KRT18 and infection: The expression of hACE2 via the keratin 18 promoter in the K18-hACE2 mice did not lead to overtly aberrant cell tropism in the lungs, with infection of bronchial and alveolar epithelia cells by omicron variants (Fig 1D and 1E) also described in settings where hACE2 is not expressed as a transgene [76,77].