MMP9 and infectious disease: In addition, in infectious diseases or sepsis, serum levels of infection indicators such as procalcitonin (PCT), heparin-binding protein (HBP), and matrix metalloproteinase-9 (MMP-9) are significantly increased [8,9], but the value of changes in PCT, HBP, and MMP-9 levels in CSF for the diagnosis of intracranial infections remains to be investigated.