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J. Virol., May 1995, 3033-3041, Vol 69, No. 5
GC Perng, RL Thompson, NM Sawtell, WE Taylor, SM Slanina, H Ghiasi, R Kaiwar, AB Nesburn and SL Wechsler
The herpes simplex virus type 1 (HSV-1) ICP34.5 gene is a neurovirulence
gene in mice. In addition, some ICP34.5 mutants have been reported to have
a reduced efficiency of induced reactivation as measured by in vitro
explantation of latently infected mouse ganglia. However, since spontaneous
reactivation is almost nonexistent in mice, nothing has been reported on
the effect of ICP34.5 mutants on spontaneous reactivation in vivo. To
examine this, we have deleted both copies of the ICP34.5 neurovirulence
gene from a strain of HSV-1 (McKrae) that has a high spontaneous
reactivation rate in rabbits and used this mutant to infect rabbit eyes.
All rabbits infected with the ICP34.5 mutant virus (d34.5) survived, even
at challenge doses greater than 4 x 10(7) PFU per eye. In contrast, a
200-fold-lower challenge dose of 2 x 10(5) PFU per eye was lethal for
approximately 50% of rabbits infected with either the wild-type McKrae
parental virus or a rescued ICP34.5 mutant in which both copies of the
ICP34.5 gene were restored. In mice, the 50% lethal dose of the ICP34.5
mutant was over 10(6) PFU, compared with a value of less than 10 PFU for
the rescued virus. The ICP34.5 mutant was restricted for replication in
rabbit and mouse eyes and mouse trigeminal ganglia in vivo. The spontaneous
reactivation rate in rabbits for the mutant was 1.4% as determined by
culturing tear films for the presence of reactivated virus. This was more
than 10-fold lower than the spontaneous reactivation rate determined for
the rescued virus (19.6%) and was highly significant (P < 0.0001, Fisher
exact test). Southern analysis confirmed that the reactivated virus
retained both copies of the ICP34.5 deletion. Thus, this report
demonstrates that (i) the ICP34.5 gene, known to be a neurovirulence gene
in mice, is also important for virulence in rabbits and (ii) in vivo
spontaneous reactivation of HSV-1 in the rabbit ocular model, although
reduced, can occur in the absence of the ICP34.5 gene.
Copyright © 1995, American Society for Microbiology
An avirulent ICP34.5 deletion mutant of herpes simplex virus type 1 is capable of in vivo spontaneous reactivation
Ophthalmology Research Laboratories, Cedars-Sinai Medical Center Research Institute, Los Angeles 90048, USA.
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