Neutrophils activate macrophages for intracellular killing of Leishmania major through recruitment of TLR4 by neutrophil elastase

PGLYRP1-mIgG2a-Fc inhibits macrophage activation via AKT/NF-κB signaling and protects against fatal lung injury during bacterial infection

Severe bacterial pneumonia leads to acute respiratory distress syndrome (ARDS), with a high incidence rate and mortality. It is well-known that continuous and dysregulated macrophage activation is vital for aggravating the progression of pneumonia. Here, we designed and produced an antibody-like molecule, peptidoglycan recognition protein 1-mIgG2a-Fc (PGLYRP1-Fc). PGLYRP1 was fused to the Fc region of mouse IgG2a with high binding to macrophages. We demonstrated that PGLYRP1-Fc ameliorated lung injury and inflammation in ARDS, without affecting bacterial clearance. Besides, PGLYRP1-Fc reduced AKT/nuclear factor kappa-B (NF-κB) activation via the Fc segment bound Fc gamma receptor (FcγR)-dependent mechanism, making macrophage unresponsive, and immediately suppressed proinflammatory response upon bacteria or lipopolysaccharide (LPS) stimulus in turn. These results confirm that PGLYRP1-Fc protects against ARDS by promoting host tolerance with reduced inflammatory response and tissue damage, irrespective of the host's pathogen burden, and provide a promising therapeutic strategy for bacterial infection.

Leishmaniasis: Immune Cells Crosstalk in Macrophage Polarization

Leishmaniasis is a complex infectious parasitic disease caused by protozoa of the genus Leishmania, belonging to a group of neglected tropical diseases. It establishes significant global health challenges, particularly in socio-economically disadvantaged regions. Macrophages, as innate immune cells, play a crucial role in initiating the inflammatory response against the pathogens responsible for this disease. Macrophage polarization, the process of differentiating macrophages into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, is essential for the immune response in leishmaniasis. The M1 phenotype is associated with resistance to Leishmania infection, while the M2 phenotype is predominant in susceptible environments. Notably, various immune cells, including T cells, play a significant role in modulating macrophage polarization by releasing cytokines that influence macrophage maturation and function. Furthermore, other immune cells can also impact macrophage polarization in a T-cell-independent manner. Therefore, this review comprehensively examines macrophage polarization's role in leishmaniasis and other immune cells' potential involvement in this intricate process.

Insights on Host-Parasite Immunomodulation Mediated by Extracellular Vesicles of Cutaneous Leishmania shawi and Leishmania guyanensis

Leishmaniasis is a parasitic disease caused by different species of Leishmania and transmitted through the bite of sand flies vector. Macrophages (MΦ), the target cells of Leishmania parasites, are phagocytes that play a crucial role in the innate immune microbial defense and are antigen-presenting cells driving the activation of the acquired immune response. Exploring parasite-host communication may be key in restraining parasite dissemination in the host. Extracellular vesicles (EVs) constitute a group of heterogenous cell-derived membranous structures, naturally produced by all cells and with immunomodulatory potential over target cells. This study examined the immunogenic potential of EVs shed by L. shawi and L. guyanensis in MΦ activation by analyzing the dynamics of major histocompatibility complex (MHC), innate immune receptors, and cytokine generation. L. shawi and L. guyanensis EVs were incorporated by MΦ and modulated innate immune receptors, indicating that EVs cargo can be recognized by MΦ sensors. Moreover, EVs induced MΦ to generate a mix of pro- and anti-inflammatory cytokines and favored the expression of MHCI molecules, suggesting that EVs antigens can be present to T cells, activating the acquired immune response of the host. Since nano-sized vesicles can be used as vehicles of immune mediators or immunomodulatory drugs, parasitic EVs can be exploited by bioengineering approaches for the development of efficient prophylactic or therapeutic tools for leishmaniasis.

Neutrophil-T cell crosstalk and the control of the host inflammatory response

While fundamental in their innate role in combating infection and responding to injury, neutrophils are emerging as key modulators of adaptive immune responses. Such functions are attained via both soluble and nonsoluble effectors that enable at least two major downstream outcomes: first, to mediate and control acute inflammatory responses and second, to regulate adaptive immunity and ultimately promoting the development and maintenance of immune tolerance either by releasing immuno-modulatory factors, including cytokines, or by directly interacting with cells of the adaptive immune system. Herein, we review these novel properties of neutrophils and redefine the pathophysiological functions of these fascinating multi-tasking cells, exploring the different mechanisms through which neutrophils are able to either enhance and orchestrate T cell pro-inflammatory responses or inhibit T cell activity to maintain immune tolerance.

Anti-leishmanial therapy: Caught between drugs and immune targets

Leishmaniasis is an enigmatic disease that has very restricted options for chemotherapy and none for prophylaxis. As a result, deriving therapeutic principles for curing the disease has been a major objective in Leishmania research for a long time. Leishmania is a protozoan parasite that lives within macrophages by subverting or switching cell signaling to the pathways that ensure its intracellular survival. Therefore, three groups of molecules aimed at blocking or eliminating the parasite, at least, in principle, include blockers of macrophage receptor- Leishmania ligand interaction, macrophage-activating small molecules, peptides and cytokines, and signaling inhibitors or activators. Macrophages also act as an antigen-presenting cell, presenting antigen to the antigen-specific T cells to induce activation and differentiation of the effector T cell subsets that either execute or suppress anti-leishmanial functions. Three groups of therapeutic principles targeting this sphere of Leishmania-macrophage interaction include antibodies that block pro-leishmanial response of T cells, ligands that activate anti-leishmanial T cells and the antigens for therapeutic vaccines. Besides these, prophylactic vaccines have been in clinical trials but none has succeeded so far. Herein, we have attempted to encompass all these principles and compose a comprehensive review to analyze the feasibility and adoptability of different therapeutics for leishmaniasis.

Neutrophil Elastase Increases Vascular Permeability and Leukocyte Transmigration in Cultured Endothelial Cells and Obese Mice

Neutrophil elastase (NE) plays a pivotal role in inflammation. However, the mechanism underlying NE-mediated inflammation in obesity remains unclear. Here, we report that NE activates protease-activated receptor-2 (PAR2), stimulates actin filament (F-actin) formation, decreases intercellular junction molecule VE-cadherin expression, and increases the permeability of human arterial endothelial cells (hECs). NE also prompts degradation of VE-cadherin and its binding proteins p120- and β-catenins via MG132-sensitive proteasomes. NE stimulates phosphorylation of myosin light-chain (MLC) and its regulator myosin phosphatase target subunit-1 (MYPT1), a target of Rho kinase (ROCK). Inhibitors of PAR2 and ROCK prohibit NE-induced F-actin formation, MLC phosphorylation, and VE-cadherin reduction in hECs, and impede monocyte transmigration through hEC monolayer pretreated with either neutrophils or NE. Further, administration of an NE inhibitor GW311616A significantly attenuates vascular leakage, leukocyte infiltration, and the expression of proinflammatory cytokines in the white adipose tissue from high-fat diet (HFD)-induced obese mice. Likewise, NE-deficient mice are resistant to HFD-induced vascular leakage in the heart. Together, NE regulates actomyosin cytoskeleton activity and VE-cadherin expression by activating PAR2 signaling in the endothelial cells, leading to increased vascular permeability and leukocyte extravasation. Hence, inhibition of NE is a potential approach to mitigate vascular injury and leukocyte infiltration in obesity-related systemic inflammation.

Immune Responses in Leishmaniases: An Overview

Leishmaniasis is a parasitic, widespread, and neglected disease that affects more than 90 countries in the world. More than 20 Leishmania species cause different forms of leishmaniasis that range in severity from cutaneous lesions to systemic infection. The diversity of leishmaniasis forms is due to the species of parasite, vector, environmental and social factors, genetic background, nutritional status, as well as immunocompetence of the host. Here, we discuss the role of the immune system, its molecules, and responses in the establishment, development, and outcome of Leishmaniasis, focusing on innate immune cells and Leishmania major interactions.

