A novel, cell-specific attenuation of a herpes simplex virus type 1 infection in vivo

We have observed a cell-specific attenuation of herpes simplex virus type 1 strain 17syn+ in vivo that was dependent upon the cell type used to grow the virus. Direct corneal infection of rabbits with 17syn+ propagated in Vero cells caused 60% (6 of 10) to develop severe central nervous system (CNS) disease as evidenced by seizures and/or paralysis; all neurologically impaired rabbits died. In contrast, infection of rabbits with 17syn+ propagated in BHK-21 cells induced seizures and was fatal in 10% (1 of 10). The cell-specific attenuation of a 17syn+ occurred after one growth cycle in BHK-21 cells. To determine whether the decreased virulence of the BHK-21 cell-grown virus correlated with a less severe CNS inflammatory reaction, CNS tissues from rabbits infected with 17syn+ grown in Vero and BHK-21 cells were compared. Histopathological analyses revealed no differences in the location or severity of inflammatory lesions from rabbits infected with virus grown in either cell type. Virus-induced corneal disease was less dependent upon the cell type used to propagate the virus as there were no significant differences in the type or severity of observed corneal lesions. Possible explanations based on differences between Vero and BHK-21 cells are discussed.