Essential role of leukotriene B4 on Leishmania (Viannia) braziliensis killing by human macrophages

High glucose heightens vulnerability to Leishmania braziliensis infection in human macrophages by hampering the production of reactive oxygen species through TLR2 and TLR4

Diabetes increases susceptibility to infections, including Leishmania braziliensis (Lb). Our group previously demonstrated that diabetic patients with cutaneous leishmaniasis (CL) take longer to heal lesions compared to non-diabetics. Since macrophages play a critical role in CL pathogenesis, we investigated how high glucose levels impact their response during Lb infection. Macrophages cultured in high glucose conditions showed increased parasite load than those in normal glucose conditions. The production of inflammatory mediators was similar between glucose conditions, but basal reactive oxygen species (ROS) production was elevated under high glucose conditions and remained unchanged after Lb infection, indicating glucose-induced oxidative stress does not control the parasite. In contrast, macrophages in normal glucose conditions, exhibited increased ROS production only after infection. Additionally, high glucose reduced TLR2 and TLR4 expression, which was also observed after Lb infection. TLR2/4 inhibition increased Lb infection in normal glucose conditions, mediated by TLR-dependent ROS production. However, this mechanism was absent under high glucose conditions, where elevated basal ROS production appeared TLR-independent. Biopsies from diabetic CL patients corroborated these findings, showing decreased TLR2 and TLR4 expression compared to non-diabetics. These findings suggest that high glucose levels induce oxidative stress and reduces TLR expression, impairing macrophage functions and rendering them less effective at controlling Lb infection.

Borges V, Pedro Soares R, Berlink Lima J. Activation Pathways of Murine Macrophages by Lipophosphoglycan from Strains of Leishmania major (FV1 and LV39)

Lipophosphoglycan (LPG) is an important Leishmania virulence factor. It is the most abundant surface glycoconjugate in promastigotes, playing an important role in the interaction with phagocytic cells. While LPG is known to modulate the macrophage immune response during infection, the activation mechanisms triggered by this glycoconjugate have not been fully elucidated. This work investigated the role that LPGs purified from two strains of Leishmania major (FV1 and LV39) play in macrophage activation, considering the differences in their biochemical structures. Bone marrow-derived macrophages from BALB/c mice were stimulated with 10 μg/mL purified LPG from the LV39 and FV1 strains. We then measured the production of nitric oxide (NO) and cytokines, the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), and the activation of MAPK pathways. LPG from the LV39 strain, which has longer poly-galactosylated side chains, induced a more pro-inflammatory profile than that from the FV1 strain. This included higher production of NO, TNF-α, and PGE2, and increased expression of COX-2 and iNOS. Additionally, the phosphorylation of ERK-1/2 and JNK was elevated in macrophages exposed to LPG from the LV39 strain. No difference in IL-10 production was observed in cells stimulated by both LPG. Thus, intraspecific structural differences in LPG contribute to distinct innate immune responses in macrophages.

Comparative proteomics analysis of samples from hepatic cystic echinococcosis patients using data-independent acquisition approach

Cystic echinococcosis is a zoonotic disease resulting from infection caused by the larval stage of Echinococcus granulosus. This study aimed to assess the specific proteins that are potential candidates for the development of a vaccine against E. granulosus. The data-independent acquisition approach was employed to identify differentially expressed proteins (DEPs) in E. granulosus samples. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis was employed to identify several noteworthy proteins. Results: The DEPs in E. granulosus samples were identified (245 pericystic wall vs. parasite-free yellowish granuloma (PYG, 1725 PY vs. PYG, 2274 PN vs. PYG). Further examination of these distinct proteins revealed their predominant enrichment in metabolic pathways, amyotrophic lateral sclerosis, and neurodegeneration-associated pathways. Notably, among these DEPs, SH3BGRL, MST1, TAGLN2, FABP5, UBE2V2, and RARRES2 exhibited significantly higher expression levels in the PYG group compared with the PY group (P < 0.05). The findings may contribute to the understanding of the pathological mechanisms underlying echinococcosis, providing valuable insights into the development of more effective diagnostic tools, treatment modalities, and preventive strategies. SIGNIFICANCE: CE is a major public health hazard in the western regions of China, Central Asia, South America, the Mediterranean countries, and eastern Africa. Echinococcus granulosus is responsible for zoonotic disease through infection Our analysis focuses on the proteins in various samples by data-dependent acquisition (DIA) for proteomic analysis. The importance of this research is to develop new strategies and targets to protect against E. granulosus infections in humans.

