A role for neutrophils in asthma?

Complex association patterns for inflammatory mediators in induced sputum from subjects with asthma

BACKGROUND

The release of various inflammatory mediators into the bronchial lumen is thought to reflect both the type and degree of airway inflammation, eosinophilic Th2, and Th9, or neutrophilic Th1, and Th17, in patients with asthma.

AIMS

We investigated whether cytokines and chemokines differed in sputum from subjects with more severe compared with milder asthma and whether unbiased factor analysis of cytokine and chemokine groupings indicates specific inflammatory pathways.

METHODS

Cell-free supernatants from induced sputum were obtained from subjects with a broad range of asthma severity (n = 158) and assessed using Milliplex^® Cytokines/Chemokine kits I, II and III, measuring 75 individual proteins. Each cytokine, chemokine or growth factor concentration was examined for differences between asthma severity groups, for association with leucocyte counts, and by factor analysis.

RESULTS

Severe asthma subjects had 9 increased and 4 decreased proteins compared to mild asthma subjects and fewer differences compared to moderate asthma. Twenty-six mediators were significantly associated with an increasing single leucocyte type: 16 with neutrophils (3 interleukins [IL], 3 CC chemokines, 4 CXC chemokines, 4 growth factors, TNF-α and CX3CL1/Fractalkine); 5 with lymphocytes (IL-7, IL-16, IL-23, IFN-α2 and CCL4/MIP1β); IL-15 and CCL15/MIP1δ with macrophages; IL-5 with eosinophils; and IL-4 and TNFSF10/TRAIL with airway epithelial cells. Factor analysis grouped 43 cytokines, chemokines and growth factors which had no missing data onto the first 10 factors, containing mixes of Th1, Th2, Th9 and Th17 inflammatory and anti-inflammatory proteins.

CONCLUSIONS

Sputum cytokines, chemokines and growth factors were increased in severe asthma, primarily with increased neutrophils. Factor analysis identified complex inflammatory protein interactions, suggesting airway inflammation in asthma is characterized by overlapping immune pathways. Thus, focus on a single specific inflammatory mediator or pathway may limit understanding the complexity of inflammation underlying airway changes in asthma and selection of appropriate therapy.

Anti‑inflammatory effects of dihydromyricetin in a mouse model of asthma

Dihydromyricetin (DHM) is a plant flavonoid and is the primary active ingredient isolated from the medicinal herb, Ampelopsis grossedentata. DHM has been shown to possess various pharmacological activities, including anti-inflammatory effects. However, the possible role of DHM in asthma treatment remains to be elucidated. The present study aimed to investigate its anti-inflammatory properties in mice with symptoms of allergic asthma. The C57BL/6 mice were sensitized and challenged with ovalbumin (OVA) to induce asthma. DHM or phosphate-buffered saline treatment was administered 1 h prior to the OVA challenge. The levels of interleukin (IL)-4, IL-5 and IL-13 in the bronchoalveolar lavage (BAL) fluid were measured by enzyme-linked immunosorbent assay (ELISA), and OVA-specific serum IgE and IgG1 levels were also determined by ELISA. Histopathological staining was performed to evaluate the infiltration of inflammatory cells into the BAL fluid, lung tissues and goblet cell hyperplasia. DHM treatment significantly reduced the total number of inflammatory cells, including eosinophils, neutrophils, lymphocytes and macrophages, in the BAL fluid. DHM also reduced the levels of IL-4, IL-5 and IL-13 in the BAL fluid, and reduced the secretion of OVA-specific IgE and IgG1 in the serum. The histological staining demonstrated that DHM treatment effectively suppressed the OVA-induced inflammatory cells in the lung tissues and in the mucus hypersecreted by goblet cells in the airway. These results showed that DHM had a potent anti-inflammatory effect in an OVA-induced mouse model of asthma, offering potential as an anti-inflammatory agent for the treatment of asthma.

