Leishmania donovanimetacyclic promastigotes impair phagosome properties in inflammatory monocytes

Leishmaniasis, a debilitating disease with clinical manifestations ranging from self-healing ulcers to life-threatening visceral pathologies, is caused by protozoan parasites of the Leishmania genus. These professional vacuolar pathogens are transmitted by infected sand flies to mammalian hosts as metacyclic promastigotes and are rapidly internalized by various phagocyte populations. Classical monocytes are among the first myeloid cells to migrate to infection sites. Recent evidence shows that recruitment of these cells contributes to parasite burden and to the establishment of chronic disease. However, the nature of Leishmania -inflammatory monocyte interactions during the early stages of host infection has not been well investigated. Here, we aimed to assess the impact of Leishmania donovani metacyclic promastigotes on antimicrobial responses within these cells. Our data showed that inflammatory monocytes were readily colonized by L. donovani metacyclic promastigotes, while infection with Escherichia coli was efficiently cleared. Upon internalization, metacyclic promastigotes inhibited superoxide production at the parasitophorous vacuole (PV) through a mechanism involving exclusion of NADPH oxidase subunits gp91 phox and p47 phox from the PV membrane. Moreover, we observed that unlike phagosomes enclosing zymosan particles, vacuoles containing parasites acidified poorly. Interestingly, whereas the parasite surface coat virulence glycolipid lipophosphoglycan was responsible for the inhibition of PV acidification, impairement of the NADPH oxidase assembly was independent of lipophosphoglycan and of the metalloprotease GP63. Collectively, these observations indicate that permissiveness of inflammatory monocytes to L. donovani may thus be related to the ability of this parasite to impair the microbicidal properties of phagosomes.