Resolution of airway disease: removal of inflammatory cells through apoptosis, egression or both?

The potential of zebrafish as drug discovery research tool in immune-mediated inflammatory disease

Immune-mediated inflammatory disease (IMID) prevalence is estimated at 3-7% for Westernised populations, with annual incidence reported at almost 1 in 100 people globally. More recently, drug discovery approaches have been evolving towards more targeted therapies with an improved long-term safety profile, while the requirement for individualisation of medicine in complex conditions such as IMIDs, is acknowledged. However, existing preclinical models-such as cellular and in vivo mammalian models-are not ideal for modern drug discovery model requirements, such as real-time in vivo visualisation of drug effects, logistically feasible safety assessment over the course of a lifetime, or dynamic assessment of physiological changes during disease development. Zebrafish share high homology with humans in terms of proteins and disease-causing genes, with high conservation of physiological processes at organ, tissue, cellular and molecular level. These and other unique attributes, such as high fecundity, relative transparency and ease of genetic manipulation, positions zebrafish as the next major role player in IMID drug discovery. This review provides a brief overview of the suitability of this organism as model for human inflammatory disease and summarises the range of approaches used in zebrafish-based drug discovery research. Strengths and limitations of zebrafish as model organism, as well as important considerations in research study design, are discussed. Finally, under-utilised avenues for investigation in the IMID context are highlighted.

Lung Cancer in the Course of COPD-Emerging Problems Today

Tobacco smoking remains the main cause of tobacco-dependent diseases like lung cancer, chronic obstructive pulmonary disease (COPD), in addition to cardiovascular diseases and other cancers. Whilst the majority of smokers will not develop either COPD or lung cancer, they are closely related diseases, occurring as co-morbidities at a higher rate than if they were independently triggered by smoking. A patient with COPD has a four- to six-fold greater risk of developing lung cancer independent of smoking exposure, when compared to matched smokers with normal lung function. The 10 year risk is about 8.8% in the COPD group and only 2% in patients with normal lung function. COPD is not a uniform disorder: there are different phenotypes. One of them is manifested by the prevalence of emphysema and this is complicated by malignant processes most often. Here, we present and discuss the clinical problems of COPD in patients with lung cancer and against lung cancer in the course of COPD. There are common pathological pathways in both diseases. These are inflammation with participation of macrophages and neutrophils and proteases. It is known that anticancer immune regulation is distorted towards immunosuppression, while in COPD the elements of autoimmunity are described. Cytotoxic T cells, lymphocytes B and regulatory T cells with the important role of check point molecules are involved in both processes. A growing number of lung cancer patients are treated with immune check point inhibitors (ICIs), and it was found that COPD patients may have benefits from this treatment. Altogether, the data point to the necessity for deeper analysis and intensive research studies to limit the burden of these serious diseases by prevention and by elaboration of specific therapeutic options.

The Correlation Between Asthma Severity and Neutrophil to Lymphocyte Ratio

Background—The prognosis is essential in management and follows up of asthmatic patients. Neutrophil to lymphocyte ratio is considered as the common prognostic marker for many diseases especially the asthma. Aim of study—To assess the relationship between asthma severity and neutrophil to lymphocyte ratio in comparison to healthy controls. Patients and methods—This study is a cross sectional study conducted in Respiratory Consultancy Clinic in Baghdad Teaching Hospital in Medical City during the period from 1st of October, 2018 to 31st of March, 2019 on sample of 50 asthmatic patients and 50 healthy controls. The diagnosis of asthma was confirmed by the supervisor through clinical symptoms, signs, spirometery with reversibility test (according to GINA guideline.). Results—A highly significant difference was observed between asthmatic cases and controls regarding age (p<0.001). A significant association was observed between obesity and asthmatic cases (p=0.001). There was a highly significant association between high neutrophil/lymphocyte ratio and asthmatic cases (p<0.001). The neutrophil/lymphocyte ratio was significantly increased with advanced age, females, severe and uncontrolled asthma. Conclusions—The neutrophil to lymphocyte ratio is useful biomarker in assessment of asthma severity.

Serum resolvin D1 levels as a marker of inflammation in constipation dominant irritable bowel syndrome

BACKGROUND/AIMS

The objective of this study is to determine the role of circulating resolvin D1 (RvD1) in patients with constipation subtype of irritable bowel syndrome (IBS-C) and evaluate the relationship between abdominal pain severity and RvD1 levels.

MATERIALS AND METHODS

This research included 55 patients with IBS-C and 36 healthy controls. Controls were selected from patients who applied to our department with similar complaints as IBS but were not diagnosed with any type of pathology after further investigations. All participants underwent complete blood count, C-reactive protein (CRP), and RvD1 levels measurements. We also recorded abdominal pain severity and the number of bowel movements. Patients with IBS-C were compared with respect to the demographic features and laboratory measurements.

RESULTS

The median CRP concentration in patients with IBS-C was significantly higher than that of controls (p=0.003). However, the median RvD1 concentration was significantly lower in the IBS group than that of the control group (p<0.001). The receiver operating characteristic curve analyses revealed that RvD1 concentration lower than 0.47 ng/mL and CRP concentration higher than 3.40 mg/L may identify patients with IBS-C with a high specificity. In the IBS group, there was a strong negative correlation between abdominal pain severity and RvD1 concentration (r=-0.766, p=0.001).

CONCLUSION

This research demonstrates that patients with IBS-C have higher CRP and lower RvD1 concentrations than healthy controls. Both RvD1 and CRP concentrations predict the presence of IBS-C. Additionally, RvD1 concentrations decreased with the increase in abdominal pain severity. Further research works are needed for investigating the role of the RvD1 analogs in the treatment of IBS.

Unravelling the complexity of tissue inflammation in uncontrolled and severe asthma

PURPOSE OF REVIEW

The clinical and inflammatory heterogeneity in asthma constitutes a major challenge for improved treatment. This review describes the nature of the inflammatory complexity and how it can be decoded to yield improved disease understanding and personalized treatment. The focus is on the difficult task of revealing the immunological complexity as it occurs inside diseased patient tissues.

RECENT FINDINGS

The inflammatory heterogeneity in asthma stretches beyond the classical division into allergic Th2 eosinophilic versus Th1 and/or Th17 neutrophilic (or paucigranulocytic) phenotypes. Rather than having one distinct type of inflammation, many patients display a patchwork of overlapping immune signatures. The patient diversity is further increased by differences in regard of distal lung involvement. Faced with this staggering complexity, calls have been made for a pragmatic biomarker-guided identification of treatable traits. In parallel, novel high-dimensional analyses and multiplex imaging aid the long-term goal of decoding the underlying molecular endotypes.

SUMMARY

Asthma is vastly heterogeneous with multiple and superimposed inflammatory and anatomical phenotypes. Despite the intensive research and introduction of highly immune-selective dugs, basic questions remain; especially as still too many of today's uncontrolled patients remain poorly understood. Here, pragmatic biomarker strategies, combined with novel methodological approaches that ultimately reveal the complete immunological complexity, will pave the way for improved differential diagnosis and personalized medication.

MUC1 downregulation promotes TNF-α-induced necroptosis in human bronchial epithelial cells via regulation of the RIPK1/RIPK3 pathway

MUC1 (mucin 1), a membrane-tethered mucin glycoprotein, is highly expressed on the surface of respiratory epithelial cells and plays a key role in anti-inflammatory and antiapoptotic responses against infections. However, little is known about the link between MUC1 and necroptosis in asthma. This study aimed to investigate the effects of MUC1 on TNF-α-induced necroptosis in human bronchial epithelial (16HBE) cells and the underlying molecular mechanism. Negative control and MUC1-siRNA cells were treated with TNF-α in the presence or absence of necrostatin-1 (Nec-1). Necroptosis was investigated using flow cytometry analyses, and the protein expression levels of MUC1, receptor-interacting protein kinase-1 (RIPK1), RIPK3, and phosphorylated RIPK1 were detected by western blot analysis. In addition, the interactions between RIPK and MUC1 were analyzed by coimmunoprecipitation. The results demonstrated that TNF-α could induce necroptosis of 16HBE cells, and MUC1 expression was increased upon treatment with TNF-α. The coimmunoprecipitation outcomes showed that MUC1 interacted with RIPK1 but not with RIPK3 in 16HBE cells, and the interaction was augmented by TNF-α. Furthermore, MUC1 downregulation obviously increased the TNF-α-induced necroptosis of 16HBE cells and enhanced the expression of p-RIPK1-Ser166 and RIPK3, whereas these phenomena were partially attenuated by Nec-1. These results may provide a new insight into the mechanism of severe asthma-related necroptosis and lay a foundation for the future development of new anti-inflammatory drugs for asthma.

