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Acute respiratory distress syndrome (ARDS) is characterized by the severe inflammation and destruction of the lung air-blood barrier, leading to irreversible and substantial respiratory function damage. Patients with coronavirus disease 2019 (COVID-19) have been encountered with a high risk of ARDS, underscoring the urgency for exploiting effective therapy. However, proper medications for ARDS are still lacking due to poor pharmacokinetics, non-specific side effects, inability to surmount pulmonary barrier, and inadequate management of heterogeneity. The increased lung permeability in the pathological environment of ARDS may contribute to nanoparticle-mediated passive targeting delivery. Nanomedicine has demonstrated unique advantages in solving the dilemma of ARDS drug therapy, which can address the shortcomings and limitations of traditional anti-inflammatory or antioxidant drug treatment. Through passive, active, or physicochemical targeting, nanocarriers can interact with lung epithelium/endothelium and inflammatory cells to reverse abnormal changes and restore homeostasis of the pulmonary environment, thereby showing good therapeutic activity and reduced toxicity. This article reviews the latest applications of nanomedicine in pre-clinical ARDS therapy, highlights the strategies for targeted treatment of lung inflammation, presents the innovative drug delivery systems, and provides inspiration for strengthening the therapeutic effect of nanomedicine-based treatment., Graphical abstract Nanomedicine has demonstrated great potential in achieving specific targeting and amplifying therapeutic efficiency. This review focuses on the recent breakthroughs and targeting strategies to provide insights into nanomedicine for acute respiratory distress syndrome treatment.Image 1

The Inflammatory Bowel Diseases (IBD), Ulcerative Colitis (UC) and Crohn’s Disease (CD) are characterised by chronic non-resolving gut mucosal inflammation involving innate and adaptive immune responses. Neutrophils, usually regarded as first responders in inflammation, are a key presence in the gut mucosal inflammatory milieu in IBD. Here, we review the role of neutrophil extracellular trap (NET) formation as a potential effector disease mechanism. NETs are extracellular webs of chromatin, microbicidal proteins and oxidative enzymes that are released by neutrophils to contain pathogens. NETs contribute to the pathogenesis of several immune-mediated diseases such as systemic lupus erythematosus and rheumatoid arthritis; and recently, as a major tissue damaging process involved in the host response to severe acute respiratory syndrome coronavirus 2 infection. NETs are pertinent as a defence mechanism at the gut mucosal interphase exposed to high levels of bacteria, viruses and fungi. On the other hand, NETs can also potentiate and perpetuate gut inflammation. In this review, we discuss the broad protective vs. pathogenic roles of NETs, explanatory factors that could lead to an increase in NET formation in IBD and how NETs may contribute to gut inflammation and IBD-related complications. Finally, we summarise therapeutic opportunities to target NETs in IBD.

