Interleukin-2 involvement in early acute respiratory distress syndrome: relationship with polymorphonuclear neutrophil apoptosis and patient survival

Inflammatory subphenotypes in patients at risk of ARDS: evidence from the LIPS-A trial

PURPOSE

Latent class analysis (LCA) has identified hyper- and non-hyper-inflammatory subphenotypes in patients with acute respiratory distress syndrome (ARDS). It is unknown how early inflammatory subphenotypes can be identified in patients at risk of ARDS. We aimed to test for inflammatory subphenotypes upon presentation to the emergency department.

METHODS

LIPS-A was a trial of aspirin to prevent ARDS in at-risk patients presenting to the emergency department. In this secondary analysis, we performed LCA using clinical, blood test, and biomarker variables.

RESULTS

Among 376 (96.4%) patients from the LIPS-A trial, two classes were identified upon presentation to the emergency department (day 0): 72 (19.1%) patients demonstrated characteristics of a hyper-inflammatory and 304 (80.9%) of a non-hyper-inflammatory subphenotype. 15.3% of patients in the hyper- and 8.2% in the non-hyper-inflammatory class developed ARDS (p = 0.07). Patients in the hyper-inflammatory class had fewer ventilator-free days (median [interquartile range, IQR] 28[23-28] versus 28[27-28]; p = 0.010), longer intensive care unit (3[2-6] versus 0[0-3] days; p < 0.001) and hospital (9[6-18] versus 5[3-9] days; p < 0.001) length of stay, and higher 1-year mortality (34.7% versus 20%; p = 0.008). Subphenotypes were identified on day 1 and 4 in a subgroup with available data (n = 244). 77.9% of patients remained in their baseline class throughout day 4. Patients with a hyper-inflammatory subphenotype throughout the study period (n = 22) were at higher risk of ARDS (36.4% versus 10.4%; p = 0.003).

CONCLUSION

Hyper- and non-hyper-inflammatory subphenotypes may precede ARDS development, remain identifiable over time, and can be identified upon presentation to the emergency department. A hyper-inflammatory subphenotype predicts worse outcomes.

Interesting effects of interleukins and immune cells on acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a medical condition characterized by widespread inflammation in the lungs with consequent proportional loss of gas exchange function. ARDS is linked with severe pulmonary or systemic infection. Several factors, including secretory cytokines, immune cells, and lung epithelial and endothelial cells, play a role in the development and progression of this disease. The present study is based on Pubmed database information (1987-2022) using the words "Acute respiratory distress syndrome", "Interleukin", "Cytokines" and "Immune cells". Cytokines and immune cells play an important role in this disease, with particular emphasis on the balance between pro-inflammatory and anti-inflammatory factors. Neutrophils are one of several important mediators of Inflammation, lung tissue destruction, and malfunction during ARDS. Some immune cells, such as macrophages and eosinophils, play a dual role in releasing inflammatory mediators, recruitment inflammatory cells and the progression of ARDS, or releasing anti-inflammatory mediators, clearing the lung of inflammatory cells, and helping to improve the disease. Different interleukins play a role in the development or inhibition of ARDS by helping to activate various signaling pathways, helping to secrete other inflammatory or anti-inflammatory interleukins, and playing a role in the production and balance between immune cells involved in ARDS. As a result, immune cells and, inflammatory cytokines, especially interleukins play an important role in the pathogenesis of this disease Therefore, understanding the relevant mechanisms will help in the proper diagnosis and treatment of this disease.

The role of G protein-coupled receptor in neutrophil dysfunction during sepsis-induced acute respiratory distress syndrome

Sepsis is defined as a life-threatening dysfunction due to a dysregulated host response to infection. It is a common and complex syndrome and is the leading cause of death in intensive care units. The lungs are most vulnerable to the challenge of sepsis, and the incidence of respiratory dysfunction has been reported to be up to 70%, in which neutrophils play a major role. Neutrophils are the first line of defense against infection, and they are regarded as the most responsive cells in sepsis. Normally, neutrophils recognize chemokines including the bacterial product N-formyl-methionyl-leucyl-phenylalanine (fMLP), complement 5a (C5a), and lipid molecules Leukotriene B4 (LTB4) and C-X-C motif chemokine ligand 8 (CXCL8), and enter the site of infection through mobilization, rolling, adhesion, migration, and chemotaxis. However, numerous studies have confirmed that despite the high levels of chemokines in septic patients and mice at the site of infection, the neutrophils cannot migrate to the proper target location, but instead they accumulate in the lungs, releasing histones, DNA, and proteases that mediate tissue damage and induce acute respiratory distress syndrome (ARDS). This is closely related to impaired neutrophil migration in sepsis, but the mechanism involved is still unclear. Many studies have shown that chemokine receptor dysregulation is an important cause of impaired neutrophil migration, and the vast majority of these chemokine receptors belong to the G protein-coupled receptors (GPCRs). In this review, we summarize the signaling pathways by which neutrophil GPCR regulates chemotaxis and the mechanisms by which abnormal GPCR function in sepsis leads to impaired neutrophil chemotaxis, which can further cause ARDS. Several potential targets for intervention are proposed to improve neutrophil chemotaxis, and we hope that this review may provide insights for clinical practitioners.

Acute respiratory distress syndrome is associated with impaired alveolar macrophage efferocytosis

Acute respiratory distress syndrome (ARDS) is an inflammatory disorder of the lungs, with sepsis as the predominant aetiology. Despite advances in ventilation strategies, mortality for moderate to severe ARDS remains at 40–46% [1]. ARDS is associated with neutrophil influx into alveoli. Persistently high neutrophil and low alveolar macrophage (AM) numbers in bronchoalveolar lavage (BAL) fluid are associated with greater mortality [2]. While the inflammatory alveolar environment of early ARDS initially delays apoptosis, these neutrophils ultimately undergo apoptosis within alveoli [3]. Efficient efferocytosis of apoptotic neutrophils by AMs is critical for resolution of inflammation [3]. Apoptotic neutrophils may accumulate in ARDS due to defective AM efferocytosis and/or overwhelmed efferocytosis capacity, then undergo secondary necrosis, releasing inflammatory mediators into the alveolar space [4]. This may contribute to the prolonged inflammation observed in ARDS. No study has previously assessed AM efferocytosis in ARDS; however, monocyte-derived macrophages (MDMs) from ARDS patients do have impaired efferocytosis [5]. We investigated whether ARDS patients have impaired AM efferocytosis and increased alveolar neutrophil apoptosis.

