Destruction of these large vesicles could give rise to smaller vesicles similar to exosomes. Other possible origins include the confluence of smaller vesicles coming from the upper tract (which may explain the actin results we have obtained). However, our findings that these vesicles have a specific protein composition, which is different from the mature sperm and to a large extent from cytoplasmic droplets, and contain proteins that are only present in the cauda region strongly suggest that they are mainly the result of a specific secretion from this region.
Different roles have been suggested for seminal plasma vesicles (prostasomes), like immunosuppression, oxidative protection, and bacterial defense (for reviews, see ). Similar properties have been also suggested for exo-somes, and these diverse roles may reflect the different biological activity of the composing proteins (see Table 2). Both seminal plasma and epididymal vesicles have been suggested to be involved in sperm membrane maturation by transferring proteins, particularly hydrophobic proteins, to the cell under very specific conditions (acidic pH, presence of zinc ).