Eosinophils in the gastrointestinal tract and their role in the pathogenesis of major colorectal disorders

Eosinophils are currently regarded as versatile mobile cells controlling and regulating multiple biological pathways and responses in health and disease. These cells store in their specific granules numerous biologically active substances (cytotoxic cationic proteins, cytokines, growth factors, chemokines, enzymes) ready for rapid release. The human gut is the main destination of eosinophils that are produced and matured in the bone marrow and then transferred to target tissues through the circulation. In health the most important functions of gut-residing eosinophils comprise their participation in the maintenance of the protective mucosal barrier and interactions with other immune cells in providing immunity to microbiota of the gut lumen. Eosinophils are closely involved in the development of inflammatory bowel disease (IBD), when their cytotoxic granule proteins cause damage to host tissues. However, their roles in Crohn’s disease and ulcerative colitis appear to follow different immune response patterns. Eosinophils in IBD are especially important in altering the structure and protective functions of the mucosal barrier and modulating massive neutrophil influx to the lamina propria followed by transepithelial migration to colorectal mucus. IBD-associated inflammatory process involving eosinophils then appears to expand to the mucus overlaying the internal gut surface. The author hypothesises that immune responses within colorectal mucus as well as ETosis exerted by both neutrophils and eosinophils on the both sides of the colonic epithelial barrier act as additional pathogenetic factors in IBD. Literature analysis also shows an association between elevated eosinophil levels and better colorectal cancer (CRC) prognosis, but mechanisms behind this effect remain to be elucidated. In conclusion, the author emphasises the importance of investigating colorectal mucus in IBD and CRC patients as a previously unexplored milieu of disease-related inflammatory responses.

The deafness gene GSDME: its involvement in cell apoptosis, secondary necrosis, and cancers

Gasdermin E (GSDME), also called DFNA5, is a member of the gasdermin family. GSDME is involved in the regulation of apoptosis and necrosis. The N-terminal domain of GSDME displays an apoptosis-inducing activity while the C-terminal domain may serve as an apoptosis-inhibiting regulator by shielding the N-terminal domain. Besides its function in the regulation of apoptosis, GSDME was recently reported to be a substrate of caspase-3 and cleavage of GSDME by caspase-3 into necrotic N-terminal fragment leads to the induction of secondary necrosis. GSDME was first identified as a deafness gene because its mutation was associated with a specific form of autosomal dominant progressive sensorineural hearing loss. Furthermore, GSDME has been considered a tumor suppressor implicated in several types of cancer. This mini-review summarized recent reports relevant to the functions of GSDME in the regulation of apoptosis and necrosis as well as its clinical relevance.

Neutrophilic Dermatoses and Their Implication in Pathophysiology of Asthma and Other Respiratory Comorbidities: A Narrative Review

Neutrophilic dermatoses (ND) are a polymorphous group of noncontagious dermatological disorders that share the common histological feature of a sterile cutaneous infiltration of mature neutrophils. Clinical manifestations can vary from nodules, pustules, and bulla to erosions and ulcerations. The etiopathogenesis of neutrophilic dermatoses has continuously evolved. Accumulating genetic, clinical, and histological evidence point to NDs being classified in the spectrum of autoinflammatory conditions. However, unlike the monogenic autoinflammatory syndromes where a clear multiple change in the inflammasome structure/function is demonstrated, NDs display several proinflammatory abnormalities, mainly driven by IL-1, IL-17, and tumor necrosis factor-alpha (TNF-a). Additionally, because of the frequent association with extracutaneous manifestations where neutrophils seem to play a crucial role, it was plausible also to consider NDs as a cutaneous presentation of a systemic neutrophilic condition. Neutrophilic dermatoses are more frequently recognized in association with respiratory disorders than by chance alone. The combination of the two, particularly in the context of their overlapping immune responses mediated primarily by neutrophils, raises the likelihood of a common neutrophilic systemic disease or an aberrant innate immunity disorder. Associated respiratory conditions can serve as a trigger or may develop or be exacerbated secondary to the uncontrolled skin disorder. Physicians should be aware of the possible pulmonary comorbidities and apply this knowledge in the three steps of patients' management, work-up, diagnosis, and treatment. In this review, we attempt to unravel the pathophysiological mechanisms of this association and also present some evidence for the role of targeted therapy in the treatment of both conditions.

Mucin 1 downregulation impairs the anti-necroptotic effects of glucocorticoids in human bronchial epithelial cells

AIMS

To investigate whether mucin 1 (MUC1) downregulation reduced the sensitivity of tumor necrosis factor-alpha (TNF-α)-induced bronchial epithelial cells to glucocorticoid-mediated necroptosis and explore the underlying mechanisms.

MAIN METHODS

The human lung bronchial epithelial cell line (16HBE) was transfected with small interfering RNA (siRNA) against MUC1 and then stimulated by TNF-α, where some cells were pretreated with dexamethasone. Flow cytometry was performed to analyze necroptosis in 16HBE cells, and western blot analysis was used to detect protein expression levels of MUC1, glucocorticoid receptor (GR)α, GRβ, NF-κB p65, phospho-p65 (p-p65), and histone deacetylase-2 (HDAC2). Additionally, nuclear translocation of MUC1 and GRα was assessed by immunofluorescence.

KEY FINDINGS

We observed that MUC1 downregulation by siRNA significantly augmented TNF-α-induced necroptosis in 16HBE cells, and that dexamethasone showed impaired anti-necroptotic effects of MUC1 downregulation. Furthermore, we found that GRα nuclear translocation was inhibited in 16HBE cells with MUC1 downregulation, and that dexamethasone-mediated inhibition of p65 phosphorylation was lower in cells transfected with MUC1-siRNA compared to those transfected with negative control siRNA.

SIGNIFICANCE

Impaired GRα nuclear translocation and inhibited p-p65 expression might contribute to glucocorticoid resistance caused by MUC1 deficiency in TNF-α-induced necroptosis in 16HBE cells, and should be considered as a potential target for the development of novel therapeutics for asthma.

Interferon-β deficiency at asthma exacerbation promotes MLKL mediated necroptosis

Defective production of antiviral interferon (IFN)-β is thought to contribute to rhinovirus-induced asthma exacerbations. These exacerbations are associated with elevated lung levels of lactate dehydrogenase (LDH), indicating occurrence of cell necrosis. We thus hypothesized that reduced lung IFN-β could contribute to necrotic cell death in a model of asthma exacerbations. Wild-type and IFN-β^−/− mice were given saline or house dust mite (HDM) intranasally for 3 weeks to induce inflammation. Double-stranded RNA (dsRNA) was then given for additional 3 days to induce exacerbation. HDM induced an eosinophilic inflammation, which was not associated with increased expression of cleaved caspase-3, cleaved PARP or elevated bronchoalveolar lavage fluid (BALF) LDH levels in wild-type. However, exacerbation evoked by HDM + dsRNA challenges increased BALF levels of LDH, apoptotic markers and the necroptotic markers receptor-interacting protein (RIP)-3 and phosphorylation of mixed linage kinase domain-like protein (pMLKL), compared to HDM + saline. Absence of IFN-β at exacerbation further increased BALF LDH and protein expression of pMLKL compared to wild-type. We demonstrate that cell death markers are increased at viral stimulus-induced exacerbation in mouse lungs, and that absence of IFN-β augments markers of necroptotic cell death at exacerbation. Our data thus suggest a novel role of deficient IFN-β production at viral-induced exacerbation.

