Cytokines and metabolic regulation: A framework of bidirectional influences affecting Leishmania infection.

Leishmania, a protozoan parasite inflicting the complex of diseases called Leishmaniases, resides and replicates as amastigotes within mammalian macrophages. As macrophages are metabolically highly active and can generate free radicals that can destroy this parasite, Leishmania also devise strategies to modulate the host cell metabolism. However, the metabolic changes can also be influenced by the anti-leishmanial immune response mediated by cytokines. This bidirectional, dynamic and complex metabolic coupling established between Leishmania and its host is the result of a long co-evolutionary process. Due to the continuous alterations imposed by the host microenvironment, such metabolic coupling continues to be dynamically regulated. The constant pursuit and competition for nutrients in the host-Leishmania duet alter the host metabolic pathways with major consequences for its nutritional reserves, eventually affecting the phenotype and functionality of the host cell. Altered phenotype and functions of macrophages are particularly relevant to immune cells, as perturbed metabolic fluxes can crucially affect the activation, differentiation, and functions of host immune cells. All these changes can deterministically direct the outcome of an infection. Cytokines and metabolic fluxes can bidirectionally influence each other through molecular sensors and regulators to dictate the final infection outcome. Our studies along with those from others have now identified the metabolic nodes that can be targeted for therapy.

Enhanced production of pro-inflammatory cytokines and chemokines in Ethiopian cutaneous leishmaniasis upon exposure to Leishmania aethiopica.

The clinical course and outcome of cutaneous leishmaniasis (CL) vary due to the infecting Leishmania species and host genetic makeup that result in different immune responses against the parasites. The host immune response to Leishmania aethiopica (L.aethiopica), the causative agent of CL in Ethiopia, is poorly understood. To contribute to the understanding of the protective immune response in CL due to L.aethiopica, we characterized the cytokine response to L. aethiopica in patients with the localized form of CL (LCL) and age-and sex-matched apparently healthy controls. By applying a whole blood based in vitro culture we found enhanced release of TNF, IL-6, MCP-1 or CCL2, IP-10 or CXCL10, MIP-1ß or CCL4 and IL-8 or CXCL8- but not of IL-10CL patients in response to L. aethiopica compared to the controls. No difference was observed between LCL cases and controls in the secretion of these cytokines and chemokines in whole blood cultures treated with the TLR-ligands LPS, MALP-2 or polyI: C. The observed increased secretion of the pro-inflammatory cytokines/chemokines reflects an enhanced response against the parasites by LCL patients as compared to healthy controls rather than a generally enhanced ability of blood leukocytes from LCL patients to respond to microbial constituents. Our findings suggest that the enhanced production of pro-inflammatory cytokines/chemokines is associated with localized cutaneous leishmaniasis caused by L.aethiopica.

Whole blood-based in vitro culture reveals diminished secretion of pro-inflammatory cytokines and chemokines in visceral leishmaniasis.

The likelihood of being bitten by sand flies infected with Leishmania (L.) donovani is considered to be high for all inhabitants living in the endemic areas, but only a small ratio of the population develop symptomatic visceral leishmanisis (VL). Since adequate activation of antimicrobial immune response plays a key role in control of pathogens early after infection we hypothesized that a dysfunction of essential cells of the immune system is associated with disease development after infection with L. donovani. In order to obtain insights into the capacity of leukocytes to respond to L. donovani, a whole blood based assay was applied to evaluate the production of cytokines and chemokines in clinical VL versus Ethiopian endemic healthy control (EHC). In response to L. donovani, VL blood cultures showed significantly lower secretion of IL-12p70, IL-6, IL-17, IL-8 and IP-10 compared to EHC. On the contrary, there was a significantly higher secretion of IL-10 observed in VL compared to EHC. In response to LPS also a lower IL-1ß, IL-12p70 and IL-6 secretion was observed in VL as compared to EHC. The data clearly indicate a diminished ability of blood leukocytes in VL to respond to L. donovani and to the TLR ligand LPS. This compromised response in VL may contribute to the severe disease development and enhanced susceptibility to secondary infections in VL.