Host–Pathogen Interaction in Leishmaniasis: Immune Response and Vaccination Strategies

Leishmaniasis is a zoonotic and vector-borne infectious disease that is caused by the genus Leishmania belonging to the trypanosomatid family. The protozoan parasite has a digenetic life cycle involving a mammalian host and an insect vector. Leishmaniasisis is a worldwide public health problem falling under the neglected tropical disease category, with over 90 endemic countries, and approximately 1 million new cases and 20,000 deaths annually. Leishmania infection can progress toward the development of species–specific pathologic disorders, ranging in severity from self-healing cutaneous lesions to disseminating muco-cutaneous and fatal visceral manifestations. The severity and the outcome of leishmaniasis is determined by the parasite’s antigenic epitope characteristics, the vector physiology, and most importantly, the immune response and immune status of the host. This review examines the nature of host–pathogen interaction in leishmaniasis, innate and adaptive immune responses, and various strategies that have been employed for vaccine development.

Antimicrobial Activity of Neutrophils Against Mycobacteria

The mycobacterium genus contains a broad range of species, including the human pathogens M. tuberculosis and M. leprae. These bacteria are best known for their residence inside host cells. Neutrophils are frequently observed at sites of mycobacterial infection, but their role in clearance is not well understood. In this review, we discuss how neutrophils attempt to control mycobacterial infections, either through the ingestion of bacteria into intracellular phagosomes, or the release of neutrophil extracellular traps (NETs). Despite their powerful antimicrobial activity, including the production of reactive oxidants such as hypochlorous acid, neutrophils appear ineffective in killing pathogenic mycobacteria. We explore mycobacterial resistance mechanisms, and how thwarting neutrophil action exacerbates disease pathology. A better understanding of how mycobacteria protect themselves from neutrophils will aid the development of novel strategies that facilitate bacterial clearance and limit host tissue damage.

Immunomodulatory role of Th17 pathway in experimental visceral leishmaniasis

Visceral leishmaniasis (VL) or Kala-azar is a vector borne protozoan infection caused by Leishmania donovani in the Indian subcontinent mainly India, Nepal and Bangladesh. It is a major public health problem in these countries mostly affecting the socio-economically poor population. Leishmaniasis ranks the third most important disease after malaria and filariasis but is still considered as one of the neglected tropical diseases of the world. For development of better therapeutic agents and effective vaccine against VL, there is a need to understand host immunological changes that play a vital role during course of infection. Therefore, we investigated the role of Th17 pathway in Balb/c mice during Leishmania donovani infection and treatment with amphotericin B. Mice were divided in four groups i.e. Control, Infected, Uninfected treated and Infected treated. The cytokine levels were estimated in the spleen of Balb/c mice on days 1, 3, 7, 14, 17, 21, 28, 35, 45 and 60 post infection and during course of treatment. The mRNA levels of the Th17 pathway during active Leishmania donovani infection and after treatment were determined by real time polymerase chain reaction (RT-PCR) and protein levels by flow cytometry and ELISA. Results of our study revealed that active infection was associated with low levels of Th17 cytokines IL-17, IL-22 and IL-23 and elevated levels of IL-6, IL-1β and TGF-β. Amphotericin B treatment restored production of pro-inflammatory cytokines IL-17 and IL-22. The levels of transcription factor RORγt were found to correlate with the levels of IL-17 during infection and also after chemotherapy whereas STAT3 levels were elevated during infection and vice versa after treatment. The findings of this study suggest that Th17 cytokines IL-17 and IL-22 are associated with protection against VL infection and development of any interventions or chemotherapeutic agents targeting Th17 pathway could be an important approach for VL treatment.

Resistance Against Leishmania major Infection Depends on Microbiota-Guided Macrophage Activation

Innate immune cells present a dual role during leishmaniasis: they constitute the first line of host defense but are also the main host cells for the parasite. Response against the infection that results in the control of parasite growth and lesion healing depends on activation of macrophages into a classical activated phenotype. We report an essential role for the microbiota in driving macrophage and monocyte-derived macrophage activation towards a resistance phenotype against Leishmania major infection in mice. Both germ-free and dysbiotic mice showed a higher number of myeloid innate cells in lesions and increased number of infected cells, mainly dermal resident and inflammatory macrophages. Despite developing a Th1 immune response characterized by the same levels of IFN-γ production as the conventional mice, germ-free mice presented reduced numbers of iNOS+ macrophages at the peak of infection. Absence or disturbance of host microbiota impaired the capacity of bone marrow-derived macrophage to be activated for Leishmania killing in vitro, even when stimulated by Th1 cytokines. These cells presented reduced expression of inos mRNA, and diminished production of microbicidal molecules, such as ROS, while presenting a permissive activation status, characterized by increased expression of arginase I and il-10 mRNA and higher arginase activity. Colonization of germ-free mice with complete microbiota from conventional mice rescued their ability to control the infection. This study demonstrates the essential role of host microbiota on innate immune response against L. major infection, driving host macrophages to a resistance phenotype.

Multi-facets of neutrophil extracellular trap in infectious diseases: Moving beyond immunity

Neutrophil extracellular traps (NETs) are networks of extracellular chromosomal DNA fibers, histones, and cytoplasmic granule proteins. The release of NET components from neutrophils is involved in the suppression of pathogen diffusion. Development of NETs around target microbes leads to disruption of the cell membrane, eventuating in kind of cell death that is called as NETosis. The very first step in the process of NETosis is activation of Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase upon signaling by innate immune receptors. Afterwards, produced Reactive oxygen species (ROS) trigger protein-arginine deiminase type 4, neutrophil elastase, and myeloperoxidase to generate decondensed chromatin and disrupted integrity of nuclear membrane. Subsequently, decondensed chromatin is mixed with several enzymes in the cytoplasm released from granules, leading to release of DNA and histones, and finally formation of NET. Several reports have indicated that NETosis might contribute to the immune responses through limiting the dissemination of microbial organisms. In this review, we discuss recent advances on the role of neutrophils, NETs, and their implications in the pathogenesis of microbial infections. Additionally, the prospective of the NET modulation as a therapeutic strategy to treat infectious diseases are clarified.

Neutrophil extracellular traps from healthy donors and HIV-1-infected individuals restrict HIV-1 production in macrophages

Neutrophils release extracellular traps (NETs) after interaction with microorganisms and physiological or synthetic products. NETs consist of decondensed chromatin complexed with proteins, some of them with microbicidal properties. Because NETs can modulate the functioning of HIV-1 target cells, we aimed to verify whether they modify HIV-1 replication in macrophages. We found that exposure of HIV-1-infected macrophages to NETs resulted in significant inhibition of viral replication. The NET anti-HIV-1 action was independent of other soluble factors released by the activated neutrophils, but otherwise dependent on the molecular integrity of NETs, since NET-treatment with protease or DNase abolished this effect. NETs induced macrophage production of the anti-HIV-1 β-chemokines Rantes and MIP-1β, and reduced the levels of integrated HIV-1 DNA in the macrophage genome, which may explain the decreased virus production by infected macrophages. Moreover, the residual virions released by NET-treated HIV-1-infected macrophages lost infectivity. In addition, elevated levels of DNA-elastase complexes were detected in the plasma from HIV-1-infected individuals, and neutrophils from these patients released NETs, which also inhibited HIV-1 replication in in vitro infected macrophages. Our results reveal that NETs may function as an innate immunity mechanism able to restrain HIV-1 production in macrophages.

