REPLICATION, ESTABLISHMENT OF LATENT INFECTION, EXPRESSION OF THE LATENCY-ASSOCIATED TRANSCRIPTS AND EXPLANT REACTIVATION OF HERPES-SIMPLEXVIRUS TYPE-1 GAMMA-34.5 MUTANTS IN A MOUSE EYE MODEL

The herpes simplex virus type 1 (HSV-1) gamma 34.5 gene is located wit hin a region that is transcriptionally active during latent HSV-1 infe ction. To determine whether the gamma 34.5 gene deletion affects laten cy-associated transcript (LAT) gene expression or latent HSV-1 infecti on, a gamma 34.5 gene deletion mutant, 1716, and a stop codon insertio n mutant, 1771, were studied in the mouse eye model. Although the gamm a 34.5 gene is not essential, 1716 and 1771 replicated poorly in mouse eyes and trigeminal ganglia (TG). When mice were inoculated with 1716 , infectious virus was detected in eyes only on the first day post-inf ection (p.i.), and was not detected at any time point in TG. Following inoculation with 1771, a small amount of virus was detected in the ey es on days 2 and 4 p.i., and in the TG of one animal on day 2 p.i. Rea ctivation of virus from mice latently infected with 1716 (0/30 TG) and 1771 (1/20 TG) was extremely low compared with the parental strain, 1 7(+), and appropriate rescuants (80 to 100 % reactivation), even thoug h latent 1716 DNA was detected by PCR in 50 % of TG. These results dif fer from those obtained following footpad inoculation; in the footpad there was limited 1716 replication and reactivatable latent infection was established in some dorsal root ganglia. The data support the hypo thesis that the role of gamma 34.5 may be tissue and/or cell type spec ific. The synthesis, processing, and stability of the 2.0 kb LAT durin g 1716 and 1771 replication was not affected by these mutations in the gamma 34.5 gene. However, during latent infection of 1716 in mice the LATs were not detectable in TG by Northern blot, and were present in reduced amounts (approximate to 10-fold less) during 1771 latency. The LATs from 1716 were barely detectable in a few neurons by in situ hyb ridization. Therefore, the gamma 34.5 gene might (i) affect replicatio n in the eye, and reduce the amount of virus available to establish la tent infection, be directly involved in (ii) establishment of latency, and/or (iii) the reactivation process.