ACE2 and COVID-19: Thus, in the course of COVID-19, ACE2 plays a complex role: high levels of ACE2-receptors on the cell surface in combination with Furin may facilitate SARS-Cov2-intrusion during the very early phase of infection, but in case of severe COVID-19 with pulmonary complications finally low levels of ACE2 can finally worsen the situation due to insufficient AT2-conversion.