Figure 2 Schematic diagram of alveolus during normal homeostasis (left panel) characterized by a balanced ACE1/ACE2 pathway, and under SARS-CoV-2 infection condition (right panel) where ACE2 receptor is downregulated by SARS-CoV-2 and increasing ACE1/ACE2 unbalance causes the renin-angiotensin system (RAS) hyper-activation leading to lung injury. AT I, AT II – alveolar type I, II epithelial cell (type I, II pneumocyte); ACE1, ACE2 – angiotensin-converting enzyme 1, 2; MasR – Mas receptor; Ang I, II – angiotensin I, II; AT1R, AT2R – angiotensin II type 1, 2 receptor.