Background Preclinical evidence implicates neutrophil elastase (NE) in pulmonary arterial hypertension (PAH) pathogenesis, and the NE inhibitor elafin is under early therapeutic investigation. Research Question Are circulating NE and elafin levels abnormal in PAH and are they associated with clinical severity? Study Design and Methods In an observational Stanford University PAH cohort (n = 249), plasma NE and elafin levels were measured in comparison with those of healthy control participants (n = 106). NE and elafin measurements were then related to PAH clinical features and relevant ancillary biomarkers. Cox regression models were fitted with cubic spline functions to associate NE and elafin levels with survival. To validate prognostic relationships, we analyzed two United Kingdom cohorts (n = 75 and n = 357). Mixed-effects models evaluated NE and elafin changes during disease progression. Finally, we studied effects of NE-elafin balance on pulmonary artery endothelial cells (PAECs) from patients with PAH. Results Relative to control participants, patients with PAH were found to have increased NE levels (205.1 ng/mL [interquartile range (IQR), 123.6-387.3 ng/mL] vs 97.6 ng/mL [IQR, 74.4-126.6 ng/mL]; P < .0001) and decreased elafin levels (32.0 ng/mL [IQR, 15.3-59.1 ng/mL] vs 45.5 ng/mL [IQR, 28.1-92.8 ng/mL]; P < .0001) independent of PAH subtype, illness duration, and therapies. Higher NE levels were associated with worse symptom severity, shorter 6-min walk distance, higher N-terminal pro-type brain natriuretic peptide levels, greater right ventricular dysfunction, worse hemodynamics, increased circulating neutrophil levels, elevated cytokine levels, and lower blood BMPR2 expression. In Stanford patients, NE levels of > 168.5 ng/mL portended increased mortality risk after adjustment for known clinical predictors (hazard ratio [HR], 2.52; CI, 1.36-4.65, P = .003) or prognostic cytokines (HR, 2.63; CI, 1.42-4.87; P = .001), and the NE level added incremental value to established PAH risk scores. Similar prognostic thresholds were identified in validation cohorts. Longitudinal NE changes tracked with clinical trends and outcomes. PAH PAECs exhibited increased apoptosis and attenuated angiogenesis when exposed to NE at the level observed in patients’ blood. Elafin rescued PAEC homeostasis, yet the required dose exceeded levels found in patients. Interpretation Blood levels of NE are increased while elafin levels are deficient across PAH subtypes. Higher NE levels are associated with worse clinical disease severity and outcomes, and this target-specific biomarker could facilitate therapeutic development of elafin.

Severe coronavirus disease 2019 (COVID-19) can result in pneumonia and acute respiratory failure. Accumulation of mucus in the airways is a hallmark of the disease and can result in hypoxemia. Here, we show that quantitative proteome analysis of the sputum from severe patients with COVID-19 reveal high levels of neutrophil extracellular trap (NET) components, which was confirmed by microscopy. Extracellular DNA from excessive NET formation can increase sputum viscosity and lead to acute respiratory distress syndrome. Recombinant human DNase (Pulmozyme; Roche) has been shown to be beneficial in reducing sputum viscosity and improve lung function. We treated five patients pwith COVID-19 resenting acute symptoms with clinically approved aerosolized Pulmozyme. No adverse reactions to the drug were seen, and improved oxygen saturation and recovery in all severely ill patients with COVID-19 was observed after therapy. Immunofluorescence and proteome analysis of sputum and blood plasma samples after treatment revealed a marked reduction of NETs and a set of statistically significant proteome changes that indicate reduction of hemorrhage, plasma leakage and inflammation in the airways, and reduced systemic inflammatory state in the blood plasma of patients. Taken together, the results indicate that NETs contribute to acute respiratory failure in COVID-19 and that degrading NETs may reduce dependency on external high-flow oxygen therapy in patients. Targeting NETs using recombinant human DNase may have significant therapeutic implications in COVID-19 disease and warrants further studies.

Background Macrophage migration inhibitory factor (MIF) is an important immuno-regulatory cytokine and is elevated in inflammatory conditions. Neutrophils are the first immune cells to migrate to sites of infection and inflammation, where they generate, among other mediators, the potent oxidant hypochlorous acid (HOCl). Here, we investigated the impact of MIF on HOCl production in neutrophils in response to phagocytic stimuli. Methods Production of HOCl during phagocytosis of zymosan was determined using the specific fluorescent probe R19-S in combination with flow cytometry and live cell microscopy. The rate of phagocytosis was monitored using fluorescently-labeled zymosan. Alternatively, HOCl production was assessed during phagocytosis of Pseudomonas aeruginosa by measuring the oxidation of bacterial glutathione to the HOCl-specific product glutathione sulfonamide. Formation of neutrophil extracellular traps (NETs), an oxidant-dependent process, was quantified using a SYTOX Green plate assay. Results Exposure of human neutrophils to MIF doubled the proportion of neutrophils producing HOCl during early stages of zymosan phagocytosis, and the concentration of HOCl produced was greater. During phagocytosis of P. aeruginosa, a greater fraction of bacterial glutathione was oxidized to glutathione sulfonamide in MIF-treated compared to control neutrophils. The ability of MIF to increase neutrophil HOCl production was independent of the rate of phagocytosis and could be blocked by the MIF inhibitor 4-IPP. Neutrophils pre-treated with MIF produced more NETs than control cells in response to PMA. Conclusion Our results suggest a role for MIF in potentiating HOCl production in neutrophils in response to phagocytic stimuli. We propose that this newly discovered activity of MIF contributes to its role in mediating the inflammatory response and enhances host defence., Graphical abstract Image 1, Highlights • MIF augments phagosomal HOCl production. • This results in increased oxidation of bacterial glutathione. • MIF increases superoxide production in response to soluble stimuli. • This results in increased NET formation.

