FIG 2 .

Infection with MHV or SARS CoV induces bulk fluid uptake consistent with macropinocytosis. (A, B) DBT cells were infected with MHV A59 at an MOI of 1 PFU/cell for 8 h. DBT-hACE2 cells were infected with SARS CoV at an MOI of 0.1 PFU/cell for 24 h. Nanoparticles were added 3 h prior to fixation, and cells were washed, fixed, stained, and imaged. Arrows denote nanoparticles (red). DAPI is blue, and nsp8 is green. (B) Data are represented as the mean ± the standard error of the mean of two replicates performed in duplicate. n = ≥30 fields per replicate. (C) Cells were mock infected or infected with MHV, UV-inactivated MHV (UV), or heat-inactivated MHV (HI) at an MOI = 1 PFU/cell (or the equivalent volume of noninfectious virus) for 8 h. Nanoparticles were added in 2-h increments, as designated, and cells were washed, fixed, stained, and imaged. Data are represented as the mean ± the standard error of the mean of two replicates performed in duplicate. (D) DBT cells on a glass bottom dish were infected with DiI-labeled MHV (white arrows) at an MOI of 25 PFU/cell, incubated at 4°C for 30 min, and imaged in a 37°C chamber incubator for 1 h. Time is in minutes:seconds. Virus fusion with the cell was observed, but membrane ruffling was absent. An image representative of triplicate experiments is shown. Significance was assessed by one-way ANOVA with Dunnett’s post hoc test. **, P < 0.005; ***, P < 0.0001.