Circulating platelet-progenitor cell coaggregate formation is increased in patients with acute coronary syndromes and augments recruitment of CD34+ cells in the ischaemic microcirculation

The aim of the present study was to evaluate the levels of platelet interaction with circulating CD34 cells in patients with stable angina pectoris (SAP) and acute coronary syndromes (ACS) and to study the functional consequence of coaggregates formation in vitro and in vivo. Platelet binding to circulating progenitor cells was defined by the presence of the platelet-specific marker glycoprotein Ib (CD42b) on the surface of CD34 cells using flow cytometry. The percentage of CD34/CD42b cell coaggregates was increased in patients with ACS (n 162), and especially in patients with ST-elevation myocardial infarction (STEMI) (n 44), compared with patients with SAP (n 116; P 0.001). In the ANCOVA analysis, platelet/CD34 cell coaggregates were independently increased in ACS after adjustment for possible confounders. In a subgroup of our cohort, we also evaluated the levels of CD34/CD133/CD42b cell coaggregates, which were also significantly increased in ACS, and especially in STEMI (P 0.05). Platelet/CD34 cell coaggregates formation correlated with platelet activation (P 0.001). In a prospective pilot study of patients with AMI (n 40) using cardiac MRI, patients with increased baseline platelet/CD34 cell coaggregates presented with a less myocardial infarct size and better left ventricular function at a 3-month follow-up compared with patients with lower coaggregates (P 0.05 for all). The adhesion of platelet/CD34 cell coaggregates onto the extracellular matrix and to endothelial monolayer was enhanced compared with CD34 under high shear rates in vitro (P 0.05) and within the microcirculation in mice after ischaemia/reperfusion injury as assessed by intravital microscopy (P 0.05). These findings imply that circulating platelet/CD34 cell coaggregate levels are increased in ACS, especially in STEMI, which may be a novel mechanism of domiciliation of CD34 progenitor cells to the injured microvasculature after acute myocardial infarction.