According to our single-cell RNA (scRNA) sequencing analysis, both V0 membrane domain (a3 and c subunits) and V1 peripheral domain (F and G1 subunits) of V-ATPase, and S100A8/S100A9 were all significantly upregulated in total epithelial cells from bronchoalveolar lavage fluid (BALF) of severe COVID-19 patients (Fig. 1A). This evidence concerns the gene S100A9 and COVID-19.