Prostaglandin E2 contributes to L. braziliensis survival and therapeutic failure in cutaneous leishmaniasis

Patients with cutaneous leishmaniasis (CL) present an exacerbated inflammatory response associated with tissue damage and ulcer development. In recent years, higher rates of failure to pentavalent antimoniate therapy have been observed, yet the underlying reason remains poorly understood. We hypothesize that the eicosanoid PGE2 favours the establishment of infection by L. braziliensis, which contributes to therapeutic failure. The aim of the present study was to investigate the influence of PGE2 on the survival of L. braziliensis in macrophages and rates of therapeutic failure in CL patients. PGE2, an eicosanoid derived from the metabolism of arachidonic acid by the COX-2 enzyme, plays several roles in immune response. We found that increased PGE2 decreases the microbicidal function of macrophages and is associated with disease severity and therapeutic failure. Additionally, the neutralization of COX-2 by NS398, a selective NSAID, increases the ability of macrophages to kill L. braziliensis and protects against the pathological inflammatory response. Our data suggest that NS398 may serve as an adjunct treatment for CL patients.

A Critical Overview of Interleukin 32 in Leishmaniases

Interleukin-32 (IL-32) has several immune regulatory properties, which have driven its investigation in the context of various diseases. IL-32 expression is reported to be induced in the lesions of patients with American tegumentary leishmaniasis (ATL) by the New World Leishmania spp. that are responsible for causing ATL and visceral leishmaniasis (VL). IL-32 expression may elevate the inflammatory process through the induction of pro-inflammatory cytokines and also via mechanisms directed to kill the parasites. The genetic variants of IL-32 might be associated with the resistance or susceptibility to ATL, while different isoforms of IL-32 could be associated with distinct T helper lymphocyte profiles. IL-32 also determines the transcriptional profile in the bone marrow progenitor cells to mediate the trained immunity induced by β-glucan and BCG, thereby contributing to the resistance against Leishmania. IL-32γ is essential for the vitamin D-dependent microbicidal pathway for parasite control. In this context, the present review report briefly discusses the data retrieved from the studies conducted on IL-32 in leishmaniasis in humans and mice to highlight the current challenges to understanding the role of IL-32 in leishmaniasis.

Analysis of Gtpases Rab 5 and Rab 7 expression from macrophages infected with biofilm-producing and non biofilm-producing strains of Corynebacterium pseudotuberculosis

Corynebacterium pseudotuberculosis is a facultative intracellular pathogen that uses various mechanisms to survive within macrophages. In phagocytosis, this survival can be attributed to the ability to inhibit phagosome-lysosome fusion. In this fusion, some proteins, including Rabs GTPases, are involved in the maturation process and are responsible for regulating membrane vesicle trafficking. Thus, to better understand these mechanisms, the capacity of biofilm-producing and non biofilm-producing strains of Corynebacterium pseudotuberculosis for modulating the expression of endosomal proteins GTPases Rab 5 and Rab 7 was evaluated in an in vitro study of infection of goat macrophages. Blood was collected from ten Canindé goats, infected with biofilm-producing and non biofilm-producing strains of C. pseudotuberculosis. Blood cells were separated in colloidal silica-polyvinylpyrrolidone gradients (GE Healthcare®). These cells were maintained at 37 °C, with 5% of CO₂. After differentiation, macrophages were infected with the mentioned strains. The bacterial pellets were marked with Rab 5 and Rab 7 antibodies, and their expression was observed by flow cytometry. Both strains of C. pseudotuberculosis (biofilm-producing and non biofilm-producing) were observed to be capable of altering the expression of Rab proteins in macrophages cultivated in vitro. Macrophages from the animals infected with the biofilm-producing strain had an increase in the expression of Rab 5 protein, mainly when these macrophages were treated with the non biofilm-producing strain. The same mechanism was shown to function with Rab 7 protein, however at a lower intensity of expression when compared with Rab 5.

