Background and Purpose - We studied matrix metalloproteinases (MMP) 2, 8, and 9 and extracellular matrix metalloproteinase inducer (EMMPRIN) levels in relation to carotid atherosclerotic plaque characteristics. Methods - Carotid atherosclerotic plaques (n=150) were stained and analyzed for the presence of collagen, smooth muscle cell (SMC), and macrophages. Adjacent segments were used to isolate total protein to assess MMP-2 and MMP-9 activities and gelatin breakdown, MMP-8 activity, and EMMPRIN levels. Results - Macrophage-rich lesions revealed higher MMP-8 and MMP-9 activities, whereas SMC-rich lesions showed higher MMP-2 activity. The levels of less glycosylated EMMPRIN-45kD were higher in SMC-rich lesions and lower in macrophage-rich plaques. EMMPRIN-45kD was associated with MMP-2 levels, whereas EMMPRIN-58kD was related to MMP-9 levels. Conclusions - MMP-2, MMP-8, and MMP-9 activities differed among carotid plaque phenotypes. Different EMMPRIN glycosylation forms are associated with either MMP-2 or MMP-9 activity, which suggests that EMMPRIN glycosylation may play a role in MMP regulation and plaque destabilization. © 2005 American Heart Association, Inc. Chemicals / CAS: collagen, 9007-34-5; gelatin, 9000-70-8; gelatinase A, 146480-35-5; gelatinase B, 146480-36-6; Antigens, CD147, 136894-56-9; Collagen, 9007-34-5; Matrix Metalloproteinase 2, EC 3.4.24.24; Matrix Metalloproteinase 8, EC 3.4.24.34; Matrix Metalloproteinase 9, EC 3.4.24.35