During virus infection, many coronaviruses, including SARS-CoV-1, SARS-CoV-2, Middle East respiratory syndrome coronavirus (MERS-CoV), and human coronavirus 229E (HCoV-229E), as well as influenza viruses, use the host protease TMPRSS2 as a tool to enter the human cells. The gene discussed is TMPRSS2; the disease is viral infectious disease.