CCL18 and pulmonary fibrosis: The study of pulmonary fibrosis biomarkers as a new way to diagnose pulmonary fibrosis that has the advantages of being noninvasive, sensitive, and accurate, is one of the hot areas in this field, including mucin-5 subtype B (MUC5B)10, matrix metalloproteinase-7 (MMP7)11,12, type II alveolar cell surface antigen (KL-6)13, chemokine ligand 18 (CCL18)14, much progress has been made.