Neutrophils Reduce the Parasite Burden in Leishmania (Leishmania) amazonensis-Infected Macrophages

Abstract

BackgroundStudies on the role of neutrophils in Leishmania infection were mainly performed with L. (L) major, whereas less information is available for L. (L) amazonensis. Previous results from our laboratory showed a large infiltrate of neutrophils in the site of infection in a mouse strain resistant to L. (L.) amazonensis (C3H/HePas). In contrast, the susceptible strain (BALB/c) displayed a predominance of macrophages harboring a high number of amastigotes and very few neutrophils. These findings led us to investigate the interaction of inflammatory neutrophils with L. (L.) amazonensis-infected macrophages in vitro.Methodology/Principal FindingsMouse peritoneal macrophages infected with L. (L.) amazonensis were co-cultured with inflammatory neutrophils, and after four days, the infection was quantified microscopically. Data are representative of three experiments with similar results. The main findings were 1) intracellular parasites were efficiently destroyed in the co-cultures; 2) the leishmanicidal effect was similar when cells were obtained from mouse strains resistant (C3H/HePas) or susceptible (BALB/c) to L. (L.) amazonensis; 3) parasite destruction did not require contact between infected macrophages and neutrophils; 4) tumor necrosis factor alpha (TNF-α), neutrophil elastase and platelet activating factor (PAF) were involved with the leishmanicidal activity, and 5) destruction of the parasites did not depend on generation of oxygen or nitrogen radicals, indicating that parasite clearance did not involve the classical pathway of macrophage activation by TNF-α, as reported for other Leishmania species.Conclusions/SignificanceThe present results provide evidence that neutrophils in concert with macrophages play a previously unrecognized leishmanicidal effect on L. (L.) amazonensis. We believe these findings may help to understand the mechanisms involved in innate immunity in cutaneous infection by this Leishmania species.

A secondary wave of neutrophil infiltration causes necrosis and ulceration in lesions of experimental American cutaneous leishmaniasis

“…A similar result was obtained in a mouse model of visceral infection, which showed that the depletion of neutrophils led to a rapid increase in the early splenic parasite burden but had no effect on the chronic disease [45]. Our failure to observe early parasite control contrasts with studies that demonstrated Leishmania killing capacity of neutrophils [13, 15, 23], as early as 3 hours post-infection [14] However, it agrees with observations indicating that L . donovani is able to safely survive in the phagosomal compartment during 24-48h [16].…”

Impact of Neutrophil-Secreted Myeloid Related Proteins 8 and 14 (MRP 8/14) on Leishmaniasis Progression

“…The same effect was observed in the control of L. amazonensis , where it was shown that TNF-α, elastase and platelet activation factor, produced by neutrophils, were responsible for parasite killing. On the other hand, this study also showed that NO and ROIs were not involved in the clearance of the parasite, as has been observed with other Leishmania species [46]; we consider that, in both cases, it is also possible that neutrophils secrete MRPs, and this secretion helps to control the infection. Contrary to what was shown by Ribeiro et at.…”

Interactions between Neutrophils and <b><i>Leishmania braziliensis</i></b> Amastigotes Facilitate Cell Activation and Parasite Clearance

“…Several studies have assessed the ability of neutrophils to reduce Leishmania burden in infected macrophages [18–20]; however, the effect of neutrophils on L. braziliensis amastigote-infected macrophages remains uncharacterized. To explore the interaction between neutrophils and infected macrophages, we loaded bone marrow-derived macrophages with amastigotes and added thioglycollate-induced (control) neutrophils for 24 h. At the end of incubation, we added parasite medium to liberate surviving parasites from macrophages and assessed subsequent parasite growth after 3–4 days.…”