DH82 Canine and RAW264.7 Murine Macrophage Cell Lines Display Distinct Activation Profiles Upon Interaction With Leishmania infantum and Leishmania amazonensis

Leishmaniasis is an anthropozoonotic disease, and dogs are considered the main urban reservoir of the parasite. Macrophages, the target cells of Leishmania sp., play an important role during infection. Although dogs have a major importance in the epidemiology of the disease, the majority of the current knowledge about Leishmania–macrophage interaction comes from murine experimental models. To assess whether the canine macrophage strain DH82 is an accurate model for the study of Leishmania interaction, we compared its infection by two species of Leishmania (Leishmania infantum and L. amazonensis) with the murine macrophage cell line (RAW264.7). Our results demonstrated that L. amazonensis survival was around 40% at 24 h of infection inside both macrophage cell lines; however, a reduction of 4.3 times in L. amazonensis infection at 48 h post-infection in RAW 264.7 macrophages was observed. The survival index of L. infantum in DH82 canine macrophages was around 3 times higher than that in RAW264.7 murine cells at 24 and 48 h post-infection; however, at 48 h a reduction in both macrophages was observed. Surprisingly at 24 h post-infection, NO and ROS production by DH82 canine cells stimulated with LPS or menadione or during Leishmania infection was minor compared to murine RAW264.7. However, basal arginase activity was higher in DH82 cells when compared to murine RAW264.7 cells. Analysis of the cytokines showed that these macrophages present a different response profile. L. infantum induced IL-12, and L. amazonensis induced IL-10 in both cell lines. However, L. infantum and L. amazonensis also induced TGF-β in RAW 264.7. CD86 and MHC expression showed that L. amazonensis modulated them in both cell lines. Conversely, the parasite load profile did not show significant difference between both macrophage cell lines after 48 h of infection, which suggests that other mechanisms of Leishmania control could be involved in DH82 cells.

Protease-activated prodrugs: strategies, challenges, and future directions

Proteases play critical roles in virtually all biological processes, including proliferation, cell death and survival, protein turnover, and migration. However, when dysregulated, these enzymes contribute to the progression of multiple diseases, with cancer, neurodegenerative disorders, inflammation, and blood disorders being the most prominent examples. For a long time, disease-associated proteases have been used for the activation of various prodrugs due to their well-characterized catalytic activity and ability to selectively cleave only those substrates that strictly correspond with their active site architecture. To date, versatile peptide sequences that are cleaved by proteases in a site-specific manner have been utilized as bioactive linkers for the targeted delivery of multiple types of cargo, including fluorescent dyes, photosensitizers, cytotoxic drugs, antibiotics, and pro-antibodies. This platform is highly adaptive, as multiple protease-labile conjugates have already been developed, some of which are currently in clinical use for cancer treatment. In this review, recent advancements in the development of novel protease-cleavable linkers for selective drug delivery are described. Moreover, the current limitations regarding the selectivity of linkers are discussed, and the future perspectives that rely on the application of unnatural amino acids for the development of highly selective peptide linkers are also presented.

The Chymase Mouse Mast Cell Protease-4 Regulates Intestinal Cytokine Expression in Mature Adult Mice Infected with Giardia intestinalis

Mast cells have been shown to affect the control of infections with the protozoan parasite Giardia intestinalis. Recently, we demonstrated that Giardia excretory-secretory proteins inhibited the activity of the connective tissue mast cell-specific protease chymase. To study the potential role of the chymase mouse mast cell protease (mMCP)-4 during infections with Giardia, mMCP-4^+/+ and mMCP-4^−/− littermate mice were gavage-infected with G. intestinalis trophozoites of the human assemblage B isolate GS. No significant changes in weight gain was observed in infected young (≈10 weeks old) mMCP-4^−/− and mMCP-4^+/+ littermate mice. In contrast, infections of mature adult mice (>18 weeks old) caused significant weight loss as compared to uninfected control mice. We detected a more rapid weight loss in mMCP-4^−/− mice as compared to littermate mMCP-4^+/+ mice. Submucosal mast cell and granulocyte counts in jejunum increased in the infected adult mMCP-4^−/− and mMCP-4^+/+ mice. This increase was correlated with an augmented intestinal trypsin-like and chymotrypsin-like activity, but the myeloperoxidase activity was constant. Infected mice showed a significantly lower intestinal neutrophil elastase (NE) activity, and in vitro, soluble Giardia proteins inhibited human recombinant NE. Serum levels of IL-6 were significantly increased eight and 13 days post infection (dpi), while intestinal IL-6 levels showed a trend to significant increase 8 dpi. Strikingly, the lack of mMCP-4 resulted in significantly less intestinal transcriptional upregulation of IL-6, TNF-α, IL-25, CXCL2, IL-2, IL-4, IL-5, and IL-10 in the Giardia-infected mature adult mice, suggesting that chymase may play a regulatory role in intestinal cytokine responses.

Neutrophil Extracellular Traps Drive Mitochondrial Homeostasis in Tumors to Augment Growth

Neutrophil infiltration and neutrophil extracellular traps (NET) in solid cancers are associated with poorer prognosis, but the mechanisms are incompletely understood. We hypothesized that NETs enhance mitochondrial function in tumor cells, providing extra energy for accelerated growth. Metastatic colorectal cancer tissue showed increased intratumoral NETs and supranormal preoperative serum MPO-DNA, a NET marker. Higher MPO-DNA correlated with shorter survival. In mice, subcutaneous tumor implants and hepatic metastases grew slowly in PAD4-KO mice, genetically incapable of NETosis. In parallel experiments, human cancer cell lines grew slower in nu/nu mice treated with DNAse, which disassembles NETs. PAD4-KO tumors manifested decreased proliferation, increased apoptosis, and increased evidence of oxidative stress. PAD4-KO tumors had decreased mitochondrial density, mitochondrial DNA, a lesser degree of ATP production, along with significantly decreased mitochondrial biogenesis proteins PGC1α, TFAM, and NRF-1. In vitro, cancer cells treated with NETs upregulated mitochondrial biogenesis-associated genes, increased mitochondrial density, increased ATP production, enhanced the percentage of cancer cells with reduced mitochondrial membrane potential, and increased the oxygen consumption rate. Furthermore, NETs increased cancer cells' expression of fission and fusion-associated proteins, DRP-1 and MFN-2, and mitophagy-linked proteins, PINK1 and Parkin. All of which were decreased in PAD4-KO tumors. Mechanistically, neutrophil elastase released from NETs activated TLR4 on cancer cells, leading to PGC1α upregulation, increased mitochondrial biogenesis, and accelerated growth. Taken together, NETs can directly alter the metabolic programming of cancer cells to increase tumor growth. NETs represent a promising therapeutic target to halt cancer progression. SIGNIFICANCE: Neutrophils through the release of NETs facilitate the growth of stressed cancer cells by altering their bioenergetics, the inhibition of which induces cell death.

Neutrophil elastase promotes Leishmania donovani infection via interferon-β

Visceral leishmaniasis is a deadly illness caused by Leishmania donovani that provokes liver and spleen inflammation and tissue destruction. In cutaneous leishmaniasis, the protein of L. major, named inhibitor of serine peptidases (ISP) 2, inactivates neutrophil elastase (NE) present at the macrophage surface, resulting in blockade of TLR4 activation, prevention of TNF-α and IFN-β production, and parasite survival. We report poor intracellular growth of L. donovani in macrophages from knockout mice for NE (ela^-/-), TLR4, or TLR2. NE and TLR4 colocalized with the parasite in the parasitophorous vacuole. Parasite load in the liver and spleen of ela^-/- mice were reduced and accompanied by increased NO and decreased TGF-β production. Expression of ISP2 was not detected in L. donovani, and a transgenic line constitutively expressing ISP2, displayed poor intracellular growth in macrophages and decreased burden in mice. Infected ela^-/- macrophages displayed significantly lower IFN-β mRNA than background mice macrophages, and the intracellular growth was fully restored by exogenous IFN-β. We propose that L. donovani utilizes the host NE-TLR machinery to induce IFN-β necessary for parasite survival and growth during early infection. Low or absent expression of parasite ISP2 in L. donovani is necessary to preserve the activation of the NE-TLR pathway.-Dias, B. T., Dias-Teixeira, K. L., Godinho, J. P., Faria, M. S., Calegari-Silva, T., Mukhtar, M. M., Lopes, U. G., Mottram, J. C., Lima, A. P. C. A. Neutrophil elastase promotes Leishmania donovani infection via interferon-β.

