Mast Cells Contribute to the Innate Defense Against Corneal HSV-1 Infection

Abstract

Purpose: The contribution of mast cells (MC) to corneal defense against herpes simplex virus type 1 (HSV-1) infection is currently unknown. Due to their proximity to the cornea, we hypothesized MC influence the host immune response to acute HSV-1 infection.

Methods: Wild type (WT) and MC-deficient (Kit^W-sh) mice were infected with 1000 plaque forming units of HSV-1 per eye following corneal scarification and compared at 24-48 hours post infection (pi) for corneal edema by pachymetry and viral titer by plaque assay. The immune response to HSV-1 was analyzed by flow cytometry, ELISA, Luminex-based arrays and real time PCR to phenotypically characterize infiltrating immune cells and measure contributing soluble factors at the mRNA and protein level. Corneolimbal button whole mounts were imaged by epifluorescent and confocal microscopy. Neutrophils (PMN) were isolated from infected corneas by immunomagnetic separation for HSV-1 lytic gene detection and adoptive transfer.

Results: Tissue-resident MC circumscribe the cornea in close proximity to the limbal vasculature of WT but not Kit^W-sh mice and undergo degranulation following corneal infection. Corneas from Kit^W-sh mice were significantly more edematous throughout the first 48 hours pi commensurate with a significant increase in infiltrating PMN and viral titer at 24 and 48 hours pi, respectively. There were modest changes in some chemokines expressed in the cornea comparing WT to Kit^W-sh mice but no significant changes in other soluble factors screened at the RNA or protein levels. Furthermore, we observed PMN colocalize with HSV-1 antigen in lesions of infected corneas in both WT and Kit^W-sh mice. In addition, the HSV-1 lytic gene thymidine kinase was expressed in PMN isolated from corneas of infected mice. Viral sentinel CD118^-/- mice deficient in the type I interferon receptor succumbed to HSV-1 infection following intravenous adoptive transfer of PMN isolated from infected corneas.

Conclusions: Collectively, these results provide a striking novel insight to the viral surveillance and pathogenesis of corneal HSV-1 infection. We have demonstrated that MC are a contributory resident immune cell population that conditions the innate response to insults in the cornea. We have also shown that PMN, which have historically been considered beneficial phagocytes, contribute to the pathogenesis of HSV-1 infection by facilitating viral replication and dissemination.

Keywords: 545 herpes simplex virus • 480 cornea: basic science • 557 inflammation