Fig. 5.

Cell fusion mediated by the S glycoprotein. (A) Syncytium formation between 293T cells transfetced with pSecTag2B-S and pCDNA3-ACE2, respectively (right panel). There was no syncytium formation between 293T cells transfected with pSecTag2B-S and pCDNA3-ACE2-Ecto (left panel). (B) Cell fusion measured by a reporter gene-based assay. S glycoprotein expressed in both pCDNA3 and pSecTag2B vectors can be used in a β-gal reporter gene-based cell–cell fusion assay. A pCDNA3-based plasmid without S insert was used as plasmid control, and fusion between S-expressing cells with ACE2-ecto expressing cells was used as negative control.