Fig. 1.

Schematic representation of the measurement procedure.

(A) The antibodies against SECD, S1, RBD, and N protein were measured. Antigen-binding beads were incubated with serum, and antibodies bound to the beads (Black) were detected by secondary antibodies (Gray) against IgG, IgA, or IgM. (B) Bead-based Spike-ACE2 inhibition assay. RBD-binding beads were incubated with serum including inhibitory antibody (Black) and then incubated with soluble ACE2 (Gray). The amount of ACE2 bound to beads was measured. (C) Cell-based Spike-ACE2 inhibition assay. Spike-transfected cells were incubated with serum including inhibitory antibody (Black) and then incubated with soluble ACE2 (Gray). The amount of ACE2 bound to beads was measured. (D) Authentic virus neutralization assay. SARS-CoV-2 virus were mixed with serially diluted sera. The mixtures were placed on VeroE6/TMRRSS2 cells and cultured. The highest sera dilution factor with 100% CPE inhibition was defined as authentic virus neutralization titer.