MMP9 and rheumatoid arthritis: According to the decreased concentration of MMP-2 and MMP-9 in culture supernatant, primary RA-FLS were treated with recombination human MMP-2 (6 ng/ml) and/or MMP-9 (12 ng/ml) to restore to the levels detected in control cells, and in combination with artesunate (60 μM) for 24 h.