Figure 4.

Foci reduction neutralization test (FRNT). Samples are serially diluted and incubated with live SARS-CoV-2 for the viral neutralization for 1 h, followed by incubation with Vero E6 cells for an additional 1 h at 37 °C and 5% CO₂. Cell culture is overlaid with methylcellulose for 24 h. After removal of the overlay, cells are fixed and permeabilized. Anti-SARS-CoV-2 primary antibody is used to detect infected cells, followed by incubation with secondary HRP-conjugated antibodies. Results are evaluated by an Immunospot analyzer to quantify the spots corresponding to the infected cells. This image represents one well from a plate. This assay can be performed at low or high throughput. The image was created with https://www.biorender.com/ (accessed on 30 June 2023).