ACE2 and COVID-19: Comparison of the ratio of neutralizing antibody responses to total SARS-CoV-2 spike antibody responses showed that ACE2 binding inhibition responses were significantly lower in individuals with fatal COVID-19 outcomes in comparison with those with nonfatal COVID-19 outcomes when measured by the MSD R-PLEX full-length spike but not the RBD inhibition assays (Figure 3D, t test: RBD P = 0.25, spike P = 0.018; ref. 13).