The Nonantibiotic Macrolide EM703 Improves Survival in a Model of Quinolone-Treated Pseudomonas aeruginosa Airway Infection

Macrolide antibiotics are used as anti-inflammatory agents, e.g., for prevention of exacerbations in chronic obstructive pulmonary disease and cystic fibrosis. Several studies have shown improved outcomes after the addition of macrolides to β-lactam antibiotics for treatment of severe community-acquired pneumonia. However, a beneficial effect of macrolides in treating Gram-negative bacterial airway infections, e.g., those caused by Pseudomonas aeruginosa, remains to be shown. Macrolide antibiotics have significant side effects, in particular, motility-stimulating activity in the gastrointestinal tract and promotion of bacterial resistance. In this study, EM703, a modified macrolide lacking antibiotic and motility-stimulating activities but with retained anti-inflammatory properties, was used as an adjunct treatment for experimental P. aeruginosa lung infection, in combination with a conventional antibiotic. Airway infections in BALB/cJRj mice were induced by nasal instillation of P. aeruginosa; this was followed by treatment with the quinolone levofloxacin in the absence or presence of EM703. Survival, inflammatory responses, and cellular influx to the airways were monitored. Both pretreatment and simultaneous administration of EM703 dramatically improved survival in levofloxacin-treated mice with P. aeruginosa airway infections. In addition, EM703 reduced the levels of proinflammatory cytokines, increased the numbers of leukocytes in bronchoalveolar lavage fluid, and reduced the numbers of neutrophils present in lung tissue. In summary, the findings of this study show that the immunomodulatory properties of the modified macrolide EM703 can be important when treating Gram-negative pneumonia, as exemplified by P. aeruginosa infection in this study.

Advanced Role of Neutrophils in Common Respiratory Diseases

Respiratory diseases, always being a threat towards the health of people all over the world, are most tightly associated with immune system. Neutrophils serve as an important component of immune defense barrier linking innate and adaptive immunity. They participate in the clearance of exogenous pathogens and endogenous cell debris and play an essential role in the pathogenesis of many respiratory diseases. However, the pathological mechanism of neutrophils remains complex and obscure. The traditional roles of neutrophils in severe asthma, chronic obstructive pulmonary diseases (COPD), pneumonia, lung cancer, pulmonary fibrosis, bronchitis, and bronchiolitis had already been reviewed. With the development of scientific research, the involvement of neutrophils in respiratory diseases is being brought to light with emerging data on neutrophil subsets, trafficking, and cell death mechanism (e.g., NETosis, apoptosis) in diseases. We reviewed all these recent studies here to provide you with the latest advances about the role of neutrophils in respiratory diseases.

DNA-fragmentation is a source of bactericidal activity against Pseudomonas aeruginosa

Pseudomonas aeruginosa airway infection is common in cystic fibrosis (CF), a disease also characterized by abundant extracellular DNA (eDNA) in the airways. The eDNA is mainly derived from neutrophils accumulating in the airways and contributes to a high sputum viscosity. The altered environment in the lower airways also paves the way for chronic P. aeruginosa infection. Here, we show that mice with P. aeruginosa airway infection have increased survival and decreased bacterial load after topical treatment with DNase. Furthermore, DNA from the sputum of CF patients showed increased bactericidal activity after treatment with DNase ex vivo. Both degraded DNA of neutrophil extracellular traps (NETs) and genomic DNA degraded by serum, acquired bactericidal activity against P. aeruginosa In vitro, small synthetic DNA-fragments (<100 base pairs) but not large fragments nor genomic DNA, were bactericidal against Gram-negative but not Gram-positive bacteria. The addition of divalent cations reduced bacterial killing, suggesting that chelation of divalent cations by DNA results in destabilization of the lipopolysaccharide (LPS) envelope. This is a novel antibacterial strategy where fragmentation of eDNA and DNA-fragments can be used to treat P. aeruginosa airway infection.

Monoclonal antibody therapy for the treatment of asthma and chronic obstructive pulmonary disease with eosinophilic inflammation

Eosinophils have been linked with asthma for more than a century, but their role has been unclear. This review discusses the roles of eosinophils in asthma and chronic obstructive pulmonary disease (COPD) and describes therapeutic antibodies that affect eosinophilia. The aims of pharmacologic treatments for pulmonary conditions are to reduce symptoms, slow decline or improve lung function, and reduce the frequency and severity of exacerbations. Inhaled corticosteroids (ICS) are important in managing symptoms and exacerbations in asthma and COPD. However, control with these agents is often suboptimal, especially for patients with severe disease. Recently, new biologics that target eosinophilic inflammation, used as adjunctive therapy to corticosteroids, have proven beneficial and support a pivotal role for eosinophils in the pathology of asthma. Nucala® (mepolizumab; anti-interleukin [IL]-5) and Cinquair® (reslizumab; anti-IL-5), the second and third biologics approved, respectively, for the treatment of asthma, exemplifies these new treatment options. Emerging evidence suggests that eosinophils may contribute to exacerbations and possibly to lung function decline for a subset of patients with COPD. Here we describe the pharmacology of therapeutic antibodies inhibiting IL-5 or targeting the IL-5 receptor, as well as other cytokines contributing to eosinophilic inflammation. We discuss their roles as adjuncts to conventional therapeutic approaches, especially ICS therapy, when disease is suboptimally controlled. These agents have achieved a place in the therapeutic armamentarium for asthma and COPD and will deepen our understanding of the pathogenic role of eosinophils.

n-3 Fatty acids and asthma

Asthma is one of the most common and prevalent problems worldwide affecting over 300 million individuals. There is some evidence from observational and intervention studies to suggest a beneficial effect of n-3 PUFA in inflammatory diseases, specifically asthma. Marine-based n-3 PUFA have therefore been proposed as a possible complementary/alternative therapy for asthma. The proposed anti-inflammatory effects of n-3 fatty acids may be linked to a change in cell membrane composition. This altered membrane composition following n-3 fatty acid supplementation (primarily EPA and DHA) can modify lipid mediator generation via the production of eicosanoids with a reduced inflammatory potential/impact. A recently identified group of lipid mediators derived from EPA including E-series resolvins are proposed to be important in the resolution of inflammation. Reduced inflammation attenuates the severity of asthma including symptoms (dyspnoea) and exerts a bronchodilatory effect. There have been no major health side effects reported with the dietary supplementation of n-3 fatty acids or their mediators; consequently supplementing with n-3 fatty acids is an attractive non-pharmacological intervention which may benefit asthma.

Emerging roles of apoptotic microtubules during the execution phase of apoptosis

Apoptosis is a genetically programmed energy-dependent process of cell demise, characterized by specific morphological and biochemical events in which the activation of caspases has an essential role. During apoptosis the cytoskeleton participates actively in characteristic morphological rearrangements of the dying cell. This reorganisation has been assigned mainly to actinomyosin ring contraction, while microtubule and intermediate filaments are depolymerized at early stages of apoptosis. However, recent reports have showed that microtubules are reformed during the execution phase of apoptosis organizing an apoptotic microtubule network (AMN). AMN is organized behind plasma membrane, forming a cortical structure. Apoptotic microtubules repolymerization takes place in many cell types and under different apoptotic inducers. It has been hypothesized that AMN is critical for maintaining plasma membrane integrity and cell morphology during the execution phase of apoptosis. AMN disorganization leads apoptotic cells to secondary necrosis and the release of potential toxic molecules which can damage neighbor cells and promotes inflammation. Therefore, AMN formation during physiological apoptosis or in pathological apoptosis induced by anti-cancer treatments is essential for tissue homeostasis and the prevention of additional cell damage and inflammation.

