The role of placental exosomes in reproduction.

Cell communication comprises cell-cell contact, soluble mediators and intercellular nanotubes. There is, however, another cell-cell communication by released membrane-bound microvesicles that convey cell-cell contact 'by proxy' transporting signals/packages of information from donor to recipient cells locally and/or at a distance. The nanosized exosomes comprise a specialized type of microvesicles generated within multivesicular bodies (MVB) and released upon MVB fusion with the plasma membrane. Exosomes are produced by a variety of immune, epithelial and tumor cells. Upon contact, exosomes transfer molecules that can render new properties and/or reprogram their recipient cells. Recently, it was discovered that the syncytiotrophoblast constitutively and throughout the pregnancy secretes exosomes. The placenta-derived exosomes are immunosuppressive and carry proteins and RNA molecules that in a redundant way influence a number of mechanisms and promote the fetal allograft survival. In this review, we summarize the current knowledge on the nature of placenta-derived exosomes and discuss their role in pregnancy.