretreated with 25, 50, or 70 mM of glucose was quantitatively lower than that of the control groups (i.e., 5 mM normal serum level). Neutrophils exposed to highly concentrated advanced glycation end products (AGEs) (0.2, 0.5, or 1.0 μM; 0.13 μM normal serum AGEs level), a product of prolonged hyperglycemia, showed that the higher the AGEs concentration was, the weaker the migration speed became. Specifically, neutrophils exposed to high concentrations of glucose or AGEs also showed a stronger drifting along with the flow, further demonstrating the change of neutrophil chemotaxis. Interestingly, adding the N-benzyl-4-chloro-N-cyclohexylbenzamide (FPS-ZM1) (i.e., high-affinity RAGE inhibitor) into the migration medium with AGEs could hinder the binding between AGEs and AGE receptor (RAGE) located on the neutrophil, thereby keeping the normal chemotaxis of neutrophils than the ones incubated with AGEs alone. These results revealed the negative effects of high concentrations of glucose and AGEs on the neutrophil chemotaxis, suggesting that patients with diabetes should manage serum AGEs and also pay attention to blood glucose indexes. Overall, this novel microfluidic device could significantly characterize the chemotaxis of neutrophils and have the potential to be further improved into a tool for risk stratification of diabetes mellitus.

Transcriptome and Literature Mining Highlight the Differential Expression of ERLIN1 in Immune Cells during Sepsis.

Simple SummarySepsis is a disease affecting 19 million people worldwide, and accounts for 5 million deaths annually. Efforts in finding predictive markers of sepsis development have been difficult due to the complex clinical features of the disease. Public data repositories are valuable resources for mining gene expression changes across different studies. Using such resources, we observed a consistent increase in ERLIN1—a gene coding for an ER membrane prohibitin and regulator of cholesterol—in whole blood, and across a variety of immune cells, during sepsis or sepsis-like conditions. We verified this finding by exposing the whole blood of healthy volunteers to a combination of lipopolysaccharide and peptidoglycan in order to simulate sepsis. We observed an increase in ERLIN1 in whole-blood neutrophils and HL60 cell lines during sepsis; however, the protein was expressed differently in other immune blood cells. The current available studies on ERLIN1 and sepsis indicate a knowledge gap between the functions of ERLIN1, calcium balance, and cholesterol and fatty acid synthesis, and sepsis. Together with experimental data, we think that ERLIN1 is modulated differently in immune cells in response to infection, and has important implications for ER functions and/or ER membrane protein components during sepsis.Sepsis results from the dysregulation of the host immune system. This highly variable disease affects 19 million people globally, and accounts for 5 million deaths annually. In transcriptomic datasets curated from public repositories, we observed a consistent upregulation (3.26–5.29 fold) of ERLIN1—a gene coding for an ER membrane prohibitin and a regulator of inositol 1, 4, 5-trisphosphate receptors and sterol regulatory element-binding proteins—under septic conditions in healthy neutrophils, monocytes, and whole blood. In vitro expression of the ERLIN1 gene and proteins was measured by stimulating the whole blood of healthy volunteers to a combination of lipopolysaccharide and peptidoglycan. Septic stimulation induced a significant increase in ERLIN1 expression; however, ERLIN1 was differentially expressed among the immune blood cell subsets. ERLIN1 was uniquely increased in whole blood neutrophils, and confirmed in the differentiated HL60 cell line. The scarcity of ERLIN1 in sepsis literature indicates a knowledge gap between the functions of ERLIN1, calcium homeostasis, and cholesterol and fatty acid biosynthesis, and sepsis. In combination with experimental data, we bring forth the hypothesis that ERLIN1 is variably modulated among immune cells in response to cellular perturbations, and has implications for ER functions and/or ER membrane protein components during sepsis.

Internalization of Neutrophil-Derived Microvesicles Modulates TNFα-Stimulated Proinflammatory Cytokine Production in Human Fibroblast-Like Synoviocytes.

