ACE2 and acute respiratory distress syndrome: Although K18-hACE2 mice have different patterns of human angiotensin-converting enzyme 2 (ACE2) expression, driven by the human keratin 18 promoter, they are considered one of the most suitable animal models for characterizing SARS-CoV-2 variants, as they have similar pathological and immunological features of COVID-19-associated acute respiratory distress syndrome.