LTB4-Driven Inflammation and Increased Expression of ALOX5/ACE2 During Severe COVID-19 in Individuals With Diabetes

Diabetes is a known risk factor for severe coronavirus disease 2019 (COVID-19), the disease caused by the new coronavirus severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, there is a lack of knowledge about the mechanisms involved in the evolution of COVID-19 in individuals with diabetes. We aimed to evaluate whether the chronic low-grade inflammation of diabetes could play a role in the development of severe COVID-19. We collected clinical data and blood samples of patients with and without diabetes hospitalized for COVID-19. Plasma samples were used to measure inflammatory mediators and peripheral blood mononuclear cells, for gene expression analysis of the SARS-CoV-2 main receptor system (ACE2/TMPRSS2), and for the main molecule of the leukotriene B₄ (LTB₄) pathway (ALOX5). We found that diabetes activates the LTB₄ pathway and that during COVID-19 it increases ACE2/TMPRSS2 as well as ALOX5 expression. Diabetes was also associated with COVID-19-related disorders, such as reduced oxygen saturation as measured by pulse oximetry/fraction of inspired oxygen (FiO₂) and arterial partial pressure of oxygen/FiO₂ levels, and increased disease duration. In addition, the expressions of ACE2 and ALOX5 are positively correlated, with increased expression in patients with diabetes and COVID-19 requiring intensive care assistance. We confirmed these molecular results at the protein level, where plasma LTB₄ is significantly increased in individuals with diabetes. In addition, IL-6 serum levels are increased only in individuals with diabetes requiring intensive care assistance. Together, these results indicate that LTB₄ and IL-6 systemic levels, as well as ACE2/ALOX5 blood expression, could be early markers of severe COVID-19 in individuals with diabetes.

The role of IL-32 in Bacillus Calmette-Guérin (BCG)-induced trained immunity in infections caused by different Leishmania spp

BACKGROUND

Cells of the innate immune system undergo long-term functional reprogramming in response to Bacillus Calmette-Guérin (BCG) exposure via a process called trained immunity, conferring nonspecific protection to unrelated infections. Here, we investigate whether BCG-induced trained immunity is able to protect against infections caused by different Leishmania spp., protozoa that cause cutaneous and mucosal or visceral lesions.

METHODS

We used training models of human monocytes with BCG and subsequent infection by L. braziliensis, L. amazonensis and L. infantum, and the vaccination of wild-type and transgenic mice for IL-32γ before in vivo challenge with parasites.

RESULTS

We demonstrated that monocytes trained with BCG presented enhanced ability to kill L. braziliensis, L. amazonensis and L. infantum through increased production of reactive oxygen species. Interleukin (IL)-32 appears to play an essential role in the development of trained immunity. Indeed, BCG exposure induced IL-32 production in human primary monocytes, both mRNA and protein. We have used a human IL-32γ transgenic mouse model (IL-32γTg) to study the effect of BCG vaccination in different Leishmania infection models. BCG vaccination decreased lesion size and parasite load in infections caused by L. braziliensis and reduced the spread of L. amazonensis to other organs in both infected wild-type (WT) and IL-32γTg mice. In addition, BCG reduced the parasite load in the spleen, liver and bone marrow of both WT and IL-32γTg mice infected with L. infantum. BCG vaccination increased inflammatory infiltrate in infected tissues caused by different Leishmania spp. In all infections, the presence of IL-32γ was not mandatory, but it increased the protective and inflammatory effects of BCG-induced training.

CONCLUSIONS

BCG's ability to train innate immune cells, providing protection against leishmaniasis, as well as the participation of IL-32γ in this process, pave the way for new treatment strategies for this neglected infectious disease.

Dynamics of Chemical Diversity during Co-Cultures: An Integrative Time-Scale Metabolomics Study of Fungal Endophytes Cophinforma mamane and Fusarium solani

A rapid and efficient metabolomic study of Cophinforma mamane and Fusarium solani co-cultivation in time-series based analysis was developed to study metabolome variations during their fungal interactions. The fungal metabolomes were studied through the integration of four metabolomic tools: MS-DIAL, a chromatographic deconvolution of liquid-chromatography-mass spectrometry (LC/MS); MS-FINDER, a structure-elucidation program with a wide range metabolome database; GNPS, an effective method to organize MS/MS fragmentation spectra, and MetaboAnalyst, a comprehensive web application for metabolomic data analysis and interpretation. Co-cultures of C. mamane and F. solani induced different patterns of metabolite production over 10 days of incubation and induced production of five de novo compounds not occurring in monocultures. These results emphasize that co-culture in time-frame analysis is an interesting method to unravel hidden metabolome in the investigation of fungal chemodiversity.

