Disconnect between sputum neutrophils and other measures of airway inflammation in asthma

To the Editor: Asthma heterogeneity has been described by the nature and intensity of granulocytic infiltration into the airways [1, 2]. Sputum, endobronchial biopsies and bronchoalveolar lavage (BAL) sample different anatomical regions of the airways. Few studies have directly compared the inflammatory cell infiltrates in these regions within a large cohort of moderate–severe asthma patients using standard techniques. In the BOBCAT (Bronchoscopic exploratory research study Of Biomarkers in Corticosteroid-refractory AsThma) study, we sampled multiple airway compartments concurrently, enabling us to evaluate relationships between granulocytic infiltrates within and between compartments in a large cohort of moderate–severe adult asthma patients. This prospective multicentre observational study was conducted in four visits over a 4–6 week period, as described previously [3]. The patients included had moderate–severe persistent asthma (forced expiratory volume in 1 s (FEV1) 40–80% predicted and Asthma Control Questionnaire (ACQ) [4] score >1.5) and, within the past 5 years, evidence of >12% post-bronchodilator reversibility or a provocative concentration of methacholine causing a 20% decline in FEV1 ≤8 mg·mL−1 despite high-dose inhaled corticosteroid (ICS) (≥1000 μg·day−1 fluticasone propionate equivalent) with or without long-acting β2-adrenergic agonist therapy. Key exclusion criteria included initiation or increase in systemic steroid use 30 days prior to screening, chronic or recent (within the past 30 days) use of immunosuppressive therapies, or other active lung disease. Patients had a prior established diagnosis of moderate–severe asthma for ≥6 months prior to screening while receiving a stable dose regimen (>6 weeks) of a high-dose ICS. Allowed concomitant medications included leukotriene receptor antagonists and oral corticosteroids. 78 patients with confirmed moderate–severe asthma were enrolled at 18 sites; 67 (86%) completed the study. All patients had persistently impaired …