ARDS patients have decreased alveolar macrophage efferocytosis, which is associated with increased alveolar inflammation, and may contribute to worse clinical outcomes, including mortality. Upregulation of efferocytosis may offer a therapeutic strategy.https://bit.ly/2Q7REdM

SSRIs: Applications in inflammatory lung disease and implications for COVID-19

Selective serotonin reuptake inhibitors (SSRIs) have anti-inflammatory properties that may have clinical utility in treating severe pulmonary manifestations of COVID-19. SSRIs exert anti-inflammatory effects at three mechanistic levels: (a) inhibition of proinflammatory transcription factor activity, including NF-κB and STAT3; (b) downregulation of lung tissue damage and proinflammatory cell recruitment via inhibition of cytokines, including IL-6, IL-8, TNF-α, and IL-1β; and (c) direct suppression inflammatory cells, including T cells, macrophages, and platelets. These pathways are implicated in the pathogenesis of COVID-19. In this review, we will compare the pathogenesis of lung inflammation in pulmonary diseases including COVID-19, ARDS, and chronic obstructive pulmonary disease (COPD), describe the anti-inflammatory properties of SSRIs, and discuss the applications of SSRIS in treating COVID-19-associated inflammatory lung disease.

Lung fluid biomarkers for acute respiratory distress syndrome: a systematic review and meta-analysis

Background

With the development of new techniques to easily obtain lower respiratory tract specimens, bronchoalveolar lavage fluid and other lung fluids are gaining importance in pulmonary disease diagnosis. We aimed to review and summarize lung fluid biomarkers associated with acute respiratory distress syndrome diagnosis and mortality.

Methods

After searching PubMed, Embase, Web of Science, and the Cochrane Library for articles published prior to January 11, 2018, we performed a meta-analysis on biomarkers for acute respiratory distress syndrome diagnosis in at-risk patients and those related to disease mortality. From the included studies, we then extracted the mean and standard deviation of the biomarker concentrations measured in the lung fluid, acute respiratory distress syndrome etiologies, sample size, demographic variables, diagnostic criteria, mortality, and protocol for obtaining the lung fluid. The effect size was measured by the ratio of means, which was then synthesized by the inverse-variance method using its natural logarithm form and transformed to obtain a pooled ratio and 95% confidence interval.

Results

In total, 1156 articles were identified, and 49 studies were included. Increases in total phospholipases A2 activity, total protein, albumin, plasminogen activator inhibitor-1, soluble receptor for advanced glycation end products, and platelet activating factor-acetyl choline were most strongly associated with acute respiratory distress syndrome diagnosis. As for biomarkers associated with acute respiratory distress syndrome mortality, interleukin-1β, interleukin-6, interleukin-8, Kerbs von Lungren-6, and plasminogen activator inhibitor-1 were significantly increased in the lung fluid of patients who died. Decreased levels of Club cell protein and matrix metalloproteinases-9 were associated with increased odds for acute respiratory distress syndrome diagnosis, whereas decreased levels of Club cell protein and interleukin-2 were associated with increased odds for acute respiratory distress syndrome mortality.

Conclusions

This meta-analysis provides a ranking system for lung fluid biomarkers, according to their association with diagnosis or mortality of acute respiratory distress syndrome. The performance of biomarkers among studies shown in this article may help to improve acute respiratory distress syndrome diagnosis and outcome prediction.

Electronic supplementary material

The online version of this article (10.1186/s13054-019-2336-6) contains supplementary material, which is available to authorized users.

T cell-directed IL-17 production by lung granular γδ T cells is coordinated by a novel IL-2 and IL-1β circuit

Immune-mediated lung is considered the result of an exacerbated innate injury immune response, although a role for adaptive lymphocytes is emerging. αβ T cells specific for S. aureus enterotoxin A orchestrate a Tγδ17 response during lung injury. However, the mechanism driving IL-17 production is unclear. Here, we show a role for IL-2 triggering IL-17 production by lung granular γδ T cells as IL-17 synthesis and neutrophil recruitment was reduced by IL-2 blocking mAbs in vitro and in vivo. Mass cytometry analysis revealed that lung γδ T cells responded directly to IL-2 as evident from STAT5 phosphorylation and RoRγt expression. IL-2 receptor blocking mAbs and JAK inhibition impaired STAT5 phosphorylation and IL-17 release. Moreover, inhalation of S. aureus enterotoxin A induced IL-2 secretion and caspase-1-dependent IL-1β activation to drive IL-17 production. This T-cell-mediated inflammasome-dependent IL-17 response is maximum when lung Tγδ17 cells were sequentially stimulated first with IL-2 then IL-1β. Interestingly, when IL-2 is given therapeutically to cancer patients it carries a known risk of lung injury that is largely indistinguishable from that seen in sepsis. Hence, this novel mechanism reveals therapeutic targets treating both acute lung injury and high-dose IL-2 toxicity in cancer.

