Pilot study of inflammatory biomarkers in matched induced sputum and bronchoalveolar lavage from 2-year-olds with cystic fibrosis

Background: In this pilot study, we investigated whether induced sputum (IS) could serve as a viable alternative to bronchoalveolar lavage (BAL) and yield robust inflammatory biomarkers in toddlers with cystic fibrosis (CF) featuring minimal structural lung disease. Methods: We collected IS, BAL (right middle lobe and lingula) and blood, and performed chest computed tomography (CT) scans from 2-year-olds with CF (N=11), all within a single visit. Inflammatory biomarkers included 20 soluble immune mediators and neutrophil elastase (NE), as well as frequency and phenotype of T cells, monocytes / macrophages and neutrophils. Results: At the molecular level, nine mediators showed similar levels in IS and BAL (CXCL1, CXCL8, IL-1, IL-1RA, IL-6, CCL2, CXCL10, M-CSF, VEGF-A), four were higher in IS than in BAL (CXCL5, IL-1, CXCL11, TNFSF10) and two were present in IS but undetectable in BAL (IL-10, IFN-). Meanwhile, soluble NE had lower activity in IS than in BAL. At the cellular level, T-cell frequency was lower in IS than in BAL. Monocytes / macrophages were dominant in IS and BAL with similar frequencies but differing expression of CD16 (lower in IS), CD115 and surface-associated NE (higher in IS). Neutrophil frequency and phenotype did not differ between IS and BAL. Conclusions: IS collected from 2-year-olds with CF yields biomarkers of early airway inflammation with good agreement with BAL notably with regards to molecular and cellular outcomes related to neutrophils and monocytes/macrophages.