Neutrophil-derived microvesicles (NDMVs) have the potential to exert anti-inflammatory effects. Our study aimed to explore the effects of NDMVs on proinflammatory cytokines expressed by tumor necrosis factor α (TNFα)-stimulated fibroblast-like synoviocytes (FLS). FLS were isolated from the synovium of knee osteoarthritis (OA) patients undergoing surgery. NDMVs, isolated from TNFα-stimulated healthy neutrophils, were characterized by electron microscopy and nanoparticle tracking analysis. MTT and scratch wound healing assays were used to measure FLS viability and migration after treatment with NDMVs, while internalization of fluorescently labeled NDMVs was appraised by flow cytometry and confocal microscopy. Levels of proinflammatory cytokines in supernatants were quantified by the Bio-Plex system. Incubation of FLS with NDMVs at a vesicle/cell ratio of 100 resulted in a time-dependent uptake, with 35% of synoviocytes containing microvesicles over a 6–24 h time period, with no significant change in cell viability. TNFα stimulated the cytokine expression in FLS, and NDMVs down-regulated TNFα-induced expression of IL-5, IL-6, IL-8, MCP-1, IFNγ and MIP-1β. However, this down-regulation was selective, as NDMVs had no significant effects on TNFα-stimulated expression of IL-2 or IL-4. NDMVs were internalized by FLS to inhibit TNFα-stimulated broad-spectrum proinflammatory cytokine secretion. NDMVs, therefore, may exhibit an anti-inflammatory role in the regulation of the FLS function.

Human variation in gingival inflammation.

Oral commensal bacteria actively participate with gingival tissue to maintain healthy neutrophil surveillance and normal tissue and bone turnover processes. Disruption of this homeostatic host-bacteria relationship occurs during experimental gingivitis studies where it has been clearly established that increases in the bacterial burden increase gingival inflammation. Here, we show that experimental gingivitis resulted in three unique clinical inflammatory phenotypes (high, low, and slow) and reveal that interleukin-1β, a reported major gingivitis-associated inflammatory mediator, was not associated with clinical gingival inflammation in the slow response group. In addition, significantly higher levels of Streptococcus spp. were also unique to this group. The low clinical response group was characterized by low concentrations of host mediators, despite similar bacterial accumulation and compositional characteristics as the high clinical response group. Neutrophil and bone activation modulators were down-regulated in all response groups, revealing novel tissue and bone protective responses during gingival inflammation. These alterations in chemokine and microbial composition responses during experimental gingivitis reveal a previously uncharacterized variation in the human host response to a disruption in gingival homeostasis. Understanding this human variation in gingival inflammation may facilitate the identification of periodontitis-susceptible individuals. Overall, this study underscores the variability in host responses in the human population arising from variations in host immune profiles (low responders) and microbial community maturation (slow responders) that may impact clinical outcomes in terms of destructive inflammation.

Transcriptomics of type 2 diabetic and healthy human neutrophils

ObjectivesChronic inflammatory diseases, including diabetes and cardiovascular disease, are heterogeneous and often co-morbid, with increasing global prevalence. Uncontrolled type 2 diabetes (T2D) can result in severe inflammatory complications. As neutrophils are essential to normal and aberrant inflammation, we conducted RNA-seq transcriptomic analyses to investigate the association between neutrophil gene expression and T2D phenotype. As specialized pro-resolving lipid mediators (SPM) act to resolve inflammation, we further surveyed the impact of neutrophil receptor binding SPM resolvin E1 (RvE1) on isolated diabetic and healthy neutrophils.MethodsCell isolation and RNA-seq analysis of neutrophils from N = 11 T2D and N = 7 healthy individuals with available clinical data was conducted. Additionally, cultured neutrophils (N = 3 T2D, N = 3 healthy) were perturbed with increasing RvE1 doses (0 nM, 1 nM, 10 nM, or 100 nM) prior to RNA-seq. Data was evaluated through a bioinformatics pipeline including pathway analysis and post hoc false discovery rate (FDR)-correction.ResultsWe observed significant differential expression of 50 genes between T2D and healthy neutrophils (p < 0.05), including decreased T2D gene expression in inflammatory- and lipid-related genes SLC9A4, NECTIN2, and PLPP3 (p < 0.003). RvE1 treatment induced dose-dependent differential gene expression (uncorrected p < 0.05) across groups, including 59 healthy and 216 T2D neutrophil genes. Comparing T2D to healthy neutrophils, 1097 genes were differentially expressed across RvE1 doses, including two significant genes, LILRB5 and AKR1C1, involved in inflammation (p < 0.05).ConclusionsThe neutrophil transcriptomic database revealed novel chronic inflammatory- and lipid-related genes that were differentially expressed between T2D cells when compared to controls, and cells responded to RvE1 dose-dependently by gene expression changes. Unraveling the mechanisms regulating abnormalities in diabetic neutrophil responses could lead to better diagnostics and therapeutics targeting inflammation and inflammation resolution.

High Purity Isolation of Low Density Neutrophils Casts Doubt on Their Exceptionality in Health and Disease.

