ACE2 and COVID-19: Like the previous two varieties, SARS and MERS, responsible for the previous two major respiratory disease outbreaks, COVID-19 shows a marked predisposition for the alveolar epithelial cells of the human lung, using angiotensin-converting enzyme 2 (ACE2) as its entry point (Zhou et al., 2020), unlike its two major predecessors, which could penetrate cells via other routes as well.