Leishmania major degrades murine CXCL1 - An immune evasion strategy

Leishmaniasis is a global health problem with an estimated report of 2 million new cases every year and more than 1 billion people at risk of contracting this disease in endemic areas. The innate immune system plays a central role in controlling L. major infection by initiating a signaling cascade that results in production of pro-inflammatory cytokines and recruitment of both innate and adaptive immune cells. Upon infection with L. major, CXCL1 is produced locally and plays an important role in the recruitment of neutrophils to the site of infection. Herein, we report that L. major specifically targets murine CXCL1 for degradation. The degradation of CXCL1 is not dependent on host factors as L. major can directly degrade recombinant CXCL1 in a cell-free system. Using mass spectrometry, we discovered that the L. major protease cleaves at the C-terminal end of murine CXCL1. Finally, our data suggest that L. major metalloproteases are involved in the direct cleavage and degradation of CXCL1, and a synthetic peptide spanning the CXCL1 cleavage site can be used to inhibit L. major metalloprotease activity. In conclusion, our study has identified an immune evasion strategy employed by L. major to evade innate immune responses in mice, likely reservoirs in the endemic areas, and further highlights that targeting these L. major metalloproteases may be important in controlling infection within the reservoir population and transmittance of the disease.

Our study discovered a highly specific role for L. major metalloprotease in cleaving and degrading murine CXCL1. Indeed, L. major metalloprotease did not cleave murine CXCL2 or human CXCL1, CXCL2 and CXCL8. CXCL1 is a critical chemokine required for neutrophil recruitment to the site of infection; thus, we propose that this metalloprotease may have evolved to evade immune responses specifically in the murine host. We have further identified that the C-terminal end on CXCL1 is targeted for cleavage by the L. major metalloprotease. Finally, this cleavage site information was used to design peptides that are able to inhibit CXCL1 degradation by L. major. Our study highlights an immune evasion strategy utilized by L. major to establish infection within a murine host.

Immunotherapy in clinical canine leishmaniosis: a comparative update

Leishmaniosis due to Leishmania infantum is a complex infection that can affect both humans and dogs, and present a wide range of clinical signs and clinicopathological abnormalities. The conventional treatment of this disease is challenging due to the fact that complete parasitological cure commonly does not occur. Furthermore, treatment of the disease with the conventionally used drugs has several shortcomings. These include the need for long-term treatment, side effects and the formation of drug resistance. Moreover, it is important to highlight that the host immune responses play a crucial role in the outcome of this infection. For this reason, the use of immunotherapy in clinical leishmaniosis to improve the result of treatment with the conventional anti-leishmanial drugs by enhancing the immune response is imperative. The aim of this review is to provide a comparative overview of the wide range of immunotherapeutical approaches and strategies for the treatment of L. infantum infection in animals focusing on dogs.

Neutrophil properties in healthy and Leishmania infantum-naturally infected dogs

Visceral leishmaniasis is a chronic disease that affects humans and dogs as well. Dogs, the domestic reservoir of Leishmania, play a central role in the transmission of visceral leishmaniasis, the most severe form of this disease. Neutrophils are the most abundant leukocytes in blood and interact with the parasite after infection. Here, we evaluate the effector properties of neutrophils from healthy and naturally Leishmania infantum-infected dogs. Our results showed that the parasite induced neutrophil extracellular trap (NET) release from neutrophils in both groups. Additionally, phagocytosis and NETs contributed differently to parasite killing by neutrophils from healthy and infected animals, and IFN-γ, IL-8, IL-4 and TNF-α production by neutrophils from both groups were differentially modulated by the parasite. Our results contribute to a better understanding of the complex role played by neutrophils in canine visceral leishmaniasis, which may favor the development of more effective therapies.

How to master the host immune system? Leishmania parasites have the solutions!

Infection by protozoan parasites of the genus Leishmania results in the development of leishmaniasis, an increasingly prevalent group of diseases affecting over 12 million people worldwide. Leishmaniasis can have very different outcomes ranging from cutaneous lesions, mucosal lesions to visceralization depending on the species of the infecting parasite and on the immune response developed by the host. As an obligate intracellular parasite, residing within macrophages, Leishmania evolved in strict contact with the host immune system, developing different mechanisms to evade or modulate the immune response. Various types of immune responses are observed during different Leishmania spp. infections, resulting in parasite clearance but also contributing to the pathogenesis, thus increasing the complexity of the course of the disease. Interestingly, depending on the type of leishmaniasis developed, opposite treatment strategies, which either boost or inhibit the inflammatory response, have shown efficacy. In this review, we summarize the contribution of different immune cell types to the development of the anti-leishmanial immune response and the parasite strategies to evade and modulate host immunity. Further, we discuss the involvement of co-infecting pathogens in the determination of the outcome of leishmaniasis and on the effectiveness of treatment and the implication of the immune response for treatment and vaccine development.

Canine neutrophils cooperate with macrophages in the early stages of Leishmania infantum in vitro infection

Leishmania infantum is the aetiological agent of human visceral leishmaniasis and canine leishmaniasis, both systemic and potentially fatal diseases. Polymorphonuclear neutrophils (PMN) are the first cells to phagocyte this parasite at the inoculation site, but macrophages (MØ) are the definitive host cells, ensuring parasite replication. The interaction between dog MØ, PMN and L infantum promastigotes was in vitro investigated. It was observed that promastigotes establish contact with blood monocyte-derived MØ mainly by the tip of the flagellum. These cells, that efficiently bind and internalize parasites, underwent major morphological changes, produced nitric oxide (NO) and released histone H1 in order to inactivate the parasite. Transfer of intracellular parasites from PMN to MØ was confirmed by flow cytometry, using L infantum expressing a green fluorescent protein. The interaction of MØ with L infantum-infected PMN lead to NO production and release of extracellular traps, which may contribute to parasite containment and inactivation. This study highlights for the first time the diversity of cellular and molecular events triggered by the interaction between canine PMN and MØ, which can promote a reduction of parasite burden in the early phase of L infantum infection.

Cytokine Effect of TLR3, TLR4, and TLR7 Agonists Alone or Associated with Leishmania infantum Antigen on Blood from Dogs

Activation of toll-like receptors (TLRs) has been shown to play an important role in leishmaniosis by enhancing the parasite specific immune responses to control infection. However, the role of TLR agonists has not been studied in detail in dogs. The aim of this study was to determine the effect of TLR3, TLR4, and TLR7 agonists (TLR3a, TLR4a, and TLR7a) alone or in combination with Leishmania infantum antigen (LSA) on TNF-α and IL-6 production in blood from dogs living in endemic areas of canine leishmaniosis (CanL). Twenty-four healthy dogs from Catalonia (n=14) and Ibizan hound dogs from the island of Mallorca (n=10) were enrolled. Whole blood with TLR3a, TLR4a, and TLR7a alone or combined with LSA were cultured separately, and IFN-γ, TNF-α, and IL-6 were measured by ELISA. A significant increase of TNF-α was found for all conditions studied compared to medium alone. Stimulation with TLR4a (p=0.0001) and TLR7a (p=0.005) presented a significantly marked increase in TNF-α and IL-6 production compared to TLR3a. Importantly, significantly higher TNF-α production was found in LSA+TLR4a (p=0.0001) stimulated blood and LSA+TLR7a (p=0.005) compared to LSA alone. All dogs showed higher TNF-α production after LSA+TLR7a compared to TLR7a (p=0.047) and LSA+TLR3a compared to TLR3a (p=0.052). These data indicate a marked inflammatory cytokine effect of TLR4a and TLR7a on blood from healthy dogs living in endemic areas of CanL. Additionally, LSA+TLR7a promoted a synergistic proinflammatory effect with TNF-α in all dogs. Those findings suggest an active role of TLRs in proinflammatory responses, which might be strongly involved in the process of disease resolution.

