Herpes simplex virus particles are unable to traverse the secretory pathway in the mouse L-cell mutant gro29

The mouse L-cell mutant gro29 was selected for its ability to survive infection by herpes simplex virus type 1 (HSV-1) and is defective in the propagation of HSV-1 and vesicular stomatitis virus (F. Tufaro, M. D. Snider, and S. L. McKnight, J. Cell Biol. 105:647-657, 1987). In this report, we show that gro29 cells harbor a lesion that inhibits the egress of HSV-1 virions during infection. We also found that HSV-1 glycoprotein D was slow to traverse the secretory pathway en route to the plasma membrane of infected gro29 cells. The movement of glycoproteins was not blocked entirely, however, and immunofluorescence experiments revealed that infected gro29 cells contained roughly 10% of the expected amount of glycoprotein D on their cell surface at 12 h postinfection. Furthermore, nucleocapsids and virions assembled inside the cells during infection, suggesting that the lesion in gro29 cells impinged on a late step in virion maturation. Electron micrographs of infected cells revealed that many of the intracellular virions were contained in irregular cytoplasmic vacuoles, similar to those that accumulate in HSV-1-infected cells treated with the ionophore monensin. We conclude from these results that gro29 harbors a defect that blocks the egress of HSV-1 virions from the infected cell without seriously impeding the flux of individual glycoproteins to the cell surface. We infer that HSV-1 maturation and egress require a host cell component that is either reduced or absent in gro29 cells and that this lesion, although not lethal to the host cell, cannot be tolerated by HSV-1 during its life cycle.