Kinetics of pulmonary neutrophil recruitment and clearance in a natural and spontaneously resolving model of airway inflammation

A CONSORT-guided, randomized controlled clinical trial of nebulized administration of dexamethasone and saline on lower airway cytokine mRNA expression in horses with moderate asthma

BACKGROUND

Nebulized administration of dexamethasone on cytokine regulation in horses with moderate asthma has not been investigated.

OBJECTIVE

To investigate the changes in expression of inflammatory cytokine mRNA after nebulized administration of dexamethasone treatment of horses with moderate asthma.

ANIMALS

Horses with naturally occurring moderate asthma (n = 16) and healthy control horses (n = 4). All horses were kept in a dusty environment during the study.

METHODS

Prospective, parallel, randomized, controlled, blinded clinical trial. Blood endogenous cortisol, tracheal mucus, and bronchoalveolar lavage (BAL) were sampled before and after 13 days treatment with either nebulized administration of dexamethasone (15 mg once daily) or 0.9% saline (3 mL). Treatment groups were randomly allocated via randomization function (Microsoft Excel). Amplification of target mRNA in BAL fluid (IL-1β, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12, IL-17, IL-23, IFN-γ, Eotaxin-2, and TNF-α) was achieved by qPCR, and the relative expression software tool was used to analyze BAL inflammatory cytokine mRNA.

RESULTS

Horses treated with nebulized administration of dexamethasone had increased relative expression of IL-5 (1.70-fold), IL-6 (1.71-fold), IL-17 (3.25-fold), IL-12 (1.66-fold), and TNF-α (1.94-fold), and decreased relative expression of IL-23 (1.76-fold; P = .04) in samples collected on Day 14, in comparison to samples collected on Day 0 (all P < .05). Horses treated with nebulized administration of saline had no significant difference in the relative expression of any gene (all P > .05).

CONCLUSIONS AND CLINICAL IMPORTANCE

Nebulized administration of dexamethasone was associated with increased expression of inflammatory cytokine mRNA. There was no improvement in inflammatory airway cytology associated with either dexamethasone or saline treatment.

Molecular and Cellular Evaluation of Horses With Summer Pasture Associated Asthma Syndrome

Equine asthma is an airway disease that affects a large number of horses annually leading to considerable economic losses in the horse industry. Despite advances in research in this area, there is still a lack of information on its etiology and molecular characterization in pasture associated asthma. The objective of the current study was to characterize the inflammatory disease of lower airways in horses maintained on pasture through cytologic and immunologic profile during the summer in a tropical environment by analysis of the gene expression of Th1 cytokines (IFN- λ, IL-8), Th2 cytokines (IL-4 and IL-5), and pro-inflammatory cytokines (IL-1, TNF-α) in the bronchoalveolar lavage (BAL) fluid in healthy and asthma horses on pasture. A group 39 of clinically healthy horses maintained on native pasture and supplemented with concentrate was evaluated by BAL analyzed for differential cellular count and assigned into a control and an asthma group. The gene expression of pro-inflammatory cytokines was analyzed in the BAL by reverse time PCR (RT-PCR) (IL-1α (alpha), IL-4, IL-5, IL-8, TNF-α alpha and IFN-λ), using β-actin as housekeeping gene. Higher gene expression of IL-1, IL-4, IL-5, IL-8, IFN-λ in the BAL of asthma horses was found. Current results indicate an increase in Th2, characterizing an allergic inflammatory reaction due to the significant increase in IL-5 in asthmatic horses (10.3 ± 1.13), when compared to the values ​​obtained in normal horses (3.27 ± 0.46). The only down regulated cytokine in the asthma group was TNF-α, suggesting a chronic antigenic reaction.

Neutrophil Extracellular Vesicles and Airway Smooth Muscle Proliferation in the Natural Model of Severe Asthma in Horses

Extracellular vesicles (EVs) contribute to intercellular communication through the transfer of their rich cargo to recipient cells. The EVs produced by LPS-stimulated neutrophils from healthy humans and horses increase airway smooth muscle (ASM) proliferation, but the roles of neutrophil EVs in asthma are largely unexplored. The aim of this study was to determine whether neutrophil-derived EVs isolated during the remission or exacerbation of asthma influence ASM proliferation differentially. Peripheral blood neutrophils were collected during remission and exacerbation in eight horses affected by severe asthma. The cells were cultured (±LPS), and their EVs were isolated by ultracentrifugation and characterized by laser scattering microscopy and proteomic analysis. The proliferation of ASM co-incubated with EVs was monitored in real time by electrical impedance. Two proteins were significantly upregulated during disease exacerbation in neutrophil EVs (MAST4 and Lrch4), while LPS stimulation greatly altered the proteomic profile. Those changes involved the upregulation of neutrophil degranulation products, including proteases known to induce myocyte proliferation. In agreement with the proteomic results, EVs from LPS-stimulated neutrophils increased ASM proliferation, without an effect of the disease status. The inhalation of environmental LPS could contribute to asthma pathogenesis by activating neutrophils and leading to ASM hyperplasia.

Neutrophil Extracellular Traps Are Found in Bronchoalveolar Lavage Fluids of Horses With Severe Asthma and Correlate With Asthma Severity

Asthma encompasses a spectrum of heterogenous immune-mediated respiratory disorders sharing a similar clinical pattern characterized by cough, wheeze and exercise intolerance. In horses, equine asthma can be subdivided into severe or moderate asthma according to clinical symptoms and the extent of airway neutrophilic inflammation. While severe asthmatic horses are characterized by an elevated neutrophilic inflammation of the lower airways, cough, dyspnea at rest and high mucus secretion, horses with moderate asthma show a milder neutrophilic inflammation, exhibit intolerance to exercise but no labored breathing at rest. Yet, the physiopathology of different phenotypes of equine asthma remains poorly understood and there is a need to elucidate the underlying mechanisms tailoring those phenotypes in order to improve clinical management and elaborate novel therapeutic strategies. In this study, we sought to quantify the presence of neutrophil extracellular traps (NETs) in bronchoalveolar lavage fluids (BALF) of moderate or severe asthmatic horses and healthy controls, and assessed whether NETs correlated with disease severity. To this end, we evaluated the amounts of NETs by measuring cell-free DNA and MPO-DNA complexes in BALF supernatants or by quantifying NETs release by BALF cells by confocal microscopy. We were able to unequivocally identify elevated NETs levels in BALF of severe asthmatic horses as compared to healthy controls or moderate asthmatic horses. Moreover, we provided evidence that BALF NETs release was a specific feature seen in severe equine asthma, as opposed to moderate asthma, and correlated with disease severity. Finally, we showed that NETs could act as a predictive factor for severe equine asthma. Our study thus uniquely identifies NETs in BALF of severe asthmatic horses using three distinct methods and supports the idea that moderate and severe equine asthma do not rely on strictly similar pathophysiological mechanisms. Our data also suggest that NETs represent a relevant biomarker, a putative driver and a potential therapeutic target in severe asthma disease.

