Pentraxin 3 (PTX3) is a called as 'brand-new protein in traditional family' because it belongs with pentraxin family included C-reactive protein(CRP) or serum protein A (SAP), but the clinical papers published explosively in clinical situation in this 3 years. Unlike CRP, PTX3 express in atherosclerotic lesion which involve macrophages, neutrophils, dendritic cells, or smooth muscle cells, predominantly. Interestingly pitavastatin suppress PTX3 gene expression mostly in human endothelial cells among more than 6000 human genes. Therefore, we expect PTX3 to be a new biomarker for inflammatory vascular disease. Recently we developed an ELISA system for the detection of human PTX3 in plasma. Using this system, we demonstrated that PTX3 predicted patients with unstable angina pectoris(UAP). But it remains unclear why levels of PTX3 are increased in patients with acute coronary syndrome (ACS). We collected blood samples directly from the site of plaque rupture in 114 subjects with ACS who underwent PCI with an aspiration catheter. In addition, we performed immunohistochemical analyses on ACS patients' aspirated-thrombi to identify the cellular populations expressing PTX3. From these results, we concluded that infiltrating neutrophils in thrombi represent a diagnostically important source of PTX3 in patients with ACS.