MMP9 and stroke disorder: Interestingly, while neutrophil invasion of ischemic brain tissue has been previously shown in stroke patients [58, 67, 68], our histological evidence provides an even stronger relationship between aging and neutrophil counts, co-localized production of extracellular matrix-degrading enzymes (i.e., MMP-9), and increased rates of hemorrhagic bleeding in the brain as a larger cohort was examined.