Altered pathogenesis in herpes simplex virus type 1 infection due to a syncytial mutation mapping to the carboxy terminus of glycoprotein B.

A syncytial (syn) variant of herpes simplex virus type 1 strain 17 syn+ was selected by serial passage in heparin, a glycosaminoglycan which potently inhibits herpes simplex virus infectivity. This virus, 17 hep syn, is sixfold more heparin resistant than its parent. By using marker transfer techniques, its syn phenotype, but not heparin resistance, was mapped first to the BamHI G fragment (0.343 to 0.415 map units) and then to a 670-bp KpnI-PstI subclone (0.345 to 0.351 map units) encoding the carboxy terminus of glycoprotein B (gB). Three cloned syncytial recombinants were generated from cotransfections of 17 syn+ with either 17 hep syn BamHI-G or the 670-bp subclone. After footpad inoculation of mice, 17 hep syn was as virulent as its parent, despite reaching lower titers in feet, sciatic nerves, dorsal root ganglia, spinal cords, and brains. Animals infected with 17 hep syn or the gB recombinant viruses developed a unique pattern of disease that was strikingly different than that seen with wild-type virus: severe inflammation and edema of the inoculated limb and death without antecedent paralysis. Histopathologic examination revealed limitation of spinal involvement by 17 hep syn to the dorsal aspect of the cord and decreased virus-induced damage in the central nervous system. The genetically unrelated syn variant MP, in contrast, was avirulent and did not cause severe local inflammation. After intracerebral inoculation, 17 hep syn was highly virulent and replicated to high titers in the brain. Yet, unlike the parental virus, it resulted in an altered distribution of herpes simplex virus antigens, which were limited to the ependymal and subependymal regions surrounding the lateral ventricles. Despite their syncytial phenotype and pathogenic properties, the recombinant viruses, unlike 17 hep syn, were not heparin resistant. We conclude that a transferable alteration in the 670-bp carboxy-terminal portion of the glycoprotein gB gene of 17 hep syn results in both its syncytial phenotype and the unique pattern of disease that it causes but does not result in heparin resistance. These observations provide direct biological evidence for an important role for herpes simplex virus gB in pathogenic events both at the peripheral site of infection and within the nervous system.