Letter to the Editor: Intravital imaging of the association between intravascular neutrophil extracellular traps and microvascular obstruction using multiphoton microscopy.

TO THE EDITOR: We read with great interest, in the American Journal of Physiology-Heart and Circulatory Physiology, the article by Ge and colleagues (3) regarding neutrophil extracellular trap (NET)-induced myocardial no-reflow in ischemiareperfusion (I/R) injury. The authors demonstrated that NET formation was detected in I/R-challenged myocardium of animal model, and the combination treatment of DNase I and recombinant tissue-type plasminogen activator (rt-PA) is synergistically more effective than DNase I or rt-PA alone regarding I/R-induced ischemic region, infarct size, and left ventricular remodeling. Since NETs have been reported to mediate microvascular thrombosis (1, 2), they concluded that the combination of DNase I (targeting NETs) and rt-PA (targeting fibrin) could reduce NET-mediated microcirculation obstruction and improve coronary artery patency. However, they did not clearly show either intravascular NETs in rat myocardium or decreased NET-mediated microvascular thrombosis. We recently reported the association between intravascular NETs and tissue microcirculation in a murine sepsis model by intravital imaging using two photon laser-scanning microscopy (4). We clearly observed two forms of intravascular NETs: circulating cell-free NETs that were released away from neutrophils and anchored NETs that were anchored to neutrophils in vivo real time. In lipopolysaccharide-induced sepsis model, circulating cell-free NETs interacted with platelets or vascular endothelium. Cell-free NETs appeared to be associated with platelet thrombus formation, the formation of platelet aggregates or leukocyte-platelet aggregates in both arterioles and venules of the intestine. Furthermore, intravascular NETs were degraded by intravenous injection of DNase I with a decrease in both its size and shape. Our observations support the findings of Ge and colleagues (3), which may indicate the reduction of NET-mediated microcirculation obstruction by DNase I and subsequent improvement of coronary artery patency. The work of Ge and colleagues (3) is enough worthy of praise as it is. If added, intravital imaging of improved NETmediated thrombotic obstruction by DNase I plus rt-PA will directly prove its significance as treatment of myocardial I/R injury.