Previous work, since 2003, had established that SARS-CoV uses a receptor called (never mind why) ACE2, which dangles from the exterior of certain human cells, including some lining the blood vessels, some in the small intestine, some in the heart and kidneys and other organs, and some (most fatefully) along the upper airway. ACE2 is there because it’s an enzyme that serves functions in human metabolism, one of which is to help regulate blood pressure. But incidentally it makes cells vulnerable, providing an opportunity for certain viruses.