Unbalanced production of LTB4/PGE2 driven by diabetes increases susceptibility to cutaneous leishmaniasis

Poorly controlled diabetes mellitus leads to several comorbidities, including susceptibility to infections. Hyperglycemia increases phagocyte responsiveness, however immune cells from people with diabetes show inadequate antimicrobial functions. We and others have shown that aberrant production of leukotriene B4 (LTB4) is detrimental to host defense in models of bacterial infection. Here, we will unveil the consequences of high glucose in the outcome of Leishmania braziliensis skin infection in people with diabetes and determine the role of LTB4 in human phagocytes. We show that diabetes leads to higher systemic levels of LTB4, IL-6 and TNF-α in cutaneous leishmaniasis. Only LTB4 correlated with blood glucose levels and healing time in diabetes comorbidity. Skin lesions of people with leishmaniasis and diabetes exhibit increased neutrophil and amastigote numbers. Monocyte-derived macrophages from these individuals showed higher L. braziliensis loads, reduced production of Reactive Oxygen Species and unbalanced LTB4/PGE2 ratio. Our data reveal a systemic inflammation driven by diabetes comorbidity in opposition to a local reduced capacity to resolve L. braziliensis infection and a worse disease outcome.

Lipid hijacking: a unifying theme in vector-borne diseases

Vector-borne illnesses comprise a significant portion of human maladies, representing 17% of global infections. Transmission of vector-borne pathogens to mammals primarily occurs by hematophagous arthropods. It is speculated that blood may provide a unique environment that aids in the replication and pathogenesis of these microbes. Lipids and their derivatives are one component enriched in blood and are essential for microbial survival. For instance, the malarial parasite Plasmodium falciparum and the Lyme disease spirochete Borrelia burgdorferi, among others, have been shown to scavenge and manipulate host lipids for structural support, metabolism, replication, immune evasion, and disease severity. In this Review, we will explore the importance of lipid hijacking for the growth and persistence of these microbes in both mammalian hosts and arthropod vectors.

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.

Linoleic Acid Inhibits the Release of Leishmania donovani Derived Microvesicles and Decreases Its Survival in Macrophages

Visceral leishmaniasis is a neglected tropical disease caused by Leishmania (L.) donovani parasite in the Indian subcontinent. Macrophages (mϕ) are the harboring cells for parasite and their interactions dictate the pathogenesis of this disease. Polyunsaturated fatty acids are an integral part of the mϕ cell membrane and are derived from linoleic acid (LA), which is a principal essential fatty acid. Here, we have investigated the effect of the simultaneous presence of LA during L. donovani infection in mϕ. Treatment with LA suppresses the parasitic load in mϕ (kDNA expression) and promotes the Th-1 type immune response (IL-12, iNOS). However, no significant change in kDNA expressions was observed when L. donovani promastigotes were treated with LA. Intrigued by this observation, we explored mechanism(s) by which LA promoted the protective type immune response in infected mϕ. Interestingly, LA decreased the release of L. donovani derived extracellular vesicle later characterized as microvesicles. Moreover, these microvesicles were suppressive concerning their bias toward the Th-2 type of immune responses (IL-10, Arginase) in mϕ. We suggest that LA plays a protective role in the immune response against L. donovani infection by inhibiting the release to Leishmania derived microvesicles and thus promoting Th-1 type immune response in mϕ.

Preventive as well as therapeutic significances of linoleic acid in the containment of Leishmania donovani infection

People suffering from malnutrition show compromised levels of ω-6 fatty acid and malnutrition is frequently observed among visceral leishmaniasis (VL) patients as disease inflicts primarily the socioeconomic destitute communities. Dietary linoleic acid (LA, 18:2; ω-6 fatty acid) is the principal source of essential fatty acid and its derivatives i.e. eicosanoids possess immune-modulatory activities. However, its role in VL is not yet established. LA was measured in VL human subjects (serum) as well as in Leishmania(L.)donovani infected hamsters (serum and visceral organs). Organ-specific mRNA expressions of various enzymes of the LA metabolic pathway were measured in visceral organs of infected hamsters. Our findings showed a decrease in the concentrations of LA in the serum samples of VL patients, suggesting malnutrition among these patients. However, in L. donovani infected hamsters, its level was not altered in the early infection (15 days) and then increased at late infection (60 days). Importantly, the supplementation of LA restored the Th-1 type of immune response and significantly reduced the parasite load within infected macrophages in vitro. This protective response of LA was mediated through 5-lipoxygenase pathway not via the cyclooxygenase pathway. Preventive usage of LA to mϕ followed by L. donovani infection also showed the strengthening of Th-1 immune response and significantly fewer parasite loads. Our findings demonstrate the protective role of LA in the containment of the parasite load. Incorporating LA rich oils in daily food habits across highly inflicted regions may be a significant advancement towards the eradication of the disease.

