Neutrophils enhance eosinophil migration across monolayers of lung epithelial cells

Diesel exhaust particulates exacerbate asthma-like inflammation by increasing CXC chemokines

Particulate matter heavily pollutes the urban atmosphere, and several studies show a link between increased ambient particulate air pollution and exacerbation of pre-existing pulmonary diseases, including asthma. We investigated how diesel exhaust particulates (DEPs) aggravate asthma-like pulmonary inflammation in a mouse model of asthma induced by a house dust extract (HDE) containing cockroach allergens and endotoxin. BALB/c mice were exposed to three pulmonary challenges via hypopharyngeal administration of an HDE collected from the home of an asthmatic child. One hour before each pulmonary challenge, mice were exposed to DEP or PBS. Pulmonary inflammation was assessed by histological features, oxidative stress, respiratory physiological features, inflammatory cell recruitment, and local CXC chemokine production. To prove the role of CXC chemokines in the augmented inflammation, CXC chemokine-specific antibodies were delivered to the lungs before DEP exposure. DEP exacerbated HDE-induced airway inflammation, with increased airway mucus production, oxidative stress, inflammatory cell infiltration, bronchoalveolar lavage concentrations of CXC chemokines, and airway hyperreactivity. Neutralization of airway keratinocyte-derived chemokine and macrophage inflammatory protein-2 significantly improves the respiratory function in addition to decreasing the infiltration of neutrophils and eosinophils. Blocking the chemokines also decreased airway mucus production. These results demonstrate that DEP exacerbates airway inflammation induced by allergen through increased pulmonary expression of the CXC chemokines (keratinocyte-derived chemokine and macrophage inflammatory protein-2).

Microtubule dynamics and Rac-1 signaling independently regulate barrier function in lung epithelial cells

Cadherin-mediated cell-cell adhesion controls the morphology and function of epithelial cells and is a critical component of the pathology of chronic inflammatory disorders. Dynamic interactions between cadherins and the actin cytoskeleton are required for stable cell-cell contact. Besides actin, microtubules also target intercellular, cadherin-based junctions and contribute to their formation and stability. Here, we studied the role of microtubules in conjunction with Rho-like GTPases in the regulation of lung epithelial barrier function using real-time monitoring of transepithelial electrical resistance. Unexpectedly, we found that disruption of microtubules promotes epithelial cell-cell adhesion. This increase in epithelial barrier function is accompanied by the accumulation of beta-catenin at cell-cell junctions, as detected by immunofluorescence. Moreover, we found that the increase in cell-cell contact, induced by microtubule depolymerization, requires signaling through a RhoA/Rho kinase pathway. The Rac-1 GTPase counteracts this pathway, because inhibition of Rac-1 signaling rapidly promotes epithelial barrier function, in a microtubule- and RhoA-independent fashion. Together, our data suggest that microtubule-RhoA-mediated signaling and Rac-1 control lung epithelial integrity through counteracting independent pathways.

The alveolar epithelial type I-like cell line as an adequate model for leukocyte migration studies in vitro

The lung is unique as leukocytes not only migrate into the bronchoalveolar space but also return to the parenchyma and then via the lymphatics to the draining lymph node. The aim of this study was to investigate the migration of leukocytes via an epithelial monolayer in a Transwell system against a chemokine gradient. Rat type I-like R3/1 alveolar epithelial cells were cultivated on a Transwell polyester membrane (pore diameter 3 microm) for 3 days until a monolayer was formed. The tightness of the monolayer was determined by transepithelial transport of horseradish peroxidase. Isolated human and rat peripheral blood mononuclear cells (PBMC) were placed in the upper chamber, and different concentrations of monocyte chemotactic protein-1 (MCP-1) in the lower chamber. The transmigration of PBMC was quantified and investigated by light and transmission electron microscopy. PBMC migrated through the epithelial cell barrier intercellularly as well as transcellularly. The migration of PBMC against the MCP-1 gradient was dose dependent. The results indicate that this model could help in the study of key events involved in chemokine-induced cell migration from the airways into tissue.

Eosinophil Trans-Basement Membrane Migration Induced by Interleukin-8 and Neutrophils

Neutrophilic inflammation observed with severe asthma is often associated with interleukin-8 (IL-8). Neutrophils can secrete a variety of mediators that may augment the migration of eosinophils. We have reported a positive correlation between the concentrations of neutrophils and eosinophils in sputum from subjects with severe asthma, suggesting a possible role of neutrophils in regulating eosinophilic inflammation. The aim of this study was to investigate whether neutrophils stimulated with IL-8 modify the trans-basement membrane migration (TBM) of eosinophils. Eosinophils and neutrophils were isolated from peripheral blood drawn from healthy donors or subjects with mild asthma. The TBM of eosinophils in response to IL-8 was evaluated in the presence or absence of neutrophils using the chambers with a Matrigel-coated transwell insert. Neither IL-8 alone nor the presence of neutrophils alone induced the TBM of eosinophils. However, when eosinophils were coincubated with neutrophils and stimulated with IL-8, the TBM of eosinophils was significantly augmented. This augmented TBM of eosinophils was inhibited by a matrix metalloproteinase-9 inhibitor, a leukotriene B4 receptor antagonist, platelet-activating factor antagonists, or an anti-TNF-alpha monoclonal antibodies. These results suggest that neutrophils migrated in response to IL-8 may lead eosinophils to accumulate in the airways of asthma and possibly aggravate this disease.