A Mitochondrial Polymorphism Alters Immune Cell Metabolism and Protects Mice from Skin Inflammation.

Several genetic variants in the mitochondrial genome (mtDNA), including ancient polymorphisms, are associated with chronic inflammatory conditions, but investigating the functional consequences of such mtDNA polymorphisms in humans is challenging due to the influence of many other polymorphisms in both mtDNA and the nuclear genome (nDNA). Here, using the conplastic mouse strain B6-mtFVB, we show that in mice, a maternally inherited natural mutation (m.7778G > T) in the mitochondrially encoded gene ATP synthase 8 (mt-Atp8) of complex V impacts on the cellular metabolic profile and effector functions of CD4+ T cells and induces mild changes in oxidative phosphorylation (OXPHOS) complex activities. These changes culminated in significantly lower disease susceptibility in two models of inflammatory skin disease. Our findings provide experimental evidence that a natural variation in mtDNA influences chronic inflammatory conditions through alterations in cellular metabolism and the systemic metabolic profile without causing major dysfunction in the OXPHOS system.

Type-1 interferons prolong the lifespan of neutrophils by interfering with members of the apoptotic cascade.

Polymorphonuclear Neutrophils (PMNs) are metabolically highly active phagocytes, present in abundant numbers in the circulation. These active cells take the onus of clearing invading pathogens by crowding at inflammatory sites in huge numbers. Though PMNs are extremely short living and die upon spontaneous apoptosis, extended lifespan has been observed among those cells arrive at the inflammation sites or tackle intracellular infections or face any microbial challenges. The delay/inhibition of spontaneous apoptosis of these short-living cells at the inflammatory core rather helps in combating pathogens. Like many candidates, type-1 interferons (type-1 IFNs) is a group of cytokines predominant at the inflammation site. Although there are some isolated reports, a systematic study is still lacking which addresses the impact of the predominant type of interferon on the spontaneous apoptosis of neutrophils. Here in, we have observed that exposure of these IFNs (IFN-ß, IFN-α & IFN-ω etc) on human neutrophils prevents the degradation of the Bfl1, an important anti-apoptotic partner in the apoptotic cascade. Treatment showed a significant reduction in the release of cytochrome-C in the cytosol, a critical regulator in the intrinsic apoptotic pathway. We also noticed a reduction in the conversion of procaspase -3 to active caspase-3, a crucial executioner caspase towards initiation of apoptosis. Taken together our results show that exposure to interferon interferes with apoptotic pathways of neutrophils and thereby delay its spontaneous apoptosis. These findings would help us further deciphering specific roles if these inflammatory agents are causing any immune-metabolomic changes on PMNs at the inflammatory and infection core.

Serological signatures of clinical cure following successful treatment with sodium stibogluconate in Ethiopian visceral leishmaniasis.

BACKGROUND: In Ethiopia, visceral leishmaniasis (VL) is a growing public health threat. Among the key challenges in VL control in Ethiopia is lack of an effective test of cure. The recommended test of cure is parasite detection. As sterile cure is not expected with the current widely used drugs, the value of parasite detection as test of cure is questionable. Moreover, the sampling is invasive, requires a well-equipped facility and highly skilled personnel, which are all hardly found in endemic set-ups. OBJECTIVE: Our aim was to assess the value of sCD40L, MMP9 and IL-10 serum levels as signature biomarkers of clinical cure in VL cases from Ethiopia. METHODS: A total of 45 VL cases before and after treatment and 30 endemic healthy controls were included in the study. Sandwich ELISA was used to measure serum levels of sCD40L, MMP9 and IL-10. RESULT: The mean sCD40L, MMP9 and IL-10 serum levels changed significantly at clinical cure. At individual case level sCD40L and MMP9 showed an increasing trend. Yet, the degree of increase in serum level of MMP9 seems to be affected by nutritional status of the individual VL case. The mean IL-10 serum level was significantly reduced at clinical cure. As seen on case by case basis, all demonstrated a declining trend except that two VL cases had a high IL10 level at clinical cure. CONCLUSION: Our result is suggestive of the possibility of developing a signature biomarker to monitor VL treatment in Ethiopia using one or a combination of parameters.

