CHI3L1 and cystic fibrosis: We quantified YKL-40 protein levels in serum and airway fluids (sputum supernatants) from individuals with CF and control subjects without pulmonary diseases, assessed BRP-39 levels and lung function in a mouse model of CF-like lung disease (βENaC-Tg mice) and analyzed the impact of YKL-40 gene variants on YKL-40 protein levels and age-adjusted CF lung disease severity.