Lutzomyia longipalpis Saliva Drives Interleukin-17-Induced Neutrophil Recruitment Favoring Leishmania infantum Infection

During bloodfeeding, the presence of sand fly saliva in the hemorrhagic pool where Leishmania is also inoculated modulates the development of host immune mechanisms creating a favorable environment for disease progression. To date, information obtained through experimental models suggests that sand fly saliva induces cellular recruitment and modulates production of eicosanoids. However, the effect of sand fly saliva in the different steps of the inflammatory response triggered by Leishmania remains undefined. Here we further investigate if interaction of Lutzomyia longipalpis salivary gland sonicate (SGS) with different host cells present during the initial inflammatory events regulate Leishmania infantum infectivity. Initially, we observed that incubation of human peripheral blood mononuclear cells (PBMC) with Lu. longipalpis SGS in the presence of L. infantum significantly increased IL-10 but did not alter expression of IFN-γ and TNF-α by CD4⁺ T cells induced by the parasite alone. Interestingly, incubation of PBMC with Lu. longipalpis SGS alone or in the presence of L. infantum resulted in increased IL-17 production. The presence of IL-17 is related to neutrophil recruitment and plays an important role at the site of infection. Here, we also observed increased migration of neutrophil using an in vitro chemotactic assay following incubation with supernatants from PBMC stimulated with L. infantum and Lu. longipalpis SGS. Neutrophil migration was abrogated following neutralization of IL-17 with specific antibodies. Moreover, culture of human neutrophils with L. infantum in the presence of Lu. longipalpis SGS promoted neutrophil apoptosis resulting in increased parasite viability. Neutrophils operate as the first line of defense in the early stages of infection and later interact with different cells, such as macrophages. The crosstalk between neutrophils and macrophages is critical to determine the type of specific immune response that will develop. Here, we observed that co-culture of human macrophages with autologous neutrophils previously infected in the presence of Lu. longipalpis SGS resulted in a higher infection rate, accompanied by increased production of TGF-β and PGE₂. Our results provide new insight into the contribution of Lu. longipalpis SGS to L. infantum-induced regulation of important inflammatory events, creating a favorable environment for parasite survival inside different host cells.

Unbalanced inflammatory reaction could increase tissue destruction and worsen skin infectious diseases - a comparative study of leishmaniasis and sporotrichosis

The clinical presentations of skin diseases produced by different pathogens, as American tegumentary leishmaniasis (ATL) and sporotrichosis can be similar and possibly influenced by the skin immune system (SIS). The aim of the study was to understand the underlying mechanisms of skin inflammation produced by different pathogens. We used immunohistochemistry to analyze 96 patients: a- localized cutaneous leishmaniasis (LCL-ATL); b- sporotrichoid cutaneous leishmaniasis (SCL-ATL); c-lymphocutaneous (LC-SP); d- fixed (F-SP) sporotrichosis. LCL-ATL and SCL-ATL had a significantly higher percentage of CD8, FasL and NOS2 than sporotrichosis. In contrast, LC-SP had a substantially higher percentage of CD4, BCl2 and neutrophils than ATL lesions. These results indicated some differences in the profile of the in situ immune response suggesting that SIS is a complex, adaptable system capable of different responses to intracellular or extracellular pathogens. However, regardless of the etiological agents, the inflammatory reaction and clinical manifestations can be similar. SCL-ATL and LC-SP presented similarities in both clinical presentation and in situ inflammatory profile (CD3, CD22, neutrophils, macrophages). The clinical presentation of ATL and sporotrichosis could be explained by a combination of factors both of the host SIS and the etiological agent. The unbalanced host parasite relationship could result in atypical manifestations of skin disease.

Cytotoxic activity in cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) is a chronic disease caused by species of the protozoan Leishmania and characterised by the presence of ulcerated skin lesions. Both parasite and host factors affect the clinical presentation of the disease. The development of skin ulcers in CL is associated with an inflammatory response mediated by cells that control parasite growth but also contribute to pathogenesis. CD8+ T cells contribute to deleterious inflammatory responses in patients with CL through cytotoxic mechanisms. In addition, natural killer cells also limit Leishmania infections by production of interferon-γ and cytotoxicity. In this review, we focus on studies of cytotoxicity in CL and its contribution to the pathogenesis of this disease.

Interleukin-4 Receptor Alpha: From Innate to Adaptive Immunity in Murine Models of Cutaneous Leishmaniasis

The interleukin (IL)-4 receptor alpha (IL-4Rα), ubiquitously expressed on both innate and adaptive immune cells, controls the signaling of archetypal type 2 immune regulators; IL-4 and IL-13, which elicit their signaling action by the type 1 IL-4Rα/gamma common and/or the type 2 IL-4Rα/IL-13Rα complexes. Global gene-deficient mouse models targeting IL-4, IL-13, or the IL-4Rα chain, followed by the development of conditional mice and generation of important cell-type-specific IL-4Rα-deficient mouse models, were indeed critical to gaining in-depth understanding of detrimental T helper (Th) 2 mechanisms in type 1-controlled diseases. A primary example being cutaneous leishmaniasis, which is caused by the protozoan parasite Leishmania major, among others. The disease is characterized by localized self-healing cutaneous lesions and necrosis for which, currently, not a single vaccine has made it to a stage that can be considered effective. The spectrum of human leishmaniasis belongs to the top 10 infectious diseases according to the World Health Organization. As such, 350 million humans are at risk of infection and disease, with an incidence of 1.5–2 million new cases being reported annually. A major aim of our research is to identify correlates of host protection and evasion, which may aid in vaccine design and therapeutic interventions. In this review, we focus on the immune-regulatory role of the IL-4Rα chain from innate immune responses to the development of beneficial type 1 and detrimental type 2 adaptive immune responses during cutaneous Leishmania infection. We discuss the cell-specific requirements of the IL-4Rα chain on crucial innate immune cells during L. major infection, including, IL-4Rα-responsive skin keratinocytes, macrophages, and neutrophils, as well as dendritic cells (DCs). The latter, contributing to one of the paradigm shifts with respect to the role of IL-4 instructing DCs in vivo, to promote Th1 responses against L. major. Finally, we extend these innate responses and mechanisms to control of adaptive immunity and the effect of IL-4Rα-responsiveness on T and B lymphocytes orchestrating the development of CD4⁺ Th1/Th2 and B effector 1/B effector 2 B cells in response to L. major infection in the murine host.

Host Antimicrobial Peptides: The Promise of New Treatment Strategies against Tuberculosis

Tuberculosis (TB) continues to be a devastating infectious disease and remerges as a global health emergency due to an alarming rise of antimicrobial resistance to its treatment. Despite of the serious effort that has been applied to develop effective antitubercular chemotherapies, the potential of antimicrobial peptides (AMPs) remains underexploited. A large amount of literature is now accessible on the AMP mechanisms of action against a diversity of pathogens; nevertheless, research on their activity on mycobacteria is still scarce. In particular, there is an urgent need to integrate all available interdisciplinary strategies to eradicate extensively drug-resistant Mycobacterium tuberculosis strains. In this context, we should not underestimate our endogenous antimicrobial proteins and peptides as ancient players of the human host defense system. We are confident that novel antibiotics based on human AMPs displaying a rapid and multifaceted mechanism, with reduced toxicity, should significantly contribute to reverse the tide of antimycobacterial drug resistance. In this review, we have provided an up to date perspective of the current research on AMPs to be applied in the fight against TB. A better understanding on the mechanisms of action of human endogenous peptides should ensure the basis for the best guided design of novel antitubercular chemotherapeutics.

Redundant and regulatory roles for Toll-like receptors in Leishmania infection

Toll-like receptors (TLRs) are germline-encoded, non-clonal innate immune receptors, which are often the first receptors to recognize the molecular patterns on pathogens. Therefore, the immune response initiated by TLRs has far-reaching consequences on the outcome of an infection. As soon as the cell surface TLRs and other receptors recognize a pathogen, the pathogen is phagocytosed. Inclusion of TLRs in the phagosome results in quicker phagosomal maturation and stronger adaptive immune response, as TLRs influence co-stimulatory molecule expression and determinant selection by major histocompatibility complex (MHC) class II and MHC class I for cross-presentation. The signals delivered by the TCR-peptide-MHC complex and co-stimulatory molecules are indispensable for optimal T cell activation. In addition, the cytokines induced by TLRs can skew the differentiation of activated T cells to different effector T cell subsets. However, the potential of TLRs to influence adaptive immune response into different patterns is severely restricted by multiple factors: gross specificity for the molecular patterns, lack of receptor rearrangements, sharing of limited number of adaptors that assemble signalling complexes and redundancy in ligand recognition. These features of apparent redundancy and regulation in the functioning of TLRs characterize them as important and probable contributory factors in the resistance or susceptibility to an infection.

