Elevated FiO increases SARS-CoV-2 co-receptor expression in respiratory tract epithelium.

The severity of coronavirus disease 2019 (COVID-19) is linked to an increasing number of risk factors, including exogenous (environmental) stimuli such as air pollution, nicotine, and cigarette smoke. These three factors increase the expression of angiotensin I converting enzyme 2 (ACE2), a key receptor involved in the entry of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-the etiological agent of COVID-19-into respiratory tract epithelial cells. Patients with severe COVID-19 are managed with oxygen support, as are at-risk individuals with chronic lung disease.