Abstract
Vaccinia virus (VACV) keratitis is a serious complication following smallpox vaccination and can lead to blindness. The pathological mechanisms involved in ocular VACV infection are poorly understood. Previous studies have used rabbits, but the lack of immune reagents and transgenic or knockout animals makes them less suitable for mechanistic studies. We report that infection of C57BL/6 mice with 1 × 10(7) PFU of vaccinia virus strain WR results in blepharitis, corneal neovascularization, and stromal keratitis. The DryVax strain of VACV was completely attenuated. Infection required corneal scarification and replication-competent virus, and the severity of ocular disease was similar in 4- to 6-week-old and 1-year-old mice. Viral titers peaked at approximately 1 × 10(6) PFU on day 5 postinfection, and virus had not cleared by day 13 postinfection. Neutrophils were found in the peripheral cornea on day 1 after infection and then declined, followed by infiltration of both CD4(+) and CD8(+) T cells, which remained peripheral throughout the infection. Blood vessel growth extended 2 to 5 mm into the cornea from the limbus. Infection of CD4(-/-), CD8(-/-), or antibody-depleted mice resulted in similar disease severity and corneal clouding, indicating that both T-cell subsets were involved in the immunopathological response. Depletion of both CD4(+) and CD8(+) T cells resulted in significantly more severe disease and failure to clear the virus. On the basis of our results, the pathology of VACV keratitis is significantly different from that of herpes simplex virus keratitis. Further studies are likely to reveal novel information regarding virulence and immune responses to viral ocular infection.