Reactivation in vivo and in vitro of herpes simplex virus from mouse dorsal root ganglia which contain different levels of latency-associated transcripts.

In the dorsal root ganglia (DRG) of mice latently infected with the herpes simplex virus type 1 mutant in1814, there are more neurons that contain latency-associated transcripts (LATs) than in DRG of mice infected with a dose of equal infectivity of either a revertant or a wild-type virus. We investigated whether higher levels of LAT+ neurons resulted in more extensive reactivation either in vivo following neurectomy of the sciatic nerve or in vitro after explantation into culture. Neurectomy appeared to induce expression of immediate early 1 mRNA (IE1mRNA) in neurons of mice latently infected with each of three viruses. However IE1mRNA was detected in no more than 0.25% of the neurons of DRG from animals 2 to 4 days after neurectomy, irrespective of the percentage of LAT+ neurons present. Of the 22 neurons shown to express IE1mRNA, none expressed LATs also. However the lack of expression of viral antigen and the absence of a reduced potential for reactivation on explanation suggested that neurectomy had not induced full reactivation involving lytic replication leading to the death of the latently infected neurons. When DRG were explanted into culture, the distribution of the frequency of reactivation was similar to the distribution of DRG that contained LAT+ neurons. The presence of a high proportion of LAT+ neurons was not directly associated with earlier detection of reactivation but such experiments cannot be regarded as quantitative. We therefore concluded that neurectomy did not result in a reduced reactivation potential as described by others and that the frequency of expression of IE1mRNA following neurectomy did not correlate with the number of LAT+ neurons present.