ACE2 and COVID-19: Although antibodies against a specific domain of the N-terminal domain (NTD) of the SARS-CoV-2 spike protein in the serum of COVID-19 patients exert an ACE2-binding enhancement effect by inducing conformational changes in the RBD, anti-NTD antibodies are usually undetectable or present at low levels in the sera of uninfected individuals [37].