The inability to produce new proteins, many of which are enzymes needed for normal metabolism and structural proteins, weakens the cell to the point of lysis. Some viruses have proteins that become inserted into the host cell plasma membrane and disrupt normal membrane structure. These proteins are fusion proteins, meaning that they cause the fusion of lipid bilayer membranes. When present in the plasma membrane, fusion proteins cause the plasma membrane to fuse with plasma membranes of neighboring cells. This results in giant, multinucleated cells called giant cells, or syncytia.
Giant cells are fragile and usually die within a day or so.
The presence of giant cells in tissue samples taken from a site of infection often helps to diagnose a viral infection. Some viruses accumulate inside of cells as inclusion bodies, arrays of hundreds to thousands of virions, usually very neatly packed, inside of cells. As inclusion bodies become too large or too numerous, cell structure is disrupted to the point of lysis. The presence of inclusion bodies in tissue samples taken from a site of infection often helps to diagnose a viral infection. Other outcomes are death, persistent infection, latent infection, or tumor formation.