Innate Immune Responses to Replication-­‐Competent and -­‐Deficient HSV-­‐2

Abstract

HSV-1 and HSV-2 infections are highly prevalent in the US population and can cause mild to severe herpetic disease. We previously constructed a replication-deficient, UL5/UL29 deletion HSV-2 vaccine virus, dl5-29, which we, and others, have shown to elicit both robust cellular and humoral adaptive immune responses in murine and guinea pig models. While adaptive immune responses are greatly influenced by the innate immune response, the innate immune responses to dl5-29 have not been studied, and the innate responses to wild-type HSV-2 are poorly understood. To determine the kinetics of induction of the innate immune responses to dl5-29 and wild-type HSV-2, we infected primary human fibroblasts in the absence or presence of components of innate immune pathways. We found that infection with dl5-29 elicited a significantly elevated TNFα and IL-6 response, relative to replication-competent wild-type and thymidine kinase mutant HSV-2 viruses, in a manner partially dependent on the adaptor protein, TRAF6, and completely dependent on expression of the canonical NF-κB subunit, p65. Interestingly, inhibition of de novo protein synthesis had no significant effect on the ratio of TNFα and IL-6 induction by dl5-29, relative to wild-type HSV-2 infections, suggesting that the elevated responses to dl5-29 were elicited by differences in viral factors present early in infection. We define, for the first time, a two-phase activation of the canonical NF-κB pathway by wild-type HSV-2, which was accelerated and enhanced in dl5-29 infections. Interestingly, we found that the HSV-2 glycoprotein D, a potential canonical NF-κB agonist, was more abundant in purified dl5-29 virus than wild-type HSV-2. Also, dl5-29 infection exhibited a delayed expression of immediate early genes encoding ICP0 and ICP27, in a primarily UL29-dependent manner, suggesting a novel role for UL29-dependent regulation of immediate early gene expression. Thus, we present novel roles for the viral gene products encoded by UL5 and UL29, previously known to function as the HSV helicase and a single stranded DNA-binding protein involved in viral DNA replication, respectively, as modulators of the canonical NF-κB response to HSV-2. These findings may prove important to the potential for fine-tuning the innate immune responses of HSV-based vaccine and gene-therapy designs.