ISG15 and infection: Analyses of gene expression in lungs indicated that infection induced a rapid and transient expression of transcripts encoding interferon (IFN)-β and IFN-λ and a more sustained expression of IFN stimulated genes (ISGs) such as Isg15, Mx2 (interferon-induced GTP-binding protein), Cxcl10 (C-X-C motif chemokine ligand 10), Stat1 (signal transducer and activator of transcription 1), and Ifi27 (IFNα inducible protein 27) (Figure 1c, left panel, Figure S1b).