MMP9 and rheumatoid arthritis: It is well known that these pathways are associated with the production and activity of numerous destructive and inflammatory mediators including the cytokines, IL-1, IL-17, IL-6, IFN-γ, and matrix-degrading enzymes, MMP-1, MMP-3 and MMP-9, all of which play a role in RA and were identified in the IPA network.