CCL2/CCR2-dependent recruitment of Th17 cells but not Tc17 cells to the lung in a murine asthma model

BACKGROUND

Interleukin (IL)-17 has been implicated in the pathogenesis of asthma and the progression of airway inflammation. Here, we used a model of allergic asthma and found that the frequencies of IL-17-secreting T helper (Th)17 and CD8 (Tc)17 cells were both significantly increased, as was the expression of the CC chemokine receptor (CCR2) on the surface of these cells. CC chemokine ligand 2 (CCL2) has been shown to mediate the activation and recruitment of inflammatory cells in asthma, which are also skewed after ovalbumin (OVA) challenge. However, the role of CCL2 on Th17 cells and Tc17 cells in asthma has not been illuminated.

METHODS

Mice that were sensitized and challenged with OVA received anti-CCL2 antibody (Ab; 5 μg/day intratracheally) or CCR2 antagonist (RS504393, 2 mg/kg/day intraperitoneally) prior to the challenge. Some mice received an isotype control Ab or vehicle alone. We then assessed the effects of allergic asthma and anti-CCL2 Ab or CCR2 antagonist treatment on the levels of IL-17 and CCL2, the Th17 and Tc17 cell frequencies and lung tissue inflammation.

RESULTS

We demonstrated that CCL2 and IL-17 levels and the frequency of Th17 and Tc17 cells in lung tissues and bronchoalveolar lavage fluid increased in the asthma group compared with the normal control mice. Blocking the CCL2/CCR2 axis greatly reduced the Th17 but not the Tc17 cell frequency, and revealed a suppressive effect on airway inflammation.

CONCLUSION

These findings indicate a role for the CCL2/CCR2 axis in mediating Th17 but not Tc17 cell migration during acute allergic airway inflammation.

Heterogeneity in mechanisms influencing glucocorticoid sensitivity: the need for a systems biology approach to treatment of glucocorticoid-resistant inflammation

Glucocorticoids (GCs) have impressive anti-inflammatory and immunosuppressive effects and show a diversity of actions across a variety of cell phenotypes. Implicit in efforts to optimize GCs as anti-inflammatory agents for any or all indications is the notion that the relevant mechanism(s) of action of GCs are fully elucidated. However, recent advances in understanding GC signalling mechanisms have revealed remarkable complexity and contextual dependence, calling into question whether the mechanisms of action are sufficiently well-described to embark on optimization. In the current review, we address evidence for differences in the mechanism of action in different cell types and contexts, and discuss contrasts in mechanisms of glucocorticoid insensitivity, with a focus on asthma and Chronic Obstructive Pulmonary Disease (COPD). Given this complexity, we consider the potential breadth of impact and selectivity of strategies directed to reversing the glucocorticoid insensitivity.

Roles of resolvins in the resolution of acute inflammation

Resolution is an active process that terminates inflammatory response to maintain health. Acute inflammation and its timely resolution are important in host response to danger signals. Unresolved inflammation is associated with widely recurrent diseases. Resolvins, including the D and E series, are endogenous lipid mediators generated during the resolution phase of acute of inflammation from the ω-3 PUFAs, DHA, and EPA. They have anti-inflammatory and pro-resolving properties that have been determined in many inflammation studies in animal models. In this review, we provide an updated overview of biosynthesis, actions, and signaling pathways of resolvins, thereby underscoring their diverse protective roles and introducing novel therapeutic strategies for inflammation-associated diseases.

Mapracorat, a selective glucocorticoid receptor agonist, causes apoptosis of eosinophils infiltrating the conjunctiva in late-phase experimental ocular allergy

Background

Mapracorat, a novel nonsteroidal selective glucocorticoid receptor agonist, has been proposed for the topical treatment of inflammatory disorders as it binds with high affinity and selectivity to the human glucocorticoid receptor and displays a potent anti-inflammatory activity, but seems to be less effective in transactivation of a number of genes, resulting in a lower potential for side effects. Contrary to classical glucocorticoids, mapracorat displays a reduced ability to increase intraocular pressure and in inducing myocilin, a protein linked to intraocular pressure elevation. Allergic conjunctivitis is the most common form of ocular allergy and can be divided into an early phase, developing immediately after allergen exposure and driven primarily by mast cell degranulation, and a late phase, developing from 6–10 hours after the antigen challenge, and characterized by conjunctival infiltration of eosinophils and other immune cells as well as by the production of cytokines and chemokines.

Methods

In this study, mapracorat was administered into the conjunctival sac of ovalbumin (OVA)-sensitized guinea pigs 2 hours after the induction of allergic conjunctivitis, with the aim of investigating its activity in reducing clinical signs of the late-phase ocular reaction and to determine its mechanism of anti-allergic effects with respect to apoptosis of conjunctival eosinophils and expression of the chemokines C-C motif ligand 5 (CCL5), C-C motif ligand 11 (CCL11), and interleukin-8 (IL-8) and the proinflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α).

Results

Mapracorat, administered into the conjunctival sac of OVA-sensitized guinea pigs 2 hours after allergen exposure, was effective in reducing clinical signs, eosinophil infiltration, and eosinophil peroxidase activity in the guinea pig conjunctiva; furthermore, it reduced conjunctival mRNA levels and protein expression of both CCL5 and CCL11. Mapracorat was more effective than dexamethasone in increasing, in conjunctival sections of OVA-treated guinea pigs, apoptotic eosinophils.

Conclusion

Mapracorat displays anti-allergic properties in controlling the late phase of ocular allergic conjunctivitis and is a promising candidate for the topical treatment of allergic eye disorders.

Inhaled dsRNA and rhinovirus evoke neutrophilic exacerbation and lung expression of thymic stromal lymphopoietin in allergic mice with established experimental asthma

Background

Rhinovirus infection or dsRNA stimulation increased thymic stromal lymphopoietin (TSLP), an upstream pro-allergic cytokine, in asthmatic bronchial epithelial cells. We hypothesized that dsRNA challenges superimposed on established experimental allergic asthma constitute a useful exacerbation model. We further hypothesized that TSLP is induced at dsRNA- and rhinoviral infection-induced exacerbations.

Methods

Allergic mice were challenged with OVA followed by three daily intranasal challenges with dsRNA or saline. Bronchoalveolar lavage fluid (BALF) was analysed for total protein, lactate dehydrogenase (LDH), CXCL1/KC, CCL2/MCP-1 and differential cell counts. Lung tissue histology, neutrophils and TSLP, TNF-α, IFN-β and IFN-λ mRNA were examined. Alternatively, allergen-challenged mice received intranasal rhinovirus-(RV)-1B followed by lung TSLP immunostaining.

Results

In mice with allergic airway inflammation, dsRNA challenges caused a significant exacerbation increasing lung tissue inflammation score and tissue neutrophilia. Bronchoalveolar lavage fluid neutrophils, total protein, LDH, CXCL1/KC and CCL2/MCP-1 were also increased (P < 0.01), and so were lung tissue expressions of TNF-α, IFN-λ and TSLP (P < 0.01), but IFN-β was not increased. TSLP, IFN-λ and LDH were not increased by allergen or dsRNA challenges alone, but increased exclusively at exacerbations. RV1B infection-induced exacerbation also increased lung tissue TSLP (P < 0.05).

Conclusions

dsRNA-induced exacerbation in mice with experimental asthma involved general inflammation, cytokines and interferons, in agreement with previous observations in exacerbating human asthma. Additionally, both dsRNA and RV1B infection increased lung TSLP exclusively at exacerbations. Our data suggest that dsRNA challenges superimposed on allergic inflammation are suited for pharmacological studies of asthma exacerbations including the regulation of lung tissue TSLP, TNF-α, IFN-β and IFN-λ.

