MMP9 and Stroke: Consistent with the known pattern of peak peripheral leukocyte infiltration after ischemic stroke at 72 hours, the present study showed that CD147 is expressed on astrocytes, endothelial cells and monocytes in the brain at 72 hours after stroke, and may contribute to secondary histological damage via augmented MMP-9 activity, exacerbated BBB damage, and enhanced infiltration of peripheral leukocytes.