Pathways of viral gene expression during acute neuronal infection with HSV-1

Pathways of viral gene expression were investigated during the acute phase of sensory ganglionic infection with HSV-1. To facilitate these studies we constructed KOS/62-3, an HSV-1 vector in which the Escherichia coli lac-Z gene was inserted behind both copies of the promoter for the viral latency-associated transcripts. Following footpad inoculation of mice with the virus, acutely infected dorsal root ganglion (DRG) neurons were assayed by dual immunofluorescence for the presence of β-galactosidase and HSV viral antigens. Most infected neurons stained for either δ-galactosidase or viral antigens. Less than 0.2% of neurons staining for viral antigens also expressed β-galactosidase, and less than 10% of neurons expressing δ-galactosidase also stained for viral antigen. As a consequence of these findings, we propose that there are essentially two populations of HSV-infected neurons during the acute phase of ganglionic infection. In one population of neurons there is abundant viral protein synthesis but minimal transcription of latency-associated transcripts, whereas in a second population of neurons viral gene expression is severely restricted except for the synthesis of latency-associated transcripts. Since DRG neurons are a heterogeneous population of cells, we further sought to determine whether either pathway of gene expression was more likely to occur in a particular neuronal phenotype. To accomplish this, antibodies were used to characterize the DRG neuronal phenotypes acutely infected with the virus. The results indicated that the pathway of neuronal infection characterized by transcription of abundant latency-associated transcripts and minimal viral protein synthesis was much more likely to occur in DRG neurons expressing the cellular antigen SSEA-3. These data indicate that the neuron plays a major role in regulating the outcome of infection with HSV. Finally, we sought to determine whether DNA replication occurs in the course of establishment of a latent infection. We found that the DNA content of neurons latently infected with KOS(M) strain HSV was not affected by treatment with nucleotide analogues during the acute phase of ganglionic infection, suggesting that viral DNA replication does not occur during the establishment of latent infection.