High YKL-40 levels have also been shown to associate with various forms of interstitial lung diseases (ILD), such as idiopathic pulmonary fibrosis (IPF), idiopathic nonspecific interstitial pneumonia (iNSIP), and cryptogenic organizing pneumonitis (COP) [15–17]. Here, CHI3L1 is linked to idiopathic pulmonary fibrosis.