Fig. 3.

PRMNT assay to identify SARS-CoV-2 NAbs, infrared staining. A and B) Confluent monolayers of Vero E6 cells were infected, fixed and stained with the primary NP 1C7 mAb as described in Fig. 2. After incubation with the primary Ab, cells were incubated, for 1 h, with IRDye 800CW goat anti-mouse IgG secondary Ab, and DRAQ5™ Fluorescent Probe Solution for nuclear staining. Cells were then imaged using an Odyssey Sa infrared imaging system. The neutralizing titer 50 (NT₅₀) was calculated as the highest dilution of the NAb-containing sample that prevents 50 % plaque formation in infected cells, determined by a sigmoidal dose response curve. Dotted line indicates 50 % neutralization. Data were expressed as mean and SD from triplicate wells.