Abstract
Purpose: :
The role of CD8+ T cells in corneal defense and pathology in response to herpes simplex virus type 1 (HSV-1) infection is currently debatable. Most, if not all adaptive immune responses to HSV-1 in the cornea are attributed to CD4+ T cells. Thus, we sought to evaluate the role, if any, of CD8+ T cells during corneal infection.
Methods: :
In the current study, we have used a transgenic mouse in which 98% of its CD8+ T cells recognize the immunodominant HSV-1 epitope gB495-505 (gBT-I.1). At the indicated time post infection (pi) with 1,000 plaque forming units of HSV-1 per eye, gBT-I.1 and wild type (WT) mice were compared for leukocyte infiltration and activation by flow cytometry, viral burden by plaque assay, chemokine production by ELISA and real time PCR, and corneal pathology by confocal microscopy and slit lamp examination.
Results: :
gBT-I.1 mice harbored significantly less virus in the cornea proper by day 7 pi, which correlated with an increased influx of HSV-specific CD8+ T cells as well as enhanced interferon-γ production compared to WT controls. The recruitment of CD8+ T cells was linked to CXCR3 expression on circulating CD8+ T cells. Subsequent CD8+ T cell depletion in gBT-I.1 mice resulted in an increase in viral burden compared to isotype-treated controls. Matrix metalloproteinase-9 expression, slit lamp examination, and confocal imaging of blood vessel invasion during acute disease revealed relatively similar corneal pathology between WT and gBT-I.1 mice. However by day 30 pi, WT corneas had drastically more blood and lymphatic vessel genesis than gBT-I.1, where only lymphatic vessel projections into the cornea proper could be appreciated. Isolated cells were then evaluated for vascular endothelial growth factor (VEGF) and identified CD8+ T cells as a source of VEGF-C in gBT-I.1 mice. VEGF-C neutralization in gBT-I.1 mice resulted in a blunting of lymphatic growth following infection.
Conclusions: :
Collectively, these results clearly define a role for CD8+ T cells in viral surveillance of the cornea. CD8+ T cells are also a contributing source of VEGF-C expression during the latent phase of herpetic keratitis resulting in lymphangiogenesis but not hemangiogenesis.
Keywords: herpes simplex virus • cornea: basic science • vascular endothelial growth factor