ISG15 and COVID-19: Moreover, through the PPI analysis of DEGs, the top 10 hub genes were extracted, including IFI44L, ISG15, MX1, IFI44, OASL, RSAD2, GBP1, OAS1, IFI6, and HERC5, which may be a therapeutic target for COVID-19 and help to find drug molecules and drug-target interactions.