MMP8 and rheumatoid arthritis: Amongst the 32 proteases associated with urinary fragments of RA-related peptides, the potential predicted activities of kallikrein 6 (KLK6) and plasminogen (PLG) were up-regulated, whereas the associated activities of matrix metalloproteinase 3 (MMP3), MMP8, MMP9 and MMP13 and cathepsin B were down-regulated in cases compared to controls (Table 4).