MUC1 and idiopathic pulmonary fibrosis: Biomarkers associated with alveolar injury, inflammation, and extracellular matrix turnover–such as serum KL-6, SP-D, CCL-18, and matrix metalloproteinases–have been studied in fibrotic lung diseases, including idiopathic pulmonary fibrosis (IPF) and connective tissue disease-associated interstitial lung disease.