ACE2 and COVID-19: Given the key role of angiotensin-converting enzyme 2 (ACE2) in facilitating the entry of SARS-CoV-2 virus particles into the lung (alveolar epithelial type II cells), gastrointestinal tract (luminal intestinal epithelial cells) and other tissues (2, 3), exploration of the potential effects on the renin–angiotensin–aldosterone system (RAAS) is of interest in understanding the pathogenesis of COVID-19.