Background : SARS-CoV-2 has led to a sharp increase in the number of hospitalizations and deaths from pneumonia and multiorgan disease worldwide; therefore, SARS-CoV-2 has become a global health problem. Supportive therapies remain the mainstay treatments against COVID-19, such as oxygen inhalation, antiviral drugs, and antibiotics. Traditional Chinese medicine (TCM) has been shown clinically to relieve the symptoms of COVID-19 infection, and TCMs can affect the pathogenesis of SARS-CoV-2 infection in vitro. Jing Si Herbal Drink (JSHD), an eight herb formula jointly developed by Tzu Chi University and Tzu Chi Hospital, has shown potential as an adjuvant treatment for COVID-19 infection. A randomized controlled trial (RCT) of JSHD as an adjuvant treatment in patients with COVID-19 infection is underway Objectives : This article aims to explore the efficacy of the herbs in JSHD against COVID-19 infection from a mechanistic standpoint and provide a reference for the rational utilization of JSHD in the treatment of COVID-19. Method : We compiled evidence of the herbs in JSHD to treat COVID-19 in vivo and in vitro. Results : We described the efficacy and mechanism of action of the active ingredients in JSHD to treat COVID-19 based on experimental evidence. JSHD includes 5 antiviral herbs, 7 antioxidant herbs, and 7 anti-inflammatory herbs. In addition, 2 herbs inhibit the overactive immune system, 1 herb reduces cell apoptosis, and 1 herb possesses antithrombotic ability. Conclusion : Although experimental data have confirmed that the ingredients in JSHD are effective against COVID-19, more rigorously designed studies are required to confirm the efficacy and safety of JSHD as a COVID-19 treatment., Graphical Abstract Image, graphical abstract

Visual Abstract, Highlights • Neutrophil adhesion to the vascular endothelium in the femoral artery of low-density lipoprotein receptor–null mice fed with HFD was significantly enhanced compared with wild-type mice fed with HFD or low-density lipoprotein receptor–null mice fed with NC. • HFD induced citrullinated histone H3 of neutrophils in LDL receptor–null mice through the up-regulation of CXCL1 in blood. • Hypercitrullination of histone H3 in neutrophils by CXCL1 enhanced neutrophil adhesion in vitro and in vivo. • Pemafibrate decreased neutrophil adhesion and citrullination of histone H3 through the reduction of CXCL1., Summary Neutrophil adhesion on the atheroprone femoral artery of high-fat diet–fed low-density lipoprotein receptor–null mice was enhanced more than in wild-type mice. The inhibition of histone H3 citrullination of neutrophils reversed the enhancement of neutrophil adhesion, suggesting that hypercitrullination contributes to enhanced neutrophil adhesion. Furthermore, pemafibrate reduced the citrullination of histone H3 in these mice. Therefore, the hypercitrullination of histone H3 in neutrophils contributes to atherosclerotic vascular inflammation.

