Abstract

Background Patients with severe asthma have increased granulocytes in their sputum compared with patients with mild to moderate asthma. Objective We hypothesized that inflammatory granulocytes in sputum may identify specific asthma severity phenotypes and are associated with different patterns of inflammatory proteins in sputum supernatants. Methods This hypothesis was tested in 242 patients with asthma enrolled in the Severe Asthma Research Program who provided sputum samples for cell count, differential cell determinations, cell lysates for Western blot, and supernatant analyses by inflammatory protein microarrays and ELISAs. ANOVA and multiple linear regression models tested mediator associations. Results Stratified by sputum granulocytes, 2-fold in sputa with ≥40% neutrophils. Microarray analyses stratified by severity of asthma identified 6 to 9 proteins increased >2-fold in sputa in subjects with severe asthma compared with nonsevere asthma. ELISA data stratified by sputum granulocytes showed significant increases in brain-derived neurotrophic factor, IL-1β, and macrophage inflammatory protein 3α/CCL20 for those with ≥40% neutrophils; these mediators demonstrated positive associations with neutrophil counts. Conclusion Combined increased sputum eosinophils and neutrophils identified patients with asthma with the lowest lung function, worse asthma control, and increased symptoms and health care requirements. Inflammatory protein analyses of sputum supernatants found novel mediators increased in patients with asthma, predominantly associated with increased sputum neutrophils.