MMP-9 knockout mice are protected from HSK pathogenesis. Groups of 129 Sv/Ev wild-type (4–5 weeks old) and MMP-9 knockout mice (4–5 weeks old) 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 lesions was scored on a 0 to 5 scale. The mean clinical scores at day 5, 10, 15, and 19 are plotted for all groups. Also, the animals were examined for the extent of angiogenesis as described in Methods. The data are compiled from three independent experiments with seven individual mice in each group. P ≤ 0.05 between wild-type and knockout mice at day 5 and beyond (angiogenic scoring; asterisk) and at day 10 and beyond (HSK lesion severity; double asterisk).