The Immune Mechanisms of Severe Equine Asthma-Current Understanding and What Is Missing

Severe equine asthma is a chronic respiratory disease of adult horses, occurring when genetically susceptible individuals are exposed to environmental aeroallergens. This results in airway inflammation, mucus accumulation and bronchial constriction. Although several studies aimed at evaluating the genetic and immune pathways associated with the disease, the results reported are inconsistent. Furthermore, the complexity and heterogeneity of this disease bears great similarity to what is described for human asthma. Currently available studies identified two chromosome regions (ECA13 and ECA15) and several genes associated with the disease. The inflammatory response appears to be mediated by T helper cells (Th1, Th2, Th17) and neutrophilic inflammation significantly contributes to the persistence of airway inflammatory status. This review evaluates the reported findings pertaining to the genetical and immunological background of severe equine asthma and reflects on their implications in the pathophysiology of the disease whilst discussing further areas of research interest aiming at advancing treatment and prognosis of affected individuals.

Randomised study of the immunomodulatory effects of azithromycin in severely asthmatic horses

Neutrophilic inflammation is believed to contribute to the airway obstruction and remodelling in equine asthma. Azithromycin, an antibiotic with immunomodulatory properties, reduces pulmonary neutrophilia and hyper-responsiveness in human asthmatics and decreases airway remodelling in rodent models of asthma. It was therefore hypothesised that azithromycin would improve lung function, mucus accumulation and central airway remodelling by decreasing luminal neutrophilia in severe equine asthma. The effects of a 10-day treatment with either azithromycin or ceftiofur, an antimicrobial without immune-modulating activity, were assessed using a blind, randomised, crossover design with six severe asthmatic horses in clinical exacerbation. Lung function, tracheal mucus accumulation, tracheal wash bacteriology, bronchial remodelling, airway neutrophilia and mRNA expression of proinflammatory cytokines (interleukin (IL)-8, IL-17A, IL-1β, tumour necrosis factor-α) in bronchoalveolar lavage fluid were evaluated. Azithromycin decreased the expression of IL-8 (P=0.03, one-tailed) and IL-1β (P=0.047, one-tailed) but failed to improve the other variables evaluated. Ceftiofur had no effect on any parameter. The reduction of neutrophilic chemoattractants (IL-8, IL-1β) justifies further efforts to investigate the effects of a prolonged treatment with macrolides on airway neutrophilia and remodelling. The lack of efficacy of ceftiofur suggests that severe equine asthma should not be treated with antibiotics at first-line therapy.

Comparative Review of Asthma in Farmers and Horses

PURPOSE OF REVIEW

Farmers are routinely exposed to organic dusts and aeroallergens that can have adverse respiratory health effects including asthma. Horses are farm-reared large animals with similar exposures and can develop equine asthma syndrome (EAS). This review aims to compare the etiology, pathophysiology, and immunology of asthma in horses compared to farmers and highlights the horse as a potential translational animal model for organic dust-induced asthma in humans.

RECENT FINDINGS

Severe EAS shares many clinical and pathological features with various phenotypes of human asthma including allergic, non-allergic, late onset, and severe asthma. EAS disease features include variable airflow obstruction, cough, airway hyperresponsiveness, airway inflammation/remodeling, neutrophilic infiltrates, excess mucus production, and chronic innate immune activation. Severe EAS is a naturally occurring and biologically relevant, translational animal disease model that could contribute to a more thorough understanding of the environmental and immunologic factors contributing to organic dust-induced asthma in humans.

The counter-intuitive role of the neutrophil in the acute respiratory distress syndrome

INTRODUCTION

Neutrophils are the primary effectors of the innate immune system but are profoundly histotoxic cells. The acute respiratory distress syndrome (ARDS) is considered to be a prime example of neutrophil-mediated tissue injury.

SOURCES OF DATA

The information presented in this review is acquired from the published neutrophil cell biology literature and the longstanding interest of the senior authors in ARDS pathogenesis and clinical management.

AREAS OF AGREEMENT

Investigators in the field would agree that neutrophils accumulate in high abundance in the pulmonary microcirculation, lung interstitium and alveolar airspace of patients with ARDS. ARDS is also associated with systemic neutrophil priming and delayed neutrophil apoptosis and clearance of neutrophils from the lungs. In animal models, reducing circulating neutrophil numbers ameliorates lung injury.

AREAS OF CONTROVERSY

Areas of uncertainty include how neutrophils get stuck in the narrow pulmonary capillary network-whether this reflects changes in the mechanical properties of primed neutrophils alone or additional cell adhesion molecules, the role of neutrophil sub-sets or polarization states including pro-angiogenic and low-density neutrophils, whether neutrophil extracellular trap (NET) formation is beneficial (through bacterial capture) or harmful and the potential for neutrophils to participate in inflammatory resolution. The latter may involve the generation of specialized pro-resolving molecules (SPMs) and MMP-9, which is required for adequate matrix processing.

GROWING POINTS

Different and possibly stable endotypes of ARDS are increasingly being recognized, yet the relative contribution of the neutrophil to these endotypes is uncertain. There is renewed and intense interest in understanding the complex 'new biology' of the neutrophil, specifically whether this cell might be a valid therapeutic target in ARDS and other neutrophil-driven diseases and developing understanding of ways to enhance the beneficial role of the neutrophil in the resolution phase of ARDS.

AREAS TIMELY FOR DEVELOPING RESEARCH

Aside from treatment of the precipitating causes of ARDS, and scrupulous fluid, infection and ventilation management, there are no pharmacological interventions for ARDS; this represents an urgent and unmet need. Therapies aimed at reducing overall neutrophil numbers risk secondary infection; hence better ways are needed to reverse the processes of neutrophil priming activation, hyper-secretion and delayed apoptosis while enhancing the pro-resolution functions of the neutrophil.

Immunomodulatory asthma therapy in the equine animal model: A dose-response study and evaluation of a long-term effect

INTRODUCTION

Equine asthma represents a naturally occurring animal model for human allergic neutrophilic asthma. Inhalative nanoparticle-bound cytosine-phosphate-guanosine (CpG-GNP) immunotherapy, independent of specific allergens, has already shown promising clinical and immunological results in previous studies and offers the possibility to treat the underlying cause of the disease. This study analyses the relationship between dose and response, and evaluates a possible long-term effect.

