SARS-CoV-2 enters the respiratory tract after contacting the source of infection, and its S protein binds to angiotensin converting enzyme 2 (ACE2) in the epithelial cells of the respiratory tract to invade the body, then the virus enters the alveoli and infects alveolar epithelial type 2 (AET2) to help itself multiply and spread. The gene discussed is ACE2; the disease is infection.