Extracellular vesicles from Leishmania (Leishmania) infantum contribute to stimulate the immune response and immunosuppression in hosts with visceral leishmaniasis

Abstract

Visceral leishmaniasis (VL) is a chronic systemic disease. In Brazil this infection is caused by Leishmania (Leishmania) infantum. Extracellular vesicles (EVs) released by Leishmania species have different functions like modulation of host immune system, inflammatory response, among others. This study evaluated the participation of EVs from L. (L.) infantum (Leish-EVs) in stimulation of the humoral and cellular immune responses of hosts with VL. Promastigotes were cultivated in 199 medium and, in the log phase of growth, they were centrifuged, washed, resuspended in RPMI medium and incubated for 2 to 24h, at 25ºC or 37°C to release Leish-EVs. This dynamic was evaluated by transmission (TEM) and scanning (SEM) electron microscopies, as well as nanoparticle tracking analysis (NTA). The results suggested that parasite penetration in mammal macrophages requires more Leish-EVs than those living in insect vectors, since promastigotes incubated at 37°C released more Leish-EVs than those incubated at 25ºC. In comparison to the control group, infected THP-1 cells produced a significantly higher concentration of EVs (THP-1 cells-EVs). Similar results were obtained when THP-1 cells were treated with Leish-EVs or a crude Leishmania antigen. These data suggest that the concentration of host-EVs-Can distinguish between infected and uninfected cells. THP-1 cells treated with Leish-EVs expressed more IL-12 than control THP-1 cells, but were unable to produce IFN-γ. These same cells produced IL-10, which inhibited TNF and IL-6. Equally, THP-1 cells treated with Leish-EVs up-expressed miR-21-5p and miR-146a-5p. These findings indicate that the increased levels of miR-21-5p and miR-146a-5p observed in Leish-EVs-treated-THP-1 cells lead to immunosuppression and the secretion of pro-inflammatory cytokines.