The retinoid-related orphan receptor alpha is essential for the end-stage effector phase of experimental epidermolysis bullosa acquisita.

Genetic studies have added to the understanding of complex diseases. Here, we used a combined genetic approach for risk-loci identification in a prototypic, organ-specific, autoimmune disease, namely experimental epidermolysis bullosa acquisita (EBA), in which autoantibodies to type VII collagen (COL7) and neutrophil activation cause mucocutaneous blisters. Anti-COL7 IgG induced moderate blistering in most inbred mouse strains, while some showed severe disease or were completely protected. Using publicly available genotyping data, we identified haplotype blocks that control blistering and confirmed two haplotype blocks in outbred mice. To identify the blistering-associated genes, haplotype blocks encoding genes that are differentially expressed in EBA-affected skin were considered. This procedure identified nine genes, including retinoid-related orphan receptor alpha (RORα), known to be involved in neurological development and function. After anti-COL7 IgG injection, RORα+/- mice showed reduced blistering and homozygous mice were completely resistant to EBA induction. Furthermore, pharmacological RORα inhibition dose-dependently blocked reactive oxygen species (ROS) release from activated neutrophils but did not affect migration or phagocytosis. Thus, forward genomics combined with multiple validation steps identifies RORα to be essential to drive inflammation in experimental EBA.

Immobilized immune complexes induce neutrophil extracellular trap release by human neutrophil granulocytes via FcγRIIIB and Mac-1.

Canonical neutrophil antimicrobial effector mechanisms, such as degranulation, production of reactive oxygen species, and release of neutrophil extracellular traps (NETs), can result in severe pathology. Activation of neutrophils through immune complexes (ICs) plays a central role in the pathogenesis of many autoimmune inflammatory diseases. In this study, we report that immobilized ICs (iICs), which are hallmarks of several autoimmune diseases, induce the release of NETs from primary human neutrophils. The iIC-induced NET formation was found to require production of reactive oxygen species by NADPH oxidase and myeloperoxidase and to be mediated by FcγRIIIb. Blocking of the ß2 integrin macrophage-1 Ag but not lymphocyte function-associated Ag-1 abolished iIC-induced NET formation. This suggests that FcγRIIIb signals in association with macrophage-1 Ag. As intracellular signaling pathways involved in iIC-induced NET formation we identified the tyrosine kinase Src/Syk pathway, which downstream regulates the PI3K/Akt, p38 MAPK, and ERK1/2 pathways. To our knowledge, the present study shows for the first time that iICs induce NET formation. Thus, we conclude that NETs contribute to pathology in autoimmune inflammatory disorders associated with surface-bound ICs.

Mechanisms of apoptosis inhibition in Chlamydia pneumoniae-infected neutrophils.

The obligatory intracellular bacterium Chlamydia pneumoniae (C. pneumoniae) can survive and multiply in neutrophil granulocytes. Since neutrophils are short living cells, inhibition of neutrophil apoptosis appears to play a major role in the productive infection of neutrophils by C. pneumoniae. In the present study, we have investigated which survival pathways and which events of the apoptotic process are modulated in C. pneumoniae-infected neutrophils. All infection experiments were carried out using primary human neutrophils in vitro. We show that infection with C. pneumoniae activates PI3K/Akt as well as the ERK1/2 and p38 MAP kinases and present evidence that activation of the PI3K/Akt and ERK1/2 pathways are essential to initiate the apoptosis delay in C. pneumoniae-infected neutrophils. Both the PI3K/Akt and ERK1/2 pathways are involved in the maintained expression of the anti-apoptotic protein Mcl-1. In addition, we also showed that the PI3K/Akt pathway leads to the activation of NF-κB-dependent release of IL-8 by infected neutrophils. Infection with C. pneumoniae activates the PI3K/Akt and ERK1/2 MAPK survival pathways in neutrophils, induces the NF-κB dependent release of IL-8 and leads to the maintenance of Mcl-1 expression in neutrophils.

