Placental exosome-mediated immune protection of the fetus: feeling groovy in a cloud of exosomes

Abstract

Exosomes are nanosized membrane-bound microvesicles that originate from the endosomal compartment and convey cell–cell contact ‘by proxy’, transporting signals/packages of information between donor and recipient cells locally and/or at a distance. 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 the recipient cells. Recently, it was discovered that the syncytiotrophoblast of human placenta continuously and constitutively secretes exosomes throughout pregnancy. These exosomes, delivered directly in the maternal blood surrounding the chorionic villi of the placenta, are immunosuppressive and pluripotent carrying proteins, mRNA and miRNA that can influence a number of biologic mechanisms and promote the fetal allograft survival. The current knowledge regarding placental exosomes and their role in pregnancy is summarized and discussed in this article.