S100A9 and COVID-19: Intriguingly, we found that S100A8 and S100A9 were considerably upregulated by different TFs in a wide range of respiratory epithelial and peripheral immune cells in patients with severe COVID-19 (Supplementary Figure 4), which suggests that their upregulation tends to be independent of certain cell types and virus-infection sites but that different regulators can be used among cell types.