MMP9 and meningitis: Another study revealed that cytokines could be used to discriminate between meningitis caused by Streptococcus pneumoniae, Neiserria meningitidis, and Haemophilus influenzae based on levels of interferon gamma (IFN-γ), monocyte chemoattractant protein-1 (MCP-1), and the enzyme matrix metallopeptidase-9 (MMP-9) [31].