Neutrophil extracellular traps in patients with pulmonary tuberculosis

Tuberculosis is a devastating infectious disease causing many deaths worldwide. Recent investigations have implicated neutrophil extracellular traps (NETs) in the host response to tuberculosis. The aim of the current study was to obtain evidence for NETs release in the circulation during human tuberculosis. For this we measured the plasma concentrations of nucleosomes in conjunction with neutrophil elastase, in 64 patients with active pulmonary tuberculosis and 32 healthy controls. Patients with active tuberculosis had elevated plasma levels of nucleosomes and elastase when compared with local healthy blood donors. Furthermore nucleosome and elastase levels showed a positive correlation. These findings provide the first evidence for the release of NETs in the circulation of patients with active pulmonary tuberculosis.

Moroccan strains of Leishmania major and Leishmania tropica differentially impact on nitric oxide production by macrophages

BACKGROUND

Cutaneous leishmaniasis (CL) is a vector-borne parasitic disease caused by protozoa of the genus Leishmania. In Morocco, CL is a public health problem mainly caused by Leishmania major and Leishmania tropica, which are responsible for zoonotic and anthroponotic CL, respectively. Macrophages are the primary cells infected by Leishmania parasites and their capacity to produce nitric oxide (NO) is of critical importance for parasite elimination. To our knowledge, the role of NO on autochthonous infections has never been investigated before. In this study, we evaluated in vitro the capacity of autochthonous primary dermotropic strains of L. major and L. tropica to modulate NO production by J774-macrophages and determine the sensitivity of both species to exogenous NO.

METHODS

The infectivity of the J774 cell line was analyzed by optical microscopy. NO production by macrophages was measured by the Griess method. The sensitivity to NO by the two strains was assessed by the MTT assay using NO donors.

RESULTS

Our results show that the percentage of infected macrophages and the average number of parasites per macrophage were similar for L. major and L. tropica strains. While L. tropica significantly inhibited NO production induced by LPS and IFN-γ stimulation in J774 macrophages, L. major did not affect it. However, soluble Leishmania antigens (SLAs) from both autochthonous primary strains significantly inhibited the production of NO by J774-macrophages in a dose-dependent manner. Finally, our results demonstrated that promastigotes and amastigotes from both strains are sensitive to SNAP NO donor in a dose-dependent manner, although L. tropica demonstrated an increased sensitivity.

CONCLUSIONS

Our results suggest a differential ability of L. major and L. tropica strains to modulate the capacity of macrophages to produce NO. The increased ability of L. tropica to inhibit NO production by macrophages might come as a necessity due to its higher sensitivity to NO donor. Our results provide one explanation for the tendency of L. tropica to cause chronic lesions and may contribute to the different physiopathology of CL in Morocco.

The circadian clock in immune cells controls the magnitude of Leishmania parasite infection

The intracellular parasite Leishmania uses neutrophils and macrophages as host cells upon infection. These immune cells harbour their own intrinsic circadian clocks, known to influence many aspects of their functions. Therefore, we tested whether the host circadian clocks regulate the magnitude of Leishmania major infection in mice. The extent of parasitic infection varied over 24 h in bone marrow-derived macrophages in vitro and in two different in vivo models, footpad and peritoneal cavity infection. In vivo this was paralleled by time of day-dependent neutrophil and macrophage infiltration to the infection site and rhythmic chemokine expression. Thus, rhythmic parasitic infection observed in vivo was likely initiated by the circadian expression of chemoattractants and the subsequent rhythmic infiltration of neutrophils and macrophages. Importantly, all rhythms were abolished in clock-deficient macrophages and when mice lacking the circadian clock in immune cells were infected. Therefore we demonstrated a critical role for the circadian clocks in immune cells in modulating the magnitude of Leishmania infection. To our knowledge this is the first report showing that the circadian clock controls infection by protozoan parasites in mammals. Understanding the timed regulation of host-parasite interactions will allow developing better prophylactic and therapeutic strategies to fight off vector-borne diseases.

LL37:DNA complexes provide antimicrobial activity against intracellular bacteria in human macrophages

As part of the innate host response neutrophils release neutrophil extracellular traps (NETs), protein:DNA complexes that contain a number of antimicrobial peptides (AMPs), such as cathelicidin. Human cathelicidin in its active form, LL37, has potent antimicrobial activity against bacteria. However, whether LL37 derived from NETs contributes to antimicrobial activity against intracellular pathogens remains unclear. Here, we report that NETs induced by mycobacteria contain cathelicidin. Human macrophages internalized NET-bound cathelicidin, which is transported to lysosomal compartments. Furthermore, using a model of in vitro-generated LL37:DNA complexes we found that LL37 derived from such complexes attacks mycobacteria in macrophage phagolysosomes resulting in antimicrobial activity. Taken together, our results suggest a mechanism by which LL37 in complex with DNA contributes to host defence against intracellular bacteria in human macrophages.

The inflammatory cytokine effect of Pam3CSK4 TLR2 agonist alone or in combination with Leishmania infantum antigen on ex-vivo whole blood from sick and resistant dogs

BACKGROUND

A wide spectrum of clinical manifestations and immune responses exist in canine L. infantum infection. Ibizan hounds are more "resistant" to disease than other dog breeds. Recognition of pathogen-associated molecule patterns by toll like receptors (TLRs) rapidly triggers a variety of anti-microbial immune responses through the induction of pro-inflammatory cytokines such as TNF-α and IL-6 which may play an important role in controlling Leishmania infection. The main objective of this study was to investigate and compare the effect of a TLR2 agonist (TLR2a) alone or in combination with L. infantum antigen (LSA) on ex vivo whole blood cytokine production from healthy seronegative IFN-γ non-producer dogs from an area of low in canine leishmaniosis endemicity (n = 11); sick seropositive dogs with low production of IFN-γ (n = 17) and healthy seronegative or low positive Ibizan hounds with a predominant IFN-γ production (n = 21) from a highly endemic area. Whole blood was stimulated with medium alone (Ø), LSA, concanavalin A, TLR2 (Pam3CSK4) receptor agonist (Ø + TLR2a) and TLR2a and LSA (LSA + TLR2a) for 48 h. Supernatants were harvested for measurement of canine TNF-α and IL-6 cytokines by ELISA.

RESULTS

A significant increase of TNF-α was found in the supernatants of stimulated blood from all groups (Ø + TLR2a and LSA + TLR2a) when compared with medium alone. A similar pattern was observed for IL-6. Interestingly, a significant increase of TNF-α production was only observed when stimulation with LSA + TLR2a was compared with TLR2a alone in Ibizan hounds. A significant increase of TNF-α production was observed with stimulation of LSA + TLR2a when compared with LSA in all groups. Significantly higher concentrations of TNF-α and IL-6 were detected in Ibizan hounds, especially for the Ø + TLR2a and LSA + TLR2a treatments compared with other groups.

CONCLUSIONS

This study demonstrated that TLR2a alone enhances the production of the inflammatory cytokines TNF-α and IL-6 in sick, "resistant" and healthy non-infected dogs. In addition, a combination of LSA+TLR2a promoted a synergistic pro-inflammatory effect with TNF-α in Ibizan hounds but not in seropositive sick dogs and seronegative healthy dogs. These findings might suggest the importance of Pam3CSK4 as a possible immunomodulator for CanL.

Screening of TNFα, IL-10 and TLR4 single nucleotide polymorphisms in individuals with asymptomatic and chronic cutaneous leishmaniasis in Colombia: a pilot study

BACKGROUND

Clinical manifestations of cutaneous leishmaniasis (CL) caused by Leishmania (Viannia) range from asymptomatic infection to self-limited, or chronic (non-healing) cutaneous lesions. Given the critical role of the immune response in the clinical outcome of CL, it is plausible that functional polymorphisms in immune-related genes contribute to define the clinical manifestations of human infection.