A zebrafish compound screen reveals modulation of neutrophil reverse migration as an anti-inflammatory mechanism

Diseases of failed inflammation resolution are common and largely incurable. Therapeutic induction of inflammation resolution is an attractive strategy to bring about healing without increasing susceptibility to infection. However, therapeutic targeting of inflammation resolution has been hampered by a lack of understanding of the underlying molecular controls. To address this drug development challenge, we developed an in vivo screen for proresolution therapeutics in a transgenic zebrafish model. Inflammation induced by sterile tissue injury was assessed for accelerated resolution in the presence of a library of known compounds. Of the molecules with proresolution activity, tanshinone IIA, derived from a Chinese medicinal herb, potently induced inflammation resolution in vivo both by induction of neutrophil apoptosis and by promoting reverse migration of neutrophils. Tanshinone IIA blocked proinflammatory signals in vivo, and its effects are conserved in human neutrophils, supporting a potential role in treating human inflammation and providing compelling evidence of the translational potential of this screening strategy.

Non-invasive optical imaging of eosinophilia during the course of an experimental allergic airways disease model and in response to therapy

BACKGROUND

Molecular imaging of lung diseases, including asthma, is limited and either invasive or non-specific. Central to the inflammatory process in asthma is the recruitment of eosinophils to the airways, which release proteases and proinflammatory factors and contribute to airway remodeling. The aim of this study was to establish a new approach to non-invasively assess lung eosinophilia during the course of experimental asthma by combining non-invasive near-infrared fluorescence (NIRF) imaging with the specific detection of Siglec-F, a lectin found predominantly on eosinophils.

METHODOLOGY/PRINCIPAL FINDINGS

An ovalbumin (OVA)-based model was used to induce asthma-like experimental allergic airway disease (EAAD) in BALB/c mice. By means of a NIRF imager, we demonstrate that 48 h-72 h after intravenous (i.v.) application of a NIRF-labeled anti-Siglec-F antibody, mice with EAAD exhibited up to 2 times higher fluorescence intensities compared to lungs of control mice. Furthermore, average lung intensities of dexamethasone-treated as well as beta-escin-treated mice were 1.8 and 2 times lower than those of untreated, EAAD mice, respectively and correlated with the reduction of cell infiltration in the lung. Average fluorescence intensities measured in explanted lungs confirmed the in vivo findings of significantly higher values in inflamed lungs as compared to controls. Fluorescence microscopy of lung cryosections localized the i.v. applied NIRF-labeled anti-Siglec-F antibody predominantly to eosinophils in the peribronchial areas of EAAD lungs as opposed to control lungs.

CONCLUSION/SIGNIFICANCE

We show that monitoring the occurrence of eosinophils, a prominent feature of allergic asthma, by means of a NIRF-labeled antibody directed against Siglec-F is a novel and powerful non-invasive optical imaging approach to assess EAAD and therapeutic response in mice over time.

p53 Codon 72 Genetic Polymorphism in Asthmatic Children: Evidence of Interaction With Acid Phosphatase Locus 1

Several lines of evidence are implicating an increased persistence of apoptotic cells in patients with asthma. This is largely due to a combination of inhibition, or defects in the apoptotic process and/or impaired apoptotic cell removal mechanisms. Among apoptosis-inducing genes, an important role is played by p53. In the present study, we have investigated the possible relationship between p53 codon 72 polymorphism and asthma and the interaction with ACP1, a genetic polymorphism involved in the susceptibility to allergic asthma. We studied 125 asthmatic children and 123 healthy subjects from the Caucasian population of Central Italy. p53 codon 72 and ACP1 polymorphisms were evaluated using a restriction fragment length polymorphism-polymerase chain reaction (RFLP-PCR) method. There is a statistically significant association between p53 codon 72 polymorphism and allergic asthma: Arg/Arg genotype is more represented in asthmatic patients than in controls (P=0.018). This association, however, is present in subjects with low ACP1 activity A/A and A/B only (P=0.023). The proportion of children with A/A and A/B genotype carrying Arg/Arg genotype is significantly high in asthmatic children than in controls (OR=1.941; 95% C.I. 1.042-3.628). Our finding could have important clinical implications since the subjects with A/A and A/B genotypes of ACP1 carrying Arg/Arg genotype are more susceptible to allergic asthma than Pro/Pro genotype.

Zebrafish as a model for the study of neutrophil biology

To understand inflammation and immunity, we need to understand the biology of the neutrophil. Whereas these cells can readily be extracted from peripheral blood, their short lifespan makes genetic manipulations impractical. Murine knockout models have been highly informative, and new imaging techniques are allowing neutrophils to be seen during inflammation in vivo for the first time. However, there is a place for a new model of neutrophil biology, which readily permits imaging of individual neutrophils during inflammation in vivo, combined with the ease of genetic and chemical manipulation. The zebrafish has long been the model of choice for the developmental biology community, and the availability of genomic resources and tools for gene manipulation makes this an attractive model. Zebrafish innate immunity shares many features with mammalian systems, including neutrophils with morphological, biochemical, and functional features, also shared with mammalian neutrophils. Transgenic zebrafish with neutrophils specifically labeled with fluorescent proteins have been generated, and this advance has led to the adoption of zebrafish, alongside existing models, by a number of groups around the world. The use of these models has underpinned a number of key advances in the field, including the identification of a tissue gradient of hydrogen peroxide for neutrophil recruitment following tissue injury and direct evidence for reverse migration as a regulatable mechanism of inflammation resolution. In this review, we discuss the importance of zebrafish models in neutrophil biology and describe how the understanding of neutrophil biology has been advanced by the use of these models.

Drift-Diffusion Analysis of Neutrophil Migration during Inflammation Resolution in a Zebrafish Model

Neutrophils must be removed from inflammatory sites for inflammation to resolve. Recent work in zebrafish has shown neutrophils can migrate away from inflammatory sites, as well as die in situ. The signals regulating the process of reverse migration are of considerable interest, but remain unknown. We wished to study the behaviour of neutrophils during reverse migration, to see whether they moved away from inflamed sites in a directed fashion in the same way as they are recruited or whether the inherent random component of their migration was enough to account for this behaviour. Using neutrophil-driven photoconvertible Kaede protein in transgenic zebrafish larvae, we were able to specifically label neutrophils at an inflammatory site generated by tailfin transection. The locations of these neutrophils over time were observed and fitted using regression methods with two separate models: pure-diffusion and drift-diffusion equations. While a model hypothesis test (the F-test) suggested that the datapoints could be fitted by the drift-diffusion model, implying a fugetaxis process, dynamic simulation of the models suggested that migration of neutrophils away from a wound is better described by a zero-drift, "diffusion" process. This has implications for understanding the mechanisms of reverse migration and, by extension, neutrophil retention at inflammatory sites.

Resolution of leucocyte-mediated mucosal diseases. A novel in vivo paradigm for drug development

Removal of disease-driving inflammatory leucocytes is central to resolution of inflammation. The current pharmacological dogma teaches leucocyte elimination through apoptosis followed by phagocytosis. However, actual resolving roles of apoptotic-phagocytic processes have been difficult to demonstrate in the major diseases that are characterized by mucosal tissue inflammation. Many current in vivo observations rather demonstrate that leucocyte elimination occurs by transepithelial locomotion. Findings in diseased gut and bladder mucosae support this notion. Respiratory disease data are particularly compelling. Eosinophils and neutrophils abound in sputum and tracheal aspirates during treatment-induced recovery from severe asthma. Prolonged sputum neutrophilia, along with clinical improvement, follows upon smoking cessation in COPD. Eosinophils, neutrophils, lymphocytes, mast cells and dendritic cells also move in large numbers into the bronchial lumen at spontaneous inflammation resolution following allergen challenge in allergic rhinitis and asthma. A corresponding reduction of infiltrated cells in the bronchial mucosal tissue demonstrates efficiency of the transepithelial elimination pathway. Underscoring its operational role, drugs impeding transepithelial elimination of leucocytes aggravate mucosal/parenchymal inflammation. Hence, relying on lumen cell data alone can lead to paradoxical conclusions regarding anti-inflammatory drug efficacy. Conversely, drugs promoting non-injurious transepithelial elimination of leucocytes could resolve mucosal inflammatory diseases.

