Leishmania (Leishmania) Infantum Living in Nature Secretes a Higher Concentration of Extracellular Vesicles,...

Visceral leishmaniasis (VL) is a chronic systemic disease that, without proper treatment, can be fatal. Extracellular vesicles released by Leishmania species (Leish-EVs) perform various functions, including modulation of the host's immune system and inflammatory responses. This study investigated whether Leish-EVs produced by circulating strains of Leishmania (Leishmania) infantum exhibited the same pattern of cytokine stimulation and modulation of inflammatory and pro-inflammatory responses as those produced by a standard strain maintained for many years in different laboratories. The assays were performed using Leish-EVs released by promastigotes of the two L. (L.) infantum strains. The Standard strain was L. (L.) infantum (MHOM/BR/1972/LD), maintained under laboratory conditions, while the Natural strain was L. (L.) infantum recently isolated from a dog living in an endemic region of São Paulo State, Brazil. Both strains were cultivated in 199 medium and, during the logarithmic growth phase, promastigotes were prepared for excretion of Leish-EVs according to previously established protocols. The Natural strain, when compared with the Standard strain, produced a higher concentration of Leish-EVs, which stimulated THP-1 cells to release large amounts of THP-1-EVs (EVs produced by THP-1 cells). In addition, stimulation of THP-1 cells with Leish-EVs induced high expression of miR-21-5p and miR-146a-5p, as well as cytokines IL-10, IL-12, and particularly TGF-β. These findings suggest that Leish-EVs released by strains living in nature have greater immunomodulatory potential than those produced by strains maintained in laboratories, impacting both miRNA regulation and cytokine expression.