METHODS

In the prospective, randomised, double-blind clinical field study, 29 horses suffering from equine asthma received 10 inhalation treatments with either 187.5 µg CpG-GNP (CpG single dose [CpGsd]; n = 11), 375 µg CpG-GNP double dose (CpG double dose [CpGdd]; n = 9) (q48h for 20 days) or 1600 µg beclomethasone (n = 9) (q24h for 10 days). Each horse was examined three times: before the treatment (I), immediately after the 10 inhalations (II), and 8 weeks after the final inhalation (III). The three groups were compared according to clinical and laboratory parameters. The study examined the sustainability of the long-term effect of the treatment after 8 weeks, as well as the tolerability of the formula as a double dose.

RESULTS

The CpGsd resulted in a significant improvement in 82% of the parameters, the CpGdd in 72%. In the long-term evaluation, the CpGsd showed a significant improvement in 100% of the parameters in comparison to the initial values, the CpGdd in 67%. On the immunological level, the bronchoalveolar lavage revealed a significant reduction of IL-4, IL-8, and interferon-γ.

CONCLUSION

Both CpG groups displayed significant improvements in clinical and laboratory parameters, especially regarding the long-term effect of CpGsd. Doubling the CpG dose did not result in any improvement in comparison to the original single dose. On the immunological level, an anti-inflammatory, as well as an immunomodulatory effect, apart from a Th2-dominated immune response, could be observed. This immunomodulatory inhalation treatment could indicate a new possibility for human allergic asthma therapy.

Modeling the pasture-associated severe equine asthma bronchoalveolar lavage fluid proteome identifies molecular events mediating neutrophilic airway inflammation

Background: Pasture-associated severe equine asthma is a warm season, environmentally-induced respiratory disease characterized by reversible airway obstruction, persistent and non-specific airway hyper-responsiveness, and chronic neutrophilic airway inflammation. During seasonal exacerbation, signs vary from mild to life-threatening episodes of wheezing, coughing, and chronic debilitating labored breathing.

Purpose: In human asthma, neutrophilic airway inflammation is associated with more severe and steroid-refractory asthma phenotypes, highlighting a need to decipher the mechanistic basis of this disease characteristic. We hypothesize that the collective biological activities of proteins in bronchoalveolar lavage fluid (BALF) of horses with pasture-associated severe asthma predict changes in neutrophil functions that contribute to airway neutrophilic inflammation.

Methods: Using shotgun proteomics, we identified 1,003 unique proteins in cell-free BALF from six horses experiencing asthma exacerbation and six control herdmates. Contributions of each protein to ten neutrophil functions were modeled using manual biocuration to determine each protein’s net effect on the respective neutrophil functions.

Results: A total of 417 proteins were unique to asthmatic horses, 472 proteins were unique to control horses (p<0.05), and 114 proteins were common in both groups. Proteins whose biological activities are responsible for increasing neutrophil migration, chemotaxis, cell spreading, transmigration, and infiltration, which would collectively bring neutrophils to airways, were over-represented in the BALF of asthmatic relative to control horses. By contrast, proteins whose biological activities support neutrophil activation, adhesion, phagocytosis, respiratory burst, and apoptosis, which would collectively shorten neutrophil lifespan, were under-represented in BALF of asthmatic relative to control horses. Interaction networks generated using Ingenuity^® Pathways Analysis further support the results of our biocuration.

Conclusion: Congruent with our hypothesis, the collective biological functions represented in differentially expressed proteins of BALF from horses with pasture-associated severe asthma support neutrophilic airway inflammation. This illustrates the utility of systems modeling to organize functional genomics data in a manner that characterizes complex molecular events associated with clinically relevant disease.

Tamoxifen inhibits chemokinesis in equine neutrophils

Neutrophils are terminally differentiated innate effector cells at the first line of host defense. Neutrophil migration within tissues is complex and involves several steps, during which these cells must be able to interpret a variety of chemical and physical signals. Exacerbated neutrophil activity can be harmful to surrounding tissues; this is important in a range of diseases, including equine asthma. Tamoxifen (TX) is a non-steroidal estrogen receptor modulator with effects on cell growth and survival. Previous studies showed that TX treatment in horses with induced acute pulmonary inflammation promoted early apoptosis of blood and bronchoalveolar lavage fluid (BALF) neutrophils, reduction of BALF neutrophil content, and improvement in animals’ clinical status. Further, TX dampens chemotactic index and respiratory burst production in vitro. The aim of this study was to provide information on the effect of TX on chemokinesis in peripheral blood neutrophils from five healthy horses. Results showed that neutrophils increased migration and travelled distance in response to IL-8; but in the presence of TX, IL-8 did not produce neutrophil migration. This suggests that TX has an inhibitory effect on the kinesis of equine peripheral blood neutrophils stimulated with IL-8. However, further studies are required to fully understand the signaling pathways of TX on neutrophil chemokinesis.

Phagocytosis, bacterial killing, and cytokine activation of circulating blood neutrophils in horses with severe equine asthma and control horses

OBJECTIVE To evaluate in vitro phagocytosis and bactericidal activity of circulating blood neutrophils in horses with severe equine asthma and control horses and to determine whether circulating blood neutrophils in horses with severe equine asthma have an increase in expression of the proinflammatory cytokine tumor necrosis factor (TNF)-α and the chemokine interleukin (IL)-8 and a decrease in expression of the anti-inflammatory cytokine IL-10 in response to bacteria. ANIMALS 6 horses with severe equine asthma and 6 control horses. PROCEDURES Circulating blood neutrophils were isolated from horses with severe equine asthma and control horses. Phagocytosis was evaluated by use of flow cytometry. Bactericidal activity of circulating blood neutrophils was assessed by use of Streptococcus equi and Streptococcus zooepidemicus as targets, whereas the cytokine mRNA response was assessed by use of a quantitative PCR assay. RESULTS Circulating blood neutrophils from horses with severe equine asthma had significantly lower bactericidal activity toward S zooepidemicus but not toward S equi, compared with results for control horses. Phagocytosis and mRNA expression of TNF-α, IL-8, and IL-10 were not different between groups. CONCLUSIONS AND CLINCAL RELEVANCE Impairment of bactericidal activity of circulating blood neutrophils in horses with severe equine asthma could contribute to an increased susceptibility to infections.