Background: The molecular cause of severe congenital neutropenia (SCN) is unknown in 30% to 50% of patients. SEC61A1 encodes the α-subunit of the Sec61 complex, which governs endoplasmic reticulum protein transport and passive calcium leakage. Recently, mutations in SEC61A1 were reported to be pathogenic in common variable immunodeficiency and glomerulocystic kidney disease. Objective: Our aim was to expand the spectrum of SEC61A1-mediated disease to include autosomal dominant SCN. Methods: Whole exome sequencing findings were validated, and reported mutations were compared by Western blotting, Ca2+ flux assays, differentiation of transduced HL-60 cells, in vitro differentiation of primary CD34 cells, quantitative PCR for unfolded protein response (UPR) genes, and single-cell RNA sequencing on whole bone marrow. Results: We identified a novel de novo missense mutation in SEC61A1 (c.A275G;p.Q92R) in a patient with SCN who was born to nonconsanguineous Belgian parents. The mutation results in diminished protein expression, disturbed protein translocation, and an increase in calcium leakage from the endoplasmic reticulum. In vitro differentiation of CD34+ cells recapitulated the patient's clinical arrest in granulopoiesis. The impact of Q92R-Sec61α1 on neutrophil maturation was validated by using HL-60 cells, in which transduction reduced differentiation into CD11b+CD16+ cells. A potential mechanism for this defect is the uncontrolled initiation of the unfolded protein stress response, with single-cell analysis of primary bone marrow revealing perturbed UPR in myeloid precursors and in vitro differentiation of primary CD34+ cells revealing upregulation of CCAAT/enhancer-binding protein homologous protein and immunoglobulin heavy chain binding protein UPR-response genes. Conclusion: Specific mutations in SEC61A1 cause SCN through dysregulation of the UPR., SCOPUS: ar.j, info:eu-repo/semantics/published

Background Pulmonary exacerbations (PEx) in children with cystic fibrosis (CF) are frequently treated in the outpatient setting with oral antibiotics. However, little is known about the characteristics of PEx managed on an outpatient basis and the effectiveness of oral antibiotic therapy. We sought to prospectively evaluate clinical and laboratory changes associated with oral antibiotic treatment for PEx. Methods Children with CF between 8 and 18 years of age prescribed two weeks of oral antibiotics for a PEx were eligible to enroll. The study consisted of a visit within 48 h of starting antibiotics and a second visit within one week of antibiotic completion. Twenty-eight participants were evaluated by exacerbation score, quality of life measurements, lung function, sputum microbiology and inflammation. Results Oral antibiotic treatment was associated with a significant improvement in exacerbation score and quality of life measured by the CF Questionnaire-Revised (CFQ-R) respiratory domain. Following treatment, forced expiratory volume in 1 s (FEV1) % predicted increased [median (range)] 9% (−8%, 31%), and 22 (81%) subjects returned to 90% or higher of baseline FEV1. Bacterial density of the primary organism identified on sputum culture decreased significantly with a median (range) decrease of 0.8 log10 cfu/mL (−8 log10, 2 log10, p = 0.03). Sputum neutrophil elastase [−37 μg/mL (−464, 272), p = 0.02] and IL-1β [−2.8 × 103μg/mL (−6.9 × 104, 3.3 × 104), p = 0.03] decreased significantly following treatment in this cohort. Conclusions Treatment of PEx with oral antibiotics was associated with measurable improvements in patient reported outcomes, lung function, bacterial density and sputum inflammatory markers.

