Asthma is characterised into eosinophilic and non-eosinophilic phenotypes based on inflammatory cell patterns in airway secretions. Neutrophils are important in innate immunity, and are increased in the airways in non-eosinophilic asthma. The present study investigated the activity of neutrophils in asthma phenotypes. Participants with eosinophilic (n=8) and non-eosinophilic asthma (n=9) and healthy controls (n=11) underwent sputum induction and blood collection. Neutrophils were isolated and cultured with or without lipopolysaccharide. Cytokines were measured by ELISA, and gene expression was analysed using a gene expression microarray and quantitative PCR. In non-eosinophilic asthma, blood neutrophils released significantly higher levels of interleukin-8 at rest. Cytokine gene expression and sputum neutrophil protein production did not differ between asthma subtypes. Microarrays demonstrated closely related expression profiles from participants with non-eosinophilic asthma that were significantly distinct from those in eosinophilic asthma. A total of 317 genes were significantly altered in resting neutrophils from participants with non-eosinophilic asthma versus eosinophilic asthma, including genes related to cell motility and regulation of apoptosis. Non-eosinophilic and eosinophilic asthma are associated with specific gene expression profiles, providing further evidence that these phenotypes of asthma involve different molecular mechanisms of disease pathogenesis at the systemic level. The mechanisms of non-eosinophilic asthma may involve enhancement of blood neutrophil chemotaxis and survival.
European Respiratory Journal Vol. 35, Issue 3, p. 522-531