First, CD147 expression increases on infiltrating monocytes, and co-localizes with astrocytes and endothelial cells at 72 hours after stroke; secondly, MMP-9 activity is increased in microglia at 72 hours after stroke without concurrent up-regulation of CD147 expression; thirdly, CD147 blockade decreases expression and activity of MMP-9; fourthly, inhibition of CD147 is neuroprotective in both young and aged mice and reduced hemorrhagic transformation in aged mice. The gene discussed is MMP9; the disease is Stroke.