KRT18 and severe acute respiratory syndrome: Since the original SARS-CoV-2 variant that caused the current pandemics does not efficiently bind to the wild-type mouse ACE2 receptor, transgenic mice expressing the human ACE2 (hACE2) under the keratin 18 (K18) promoter have been established as an animal model of COVID-19.20,33 This model was initially developed to study the SARS-CoV infection,27,31 for which viral invasion and replication in the brain is currently well described.41