SUMMARY

The role of herpes implex virus type 1 (HSV-1) glycoprotein E (gE) in the induction of multinucleate cell (syncytium) formation was investigated using monoclonal antibodies and agE deletion mutant, R7023. We found that monoclonal antibodies directed against gE blocked HSV-l-induced syncytium formation in human ce~ls. R7023 also failed to induce syncytium formation in tissue culture cells. The results indicate that gE, in addition to glycoproteins B, D, H and the gene sequence located between 0.732 and 0-745 map units, is involved in cell fusion. Thus, this important biological property appears to be regulated by several HSV-1 gene products. Envelope glycoproteins ofa variety of animal viruses are essential for adsorption, penetration and, in some instances, cell-to-cell fusion resulting in the formation of multinucleate c lls or syncytia. Viral glycoproteins are transported to the plasma membrane and presumably mediate cell fusion, an event which leads to cell-to-cell spread of infection (Hoggan & Roizman, 1959; Hoggan et al., 1960; Lodmell & Notkins, 1974). The exact role of glycosylation i this important biological process is not well understood. It has been reported that glycosylation of the fusion-inducing product synthesized by Mason-Pfizer monkey virus is not required for syncytium formation (Chatterjee et al., 1981). However, with Newcastle disease virus and herpes implex virus type 1 (HSV-1), the ability to induce multinucleate c lls can be prevented if glycosylation is blocked (Gallaher et al., 1973). The specific glycoprotein(s) involved in HSV-l-induced cell fusion is unclear. Although several cell surface glycoproteins, gB, gC, gD, gE, gG, gH and gI, have been identified in HSV-infected cells (Baucke & Spear, 1979; Eberle & Courtney, 1980