Figure 2. Impact of TMPRSS2 and IFITMs on syncytia formation by U2OS‐ACE2‐infected cells.

Cells were infected at the indicated multiplicity of infection (MOI) and analyzed after 20 h. Image quantification method is described in Fig EV2.

• A
  TMPRSS2 increases fusion and cell mortality. Right panel: Areas of GFP⁺ cells and nuclei count normalized to NI.
• B
  IFITM1, but not IFITM2 and 3, inhibits SARS‐CoV‐2‐induced syncytia formation. Right panels: Area of GFP⁺ cells
• C
  The fusion of IFITM1⁺ cells with U2OS‐ACE2 syncytia is drastically reduced. Right panel: Area of IFITM⁺ GFP⁺ cells
• D
  IFITM1 decreases the number of infected cells. Right panel: Fraction of cells positive for S, normalized to control cells (transduced with pQCXIP‐empty vector).

Data information: Left panels: one representative experiment is shown. Scale bars: 100 µm. Right panels: Data are mean ± SD of 3–9 independent experiments. Statistical analysis: B–C: One‐way ANOVA, D: Two‐way ANOVA. ns: non‐significant, *P < 0. 05, **P < 0.01, ***P < 0.001, ****P < 0.0001.