Abstract
Purpose :
The innate immune response to herpes simplex virus type 1 (HSV-1) infection in the retina is poorly understood despite the clinical significance of this potentially blinding condition. Thus, we sought to identify the critical host innate antiviral pathways activated following viral infection of the retina to identify additional therapeutic targets for the blinding condition.
Methods :
In the current study, various innate immune deficient and wild type (WT) mice were infected with 1,000 plaque forming units of subretinal HSV-1 and at the indicated time post infection (pi), retinas isolated, and viral burden assessed by plaque assay, type I interferon (IFN) production by real-time (RT)-PCR, immunofluorescence, and bead array, and retinal pathology by histology.
Results :
We found that mice with a TLR-3 adaptor protein (TRIF-/-) or IFN receptor deficiency (IFNAR-/-) harbored significantly more virus than MyD88 knock out mice (MyD88-/-) and WT controls by day 5 pi. This correlated with significantly worse retinal pathology in TRIF-/- and IFNAR-/- mice compared to WT and uninfected controls. To then identify what downstream immune mechanisms were lost leading to an increased susceptibility to HSV-1 in TRIF-/- mice, mRNA transcripts of multiple type I IFN subtypes and downstream effectors were evaluated by RT-PCR. TRIF-/- mice had reduced IFN-a4 and downstream effector transcripts compared to WT by 2 days pi. IFN-b could not be detected until 5 days pi by RT-PCR and these findings were confirmed by chemokine bead array. Immunofluorescence affirmed the production of IFN-a 5 days pi. To then confirm the importance of this IFN subtype in viral retinitis, TRIF-/- mice were pretreated with intravitreal PBS or increasing units of the IFN-a subtype and then infected with HSV-1. Viral titer was then assessed 5 days pi and found to be significantly lower in mice pretreated with IFN-a compared to PBS controls.
Conclusions :
Collectively, these results clearly define the role of the TLR-3-Trif pathway in activating IFN-a production within the retina to herpesviruses. A loss of this pathway can be overcome by exogenous IFN-a suggesting that type I IFNs could serve as an additional therapeutic option for herpes infections of the retina.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.