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

Disconnect between sputum neutrophils and other measures of airway inflammation in asthmaTo 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 f8 mg?mL -1 despite high-dose inhaled corticosteroid (ICS) (o1000 mg?day -1 fluticasone propionate equivalent) with or without long-acting b 2 -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 o6 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 lung function and uncontrolled symptoms despite high-dose ICS treatment of o1000 mg?day -1 fluticasone propionate equivalent.11 (14%) patients did not complete the study, due to an adverse event (n51), physician's decision (n55), subject's decision (n53) or the sponsor's decision (n52).One patient experienced increased bronchospasm following bronchoscopy, requiring additional observation and oral corticosteroid treatment prior to being discharged home from the final study visit.We enumerated sputum, tissue and BAL eosinophils and neutrophils using standard techniques as described previously [5, 6].Both granulocyte types spanned broad ranges and had a unimodal distribution in each compartment (fig.1).The majority of nonsquamous cells in sputum from most subjects were neutrophils, while a much smaller percentage of sputum cells were eosinophils.The majority of BAL cells were macrophages (data not shown), with eosinophils and neutrophils comprising ,10% of total BAL cells in most cases.Within each compartment, eosinophils and neutrophils were significantly intercorrelated.However, these correlations were positive in biopsy tissue and BAL but negative in sputum (fig.1).The correlation within any single compartment was greatest in biopsy tissue (Spearman's rank correlation (rS)50.68,p,0.0001).Across compartments, sputum eosinophils were significantly, albeit weakly, positively correlated with both biopsy tissue eosinophils (rS50.36,p,0.05) and BAL eosinophils (rS50.33,p,0.05), while neutrophils were not intercorrelated across any compartments.Sputum neutrophils were negatively correlated with tissue eosinophils (rS5 -0.37, p,0.01) and BAL eosinophils (rS5 -0.34, p,0.05).These findings show generally positive relationships between eosinophils and neutrophils within and across airway compartments, with the exception of sputum neutrophil percentage.Serum periostin and exhaled nitric oxide fraction (FeNO) are positively correlated with sputum and biopsy eosinophils in BOBCAT [3].Both serum periostin and FeNO trend towards a positive correlation with biopsy neutrophils (rS50.25,p50.06 for periostin; rS50.23,p50.08 for FeNO), and exhibit significantly negative correlations with sputum neutrophils (rS5 -0.31 for periostin, rS5 -0.35 for FeNO; p,0.05 for each).