Role of neutrophils in equine asthma

Neutrophilic bronchiolitis is the primary lesion in asthma-affected horses. Neutrophils are key actors in host defense, migrating toward sites of inflammation and infection, where they act as early responder cells toward external insults. However, neutrophils can also mediate tissue damage in various non-infectious inflammatory processes. Within the airways, these cells likely contribute to bronchoconstriction, mucus hypersecretion, and pulmonary remodeling by releasing pro-inflammatory mediators, including the cytokines interleukin (IL)-8 and IL-17, neutrophil elastase, reactive oxygen species (ROS), and neutrophil extracellular traps (NETs). The mechanisms that regulate neutrophil functions in the tissues are complex and incompletely understood. Therefore, the inflammatory activity of neutrophils must be regulated with exquisite precision and timing, a task achieved through a complex network of mechanisms that regulates neutrophil survival. The discovery and development of compounds that can help regulate ROS, NET formation, cytokine release, and clearance would be highly beneficial in the design of therapies for this disease in horses. In this review, neutrophil functions during inflammation will be discussed followed by a discussion of their contribution to airway tissue injury in equine asthma.

Equine neutrophils and their role in ischemia reperfusion injury and lung inflammation

Horses are susceptible to a multitude of inflammatory conditions that are characterized by a strong neutrophilic response. Here, we review basic equine neutrophil biology and explore the role of neutrophils in inflammatory conditions with emphasis on intestinal ischemia and reperfusion injury and lung inflammation. In addition, unique aspects of equine neutrophil biology have been highlighted. Neutrophils comprise the highest proportion of circulating white blood cells in equine blood. The concentration of circulating equine neutrophils is a primary indicator of systemic inflammation. Additionally, equine neutrophils exposed to various stimulants develop "toxic" changes characterized as cytoplasmic basophilia, presence of Döhle bodies, cytoplasmic vacuolation and toxic granulation. In contrast to human neutrophils, equine neutrophils fail to undergo chemotaxis in response to the peptide N-formyl-methionyl-leucyl-phenylalanine and are dependent on the addition of arachidonic acid due to reduced activity of phospholipase A₂ to synthesize leukotrienes as part of the arachidonic acid pathway. Understanding the biologic function of neutrophils in horses is integral to developing methods to modulate inflammation associated with ischemia reperfusion injury and lung disease.

Characterization of Circulating Low-Density Neutrophils Intrinsic Properties in Healthy and Asthmatic Horses

Low-density neutrophils (LDNs) are a subset of neutrophils first described in the bloodstream upon pathological conditions, and recently, in the blood of healthy humans. LDNs may have an enhanced pro-inflammatory (low-density granulocytes, LDGs) or an immunosuppressive (Granulocytic myeloid-derived suppressor cells, G-MDSCs) profile. Whether these characteristics are specific to LDNs or related to disease states is unknown. Thus, we sought to investigate the properties of LDNs in both health and disease states, and to compare them to those of autologous normal-density neutrophils (NDNs). We studied 8 horses with severe equine asthma and 11 healthy animals. LDNs were smaller and contained more N-formylmethionine-leucyl-phenylalanine receptors than NDNs, but the myeloperoxidase content was similar in both cell populations. They also had an increased capacity to produce neutrophil extracellular traps, and were more sensitive to activation by phorbol-12-myristate-13-acetate. This profile is suggestive of LDGs. These characteristics were similar in both healthy and diseased animals, indicating that these are intrinsic properties of LDNs. Furthermore, these results suggest that LDNs represent a population of primed and predominantly mature cells. This study is the first to characterize LDNs in health, and to compare their properties with those of NDNs and of animals with a naturally occurring disease.

Pulmonary Remodeling in Equine Asthma: What Do We Know about Mediators of Inflammation in the Horse?

Equine inflammatory airway disease (IAD) and recurrent airway obstruction (RAO) represent a spectrum of chronic inflammatory disease of the airways in horses resembling human asthma in many aspects. Therefore, both are now described as severity grades of equine asthma. Increasing evidence in horses and humans suggests that local pulmonary inflammation is influenced by systemic inflammatory processes and the other way around. Inflammation, coagulation, and fibrinolysis as well as extracellular remodeling show close interactions. Cytology of bronchoalveolar lavage fluid and tracheal wash is commonly used to evaluate the severity of local inflammation in the lung. Other mediators of inflammation, like interleukins involved in the chemotaxis of neutrophils, have been studied. Chronic obstructive pneumopathies lead to remodeling of bronchial walls and lung parenchyma, ultimately causing fibrosis. Matrix metalloproteinases (MMPs) are discussed as the most important proteolytic enzymes during remodeling in human medicine and increasing evidence exists for the horse as well. A systemic involvement has been shown for severe equine asthma by increased acute phase proteins like serum amyloid A and haptoglobin in peripheral blood during exacerbation. Studies focusing on these and further possible inflammatory markers for chronic respiratory disease in the horse are discussed in this review of the literature.

Inability of FMDV replication in equine kidney epithelial cells is independent of integrin αvβ3 and αvβ6

Integrins can function as receptors for foot-and-mouth disease virus (FMDV) in epithelium. Horses are believed to be insusceptible to this disease, but the mechanism of resistance remains unclear. To detect whether FMDV can use integrin to attach to equine epithelial, we compared the utilities of αvβ3 and αvβ6 between bovine and equine kidney epithelial cells (KECs). Equine KECs showed almost equal efficiency to those of bovine. Further, the integrin αv, β3, and β6 subunits from bovine and equine were cloned and vectors were transfected into SW480 cells and COS-1 cells alone or together, and virus titers were used to determine the viral replication. In all cases, the virus reproduced successfully. Overall, FMDV can replicate in SW480 cells transfected with equine β3/β6 subunits and COS-1 cells transfected with equine αvβ3/αvβ6 integrins, but not in EKECs. These results indicated that failure of FMDV replication in EKECs was not attributed to integrin receptors.

Tamoxifen as a new therapeutic tool for neutrophilic lung inflammation

BACKGROUND AND OBJECTIVE

Neutrophilic asthma is an important disease subgroup, including patients with severe phenotypes and erratic responses to standard treatments. Tamoxifen (TX), a selective estrogen receptor modulator (SERM) used as treatment of human breast cancer, has been shown to induce early apoptosis of equine blood and bronchoalveolar lavage fluid (BALF) neutrophils in vitro. Equine recurrent airway obstruction (RAO) is a naturally occurring neutrophilic condition, closely related with human asthma. Our purpose was to investigate the therapeutic potential of tamoxifen in horses with neutrophilic lung inflammation.

