A long standing goal of this Section has been the development of new therapeutic and preventative strategies for human herpesvirus infections and better definition of their pathogenesis. While earlier work was heavily clinical, over the past few years, the major efforts have been in the laboratory. Our goal has been to elucidate pivotal molecular and cellular events which define and contribute to the pathogenesis of acute , chronic, and recurring infections with human herpesviruses. Major current projects fall into two areas: (1) Analysis of latent HSV-1 and -2 genome loads in human trigeminal and sacral ganglia harvested at autopsy and in experimentally infected animals. (2) Characterization of cytokine and other inflammatory contributors to HSV reactivation, through the provocation of reactivation and through the study of targeted knockout mice infected with HSV-1 or -2. As regards studies of HSV latency, we developed sensitive model sytems of HSV-1 and 2 infection in mice and guinea pigs through the ocular, nasal, systemic and vaginal routes. We can establish latency, quantitate virus load, latency gene expression, and induce virus reactivation efficiently with heat or ultraviolet heat. We used this model to study the relative potency of new antiviral drugs in preventing latency, and the role of several cytokines in establishment of latency and reactivates by infecting gene knockout mice. Specifically, we showed that IL-1a, IL-6, Fas , IFN-gamma, and TNF-alpha have no primary role to play in the establishment of latency or the reactivation of virus following UV irradiation. Loss of IL-6 or IFN-gamma, but not of the other genes, lead to more severe primary infections. Most recent emphases have been on novel and sensitive means of measuring the amount and distribution of latent HSV DNA in latently infected neurons. Quantitative, real-time PCR revealed and average of 3x10exp3 HSV-1 genome copies/10exp5 trigeminal ganglion cells, but only 10exp2 copies of HSV-2 DNA in few ganglia. In contrast, we found abundant HSV-2 but no HSV-1 DNA in some sacral ganglia. This past year, we perfected a means, using laser capture microdissection, for retreaving single neurons from human ganglia. By quantitative PCR we showed that up to 26% of trigeminal neurons harbor latent viral DNA in copy numbers ranging from a few to a few thousand per cell. In a second study of HSV latency, we generated and analyzed mice transgenic for the HSV-2 genome region encoding the major latency associated transcripts (LATs). Transgenic expression of LAT had no effect on the course of acute HSV-2 infection, on the establishment of latency, nor on the rate of reactivation following UV irradiation. We are currently exploring the implications of LAT transgene expression on cellular apoptosis.