On the presence and immunoregulatory functions of extracellular micro RNA s in the trematode Fasciola hepatica

Summary Liver flukes represent a paraphyletic group of endoparasitic flatworms that significantly affect man either indirectly due to economic damage on livestock or directly as pathogens. A range of studies have focussed on how these macroscopic organisms can evade the immune system and live inside a hostile environment such as the mammalian liver and bile ducts. Recently, micro RNA s, a class of short noncoding gene regulators, have been proposed as likely candidates to play roles in this scenario. Micro RNA s (mi RNA s) are key players in development and pathogenicity and are highly conserved between metazoans: identical mi RNA s can be found in flatworms and mammalians. Interestingly, mi RNA s are enriched in extracellular vesicles ( EV s) which are secreted by most cells. EV s constitute an important mode of parasite/host interaction, and recent data illustrate that mi RNA s play a vital part. We have demonstrated the presence of mi RNA s in the EV s of the trematode species Dicrocoelium dendriticum and Fasciola hepatica (Fhe) and identified potential immune‐regulatory miRNAs with targets in the host. After our initial identification of miRNAs expressed by F. hepatica , an assembled genome and additional miRNA data became available. This has enabled us to update the known complement of miRNAs in EV s and speculate on potential immune‐regulatory functions that we review here.