MMP9 and rheumatoid arthritis: In separate experiments to determine whether freshly isolated human PBMCs reacted similarly to the U-937 cell line utilized above, HFLS-RA cells were stimulated with MP-SN activated with unmodified or modified FIB antigens and showed analogous increases in mRNA levels for IL-6, MMP-9, and MMP-10 as observed following HFLS-RA cell stimulation with the Mφ-SN (U-937 derived Mφ-SN) (Figure 3A; Supplemental Figure 3A).