Human cathelicidin LL-37 is a chemoattractant for eosinophils and neutrophils that acts via formyl-peptide receptors

BACKGROUND

Inflammatory lung diseases such as asthma and chronic obstructive pulmonary disease (COPD) are characterized by the presence of eosinophils and neutrophils. However, the mechanisms that mediate the influx of these cells are incompletely understood. Neutrophil products, including neutrophil elastase and antimicrobial peptides such as neutrophil defensins and LL-37, have been demonstrated to display chemotactic activity towards cells from both innate and adaptive immunity. However, chemotactic activity of LL-37 towards eosinophils has not been reported. Therefore, the aim of the present study was to investigate the chemotactic activity of LL-37 for eosinophils and to explore the mechanisms involved in LL-37-mediated attraction of neutrophils and eosinophils.

METHODS

Neutrophils and eosinophils were obtained from venous blood of healthy donors. Chemotaxis was studied using a modified Boyden chamber technique. Involvement of formyl-peptide receptors (FPRs) was studied using the antagonistic peptide tBoc-MLP. Activation of the mitogen-activated protein kinase (MAPK) ERK1/2 was studied by Western blotting using antibodies directed against phosphorylated ERK1/2.

RESULTS

Our results show that LL-37 chemoattracts both eosinophils and neutrophils. The FPR antagonistic peptide tBoc-MLP inhibited LL-37-induced chemotaxis. Whereas the FPR agonist fMLP activated ERK1/2 in neutrophils, LL-37 did not, indicating that fMLP and LL-37 deliver different signals through FPRs.

CONCLUSIONS

LL-37 displays chemotactic activity for eosinophils and neutrophils, and this activity is mediated via an FPR. These results suggest that LL-37 may play a role in inflammatory lung diseases such as asthma and COPD.

CXC chemokines modulate IgE secretion and pulmonary inflammation in a model of allergic asthma

The pathophysiology of asthma is influenced by exposure to allergens and endotoxin. Although the role of allergen-induced eosinophilia has been widely studied, neutrophil-mediated responses remain elusive. A role for neutrophils in the asthmatic responses is likely since human neutrophils have been shown to express IgE receptors, as well as receptors for many cytokines and chemokines implicated in the pathogenesis of asthma. In this study we investigated neutrophil involvement in a novel, house dust extract (HDE) induced model of asthma-like pulmonary inflammation. Mice were immunized and challenged with HDE containing high levels of cockroach allergens, 377 U/ml Bla g1 and 6249 ng/ml Bla g2. The biological activity of the murine chemokines KC and MIP-2 was inhibited with specific rabbit antisera. Differential counting of cells recovered from the bronchoalveolar lavage (BAL) fluid showed that neutralization of KC and MIP-2 significantly decreased pulmonary recruitment of neutrophils (reduced 86%) and lymphocytes (reduced 76%). Neutralization of these chemokines also exerted a systemic effect with a significant decrease in plasma IgE levels, 547 ng/ml+/-65 compared to 1314 ng/ml+/-247 for control sera treated animals. This study shows that CXC chemokines play an important role in allergy and asthma both at the level of pulmonary cell recruitment and systemic immune responses.

Association between neutrophilic and eosinophilic inflammation in patients with severe persistent asthma

BACKGROUND

Eosinophils are generally recognized as effector cells in asthma. Recently, neutrophils have been suggested to contribute to the development of chronic severe asthma. The mechanisms by which neutrophils contribute to the pathophysiology of asthma remain to be elucidated; however, neutrophils may affect either accumulation or functional status of eosinophils via the generation of inflammatory mediators. The objective of this study was to evaluate whether neutrophilic inflammation is associated with eosinophilic inflammation in severe asthma.

METHODS

Following the inhalation of hypertonic saline, induced sputum was obtained from 12 healthy controls, 10 mild persistent asthmatics who were treated with low-dose inhaled corticosteroids, and 8 severe persistent asthmatics who were treated with combinations of drugs including high-dose inhaled corticosteroids and oral prednisolone. Subsequently, differential inflammatory cell counts were evaluated.

RESULTS

The percentage of eosinophils in induced sputum was significantly higher in patients who showed airway neutrophilia. In severe persistent asthmatics, the percentage of neutrophils was significantly correlated with the percentage of eosinophils in induced sputum.

CONCLUSIONS

The results of the present study suggest that accumulated neutrophils may contribute to the development of eosinophilic inflammation in severe persistent asthmatics who were treated with oral and high-dose inhaled corticosteroids. This effect may contribute to the eventual manifestation of airway inflammation in severe asthma.