Photobiomodulation prevents DNA fragmentation of alveolar epithelial cells and alters the mRNA levels of caspase 3 and Bcl-2 genes in acute lung injury

Acute respiratory distress syndrome (ARDS) and acute lung injury (ALI) are defined as pulmonary inflammation that could occur from sepsis and lead to pulmonary permeability and alveolar edema making them life-threatening diseases. Photobiomodulation (PBM) properties have been widely described in the literature in several inflammatory diseases; although the mechanisms of action are not always clear, this could be a possible treatment for ARDS/ALI. Thus, the aim of this study was to evaluate the mRNA levels from caspase-3 and BCL-2 genes and DNA fragmentation in lung tissue from Wistar rats affected by ALI and subjected to photobiomodulation by exposure to a low power infrared laser (808 nm; 100 mW; 3.571 W cm-2; four points per lung). Adult male Wistar rats were randomized into 6 groups (n = 5, for each group): control, PBM10 (10 J cm-2, 2 J and 2 seconds), PBM20 (20 J cm-2, 5 J and 5 seconds), ALI, ALI + PBM10 and ALI + PBM20. ALI was induced by intraperitoneal Escherichia coli lipopolysaccharide injection. Lung samples were collected and divided for mRNA expression of caspase-3 and Bcl-2 and DNA fragmentation quantifications. Data show that caspase-3 mRNA levels are reduced and Bcl-2 mRNA levels increased in ALI after low power infrared laser exposure when compared to the non-exposed ALI group. DNA fragmentation increased in inflammatory infiltrate cells and reduced in alveolar cells. Our research shows that photobiomodulation can alter relative mRNA levels in genes involved in the apoptotic process and DNA fragmentation in inflammatory and alveolar cells after lipopolysaccharide-induced acute lung injury. Also, inflammatory cell apoptosis is part of the photobiomodulation effects induced by exposure to a low power infrared laser.

Therapeutic blockade of CD54 attenuates pulmonary barrier damage in T cell-induced acute lung injury

Acute respiratory distress syndrome (ARDS) is a serious, often fatal condition without available pharmacotherapy. Although the role of innate cells in ARDS has been studied extensively, emerging evidence suggests that T cells may be involved in disease etiology. Staphylococcus aureus enterotoxins are potent T-cell mitogens capable of triggering life-threatening shock. We demonstrate that 2 days after inhalation of S. aureus enterotoxin A, mice developed T cell-mediated increases in vascular permeability, as well as expression of injury markers and caspases in the lung. Pulmonary endothelial cells underwent sequential phenotypic changes marked by rapid activation coinciding with inflammatory events secondary to T-cell priming, followed by reductions in endothelial cell number juxtaposing simultaneous T-cell expansion and cytotoxic differentiation. Although initial T-cell activation influenced the extent of lung injury, CD54 (ICAM-1) blocking antibody administered well after enterotoxin exposure substantially attenuated pulmonary barrier damage. Thus CD54-targeted therapy may be a promising candidate for further exploration into its potential utility in treating ARDS patients.

Higher mini-BAL total protein concentration in early ARDS predicts faster resolution of lung injury measured by more ventilator-free days

The protein concentration of alveolar edema fluid in acute respiratory distress syndrome (ARDS) is dynamic. It reflects alveolar flooding during acute injury, as well as fluid and protein clearance over time. We hypothesized that among ARDS patients treated with low tidal volume ventilation, higher concentrations of protein in mini-bronchoalveolar lavage (mBAL) samples would predict slower resolution of lung injury and worse clinical outcomes. Total protein and IgM concentrations in day 0 mBAL samples from 79 subjects enrolled in the aerosolized albuterol (ALTA) ARDS Network Albuterol Trial were measured by colorimetric assay and ELISA, respectively. Linear regression models were used to test the association of mBAL proteins with clinical outcomes and measures of length of illness, including ventilator-free days (VFDs). Median mBAL total protein concentration was 1,740 μg/ml [interquartile range (IQR): 890-3,170]. Each 500 μg/ml increase in day 0 mBAL total protein was associated with an additional 0.8 VFDs [95% confidence interval (CI): 0.05-1.6, P value = 0.038]. Median mBAL IgM concentration was 410 ng/ml (IQR: 340-500). Each 50 ng/ml increase in mBAL IgM was associated with an additional 1.1 VFDs (95% CI 0.2-2.1, P value = 0.022). These associations remained significant and were not attenuated in multivariate models adjusted for age, serum protein concentration, and vasopressor use in the 24 h before enrollment. Thus, higher mBAL total protein and IgM concentrations at day 0 are associated with more VFDs in patients with ARDS and may identify patients with preserved alveolar epithelial mechanisms for net alveolar fluid clearance.

Extremes of Interferon-Stimulated Gene Expression Associate with Worse Outcomes in the Acute Respiratory Distress Syndrome

Acute Respiratory Distress Syndrome (ARDS) severity may be influenced by heterogeneity of neutrophil activation. Interferon-stimulated genes (ISG) are a broad gene family induced by Type I interferons, often as a response to viral infections, which evokes extensive immunomodulation. We tested the hypothesis that over- or under-expression of immunomodulatory ISG by neutrophils is associated with worse clinical outcomes in patients with ARDS. Genome-wide transcriptional profiles of circulating neutrophils isolated from patients with sepsis-induced ARDS (n = 31) and healthy controls (n = 19) were used to characterize ISG expression. Hierarchical clustering of expression identified 3 distinct subject groups with Low, Mid and High ISG expression. ISG accounting for the greatest variability in expression were identified (MX1, IFIT1, and ISG15) and used to analyze a prospective cohort at the Colorado ARDS Network site. One hundred twenty ARDS patients from four urban hospitals were enrolled within 72 hours of initiation of mechanical ventilation. Circulating neutrophils were isolated from patients and expression of ISG determined by PCR. Samples were stratified by standard deviation from the mean into High (n = 21), Mid, (n = 82) or Low (n = 17) ISG expression. Clinical outcomes were compared between patients with High or Low ISG expression to those with Mid-range expression. At enrollment, there were no differences in age, gender, co-existing medical conditions, or type of physiologic injury between cohorts. After adjusting for age, race, gender and BMI, patients with either High or Low ISG expression had significantly worse clinical outcomes than those in the Mid for number of 28-day ventilator- and ICU-free days (P = 0.0006 and 0.0004), as well as 90-day mortality and 90-day home with unassisted breathing (P = 0.02 and 0.004). These findings suggest extremes of ISG expression by circulating neutrophils from ARDS patients recovered early in the syndrome are associated with poorer clinical outcomes.