Bufalin Inhibits the Inflammatory Effects in Asthmatic Mice through the Suppression of Nuclear Factor-Kappa B Activity

Asthma is an inflammatory airway disease characterized by increased infiltration of inflammatory cells into the airways and poor respiratory function. Bufalin is one of the biological ingredients obtained from Chansu. Bufalin was found to possess various pharmacological properties including anti-inflammatory activities. However, the effect of bufalin treatment on asthma has not yet been reported. Therefore, this study aimed to investigate the inhibitory effect of bufalin on asthmatic response in a murine model. A mouse asthma model was developed by ovalbumin (OVA) sensitization and challenge in the BALB/c mice. OVA-specific serum IgE and the levels of interleukin (IL)-4, IL-5, and IL-13 in bronchoalveolar lavage fluid (BALF) were determined by an enzyme-linked immunosorbent assay. Recruitment of inflammatory cells into BALF or lung tissues, and goblet cell hyperplasia were evaluated by histological staining. The expression levels of inhibitory subunit of nuclear factor-kappa B (NF-κB) alpha (IκBα) and phosphorylated p65 protein were measured by Western blot analyses. The results demonstrated that bufalin (5 and 10 mg/kg) markedly attenuated hyperresponsiveness, and strongly suppressed the OVA-induced increases of total inflammatory cells including macrophages, eosinophils, lymphocytes, and neutrophils in BALF. The levels of IL-4, IL-5, and IL-13 in BALF and OVA-specific IgE in serum were significantly reduced by bufalin. Histological staining of lung tissues showed that bufalin reduced inflammatory cell infiltration and goblet cell hyperplasia. The results of Western blotting indicated that bufalin suppressed the IκBα degradation from NF-κB, and reduced the level of phosphorylated p65 protein in the lung tissues. These data suggest that bufalin can exert its anti-inflammatory effects possibly through the inhibition of the NF-κB activity.

The Temporal Evolution of Airways Hyperresponsiveness and Inflammation

Airways hyperresponsiveness (AHR) is usually produced within days of first antigen exposure in mouse models of asthma. Furthermore, continual antigen challenge eventually results in the resolution of the AHR phenotype. Human asthma also waxes and wanes with time, suggesting that studying the time course of AHR in the allergic mouse would offer insights into the variation in symptoms seen in asthmatics. Mice were sensitized with ovalbumin (OVA) on days 0 and 14. As assessed by airway resistance (R_n ), lung elastance (H) and tissue damping (G), AHR was measured post an OVA inhalation on day 21 (Short Challenge group), after three days of OVA inhalation on day 25 (Standard Challenge group) and following an OVA inhalation on day 55 in mice previously challenged on days 21-23 (Recall Challenge group). Bronchoalveolar lavage was analyzed for inflammatory cells, cytokines and protein. AHR in the Short Challenge group was characterized by an increase in R_n and neutrophil accumulation in the lavage. AHR in the Standard Challenge group was characterized by increases in H and G but by only a modest response in R_n , while inflammation was eosinophilic. In the Standard Challenge protocol, mice lacking fibrinogen were no different from control in their AHR response. AHR in the Recall Challenge group was characterized by increases only in G and H and elevated numbers of both neutrophils and eosinophils. Lavage cytokines were only elevated in the Recall Challenge group. Lavage protein was significantly elevated in all groups. The phenotype in allergically inflamed mice evolves distinctly over time, both in terms of the nature of the inflammation and the location of the AHR response. The study of mouse models of AHR might be better served by focusing on this variation rather than simply on a single time point at which AHR is maximal.

Human asthma phenotypes: from the clinic, to cytokines, and back again

A large body of experimental evidence supports the hypothesis that T-helper 2 (Th2) cytokines orchestrate allergic airway inflammation in animal models. However, human asthma is heterogeneous with respect to clinical features, cellular sources of inflammation, and response to common therapies. This disease heterogeneity has been investigated using sputum cytology as well as unbiased clustering approaches using cellular and clinical data. Important differences in cytokine-driven inflammation may underlie this heterogeneity, and studies in human subjects with asthma have begun to elucidate these molecular differences. This molecular heterogeneity may be assessed by existing biomarkers (induced sputum evaluation or exhaled nitric oxide testing) or may require novel biomarkers. Effective testing and application of emerging therapies that target Th2 cytokines will depend on accurate and easily obtained biomarkers of this molecular heterogeneity in asthma. Furthermore, whether other non-Th2 cytokine pathways underlie airway inflammation in specific subsets of patients with asthma is an unresolved question and an important goal of future research using both mouse models and human studies.

