ACE2 and infection: Additionally, Busnadiego et al found that, although IFNs upregulated ACE2 mRNA, pretreatment of Calu-3s with IFN-β and -γ prior to infection with SARS-CoV-2 actually led to a severe drop in progeny virus titers, arguing that the antiviral effects of interferon outweighed any increase in ACE2 levels [33].