Regulation of Herpes Simplex Virus Latency in Neurons in Culture

in neurons that mimics many aspects of latency in vivo has

been developed (Wilcox and Johnson 1987; Wilcox and Johnson 1988;

Wilcox, Smith et al. 1990). In many respects the in

vitro model resembles the in vivo models of latency

and the human disease. The in vitro model has been used to

demonstrate that nerve growth factor (NGF) is required to

maintain latency of either HSV-1 or HSV-2 in sympathetic or

sensory neurons in vitro. HSV-1 latency can be established

in essentially all of the neutrons in culture. The treatment of

neuronal cultures, with acyclovir for 7 days after inoculation

allows high multiplicities of virus to be used, but acyclovir

treatment is not required to establish latency. Latency is

maintained in neurons in culture for as long as 10 weeks in the

presence of NGF. Viral antigens associated with the productive

infection are not detected during the latent infection. Viral

transcription is restricted to LATs during the latent infection.

Upon removal of NGF from the medium for only 1 hour, reactivation

of latent virus occurs, and viral antigens associated with the

productive infection and infectious virus are detected between

48-72 hours after NGF deprivation. Activation of second-messenger

pathways induces the reactivation of latent virus, suggesting

that there may be several signals that are capable of inducing

reactivation. The advantage of the in vitro model is that

the majority of neurons harbor virus, mutant virus may be studied

without involving questions of viral replication, and