Regulatory T Cells Resist Cyclosporine-Induced Cell Death via CD44-Mediated Signaling Pathways

Cyclosporine A (CSA) is an immunosuppressive agent that specifically targets T cells and also increases the percentage of pro-tolerogenic CD4+Foxp3+ regulatory T cells (Treg) through unknown mechanisms. We previously reported that CD44, a receptor for the extracellular matrix glycosaminoglycan hyaluronan (HA), promotes Treg stability in IL-2-low environments. Here, we asked whether CD44 signaling also promotes Treg resistance to CSA. We found that CD44 cross-linking promoted Foxp3 expression and Treg viability in the setting of CSA treatment. This effect was IL-2 independent but could be suppressed using sc-355979, an inhibitor of Stat5-phosphorylation. Moreover, we found that inhibition of HA synthesis impairs Treg homeostasis but that this effect could be overcome with exogenous IL-2 or CD44-cross-linking. Together, these data support a model whereby CD44 cross-linking by HA promotes IL-2-independent Foxp3 expression and Treg survival in the face of CSA.

NF-κB RNAi decreases the Bax/Bcl-2 ratio and inhibits TNF-α-induced apoptosis in human alveolar epithelial cells

OBJECTIVE

Apoptosis of alveolar epithelial cells (AECs) plays a key role in acute lung injury (ALI). Understanding the underlying mechanism is conducive to the treatment of ALI. The goal of this study was to determine the possible involvement of nuclear factor-κB (NF-κB)/p65 and Bax/Bcl-2 in tumor necrosis factor-α (TNF-α)-induced apoptosis in AECs.

METHODS

Type II AECs, A549, with or without NF-κB/p65 expression silenced by small interfering RNA (siRNA) were challenged with TNF-α. The levels of NF-κB/p65, Bcl-2 and Bax were detected by reverse transcription-polymerase chain reaction, Western blotting, and immunocytochemical staining. The apoptosis rate was measured by flow cytometry.

RESULTS

TNF-α challenge significantly increased the transcription and translation of NF-κB/p65 and Bax genes, but significantly decreased the Bcl-2 gene level. siRNA silencing of NF-κB/p65 reversed the effect of TNF-α on NF-κB/p65, Bcl-2 and Bax, and significantly decreased the TNF-α-induced apoptosis rate of AECs, as compared to the non-silenced cells.

CONCLUSIONS

This study indicates that NF-κB plays an important role in the process of TNF-α-induced apoptosis in AECs, via regulation of the expression of Bcl-2 and Bax.

Bacteria-specific neutrophil dysfunction associated with interferon-stimulated gene expression in the acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is a poorly understood condition with greater than 30% mortality. Massive recruitment of neutrophils to the lung occurs in the initial stages of the ARDS. Significant variability in the severity and duration of ARDS-associated pulmonary inflammation could be linked to heterogeneity in the inflammatory capacity of neutrophils. Interferon-stimulated genes (ISGs) are a broad gene family induced by Type I interferons. While ISGs are central to anti-viral immunity, the potential exists for these genes to evoke extensive modification in cellular response in other clinical settings. In this prospective study, we sought to determine if ISG expression in circulating neutrophils from ARDS patients is associated with changes in neutrophil function. Circulating neutrophil RNA was isolated, and hierarchical clustering ranked patients' expression of three ISGs. Neutrophil response to pathogenic bacteria was compared between normal and high ISG-expressing neutrophils. High neutrophil ISG expression was found in 25 of 95 (26%) of ARDS patients and was associated with reduced migration toward interleukin-8, and altered responses to Staphylococcus aureus, but not Pseudomonas aeruginosa, which included decreased p38 MAP kinase phosphorylation, superoxide anion release, interleukin-8 release, and a shift from necrotic to apoptotic cell death. These alterations in response were reflected in a decreased capacity to kill S. aureus, but not P. aeruginosa. Therefore, the ISG expression signature is associated with an altered circulating neutrophil response phenotype in ARDS that may predispose a large subgroup of patients to increased risk of specific bacterial infections.

Inhibition of neutrophil apoptosis via sphingolipid signaling in acute lung injury

Acute lung injury (ALI) is characterized by lung inflammation and diffuse infiltration of neutrophils into the alveolar space. The inhibition of alveolar neutrophil apoptosis has been implicated in the pathogenesis of ALI. Although sphingolipids may regulate cell apoptosis, the role of sphingolipids in activated neutrophils during ALI is not clear. In this study, we test the hypothesis that sphingolipids would attenuate neutrophil apoptosis that contributes to the development of ALI. Lipopolysaccharide (LPS)-stimulated human neutrophils, with or without inhibitor treatment, were analyzed for apoptosis. We found that the inhibitory effect of LPS on neutrophil apoptosis was blocked by treatment with the neutral sphingomyelinase (nSMase) inhibitor sphingolactone-24 (Sph-24), sphingosine kinase inhibitor II, and p38 mitogen-activated protein kinase (MAPK) inhibitor 4-[4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-1H-imidazol-5-yl]pyridine (SB203580) but not by the acidic sphingomyelinase inhibitor chlorpromazine. LPS-activated phosphorylation of p38 MAPK also was attenuated by treatment with Sph-24 and sphingosine kinase inhibitor II. Furthermore, mice with LPS-induced lung injury were treated with the nSMase inhibitor Sph-24 to evaluate its impact on lung injury and survival. The severity of LPS-induced ALI was reduced, and the survival rate was increased in mice treated with Sph-24 compared with that in those given LPS alone. Intracellular levels of sphingolipids in alveolar neutrophils from patients with acute respiratory distress syndrome also were measured. We found that intracellular levels of ceramide and phospho-p38 MAPK were elevated in alveolar neutrophils from acute respiratory distress syndrome patients. Our results demonstrate that activation of the nSMase/sphingosine-1-phosphate pathway to induce p38 MAPK phosphorylation results in inhibition of neutrophil apoptosis, which may contribute to the development of ALI.