Low density neutrophils (LDNs) are described in a number of inflammatory conditions, cancers and infections and associated with immunopathology, and a mechanistic role in disease. The role of LDNs at homeostasis in healthy individuals has not been investigated. We have developed an isolation protocol that generates high purity LDNs from healthy donors. Healthy LDNs were identical to healthy normal density neutrophils (NDNs), aside from reduced neutrophil extracellular trap formation. CD66b, CD16, CD15, CD10, CD54, CD62L, CXCR2, CD47 and CD11b were expressed at equivalent levels in healthy LDNs and NDNs and underwent apoptosis and ROS production interchangeably. Healthy LDNs had no differential effect on CD4+ or CD8+ T cell proliferation or IFNγ production compared with NDNs. LDNs were generated from healthy NDNs in vitro by activation with TNF, LPS or fMLF, suggesting a mechanism of LDN generation in disease however, we show neutrophilia in people with Cystic Fibrosis (CF) was not due to increased LDNs. LDNs are present in the neutrophil pool at homeostasis and have limited functional differences to NDNs. We conclude that increased LDN numbers in disease reflect the specific pathology or inflammatory environment and that neutrophil density alone is inadequate to classify discrete functional populations of neutrophils.

P143 The effect of JAK inhibition on the metabolome of neutrophils from patients with rheumatoid arthritis

Abstract Background/Aims Janus kinase inhibitors (JAKi) including baricitinib and tofacitinib target the JAK/STAT pathway and are clinically effective in treating rheumatoid arthritis (RA). Neutrophils play a key role in the pathophysiology of RA and their function is directly affected by these drugs as shown by clinical trials of JAKi which report increased infection rates and transient neutropenia during therapy. The aim of this work is to determine difference in the metabolome of neutrophils from healthy controls and patients with RA, and the effect of JAKi on the metabolome of healthy and RA neutrophils. Methods Neutrophils were isolated from healthy controls (HC) (n = 10) and patients with RA (n = 10 DMARD-naïve, n = 10 Biologics-naive) and pre-incubated with baricitinib, tofacitinib or a pan-JAK inhibitor (all 200ng/mL) for 2h before snap-freezing. Metabolites were extracted by 50:50 v/v AcN:H2O and analysed by 1H NMR spectroscopy using a 700 MHz Avance IIIHD Bruker NMR spectrometer equipped with a TCI cryoprobe. Chenomx, Bruker TopSpin and tameNMR software were used to identify metabolites and process spectra. Statistical analysis and machine learning models were implemented using R and the Mixomics package. Pathway analysis was carried out using Ingenuity (IPA). ROS production in response to 15 min fMLP stimulation was measured using DHR-123 and flow cytometry. Results At 0h, changes in levels of NADP+, NADPH and hypoxanthine in RA neutrophils indicated increased production of ROS via NADPH oxidase and xanthine oxidase compared to HC. Lower levels of glucose and increased levels of lactic acid also suggested increased glycolysis in RA neutrophils compared to HC. However after 2h incubation with JAKi, a difference in the response to these drugs was observed. 80 metabolites were higher in RA neutrophils compared to HC following 2h JAKi treatment. IPA analysis revealed the metabolites higher in RA neutrophils were involved in NAD biosynthesis, NAD phosphorylation/dephosphorylation, amino acid synthesis and transport, and carbohydrate metabolism. Changes in the levels of NADP+, NADPH and hypoxanthine in RA neutrophils indicate that JAKi inhibit ROS production. We therefore confirmed experimentally that JAKi inhibit ROS production in response to fMLP (p &amp;lt; 0.05). IPA also predicted altered neutrophil cell functions including cell death and cell-to-cell signalling. We previously showed that JAKi did not affect the constitutive rate of neutrophil apoptosis, however JAKi significantly inhibit the delay in apoptosis induced by GM-CSF (p &amp;lt; 0.05). No significant difference in the metabolome was observed when comparing tofacinib-treatment and baricitinib-treatment in either the HC or RA patient group. Conclusion The metabolome of RA and HC neutrophils is different at baseline. JAKi alter the levels of intracellular metabolites involved in neutrophil activation and ROS production in RA. This may explain, in part, the efficacy of JAKi in decreasing disease activity and joint damage in RA. Disclosure M. Fresneda Alarcon: None. R. Grosman: None. S. Chokesuwattanaskul: None. M. Phelan: None. H. Wright: None.

