Meanwhile, we found marked elevation of antioxidant protection proteins (GPX3, GSR, CAT, and ceruloplasmin) and pulmonary protection proteins such as proteolytic destruction inhibitors (SERPINA1 and SERPINB1) and alveolar stabilizer (SFTPB) in severe and critical COVID-19 patients (Figure 2), suggesting the induction of a body self-protection mechanism. Here, CAT is linked to COVID-19.