Sepsis, leukocytes, and nitric oxide (NO): an intricate affair

Sepsis is exceedingly burdensome for hospital intensive care unit caregivers, and its incidence, as well as sepsis-related deaths, is increasing steadily. Sepsis is characterized by a robust increase in NO production throughout the organism that is driven by iNOS. Moreover, NO is an important factor in the development of septic shock and is synthesized by NOS, an enzyme expressed by a variety of cells, including vascular endothelium, macrophages, and neutrophils. However, the effects of NO on leukocyte functions, and the underlying mechanisms, are relatively unknown. Thus, the present review focuses on the effects of NO and its derivatives on cells of the immune system. Experimental evidences discussed herein show that NO induces posttranslational modifications of key proteins in targeted processes with the potential of deterring cellular physiology. Consequently, the manipulation of NO distribution in septic patients, used in conjunction with conventional treatments aimed at restoring normal immune functions, may represent a valuable therapeutic strategy.

Phagocytic clearance of apoptotic cells: role in lung disease

Apoptosis and apoptotic clearance are matched processes that are centered in the maintenance of homeostasis. Similar to apoptosis, apoptotic cell clearance is a conserved mechanism that is highly efficient and redundant, highlighting its overall functional importance in homeostasis. Increasing evidence suggests that the mismatch between apoptosis and apoptotic cell clearance underlies pathologic conditions including inflammatory lung diseases, such as chronic obstructive pulmonary disease, cystic fibrosis, asthma, acute lung injury/acute respiratory distress syndrome and cancer immunity. Although direct causality has yet to be established, this paradigm opens novel approaches towards the understanding and treatment of lung diseases. Glucocorticoids, statins and macrolide antibiotics, which are already in use for treating lung conditions, have a positive effect on apoptotic clearance and are among novel agents that are potential candidates for treatment of these disorders.

Cyclooxygenase-2 suppresses polymorphonuclear neutrophil apoptosis after acute lung injury

BACKGROUND

Polymorphonuclear neutrophil (PMN) apoptosis is suppressed after acute lung injury (ALI), and strategies aimed at inducing PMN apoptosis are thought to be promising therapies for ALI. However, the mechanisms underlying PMN apoptotic suppression are unknown. Cyclo-oxygenase-2 (COX-2) has been shown to regulate tumor cell apoptosis and is up-regulated by inflammatory mediators in PMN. Therefore, we set out to determine whether up-regulation of COX-2 expression contributes to PMN apoptosis after ALI.

METHODS

Experimental ALI was established in New Zealand rabbits by blunt chest trauma, and a correlation analysis of COX-2 immunohistochemical staining in lung tissue and PMN apoptosis in bronchoalveolar lavage fluid (BALF) was performed. Apoptosis was measured by flow cytometric analysis of annexin V and propidium iodide dual staining. As an in vitro correlate, normal PMNs were treated with BALF from injured lung (BALFALI) in the presence or absence of the COX-2 inhibitor, NS398. COX-2 mRNA levels and PMN apoptosis were then measured.

RESULTS

PMN apoptosis was significantly decreased in BALF after injury. In contrast, COX-2 expression was significantly increased after injury. COX-2 protein expression and PMN apoptosis exhibited a strong inverse correlation (gamma = -0.75, p < 0.01). In vitro experiments revealed apoptosis of normal PMNs was significantly decreased by the addition of BALFALI. The addition of BALFALI was also associated with increased COX-2 mRNA levels. Treatment of cultures with NS398, 10 minutes before BALFALI addition, partially reversed all of these effects.

CONCLUSIONS

Up-regulation of intrapulmonary COX-2 expression contributes to the suppression of PMN apoptosis after ALI.

Apoptosis and Cell Death: Relevance to Lung

In multicellular organisms, cell death plays an important role in development, morphogenesis, control of cell numbers, and removal of infected, mutated, or damaged cells. The term apoptosis was first coined in 1972 by Kerr et al.1 to describe the morphologic features of a type of cell death that is distinct from necrosis and is today considered to represent programmed cell death. In fact, the evidence that a genetic program existed for physiologic cell death came from the developmental studies of the nematode Caenorhabditis elegans.2 As time has progressed, however, apoptotic cell death has been shown to occur in many cell types under a variety of physiologic and pathologic conditions. Cells dying by apoptosis exhibit several characteristic morphologic features that include cell shrinkage, nuclear condensation, membrane blebbing, nuclear and cellular fragmentation into membrane-bound apoptotic bodies, and eventual phagocytosis of the fragmented cell (Figure 4.1). Figure 4.1

Evaluation of bronchoalveolar lavage fluid from ARDS patients with regard to apoptosis

BACKGROUND

Apoptosis is thought to play an important role in the development of acute respiratory distress syndrome (ARDS). We evaluated the bronchoalveolar lavage (BAL) fluid from ARDS patients focusing on apoptosis.

METHODS

The study enrolled 31 ARDS patients and 20 healthy controls. BAL fluid levels of caspase-cleaved cytokeratin-18 (CK-18) and soluble mediators such as interleukin-8 (IL-8), soluble Fas (sFas), soluble Fas ligand (sFasL), growth-related oncogene-alpha (GRO-alpha), granulocyte colony-stimulating factor (G-CSF), and tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) were measured using enzyme-linked immunosorbent assay (ELISA).

RESULTS

The BAL fluid caspase-cleaved CK-18 levels in ARDS patients were higher than those in controls, reflecting increased epithelial apoptosis, and were correlated with lung injury scores (rs=0.49). The BAL fluid levels of all mediators were significantly higher in ARDS patients than in controls. In ARDS patients, the BAL fluid IL-8 level was positively correlated with the levels of sFas (rs=0.57), GRO-alpha (rs=0.47), and TRAIL (rs=0.45). The BAL fluid IL-8 (rs=0.61), sFas (rs=0.57), G-CSF (rs=0.44), and TRAIL (rs=0.33) levels were correlated with the BAL fluid neutrophil count. The G-CSF levels were significantly higher in non-surviving than in surviving ARDS patients [median 183.4 pg/mL (interquartile range 76.7-315.9) vs. 63.8 pg/mL (36.2-137.2); p<0.05]. The sFas levels were positively correlated with the PaO2/FiO2 ratio (rs=0.40), and the TRAIL levels were negatively correlated with the multiple organ dysfunction scores (rs=-0.37).