Graphical abstract Image, graphical abstract, Background Inflammation-mediated lung injury is a major cause of health problems in many countries and has been the leading cause of morbidity/mortality in intensive care units. In the current COVID-19 pandemic, the majority of the patients experienced serious pneumonia resulting from inflammation (Acute respiratory distress syndrome/ARDS). Pathogenic infections cause cytokine release syndrome (CRS) by hyperactivation of immune cells, which in turn release excessive cytokines causing ARDS. Currently, there are no standard therapies for viral, bacterial or pathogen-mediated CRS. Purpose This study aimed to investigate and validate the protective effects of Dehydrozingerone (DHZ) against LPS induced lung cell injury by in-vitro and in-vivo models and to gain insights into the molecular mechanisms that mediate these therapeutic effects. Methods The therapeutic activity of DHZ was determined in in-vitro models by pre-treating the cells with DHZ and exposed to LPS to stimulate the inflammatory cascade of events. We analysed the effect of DHZ on LPS induced inflammatory cytokines, chemokines and cell damage markers expression/levels using various cell lines. We performed gene expression, ELISA, and western blot analysis to elucidate the effect of DHZ on inflammation and its modulation of MAPK and NF-κB pathways. Further, the prophylactic and therapeutic effect of DHZ was evaluated against the LPS induced ARDS model in rats. Results DHZ significantly (p

Background Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are life-threatening diseases and could occur in severe COVID-19 patients. Re-Du-Ning injection (RDN) is a tradition Chinese medicine preparation which has been clinically used for treatment of respiratory diseases including COVID-19. Purpose To elucidate the potential mechanisms of RDN for the treatment of ALI. Methods Female C57BL/6J mice were used to establish ALI model by intraperitoneal injection 10 mg/kg LPS, and RDN injection was intraperitoneally administered with the dose of 5 and 10 mL/kg. The cytokines were measured by ELISA and qPCR. The data related to NETs were analyzed by ELISA, immunofluorescence, Western blotting and network pharmacological approach. Results RDN robustly alleviated LPS-induced ALI. Meanwhile, RDN downregulated the expression of pro-inflammatory cytokines, such as IL-1β, IL-6 and TNF-α. Specifically, RDN treatment inhibited the formation of neutrophil extracellular traps (NETs) and remarkably suppressed the protein of PAD4. The active compound from RDN decreased the phosphorylation of ERK1/2. Conclusion These findings demonstrate that RDN ameliorates LPS-induced ALI through suppressing MAPK pathway to inhibit the formation of NETs., Graphical abstract Image, graphical abstract

The coronavirus disease 19 (COVID-19) has turned out to be a pandemic in short period of time due to the high transmissibility of its causative agent, severe acute respiratory syndrome coronavirus 2. Various reports have suggested the promising link between overexpression of angiotensin converting enzyme 2 (ACE2) and COVID-19 pathogenesis. The severity of COVID-19 pathophysiology is greatly depended on several comorbidities, like hypertension, diabetes mellitus (DM), respiratory and cardiovascular disease, out of which DM has emerged as a major risk factor. The current review focuses on the link among the expression of ACE2, use of ACE inhibitors (ACEIs) and angiotensin II type 1 receptor blockers (ARBs), and risk of COVID-19 pathogenesis in DM. The review also emphasizes on synergistic detrimental effect of DM and COVID-19 on the immune system in provoking uncontrolled cytokine storm which eventually leads to lethal consequences. Finally, several possible therapeutic strategies have been highlighted to reduce the excess of risk associated with COVID-19 in people with DM.

Visual Abstract, Highlights • As expected, ticagrelor reduced ex-vivo ADP-induced aggregation in patients with pneumonia compared with placebo. • Ticagrelor reduced platelet–leukocyte interactions as well as plasma interleukin-6 within 24 h in patients with pneumonia compared with placebo. • Ticagrelor acutely altered NETosis biomarkers, whereas placebo had no effect. • Ticagrelor improved lung function and reduced need for supplemental oxygen in patients with pneumonia compared with placebo., Summary Despite treatment advances for sepsis and pneumonia, significant improvements in outcome have not been realized. Antiplatelet therapy may improve outcome in pneumonia and sepsis. In this study, the authors show that ticagrelor reduced leukocytes with attached platelets as well as the inflammatory biomarker interleukin (IL)-6. Pneumonia patients receiving ticagrelor required less supplemental oxygen and lung function tests trended toward improvement. Disruption of the P2Y12 receptor in a murine model protected against inflammatory response, lung permeability, and mortality. Results indicate a mechanistic link between platelets, leukocytes, and lung injury in settings of pneumonia and sepsis, and suggest possible therapeutic approaches to reduce complications.(Targeting Platelet-Leukocyte Aggregates in Pneumonia With Ticagrelor [XANTHIPPE]; NCT01883869)

