Fig. 2.

NAC and GSH impaired spike-mediated cell-cell fusion and syncytium formation.

(A) Spike-expressing 293T cells were overlaid on VeroE6/TMPRSS2 cells in the presence of GSH for 3 h at the indicated doses. Cell-cell fusion, recognized as the generation of adherent green cells, was suppressed by 20 mM GSH treatment.(B) Spike-induced syncytium formation was inhibited by thiol-reactive GSH and NAC. The inhibition protocol is shown at bottom. Three independent field images are shown (#1–3). White arrowheads indicate giant syncytium cells. Experiments were repeated independently twice and representative images are shown. GFP-positive area/image (A) or syncytium multinuclear cells (B) were quantified with ImageJ software, and results from three images were expressed as the means ± standard SD (Right graphs). One-way ANOVA was performed to assess statistical significance. ∗ indicates p < 0.05, and ∗∗ indicates p < 0.01.