Pulmonary fibrosis means that the regeneration ability of alveoli is inhibited after long-term chronic injury (such as idiopathic pulmonary fibrosis (IPF), chronic obstructive pulmonary disease (COPD), asthma), and biomarkers with diagnostic specificity (such as matrix metalloproteinase 7 (MMP7) and Krebs Von Den Lungen-6 (KL-6, also known as mucin 1)) are expressed. The gene discussed is MMP7; the disease is pulmonary fibrosis.