COPD (chronic obstructive pulmonary disease) is a major incurable global health burden and will become the third largest cause of death in the world by 2020. It is currently believed that an exaggerated inflammatory response to inhaled irritants, in particular cigarette smoke, causes progressive airflow limitation. This inflammation, where macrophages, neutrophils and T-cells are prominent, leads to oxidative stress, emphysema, small airways fibrosis and mucus hypersecretion. The mechanisms and mediators that drive the induction and progression of chronic inflammation, emphysema and altered lung function are poorly understood. Current treatments have limited efficacy in inhibiting chronic inflammation, do not reverse the pathology of disease and fail to modify the factors that initiate and drive the long-term progression of disease. Therefore there is a clear need for new therapies that can prevent the induction and progression of COPD. Animal modelling systems that accurately reflect disease pathophysiology continue to be essential to the development of new therapies. The present review highlights some of the mouse models used to define the cellular, molecular and pathological consequences of cigarette smoke exposure and whether they can be used to predict the efficacy of new therapeutics for COPD.

COPD (chronic obstructive pulmonary disease) is caused by exposure to toxic gases and particles, most often CS (cigarette smoke), leading to emphysema, chronic bronchitis, mucus production and a subsequent decline in lung function. The disease pathogenesis is related to an abnormal CS-induced inflammatory response of the lungs. Similar to active (mainstream) smoking, second hand (sidestream) smoke exposure severely affects respiratory health. These processes can be studied in vivo in models of CS exposure of mice. We compared the acute inflammatory response of female C57BL/6 mice exposed to two concentrations [250 and 500 mg/m3 TPM (total particulate matter)] of sidestream and mainstream CS for 3 days and interpreted the biological effects based on physico-chemical differences in the gas and particulate phase composition of CS. BAL (bronchoalveolar lavage fluid) was obtained to perform differential cell counts and to measure cytokine release. Lung tissue was used to determine mRNA and protein expression of proinflammatory genes and to assess tissue inflammation. A strong acute inflammatory response characterized by neutrophilic influx, increased cytokine secretion [KC (keratinocyte chemoattractant), TNF-α (tumour necrosis factor α), MIP-2 (macrophage inflammatory protein 2), MIP-1α and MCP-1 (monocyte chemoattractant protein-1)], pro-inflammatory gene expression [KC, MIP-2 and MMP12 (matrix metalloproteinase 12)] and up-regulated GM-CSF (granulocyte macrophage colony-stimulating factor) production was observed in the mainstream model. After sidestream exposure there was a dampened inflammatory reaction consisting only of macrophages and diminished GM-CSF levels, most likely caused by elevated CO concentrations. These results demonstrate that the composition of CS determines the dynamics of inflammatory cell recruitment in COPD mouse models. Different initial inflammatory processes might contribute to COPD pathogenesis in significantly varying ways, thereby determining the outcome of the studies.

The 2',5'-oligoadenylate synthetase 1 (OAS1) is one of the major interferon-inducible proteins and a critical component of the host defense system against viral infection. A single nucleotide polymorphism (SNP), rs10774671, presumably responsible for alternate splicing of this gene, has frequently been associated with a variety of viral diseases, including emerging respiratory infections. We investigated the SNP-dependent expression of OAS1 variants in primary cultured human bronchial epithelial cells. Total RNA was subjected to real-time RT-PCR with specific primer sets designed to amplify each transcript variant. We found that the p46 transcript was mainly expressed in cells with the GG genotype, whereas the p42 transcript was highly expressed, and the p44a (alternate exon in intron 5), p48, and p52 transcripts were expressed to a lesser extent, in cells with the AA genotype. Immunoblot analysis revealed that the p46 isoform and a smaller amount of the p42 isoform were present in cells with the GG genotype, whereas only the p42 isoform was clearly observed in cells with the AA genotype. Cellular DNA fragmentation induced by neutrophil elastase was more preferentially found in cells with the AA genotype. Thus, our findings provide insights into the potential role of OAS1 polymorphisms in respiratory infection.

