ACE2 and susceptibility to pneumonia measurement: The model mouse line expresses human angiotensin I-converting enzyme 2 (hACE2) in epithelial lineages including airway epithelium under the control of the cytokeratin-18 promoter (K18), and the pathological signs of severe COVID-19, such as pneumonia and pulmonary dysfunction, has been reported to be recapitulated in these mice in several studies5,31,32.