Figure 1.

Molecular mechanisms and cellular manifestations of henipavirus-induced syncytium formation. (a) Syncytia are multinucleated cells formed from the fusion of an infected cell with a susceptible cell. Syncytia can be observed both in vitro (in cell culture) and in vivo (here in a Guinea pig). In vivo, syncytia are observed in a wide range of tissues, including the vascular, respiratory, nervous, lymphatic, and urinary systems, particularly (but not exclusively) at endothelial and epithelial interfaces. Syncytia can occur both between infected and non-infected cells, and between infected cells. (b) Fusion protein maturation via the proteolytic activation by host cathepsins in endosomes. (c) Membrane fusion cascade via the interactions between viral envelope proteins (G and F) and host receptors (ephrins). Membrane fusion is a pH-independent process using an attachment-mediated triggering mechanism of the fusion protein. Steps preceding membrane fusion (in particular infection, viral replication, and viral protein expression and egress) are detailed in Howley and Knipe 2020 [46]. Visual created using BioRender.com on 21 August 2021.