Endothelial Microparticle Binding to Neutrophils Is an Important Determinant of Neutrophil Activation In Vivo in Different Clinical Conditions

Abstract number: P1763

Chirinos^1,2 JA, Castrellon¹ A, Soriano³ AO, Arteaga¹ R, Heresi¹ GA, Velásquez¹ H, Jy² W, Jiménez² JJ, Horstman² LL, Ahn² E, Ahn² YS

^1,21Divisions of Cardiology, Critical Care, and Internal Medicine, Department of Medicine, University of Miami School of Medicine. Miami, FL, USA ¹¹Divisions of Cardiology, Critical Care, and Internal Medicine, Department of Medicine, University of Miami School of Medicine. Miami, FL, USA ²²Wallace H. Coulter Platelet Laboratory, Division of Hematology/Oncology, University of Miami School of Medicine. Miami, FL, USA ³³Division of Medical Oncology, MD Anderson Cancer Center, Houston, TX, USA

Background:  In vitro studies have shown that microparticles released from endothelial cells bind and activate neutrophils. We examined this phenomenon in vivo by analyzing the correlation between levels of endothelial microparticles (EMP) bound to neutrophils (EMP-neutrophil conjugates) and neutrophil activation in different conditions.

Methods:  We studied a total of 190 patients with atrial fibrillation (n= 48), acute venous thromboembolism (n= 25), sepsis (n= 35), metabolic syndrome (n= 50) and normal controls (n= 32). Using flow cytometry, we measured neutrophil expression of activation marker CD11b and 2 different populations of EMP-neutrophil conjugates. Bitmapping by forward- and side-scatter gating was used to identify neutrophils; EMP62E-neutrophil conjugates and EMP54-neutrophil conjugates were measured based on the detection of E-selectin (CD62E) or CD54, respectively, coexpressed with CD45 in neutrophils.

Results:  CD11b expression consistently and significantly correlated with the levels of EMP62E-neutrophil conjugates. This finding was present in normal controls (r= 0.86; P < 0.0001), patients with the metabolic syndrome (r= 0.56; P < 0.0001), sepsis (r= 0.50; P= 0.003), atrial fibrillation (r= 0.42; P= 0.003) and acute venous thromboembolism (r= 0.46; P= 0.02). In contrast, a correlation between EMP54-neutrophil conjugates and neutrophil activation was not found in any of the populations studied.

Conclusions:  EMP62E-neutrophil conjugates strongly correlate with neutrophil activation in normal adults, as well as in several pro-inflammatory and pro-thrombotic disease states. Our results combined with prior in vitro studies suggest that EMP62E binding to neutrophils is an important determinant of neutrophil activation in vivo. In contrast, binding of EMP54 to neutrophils does not seem to regulate neutrophil activation. These findings also support the concept that different species of endothelial microparticles have different biologic roles.