To which extent the diameter of single vesicles and the size distribution of a population of vesicles as determined by TEM reflects the true size and size distribution of vesicles in solution, however, are unknown, because TEM measurements require

sample fixation and dehydration, i.e. processes RG7204 price likely to affect the size and morphology of vesicles. New methodologies such as atomic force microscopy (AFM), nanoparticle tracking analysis (NTA) or resistive pulse sensing (RPS) are capable of detecting single vesicles directly in solution and no fixation or dehydration is required. Thus, these methodologies are more likely to provide information on the real diameter of vesicles. Importantly, development of commonly accepted and acceptable reference materials will be essential, not only to define the original diameter Adriamycin cost and size distribution of EVs, but also to be able to compare results between laboratories. In this review, we will present an overview on the presence and biological relevance of EVs in human body fluids in normal and pathological conditions, and we will provide an overview

on their potential clinical applications, including their use as biomarkers and novel therapeutic agents. As mentioned before, there is no consensus regarding the classification and terminology of different types of EVs.3 Recent evidence suggests that different types of EVs have more similarities than thought previously.[4] and [21] For example, the membranes of EVs are relatively enriched in detergent-resistant membrane domains, also known as lipid rafts, compared to plasma membranes[23], [24], [25] and [26] and there is much overlap

in the density and diameter of EVs.[3] and [4] In fact, even for a single type of vesicle conflicting size ranges have been reported, and there is no consensus on this matter as illustrated in Table 1. The size of exosomes is below 100 nm in most references, but the size of the MVs (also called microparticles) varies widely between investigators. Sclareol Furthermore, supposedly different types of EVs may share common membrane proteins. For example, P-Selectin (CD62p), which is exposed on activated platelets and platelet derived-MVs (PMVs), is also exposed on platelet-derived exosomes.20 In addition, it cannot be excluded that many unique characteristics that have been ascribed to an isolated and purified population of vesicles, such as the presence of a particular mRNA or miRNA in exosomes, are due to contamination by larger vesicles, vice versa. Thus, extreme care is necessary when terms for specific subsets of vesicles are being used. Cells release EVs upon activation and during apoptosis in vitro, i.e. under conditions of cell stress.[10], [11], [25], [27], [28], [29] and [30] Under cell stress MVs and exosomes are being formed (Fig. 1).