Role of neutrophils in persistent airway obstruction due to refractory asthma

Abstract

One of the clinical manifestations of refractory asthma (RA) in a certain group of patients is persistent airway obstruction (PAO), despite treatment with high doses of inhaled and/or systemic corticosteroids. Airway neutrophilic inflammation is frequently observed in RA; however, the relationship between neutrophilic inflammation and PAO has not been evaluated in this group of patients. The aim of this study was to compare the clinical parameters and patterns of inflammatory cells between patients with or without PAO due to RA, and to identify the factors associated with PAO. Seventy-seven patients with RA were recruited from a cohort of 2298 asthmatic patients. Sputum differential cell counts were performed at initial presentation. Clinical and physiological parameters were compared between patients with (n = 19) or without PAO (n = 58). The group with PAO had a longer duration of asthma and a higher frequency of near-fatal asthma than the non-PAO group, although higher doses of inhaled corticosteroids were used in the PAO group (P = 0.037). Neutrophilic inflammation was predominant in the group with PAO, whereas eosinophilic inflammation was predominant in the non-PAO group (P = 0.003). When both groups were stratified according to smoking status, the non-smoking PAO group had the longest duration of asthma, with early onset of asthma (P < 0.05). The non-smoking PAO group tended to have the highest percentage of sputum neutrophils. Irrespective of smoking status, the percentage of sputum eosinophils was significantly higher in the non-PAO group than in the PAO group. Patients with PAO due to RA show different clinical manifestations when compared with those without PAO and have neutrophil-dominant airway inflammation.