MUC5B and idiopathic pulmonary fibrosis: Serum and BALF biomarkers associated with disease progression or prognosis of IPF can be categorized into those that function in alveolar epithelial injury (e.g., KL-6 and MUC5B), extracellular matrix turnover (e.g., MMPs and periostin), and immunological changes (e.g., CCL18 and IL-6) [4, 34].