Leishmania Spp-Host Interaction: There Is Always an Onset, but Is There an End?

For a long time Leishmaniasis had been considered as a neglected tropical disease. Recently, it has become a priority in public health all over the world for different aspects such as geographic spread, number of population living at risk of infection as well as the potential lethality and/or the development of disfiguring lesions in the, respectively, visceral and tegumentary forms of the disease. As a result, several groups have been bending over this issue and many valuable data have been published. Nevertheless, parasite-host interactions are still not fully known and, consequently, we do not entirely understand the infection dynamics and parasite persistence. This knowledge may point targets for modulation or blockage, being very useful in the development of measures to interfere in the course of infection/ disease and to minimize the risks and morbidity. In the present review we will discuss some aspects of the Leishmania spp-mammalian host interaction in the onset of infection and after the clinical cure of the lesions. We will also examine the information already available concerning the parasite strategy to evade immune response mainly at the beginning of the infection, as well as during the parasite persistence. This knowledge can improve the conditions of treatment, follow-up and cure control of patients, minimizing the potential damages this protozoosis can cause to infected individuals.

Excessive localized leukotriene B4 levels dictate poor skin host defense in diabetic mice

Poorly controlled diabetes leads to comorbidities and enhanced susceptibility to infections. While the immune components involved in wound healing in diabetes have been studied, the components involved in susceptibility to skin infections remain unclear. Here, we examined the effects of the inflammatory lipid mediator leukotriene B4 (LTB4) signaling through its receptor B leukotriene receptor 1 (BLT1) in the progression of methicillin-resistant Staphylococcus aureus (MRSA) skin infection in 2 models of diabetes. Diabetic mice produced higher levels of LTB4 in the skin, which correlated with larger nonhealing lesion areas and increased bacterial loads compared with nondiabetic mice. High LTB4 levels were also associated with dysregulated cytokine and chemokine production, excessive neutrophil migration but impaired abscess formation, and uncontrolled collagen deposition. Both genetic deletion and topical pharmacological BLT1 antagonism restored inflammatory response and abscess formation, followed by a reduction in the bacterial load and lesion area in the diabetic mice. Macrophage depletion in diabetic mice limited LTB4 production and improved abscess architecture and skin host defense. These data demonstrate that exaggerated LTB4/BLT1 responses mediate a derailed inflammatory milieu that underlies poor host defense in diabetes. Prevention of LTB4 production/actions could provide a new therapeutic strategy to restore host defense in diabetes.

Too much of a good thing: How modulating LTB4 actions restore host defense in homeostasis or disease

The ability to regulate inflammatory pathways and host defense mechanisms is critical for maintaining homeostasis and responding to infections and tissue injury. While unbalanced inflammation is detrimental to the host; inadequate inflammation might not provide effective signals required to eliminate pathogens. On the other hand, aberrant inflammation could result in organ damage and impair host defense. The lipid mediator leukotriene B₄ (LTB₄) is a potent neutrophil chemoattractant and recently, its role as a dominant molecule that amplifies many arms of phagocyte antimicrobial effector function has been unveiled. However, excessive LTB₄ production contributes to disease severity in chronic inflammatory diseases such as diabetes and arthritis, which could potentially be involved in poor host defense in these groups of patients. In this review we discuss the cellular and molecular programs elicited during LTB₄ production and actions on innate immunity host defense mechanisms as well as potential therapeutic strategies to improve host defense.

