Sputum induction, processing and airway inflammatory cytokine assay
Sputum induction and processing were performed based on standard methods as described in our previous studies18,19. Additional details are described in the Online Data Supplement. In the validation set, sputum supernatant cytokines, regarded as airway inflammatory biomarkers, including IL-1β, IL-5, IL-8, IL-13, IL-17A, IFN-γ, and TNF-α, were detected using a Luminex-based MILLIPLEX MAP Human Cytokine/Chemokine Magnetic Bead Panel Kit (EMD Millipore Corporation, Billerica, Mass) with the MILLIPLEX Analyst 5.1 software. Spiking experiments on cytokines in sputum supernatants showed that recovery ranged from 70% to 130% in all detectable analyses20,21