TMPRSS2 and pulmonary fibrosis: After SARS-CoV-2 combines with ACE2, the protease transmembrane protease serine 2 (TMPRSS2) is activated by the viral spike protein, resulting in various degrees of pulmonary interstitial fibrosis; intestinal, esophageal, and gastric mucosa degeneration; necrosis; abscissions; and other acute injuries (5).