Cellular resolution of inflammation--catabasis

Controlled inflammation has become a central focus in chronic disease therapeutics. Exaggerated inflammation is a common factor that contributes to matrix destruction, cellular senescence, and nonhealing in a variety of disease processes. Efforts at controlling inflammation have traditionally concentrated on systemic antagonists to inflammation such as nonsteroidal anti-inflammatory agents. More recently, following increased appreciation of local biological cellular and molecular events occurring at the wound interface, efforts are being focused on local targeted approaches to catabasis, the resolution of inflammation. These efforts relate to the isolation and understanding of the mechanisms of actions of various "stop signal mediators." These lipoxins, resolvins, and protectins are produced and stimulated by cellular interactions in the blood stream, extracellular matrix, and in cells themselves. Transmission of these signals between cells and the extracellular matrix and between cells themselves occurs via a variety of mechanisms including through intracellular gap junctions, connexins, and cadherins. The existence of these mediators, signals, and channels of communication all provide new therapeutic options for achieving catabasis in a more defined and targeted fashion.

A model 450 million years in the making: zebrafish and vertebrate immunity

Since its first splash 30 years ago, the use of the zebrafish model has been extended from a tool for genetic dissection of early vertebrate development to the functional interrogation of organogenesis and disease processes such as infection and cancer. In particular, there is recent and growing attention in the scientific community directed at the immune systems of zebrafish. This development is based on the ability to image cell movements and organogenesis in an entire vertebrate organism, complemented by increasing recognition that zebrafish and vertebrate immunity have many aspects in common. Here, we review zebrafish immunity with a particular focus on recent studies that exploit the unique genetic and in vivo imaging advantages available for this organism. These unique advantages are driving forward our study of vertebrate immunity in general, with important consequences for the understanding of mammalian immune function and its role in disease pathogenesis.

Peptidylarginine deiminases present in the airways during tobacco smoking and inflammation can citrullinate the host defense peptide LL-37, resulting in altered activities

Bacterial colonization of the lower respiratory tract is frequently seen in chronic obstructive pulmonary disease (COPD), and may cause exacerbations leading to disease progression. Antimicrobial peptides comprise an important part of innate lung immunity, and not least the cathelicidin human cationic antimicrobial protein-18/LL-37. Peptidylarginine deiminases (PADIs) post-translationally modify proteins by converting cationic peptidylarginine residues to neutral peptidylcitrulline. An increased presence of PADI2 and citrullinated proteins was demonstrated in the lungs of smokers. In this study, preformed PADI4, stored in granulocytes and extracellularly in the lumina of bronchi, was found in lung tissue of individuals suffering from COPD. In vitro, recombinant human PADI2 and PADI4 both caused a time- and dose-dependent citrullination of LL-37. The citrullination resulted in impaired antibacterial activity against Staphylococcus aureus, Streptococcus pneumoniae, and nontypable Haemophilus influenzae, but less so against Pseudomonas aeruginosa. Using artificial lipid bilayers, we observed discrete differences when comparing the disrupting activity of native and citrullinated LL-37, suggesting that differences in cell wall composition are important during interactions with whole bacteria. Furthermore, citrullinated LL-37 showed higher chemotactic activity against mononuclear leukocytes than did native LL-37, but was less efficient at neutralizing lipolysaccharide, and also in converting apoptotic neutrophils into a state of secondary necrosis. In addition, citrullinated LL-37 was more prone to degradation by proteases, whereas the V8 endopetidase of S. aureus cleaved the modified peptide at additional sites, compared with native LL-37. Together, these findings demonstrate novel mechanisms whereby the inflammation-dependent deiminases PADI2 and PADI4 can alter the activites of antibacterial polypeptides, affecting the course of inflammatory disorders such as COPD.

Activation of hypoxia-inducible factor-1α (Hif-1α) delays inflammation resolution by reducing neutrophil apoptosis and reverse migration in a zebrafish inflammation model

The oxygen-sensing transcription factor hypoxia-inducible factor-1α (HIF-1α) plays a critical role in the regulation of myeloid cell function. The mechanisms of regulation are not well understood, nor are the phenotypic consequences of HIF modulation in the context of neutrophilic inflammation. Species conservation across higher metazoans enables the use of the genetically tractable and transparent zebrafish (Danio rerio) embryo to study in vivo resolution of the inflammatory response. Using both a pharmacologic approach known to lead to stabilization of HIF-1α, and selective genetic manipulation of zebrafish HIF-1α homologs, we sought to determine the roles of HIF-1α in inflammation resolution. Both approaches reveal that activated Hif-1α delays resolution of inflammation after tail transection in zebrafish larvae. This delay can be replicated by neutrophil-specific Hif activation and is a consequence of both reduced neutrophil apoptosis and increased retention of neutrophils at the site of tissue injury. Hif-activated neutrophils continue to patrol the injury site during the resolution phase, when neutrophils would normally migrate away. Site-directed mutagenesis of Hif in vivo reveals that hydroxylation of Hif-1α by prolyl hydroxylases critically regulates the Hif pathway in zebrafish neutrophils. Our data demonstrate that Hif-1α regulates neutrophil function in complex ways during inflammation resolution in vivo.

Behavioral and structural differences in migrating peripheral neutrophils from patients with chronic obstructive pulmonary disease

RATIONALE

There are increased neutrophils in the lungs of patients with chronic obstructive pulmonary disease (COPD), but it is unclear if this is due to increased inflammatory signal or related to the inherent behavior of the neutrophils. This is critical, because inaccurate or excessive neutrophil chemotaxis could drive pathological accumulation and tissue damage.

OBJECTIVES

To assess migratory dynamics of neutrophils isolated from patients with COPD compared with healthy smoking and nonsmoking control subjects and patients with α(1)-antitryspin deficiency.

METHODS

Migratory dynamics and structure were assessed in circulating neutrophils, using phase and differential interference contrast microscopy and time-lapse photography. The effect of COPD severity was studied. Surface expression of receptors was measured using flow cytometry. The in vitro effects of a phosphoinositide 3-kinase inhibitor (LY294002) were studied.

MEASUREMENTS AND MAIN RESULTS

COPD neutrophils moved with greater speed than cells from either control group but with reduced migratory accuracy, in the presence of IL-8, growth-related oncogene α, formyl-methionyl-leucyl-phenylalanine, and sputum. This was present across all stages of COPD. Structurally, COPD neutrophils formed fewer pseudopods during migration. There were no differences in surface expression of the receptors CXCR1, CXCR2, or FPR1. LY294002 reduced COPD neutrophil migratory speed while increasing chemotactic accuracy, returning values to normal. The inhibitor did not have these effects in healthy control subjects or patients with a similar degree of lung disease.

CONCLUSIONS

COPD neutrophils are intrinsically different than cells from other studied populations in their chemotactic behavior and migratory structure. Differences are not due to surface expression of chemoattractant receptors but instead appear to be due to differences in cell signaling.

Resolvins: natural agonists for resolution of pulmonary inflammation

Inappropriate or excessive pulmonary inflammation can contribute to chronic lung diseases. In health, the resolution of inflammation is an active process that terminates inflammatory responses. The recent identification of endogenous lipid-derived mediators of resolution has provided a window to explore the pathobiology of inflammatory disease and structural templates for the design of novel pro-resolving therapeutics. Resolvins (resolution-phase interaction products) are a family of pro-resolving mediators that are enzymatically generated from essential omega-3 polyunsaturated fatty acids. Two molecular series of resolvins have been characterised, namely E- and D-series resolvins which possess distinct structural, biochemical and pharmacological properties. Acting as agonists at specific receptors (CMKLR1, BLT1, ALX/FPR2 and GPR32), resolvins can signal for potent counter-regulatory effects on leukocyte functions, including preventing uncontrolled neutrophil swarming, decreasing the generation of cytokines, chemokines and reactive oxygen species and promoting clearance of apoptotic neutrophils from inflamed tissues. Hence, resolvins provide mechanisms for cytoprotection of host tissues to the potentially detrimental effects of unresolved inflammation. This review highlights recent experimental findings in resolvin research, and the impact of these stereospecific molecules on the resolution of pulmonary inflammation and tissue catabasis.