Heat shock protein 90 is required for ex vivo neutrophil-driven autoantibody-induced tissue damage in experimental epidermolysis bullosa acquisita.

A broad range of immunosuppressive and immunomodulatory effects of heat shock protein 90 (Hsp90) blockade has been described in models of autoimmune bullous diseases, but the direct contribution of this chaperone to neutrophil effector pathways in the context of autoantibody-driven blistering is generally unknown. Therefore, this has been addressed in the current study on the basis of the subepidermal blistering disease epidermolysis bullosa acquisita (EBA) characterized by autoantibodies against type VII collagen, in which a crucial role of neutrophils and both their reactive oxygen species and matrix metalloproteinases in mediating tissue injury has been established. First, the Hsp90 antagonist 17-DMAG dose-dependently inhibited dermal-epidermal separation ex vivo in cryosections of human skin induced by co-incubation of EBA patient autoantibodies with neutrophils from healthy blood donors. Next, 17-DMAG dose-dependently suppressed production and release of reactive oxygen species by human neutrophils induced by both fMLP ± LPS and EBA-specific immune complexes. In addition, co-immunoprecipitation studies revealed that extracellular Hsp90 interacted with secreted matrix metalloproteinases 2 and 12 in sera of EBA patients, suggesting that these basement membrane-degrading proteolytic enzymes are client proteins of Hsp90 and dependent on its chaperone function. Our findings add to the knowledge of the multimodal anti-inflammatory effects of Hsp90 blockade and implicate that Hsp90 is closely involved in the effector mechanisms of neutrophil-driven autoantibody-induced tissue damage, thus being a relevant therapeutic target in patients with neutrophil-mediated autoimmune diseases such as inflammatory types of EBA.

Infection of neutrophil granulocytes with Leishmania major activates ERK 1/2 and modulates multiple apoptotic pathways to inhibit apoptosis.

Neutrophil granulocytes provide the first line of defense against bacterial, fungal, and parasitic infections. They phagocytose and kill many invading pathogens. Certain pathogenic microorganisms such as the intracellular protozoan parasite Leishmania major (L. major) can survive inside neutrophils. Mature neutrophils have a very short life span due to spontaneous apoptosis. Previously, we have reported that infections with L. major are able to delay spontaneous apoptosis. In the present study, we addressed the underlying mechanisms of regulation of both extrinsic and intrinsic apoptosis. We show that interaction with L. major transiently activates ERK1/2 phosphorylation. Pharmacological inhibition of ERK1/2 phosphorylation reversed the apoptosis delay. Moreover, infection leads to the enhanced and sustainable expression of the anti-apoptotic proteins Bcl-2 and Bfl-1, respectively. As downstream events, the release of cytochrome c from mitochondria and processing of caspase-6 were inhibited. We also confirm that infection with L. major results in reduced FAS expression on the surface of neutrophils. The presented data indicate that infection with L. major affects both intrinsic as well as extrinsic pathways of neutrophil apoptosis. Enhanced life span of host neutrophils enables the parasite to survive within neutrophils.

Genetic identification and functional validation of FcγRIV as key molecule in autoantibody-induced tissue injury.

