TMPRSS2 and COVID-19: In Figure 4, the hyperinflammatory response in COVID-19 begins its steps through the cellular phenomena of viral invasion and is characterized in chronological order by SARS-CoV-2 invades alveolar lung epithelial cells through the Spike (S) protein that binds to angiotensin-converting enzyme 2 (ACE2), which is cleaved by the protease TMPRSS2.