Leishmania amazonensispromastigotes induce and are killed by neutrophil extracellular traps

Abstract

Neutrophils are short-lived leukocytes that die by apoptosis, necrosis, and NETosis. Upon death by NETosis, neutrophils release fibrous traps of DNA, histones, and granule proteins named neutrophil extracellular traps (NETs), which can kill bacteria and fungi. Inoculation of the protozoan Leishmania into the mammalian skin causes local inflammation with neutrophil recruitment. Here, we investigated the release of NETs by human neutrophils upon their interaction with Leishmania parasites and NETs' ability to kill this protozoan. The NET constituents DNA, elastase, and histones were detected in traps associated to promastigotes by immunofluorescence. Electron microscopy revealed that Leishmania was ensnared by NETs released by neutrophils. Moreover, Leishmania and its surface lipophosphoglycan induced NET release by neutrophils in a parasite number-and dose-dependent manner. Disruption of NETs by DNase treatment during Leishmania-neutrophil interaction increased parasite survival, evidencing NETs' leishmanicidal effect. Leishmania killing was also elicited by NET-rich supernatants from phorbol 12-myristate 13-acetate-activated neutrophils. Immunoneutralization of histone during Leishmania-neutrophil interaction partially reverted Leishmania killing, and purified histone killed the parasites. Meshes composed of DNA and elastase were evidenced in biopsies of human cutaneous leishmaniasis. NET is an innate response that might contribute to diminish parasite burden in the Leishmania inoculation site.histone ͉ protozoa ͉ trypanosomatid

Neutrophils and Macrophages Cooperate in Host Resistance againstLeishmania braziliensisInfection

“…In Lb infection, patients displaying lymphadenopathy without ulceration exhibited a higher proportion of neutrophils and eosinophils in lymph node aspirates (35). It is possible that neutrophils are able to directly kill Lb promastigotes in vivo through, for example, the formation of neutrophil extracellular traps, as recently documented with L. amazonensis (36). Nonetheless, the macrophage is considered a major effector cell of the immune response during cutaneous leishmaniasis since it is able to produce inflammatory cytokines that are ultimately responsible for parasite killing and elimination.…”

Histones as Mediators of Host Defense, Inflammation and Thrombosis

“…Leishmania promastigotes, the infectious form transmitted through the insect vector, are trapped in NETs, resulting in rapid killing [32]. Immunoneutralization of histones can abrogate killing of the parasites, supporting the antiparasitic activity of histones.…”

Neutrophil extracellular trap cell death requires both autophagy and superoxide generation

“…The results showed that NETs are formed during the early stages of infection. In addition to the reported induction of NETosis formation by bacteria [3,6,12,13], fungi [17][18][19] and protozoa [15], NETosis has also been shown to be induced by LPS-activated platelets [14] and by antineutrophil autoantibodies isolated from patients with SVV [16], whereas impaired degradation of NETs has been associated with systemic lupus erythematosus as well [20].…”

“…Data collected over the past 5 years demonstrate the in vivo occurrence of NETosis in different clinical settings such as appendicitis [3], necrotizing fasciitis [12], pneumonia [13], sepsis [14], leishmaniasis [15] and small vessel vasculitis (SVV) [16], suggesting a pathophysiological relevance in these conditions. Recently, the kinetics of in vivo NET formation in murine lungs in response to Aspergillus infection was monitored [17].…”