Autoantibody-mediated diseases are clinically heterogeneous and often fail conventional therapeutic strategies. Gene expression profiling has helped to identify new molecular pathways in these diseases, although their potential as treatment targets largely remains to be functionally validated. Based on weighted gene co-expression network analysis, we determined the transcriptional network in experimental epidermolysis bullosa acquisita (EBA), a paradigm of an antibody-mediated organ-specific autoimmune disease characterized by autoantibodies directed against type VII collagen. We identified 33 distinct and differentially expressed modules, including Fcγ receptor (FcγR) IV and components of the neutrophil-associated enzyme system in autoantibody transfer-induced EBA. Validation experiments, including functional analysis, demonstrated that FcγRIV expression on neutrophils crucially contributes to autoantibody-induced tissue injury in the transfer model of EBA. Mice lacking the common γ-chain of activating FcγRs, deficient in FcγRIV or treated with FcγRIV function blocking antibody, but not mice deficient in FcγRI, FcγRIIB, FcγRIII or both FcγRI and FcγRIII, were effectively protected from EBA. Skin disease was restored in γ-chain-deficient mice locally reconstituted with neutrophils from wild-type, but not from γ-chain-deficient, mice. Our findings both genetically and functionally identify a novel disease-related molecule, FcγRIV, in an autoantibody-mediated disorder, which may be of importance for the development of novel targeted therapies.

Flavonoids and 5-aminosalicylic acid inhibit the formation of neutrophil extracellular traps.

Neutrophil extracellular traps (NETs) have been suggested to play a pathophysiological role in several autoimmune diseases. Since NET-formation in response to several biological and chemical stimuli is mostly ROS dependent, in theory any substance that inhibits or scavenges ROS could prevent ROS-dependent NET release. Therefore, in the present comprehensive study, several antioxidative substances were assessed for their capacity to inhibit NET formation of primary human neutrophils in vitro. We could show that the flavonoids (-)-epicatechin, (+)-catechin hydrate, and rutin trihydrate as well as vitamin C and the pharmacological substances N-acetyl-L-cysteine and 5-aminosalicylic acid inhibited PMA induced ROS production and NET formation. Therefore, a broad spectrum of antioxidative substances that reduce ROS production of primary human neutrophils also inhibits ROS-dependent NET formation. It is tempting to speculate that such antioxidants can have beneficial therapeutic effects in diseases associated with ROS-dependent NET formation.

Infection with Anaplasma phagocytophilum activates the phosphatidylinositol 3-Kinase/Akt and NF-κB survival pathways in neutrophil granulocytes.

Anaplasma phagocytophilum, a Gram-negative, obligate intracellular bacterium infects primarily neutrophil granulocytes. Infection with A. phagocytophilum leads to inhibition of neutrophil apoptosis and consequently contributes to the longevity of the host cells. Previous studies demonstrated that the infection inhibits the executionary apoptotic machinery in neutrophils. However, little attempt has been made to explore which survival signals are modulated by the pathogen. The aim of the present study was to clarify whether the phosphatidylinositol 3-kinase (PI3K)/Akt and NF-κB signaling pathways, which are considered as important survival pathways in neutrophils, are involved in A. phagocytophilum-induced apoptosis delay. Our data show that infection of neutrophils with A. phagocytophilum activates the PI3K/Akt pathway and suggest that this pathway, which in turn maintains the expression of the antiapoptotic protein Mcl-1, contributes to the infection-induced apoptosis delay. In addition, the PI3K/Akt pathway is involved in the activation of NF-κB in A. phagocytophilum-infected neutrophils. Activation of NF-κB leads to the release of interleukin-8 (IL-8) from infected neutrophils, which, in an autocrine manner, delays neutrophil apoptosis. In addition, enhanced expression of the antiapoptotic protein cIAP2 was observed in A. phagocytophilum-infected neutrophils. Taken together, the data indicate that upstream of the apoptotic cascade, signaling via the PI3K/Akt pathway plays a major role for apoptosis delay in A. phagocytophilum-infected neutrophils.

The protective Th1 response in mice is induced in the T-cell zone only three weeks after infection with Leishmania major and not during early T-cell activation.

