Abstract / Summary
Abstract Airway inflammation in acute exacerbations of asthma is frequently neutrophilic. Macrophages have the potential to promote inflammation or to accelerate resolution of inflammation, however, little is known about their contribution to the pathogenesis of asthma. The aim of the study was to explore the relationship between sputum macrophages in exacerbations of neutrophilic and paucigranulocytic asthma with clinical outcomes. Paucigranulocytic (PA; n = 18) and neutrophilic (NA; n = 21) asthmatic subjects were recruited upon an exacerbation of asthma. Clinical data [lung function, exhaled nitric oxide (FeNO), and the Asthma Control Questionnaire (ACQ-6)] and sputum were collected at presentation and on 14- and 28-days. Sputum macrophage subtypes were characterized by flow cytometry. Sputum cells were further assessed by bulk RNA sequencing. Both PA and NA groups displayed impaired lung function upon exacerbation that improved by day 28. Sputum monocytes and alveolar macrophages were significantly elevated upon exacerbation among NA participants compared to PA participants. However, neither macrophage number nor immunophenotype correlated with any clinical outcome assessed. These findings were further supported by bulk RNA sequencing as macrophage enrichment did not correlate with clinical outcomes at the time of exacerbation. Macrophage characteristics do not correlate with clinical outcomes during exacerbations or during recovery, regardless of asthma phenotype.