Exosome secretion by Leishmania infantum modulate the chemotactic behavior and cytokinic expression creating an environment permissive for early infection.

In recent years, several studies demonstrated the role of exosomes in intercellular communications, several Leishmania species belonging to subgenera Leishmania and Viannia have been demonstrated to release exosomes, and their role in parasite-macrophage interactions and in leishmaniasis development has been investigated. However, the release of exosomes by Leishmania infantum has not been studied so far. The aim of this study was to isolate and characterize L. infantum exosomes, and to investigate the biological activity of these exosomes in macrophage cultures. To this end, exosomes were collected from both amastigote and promastigote L. infantum conditioned medium by ultracentrifugation. Exosomes were then characterized by monitoring the presence of HSP70, HSP83/90 and acetylcholinesterase activity. Moreover, extracellular vesicles-tracking analysis revealed that promastigote and amastigote exosomes had mean diameter of 122 ± 56 nm and 115 ± 65 nm, respectively. Human monocytic cell line U937-derived macrophages treated with promastigote and amastigote exosomes showed an increase in motility and an overproduction of interleukin IL-10 and IL-18 reduction, involved in immune response. Since L. infantum exosomes demonstrated the capacity to modulate the chemotactic behaviour of the cells studied and cytokines production, they could contribute in the disease establishment and may be considered an appropriate candidate for a vaccine therapy in prophylaxis and treatment.