SARS-CoV-2 Spike Protein Antibody Assay

In brief, recombinant SARS- CoV-2 spike ectodomain protein or VZV gE protein (Genscript) diluted in coating buffer (Biolegend) were used to coat 96-well EIA/RIA plates (Greiner Bio-one, 100 ng per well) at 4 °C overnight. The plates were then washed with 1 $\times$ PBS-T (0.05% Tween-20) and blocked with 2% BSA in PBS-T for 2 h at room temperature. Serum samples with serial dilutions were added and incubated for 2 h at room temperature. After washing, HRP-conjugated goat anti-mouse IgG antibody (1:10,000) was added and incubated for 1 h. TMB substrate (Invitrogen) was then used for colour development and the absorbance was read at 450 nm using BioTek microplate reader. End-point titres were calculated as the largest sample dilution factor yielding a signal that exceeds 2.1-fold value of the background^{58 (link)}.