Characterization of nerve growth factor-dependent herpes simplex virus latency in neurons in vitro.

Primary sympathetic neuronal cultures were maintained for up to 5 weeks after inoculation with herpes simplex virus (HSV) without evidence of viral infection. Treatment with acyclovir for the first 7 days after viral inoculation prevented lytic infections in 100% of the cultures and resulted in viral latency in 100% of the cultures; reactivation occurred as the result of nerve growth factor (NGF) deprivation. Treatment of the cultures with several different inhibitors of viral DNA polymerase (acyclovir, aphidicolin, and phosphonoacetic acid) for 7 days after viral inoculation did not prevent the establishment of latency, which suggests that viral DNA replication was not required. During the latent phase of the infection, viral antigens were not detected with HSV-specific immunohistochemistry. However, 24 h after NGF deprivation, viral antigens were detected in essentially all of the neurons, indicating that the majority of neurons harbored latent HSV. The establishment of latency was not strain or type specific since latency was established with HSV type 2 and four strains of HSV type 1 and reactivation occurred in response to NGF deprivation.