ACE2 and infection: In this study, it was shown that low expression levels of ACE2 along with high expression levels of TMPRSS2 in nasopharyngeal samples before infection may be a risk factor for the development of COVID-19 symptoms, and SARS-CoV-2 infection seems to increase ACE2 expression and decrease TMPRSS2 levels in symptomatic patients, possibly showing a host response to the replication of SARS-CoV-2.