Infection of Human Neutrophils With Leishmania infantum or Leishmania major Strains Triggers Activation and Differential Cytokines Release

Abstract

Leishmaniases are neglected diseases, caused by intracellular protozoan parasites of the <i>Leishmania</i> (<i>L</i>.) genus. Although the principal host cells of the parasites are macrophages, neutrophils are the first cells rapidly recruited to the site of parasites inoculation, where they play an important role in the early recognition and elimination of the parasites. The nature of early interactions between neutrophils and <i>Leishmania</i> could influence the outcome of infection. Herein we aimed to evaluate whether different <i>Leishmania</i> strains, responsible for distinct clinical manifestations, could influence <i>ex vivo</i> functional activity of neutrophils. Human polymorphonuclear leukocytes were isolated from 14 healthy volunteers and the <i>ex vivo</i> infection of these cells was done with two <i>L. infantum</i> and one <i>L. major</i> strains. Infection parameters were determined and neutrophils activation was assessed by oxidative burst, degranulation, DNA release and apoptosis; cytokine production was measured by a multiplex flow cytometry analysis. Intracellular amastigotes were rescued to determine <i>Leishmania</i> strains survival. The results showed that <i>L. infantum</i> and <i>L. major</i> promastigotes similarly infected the neutrophils. Oxidative burst, neutrophil elastase, myeloperoxidase activity and apoptosis were significantly increased in infected neutrophils but with no differences between strains. The <i>L. infantum</i>-infected neutrophils induced more DNA release than those infected by <i>L. major</i>. Furthermore, <i>Leishmania</i> strains induced high amounts of IL-8 and stimulated the production of IL-1β, TNF-α, and TGF-β by human neutrophils. We observed that only one strain promoted IL-6 release by these neutrophils. The production of TNF-α was also differently induced by the parasites strains. All these results demonstrate that <i>L. infantum</i> and <i>L. major</i> strains were able to induce globally a similar <i>ex vivo</i> activation and apoptosis of neutrophils; however, they differentially triggered cytokines release from these cells. In addition, rescue of intracellular parasites indicated different survival rates further emphasizing on the influence of parasite strains within a species on the fate of infection.