Induction of IL-8 by Mycoplasma pneumoniae membrane in BEAS-2B cells

Mycoplasma pneumoniae is an extracellular pathogen, residing on mucosal surfaces of the respiratory and genital tracts. The lack of cell walls in mycoplasmas facilitates the direct contact of the bacterial membrane with the host cell. The cell membrane of mycoplasma is the major inducer of the host pathogenic response. Airway diseases caused by M. pneumoniae include bronchiolitis, bronchitis, and rarely bronchiectasis. In such disorders, neutrophil infiltration of the airways predominates. More recently, M. pneumoniae has been implicated in the pathogenesis of asthma. Epithelial cells play an important role in recruiting inflammatory cells into the airways. Since M. pneumoniae infection of human epithelial cells induces expression of IL-8-a potent activator of neutrophils-we investigated the signaling and transcriptional mechanisms by which mycoplasma membrane induces expression of this chemokine. In BEAS-2B human bronchial epithelial cells, mycoplasma membrane fraction (MMF) increased IL-8 mRNA and protein production. Activation of the transcriptional elements activating protein-1, nuclear factor-interleukin-6, and particularly NF-kappaB are essential for optimal IL-8 production by MMF. The mitogen-activated protein kinases individually played a modest role in MMF-induced IL-8 production. Toll-like receptor-2 did not play a significant role in MMF-induction of IL-8. Antibiotics with microbicidal activity against M. pneumoniae are also known to have anti-inflammatory effects. Whereas clarithromycin, azithromycin, and moxifloxacin individually were able to inhibit TNF-alpha-induction of IL-8, each failed to inhibit MMF-induction of IL-8.

Association between neutrophilic airway inflammation and airflow limitation in adults with asthma

BACKGROUND

There is debate about the mechanisms of persistent airflow limitation in patients with asthma. Chronic inflammation is assumed to be important, although there is limited and contradictory information about the relationship between airway inflammation and postbronchodilator FEV1.

METHODS

We have assessed the cross-sectional relationship between prebronchodilator and postbronchodilator FEV1 and measures of airway inflammation after allowing for the effects of potential confounding factors. Multivariate analysis was performed on data collected from 1,197 consecutive patients with asthma seen at the respiratory outpatient clinic at Glenfield Hospital between 1997 and 2004. Relationships between induced sputum total neutrophil and differential eosinophil cell counts, and prebronchodilator and postbronchodilator lung function were examined.

RESULTS

Sputum total neutrophil but not differential eosinophil count was associated with lower postbronchodilator FEV1. Both differential eosinophil and total neutrophil count were associated with lower prebronchodilator FEV1. These effects were independent after adjustment for age, smoking, ethnicity, asthma duration, and inhaled corticosteroid use. A 10-fold increase in neutrophil count was associated with a 92 mL reduction (95% confidence interval, 29 to 158; p = 0.007) in postbronchodilator FEV1.

CONCLUSIONS

In this large heterogeneous population of adults with asthma, we have shown that prebronchodilator FEV1 is associated with neutrophilic and eosinophilic airway inflammation, whereas sputum total neutrophil counts alone are associated with postbronchodilator FEV1. This supports the hypothesis that neutrophilic airway inflammation has a role in the progression of persistent airflow limitation in asthma and raises the possibility that this progression and the development of COPD share a common mechanism.

A role for neutrophils in intermittent allergic rhinitis

OBJECTIVE

In patients with intermittent allergic rhinitis, allergen challenge may induce both early- and late-phase responses. The aim of this study was to examine the correlation between inflammatory cells in the nasal lavage fluid and clinical parameters following pollen challenge.

MATERIAL AND METHODS

Nasal lavage fluids were obtained from 29 patients with intermittent allergic rhinitis before and 1 and 6 h after allergen provocation, representing the control, early and late phases, respectively. Symptom and rhinoscopic scores were registered on the same occasions. Inflammatory cells were determined in the nasal fluid.

