Association of Tumor Necrosis Factor-α and Neutrophilic Inflammation in Severe Asthma

Background: There is evidence that neutrophils are increased in the airway of severe disease or acute exacerbations of asthma. The mechanisms by which neutrophils are recruited to the airways and contribute to the pathophysiology of asthma remain to be elucidated. Tumor necrosis factor (TNF-α), which can induce both tissue accumulation and activation of neutrophils and eosinophils, has been shown to be increased in the airways of severe asthma. The objective of this study is to evaluate whether TNF-α is associated with neutrophilic inflammation in asthma. Methods: Following an inhalation of hypertonic saline, induced sputum was obtained from 9 healthy controls, 9 mild persistent asthma patients who were treated with low-dose inhaled corticosteroids; and 7 severe persistent asthma patients who were treated with combinations of drugs including high-dose inhaled corticosteroids, oral prednisolone, bronchodilators, and leukotriene receptor antagonist. After 0.1% dithiothreitol (DTT) homog- enization, they were examined for total cell count, cellular differentiation, and the concentrations of TNF-α and myeloperoxidase (MPO). Results: The concentration of TNF-α was not correlated with neutrophils in healthy controls or mild asthma patients. In sputum from severe asthma patients, however, the concentration of TNF-α is significantly correlated with both the percentage of neutrophils and the concentration of MPO. The concentration of TNF-α is not correlated with the percentage of eosinophils in healthy controls, mild asthma patients, or severe asthma patients. Conclusions: TNF-α may be a contributing molecule for both accumulation and activation of neutrophils in the airways of severe asthma