Kinetics of immune cell infiltration in vaccinia virus keratitis

PURPOSE. Vaccinia virus keratitis leading to blindness is a severe complication of smallpox vaccination. The clinical manifestations of vaccinia virus keratitis are similar to those of herpes simplex virus keratitis, a well-studied immunopathologic disease. Vaccinia virus keratitis is likely to involve an immunopathologic component, but little is known about the pathogenesis of the disease. The goal of this study was to determine type and kinetics of immune cell infiltration in the cornea during vaccinia virus keratitis. METHODS. Rabbit eyes were trephined and inoculated with 1 × 10⁵ pfu of the Dryvax strain of the vaccinia virus. On days 2, 4, 7, 10, 14, and 28 after infection, the animals were scored for clinical disease and eye sections were stained for B cells, CD4⁺ cells, CD8⁺ cells, and neutrophils. The eyelid, ciliary body, cornea, iris, iridocorneal angle, and choroid were examined. RESULTS. Corneal vaccinia virus challenge resulted in the infiltration of B cells, CD4⁺ cells, CD8⁺ cells, and neutrophils into the cornea and eyelids. Neutrophils were the predominant cell type on days 2 and 3 after infection, whereas CD4⁺ cells were the predominant cell type detected in corneas on days 4 through 10. CD8⁺ cells and B cells peaked on day 10, but at lower levels than CD4⁺ cells and neutrophils. CONCLUSIONS. These results suggest that sequential migration of neutrophils, then CD4⁺ cells, plays an important role in vaccinia virus keratitis.