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: ObjectivesTo examine whether the Fas/Fas ligand system is involved in the pathogenesis of acute myocardial infarction (AMI), we measured the levels of the soluble form of the Fas ligand (sFasL) in the plasma of patients with AMI and stable or unstable angina pectoris (AP).: BackgroundThe Fas ligand (FasL) is rapidly cleaved off by a metalloproteinase from the cell membrane to become a soluble form as a cytokine. Fas is expressed in most cells, including cardiomyocytes, whereas FasL is mainly expressed in inflammatory cells such as macrophages, which are greatly accumulated in unstable plaque.: MethodsThirty patients with AMI, 10 patients with unstable AP, 10 patients with stable AP and 30 control subjects were enrolled in the present study.: ResultsPlasma sFasL levels were significantly elevated on hospital admission in patients with AMI and unstable AP, compared with control subjects. Time-course studies revealed that plasma sFasL levels rapidly decreased within 3 h and then increased again after percutaneous transluminal coronary angioplasty in patients with AMI, but not in patients with stable AP. Importantly, the sFasL levels were higher in the coronary sinus than in the circulation. In addition, in vitro studies showed that the expression of FasL messenger ribonucleic acid was upregulated in mononuclear cells isolated from patients with AMI and that hypoxia stimulated the release of sFasL from isolated mononuclear cells.: ConclusionsThis demonstration of elevated levels of sFasL in patients with AMI and unstable AP suggests that activation of the Fas/FasL system may play a pathogenic role in AMI and acute coronary syndromes. [Copyright &y& Elsevier]