DESCRIPTION: Reactivation of herpes simplex virus (HSV) from latent infection of neurons in the trigeminal ganglion is a major cause of blindness. In order to define the molecular mechanisms of HSV reactivation from latency, we propose to study the hypothesis that the establishment of HSV latency reflects specific interactions between the phenotype of the individual neuron and promoter elements in the HSV genome, and the hypothesis that viral reactivation from latency results from identifiable alterations in the neuronal gene expression. Three specific aims are outlined. (1) To define the cellular phenotype of neurons containing latent viral genomes, comparing neurons in which the latent genomes express detectable LATs. The PI will use double- label immunocytochemistry, in situ hybridization and in situ PCR on serial 1 ym sections of ganglion to characterize cells into latent HSV genomes by neurotransmitter phenotype, expression of high affinity growth factor receptor, and the presence of transcriptional regulatory elements. (2) To define the mechanisms responsible for reactivation of HSV from latency on a cell specific basis. He will use similar methods after reactivating the virus containing the earliest reactivating genomes. (3) To empirically test the role of NGF and of the cellular immediate early genes c-fos and c-jun in reactivation he will construct a virus with the NGF gene driven by the ICP0 promoter to express NGF early in the reactivation cascade in order to test whether NGF expression blocks reactivation, and will construct a second recombinant lacking the cyclic AMP response element (CRE) in ICP0 promoter in order to test whether elevated expression of c-fos or c-jun by the cell activates ICP0 expression to cause entry of the latent genome into lytic cycle activity. The descriptive studies will define the phenotype of the cells harboring latent genomes and the alterations in that phenotype which occur early in the reactivation cascade. The viral constructs will empirically test the potential role of specific elements. Together, these studies will allow use to better understand the interaction between cellular and viral elements that results in reactivation of latent genomes from the trigeminal ganglion; an understanding that has important implications for strategies to prevent viral reactivation from latency, and the blindness which results from that reactivation.