5-Lipoxygenase Knockout Aggravated Apical Periodontitis in a Murine Model

5-Lipoxygenase (5-LO) plays a vital role in the host innate immune response, including bacteria-induced inflammation. Apical periodontitis (AP) is due to immune disorders caused by imbalances between bacterial invasion and subsequent host defense response. In this work, we investigated the role of 5-lipoxygenase in AP by using 5- lo knockout mice (5- lo-/- mice). Results showed that 5- lo-/- mice had greater periapical bone loss and more osteoclasts positive for tartrate-resistant acid phosphatase staining than did wild-type mice, as determined by micro-computed tomography and histologic staining. The inflammation- and osteoclastogenesis-related factors IL-1β, TNF-α, RANK, and RANKL were also significantly elevated in 5- lo-/- mice, whereas osteoprotegerin was reduced. Furthermore, peritoneal macrophages from 5- lo-/- mice revealed an obviously impaired ability to phagocytose the AP pathogenic bacteria Fusobacterium nucleatum. In vivo experiments confirmed that 5- lo knockout led to decreased macrophage recruitment and increased F. nucleatum infection around the periapical area due to decreased leukotriene B₄ and LXA4 production. All these results showed that 5- lo knockout impaired the host innate immune system to promote the release of bone resorption-related factors. Therefore, 5- lo deficiency aggravated AP in an experimental murine AP model.

The NOD2 receptor is crucial for immune responses towards New World Leishmania species

American Tegumentary Leishmaniasis is a chronic infection caused by Leishmania protozoan. It is not known whether genetic variances in NOD-like receptor (NLR) family members influence the immune response towards Leishmania parasites and modulate intracellular killing. Using functional genomics, we investigated whether genetic variants in NOD1 or NOD2 influence the production of cytokines by human PBMCs exposed to Leishmania. In addition, we examined whether recognition of Leishmania by NOD2 contributes to intracellular killing. Polymorphisms in the NOD2 gene decreased monocyte- and lymphocyte-derived cytokine production after stimulation with L. amazonensis or L. braziliensis compared to individuals with a functional NOD2 receptor. The phagolysosome formation is important for Leishmania-induced cytokine production and upregulation of NOD2 mRNA expression. NOD2 is crucial to control intracellular infection caused by Leishmania spp. NOD2 receptor is important for Leishmania recognition, the control of intracellular killing, and the induction of innate and adaptive immune responses.

Early Production of the Neutrophil-Derived Lipid Mediators LTB4 and LXA4 Is Modulated by Intracellular Infection with Leishmania major

Recruitment of neutrophil granulocytes to sites of infectious tissue damage is an early event in innate immune responses. Following chemotactic signals neutrophils establish a first line of defense in a swarm-like manner. Intracellular pathogens such as Leishmania major can, however, evade neutrophil-mediated killing and survive inside neutrophils. To achieve this the parasites evolved potent evasion mechanisms. Since neutrophils are a major source of inflammation regulating lipid mediators, we hypothesized that intracellular infection modifies the release of pro- and anti-inflammatory lipid mediators like leukotriene B4 (LTB₄) and lipoxin A4 (LXA₄), respectively. In the present study, we demonstrated in vitro that L. major-infected primary human neutrophils release an increased amount of LTB₄, whereas LXA₄ liberation is reduced during the first hours of infection. To investigate whether lipid mediator modulation is a common feature in intracellular infections, we tested the impact of an infection with Anaplasma phagocytophilum. Similarly to L. major, neutrophil infection with A. phagocytophilum led to an enhanced release of LTB₄ and decreased LXA₄ production. Together, our findings indicate that intracellular infections modulate the lipid mediator profile of neutrophils. This effect is likely to contribute to the survival of the pathogens in neutrophils and to the outcome of the infections.

Crosstalk between purinergic receptors and lipid mediators in leishmaniasis

Leishmaniasis is a neglected tropical disease affecting millions of people around the world caused by organisms of the genus Leishmania. Parasite escape mechanisms of the immune system confer the possibility of resistance and dissemination of the disease. A group of molecules that has become a target for Leishmania survival strategies are lipid mediators. Among them, leukotriene B₄ (LTB₄) has been described as a pro-inflammatory molecule capable of activating cells of the immune system to combat Leishmania. In an opposite way, prostaglandin E₂ (PGE₂) is a lipid mediator described as a deactivator of macrophages and neutrophils. The balance of these two molecules can be generated by extracellular nucleotides, such as adenosine 5'-triphosphate (ATP) and adenosine (Ado), which activate the purinergic receptors system. Herein, we discuss the role of extracellular nucleotides and the resulting balance of LTB₄ and PGE₂ in Leishmania fate, survival or death.

