MMP9 and myocardial infarction: Coincidently, a previous report showed that release of neutrophil-related matrix metalloproteinase-9 (MMP-9), a collagen-degrading enzyme, was increased in CEACAM1-deficient mice with ischemic stroke51, while it has been reported that MMP-2/9 can attenuate post-MI fibrosis by preventing the accumulation of collagen52.