Specialized pro-resolving lipid mediators in the inflammatory response: An update

A new genus of specialized pro-resolving mediators (SPM) which include several families of distinct local mediators (lipoxins, resolvins, protectins, and maresins) are actively involved in the clearance and regulation of inflammatory exudates to permit restoration of tissue homeostasis. Classic lipid mediators that are temporally regulated are formed from arachidonic acid, and novel local mediators were uncovered that are biosynthesized from ω-3 poly-unsaturated fatty acids, such as eicosapentaenoic acid, docosapentaenoic acid and docosahexaenoic acid. The biosynthetic pathways for resolvins are constituted by fatty acid lipoxygenases and cyclooxygenase-2 via transcellular interactions established by innate immune effector cells which migrate from the vasculature to inflamed tissue sites. SPM provide local control over the execution of an inflammatory response towards resolution, and include recently recognized actions of SPM such as tissue protection and host defense. The structural families of the SPM do not resemble classic eicosanoids (PG or LT) and are novel structures that function uniquely via pro-resolving cellular and molecular targets. The extravasation of inflammatory cells expressing SPM biosynthetic routes are matched by the temporal provision of essential fatty acids from circulation needed as substrate for the formation of SPM. The present review provides an update and overview of the biosynthetic pathways and actions of SPM, and examines resolution as an integrated component of the inflammatory response and its return to homeostasis via biochemically active resolution mechanisms.

Secondary necrosis: the natural outcome of the complete apoptotic program

The predominant definition of apoptosis considers that the elimination of the apoptosing cell is by heterolytic degradation following phagocytosis by an assisting scavenger (efferocytosis). However, an alternative and largely underestimated outcome of apoptosis is secondary necrosis, an autolytic process of cell disintegration with release of cell components that occurs when there is no intervention of scavengers and the full apoptotic program is completed. Secondary necrosis is the typical outcome of apoptosis in unicellular eukaryotes but, importantly, it may also occur in multicellular animals and has been implicated in the genesis of important human pathologies. Secondary necrosis is a mode of cell elimination with specific molecular and morphological features and should be considered the natural outcome of the complete apoptotic program.

Sphingolipid-mediated inhibition of apoptotic cell clearance by alveolar macrophages

A decreased clearance of apoptotic cells (efferocytosis) by alveolar macrophages (AM) may contribute to inflammation in emphysema. The up-regulation of ceramides in response to cigarette smoking (CS) has been linked to AM accumulation and increased detection of apoptotic alveolar epithelial and endothelial cells in lung parenchyma. We hypothesized that ceramides inhibit the AM phagocytosis of apoptotic cells. Release of endogenous ceramides via sphingomyelinase or exogenous ceramide treatments dose-dependently impaired apoptotic Jurkat cell phagocytosis by primary rat or human AM, irrespective of the molecular species of ceramide. Similarly, in vivo augmentation of lung ceramides via intratracheal instillation in rats significantly decreased the engulfment of instilled target apoptotic thymocytes by resident AM. The mechanism of ceramide-induced efferocytosis impairment was dependent on generation of sphingosine via ceramidase. Sphingosine treatment recapitulated the effects of ceramide, dose-dependently inhibiting apoptotic cell clearance. The effect of ceramide on efferocytosis was associated with decreased membrane ruffle formation and attenuated Rac1 plasma membrane recruitment. Constitutively active Rac1 overexpression rescued AM efferocytosis against the effects of ceramide. CS exposure significantly increased AM ceramides and recapitulated the effect of ceramides on Rac1 membrane recruitment in a sphingosine-dependent manner. Importantly, CS profoundly inhibited AM efferocytosis via ceramide-dependent sphingosine production. These results suggest that excessive lung ceramides may amplify lung injury in emphysema by causing both apoptosis of structural cells and inhibition of their clearance by AM.

The airway epithelium as regulator of inflammation patterns in asthma

INTRODUCTION

Asthma is a complex, heterogeneous and mutifactorial disease and represents a major health problem in Westernized countries. The airway epithelium, with its direct physical contact with luminal triggers, has a major role in determining the nature of inflammation that develops in asthmatic airways.

OBJECTIVE

The present review aims to provide a brief overview of the numerous ways the airway epithelium can affect and influence the histopathological picture in asthma.

RESULTS AND CONCLUSION

The ways the epithelium aggravates inflammation range from acute responses to luminal triggers such as allergens and infections to the multipathogenic events occurring as a consequence of repeated epithelial damage-repair responses. The airway epithelium also facilitates the selective migration of leukocytes into the airway lumen, a process that is important in regulating inflammatory cell homeostasis. The fact that only some of the important leukocyte subtypes participate in this process cause translational problems and difficulties in the interpretation of luminal samples. To further reveal the nature of the multifaceted involvement of the airway epithelium in inflamed asthmatic airways emerges as a promising goal for identifying new therapeutic strategies.

Bacteria-induced phagocyte secondary necrosis as a pathogenicity mechanism

Triggering of phagocyte apoptosis is a major virulence mechanism used by some successful bacterial pathogens. A central issue in the apoptotic death context is that fully developed apoptosis results in necrotic cell autolysis (secondary necrosis) with release of harmful cell components. In multicellular animals, this occurs when apoptosing cells are not removed by scavengers, mainly macrophages. Secondary necrotic lysis of neutrophils and macrophages may occur in infection when extensive phagocyte apoptosis is induced by bacterial cytotoxins and removal of apoptosing phagocytes is defective because the apoptotic process exceeds the available scavenging capacity or targets macrophages directly. Induction of phagocyte secondary necrosis is an important pathogenic mechanism, as it combines the pathogen evasion from phagocyte antimicrobial activities and the release of highly cytotoxic molecules, particularly of neutrophil origin, such as neutrophil elastase. This pathogenicity mechanism therefore promotes the unrestricted multiplication of the pathogen and contributes directly to the pathology of several necrotizing infections, where extensive apoptosis and necrosis of macrophages and neutrophils are present. Here, examples of necrotizing infectious diseases, where phagocyte secondary necrosis is implicated, are reviewed.

Resolution of cell-mediated airways diseases

"Inflammation resolution" has of late become a topical research area. Activation of resolution phase mechanisms, involving select post-transcriptional regulons, transcription factors, 'autacoids', and cell phenotypes, is now considered to resolve inflammatory diseases. Critical to this discourse on resolution is the elimination of inflammatory cells through apoptosis and phagocytosis. For major inflammatory diseases such as asthma and COPD we propose an alternative path to apoptosis for cell elimination. We argue that transepithelial migration of airway wall leukocytes, followed by mucociliary clearance, efficiently and non-injuriously eliminates pro-inflammatory cells from diseased airway tissues. First, it seems clear that numerous infiltrated granulocytes and lymphocytes can be speedily transmitted into the airway lumen without harming the epithelial barrier. Then there are a wide range of 'unexpected' findings demonstrating that clinical improvement of asthma and COPD is not only associated with decreasing numbers of airway wall inflammatory cells but also with increasing numbers of these cells in the airway lumen. Finally, effects of inhibition of transepithelial migration support the present hypothesis. Airway inflammatory processes have thus been much aggravated when transepithelial exit of leukocytes has been inhibited. In conclusion, the present hypothesis highlights risks involved in drug-induced inhibition of transepithelial migration of airway wall leukocytes. It helps interpretation of common airway lumen data, and suggests approaches to treat cell-mediated airway inflammation.

