HERPES-SIMPLEX VIRUS TYPE-1 DNA-REPLICATION AND GENE-EXPRESSION DURING EXPLANT-INDUCED REACTIVATION OF LATENTLY INFECTED MURINE SENSORY GANGLIA

Infectious virus assays and PCR amplification of DNA and RNA were used to investigate herpes simplex virus DNA replication and gene expressi on in two murine in vitro models for virus reactivation. We examined l atent infections with wild-type (wt), precisely defined latency-associ ated transcript-negative (LAT(-)) mutants, and LAT(+) rescuants of the se mutants of the 17syn(+) strain of virus in both murine trigeminal a nd lumbosacral ganglia and of the KOS(M) strain in the latter. In expl ants of ganglia latently infected with the LAT(-) mutant of strain 17s yn(+) virus, a reduction in number of cultures exhibiting cytopathic e ffects due to virus reactivation and measurable delays in virus recove ry were observed compared with wt or the LAT(+) rescuant. This LAT-spe cific effect was not seen in explants of lumbosacral ganglia latently infected with mutants derived from the KOS(M) strain of virus. Althoug h there was appreciable variation between individual animals, no signi ficant difference between LAT(+) and LAT(-) virus in time of onset of viral DNA replication in explanted ganglia was seen with use of either virus strain. There was a slight decrease in the relative amount of v iral DNA recovered compared with internal cellular controls in latentl y infected ganglia harboring the LAT(-) mutant of 17syn(+) compared wi th the wt virus or the LAT(+) rescuant. This reduced relative amount r anged from 0 to as much as 50% but averaged 20%. Such differences were not seen in infections with KOS(M)-derived mutants. In contrast, alth ough expression of productive-cycle transcripts could be detected with in 4 h following explant cultivation of latently infected ganglia, no differences between LAT(+) and LAT(-) viruses could be seen. As discus sed, these data place specific constraints on possible models for the role of LAT expression in in vitro reactivation systems.