METHODS

Twelve horses underwent acute lung inflammation through exposure to allergens known to cause RAO, after which they received treatment with either tamoxifen or dexamethasone. Outcome measures included evaluation of clinical signs, BALF cytology, and early apoptosis of blood and BALF neutrophils.

RESULTS

Tamoxifen treatment decreased BALF neutrophil counts (65.3 ± 19.38% before treatment; 7.6 ± 4.5% 2 days post-treatment,; and 13.6 ± 9.3% 5 days post-treatment). A similar decrease was observed with dexamethasone treatment (48.6 ± 5.88% before treatment; 11.5 ± 8.1% 2 days post-treatment; 14.6 ± 10.3% 5 days post-treatment). Clinical and endoscopic scores improved in both treatment groups. Tamoxifen treatment significantly increased early apoptosis of peripheral blood neutrophils at 5 days post-treatment (27.04 ± 15.2%), and in BALF neutrophils at 2 and 5 days post-treatment (42.11 ± 11.67% and 48.98 ± 2.6%, respectively).

CONCLUSION

Tamoxifen treatment in horses with induced acute pulmonary inflammation promoted early apoptosis of blood and BALF neutrophils, reduction in BALF neutrophils and improvement in the animals' clinical status.

Expression of surface platelet receptors (CD62P and CD41/61) in horses with recurrent airway obstruction (RAO)

Recurrent airway obstruction (RAO) is an allergic disease of horses similar to human asthma, which is characterized by airway inflammation and activation of neutrophils, lymphocytes and platelets. Platelet activation and an increase in circulating platelet-leukocyte aggregates may lead to airway remodeling. The aim of this study was to investigate platelet status in RAO-affected horses based on the platelet morphology and platelet surface expression of CD41/61 and CD62P. Ten RAO-affected horses and ten healthy horses were included in this study. Blood samples were obtained to determine the platelet count (PLT), mean platelet volume (MPV) and platelet large cell ratio (P-LCR). Expression of CD62P and CD41/61 was detected by flow cytometry on activated platelets. The median PLT was significantly reduced in horses with RAO compared to the controls. The MPV and the P-LCR values were significantly higher in RAO horses than controls. Expression of CD41/61 on platelets was increased in RAO horses, while CD62P expression was reduced. This study demonstrated the morphological changes in platelets and expression of platelet surface receptors. Despite the decrease of CD62P expression, the observed increased surface expression of CD41/61 on platelets in horses with RAO may contribute to the formation of platelet aggregates in their respiratory system.

Asthma "of horses and men"--how can equine heaves help us better understand human asthma immunopathology and its functional consequences?

Animal models have been studied to unravel etiological, immunopathological, and genetic attributes leading to asthma. However, while experiments in which the disease is artificially induced have helped discovering biological and molecular pathways leading to allergic airway inflammation, their contribution to the understanding of the causality of the disease has been more limited. Horses naturally suffer from an asthma-like condition called "heaves" which presents sticking similarities with human asthma. It is characterized by reversible airway obstruction, airway neutrophilic inflammation, and a predominant Th2 immune response. This model allows one to investigate the role of neutrophils in asthma, which remains contentious, the regulation of chronic neutrophilic inflammation, and their possible implication in pulmonary allergic responses. Furthermore, the pulmonary remodeling features in heaves closely resemble those of human asthma, which makes this model unique to investigate the kinetics, reversibility, as well as the physiological consequences of tissue remodeling. In conclusion, heaves and asthma share common clinical presentation and also important immunological and tissue remodeling features. This makes heaves an ideal model for the discovery of novel pathways implicated in the asthmatic inflammation and associated tissue remodeling.

The equine immune responses to infectious and allergic disease: a model for humans?

The modern horse, Equus caballus has historically made important contributions to the field of immunology, dating back to Emil von Behring's description of curative antibodies in equine serum over a century ago. While the horse continues to play an important role in human serotherapy, the mouse has replaced the horse as the predominant experimental animal in immunology research. Nevertheless, continuing efforts have led to an improved understanding of the equine immune response in a variety of infectious and non-infectious diseases. Based on this information, we can begin to identify specific situations where the horse may provide a unique immunological model for certain human diseases.

Constitutive apoptosis in equine peripheral blood neutrophils in vitro

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Equine peripheral blood neutrophils underwent spontaneous time-dependent constitutive apoptosis when aged in culture for up to 36 h.

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Equine neutrophils undergoing apoptosis develop the structural and functional features of apoptosis observed in many cell types, including human neutrophils.

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Neutrophils undergoing apoptosis had diminished zymosan activated serum-stimulated chemiluminescence, but maintained responsiveness to phorbol myristate acetate.

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The constitutive rate of neutrophil apoptosis was promoted by lipopolysaccharide, tumour necrosis factor α and phagocytosis of opsonised ovine erythrocytes, while it was inhibited by dexamethasone and ZAS (a source of C5a).

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Equine and human neutrophil apoptosis differed in terms of responses to lipopolysaccharide and in the time-dependence of the response to dexamethasone.

The aim of this study was to characterise constitutive apoptosis in equine peripheral blood neutrophils, including assessment of factors that potentially modulate neutrophil survival through alteration of the rate of constitutive apoptosis. Cells underwent spontaneous time-dependent constitutive apoptosis when aged in culture for up to 36 h, developing the structural and functional features of apoptosis observed in many cell types, including human neutrophils. Neutrophils undergoing apoptosis also had diminished zymosan activated serum (ZAS)-stimulated chemiluminescence, but maintained responsiveness to phorbol myristate acetate (PMA). The constitutive rate of equine neutrophil apoptosis was promoted by lipopolysaccharide (LPS), tumour necrosis factor α and phagocytosis of opsonised ovine erythrocytes, while it was inhibited by dexamethasone and ZAS (a source of C5a). Formyl-Met-Leu-Phe, leukotriene B₄, platelet activating factor and PMA had no demonstrable effect on equine neutrophil apoptosis. There was a difference between equine and human neutrophil apoptosis in response to LPS and the time-dependence of the response to dexamethasone.