CONCLUSIONS

Among the mediators in BAL fluid from ARDS patients, G-CSF had the most significant prognostic implications, and the sFas and TRAIL levels were correlated with clinical severity.

Neutrophil apoptosis: a marker of disease severity in sepsis and sepsis-induced acute respiratory distress syndrome

Introduction

Apoptosis of neutrophils (polymorphonuclear neutrophils [PMNs]) may limit inflammatory injury in sepsis and acute respiratory distress syndrome (ARDS), but the relationship between the severity of sepsis and extent of PMN apoptosis and the effect of superimposed ARDS is unknown. The objective of this study was to correlate neutrophil apoptosis with the severity of sepsis and sepsis-induced ARDS.

Methods

A prospective cohort study was conducted in intensive care units of three tertiary hospitals in Porto Alegre, southern Brazil. Fifty-seven patients with sepsis (uncomplicated sepsis, septic shock, and sepsis-induced ARDS) and 64 controls were enrolled. Venous peripheral blood was collected from patients with sepsis within 24 hours of diagnosis. All surgical groups, including controls, had their blood drawn 24 hours after surgery. Control patients on mechanical ventilation had blood collected within 24 hours of initiation of mechanical ventilation. Healthy controls were blood donors. Neutrophils were isolated, and incubated ex vivo, and apoptosis was determined by light microscopy on cytospun preparations. The differences among groups were assessed by analysis of variance with Tukeys.

Results

In medical patients, the mean percentage of neutrophil apoptosis (± standard error of the mean [SEM]) was lower in sepsis-induced ARDS (28% ± 3.3%; n = 9) when compared with uncomplicated sepsis (57% ± 3.2%; n = 8; p < 0.001), mechanical ventilation without infection, sepsis, or ARDS (53% ± 3.0%; n = 11; p < 0.001) and healthy controls (69% ± 1.1%; n = 33; p < 0.001) but did not differ from septic shock (38% ± 3.7%; n = 12; p = 0.13). In surgical patients with sepsis, the percentage of neutrophil apoptosis was lower for all groups when compared with surgical controls (52% ± 3.6%; n = 11; p < 0.001).

Conclusion

In medical patients with sepsis, neutrophil apoptosis is inversely proportional to the severity of sepsis and thus may be a marker of the severity of sepsis in this population.

Neutrophils in development of multiple organ failure in sepsis

Multiple organ failure is a major threat to the survival of patients with sepsis and systemic inflammation. In the UK and in the USA, mortality rates are currently comparable with and projected to exceed those from myocardial infarction. The immune system combats microbial infections but, in severe sepsis, its untoward activity seems to contribute to organ dysfunction. In this Review we propose that an inappropriate activation and positioning of neutrophils within the microvasculature contributes to the pathological manifestations of multiple organ failure. We further suggest that targeting neutrophils and their interactions with blood vessel walls could be a worthwhile therapeutic strategy for sepsis.

Granulocyte apoptosis in the pathogenesis and resolution of lung disease

Apoptosis, programmed cell death, of neutrophil and eosinophil granulocytes is a potential control point in the physiological resolution of innate immune responses. There is also increasing evidence that cellular processes of apoptosis can be dysregulated by pathogens as a mechanism of immune evasion and that delayed apoptosis, resulting in prolonged inflammatory cell survival, is important in persistence of tissue inflammation. The identification of cell-type specific pathways to apoptosis may allow the design of novel anti-inflammatory therapies or agents to augment the innate immune responses to infection. This review will explore the physiological roles of granulocyte apoptosis and their importance in infectious and non-infectious lung disease.

Induction of secondary apoptosis, inflammation, and lung fibrosis after intratracheal instillation of apoptotic cells in rats

Uncontrolled apoptosis has been associated with several pulmonary disorders; however, the molecular mechanism underlying this process and the fate of apoptotic cells in vivo are unclear. Here we show that direct administration of apoptotic cells to the lungs of rats caused pulmonary inflammation and fibrosis, as indicated by emigration of inflammatory cells to the air spaces, TNF-alpha immunoreactivity, and connective tissue accumulation, indicating a direct relationship between apoptotic cells and the observed lung pathologies. To determine how the lungs process the accumulated apoptotic cells, normal or apoptotic cells from autologous donor rats were labeled with fluorescent nanobeads and intratracheally instilled into the lungs of rats. Probe distribution and lung cell apoptosis were determined at various times over a 28-day period by confocal fluorescence microscopy and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, respectively. Labeled apoptotic cells were cleared by lung macrophages within 1 wk after the treatment. However, the total number of apoptotic cells in the lung remained high at 28 days posttreatment. The results indicate a continuous induction of secondary apoptosis by apoptotic cell instillation, which may contribute to the observed lung pathology. Analysis of lung cell apoptosis by caspase assays showed an elevation of caspase-8 but not caspase-9 in the treatment group at 28 days posttreatment, indicating involvement of the death receptor-mediated pathway in the apoptotic process. Together, our results demonstrate a direct effect of apoptotic cell accumulation on inflammatory and fibrotic pulmonary responses and the continuous induction of lung cell apoptosis by apoptotic cell instillation.

Elastin peptides induced oxidation of LDL by phagocytic cells

The degradation products of one of the major component of vascular wall, elastin, have several important biological activities. Elastin peptides (KE) are mostly generated during vascular aging and the atherosclerotic process. They induce free radical and proteases production from cells, which are the major components of the atherosclerotic process. In the present study, we investigated whether the interaction between elastin peptides and neutrophils as well as monocytes contributes to low density lipoproteins (LDL) oxidation, being one of the most important initiator of the chronic inflammatory process contributing to the development of atherosclerosis. Here, we present data on the link between the elastin degradation products and LDL oxidation by the chemotactically attracted neutrophils and monocytes. The KE as well as the active epitope, the hexapeptide VGVAPG is able, in a differential concentration and time dependence, to induce the oxidation of LDL. KE is able to induce via the production of free radicals by neutrophils the oxidation of LDL very rapidly and in higher concentration compared to monocytes. These effects of KE are occurring through the stimulation of the 67 kDa elastin-laminin receptor (ELR), as demonstrated by the uncoupling effect of lactose. In our present study, the HDL was able to decrease the LDL oxidation by KE. This is a new mechanism by which elastin peptides might participate in the initiation and progression of the atherosclerotic process.

