Characterization of Microvesicles in Septic Shock Using High-Sensitivity Flow Cytometry

Purpose:Endothelial pathology is considered to play a key role in septic shock. Since endothelial-derived microvesicles (MV) are elevated in various diseases associated with endothelial pathology, they are considered surrogate markers of the endothelial state. By analyzing the signature of circulating MV with high-sensitivity flow cytometry (hsFC), we wanted to test the hypothesis whether endothelial-derived MV are increased in septic shock.Methods:MV in blood from healthy volunteers and patients with septic shock treated in a medical intensive care unit were quantified by hsFC, which has an improved detection limit of approximately 0.3m.Results:Patients with septic shock (n=30) showed 3-fold higher levels of CD31+/CD41- MV (58.5 (26.4-101.2) [median (25th-75th percentile)] vs. 19.5 (12.8-25.4) MV/L; P<0.001) compared with healthy volunteers (n=18). Absolute counts of CD144+, CD62E+, and CD106+ MV, specific for endothelial-derived MV, were low in all groups. The number of CD31+/CD41- MV correlated significantly with leukocyte count (r(s)=0.64; P<0.001). Platelet-derived CD41+ MV were significantly elevated in the group dying within 48h after inclusion (639.1 (321.3-969.7) vs. 221.5 (119.5-456.9) MV/L; P=0.037). Patients dying within 48h had also significantly higher levels of CD31+/CD41-/AnnexinV- MV (51.9 (24.9-259.8) vs. 18.9 (9.7-31) MV/L; P=0.028).Conclusions:Despite an improved detection limit for MV by using hsFC, counts of endothelial-specific MV are unexpectedly low in patients with septic shock. Increased amounts of CD41+ and CD31+/CD41-/AnnexinV- MV indicate release by activated platelets and possibly leukocytes correlating with unfavorable outcome.