Specifically YKL-40 in BAL reflects inflammation in the lungs, with positive associations seen with: the number of neutrophils and macrophages; concentration of NE; other markers of inflammation, such as IL-1β and CXCL8 concentrations; and with infection, in particular with P. aeruginosa. However, while YKL-40 was detectable in the serum of children in CF, the serum levels did not correlate with the BAL levels in the same patient nor with pulmonary inflammation. Here, CHI3L1 is linked to infection.