Enumeration and phenotyping of circulating microvesicles by flow cytometry and nanoparticle tracking analysis: Plasma versus serum.

Introduction: Microvesicles (MVs) are bioactive, submicron-sized (0.01-1000 nm) membrane vesicles released from various types of cells under normal physiological and pathophysiological conditions. MVs have emerged as important mediators of cell-to-cell communication in a diverse range of normal and pathological processes. MVs have been recognized as potential biomarkers in coagulation, inflammation, and cancer. However, for clinical use, minimizing factors which could affect enumeration and phenotypic characterization of MVs during pre-analytical steps is crucial. In this study, we used flow cytometry and nanoparticle tracking analysis (NTA) to investigate the impact of blood collection using with and without anticoagulant on the number and phenotype of MVs in blood samples.

Methods: Blood from 30 healthy volunteers was collected by venipuncture into 3.2% sodium citrate and clot activator tubes. MV subpopulations and their concentrations were investigated using flow cytometry and NTA. MV morphology was examined by transmission electron microscopy.

Results: Results showed that the concentration of MVs was significantly lower in serum than in plasma and that CD41 MV, CD41 /CD62P MV, CD45 MV, and CD142 MV levels from serum were significantly lower than those from plasma, whereas no significant differences in Annexin V (Anx V) MV, CD235a MV, and CD144 MV levels were found. Interestingly, serum MVs had a higher proportion of small-sized MVs and lower proportion of large-sized MVs than did plasma MVs.

Conclusion: Although plasma samples are commonly used, our results suggest that serum can also be used in enumeration of MVs, but care must be taken if coagulation is an aspect of the research.