Induction of Epithelial-Mesenchymal Transition (EMT) by Neutrophil Extracellular Traps (NETs) as Possible Molecular Mechanism in CLAD

Purpose Chronic Lung Allograft Dysfunction (CLAD) is the main limitation to long term post lung transplant survival and is characterized by interstitial or airway fibrosis. Recruitment and activation of Neutrophils in the graft has been described in CLAD. Neutrophils are an essential component of the innate immune system which can undergo different activation processes, among which NETosis. NETs can drive epithelial cell injury and induce endothelial mesenchymal transition or epithelial mesenchymal transition (EMT) of breast cancer cells. We here aim to investigate whether NETs can induce EMT on a human alveolar basal epithelial cell line (A549) as possible mechanism of fibrosis in CLAD. Methods NETosis was induced on healthy donor-derived neutrophils (Neu) with PMA. EMT was studied on A549 cells in three conditions (PMA-activated Neu (PMA-Neu), purified NETs from PMA-Neu and TGF-β). To study the induction of EMT, we evaluate the expression of two main proteins representative of EMT mechanism (α-SMA and E-cadherin) by western blot of cell lysates. Since it is known that neutrophils activated against NETosis can induce cell damage, we decided to evaluate cell toxicity after treatments with PMA-Neu or NETs by flow cytometry. Results Confocal microscope images confirmed that PMA treatment leads to release NETs by neutrophils. NETs changed the typical epithelial morphology of A549 cells into a mesenchymal phenotype. These morphological changes are also visible after treatment with TGF-β, the best known EMT effector. Morphological changes were confirmed by western blot analysis of EMT markers expression. Both PMA-Neu and purified NETs induced EMT in A549 after 24h, increasing α-SMA (1.21±0.025 and 1.34±0.025, respectively) and decreasing E-Cadherin expression (0.245±0.10 and 0.08±0.002, respectively). Moreover we observed that NETs activate EMT without toxic effects rather than PMA-Neu which induced 33.70 ± 4.37 % cell death compared to control cells. Conclusion This study highlights the contribution NETs as trigger of lung fibrosis, and suggest this mechanism might contribute to CLAD pathogenesis.

Circulating Neutrophil Dysfunction in HBV-Related Acute-on-Chronic Liver Failure.

Background and AimsAcute-on-chronic liver failure (ACLF) is characterized by systemic inflammation accompanied by defective anti-bacterial immunity. The role of neutrophils in immune derangement of ACLF has not been fully elucidated. This study is aimed to characterize the role of circulating neutrophils in HBV-related ACLF patients.MethodsQuantitative, phenotypic, transcriptomic, and functional alterations of circulating neutrophils were compared in ACLF and non-ACLF subjects and analyzed for associations with short-term outcomes. Interventional experiments were performed to test the impact on ACLF-patient neutrophil function in vitro.ResultsCirculating absolute neutrophil count was significantly increased in patients with ACLF and was an independent risk factor for 28-day mortality. ACLF-patient neutrophils differentially expressed a panel of surface markers (include TLR-1, TLR-2, TLR-4, CEACAM-1 and FPR1), as well as a distinct transcriptomic signature. ACLF-neutrophils displayed significantly impaired phagocytosis but an increased capacity to form neutrophil extracellular traps (NETs), which was more pronounced in patients with poor outcome. Healthy neutrophils mimicked functional characteristics of ACLF counterpart after co-cultured with plasma from ACLF patients. The oxidative burst and cytokine production capacities remained unchanged. Plasma GM-CSF, IL-6, IL-8, IL-10, and IP-10 levels, as well as lipopolysaccharide (LPS) concentration, were markedly elevated in ACLF patients but not DAMP molecules HMGB-1 and HSP70. Finally, a glycolysis inhibitor, 2-deoxy-glucose, reduced NET formation of ACLF patients’ neutrophils.ConclusionsCirculating ACLF-patient neutrophils exhibit alterations in number, phenotype, gene expression and function, which was associated with poor outcome and shaped by the ACLF circulatory environment. Inhibiting glycolysis can reverse neutrophil dysfunction in ACLF patients.

The impact of neutrophil extracellular trap from patients with systemic lupus erythematosus on the viability, CD11b expression and oxidative burst of healthy neutrophils

BackgroundNET (neutrophil extracellular trap) has been shown to directly influence inflammation; in SLE (systemic lupus erythematosus), it is reportedly a plausible cause for the broken self-tolerance that contributes to this pathology. Meanwhile, the role of NET is not easily explicable, and there is a serious discrepancy in the role of NET in SLE pathology and generally inflammation; in particular, the interactions of neutrophils with NET have been rarely inspected. This study evaluates the effect of NET on neutrophils in the context of SLE. The neutrophils were incubated by the collected NET (from SLE patients and healthy controls) and their expression of an activation marker, viability and oxidative burst ability were measured.ResultsThe level of cell mortality, CD11b expression and the oxidative burst capacity were elevated in NET-treated neutrophils. Also, the elevation caused by the SLE NET was higher than that produced by the healthy NET.ConclusionThe decreased neutrophil viability was not due to the increase in apoptosis; rather, it was because of the augmentation of other inflammatory cell-death modes. The upregulation of CD11b implies that NET causes neutrophils to more actively contribute to inflammation. The increased oxidative burst capacity of neutrophils can play a double role in inflammation. Overall, the effects induced by NET on neutrophils help prolong inflammation; accordingly, the NET collected from SLE patients is stronger than the NET from healthy individuals.