METHODS

DNA samples from a retrospective cohort of individuals from an endemic area of L. V. panamensis transmission in Colombia were used to determine the frequency of SNPs in TNFα, IL-10 and TLR4 genes. DNA samples were obtained from 74 adult participants: 38 patients presenting chronic cutaneous leishmaniasis (CCL) and 36 individuals with asymptomatic infection. Genotyping of TNFα-308G/A, IL-10-819C/T, and TLR4 Asp299Gly and Thr399Ile SNPs, was conducted by PCR-restriction fragment length polymorphisms. Allele, genotype frequencies and associations between SNPs and clinical groups were evaluated.

RESULTS

The A allele in TNFα-308G/A SNP was found more frequently in individuals with asymptomatic infection (16% vs 7%), whereas the CC genotype in IL-10-819 C/T SNP was more frequent in patients with CCL (34% vs. 27% in asymptomatic individuals). No differences in allele frequencies for TLR4 SNPs were found among groups.

CONCLUSION

This study provides a reference base for statistical power calculation and design of association studies of genetic polymorphisms in immune response related-genes and the pathogenesis of infections caused by L. V. panamensis.

Efferocytosis of Pathogen-Infected Cells

The prompt and efficient clearance of unwanted and abnormal cells by phagocytes is termed efferocytosis and is crucial for organism development, maintenance of tissue homeostasis, and regulation of the immune system. Dying cells are recognized by phagocytes through pathways initiated via "find me" signals, recognition via "eat me" signals and down-modulation of regulatory "don't eat me" signals. Pathogen infection may trigger cell death that drives phagocytic clearance in an immunologically silent, or pro-inflammatory manner, depending on the mode of cell death. In many cases, efferocytosis is a mechanism for eliminating pathogens and pathogen-infected cells; however, some pathogens have subverted this process and use efferocytic mechanisms to avoid innate immune detection and assist phagocyte infection. In parallel, phagocytes can integrate signals received from infected dying cells to elicit the most appropriate effector response against the infecting pathogen. This review focuses on pathogen-induced cell death signals that drive infected cell recognition and uptake by phagocytes, and the outcomes for the infected target cell, the phagocyte, the pathogen and the host.

Leishmania infection: painful or painless?

The complex life cycle and immunopathological features underpinning the interaction of Leishmania parasites and their mammalian hosts poses frequent poorly explored and inconclusively resolved questions. The altered nociceptive signals over the course of leishmaniasis remain an intriguing issue for nociceptive and parasitology researchers. Experimental investigations have utilized behavioral, morphological, and neuro-immune approaches in the study of experimental cutaneous leishmaniasis (CL). The data generated indicates new venues for the study of the pathological characteristics of nociceptive processing in this parasitic disease. Leishmania-induced pain may be easily observed in mice and rats. However, nociceptive data is more complex in human investigations, including the occurrence of painless lesions in mucocutaneous and cutaneous leishmaniasis. Data from recent decades indicate that humans can also be affected by pain-related symptoms, often distinct from the region of body infection. The molecular and cellular mechanisms underlying such variable nociceptive states in humans during the course of leishmaniasis are an active area of research. The present article reviews nociception in leishmaniasis, including in experimental models of CL and clinical reports.

Lipocalin-2 mediates non-alcoholic steatohepatitis by promoting neutrophil-macrophage crosstalk via the induction of CXCR2

BACKGROUND & AIMS

Inflammatory cell infiltration in the liver is a hallmark of non-alcoholic steatohepatitis (NASH). However, the pathological events which trigger the infiltration of inflammatory cells to mediate NASH pathogenesis remains poorly understood. This study aims to investigate the role of neutrophil-derived lipocalin 2 (LCN2) in mediating the transition from simple steatosis to NASH.

METHODS

Animal models of NASH were induced by high fat high cholesterol (HFHC) diet and methionine- and choline-deficient (MCD) diet in LCN2 knockout mice and wild-type controls.

RESULTS

Circulating levels of LCN2 and its hepatic expression were markedly increased in both murine models and human subjects with NASH, and these changes were associated with increased infiltration of neutrophils. In diet-induced NASH models, hepatic injury, necroinflammation and infiltration of neutrophils and macrophages were substantially attenuated by genetic depletion of LCN2. In contrast, chronic infusion of recombinant LCN2 exacerbated diet-induced liver injury, inflammation and macrophage accumulation in a neutrophil-dependent manner. Primary mouse neutrophils lacking LCN2 exhibited a defective migration capacity, which can be reversed by replenishment with recombinant LCN2. Mechanistically, LCN2 induced the expression of the chemokine (C-X-C motif) receptor 2 (CXCR2), thereby leading to activation of ERK1/2 and production of proinflammatory chemokines. LCN2-induced inflammation, infiltration of macrophages and liver injury was abrogated in CXCR2-deficient mice.

CONCLUSIONS

These findings demonstrated that LCN2 acts as a central mediator to facilitate the crosstalk between neutrophils and hepatic macrophages via induction of the chemokine receptor CXCR2, thereby exacerbating steatohepatitis.

LAY SUMMARY

Lipocalin-2 levels in blood and the liver were markedly increased in both mouse models and human subjects with NASH, and these changes were associated with increased infiltration of neutrophils in the liver. In diet-induced NASH models, hepatic injury, necroinflammation and infiltration of neutrophils and macrophages were substantially attenuated by genetic depletion of lipocalin-2, but was augmented by chronic infusion of recombinant lipocalin-2. Lipocalin-2 induced the expression of the chemokine receptor CXCR2, thereby leading to activation of the mitogen-activated protein (MAP) kinase ERK1/2 and production of proinflammatory chemokines. Lipocalin-2-induced inflammation, infiltration of macrophages and liver injury was abrogated in CXCR2-deficient mice.

Toll-like receptor 2 (TLR2) plays a role in controlling cutaneous leishmaniasis in vivo, but does not require activation by parasite lipophosphoglycan

Background

Leishmaniasis is a neglected tropical disease affecting millions of individuals worldwide. Despite several studies reporting involvement of the innate immune receptor Toll-like receptor 2 (TLR2) in the recognition of surface glycolipids from Leishmania parasites in vitro, the role of TLR2 and its co-receptors during cutaneous leishmaniasis infection in vivo is unknown.

Methods

To explore the role of TLR2 and its co-receptors in cutaneous leishmaniasis, mice deficient in either TLR2, 4, 1 or 6, or wild-type (WT) controls, were infected with either Leishmania major promastigotes, L. mexicana promastigotes, L. mexicana amastigotes, or LPG1^−/−L. mexicana promastigotes. For each infection, lesion sizes were monitored and parasite burden was assessed at various time points. To assess immune responses, draining lymph node (DLN) cells were re-stimulated with parasite antigens and the production of cytokines and parasite-specific antibody isotypes in blood was determined by ELISA.

Results

Mice deficient in TLR2 and TLR4 presented with larger lesions and higher parasite burdens than WT controls. Mice lacking TLR2 co-receptors TLR1 or TLR6 did not show exacerbated infection, suggesting that TLR2 does not require either co-receptor in the recognition of Leishmania infection. Furthermore, it appears that lipophosphoglycan (LPG) is not the major mediator of TLR2 activation during infection with L. mexicana, as parasites lacking LPG (axenic amastigotes and LPG1^−/− promastigotes) also resulted in exacerbated disease in TLR2^−/− mice. Infected TLR2^−/− mice show a skewed Th2 immune response to Leishmania parasites, as demonstrated by elevated IL-4, IL-13 and IL-10 production by DLN cells from L. mexicana infected mice in response to antigen. Furthermore, L. major infected TLR2^−/− mice have elevated antigen-specific IgG1 antibodies.

Conclusions

TLR2 deficiency leads to exacerbation of disease and parasite burden through promotion of Th2 immunity. TLR2 activation in vivo occurs independently of parasite LPG, suggesting other parasite ligands are involved in TLR2 recognition of Leishmania.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1807-8) contains supplementary material, which is available to authorized users.