RESULTS

The early phase was characterized by increased symptom scores, rhinoscopic signs of oedema and secretion and neutrophilia. In the late phase, symptom scores had diminished, but the signs of ongoing secretion remained. Both the total nasal symptom score and the secretion score correlated with the number of neutrophils in lavage fluids at 1 h. The eosinophil count did not increase during the early or late phases.

CONCLUSION

A single allergen provocation induces an early-phase response dominated by neutrophils, with secretion being the only clinical sign remaining during the late phase. The increase in neutrophil numbers correlated with the registration of secretory symptoms. The presented data indicate a role for neutrophils in intermittent allergic rhinitis and their relation with secretory parameters makes it intriguing to speculate that neutrophils may function as promoters of nasal secretion.

Pro-apoptotic effect of high concentrations of histamine on human neutrophils

Histamine receptors are expressed on neutrophils, and therefore, are likely to modulate neutrophil function. In this study, we investigated whether histamine modulates human neutrophil survival. Neutrophils were found to rapidly undergo spontaneous apoptosis upon culture in vitro and this was accelerated by high concentrations of histamine. Moreover, the percentage of apoptotic neutrophils was also markedly increased by treating with 10 mM histamine in the presence of inflammatory mediators, such as lipopolysaccharide (LPS), granulocyte macrophage-colony stimulating factor (GM-CSF), dibutyryl-cAMP (db-cAMP), or dexamethasone. Histamine-induced neutrophil apoptosis was inhibited by pyrilamine, a histamine receptor 1 antagonist, and by ranitidine, a selective histamine receptor 2 antagonist. In addition, diphenylene iodonium (DPI), an inhibitor of NADPH-oxidase, significantly blocked the apoptotic effect of histamine. Moreover, the induction of apoptosis by histamine was almost completely inhibited by zVAD-fmk, a pan-caspase inhibitor. In addition, immunoblotting showed that histamine induced the proteolytic activation of procaspase-3 in cell lysates treated with histamine. And, the protein kinase C (PKC)-delta inhibitor, rottlerin (5 microM) significantly blocked the apoptotic effect of histamine, though the cleavage of PKC-delta in 20 h cultured neutrophils was increased by histamine. However, an inhibitor of conventional PKC, Go6976 (100 nM) and a p38 mitogen-activated protein kinase inhibitor, SB203580 (10 microM), failed to block histamine-induced neutrophil apoptosis. These results suggest that high concentrations of histamine in local inflammatory and allergic lesions induce neutrophil apoptosis, and that this histamine-induced apoptosis is mediated by caspase activation and PKC-delta signaling.

Increased expression of surface activation markers on neutrophils following migration into the nasal lumen

BACKGROUND

The sequence of events following the recruitment of a free-flowing neutrophil in the peripheral circulation, via adhesion, migration and release of mediators, to a neutrophil on the surface of the nasal epithelium is a co-ordinated process. Little is known about the state of neutrophil activation following this course of events.

OBJECTIVES

To investigate the expression of surface activation markers on neutrophils, reflecting activation during their recruitment to the nose, and to see whether the inflammatory process during allergic rhinitis influences this process.

METHOD

Nine healthy controls and 12 patients with grass pollen-induced intermittent allergic rhinitis were investigated during the peak of the pollen season. The expression of CD11b, CD66b and CD63 on the neutrophil cell surface, as a reflection of activation, was analysed using flow cytometry. Neutrophils were derived from peripheral blood and nasal lavage fluid. In addition, eosinophil cationic protein (ECP) and myeloperoxidase (MPO) as well as L-, P- and E-selectins in the nasal lavage fluid were analysed using RIA and ELISA, respectively.

RESULTS

A marked increase in the expression of all three CD markers on the neutrophil cell surface was noticed following migration from the bloodstream to the surface of the nasal mucosa. At the peak of the grass pollen season, the MPO levels increased, reflecting an increase in the total number of nasal fluid neutrophils. In parallel, the expression of CD11b was further augmented. The expression of the CDb11b was reduced on neutrophils remaining in the circulation. In addition, the level of L-selectin was reduced on neutrophils derived from the blood during allergic inflammation.

