**2. Extracellular vesicles (EVs)**

Extracellular vesicles are nano-sized messengers secreted by all cell types. They consist of a lipid bilayer membrane, proteins, nucleic acids and other biomolecules, *The Role of Extracellular Vesicles in Immunomodulation and Pathogenesis of* Leishmania*… DOI: http://dx.doi.org/10.5772/intechopen.101682*

which together make up the "message" to be conveyed to other cells. The composition of molecules that control the message differs in different cell types, and under different physiological conditions.

EVs' size ranges between 20 and 1000 nm in diameter, and they can be produced through a variety of different biogenesis pathways, with different physical and structural properties. Budding from the cellular membrane generally forms larger vesicles called microvesicles – however, this biogenesis pathway may also form vesicles that are smaller than 200 nm. Small extracellular vesicles can also be formed through the invagination of the cellular membrane into endosomes, collected and secreted together in multivesicular bodies (MVBs), or so-named exosomes [55]. However, it should be noted that most of the EV isolation methods used today cannot separate exosomes from small EVs formed through membrane budding, resulting in mixed populations of EVs in the working medium. The full extent of the biogenesis pathways remains to be unknown to researchers, and this is even more apparent in nonmammalian EVs [12]. However, evidence indicates that parasites secrete EVs through both the membrane budding and the multivesicular body pathways, mimicking the previously studied EV secretion pathways of mammalian cells [45].
