Importantly, a recent study was able to demonstrate that YKL-40 levels are increased in sputum and serum of CF patients compared to healthy control individuals [40], and in both CF patients and bENaC-Tg mice, a murine model mirroring CF lung disease [41], airway levels of YKL-40 and its murine analogue BRP-39 airway levels correlated with the severity of pulmonary obstruction [40]. Here, CHI3L1 is linked to cystic fibrosis.