The impact of interferon regulatory factor 3 on the immune response to herpes simplex virus type I infection

The type I interferon (IFN) cascade is critical in control of herpes simplex virus type I (HSV-1) infection and relies on specific recognition molecules to rapidly signal viral infection via interferon regulatory factor-3 (IRF-3)-dependent pathways. The absence of these recognition molecules or the loss of IRF-3 would be predicted to render early recognition pathways inoperative and thus impact viral infection. However, previous results had produced contradictory results in terms of the role of IRF-3 during HSV-1 infection. In this study, infected IRF-3-/- immune cells were found to support increased HSV-1 replication compared to control cells. In addition, IRF-3 deficient cells exhibited delayed type I IFN synthesis following infection and were partially restored in the presence of exogenous IFN; blockade of the type I IFN receptor resulted in similar titers in control and IRF-3 -/- cells. Together, the data demonstrated that defective and deficient type I IFN production in IRF-3-/- cells resulted in increased HSV-1 replication in vitro. In vivo, IRF-3 deficiency was found to have no significant impact on HSV-1 replication in peripheral tissues following ocular challenge with a laboratory (17) or a neurovirulent strain (McKrae) of virus. However, IRF-3-/- mice were significantly more susceptible to central nervous system infection following both peripheral and intracranial infection with HSV-1. Increased viral replication and inflammatory cytokine production were observed in brain tissues of IRF-3 -/- mice compared to control mice. In addition, the production of IFNbeta and IFNalpha was delayed and reduced in IRF-3-/- brains. These data demonstrate a critical role for IRF-3 in control of central nervous system infection following HSV-1 challenge. Together, the data illustrate the importance of IRF-3 mediated pathways in initiating the type I IFN cascade necessary to control HSV-1 infection both in vitro and in vivo.