SARS-CoV-2 Spike Protein and RBD IgG ELISA

The IgG ELISAs for spike protein and RBD were conducted as previously described [61 (link)]. Briefly, ELISA plates were coated with recombinant Wuhan-Hu-1 (purified and prepared as described in [61 (link)]) or Delta RBD (ACRO Biosystems SPD-C52Hh) and RBD (ACROBiosystems, SPD-C52Hp) antigens at 0.5 μg/mL. Five 3-fold serial dilutions of sera beginning at 1:100 or 1:500 were performed in PBS with 0.1% Tween with 1% nonfat dry milk. Secondary labeling was performed with goat anti-human IgG-Fc horseradish peroxidase (HRP) (1:3000, Bethyl Labs, A80-104P). Antibody binding was detected with TMB/E HRP substrate (Millipore Sigma, ES001) and 1 N HCl was used to stop the reaction. OD₄₅₀ was read on a Tecan infinite M1000Pro plate reader.