Small Extracellular Vesicles
An operational category generally based on physical properties or separation conditions, rather than proven intracellular origin.
CELLMEX Scientific Library
Extracellular Vesicles
Extracellular vesicles are heterogeneous, membrane-enclosed particles released by cells. They participate in intercellular communication by carrying proteins, lipids, nucleic acids and other molecular components between cells and tissues.
Scientific Definition
A heterogeneous system of cell-released particles
Extracellular vesicles, abbreviated as EVs, are lipid-bilayer-enclosed particles released from cells into the surrounding environment.
EVs do not contain a functional nucleus and cannot reproduce independently. They may transport molecular material from an originating cell to neighbouring or distant recipient cells.
EV populations differ in size, density, composition, cellular origin and route of formation. A biological sample may therefore contain several overlapping vesicle populations together with soluble proteins and non-vesicular particles.
Exosomes
EVs associated with formation inside endosomal multivesicular bodies and subsequent release at the plasma membrane.
Plasma-Membrane-Derived EVs
Vesicles released through outward budding or shedding from the plasma membrane.
Vesicle Biogenesis
Extracellular vesicles arise through different cellular pathways
The term extracellular vesicle describes the released particle. It does not, by itself, identify the exact pathway through which that particle was formed.
Endosomal Pathway
Intraluminal vesicles form inside multivesicular endosomal compartments. Fusion of these compartments with the plasma membrane releases the vesicles into the extracellular space.
Plasma-Membrane Budding
Vesicles may form through outward deformation and release directly from the cell's plasma membrane.
Apoptotic and Stress-Related Release
Cells undergoing apoptosis, activation or stress may release additional vesicle populations with distinct composition and biological significance.
Molecular Composition
EV cargo reflects the originating cell and its environment
Vesicle composition is influenced by cell type, physiological state, disease, culture conditions, environmental signals and the mechanism of vesicle formation.
Proteins
EVs may carry membrane-associated and internal proteins related to their cellular source and biological function.
- Membrane receptors
- Adhesion proteins
- Enzymes
- Cytoskeletal proteins
- Signalling proteins
Lipids
The lipid bilayer provides structural protection and may itself participate in recipient-cell recognition and signalling.
- Phospholipids
- Cholesterol
- Sphingolipids
- Bioactive lipid mediators
Nucleic Acids
EV preparations may contain several classes of RNA and, in some preparations, DNA-associated material.
- Messenger RNA
- MicroRNA
- Other non-coding RNA
- DNA-associated material
Metabolites and Other Components
Vesicles may also contain metabolites, ions and other molecules reflecting cellular metabolism and environmental conditions.
Intercellular Communication
From vesicle release to recipient-cell response
EV interaction does not always require complete delivery of molecular cargo into the recipient-cell cytoplasm. Surface binding and endosomal signalling may also contribute to biological effects.
Vesicle Release
The originating cell releases heterogeneous vesicles into tissue, culture medium or a biological fluid.
Distribution
Vesicles move through the surrounding environment according to their physical and molecular properties.
Surface Recognition
Vesicle-associated molecules may bind to receptors or other structures on recipient cells.
Uptake or Membrane Interaction
EVs may undergo endocytosis, membrane fusion or other forms of cellular interaction.
Biological Response
Recipient-cell signalling, gene expression, metabolism or functional behaviour may be altered.
Separation and Enrichment
Processing method defines the resulting preparation
EV preparations are generally enriched rather than isolated as one absolutely pure and uniform population. Each method has different strengths and limitations.
Differential Centrifugation
Sequential centrifugal forces remove cells, debris and selected particle populations according to sedimentation behaviour.
Ultracentrifugation
High centrifugal force can concentrate vesicles, but may also recover protein aggregates and other particles.
Size-Exclusion Chromatography
Separation according to hydrodynamic size can help distinguish vesicles from smaller soluble components.
Filtration
Membrane systems may remove larger material, concentrate samples or support size-based processing.
Density-Based Separation
Density gradients may improve separation of EVs from selected non-vesicular components.
Affinity and Combined Methods
Surface-binding methods or combined processing strategies may enrich selected vesicle subpopulations.
Scientific Characterisation
No single analytical method is sufficient
A credible EV study combines complementary analyses of particle properties, composition, contaminants and biological function.
Particle Concentration and Size
Particle-tracking, resistive-pulse or related methods may estimate concentration and size distribution.
Morphology
Electron microscopy and other imaging methods may demonstrate membrane-enclosed vesicular structures.
EV-Associated Components
Protein or lipid analysis may identify selected characteristics expected within the preparation.
Non-Vesicular Contaminants
Analysis should consider soluble proteins, lipoproteins, media components and protein aggregates.
Source and Process Controls
Source cells, culture conditions, collection, pre-processing, separation and storage should be documented.
Functional Assessment
Fit-for-purpose assays should measure a biological activity relevant to the proposed mechanism and intended application.
Translational Research
Principal areas of EV investigation
EV research includes physiological communication, disease mechanisms, diagnostic biomarkers, engineered delivery systems and cell-free regenerative medicine.
Regenerative Signalling
Investigation of EV-mediated effects on cellular survival, angiogenesis, tissue response and local repair mechanisms.
Immune Regulation
Study of vesicle interactions with macrophages, lymphocytes, dendritic cells and inflammatory pathways.
Neurological Biology
Evaluation of EV signalling within the nervous system and interactions with specialised biological barriers.
Biomarker Development
Analysis of body-fluid EVs as potential indicators of disease, biological state or treatment response.
Therapeutic Delivery
Engineering vesicles or vesicle-associated systems to transport selected therapeutic molecules.
Manufacturing Science
Development of reproducible source-cell, production, purification, formulation, storage and potency methods.
Clinical and scientific qualification
Extracellular vesicles, small extracellular vesicles and exosomes should not be treated as interchangeable terms unless the evidence supports the specific classification being used.
EV preparations produced by different laboratories cannot be assumed to be equivalent. Source cells, culture conditions, collection, separation, concentration, formulation and storage can materially alter the final preparation.
Biological effects observed in cell culture or animal models do not independently establish safety or effectiveness in human patients.
EV-based interventions should not be represented as established cures or guaranteed methods of tissue regeneration without appropriate product-specific clinical evidence.
The CELLMEX Approach
EV development begins with source and process control
Defined Source Cells
Cell identity, tissue origin, passage number and culture history should be documented.
Controlled Production
Culture medium, conditioning period, cellular density and environmental variables should be defined.
Appropriate Fractionation
Separation methods should reflect the intended vesicle population, purity requirements and downstream use.
Integrated Characterisation
Particle, morphology, compositional, contaminant and functional data should be interpreted together.
Selected Scientific References
Extracellular-vesicle biology and research standards
Welsh JA, et al. Minimal information for studies of extracellular vesicles: MISEV2023.
Journal of Extracellular Vesicles. 2024;13:e12404.
View publicationThéry C, et al. Minimal information for studies of extracellular vesicles 2018: MISEV2018.
Journal of Extracellular Vesicles. 2018;7(1):1535750.
View publicationvan Niel G, D'Angelo G, Raposo G. Shedding Light on the Cell Biology of Extracellular Vesicles.
Nature Reviews Molecular Cell Biology. 2018;19:213–228.
View publicationYáñez-Mó M, et al. Biological properties of extracellular vesicles and their physiological functions.
Journal of Extracellular Vesicles. 2015;4:27066.
View publicationZaborowski MP, et al. Extracellular Vesicles: Composition, Biological Relevance, and Methods of Study.
BioScience. 2015;65(8):783–797.
View publication
Scientific Information
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