HUMAN CYTOMEGALOVIRUS GLYCOPROTEIN-H GLYCOPROTEIN L-COMPLEX MODULATESFUSION-FROM-WITHOUT

Glycoprotein H/glycoprotein L (gH/gL) complexes of herpesviruses are r equired for fusion of infecting virions with host cell membranes, In h uman cytomegalovirus (HCMV), neutralizing monoclonal antibodies (MAb) specific for gH inhibit the transfer of a fluorescent probe to the hos t cell from labelled virus particles, In similar fashion, in the prese nt study, neutralizing gH-specific MAb inhibited HCMV-induced fusion-f rom-without in monolayers of both human embryonic fibroblasts and cont inuous astrocytoma cells (U373), No fusion was detected in cells co-in fected with defective recombinant adenovirus vectors that elicited hig h-level expression of gH and gL, indicating that surface-expressed gH was not intrinsically fusogenic, However, when such cells were superin fected with HCMV that gave fusion-from-without, the resulting cell-to- cell fusion was considerably enhanced, Thus, under our experimental co nditions, gH/gL on the cell surface functioned to increase membrane fu sion once this was initiated by other components in the virus envelope .