MMP13 and rheumatoid arthritis: In RA, fibroblast-like synoviocytes (FLS), resident cells of the synovial tissue, acquire an aggressive phenotype including hyperproliferation, apoptosis resistance and invasion ability [partly linked to the secretion of matrix metalloproteinases (MMPs) such as MMP-2 and MMP-13 (15, 16)] persisting even after the inflammation has been suppressed (7).