| Herpes simplex virus type 1 (HSV-1) is a ubiquitous human pathogen that establishes a latent infection in sensory ganglia and upon reactivation, can cause severe ocular disease. During lytic replication, viral proteins are expressed in a temporal cascade of immediate early (alpha), early (beta) and late (gamma) genes. The gamma genes are further sub-classified into gamma1 genes which are expressed prior to DNA replication and gamma2 genes which are absolutely dependent on DNA replication for their expression. During a latent infection of the trigeminal ganglia (TG), no infectious virus is produced and latency is associated with a persistent virus-specific CD8 + T cell infiltrate that actively block reactivation. In C57BL/6 mice, approximately 50% of these CD8+ T cells are specific to a single epitope on a a1 protein glycoprotein B (gB498-505; gB-CD8). In the TG, gB-CD8 are retained with an activated phenotype suggesting recent exposure to antigen during abortive reactivation events. While the kinetics of gene expression during lytic infection has been appreciated for some time, little is known about antigen expression during latency and reactivation, and its influence on antigen-specific CD8+ T cells in the TG. Using gB as our model antigen, in this work we show that during reactivation, gB expression occurs much sooner than gC expression, indicating that it expressed fairly early even during reactivation. Furthermore, by delaying gB expression to after DNA replication we observed a severe impairment in viral replication in the TG and a significant diminishment in the retention and activation phenotype of gB-CD8 in latently infected TG. However delaying gB did not prevent the ability of gB-CD8 to block reactivation indicating they can act very quickly even after DNA replication. Finally we demonstrate that by mutating the gB epitope such that it does not induce a gB-CD8 response, we abrogate the gB-CD8 infiltrate in the TG. These studies all demonstrate that during an HSV-1 infection, only antigen-specific CD8+ T cells infiltrate the TG and antigen exposure during latency is responsible for their retention in the TG. This work has great implications toward designing better immunogens for therapeutic vaccines to prevent HSV-1 reactivation. |
