Figure 5
ELISA results (mean optical density at 492 nm [OD492], error bars are standard deviations of the mean) comparing plasma from 6 COVID-19 persons and 5 controls taken before November 2019 using anti-IgG conjugated to horseradish peroxidase (HRP). Performance of spike-receptor binding domain (S-RBD) and nucleoprotein in selective reaction with COVID-19 plasma IgG is far superior to nsp9, complexes of nsp7/8, complexes of nsp10/16, or nsp15. Note: the N-terminal portion of nucleoprotein (N-Nt) retains the superior signal of full-length nucleoprotein (Nuc) but improves the signal-to-noise ratio of the assay by nearly twofold, to 4.2 from 2.3, respectively. This implies that epitopes on the C-terminal portion of Nuc are non-specific for SARS-CoV-2, as predicted.