Airway collagen and elastic fiber content correlates with lung function in equine heaves

The consequences on lung function and inflammation of alterations in the extracellular matrix affecting the peripheral airway wall in asthma are largely unknown. We hypothesized that remodeling of collagen and elastic fibers in the peripheral airway wall leads to airway obstruction and contributes to neutrophilic airway inflammation. Animals used were six heaves-affected horses and five controls. Large peripheral lung biopsies were obtained from horses with heaves in clinical remission (Baseline) and during disease exacerbation and from age-matched controls. The area of collagen and elastic fiber content in the lamina propria was measured by histological staining techniques and corrected for airway size. Collagen type 1 and type 3 content was further assessed from additional horses after postmortem lung samples by immunohistochemistry. The collagen breakdown products proline-glycine-proline (PGP) and N-acetylated-PGP (N-α-PGP) were also measured in bronchoalveolar lavage fluids (BALF) by mass spectrometry. Compared with controls, heaves-affected horses had an increase in collagen (P = 0.05) and elastic fiber contents (P = 0.04) at baseline. Collagen types 1 and 3 content was also significantly increased in diseased horses (P = 0.015) when both collagen types were combined. No further change in collagen content was observed after a 30-day antigenic challenge. Airway collagen at baseline was positively correlated with pulmonary resistance in asthmatic horses (r(2) = 0.78, P = 0.03) and elastic fiber content was positively associated with pulmonary elastance in controls (r(2) = 0.95, P = 0.02). No difference between groups was appreciated in PGP and N-α-PGP peptides in BALF. Increased airway wall collagen and elastic fiber content may contribute to residual obstruction in the asthmatic airways.

Heaves, an asthma-like disease of horses

Animal models have been developed to investigate specific components of asthmatic airway inflammation, hyper-responsiveness or remodelling. However, all of these aspects are rarely observed in the same animal. Heaves is a naturally occurring disease of horses that combines these features. It is characterized by stable dust-induced inflammation, bronchospasm and remodelling. The evaluation of horses during well-controlled natural antigen exposure and avoidance in experimental settings allows the study of disease mechanisms in the asymptomatic and symptomatic stages, an approach rarely feasible in humans. Also, the disease can be followed over several years to observe the cumulative effect of repeated episodes of clinical exacerbation or to evaluate long-term treatment, contrasting most murine asthma models. This model has shown complex gene and environment interactions, the involvement of both innate and adaptive responses to inflammation, and the contribution of bronchospasm and tissue remodelling to airway obstruction, all occurring in a natural setting. Similarities with the human asthmatic airways are well described and the model is currently being used to evaluate airway remodelling and its reversibility in ways that are not possible in people for ethical reasons. Tools including antibodies, recombinant proteins or gene arrays, as well as methods for sampling tissues and assessing lung function in the horse are constantly evolving to facilitate the study of this animal model. Research perspectives that can be relevant to asthma include the role of neutrophils in airway inflammation and their response to corticosteroids, systemic response to pulmonary inflammation, and maintaining athletic capacities with early intervention.

Induction of eosinophil apoptosis by the cyclin-dependent kinase inhibitor AT7519 promotes the resolution of eosinophil-dominant allergic inflammation

Background

Eosinophils not only defend the body against parasitic infection but are also involved in pathological inflammatory allergic diseases such as asthma, allergic rhinitis and contact dermatitis. Clearance of apoptotic eosinophils by macrophages is a key process responsible for driving the resolution of eosinophilic inflammation and can be defective in allergic diseases. However, enhanced resolution of eosinophilic inflammation by deliberate induction of eosinophil apoptosis using pharmacological agents has not been previously demonstrated. Here we investigated the effect of a novel cyclin-dependent kinase inhibitor drug, AT7519, on human and mouse eosinophil apoptosis and examined whether it could enhance the resolution of a murine model of eosinophil-dominant inflammation in vivo.

Methodology/Principal Findings

Eosinophils from blood of healthy donors were treated with AT7519 and apoptosis assessed morphologically and by flow-cytometric detection of annexin-V/propidium iodide staining. AT7519 induced eosinophil apoptosis in a concentration dependent manner. Therapeutic administration of AT7519 in eosinophil-dominant allergic inflammation was investigated using an established ovalbumin-sensitised mouse model of allergic pleurisy. Following ovalbumin challenge AT7519 was administered systemically at the peak of pleural inflammation and inflammatory cell infiltrate, apoptosis and evidence of macrophage phagocytosis of apoptotic eosinophils assessed at appropriate time points. Administration of AT7519 dramatically enhanced the resolution of allergic pleurisy via direct induction of eosinophil apoptosis without detriment to macrophage clearance of these cells. This enhanced resolution of inflammation was shown to be caspase-dependent as the effects of AT7519 were reduced by treatment with a broad spectrum caspase inhibitor (z-vad-fmk).

Conclusions

Our data show that AT7519 induces human eosinophil apoptosis and enhances the resolution of a murine model of allergic pleurisy by inducing caspase-dependent eosinophil apoptosis and enhancing macrophage ingestion of apoptotic eosinophils. These findings demonstrate the utility of cyclin-dependent kinase inhibitors such as AT7519 as potential therapeutic agents for the treatment of eosinophil dominant allergic disorders.

Toward managing chronic rejection after lung transplant: the fate and effects of inhaled cyclosporine in a complex environment

The fate and effects of inhaled cyclosporine A (CsA) are considered after deposition on the lung surface. Special emphasis is given to a post-lung transplant environment and to the potential effects of the drug on the various cell types it is expected to encounter. The known stability, metabolism, pharmacokinetics and pharmacodynamics of the drug have been reviewed and discussed in the context of the lung microenvironment. Arguments support the contention that the immuno-inhibitory and anti-inflammatory effects of CsA are not restricted to T-cells. It is likely that pharmacologically effective concentrations of CsA can be sustained in the lungs but due to the complexity of uptake and action, the elucidation of effective posology must ultimately rely on clinical evidence.

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.

Dose tolerability of chronically inhaled voriconazole solution in rodents

Invasive pulmonary aspergillosis (IPA) is a fungal disease of the lung associated with high mortality rates in immunosuppressed patients despite treatment. Targeted drug delivery of aqueous voriconazole solutions has been shown in previous studies to produce high tissue and plasma drug concentrations as well as improved survival in a murine model of IPA. In the present study, rats were exposed to 20 min nebulizations of normal saline (control group) or aerosolized aqueous solutions of voriconazole at 15.625 mg (low dose group) or 31.25mg (high dose group). Peak voriconazole concentrations in rat lung tissue and plasma after 3 days of twice daily dosing in the high dose group were 0.85+/-0.63 microg/g wet lung weight and 0.58+/-0.30 microg/mL, with low dose group lung and plasma concentrations of 0.38+/-0.01 microg/g wet lung weight and 0.09+/-0.06 microg/mL, respectively. Trough plasma concentrations were low but demonstrated some drug accumulation over 21 days of inhaled voriconazole administered twice daily. Following multiple inhaled doses, statistically significant but clinically irrelevant abnormalities in laboratory values were observed. Histopathology also revealed an increase in the number of alveolar macrophages but without inflammation or ulceration of the airway, interstitial changes, or edema. Inhaled voriconazole was well tolerated in a rat model of drug inhalation.

