Reactivation of latent herpes simplex virus from explanted dorsal root ganglia

Reactivation was induced by explantation of dorsal root ganglia (DRG) from mice that were latently infected with herpes simplex virus type 1. Reactivation was first detected, using combined in situ hybridization and immunocytochemistry, at 2 or 3 days post-explantation (p.e.). Evidence of reactivation was found primarily in neurons that did not also contain latency-associated transcripts (LATs). Occasionally, mRNA of immediate early gene 2 (IE2) or IE4/5, in the absence of other viral mRNAs or antigen, was found in LAT+ neurons. Thus, if reactivation was occurring in LAT+ neurons, the LATs must have been lost as an early consequence; however we could detect neither a decrease in the percentages of LAT+ neurons nor a reduction in the intensity of the LAT signal during the period of reactivation. However, the number of foci of reactivation was generally less than 2.9% of the estimated number of LAT+ cells in the DRG; this may account for our failure to see such changes. A redistribution of the LATs into the cytoplasm was found in some cells but this could reflect the poor survival and consequent death of the explanted neurons. We conclude that the majority of LAT+ neurons did not reactivate on explantation and that if reactivation occurred only in LAT+ neurons, the LATs must have been removed from the nucleus as an early consequence of reactivation. Alternatively, there may be a population of latently infected cells that do not express LATs.