International audience; The serine proteases released by activated polymorphonuclear neutrophils [NSPs (neutrophil serine proteases)] contribute to a variety of inflammatory lung diseases, including CF (cystic fibrosis). They are therefore key targets for the development of efficient inhibitors. Although rodent models have contributed to our understanding of several diseases, we have previously shown that they are not appropriate for testing anti-NSP therapeutic strategies [Kalupov, Brillard-Bourdet, Dade, Serrano, Wartelle, Guyot, Juliano, Moreau, Belaaouaj and Gauthier (2009) J. Biol. Chem. 284, 34084–34091). Thus NSPs must be characterized in an animal model that is much more likely to predict how therapies will act in humans in order to develop protease inhibitors as drugs. The recently developed CFTR−/− (CFTR is CF transmembrane conductance regulator) pig model is a promising alternative to the mouse model of CF [Rogers, Stoltz, Meyerholz, Ostedgaard, Rokhlina, Taft, Rogan, Pezzulo, Karp, Itani et al. (2008) Science 321, 1837–1841]. We have isolated blood neutrophils from healthy pigs and determined their responses to the bacterial pathogens Pseudomonas aeruginosa and Staphylococcus aureus, and the biochemical properties of their NSPs. We used confocal microscopy and antibodies directed against their human homologues to show that the three NSPs (elastase, protease 3 and cathepsin G) are enzymatically active and present on the surface of triggered neutrophils and NETs (neutrophil extracellular traps). All of the porcine NSPs are effectively inhibited by human NSP inhibitors. We conclude that there is a close functional resemblance between porcine and human NSPs. The pig is therefore a suitable animal model for testing new NSP inhibitors as anti-inflammatory agents in neutrophil-associated diseases such as CF.

Leukocytes invade newly formed thrombi through interactions with platelets and fibrin and later contribute to the removal of fibrin deposits mainly through the action of neutrophil elastase. The present study attempts to express in quantitative terms the impact of neutrophils on the lytic processes in obliterative thrombi based on the local presence of elastase-specific fibrin degradation products (NE-FDP) in relation to the leukocyte, platelet and fibrin content of thrombi. Immunofluorescent detection of fibrin, NE-FDP and platelet antigens was performed in sections of thrombi from 28 patients subjected to thrombectomy in combination with DNA-staining for identification of nucleated cells. The digitalized fluorescent microscopic images were decomposed according to the color channel of each thrombus constituent. The integrated intensity values for all thrombus constituents were statistically evaluated with correlation, hierarchical agglomerative clustering , Hotelling'sT2 and F-statistics. Association between NE-FDP and leukocyte content of thrombi is evidenced by a significant Pearson correlation coefficient of 0.71 (p=0.00002). Cluster analysis reveals two classes of thrombi according to NE-FDP, leukocyte and platelet content and also two according to NE-FDP, leukocyte and fibrin content. When NE-FDP, fibrin and platelet content is normalized to the leukocyte count in the same thrombus, clusters with platelet-related thrombolytic resistance (inversely related NE-FDP and platelet content) and advanced cell-dependent thrombolysis (inversely related NE-FDP and fibrin content) are identified. These distinct patterns of thrombus constituents are snapshots of characteristic stages in the cell-dependent thrombolysis, which indicate a clot-stabilizing role for platelets in this process similar to their impact on the plasmin-dependent lysis.