Discussion

There is increasing evidence of the release of extracellular vesicles (EVs) in parasitic diseases, with roles both in parasite-parasite inter-communication as well as in parasite-host interactions. EVs are known to transfer molecules from one cell to another via membrane vesicle trafficking, thus explaining the broad array of functional activities attributable to them. There are many subclasses of EVs, with current research interest focusing principally on exosomes. We have described a protocol for the isolation of adult Schistosoma mansoni-derived exosomes by differential centrifugation, followed by sedimentation on sucrose density gradients. We have shown that S. mansoni releases EVs in vitro and characterized their protein and miRNA content. Using quantitative PCR, we have been able to detect some of the most abundant S. mansoni exosomal miRNAs in infected mouse serum, suggesting the release of these vesicles in vivo.

Here, using lectin microarrays, we have identified several lectins that exhibit strong association with S.m. EVs, including SNA-II, DSA, LEL, Calsepa, NPA, GNA, HHA, WGA, SNA-I, PHA-E, RCA-I and CAA. These results indicate the presence of several glycan structures on these vesicles. In order to identify glycosylated exosomal proteins, we have performed mass spectrometry analysis on glycoproteins segregated using a lectin-bead approach with DSA, RCA-I and SNA-I. Moreover, in an effort to identify worm structure(s) responsible for the release of EVs, we have performed lectin histochemistry assays on whole adult worms.

We are currently working to profile glycans at the surface of S.m. exosomes and to identify the glycosylated exosomal proteins, which is of great interest as glycoproteins secreted by helminth parasites are immunogenic and represent appealing components of vaccine preparations. A better understanding of the vesicles secreted by the parasite could lead to the identification of novel biomarkers for the development of superior results diagnostic tools as well as new targets for the potential prevention and therapy of schistosomiasis.