CHI3L1 and idiopathic pulmonary fibrosis: Four highly relevant disease biomarkers, i.e. PDGF-BB [28–31], CCL18 [32, 33], PAI-1 [34–38] and YKL-40 [39–41], have been shown to have prognostic significance in IPF and have well-described effects on myofibroblast activity in vitro.