Rheumatoid Arthritis Synovial Fluid Neutrophils Drive Inflammation Through Production of Chemokines, Reactive Oxygen Species, and Neutrophil Extracellular Traps.

Rheumatoid arthritis (RA) is a chronic inflammatory disorder affecting synovial joints. Neutrophils are believed to play an important role in both the initiation and progression of RA, and large numbers of activated neutrophils are found within both synovial fluid (SF) and synovial tissue from RA joints. In this study we analyzed paired blood and SF neutrophils from patients with severe, active RA (DAS28>5.1, n=3) using RNA-seq. 772 genes were significantly different between blood and SF neutrophils. IPA analysis predicted that SF neutrophils had increased expression of chemokines and ROS production, delayed apoptosis, and activation of signaling cascades regulating the production of NETs. This activated phenotype was confirmed experimentally by incubating healthy control neutrophils in cell-free RA SF, which was able to delay apoptosis and induce ROS production in both unprimed and TNFα primed neutrophils (p<0.05). RA SF significantly increased neutrophil migration through 3μM transwell chambers (p<0.05) and also increased production of NETs by healthy control neutrophils (p<0.001), including exposure of myeloperoxidase (MPO) and citrullinated histone-H3-positive DNA NETs. IPA analysis predicted NET production was mediated by signaling networks including AKT, RAF1, SRC, and NF-κB. Our results expand the understanding of the molecular changes that take place in the neutrophil transcriptome during migration into inflamed joints in RA, and the altered phenotype in RA SF neutrophils. Specifically, RA SF neutrophils lose their migratory properties, residing within the joint to generate signals that promote joint damage, as well as inflammation via recruitment and activation of both innate and adaptive immune cells. We propose that this activated SF neutrophil phenotype contributes to the chronic inflammation and progressive damage to cartilage and bone observed in patients with RA.

Loss of Coordinated Neutrophil Responses to the Human Fungal Pathogen, Candida albicans, in Patients With Cirrhosis.

Neutrophils are the most abundant white blood cell in the body and are key participants in the defense against fungal infections. Fungal infections occur often in patients with cirrhosis and are associated with increased 30‐day and 90‐day mortality. Previous studies have shown that specific neutrophil functions are abnormal in patients with cirrhosis, although the extent of neutrophil dysfunction is not well understood. We tested the ability of neutrophils from 21 hospitalized patients with cirrhosis and 23 healthy control patients to kill Candida albicans, a common fungal pathogen in patients with cirrhosis. Using an assay, we also measured the ability of neutrophils to coordinate multicellular, synchronized control of C. albicans hyphae through a process known as swarming. We found that neutrophils from patients with cirrhosis have significantly decreased fungicidal capacity compared with healthy control neutrophils (53% vs. 74%, P < 0.0001) and diminished ability to control hyphal growth normalized as a ratio to healthy control (0.22 vs. 0.65, P < 0.0001). Moreover, serum from patients with cirrhosis decreases the ability of healthy control neutrophils to kill C. albicans (from 60% to 41%, P < 0.003). Circulating concentration of the inflammatory cytokines tumor necrosis factor α, interleukin‐6, and interleukin‐8 were found to be significantly elevated in patients with cirrhosis compared to healthy controls. Following pretreatment with granulocyte‐colony stimulating factor and granulocyte‐macrophage colony‐stimulating factor, neutrophil function was restored to almost that of healthy controls. Conclusion: Our data establish profound neutrophil dysfunction against, and altered swarming to, C. albicans in patients with cirrhosis. This dysfunction can be partially reversed with cytokine augmentation ex vivo.