Role of pro-inflammatory cytokine IL-17 in Leishmania pathogenesis and in protective immunity by Leishmania vaccines

The clinical outcome of Leishmania pathogenesis ranges from active skin lesions to fatal visceral dissemination and severely impaired T cell immunity. It is well established that a strong Th1 immune response is protective against cutaneous forms of the disease, however a mixed Th1/Th2 response is most commonly observed against visceral infections as evident from previous studies. Aside from Th1/Th2 cytokines, the pro-inflammatory IL-17 cytokine family plays an important role in the clearance of intracellular pathogens. In Leishmania induced skin lesions, IL-17 produced by Th17 cells is shown to exacerbate the disease, suggesting a role in pathogenesis. However, a protective role for IL-17 is indicated by the expansion of IL-17 producing cells in vaccine-induced immunity. In human visceral leishmaniasis (VL) it has been demonstrated that IL-17 and IL-22 are associated with protection against re-exposure to Leishmania, which further suggests the involvement of IL-17 in vaccine induced protective immunity. Although there is no vaccine against any form of leishmaniasis, the development of genetically modified live attenuated parasites as vaccine candidates prove to be promising, as they successfully induce a robust protective immune response in various animal models. However, the role of IL-17 producing cells and Th17 cells in response to these vaccine candidates remains unexplored. In this article, we review the role of IL-17 in Leishmania pathogenesis and the potential impact on vaccine induced immunity, with a special focus on live attenuated Leishmania parasites.

Neutrophil Attack Triggers Extracellular Trap-Dependent Candida Cell Wall Remodeling and Altered Immune Recognition

Pathogens hide immunogenic epitopes from the host to evade immunity, persist and cause infection. The opportunistic human fungal pathogen Candida albicans, which can cause fatal disease in immunocompromised patient populations, offers a good example as it masks the inflammatory epitope β-glucan in its cell wall from host recognition. It has been demonstrated previously that β-glucan becomes exposed during infection in vivo but the mechanism behind this exposure was unknown. Here, we show that this unmasking involves neutrophil extracellular trap (NET) mediated attack, which triggers changes in fungal cell wall architecture that enhance immune recognition by the Dectin-1 β-glucan receptor in vitro. Furthermore, using a mouse model of disseminated candidiasis, we demonstrate the requirement for neutrophils in triggering these fungal cell wall changes in vivo. Importantly, we found that fungal epitope unmasking requires an active fungal response in addition to the stimulus provided by neutrophil attack. NET-mediated damage initiates fungal MAP kinase-driven responses, particularly by Hog1, that dynamically relocalize cell wall remodeling machinery including Chs3, Phr1 and Sur7. Neutrophil-initiated cell wall disruptions augment some macrophage cytokine responses to attacked fungi. This work provides insight into host-pathogen interactions during disseminated candidiasis, including valuable information about how the C. albicans cell wall responds to the biotic stress of immune attack. Our results highlight the important but underappreciated concept that pattern recognition during infection is dynamic and depends on the host-pathogen dialog.

Opportunistic fungal infections, including those caused by C. albicans, have emerged as a significant global health burden and the disseminated form of these infections still have unacceptably high mortality rates despite modern antifungal treatments. The fungal cell wall controls its interaction with the host environment and immune recognition, although cell wall dynamics during infection are poorly understood. C. albicans organizes its cell wall to mask the inflammatory β-glucan as a form of immune evasion and it is known that during infection this β-glucan becomes exposed. Here, we investigated how β-glucan becomes exposed and discovered a dynamic interaction where host NETs provoke an active fungal response that disrupts cell wall architecture and unmasks β-glucan. We revealed an unexpected level of local fungal cell wall dynamics in response to immune mediated stress, suggesting this may represent a model that can be leveraged to identify novel drug targets. Our results highlight the understudied concept that the cell wall is a dynamic landscape during infection and can be influenced by the host.

Mechanisms of immune evasion in leishmaniasis

Diseases caused by Leishmania present a worldwide problem, and current therapeutic approaches are unable to achieve a sterile cure. Leishmania is able to persist in host cells by evading or exploiting host immune mechanisms. A thorough understanding of these mechanisms could lead to better strategies for effective management of Leishmania infections. Current research has focused on parasite modification of host cell signaling pathways, entry into phagocytic cells, and modulation of cytokine and chemokine profiles that alter immune cell activation and trafficking to sites of infection. Immuno-therapeutic approaches that target these mechanisms of immune evasion by Leishmania offer promising areas for preclinical and clinical research.

Neutrophils Contribute to the Protection Conferred by ArtinM against Intracellular Pathogens: A Study on Leishmania major

ArtinM, a D-mannose binding lectin from Artocarpus heterophyllus, has immunomodulatory activities through its interaction with N-glycans of immune cells, culminating with the establishment of T helper type 1 (Th1) immunity. This interaction protects mice against intracellular pathogens, including Leishmania major and Leishmania amazonensis. ArtinM induces neutrophils activation, which is known to account for both resistance to pathogens and host tissue injury. Although exacerbated inflammation was not observed in ArtinM-treated animals, assessment of neutrophil responses to ArtinM is required to envisage its possible application to design a novel immunomodulatory agent based on carbohydrate recognition. Herein, we focus on the mechanisms through which neutrophils contribute to ArtinM-induced protection against Leishmania, without exacerbating inflammation. For this purpose, human neutrophils treated with ArtinM and infected with Leishmania major were analyzed together with untreated and uninfected controls, based on their ability to eliminate the parasite, release cytokines, degranulate, produce reactive oxygen species (ROS), form neutrophil extracellular traps (NETs) and change life span. We demonstrate that ArtinM-stimulated neutrophils enhanced L. major clearance and at least duplicated tumor necrosis factor (TNF) and interleukin-1beta (IL-1β) release; otherwise, transforming growth factor-beta (TGF-β) production was reduced by half. Furthermore, ROS production and cell degranulation were augmented. The life span of ArtinM-stimulated neutrophils decreased and they did not form NETs when infected with L. major. We postulate that the enhanced leishmanicidal ability of ArtinM-stimulated neutrophils is due to augmented release of inflammatory cytokines, ROS production, and cell degranulation, whereas host tissue integrity is favored by their shortened life span and the absence of NET formation. Our results reinforce the idea that ArtinM may be considered an appropriate molecular template for the construction of an efficient anti-infective agent.

Vaccination is a successful way to eliminate infectious diseases. The generated antibodies neutralize the invading microbe and avoid the establishment of infection. Vaccines are efficient to prevent infections by pathogens living outside rather than inside the host`s cells. This occurs because protection against intracellular pathogens requires the engagement of T lymphocytes. The discovery of receptors on innate immunity cells opened new perspectives in trying manners to stimulate effective response against intracellular pathogens. Frequently the microbial sensing by Toll-like receptors (TLRs) besides triggering immediate defense also orchestrates adaptative immunity towards T-cell response. Therefore, TLR ligands started to be assayed in new anti-infective approaches. Our laboratory has been investigating the immunomodulation induced by lectins, which are ubiquitous sugar-binding proteins. Our primary model is ArtinM, from the seeds of jackfruit, a lectin that binds to TLR2 sugar chains on macrophages and dendritic cells and promotes production of cytokines that engages T lymphocytes in a process that culminate with elimination of intracellular pathogens. Concomitantly, ArtinM activates other immune cells, including neutrophils, which contributes to the pathogen elimination, but may also account for tissue damage. This last possibility led us to investigate the lectin effects on neutrophils deeply. We analyzed neutrophils treated with ArtinM and infected with Leishmania major. We concluded that the leishmanicidal ability of ArtinM-stimulated neutrophils was due to augmented release of inflammatory cytokines, ROS production, and cell degranulation. Otherwise, host tissue integrity is favored by shortened cells lifespan and absence of NET formation. This work reinforces the idea that ArtinM can be an appropriate molecular template for the construction of an efficient anti-infective agent.

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.