TMPRSS2 and COVID-19: The etiological agent of the COVID-19, that is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), attaches and enters target human cells via the human host’s angiotensin converting enzyme receptor 2 (ACE2) and neuropilin-1 (NRP1) cell receptors with the activation of the serine transmembrane protease 2 (TMPRSS2) host receptor as it enters the target cells.