Replication of herpes simplex virus type 1 within trigeminal ganglia is required for high frequency but not high viral genome copy number latency.
The replication properties of a thymidine kinase-negative (TK(-)) mutant of herpes simplex virus type 1 (HSV-1) were exploited to examine the relative contributions of replication at the body surface and within trigeminal ganglia (TG) on the establishment of latent infections. The replication of a TK(-) mutant, 17/tBTK(-), was reduced by approximately 12-fold on the mouse cornea compared to the rescued isolate 17/tBRTK(+), and no replication of 17/tBTK(-) in the TG of these mice was detected. About 1.8% of the TG neurons of mice infected with 17/tBTK(-) harbored the latent viral genome compared to 23% of those infected with 17/tBRTK(+). In addition, the latent sites established by the TK(-) mutant contained fewer copies of the HSV-1 genome (average, 2.3/neuron versus 28/neuron). On the snout, sustained robust replication of 17tBTK(-) in the absence of significant replication within the TG resulted in a modest increase in the number of latent sites. Importantly, these latently infected neurons displayed a wild-type latent-genome copy number profile, with some neurons containing hundreds of copies of the TK(-) mutant genome. As expected, the replication of the TK(-) mutant appeared to be blocked prior to DNA replication in most ganglionic neurons in that (i) virus replication was severely restricted in ganglia, (ii) the number of neurons expressing HSV proteins was reduced 30-fold compared to the rescued isolate, (iii) cell-to-cell spread of virus was not detected within ganglia, and (iv) the proportion of infected neurons expressing late proteins was reduced by 89% compared to the rescued strain. These results demonstrate that the viral TK gene is required for the efficient establishment of latency. This requirement appears to be primarily for efficient replication within the ganglion, which leads to a sixfold increase in the number of latent sites established. Further, latent sites with high genome copy number can be established in the absence of significant virus genome replication in neurons. This suggests that neurons can be infected by many HSV virions and still enter the latent state.
Thompson
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RL
Department of Molecular Genetics, Microbiology, and Biochemistry, University of Cincinnati Medical Center, Cincinnati, Ohio 45267-0524, USA.
Sawtell
N M
NM
D000818:Animals; D002213:Capsid / Q000096:biosynthesis; D036022:Capsid Proteins; D004261:DNA Replication; D004279:DNA, Viral / Q000096:biosynthesis; D017353:Gene Deletion; D018628:Gene Dosage; D016679:Genome, Viral; D017405:Herpes Simplex Virus Protein Vmw65 / Q000096:biosynthesis; D018259:Herpesvirus 1, Human / Q000235:genetics / Q000502:physiology*; D006801:Humans; D017874:Immediate-Early Proteins / Q000096:biosynthesis; D008297:Male; D051379:Mice; D009474:Neurons / Q000821:virology; D011817:Rabbits; D013937:Thymidine Kinase / Q000235:genetics; D012668:Trigeminal Ganglion / Q000821:virology*; D014764:Viral Proteins / Q000235:genetics; D017735:Virus Latency; D014779:Virus Replication
D036022:Capsid Proteins; D004279:DNA, Viral; D017405:Herpes Simplex Virus Protein Vmw65; C070109:ICP5 capsid protein, herpes simplex virus type 1; D017874:Immediate-Early Proteins; C086267:UL24 protein, Human herpesvirus 1; D014764:Viral Proteins; C048925:herpes simplex virus, type 1 protein ICP4; D013937:Thymidine Kinase