Therefore, if our data is translated to humans, induction of CHI3L1 by PPIs might have been responsible, at least in part, for the reported incidences of fewer acute exacerbations associated with the use of PPIs in patients with respiratory diseases including IPF [9] and chronic obstructive pulmonary disease (COPD) [43]. Here, CHI3L1 is linked to chronic obstructive pulmonary disease.