ACE2 and infection: PM2.5-mediated upregulation of ACE2 in the lungs has also been suggested and supported by an animal study [955] and a human cell culture experiment [956], but a bioinformatic analysis of transcriptomic data related to COVID-19 lung biopsy, SARS-CoV-2 infection in epithelial cells and PM exposure failed to find significant ACE2 upregulation in human infections [952].