Binding to cells of virosomes containing herpes simplex virus type 1 glycoproteins and evidence for fusion.

Envelope proteins and lipids were extracted from purified herpes simplex virus type 1 virions with octyl glucoside and mixed with phosphatidylcholine for preparation of virosomes by removal of the detergent. Greater than 85% of the extracted envelope proteins, including all the glycoproteins and the nonglycosylated protein designated VP16, were associated with virosomes, which ranged in density from ca. 1.07 to 1.13 g/cm3. All the glycoproteins except gC were as susceptible to degradation by added protease in virosomes as in virions, indicating similar orientations in both. Approximately 30 to 40% of radiolabel incorporated into virosomes bound to HEp-2 cells within 1.5 h at either 4 or 37 degrees C. The cell-bound virosomes were enriched for gB and deficient in other glycoproteins, in comparison with unbound or total virosomes. Binding of virosomes to HEp-2 cells could be inhibited by purified virus, heparin, and monospecific antiviral antibodies. Polyclonal and monoclonal anti-gB antibodies were more effective at inhibiting virosome binding than were anti-gD or anti-gC antibodies. Virosomes depleted of gB or gD did not bind to cells as efficiently as did virosomes containing all the extracted enveloped components; this loss of binding activity was especially pronounced on depletion of gB. The binding of herpes simplex virus type 1 virosomes to cells is discussed in relation to possible heterogeneity of the virosomes and comparisons with binding of virions to cells. We also present electron microscopic evidence that bound virosomes can fuse with the cell surface.