A 437-base-pair deletion at the beginning of the latency-associated transcript promoter significantly reduced adrenergically induced herpes simplex virus type 1 ocular reactivation in latently infected rabbits

In this study we used a herpes simplex virus type 1 (HSV-1) deletion mutant to identify a segment of the genome necessary for epinephrine-induced reactivation in the rabbit eye model of herpetic recurrent disease. In HSV-1 latently infected neural tissue, the only abundant viral products are the latency-associated transcripts (LATs). At least one promoter of LAT has been identified, and mutations in the LAT domain have been used to investigate HSV-1 reactivation. We used an ocular rabbit model of epinephrine-induced HSV-1 reactivation to study the effects of deleting a 437-bp region beginning 796 bp upstream of the LAT CAP site. Specifically, the 437-bp deletion is located between genomic positions 118006 and 118443 of the parent 17Syn⁺, and the construct is designated 17ΔS/N. This region also controls a portion of the genome encoding two transcripts (1.1 and 1.8 kb) from the LAT domain. A rescuant, 17ΔS/N-Res, was constructed from 17ΔS/N. Following ocular infection, all three viruses produced similar acute dendritic lesions in rabbits. Five weeks after infection, rabbits received transcorneal iontophoresis of epinephrine. The parent, 17Syn⁺, and the rescuant, 17ΔS/N- Res, underwent a high frequency of HSV-1 ocular reactivation as determined by recovery of infectious virus in the tear film. Rabbits infected with 17ΔS/N had a significantly lower frequency of ocular reactivation. Analysis of the trigeminal ganglia from all three groups of latently infected rabbits revealed (i) similar amounts of HSV DNA (genomic equivalents), (ii) accumulation of 2.0-and- 1.45-kb LATs, and (iii) explant reactivation at the same high frequency. Therefore, these studies indicate that the 437-bp deleted region in 17ΔS/N is essential for epinephrine-induced reactivation and could implicate the 1.1- and 1.8-kb transcripts in the mechanisms controlling HSV-1 reactivation.