Leukocyte elastase induces lung epithelial apoptosis via a PAR-1-, NF-kappaB-, and p53-dependent pathway

Leukocyte elastase induces apoptosis of lung epithelial cells via alterations in mitochondrial permeability, but the signaling pathways regulating this response remain uncertain. Here we investigated the involvement of proteinase-activated receptor-1 (PAR-1), the transcription factor NF-kappaB, and the protooncogene p53 in this pathway. Elastase-induced apoptosis of lung epithelial cells correlated temporally with activation of NF-kappaB, phosphorylation, and nuclear translocation of p53, increased p53 up-regulated modulator of apoptosis (PUMA) expression, and mitochondrial translocation of Bax resulting in enhanced permeability. Elastase-induced apoptosis was also prevented by pharmacologic inhibitors of NF-kappaB and p53 and by short interfering RNA knockdown of PAR-1, p53, or PUMA. These inhibitors prevented elastase-induced PUMA expression, mitochondrial translocation of Bax, increased mitochondrial permeability, and attenuated apoptosis. NF-kappaB inhibitors also reduced p53 phosphorylation. We conclude that elastase-induced apoptosis of lung epithelial cells is mediated by a PAR-1-triggered pathway involving activation of NF-kappaB and p53, and a PUMA- and Bax-dependent increase in mitochondrial permeability leading to activation of distal caspases. Further, p53 contributes to elastase-induced apoptosis by both transcriptional and post-transcriptional mechanisms.

Targeted deletion of tumor suppressor PTEN augments neutrophil function and enhances host defense in neutropenia-associated pneumonia

Neutropenia and related infections are the most important dose-limiting toxicities in anticancer chemotherapy and radiotherapy. In this study, we explored a new strategy for augmenting host defense in neutropenia-related pneumonia. Phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P(3)) signaling in neutrophils was elevated by depleting PTEN, a phosphatidylinositol 3'-phosphatase that hydrolyzes PtdIns(3,4,5)P(3). In myeloid-specific PTEN knockout mice, significantly more neutrophils were recruited to the inflamed lungs during neutropenia-associated pneumonia. Using an adoptive transfer technique, we demonstrated that this enhancement could be caused directly by PTEN depletion in neutrophils. In addition, disruption of PTEN increased the recruitment of macrophages and elevated proinflammatory cytokines/chemokine levels in the inflamed lungs, which could also be responsible for the enhanced neutrophil recruitment. Depleting PTEN also significantly delayed apoptosis and enhanced the bacteria-killing capability of the recruited neutrophils. Finally, we provide direct evidence that enhancement of neutrophil function by elevating PtdIns(3,4,5)P(3) signaling can alleviate pneumonia-associated lung damage and decrease pneumonia-elicited mortality. Collectively, these results not only provide insight into the mechanism of action of PTEN and PtdIns(3,4,5)P(3) signaling pathway in modulating neutrophil function during lung infection and inflammation, but they also establish PTEN and related pathways as potential therapeutic targets for treating neutropenia-associated pneumonia.

Airway inflammatory cell responses to intra-amniotic lipopolysaccharide in a sheep model of chorioamnionitis

Chorioamnionitis, a risk factor for bronchopulmonary dysplasia in preterm infants, causes an influx of inflammatory cells into the fetal lung. Using a fetal sheep model, we evaluated the time course of activation, functional maturity, and apoptosis of the leukocytes recruited to the fetal air spaces by lipopolysaccharide (LPS). Time-mated sheep were given intra-amniotic injections with 10 mg of Escherichia coli LPS or saline 2 or 7 days before preterm delivery at 124 days of gestation (term is 150 days). Both neutrophils and monocytes in bronchoalveolar lavage fluid (BALF) had activated NF-kappaB after 2- and 7-day LPS exposures. These neutrophils and monocytes expressed the activation factor CD11b and the maturation factor PU.1 at 2 days, and increased PU.1 expression was detected in macrophages at 7 days. Leukocyte oxidative burst activity was greatest at 7 days. BALF lipid peroxidation increased fivefold at 2 days, while protein carbonyls increased eightfold at 7 days. Nitrative stress was not detected in the BALF, but leukocytes in the lung expressed nitric oxide synthase (NOS)II (inducible NOS). BALF leukocytes expressed the antioxidant peroxiredoxin V. Lung glutathione peroxidase was also increased with LPS exposure. There was minimal apoptosis of airway and lung leukocytes assessed by caspase-3 activation. Intra-amniotic LPS recruits leukocytes to the fetal air space that have a persistent activation. These results have implications for the pathogenesis of lung inflammatory disorders in the preterm.

Cytokine expression by peripheral blood neutrophils from heaves-affected horses before and after allergen challenge

Heaves, also known as recurrent airway obstruction, is a common condition of horses characterised by pulmonary neutrophilia and reversible airway obstruction. This study evaluated the role of neutrophils in producing cytokines and chemokines that might be involved in the recruitment and activation of inflammatory cells in horses with heaves. Peripheral neutrophils were isolated from heaves-affected (n = 9) and control (n = 4) horses before and after 5 h of natural inhalation challenge. Expression of mRNA of two pro-inflammatory cytokines, tumour necrosis factor (TNF)-alpha and interleukin (IL)-1beta, along with two chemokines, IL-8 and macrophage inflammatory protein (MIP)-2, was evaluated. After exposure to mouldy hay, horses with heaves had significant airway obstruction and increased numbers of neutrophils in bronchoalveolar lavage samples, compared to control horses. However, there were no differences in the expression of mRNAs of TNF-alpha, IL-1beta, IL-8 and MIP-2 between the two groups, suggesting that the release of cytokines and chemokines by peripheral blood neutrophils is not necessary for the development of heaves.

Apoptosis, airway inflammation and anti-asthma therapy: from immunobiology to clinical application

T lymphocyte apoptosis is essential for maintaining immune system homeostasis. Experimental evidence suggests apoptosis control mechanisms may be impaired in inflammatory conditions, particularly airway Th2-type allergic diseases. This review briefly examines the mucosal immune system homeostasis and common apoptotic pathways and discusses impaired apoptosis, allergy, airway inflammation, remodelling and fibrosis. Finally, the paper presents an update on pharmacological targeting of apoptosis to control airway inflammation in patients with allergic asthma.

