ACE2 and COVID-19: Considering the fact that expression of circulating, enzymatically active ACE2 is generated mostly by the proteolytic cleavage of the membrane-bound form [30,31,34], it is reasonable to speculate that the bulk of increased soluble ACE2 in the blood and other body fluids of COVID-19 patients is not necessarily released from the primary sites of infection, such as upper respiratory tract and lungs.