According to the study, the primary target or receptor for SARS-CoV-2 is angiotensin-converting enzyme 2 (ACE2) in type II pneumocyte in the lungs, goblet cells, and epithelial cells in the nose, which causes postinflammatory immunoreaction, so the severity of viral infection is closely related to the maturity and binding capacity of ACE2. The gene discussed is ACE2; the disease is viral infectious disease.