RBD-binding IgG assay
SECONDARY
RBD-binding IgG antibodies in the heat-inactivated human serum samples and the culture supernatant of PBMCs stimulated for 4 days with R848 + IL-2 were detected with an RBD-binding IgG ELISA kit (Beijing, Kewei). Briefly, diluted samples and a reference standard were added in duplicate to rSARS-CoV-2 RBD-precoated wells and incubated for 30 min at 37°C. The microplates were washed, and a horseradish peroxidase (HRP)-conjugated goat anti-human IgG secondary antibody was added to bind the RBD-bound human antibodies. After 30 min of incubation, the microplates were washed, and TMB chromogenic substrate was added to generate a colorimetric signal for 10 min. A stop solution was added to stop color development, and the signal was read on a microplate reader. The total anti-RBD IgG antibody levels were quantitated in ELISA units (EU) ml