Quantitative analysis of herpes simplex virus DNA and transcriptional activity in ganglia of mice latently infected with wild-type and thymidine kinase-deficient viral strains.

The relationship between herpes simplex virus (HSV) DNA replication and establishment of latent infection was examined using an experimental model that makes use of the segmental sensory innervation of mouse flanks (T7 to T12). Ganglia from consecutive thoracic segments of C57BL/10 mice latently infected with a virulent strain of HSV-1 (SC16) were compared with respect to (i) HSV DNA levels, (ii) latency-associated transcripts (LATs) and (iii) numbers of LAT+ neurons. In concordance with previous results, two patterns of virus persistence were detected distinguished by either a low (10 to 23) or high (approx. 200) number of viral genomes/LAT+ neuron. The high copy pattern was associated, anatomically, with ganglia directly innervating inoculated skin (T7/8). Paradoxically, the highest number of LAT+ neurons and the highest concentrations of LATs were detected in spinal segments (e.g. T10) containing the lowest number of viral genomes, implying that most of the latent SC16 DNA detected at T7 and T8 was transcriptionally repressed. When neuronal amplification of HSV DNA during the establishment phase was prevented by infecting mice with a viral thymidine kinase deletion mutant (TKDM21), the high copy pattern was eliminated and each LAT+ neuron contained, on average, 22 TKDM21 genomes. We conclude that input (i.e. unamplified) and progeny (i.e. amplified) DNA sequences persist in the peripheral nervous systems of mice infected with SC16. Structurally, latent TKDM21 DNA lacked free genomic termini, consistent with persistence of input DNA in an integrated or circular episomal configuration.