In vivo and in vitro reactivation impairment of a herpes simplex virus type 1 latency-associated transcript variant...

Many recent studies of latent herpes simplex virus type 1 (HSV-1) infections within the nervous system have focused on the diploid genes encoding the latency-associated transcripts (LATs). The impaired explant reactivation of LAT variants from mouse trigeminal ganglia has implicated the LATs in the efficiency or speed of the reactivation process (D. A. Leib, C. L. Bogard, M. Kosz-Vnenchak, K. A. Hicks, D. M. Coen, D. M. Knipe, and P. A. Schaffer, J. Virol. 63:2893-2900, 1989; I. Steiner, J. G. Spivack, R. P. Lirette, S. M. Brown, A. R. MacLean, J. H. Subak-Sharpe, and N. W. Fraser, EMBO J. 8:505-511, 1989). However, it is not known how closely explant reactivation mimics the reactivation process in vivo. In the current study, a LAT variant (1704), parental strain (17+), and rescuant (1704R) were compared in vivo for reactivation of latent infection by iontophoresis in the rabbit eye model and in vitro by explant cocultivation of trigeminal ganglia from rabbits. Following iontophoresis, 17+ and 1704R reactivated in vivo from 76 and 64% of rabbits, respectively, while 1704 reactivated only from 4% (1 of 25) of the animals. In explant reactivation experiments, 17+ and 1704R reactivated from 98 and 67% of rabbit trigeminal ganglia, while 1704 reactivated from only 28% of trigeminal ganglia. The mean time required for the appearance of reactivated 1704 in explant culture, 17 days, was significantly longer than for 17+ and 1704R, 8 to 9 days. Thus, the explant reactivation kinetics in rabbit trigeminal ganglia reflect the behavior of LAT variant 1704 in vivo in the rabbit eye model. These data support the role of the LATs in the reactivation process and support the hypothesis that explant reactivation is a suitable system for analyzing the biological behavior of HSV-1 variants with defined genetic alterations in the LAT gene.