To substantiate this viral infection and microglial activation in vivo model, we used transgenic mice expressing the human ACE2, driven by the cytokeratin-18 gene promoter (K18-hACE2 mice), which were established for a model of SARS-CoV-2 infection and viral spread through the olfactory pathway (44, –, 46). Here, ACE2 is linked to viral infectious disease.