Figure 4.

Comparison of the angiotensin-converting enzyme 2 (ACE2)–trimer binding inhibition assay with a pseudovirus neutralization assay. A, The log(50% inhibitory concentration [IC₅₀]) value obtained from a lentiviral pseudovirus assay for 13 coronavirus disease 2019 (COVID-19)–positive and 12 control samples is plotted against anti-trimer immunoglobulin G (IgG) data (median fluorescence intensity [MFI]). B, C, A regression line for all COVID-19–positive samples is shown (r² = 0.60). Percentage inhibition on the trimer-ACE2 binding inhibition assay (B) or receptor-binding domain (RBD)–ACE2 binding inhibition assay (C) is plotted against log(IC₅₀) values from the lentiviral pseudovirus assay for 13 COVID-19–positive and 12 control samples. A regression line for all COVID-19–positive samples is shown (trimer, r² = 0.52; RBD, r² = 0.02).