Figure 4. Kinetics of viral nucleoprotein expression in SARS-CoV-2 infected Vero E6 cells.

(A) Vero E6 cells were exposed to SARS-CoV-2 (20A.EU2 variant; MOI = 1.5) for 2 h, washed and incubated with culture medium. At the indicated time points, cells were collected, fixed, permeabilized and stained with an antibody that binds to the viral nucleoprotein N. (B) Same as in (A) but for the infection with the Gamma variant (MOI = 2). Dot plots show N expression in noninfected (lower left quadrant) and infected (lower right quadrant) Vero E6 cells from a representative experiment with multiple individual samples. Single cell analysis was done on numerous independent cells, and the individual plots shown in the figure are based on the analysis of 8,000 – 10,000 cells by flow cytometry, resulting in a very accurate analysis. The numbers in each quadrant refer to the distribution of the cells (i.e., percentage of total cell population). The dot plot in black (left panel) represents the non-infected cell control.

FSC: Forward scatter; MFI: Mean fluorescence intensity; p.i.: Postinfection.