These results further revealed that fibrosis of COVID-19 patients can be induced by EMT accompanied by a significantly increased EMT score (Fig. 4F), and the decrease of epithelial cell marker genes MAL2, CLND4, and TJP1, as well as the increase of VIM and CDH2 of mesenchymal cell (Fig. S4A, B). Here, MAL2 is linked to COVID-19.