Fig. 2

hACE2 expression controls the preference of SARS-CoV-2 infection between cell-free and cell-to-cell transmission. a and b The hACE2 expression level in each hACE2-A549 clone was determined using Western blotting with an anti-ACE2 antibody, and then quantified utilizing ImageJ software. hACE2 expression was normalized to actin expression, and the #1–1 clone was defined as 1. c–e, hACE2-A549 clones were adsorbed with SARS-CoV-2 at an MOI of 0.01 for 1 h, and then the cells were replenished with fresh medium containing NAb or Ctrl Ab. At 24, 48, and 72 hpi, the cells were fixed for IFA with anti-NSP3 antibody (d), and the virus infection rate was quantified with a high-content image analysis system (e). f The sizes of infected foci in NAb treatment groups at 48 hpi were measured with over 200 infected foci for each clone. g The supernatants at each time point were harvested for virus infectivity assay. The virus infectivity in supernatant from the #1–1 hACE2-A549 clone at 24 hpi was defined as 1. h vRNA in supernatant from each hACE2-A549 clone was quantified using real-time RT-PCR at 24 hpi. Low: low hACE2 expression; High: high hACE2 expression; scale bar, 200 μm; data indicated means (f) or means with SD (n = 3) (b, e, g and h) of each group; *p < 0.05, **p < 0.01, ***p < 0.001, determined using two-tailed unpaired Student’s t test