Early phase resolution of mucosal eosinophilic inflammation in allergic rhinitis

BACKGROUND

It is widely assumed that apoptosis of eosinophils is a central component of resolution of allergic airway disease. However, this has not been demonstrated in human allergic airways in vivo. Based on animal in vivo observations we hypothesised that steroid-induced resolution of human airway eosinophilic inflammation involves inhibition of CCL5 (RANTES), a CC-chemokine regulating eosinophil and lymphocyte traffic, and elimination of eosinophils without evident occurrence of apoptotic eosinophils in the diseased tissue.

OBJECTIVE

To determine mucosal eosinophilia, apoptotic eosinophils, general cell apoptosis and cell proliferation, and expression of CCL5 and CCL11 (eotaxin) in human allergic airway tissues in vivo at resolution of established symptomatic eosinophilic inflammation.

METHODS

Twenty-one patients with intermittent (birch and/or grass) allergic rhinitis received daily nasal allergen challenges for two seven days' periods separated by more than two weeks washout. Five days into these "artificial pollen seasons", nasal treatment with budesonide was instituted and continued for six days in a double blinded, randomized, placebo-controlled, and crossover design. This report is a parallel group comparison of nasal biopsy histochemistry data obtained on the final day of the second treatment period.

RESULTS

Treatments were instituted when clinical rhinitis symptoms had been established. Compared to placebo, budesonide reduced tissue eosinophilia, and subepithelial more than epithelial eosinophilia. Steroid treatment also attenuated tissue expression of CCL5, but CCL11 was not reduced. General tissue cell apoptosis and epithelial cell proliferation were reduced by budesonide. However, apoptotic eosinophils were not detected in any biopsies, irrespective of treatment.

CONCLUSIONS

Inhibition of CCL5-dependent recruitment of cells to diseased airway tissue, and reduced cell proliferation, reduced general cell apoptosis, but not increased eosinophil apoptosis, are involved in early phase steroid-induced resolution of human allergic rhinitis.

Resolvins and protectins: natural pharmacophores for resolution biology

Dietary ingestion of fish is associated with a reduced risk for many common human illnesses. Fish oils are enriched with n-3 polyunsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid. Resolvins and protectins are newly discovered mediators that are enzymatically generated from these n-3 fatty acid precursors to orchestrate inflammation resolution. These natural compounds and their mimetics are providing intriguing evidence in model systems and translational research for cellular and molecular mechanisms that are active during catabasis. This review provides information on the biosynthesis and actions of these recently identified chemical mediators with particular reference to resolution of mucosal inflammatory responses.

Pivotal Advance: Pharmacological manipulation of inflammation resolution during spontaneously resolving tissue neutrophilia in the zebrafish

Zebrafish are a unique model for pharmacological manipulation of physiological processes such as inflammation; they are small and permeable to many small molecular compounds, and being transparent, they permit the visualization and quantitation of the inflammatory response by observation of transgenically labeled inflammatory cell populations. Using a transgenic line specifically labeling neutrophils in vivo (mpx:GFP), we studied the effects of a range of pharmacological agents on the resolution of inflammation in vivo. These agents were selected for their ability to modulate neutrophil function and lifespan in human neutrophils in vitro. Agents delaying neutrophil apoptosis (LPS, dbcAMP, and several caspase inhibitors) all lead to a delay in resolution of neutrophilic inflammation. Reciprocally, pyocyanin and roscovitine (inducers of neutrophil apoptosis) lead to reduced neutrophil numbers. The occurrence of apoptosis was observed by time-lapse analysis and confirmed by dual staining for neutrophil-specific mpx activity (TSA staining) and an apoptotic marker (TUNEL). During inflammation, macrophages follow neutrophils into the inflamed site, and TUNEL/TSA dual-positive material can be demonstrated within macrophages, consistent with their uptake of apoptotic neutrophils. This model has several advantages over mammalian models and lends itself to the study of pharmaceutical agents modulating inflammation.

Prevalence of apoptotic epidermal keratinocytes in eosinophilic dermatoses of the cat: a retrospective light-microscopic study of 145 skin-biopsy specimens

A retrospective light-microscopic study was performed on skin-biopsy specimens from 145 cats with eosinophilic inflammatory dermatoses in order to determine the prevalence of apoptotic epidermal keratinocytes (AKs), the prevalence of eosinophils in close proximity to AKs, and whether there was a difference in the prevalence of AKs or the prevalence of eosinophils in close proximity to AKs based on histopathological reaction pattern. Overall, 62/145 (43%) specimens had AKs. Of the cases in which AKs were seen, 18% had eosinophils in close proximity to the AKs. The specimens were divided into three groups based on histopathological reaction pattern: perivascular-to-interstitial, diffuse, and nodular. No difference in the prevalence of AKs was found among the three histological groups. Because the sample size containing eosinophils in close proximity to AKs was too small to compare the three histological patterns individually, nodular and non-nodular patterns were compared. No difference in the presence of eosinophils in close proximity to AKs was found in these two subsets. More AKs were present if eosinophils were in close proximity to the AKs (range 1-9 with eosinophils near compared to 0-7 without).

Effect of a matrix metalloproteinase-12 inhibitor, S-1, on allergic airway disease phenotypes in mice

OBJECTIVE

Matrix metalloproteinase-12 (MMP-12) has been reported to play an important role in chronic airway inflammatory diseases, but its detailed role in allergic airway disease is not well known. In this study, we investigated the expressions of MMP-12 and the effect of S-1, an MMP-12 inhibitor, in a mouse model of allergic airway inflammation.

MATERIALS AND METHODS

The expressions and activity of MMP-12 were measured by RT-PCR western blot and zymography, respectively. The locations in the airways of MMP-12 and elastin fiber were histologically studied. The mice were orally administered with S-1 during the period of antigen challenge. Bronchoalveolar lavage fluid (BALF) cells were counted, and the activity of MMP-12 in BALF was measured by zymography after the treatment with S-1.

RESULTS

The allergen challenge model resulted in increased eosinophil number in BALF and damage to elastin fiber. Upregulation of MMP-12 was also found in the airways of challenged mice. The increased eosinophil number in the BALF after antigen challenge was inhibited by S-1.

CONCLUSION

These findings suggest that MMP-12 may play an important role in the eosinophil infiltration of the allergic airway.

Alterations in lung mast cell populations in patients with chronic obstructive pulmonary disease

RATIONALE

Mast cells have important roles in innate immunity and tissue remodeling but have remained poorly studied in inflammatory airway diseases like chronic obstructive pulmonary disease (COPD).

OBJECTIVES

To perform a detailed histological characterization of human lung mast cell populations at different severities of COPD, comparing with smoking and never-smoking control subjects.

METHODS

Mast cells were analyzed in lung tissues from patients with mild to very severe COPD, GOLD I-IV (n = 25, 10 of whom were treated with corticosteroids). Never-smokers and smokers served as controls. The density, morphology, and molecular characteristics of mucosal and connective tissue mast cells (MC(T) and MC(TC), respectively) were analyzed in several lung regions.

MEASUREMENTS AND MAIN RESULTS

In all compartments of COPD lungs, especially at severe stages, the MC(TC) population increased in density, whereas the MC(T) population decreased. The net result was a reduction in total mast cell density. This phenomenon was paralleled by increased numbers of luminal mast cells, whereas the numbers of terminal transferase dUTP nick end labeling (TUNEL)(+) apoptotic mast cells remained unchanged. In COPD lungs, the MC(T) and MC(TC) populations showed alterations in morphology and expression of CD88 (C5a-R), transforming growth factor (TGF)-beta, and renin. Statistically significant correlations were found between several COPD-related mast cell alterations and lung function parameters.

CONCLUSIONS

As COPD progresses to its severe stages, the mast cell populations in the lung undergo changes in density, distribution, and molecular expression. In COPD lungs, these novel histopathological features were found to be correlated to lung function and they may thus have clinical consequences.