The protozoan parasite Leishmania spp. causes clinical pictures ranging in severity from spontaneously healing skin ulcers to systemic disease. The immune response associated with healing involves the differentiation of IFNγ-producing Th1 cells, whereas the non-healing phenotype is associated with IL4-producing Th2 cells. The widespread assumption has been that the T-cell differentiation that leads to a healing or non-healing phenotype is established at the time of T-cell activation early after infection. By selectively analyzing the expression of cytokine genes in the T-cell zones of lymph nodes of resistant (Th1) C57BL/6 mice and susceptible (Th2) BALB/c mice during an infection with Leishmania major in vivo, we show that the early T-cell response does not differ between C57BL/6 mice and BALB/c mice. Instead, Th1/Th2 polarization appears suddenly 3 weeks after infection. At the same time point, the number of parasites increases in lymph nodes of both mouse strains, but about 100-fold more in susceptible BALB/c mice. We conclude that the protective Th1 response in C57BL/6 mice is facilitated by the capacity of their innate effector cells to keep parasite numbers at low levels.

Phagocytosis of apoptotic cells by neutrophil granulocytes: diminished proinflammatory neutrophil functions in the presence of apoptotic cells.

Neutrophil granulocytes are rapidly recruited from the bloodstream to the site of acute inflammation where they die in large numbers. Because release of toxic substances from dead neutrophils can propagate the inflammatory response leading to tissue destruction, clearance of dying inflammatory neutrophils has a critical function in the resolution of the inflammatory response. Apoptotic neutrophils are phagocytosed primarily by macrophages, provided these cells are present in adequate numbers. However, macrophages are rare at sites of acute inflammation, whereas the number of neutrophils can be extremely high. In the current study, in vitro experiments with human neutrophils were carried out to investigate whether neutrophils can ingest apoptotic neutrophils. We show that naïve granulocytes isolated from venous blood have a limited capacity to phagocytose apoptotic cells. However, exposure to activating stimuli such as LPS, GM-CSF and/or IFN-gamma results in enhanced phagocytosis of apoptotic cells. The efficient uptake of apoptotic cells by neutrophils was found to depend on the presence of heat labile serum factors. Importantly, the contact to or uptake of apoptotic cells inhibited neutrophil functions such as respiratory burst and the release of the proinflammatory cytokines TNF-alpha and interferon-inducible protein-10. Contact to apoptotic cells, however, induced the secretion of IL-8 and growth-related oncogene-alpha, which was independent of NF-kappaB and p38 MAPK but involved C5a and the ERK1/2 pathway. The data suggest that activated neutrophils participate in the clearance of apoptotic cells. In addition, because apoptotic cells inhibit proinflammatory functions of neutrophils, uptake of apoptotic cells by neutrophils contributes to the resolution of inflammation.

The impact of various reactive oxygen species on the formation of neutrophil extracellular traps.

The formation of neutrophil extracellular traps (NETs) depends on the generation of reactive oxygen species (ROS). Previous studies revealed that both NADPH oxidase and myeloperoxidase (MPO) are required for NET release. However, the contribution of various ROS as well as the role of mitochondria-derived ROS has not been addressed so far. In the present study we aimed to investigate in a systematic and comprehensive manner the contribution of various ROS and ROS-generating pathways to the PMA-induced NET release. By using specific inhibitors, the role of both NADPH oxidase- and mitochondria-derived ROS as well as the contribution of superoxide dismutase (SOD) and MPO on the NET release was assessed. We could demonstrate that NADPH oxidase function is crucial for the formation of NETs. In addition, we could clearly show the involvement of MPO-derived ROS in NET release. Our results, however, did not provide evidence for the role of SOD- or mitochondria-derived ROS in NET formation.

Method for simultaneous tracking of thousands of unlabeled cells within a transparent 3D matrix.

