ISG15 and COVID-19: Interestingly, when comparing PBMCs and the BAL-derived data from the two independent cohorts, we observed 11 genes (IFI27, IFITM3, IFI6, ISG15, IFIT3, RSAD2, MX1, IFIT1, OASL, IFI30, and OAS1) that were found in all three categories, PBMCs, BAL from severe-COVID-19 patients, and BAL from mild-COVID-19 patients.