MMP9 and multiple sclerosis: In addition, in human multiple sclerosis , MMP-9 activity in the cerebrospinal fluid (CSF) is a marker of disease progression, and the use of injectable probes in molecular imaging has confirmed MMP-2/MMP-9 activity as an early marker of leukocyte infiltration into the brain parenchyma—to date, the only specific marker of an ongoing neuroinflammation (8).