Trafficking of Leishmania donovani promastigotes in non-lytic compartments in neutrophils enables the subsequent transfer of parasites to macrophages

Abstract

SummaryInoculation of Leishmania (L.) spp. promastigotes in the dermis of mammals by blood-feeding sand flies can be accompanied by the rapid recruitment of neutrophils, inflammatory monocytes and dendritic cells. Despite the presence of these lytic leucocytes, parasitism is efficiently established. We show here that Leishmania donovani promastigotes are targeted to two different compartments in neutrophils. The compartments harbouring either damaged or non-damaged parasites were characterized at the electron microscopy (EM) level using the glucose 6-phosphatase cytochemistry and endosomephagosome fusion assays. One involves the contribution of lysosomes leading to the formation of highly lytic compartments where parasites are rapidly degraded. The other is lysosome-independent and involves the contribution of a compartment displaying some features of the endoplasmic reticulum (ER) where parasites are protected from degradation. Using genetically modified parasites, we show that the promastigote surface lipophosphoglycan (LPG) is required to inhibit lysosome fusion and maintain parasites in neutrophil compartments displaying ER features. L. donovani-harbouring neutrophils that eventually enter apoptosis can be phagocytosed by macrophages enabling the stealth entry of parasites into their final replicative host cells. Thus, the ability of L. donovani to avoid trafficking into lysosomesderived compartments in short-lived neutrophils constitutes a key process for the subsequent establishment of long-term parasitism.

Leishmania amazonensispromastigotes induce and are killed by neutrophil extracellular traps

“…The higher NET induction by promastigotes relative to LPG could be explained by other NET-inducing molecules and/or the complex membrane structure of the promastigotes, including the fact that LPG shares domains with other Leishmania membrane molecules, such as acid phosphatase, proteophosphoglycan, and glycosylinositolphospholipids (10), which might contribute to NET formation. Previous reports showed that human neutrophils are able to ingest and kill Leishmania (19), but recent studies described that not all ingested promastigotes are destroyed within these cells (13,20,21). Here, we report that a phagocytosis-independent killing mechanism, mediated by neutrophil NETs, is effective against Leishmania promastigotes, and, as reported for bacteria and fungi (2,3,5), Leishmania are killed by NETs.…”

Infection and Activation of Human Neutrophils with Fluorescent Leishmania infantum

“…Our observation that neutrophil populations exhibit heterogeneous responses to parasites in culture is consistent with observations in vitro and in vivo that PMNs take up, and though they may kill some parasites early in infection [13], they are unable to control Leishmania infection [5,22,23,25]. Our data raise the curious possibility of “silent” parasite uptake by a neutrophil subset.…”

“…Studies examining interactions between PMNs and Leishmania species show that PMNs take up but do not eliminate all internalized parasites [4,25]. We questioned how internalization of L. infantum would alter the PMNs’ activation status and production of microbicidal compounds such as ROS.…”

Myeloid Cell IL-10 Production in Response to Leishmania Involves Inactivation of Glycogen Synthase Kinase-3β Downstream of Phosphatidylinositol-3 Kinase

“…Infection is initiated when motile infectious promastigotes are inoculated into a mammalian host when an infected sandfly takes a blood meal. Subsequently, promastigotes are taken up by granulocytes (1,2) and then monocytes and macrophages where they convert into nonmotile amastigotes inside phagocytic vacuoles. Here, they survive and replicate quite readily, despite the ostensibly hostile environment of the phagolysosome.…”