ACE2 and COVID-19: Among these 20 genes, the tumor suppressor DMBT1, a glycoprotein that has been shown previously to be highly expressed in ACE2 + AT2 cells54 and can bind to SARS-CoV-2 spike proteins55, and the cartilage acidic protein 1 (CRTAC1), previously known to be downregulated significantly in COVID-19 patients with severe infection56, were upregulated in ACE2 + compared to ACE2- AT2 CLD cells (Fig. 3d).