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.

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.

Background: There is evidence that eosinophils and neutrophils are simultaneously increased in the airways of some patients with chronic refractory asthma. The mechanisms by which neutrophils accumulate in the airways of asthmatics remain to be elucidated, however, chemoattractants for neutrophils such as CXC chemokines may affect either the accumulation or functional status of neutrophils in such patients. The objective of the present study was to identify the CXC chemokine responsible for the neutrophilic and possibly eosinophilic inflammation observed in the airways of patients with refractory asthma. Methods: Following the inhalation of hypertonic saline, induced sputum was obtained from 14 healthy controls, 16 patients with mild well-controlled nonrefractory asthma, and 14 patients with refractory asthma. Concentrations of CXC chemokines and differential inflammatory cell counts were determined. Results: The percentages of induced sputum eosinophils were significantly higher both in patients with nonrefractory asthma and in patients with refractory asthma. On the other hand, the percentages of neutrophils were increased only in sputum from patients with refractory asthma. The concentration of IL-8, but not ENA-78 or GRO-α, was also significantly increased in induced sputum from patients with refractory asthma. The concentration of IL-8 correlated significantly with the percentages of neutrophils. Conclusions: The results of the present study suggest that IL-8, but not ENA-78 or GRO-α, may contribute to the observation of neutrophilic inflammation in patients with refractory asthma.

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