A group from Georg-August-University Göttingen, Wilhelmsplatz 1, 37073 Göttingen, Germany, etc. has reported that syncytium formation (cell-to-cell fusion) could contribute to efficient spread of the SARS-CoV-2 delta variant.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8487035/
Vero, 293T, Caco-2, and Calu-3, these cell lines express endogenous ACE2 and Vero, Caco-2, and Calu-3 cells are often used for infection studies with authentic SARS-CoV-2. The delta variant S protein mediated entry into 293T and Vero cells with the same efficiency as the wild-type (WT) S protein, while entry into Caco-2 and Calu-3 cells was enhanced by 1.5 times and 2.0 times comparing with wild type. However, any increased ACE2 binding of the delta variant S protein was not observed, suggesting that increased entry into Caco-2 and Calu-3 cells was not due to augmented ACE2 binding.
SARS-CoV-2 S protein-driven syncytium formation is believed to contribute to the increased infectivity of the delta variant. To confirm syncytium formation drove by the delta variant, human lung cell line A549 expressing high level of ACE2 was adopted. As expected, WT S led to the formation of syncytia, while syncytia formation was not observed when cells were transfected with empty expression plasmid. Strikingly, the delta variant S protein caused more and larger syncytia, and quantification of cell-to-cell fusion revealed that fusion by the delta variant S protein was ∼2.5-fold more effective as compared to the WT S protein.
In conclusion, syncytium formation (cell-to-cell fusion) could contribute to efficient spread of the delta variant.