Longitudinal Characterization of Circulating Neutrophils Uncovers Distinct Phenotypes Associated with Disease Severity in Hospitalized COVID-19 Patients

Multiple studies have identified an association between neutrophils and COVID-19 disease severity; however, the mechanistic basis of this association remains incompletely understood. Here we collected 781 longitudinal blood samples from 306 hospitalized COVID-19 + patients, 78 COVID-19 - acute respiratory distress syndrome patients, and 8 healthy controls, and performed bulk RNA-sequencing of enriched neutrophils, plasma proteomics, cfDNA measurements and high throughput antibody profiling assays to investigate the relationship between neutrophil states and disease severity or death. We identified dynamic switches between six distinct neutrophil subtypes using non-negative matrix factorization (NMF) clustering. At days 3 and 7 post-hospitalization, patients with severe disease had an enrichment of a granulocytic myeloid derived suppressor cell-like state gene expression signature, while non-severe patients with resolved disease were enriched for a progenitor-like immature neutrophil state signature. Severe disease was associated with gene sets related to neutrophil degranulation, neutrophil extracellular trap (NET) signatures, distinct metabolic signatures, and enhanced neutrophil activation and generation of reactive oxygen species (ROS). We found that the majority of patients had a transient interferon-stimulated gene signature upon presentation to the emergency department (ED) defined here as Day 0, regardless of disease severity, which persisted only in patients who subsequently died. Humoral responses were identified as potential drivers of neutrophil effector functions, as enhanced antibody-dependent neutrophil phagocytosis and reduced NETosis was associated with elevated SARS-CoV-2-specific IgG1-to-IgA1 ratios in plasma of severe patients who survived. In vitro experiments confirmed that while patient-derived IgG antibodies mostly drove neutrophil phagocytosis and ROS production in healthy donor neutrophils, patient-derived IgA antibodies induced a predominant NETosis response. Overall, our study demonstrates neutrophil dysregulation in severe COVID-19 and a potential role for IgA-dominant responses in driving neutrophil effector functions in severe disease and mortality.Funding:We acknowledge support from the Ragon Institute of MGH, MIT and Harvard, the Massachusetts Consortium on Pathogen Readiness (MassCPR), the NIH (3R37AI080289-11S1, R01AI146785, U19AI42790-01, U19AI135995-02, U19AI42790-01, 1U01CA260476 – 01, CIVIC75N93019C00052, T32 GM007592), the American Lung Association, and the MGH Executive Committee on Research. A.-C.V. acknowledges funding support from the COVID-19 Clinical Trials Pilot grant from the Executive Committee on Research at MGH, a COVID-19 Chan Zuckerberg Initiative grant (2020-216954), and funds from the Manton Foundation and the Klarman Family Foundation.Declaration of Interests: M.S.F receives funding from Bristol-Myers Squibb. G.A. is a founder of Seromyx Systems Inc. N.H. holds equity in Biontech and holds equity in and advises Danger Bio. Ethics Approval Statement: The study was approved by the Mass General Brigham Institutional Review Board under protocol 2017P001681, with an approval for a waiver of informed consent in compliance with the 45CFR 46, 2018 Common rule.

Kinetics of peripheral blood neutrophils in severe coronavirus disease 2019.

ObjectivesEmerging evidence of dysregulation of the myeloid cell compartment urges investigations on neutrophil characteristics in coronavirus disease 2019 (COVID‐19). We isolated neutrophils from the blood of COVID‐19 patients receiving general ward care and from patients hospitalised at intensive care units (ICUs) to explore the kinetics of circulating neutrophils and factors important for neutrophil migration and activation.MethodsMulticolour flow cytometry was exploited for the analysis of neutrophil differentiation and activation markers. Multiplex and ELISA technologies were used for the quantification of protease, protease inhibitor, chemokine and cytokine concentrations in plasma. Neutrophil polarisation responses were evaluated microscopically. Gelatinolytic and metalloproteinase activity in plasma was determined using a fluorogenic substrate. Co‐culturing healthy donor neutrophils with severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) allowed us to investigate viral replication in neutrophils.ResultsUpon ICU admission, patients displayed high plasma concentrations of granulocyte–colony‐stimulating factor (G‐CSF) and the chemokine CXCL8, accompanied by emergency myelopoiesis as illustrated by high levels of circulating CD10−, immature neutrophils with reduced CXCR2 and C5aR expression. Neutrophil elastase and non‐metalloproteinase‐derived gelatinolytic activity were increased in plasma from ICU patients. Significantly higher levels of circulating tissue inhibitor of metalloproteinase 1 (TIMP‐1) in patients at ICU admission yielded decreased total MMP proteolytic activity in blood. COVID‐19 neutrophils were hyper‐responsive to CXCL8 and CXCL12 in shape change assays. Finally, SARS‐CoV‐2 failed to replicate inside human neutrophils.ConclusionOur study provides detailed insights into the kinetics of neutrophil phenotype and function in severe COVID‐19 patients, and supports the concept of an increased neutrophil activation state in the circulation.

