MUC1 and idiopathic pulmonary fibrosis: KL-6 is a mucin like glycoprotein distributed mainly on the surface of type II alveolar epithelial cells (AECs) and respiratory bronchiolar epithelia cells [15], and it has been well-explored in idiopathic pulmonary fibrosis (IPF) and ARDS patients, and is recognized as one of the specific biomarkers of AECs damage [16].