Ozone inhalation induces exacerbation of eosinophilic airway inflammation and hyperresponsiveness in allergen-sensitized mice

BACKGROUND

Ozone (O(3)) exposure evokes asthma exacerbations by mechanisms that are poorly understood. We used a murine model to characterize the effects of O(3) on allergic airway inflammation and hyperresponsiveness and to identify factors that might contribute to the O(3)-induced exacerbation of asthma.

METHODS

BALB/c mice were sensitized and challenged with Aspergillus fumigatus (Af). A group of sensitized and challenged mice was exposed to 3.0 ppm of O(3) for 2 h and studied 12 h later (96 h after Af challenge). Naive mice and mice exposed to O(3) alone were used as controls. Bronchoalveolar lavage (BAL) cellular and cytokine content, lung function [enhanced pause (P(enh))], isometric force generation by tracheal rings and gene and protein expression of Fas and FasL were assessed. Apoptosis of eosinophils was quantified by FACS.

RESULTS

In sensitized mice allergen challenge induced a significant increase of P(enh) and contractile force in tracheal rings that peaked 24 h after challenge and resolved by 96 h. O(3) inhalation induced an exacerbation of airway hyperresponsiveness accompanied by recurrence of neutrophils and enhancement of eosinophils 96 h after allergen challenge. The combination of allergen and O(3) exposure inhibited Fas and FasL gene and protein expression and eosinophil apoptosis and increased interleukin-5 (IL-5), granulocyte-macrophage-colony stimulating factor (GM-CSF) and G-CSF protein levels.

CONCLUSIONS

O(3) affects airway responsiveness of allergen-primed airways indirectly by increasing viability of eosinophils and eosinophil-mediated pathological changes.

Secondary necrosis in multicellular animals: an outcome of apoptosis with pathogenic implications

In metazoans apoptosis is a major physiological process of cell elimination during development and in tissue homeostasis and can be involved in pathological situations. In vitro, apoptosis proceeds through an execution phase during which cell dismantling is initiated, with or without fragmentation into apoptotic bodies, but with maintenance of a near-to-intact cytoplasmic membrane, followed by a transition to a necrotic cell elimination traditionally called “secondary necrosis”. Secondary necrosis involves activation of self-hydrolytic enzymes, and swelling of the cell or of the apoptotic bodies, generalized and irreparable damage to the cytoplasmic membrane, and culminates with cell disruption. In vivo, under normal conditions, the elimination of apoptosing cells or apoptotic bodies is by removal through engulfment by scavengers prompted by the exposure of engulfment signals during the execution phase of apoptosis; if this removal fails progression to secondary necrosis ensues as in the in vitro situation. In vivo secondary necrosis occurs when massive apoptosis overwhelms the available scavenging capacity, or when the scavenger mechanism is directly impaired, and may result in leakage of the cell contents with induction of tissue injury and inflammatory and autoimmune responses. Several disorders where secondary necrosis has been implicated as a pathogenic mechanism will be reviewed.

Defective apoptotic cell clearance in asthma and COPD--a new drug target for statins?

Asthma and chronic obstructive pulmonary disease represent increasingly common respiratory conditions with a clear unmet need for more effective and safer therapy. Airway inflammation is key to both asthma pathogenesis and exacerbations of symptoms in chronic obstructive pulmonary disease. Several lines of evidence are now emerging implicating the increased persistence of apoptotic cells in patients with chronic inflammatory lung diseases and that this is largely due to a combination of inhibition of, or defects in, the apoptotic process and/or impaired apoptotic cell removal mechanisms.

Modeling inflammation in the zebrafish: how a fish can help us understand lung disease

Neutrophilic inflammation is responsible for much of the tissue damage seen in many lung diseases. For resolution of inflammation to occur, neutrophils must die by apoptosis, allowing their recognition and removal by macrophages. The molecular events controlling this important regulatory step are poorly understood, in large part due to the genetic intractability of the human neutrophil granulocyte. The authors have established a model of inflammation in the Zebrafish, which shares many features of the innate immune system with those of humans. Injury to the Zebrafish tailfin induces a reproducible and quantifiable inflammatory response, which resolves with kinetics similar to mammalian models of neutrophilic inflammation, including pulmonary inflammation. Pharmacological modulation of neutrophil apoptosis can modulate the outcome of experimentally induced inflammation. In addition, the authors have generated a construct that expresses green fluorescent protein under the myeloperoxidase promoter, allowing in vivo visualization of neutrophils during experimentally induced inflammation. The authors are also performing an unbiased forward genetic screen for mutants with defective resolution of inflammation, and to date have identified a number of putative mutants. Further study and characterization of these mutants is underway. The authors have thus established an important experimental link between apoptosis and resolution of inflammation in an in vivo system, and defined an important new model for the study of inflammation resolution. The authors hope that these tools will permit detailed study of the genetic controls of the resolution of inflammation, and provide insights with potential clinical utility.

Equine recurrent airway obstruction and insect bite hypersensitivity: understanding the diseases and uncovering possible new therapeutic approaches

Recurrent airway obstruction (RAO) and insect bite hypersensitivity (IBH) are allergic conditions that are commonly encountered in the horse. Whilst complete allergen avoidance is an effective management strategy for both diseases, this may not be achievable in all cases and treatment options are therefore required. The inflammatory response is the main therapeutic target for glucocorticoids given to horses with RAO and severe cases of IBH, whilst the bronchodilators used in RAO primarily target airway smooth muscle. Such drugs are effective in most but not all individuals and there may be unwanted adverse effects. This article will review how knowledge of drug action and the pathogenesis of RAO and IBH can be utilised to identify potential targets for novel therapeutic agents that, in the longer term, may be safer and/or more effective in managing the allergic horse.

Platelets in equine recurrent airway obstruction

Platelets contribute to the pathogenesis of human allergic airway disease. The aim of this study was to compare platelet activating factor (PAF)-induced platelet aggregation and thromboxane (Tx) production, plasma Tx and 5-hydroxytryptamine (5-HT) in ponies with recurrent airway obstruction (RAO), an hypersensitivity to inhaled antigens, and normal ponies, before and after antigen exposure. Plasma 5-HT was significantly higher in ponies with RAO but was not further increased by antigen challenge. There was no difference between PAF-induced platelet aggregation or Tx production, or in plasma Tx before or after challenge. These data suggest there may be a difference between platelet 5-HT uptake in RAO and normal ponies but do not provide evidence of platelet activation following antigen exposure.