Neutrophils From Patients With Invasive Candidiasis Are Inhibited by Candida albicans Biofilms.

Invasive candidiasis frequently involves medical device placement. On the surfaces of these devices, Candida can form biofilms and proliferate in adherent layers of fungal cells surrounded by a protective extracellular matrix. Due in part to this extracellular matrix, biofilms resist host defenses and antifungal drugs. Previous work (using neutrophils from healthy donors) found that one mechanism employed to resist host defenses involves the inhibition of neutrophil extracellular traps (NET) formation. NETs contain nuclear DNA, as well as antimicrobial proteins that can ensnare pathogens too large or aggregated to be effectively killed by phagocytosis. Given that these neutrophil structures are anticipated to have activity against the large aggregates of C. albicans biofilms, understanding the role of this inhibition in patients could provide insight into new treatment strategies. However, prior work has not included patients. Here, we examine NET formation by neutrophils collected from patients with invasive candidiasis. When compared to neutrophils from healthy participants, we show that patient neutrophils exhibit a heightened background level of NET release and respond to a positive stimulus by producing 100% more NETs. However, despite these physiologic differences, patient neutrophil responses to C. albicans were similar to healthy neutrophils. For both groups, planktonic cells induce strong NET release and biofilms inhibit NET formation. These results show that a mechanism of immune evasion for fungal biofilms translates to the clinical setting.

Neutrophil Extracellular Traps Induce MCP-1 at the Culprit Site in ST-Segment Elevation Myocardial Infarction.

BackgroundLeukocyte-mediated inflammation is crucial in ST-segment elevation myocardial infarction (STEMI). We recently observed that neutrophil extracellular traps (NETs) are increased at the culprit site, promoting activation and differentiation of fibrocytes, cells with mesenchymal and leukocytic properties. Fibrocyte migration is mediated by monocyte chemoattractant protein (MCP)-1 and C-C chemokine receptor type 2 (CCR2). We investigated the interplay between NETs, fibrocyte function, and MCP-1 in STEMI.MethodsCulprit site and peripheral blood samples of STEMI patients were drawn during primary percutaneous coronary intervention. MCP-1 and the NET marker citrullinated histone H3 (citH3) were measured by ELISA while double-stranded DNA was stained with a fluorescent dye. The influence of MCP-1 on NET formation in vitro was assessed using isolated healthy donor neutrophils. Human coronary artery endothelial cells (hCAECs) were stimulated with isolated NETs, and MCP-1 gene expression was measured by ELISA and qPCR. CCR2 expression of culprit site and peripheral blood fibrocytes was characterized by flow cytometry. Healthy donor fibrocyte receptor expression and chemotaxis were investigated in response to stimulation with MCP-1 and NETs in vitro.ResultsNETs and concentrations of MCP-1 were increased at the culprit site of 50 consecutive STEMI patients. NET stimulation of hCAECs induced transcription of ICAM-1, IL-6, and MCP-1, and secretion of MCP-1. MCP-1 promoted NET formation of healthy donor neutrophils in vitro. An increasing MCP-1 gradient correlated with fibrocyte accumulation at the culprit site. Locally increased MCP-1 levels were negatively correlated with CCR2 expression on fibrocytes. MCP-1 and NETs induced CCR2 downregulation on fibrocytes in vitro. NETs did not function as a chemotactic stimulus for fibrocytes or monocytes and could block migration in response to MCP-1 for both cell populations.ConclusionNETs function as signaling scaffolds at the culprit site of STEMI. NETs assist MCP-1 and ICAM-1 release from culprit site coronary artery endothelial cells. MCP-1 facilitates further NETosis. Monocytes enter the culprit site along an MCP-1 gradient, to transdifferentiate into fibrocytes in the presence of NETs.

