SARS-CoV-2 viruses binding to ACE-2 receptors on a human cell, the initial stage of COVID-19 infection, conceptual 3D illustration credit: Kateryna Kon / Shutterstock
https://www.news-medical.net/news/20200525/The-infection-of-lung-stem-cells-may-determine-SARS-CoV-2-pathogenicity.aspx