Three-dimensional tracking of cells is one of the most powerful methods to investigate multicellular phenomena, such as ontogenesis, tumor formation or wound healing. However, 3D tracking in a biological environment usually requires fluorescent labeling of the cells and elaborate equipment, such as automated light sheet or confocal microscopy. Here we present a simple method for 3D tracking large numbers of unlabeled cells in a collagen matrix. Using a small lensless imaging setup, consisting of an LED and a photo sensor only, we were able to simultaneously track ~3000 human neutrophil granulocytes in a collagen droplet within an unusually large field of view (>50 mm2) at a time resolution of 4 seconds and a spatial resolution of ~1.5 µm in xy- and ~30 µm in z-direction. The setup, which is small enough to fit into any conventional incubator, was used to investigate chemotaxis towards interleukin-8 (IL-8 or CXCL8) and N-formylmethionyl-leucyl-phenylalanine (fMLP). The influence of varying stiffness and pore size of the embedding collagen matrix could also be quantified. Furthermore, we demonstrate our setup to be capable of telling apart healthy neutrophils from those where a condition of inflammation was (I) induced by exposure to lipopolysaccharide (LPS) and (II) caused by a pre-existing asthma condition. Over the course of our experiments we have tracked more than 420.000 cells. The large cell numbers increase statistical relevance to not only quantify cellular behavior in research, but to make it suitable for future diagnostic applications, too.

Proinflammatory stimuli enhance phagocytosis of apoptotic cells by neutrophil granulocytes.

Recently, we have reported that, in addition to macrophages, also neutrophil granulocytes can phagocytose apoptotic neutrophils. Based on this finding, we hypothesized that "cannibalistic" neutrophils at sites of acute infection/inflammation play a major role in the clearance of apoptotic neutrophils. Since at sites of infection/inflammation neutrophils are exposed to microbial constituents and proinflammatory cytokines, in the present study we analyzed the effect of TLR-ligands and cytokines on the ability of neutrophils to phagocytose apoptotic cells in vitro. We observed that exposure to ligands of TLR2 (Malp2, Pam3CSK4), TLR4 (LPS), TLR7/TLR8 (R848), and TLR9 (ODN 2006) led to increased phagocytosis of apoptotic cells by neutrophils. In addition, proinflammatory cytokines such as TNF and GM-CSF strongly enhanced the uptake of apoptotic cells by neutrophils. These results support the hypothesis that neutrophils acquire the ability to phagocytose apoptotic cells at sites of acute infection/inflammation and thereby can contribute to the resolution of inflammation.

Purinergic Enhancement of Anti-Leishmanial Effector Functions of Neutrophil Granulocytes.

Although macrophages are considered for host cells for the multiplication of Leishmania, recent studies indicate the important role of neutrophil granulocytes as host cells for these intracellular parasites. Neutrophils have been shown to be massively and rapidly recruited to the site of Leishmania infection where they represent the first cells to encounter the parasites. Exposure to ATP and UTP have been shown to enhance anti-Leishmania activity of macrophages and intralesional injection of UTP led to strongly reduced parasite load in vivo. Since the in vivo anti-leishmanial effect of extracellular UTP correlated with enhanced neutrophil recruitment and enhanced ROS production at the site of Leishmania infection we hypothesized that exposure to extracellular nucleotides can directly enhance the killing of Leishmania by neutrophils. Since purinergic signaling is an essential mechanism of neutrophil activation the aim of the present study was to assess whether purinergic exposure results in the activation of anti-leishmanial neutrophil functions and, therefore, represent an essential component of enhanced anti-leishmanial defense in leishmaniasis. We could show that exposure to ATP and UTP led to activation and enhanced CD11b expression of primary human neutrophils in vitro. Leishmania-induced ROS production was strongly enhanced by extracellular ATP and UTP. Importantly, exposure to ATP and UTP resulted in enhanced killing of Leishmania donovani by neutrophils. In addition, ATP strongly enhanced the secretion of IL-8 and IL-1ß by Leishmania-exposed neutrophils. Our results suggest that signaling via the P2 receptor and phosphorylation of Erk1/2, Akt and p38 are involved in the purinergic enhancement of anti-leishmanial functions of neutrophils.