Latency in vitro using irradiated herpes simplex virus.

Human embryonic fibroblasts infected with u.v.-irradiated herpes simplex virus type 2 (HSV-2, strain 186) and maintained at 40.5 degrees C did not yield detectable virus. Virus synthesis was induced by temperature shift-down to 36.5 degrees C. The induced virus grew very poorly and was inactivated very rapidly at 40.5 degrees C. Non-irradiated virus failed to establish latency at 40.5 degrees C in infected cells. Enhanced reactivation of HSV-2 was observed when latently infected cultures were superinfected with human cytomegalovirus (HCMV) or irradiated with a small dose of u.v. light at the time of temperature shift-down. HCMV did not enhance synthesis of HSV-2 during a normal growth cycle but did enhance synthesis of u.v.-irradiated HSV-2. These observations suggest that in this in vitro latency system, some HSV genomes damaged by u.v. irradiation were maintained in a non-replicating state without being destroyed or significantly repaired.