MMP1 and rheumatoid arthritis: Stimulation of RA FLS with TNF-α (100 ng/mL) for 24 h resulted in a 2.5-, 2-, 2.3-, and 1.8-fold induction of IL-6, IL-8, MMP-1, and MMP-3 production, respectively, compared to that in the control group, when measured in culture media using ELISA (Fig 3A–3D).