Serum biomarkers in acute respiratory distress syndrome an ailing prognosticator

The use of biomarkers in medicine lies in their ability to detect disease and support diagnostic and therapeutic decisions. New research and novel understanding of the molecular basis of the disease reveals an abundance of exciting new biomarkers who present a promise for use in the everyday clinical practice. The past fifteen years have seen the emergence of numerous clinical applications of several new molecules as biologic markers in the research field relevant to acute respiratory distress syndrome (translational research). The scope of this review is to summarize the current state of knowledge about serum biomarkers in acute lung injury and acute respiratory distress syndrome and their potential value as prognostic tools and present some of the future perspectives and challenges.

Differential regulation of Th1/Th2 in relevant tissues for sepsis pathogenesis with a Limulus anti-LPS factor-derived peptide increases survival in Gram-positive sepsis

Severe sepsis and septic shock are important causes of death in intensive care units. Although Gram-negative infections were predominant in the 1960s, Gram-positive infections have increased in the past two decades and now account for about half of the cases of severe sepsis. In this study, we examined the effect of a Limulus anti-LPS factor (LALF)-derived peptide on lung and liver Th1/Th2 cytokine mRNA levels during a Gram-positive sepsis. We also examined the morphopathological changes observed in these organs during the disease. Mice challenged with a high dose of Staphylococcus haemolyticus showed severe damage in lung. In contrast, the liver of challenged mice showed an accumulation of bacterial particles in the sinusoids, associated with a severe inflammatory response due to high levels of tissue mRNA proinflammatory cytokines. Treatment with the peptide LALF(32-51) ameliorated the sepsis-induced effects in the lung and liver and increased the survival of mice in a dose- and time-dependent manner. Pretreatment with the peptide LALF(32-51) differentially regulates TNF-alpha, IFN-gamma, IL-12p40, IL-2 and IL-10 mRNA levels in lung and liver of peptide-treated mice, and limits the systemic inflammatory response. These findings support for the first time the effectiveness of an LALF-derived peptide in the treatment of a Gram-positive sepsis. Modulation of the Th1/Th2 pattern in tissues relevant for sepsis correlates with an improved outcome of the disease as denoted by increased survival.

Aspirin preserves neutrophil apoptosis after cardiopulmonary bypass

The aim of this study was to test the hypothesis that ongoing aspirin therapy preserves neutrophil apoptosis after cardiac surgery with cardiopulmonary bypass (CPB) by a cyclooxygenase mechanism. Twenty patients undergoing coronary revascularization with CPB were enrolled in a prospective cohort study. Patients who had continued taking 300 mg of aspirin until the day before surgery (n = 10) were compared with 10 patients not taking aspirin or who had discontinued it more than 5 days before surgery. Neutrophils were isolated from arterial blood before and 6 h after surgery and apoptosis was measured after 24 h in culture using flow cytometry. Serum was collected and assessed for IL-6, IL-8 and PGE2 by enzyme-linked immunoabsorbant assay. Patients were followed for clinical indices of sepsis for 7 days postoperatively. Spontaneous rates of neutrophil apoptosis were significantly reduced in postoperative compared with preoperative samples. There was no difference between aspirin and control preoperative neutrophil apoptosis rates (23.0% +/- 11.3% vs. 23.0% +/- 20.7%, P = 0.99). Postoperative neutrophil apoptosis was delayed in control patients (3.6% +/- 1.2% apoptosis), but this was significantly (P = 0.045) reversed in the aspirin-treated group (7.2% +/- 5.1% apoptosis). There were lower postoperative PGE2 levels in the aspirin group (136 +/- 69 pg/mL vs. 372 +/- 210 pg/mL, P = 0.04). There was no difference in clinical indices of sepsis. We conclude that the delay in postoperative neutrophil apoptosis is significantly preserved in patients taking 300 mg of aspirin on the day before surgery. This was associated with greater inhibition of PGE2, consistent with the hypothesis that aspirin exerts its effect on apoptosis after CPB via a cyclooxygenase-mediated mechanism.

Regulation of Fas (CD95)-induced apoptotic and necrotic cell death by reactive oxygen species in macrophages

Although reactive oxygen species (ROS) have long been suspected to play a key role in Fas (CD95)-induced cell death, the identity of specific ROS involved in this process and the relationship between apoptotic and necrotic cell death induced by Fas are largely unknown. Using electron spin resonance (ESR) spectroscopy, we showed that activation of Fas receptor by its ligand (FasL) in macrophages resulted in a rapid and transient production of hydrogen peroxide (H2O2) and hydroxyl radicals (*OH). The response was visible as early as 5 min and peaked at approximately 45 min post-treatment. Morphological analysis of total death response (apoptosis vs. necrosis) showed dose and time dependency with apoptosis significantly increased at 6 h after the treatment, while necrosis remained at a baseline level. Only at a 35-fold increase in apoptosis did necrosis become significant. Inhibition of apoptosis by a pan-caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-(OMe) fluoromethyl ketone (zVAD-fmk), significantly inhibited cell necrosis, indicating the linkage between the two events. Catalase (H2O2 scavenger) and deferoxamine (*OH scavenger) effectively inhibited the total death response as well as the ESR signals, while superoxide dismutase (SOD) (O2*- scavenger) had minimal effects. These results established the role for H2O2 and *OH as key participants in Fas-induced cell death and indicated apoptosis as a primary mode of cell death preceding necrosis. Because the Fas death pathway is implicated in various inflammatory and immunologic disorders, utilization of antioxidants and apoptosis inhibitors as potential therapeutic agents may be advantageous.