Degranulating Neutrophils Promote Leukotriene B4 Production by Infected Macrophages To Kill Leishmania amazonensis Parasites

Neutrophils mediate early responses against pathogens, and they become activated during endothelial transmigration toward the inflammatory site. In the current study, human neutrophils were activated in vitro with immobilized extracellular matrix proteins, such as fibronectin (FN), collagen, and laminin. Neutrophil activation by FN, but not other extracellular matrix proteins, induces the release of the granules' contents, measured as matrix metalloproteinase 9 and neutrophil elastase activity in culture supernatant, as well as reactive oxygen species production. Upon contact with Leishmania amazonensis-infected macrophages, these FN-activated neutrophils reduce the parasite burden through a mechanism independent of cell contact. The release of granule proteases, such as myeloperoxidase, neutrophil elastase, and matrix metalloproteinase 9, activates macrophages through TLRs, leading to the production of inflammatory mediators, TNF-α and leukotriene B4 (LTB4), which are involved in parasite killing by infected macrophages. The pharmacological inhibition of degranulation reverted this effect, abolishing LTB4 and TNF production. Together, these results suggest that FN-driven degranulation of neutrophils induces the production of LTB4 and TNF by infected macrophages, leading to the control of Leishmania infection.

Differential Expression of the Eicosanoid Pathway in Patients With Localized or Mucosal Cutaneous Leishmaniasis

Unfettered inflammation is thought to play critical role in the development of different clinical forms of tegumentary leishmaniasis. Eicosanoids are potent mediators of inflammation and tightly associated with modulation of immune responses. In this cross-sectional exploratory study, we addressed whether targets from the eicosanoid biosynthetic pathway, assessed by multiplexed expression assays in lesion biopsy and plasma specimens, could highlight a distinct biosignature in patients with mucocutaneous leishmaniasis (MCL) or localized cutaneous leishmaniasis (LCL). Differences in immunopathogenesis between MCL and LCL may result from an imbalance between prostaglandins and leukotrienes, which may serve as targets for future host-directed therapies.

Natural Products: Insights into Leishmaniasis Inflammatory Response

Leishmaniasis is a vector-borne disease that affects several populations worldwide, against which there are no vaccines available and the chemotherapy is highly toxic. Depending on the species causing the infection, the disease is characterized by commitment of tissues, including the skin, mucous membranes, and internal organs. Despite the relevance of host inflammatory mediators on parasite burden control, Leishmania and host immune cells interaction may generate an exacerbated proinflammatory response that plays an important role in the development of leishmaniasis clinical manifestations. Plant-derived natural products have been recognized as bioactive agents with several properties, including anti-protozoal and anti-inflammatory activities. The present review focuses on the antileishmanial activity of plant-derived natural products that are able to modulate the inflammatory response in vitro and in vivo. The capability of crude extracts and some isolated substances in promoting an anti-inflammatory response during Leishmania infection may be used as part of an effective strategy to fight the disease.

Two distinct leukotriene B4 receptors, BLT1 and BLT2

Leukotriene B4 (LTB4) is a potent inflammatory mediator derived from arachidonic acid. Two G protein-coupled receptors for LTB4 have been identified: a high-affinity receptor, BLT1, and a low-affinity receptor, BLT2. Both receptors mainly couple to pertussis toxin-sensitive Gi-like G proteins and induce cell migration. 12(S)-hydroxy-5Z,8E,10E-heptadecatrienoic acid (12-HHT) was identified to bind BLT2 with higher affinity than LTB4. Expression of BLT1 was confirmed in type 1 helper T cells, type 2 helper T cells, type 17 helper T cells, effector CD8(+) T cells, dendritic cells and osteoclasts in addition to granulocytes, eosinophils and macrophages, and BLT1-deficient mice showed greatly reduced phenotypes in models of various inflammatory diseases, such as peritonitis, bronchial asthma, rheumatoid arthritis, atherosclerosis and osteoporosis. In mice, BLT2 expression is restricted to intestinal epithelial cells and epidermal keratinocytes. BLT2-deficient mice showed enhanced colitis after administration of dextran sulfate, possibly due to reduced intestinal barrier function. An aspirin-dependent reduction in 12-HHT production was responsible for delayed skin wound healing, showing that the 12-HHT/BLT2 axis also plays an important role in skin biology. BLT1 and BLT2 are therefore potential targets for the development of novel drugs.