To comprehensively characterize differences between these strains in the lung of K18-hACE2 mice, we evaluated the histologic alterations in both infected groups as well as viral tropism, abundance, and spread of viral antigen via immunohistochemistry (IHC) and quantitative image analysis throughout the course of infection (Fig. 2C and Fig. 2E to T). This evidence concerns the gene KRT18 and infection.