MMP-9 is present in cornea during HSK, and MMP-9 activities are highly correlated with HSK lesion severity. Groups of animals were infected with 10⁶ PFU of HSV-1 RE on their scarified corneas. The mice were examined clinically by slit-lamp microscopy, and the severity of lesion was scored on a 0 to 5 scale. At day 2 after infection, animals were sacrificed, and corneas were excised and pooled from six eyes and homogenized. The concentrations of protein were measured by the Bradford method. Corneal extract samples (20 μg/lane) were analyzed by gelatin zymography. Numbers above the gel represent days after infection. High MMP-9 activities were measured at day 2, 15, 18, and 20 after infection. Data represent the results of a single experiment, which was one of three with similar results.