Role of IFN-gamma and IL-2 in rat lung epithelial cell migration and apoptosis after oxidant injury

In the present study, IFN-gamma exposure to primary cultures of rat type II epithelial cells (TIIP) upregulated membrane expression of the common gamma-chain of the IL-2 receptor (approximately 2.5- to 4-fold increase) and redistributed receptor affinity in TIIP, as assessed by Western blot, cell, and tissue histochemistry and Scatchard analysis. As for restitution processes of the lung epithelium, functionality of IL-2R on TIIP was conditional to IFN-gamma exposure: 1) IFN-gamma priming promoted a fivefold increase of IL-2-driven TIIP locomotion (P < 0.05 vs. control at 100 U/ml) and 2) IFN-gamma coincubation with IL-2 reduced bleomycin-induced TIIP apoptosis in vitro by 25% (caspase-3 activity) and by approximately 70% (TdT-mediated dUTP nick end labeling/4',6'-diamidino-2-phenylindole assay) as well as in vivo by approximately 90% (caspase-3 activity; P < 0.05 vs. control). Sustained p42/44 extracellular signal-regulated kinase activity played a protective role in this process, whereas specific inhibition by PD-98059 (50 microM) significantly reversed bleomycin-induced TIIP apoptosis (P < 0.05 vs. control). From these in vitro and in vivo data, it is proposed that combinations of IFN-gamma and IL-2 can drive repair activity of TIIP by stimulating migration and preventing programmed cell death, both of which are speculated to be very fast restitution events after oxidant-induced acute lung injury.

The role of neutrophil apoptosis in the resolution of acute lung injury in newborn infants

BACKGROUND

The persistent airway neutrophilia observed in chronic lung disease of prematurity (CLD) may reflect inappropriate suppression of neutrophil apoptosis.

METHODS

134 bronchoalveolar lavage (BAL) samples were obtained from 32 infants requiring mechanical ventilation for respiratory distress syndrome (RDS): 13 infants (median gestation 26 weeks, range 23 to 28) subsequently developed CLD (CLD group), and 19 infants (gestation 31 weeks, range 25 to 39) recovered fully (RDS group). A further 73 BAL samples were obtained from 20 infants (median age 2 days, range 1 to 402) receiving extracorporeal membrane oxygenation (ECMO) for severe respiratory failure.

RESULTS

Neutrophil apoptosis was increased in the RDS group (mean (SEM) neutrophil apoptosis on day 7 BAL: RDS 17.0 (8.6)% v CLD 0.7 (0.2)% (p<0.05)). BAL fluid obtained from RDS but not CLD patients was proapoptotic to neutrophils (apoptosis ratio BAL fluid/saline control: day 1, RDS 9.8 (5.5) v CLD 1.2 (0.1) (p<0.05); day 2, RDS 4.32 (2.8) v CLD 0.5 (0.4) (p<0.05)). There were similar findings in the ECMO group: survivors had proapoptotic BAL fluid compared with non-survivors (apoptosis ratio day 1, survivors 7.9 (2.1) v non-survivors 2.1 (0.7) (p<0.05)).

CONCLUSIONS

Inappropriate suppression of neutrophil apoptosis may be associated with a poor outcome in newborn infants with respiratory failure.

Science review: apoptosis in acute lung injury

Apoptosis is a process of controlled cellular death whereby the activation of specific death-signaling pathways leads to deletion of cells from tissue. The importance of apoptosis resides in the fact that several steps involved in the modulation of apoptosis are susceptible to therapeutic intervention. In the present review we examine two important hypotheses that link apoptosis with the pathogenesis of acute lung injury in humans. The first of these, namely the 'neutrophilic hypothesis', suggests that during acute inflammation the cytokines granulocyte colony-stimulating factor and granulocyte/macrophage colony-stimulating factor prolong the survival of neutrophils, and thus enhance neutrophilic inflammation. The second hypothesis, the 'epithelial hypothesis', suggests that epithelial injury in acute lung injury is associated with apoptotic death of alveolar epithelial cells triggered by soluble mediators such as soluble Fas ligand. We also review recent studies that suggest that the rate of clearance of apoptotic neutrophils may be associated with resolution of neutrophilic inflammation in the lungs, and data showing that phagocytosis of apoptotic neutrophils can induce an anti-inflammatory phenotype in activated alveolar macrophages.

Association between increased levels of IL-2 and IL-15 and outcome in patients with early acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome remains a serious, often fatal, condition, despite progress in modern critical care treatment. Cytokines play an important role in the pathogenesis of the syndrome, although their role in the evolution and outcome has not been clearly elucidated. We explored whether the measurement of serum and bronchoalveolar lavage IL-2 and IL-15 at the time of hospital admission can predict the outcome of this syndrome.

METHODS

Serum and bronchoalveolar lavage levels of IL-2 and IL-15 were measured in eight patients with ARDS (group A) and 26 patients on high risk for ARDS development who never developed ARDS (group B) from samples obtained at the time of admission.

RESULTS

Serum IL-2 (P > 0.05) and IL-15 (P < 0.05) levels were higher in group A than in group B. Serum levels of both cytokines were higher in patients who did not survive in both of the groups A and B compared to those who survived (P < 0.05, and P < 0.0001, respectively). The only significant change in BALF was the higher level of IL-15 in surviving group A patients (P < 0.05) when compared with the non survivors of the same group. For a serum cut-off level of 173 pg mL(-1) for IL-2 and 250 pg mL(-1) for IL-15, they exhibited a very high positive predictive value (PPV), negative predictive value (NPV), sensitivity and specificity for survival (100% in all). A positive correlation was found between serum levels of both cytokines and APACHE II score (IL-2, r = 0.61, and IL-15, r = 0.62, respectively, and P < 0.0001 for both).

CONCLUSION

Determination of serum IL-2 and IL-15 levels may be a valuable and simple aid to improve identification of patients with ARDS or at risk for ARDS who are at high risk of subsequent mortality.