By using IF staining, we further demonstrated over-secretion of MUC5B+ mucus in the conducting airway lumens of IPF patients (Figures 5A–C), accompanied with 93.55% (29/31) IPF patients that had obvious MUC5B+ mucus plugs in alveolar regions surrounded by fibrosis (Figure 5C). This evidence concerns the gene MUC5B and idiopathic pulmonary fibrosis.