Neutrophil extracellular traps induce MCP-1 release from endothelial cells at the plaque rupture site in acute myocardial infarction

Abstract Introduction Leukocyte-mediated inflammation is crucial in acute myocardial infarction (AMI). We recently observed that neutrophil extracellular traps (NETs) are increased at the culprit site, promoting activation and differentiation of fibrocytes, cells with mesenchymal and leukocytic properties. Fibrocyte migration is mediated by monocyte chemoattractant protein (MCP)-1 and C-C chemokine receptor type 2 (CCR2). We investigated the interplay between NETs, fibrocyte function, and MCP-1 in AMI. Methods Culprit site and femoral blood of AMI patients was drawn during percutaneous coronary intervention. We characterized CCR2 expression of fibrocytes by flow cytometry. MCP-1 and the NET marker citrullinated histone H3 (citH3) were measured by ELISA. Fibrocytes were treated in vitro with MCP-1. Human coronary arterial endothelial cells (hCAECs) were stimulated with isolated NETs, and MCP-1 was measured by ELISA and qPCR. The influence of MCP-1 on NET formation in vitro was assessed using isolated neutrophils. Results We have included 50 consecutive AMI patients into the study. NETs and concentrations of MCP-1 were increased at the CLS. NET stimulation of hCAECs induced MCP-1 on mRNA and protein level. Increasing MCP-1 gradient was associated with fibrocyte accumulation at the site of occlusion. In the presence of higher MCP-1 these fibrocytes expressed proportionally less CCR2 than peripheral fibrocytes. In vitro, MCP-1 dose-dependently decreased fibrocyte CCR2 and reduced ex vivo NET release of healthy donor neutrophils. Conclusions NETs induce endothelial MCP-1 release, presumably promoting a chemotactic gradient for leukocyte and fibrocyte migration. MCP-1 mediated inhibition of NET formation could point to a negative feedback loop. These data will shed light on vascular healing. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): Austrian Science Fund

Type I interferon regulates cytokine-delayed neutrophil apoptosis, reactive oxygen species production and chemokine expression.

Interferons (IFNs) are key regulators of a number of inflammatory conditions in which neutrophils play an important role in pathology, such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), where type I IFNs are implicated in disease pathology. However, IFNs are usually generated in vivo together with other cytokines that also have immunoregulatory functions, but such interactions are poorly defined experimentally. We measured the effects of type I (IFN-α) IFN, elevated in both RA and SLE, on the functions of healthy neutrophils incubated in vitro in the absence and presence of proinflammatory cytokines typically elevated in inflammatory diseases [tumour necrosis factor (TNF-α), granulocyte-macrophage colony-stimulating factor (GM-CSF)]. IFN-α alone had no effect on neutrophil apoptosis; however, it abrogated the anti-apoptotic effect of GM-CSF (18h, P<0·01). The enhanced stability of the anti-apoptotic protein myeloid cell leukaemia 1 (Mcl-1) and delayed activation of caspase activation normally regulated by GM-CSF were blocked by IFN-α: this effect was mediated, in part, by activation of p38 mitogen-activated protein kinase (MAPK). IFN-α alone also primed reactive oxygen species (ROS) production and maintained the transient priming effect of TNF-α for up to 4h: it also down-regulated GM-CSF- and TNF-α-activated expression of chemokine (C-X-C motif) ligand (CXCL)1, CXCL2, CXCL3, CXCL8, CCL3 and CCL4 but, in contrast, increased the expression of CXCL10. These novel data identify complex regulatory signalling networks in which type I IFNs profoundly alter the response of neutrophils to inflammatory cytokines. This is likely to have important consequences in vivo and may explain the complexity and heterogeneity of inflammatory diseases such as RA, in which multiple cytokine cascades have been activated.

Contrasting effects of linezolid on healthy and dysfunctional human neutrophils: reducing C5a-induced injury

Methicillin-resistant Staphylococcus aureus (MRSA) is an important cause of ventilator-associated pneumonia (VAP). Patients with VAP have poorly functioning neutrophils, related to increased levels of the complement fragment C5a. The antibiotic linezolid has been useful in controlling MRSA-related VAP infections; however clinical benefit does not always correlate with antimicrobial effect, suggesting the possibility of immunomodulatory properties. Here the effects of linezolid on healthy and dysfunctional neutrophils (modelled by C5a-induced injury) was investigated. Functional assays (killing, phagocytosis, transmigration, and respiratory burst) were used to assess the effects of pre-, co- and post-incubating linezolid (0.4–40 mg/L) with healthy neutrophils relative to those with C5a-induced injury. C5a decreased neutrophil killing, and phagocytosis of MRSA. Furthermore, C5a significantly decreased neutrophil transmigration to IL-8, but did not affect respiratory burst. Co-incubation of linezolid significantly improved killing of MRSA by dysfunctional neutrophils, which was supported by concomitant increases in phagocytosis. Conversely linezolid impaired killing responses in healthy neutrophils. Pre- or post-incubation of linezolid prior or following C5a induced injury had no effect on neutrophil function. This study suggests that linezolid has immunomodulatory properties that protect human neutrophils from injury and provides insight into its mode of action beyond a basic antibiotic.