CONCLUSION

Neutrophils might become activated during their transfer from the blood to the surface of the nasal mucosa, but these changes may also be due to depletion of activated neutrophils in the blood via activated endothelial/epithelial adhesion and chemoattractant measures. The increased expression of surface activation markers during allergic rhinitis suggests roles for neutrophils in the inflammatory process.

Allergen-induced airway disease is mouse strain dependent

We investigated the development of airway hyperreactivity (AHR) and inflammation in the lungs of nine genetically diverse inbred strains of mice [129/SvIm, A/J, BALB/cJ, BTBR+(T)/tf/tf, CAST/Ei, C3H/HeJ, C57BL/6J, DBA/2J, and FVB/NJ] after sensitization and challenge with ovalbumin (OVA). At 24, 48, and 72 h post-OVA exposure, the severity of AHR and eosinophilic inflammation of the mouse strains ranged from relatively unresponsive to responsive. The severity of the airway eosinophilia of some strains did not clearly correlate with the development of AHR. The temporal presence of T helper type 2 cytokines in lung lavage fluid also varied markedly among the strains. The levels of IL-4 and IL-13 were generally increased in the strains with the highest airway eosinophilia at 24 and 72 h postexposure, respectively; the levels of IL-5 were significantly increased in most of the strains with airway inflammation over the 72-h time period. The differences of physiological and biological responses among the inbred mouse strains after OVA sensitization and challenge support the hypothesis that genetic factors contribute, in part, to the development of allergen-induced airway disease.

Airway hypersecretion in allergic rhinitis and asthma: new pharmacotherapy

Mucus hypersecretion is a prominent feature of allergic rhinitis and asthma. Biologic targets for suppression of hypersecretion range from the inflammatory cells that initiate airway inflammation, to specific cellular elements such as calcium-activated chloride (CLCA) channels, epidermal growth factor receptor tyrosine kinase, and antiapoptotic factors (eg, Bcl-2). Identification of these targets is driving development of new pharmacotherapeutic compounds. Aside from specific instances in which a single mediator has a major impact on hypersecretion--for example, histamine in rhinitis--it is likely that compounds with broad-spectrum anti-inflammatory activity are more effective than compounds with restricted activity. However, certain highly specific targets, such as CLCA channels, seem to be intimately associated with development of a hypersecretory phenotype. Data from clinical trials with blockers of these targets are awaited with great interest, not only for disease management but also to determine the clinical benefit of selective inhibition of airway hypersecretion.

Pathogenesis of asthma

There is now strong evidence that airway inflammation is a predominant underlying problem in patients with asthma, and it has been suggested that ongoing inflammation may lead to airway injury and remodeling. There is also recent evidence that longstanding asthma could be associated with loss of elastic recoil, which can enhance airway obstruction and worsen asthma control [82,83]. Therefore, the use of anti-inflammatory therapy has been advocated in all guidelines, including the National Asthma Education and Prevention Program (NAEPP) Expert Panel Report [84] and its recent update [85] that recommended inhaled steroids as a first mode of therapy for patients with mild, moderate, or severe, persistent asthma. There is preliminary evidence that early institution of anti-inflammatory therapy might lead to disease modification and limit the progression of subepithelial fibrosis and airway remodeling. The pathogenesis of asthma clearly involves many cells and mediators, although the contribution of each individual factor is probably different from patient to patient depending on the setting and stimulus. Although currently available therapies are highly effective in controlling asthma symptoms and limiting exacerbations in the majority of patients, there is still a subset of patients that proceed to develop severe asthma with decreased lung function, lack of responsiveness to therapy, or frequent exacerbations. It is hoped that rapid progress in the area of asthma genetics and pharmacogenetics will yield a more precise and patient-specific understanding of asthma pathogenesis and allow practitioners to prescribe therapies that are designed for a particular patient or exacerbation. That will undoubtedly help to improve the care of asthma, limit its morbidity, and reduce the side effect of medications.