ISG15 and infection: To evaluate differences in the innate immune response induced in the lungs of mice by SARS-CoV-2-WT and SARS-CoV-2-∆8 infections, a set of host mRNAs encoding interferon-related genes (IFN-β, IFNλ3, MX1, ISG15, IFIT1, OAS1, and XAF1) (Fig. 4A and B) and pro-inflammatory cytokines (IL-6, tumor necrosis factor alpha [TNF-α], chemokine [C-X-C motif] ligand [CXCL10], chemokine [C-C motif] ligand [CCL2], CCL7, and CXCL11) (Fig. 4B) were analyzed by quantitative PCR (qPCR) at 3 and 6 dpi.