ACE2 also plays an important role in the renin-angiotensin system (RAS), and the imbalance between ACE/Ang II/AT1R pathway and ACE2/Ang (1–7)/Mas receptor pathway in the RAS will lead to multisystem inflammation, and studies have shown that RAS inhibitors could effectively relieve symptoms of acute severe pneumonia and respiratory failure [70]. Here, ACE2 is linked to pneumonia.