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P. R. Kinchington, K. Davoli, S. Ramachandan, V. Imbrogno, R. L. Hendricks; Acute Ocular and Trigeminal Ganglionic Replication of Herpes Simplex Virus Type 1 Are Attenuated by Conversion of Glycoprotein B From a "Leaky Late" to a "True-Late" Regulated Gene. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2486. doi: https://doi.org/.
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Following HSV-1 corneal infection, viral latency is established in the trigeminal ganglion (TG). HSV-specific CD8+ T cells that are retained in the latently infected TG maintain an activation phenotype, and have been shown to block HSV-1 reactivation in sensory neurons prior to production of infectious virions. In the C57Bl6 mouse model, a majority of HSV-1 specific CD8+ T cells are directed to one epitope (gB498-505) on glycoprotein B, a critical antigen that is classed as a "leaky late" gene but which can be detected very early in infection. We hypothesized that gB expression early in reactivation is important for the capacity of CD8+ T cells to block reactivation from latency. To test this hypothesis, we created a recombinant HSV-1 that expresses gB as a true late gene.
Using standard recombination, HSV were created that express EGFP under control of the gB promoter and gB under control of the true late promoters for gC, p38 and gH, which are only transcribed following initiation of viral DNA replication. Rescuant viruses, in which gB was restored to its own promoter, were made. Viruses were evaluated for gene expression, growth in culture and in acute stage replication in corneas and TG of mice infected by scarification.
HSV-1 with true late promoter-driven gB were viable and gC and gH promoter gB viruses showed silghtly smaller plaques and only marginal impaired growth in Vero cell culture at low and high multiplicity of infection (m.o.i.). The altered promoters resulted in a delay of approximately 4 h in expression of gB in single step, high m.o.i. infections. Inoculation into scarified corneas of Balb/C and C57Bl6 mice resulted in more severe attenuation of corneal replication and more than 6 fold reduction of acute TG titers. Rescuant viruses were largely restored for both corneal and TG growth.
The modest delay of the expression of an essential viral glycoprotein affect replication of HSV-1, with much greater effect being seen in vivo, suggesting that the low levels of early expression of gB have important, as yet undefined functions in replication in the host.
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