The state of art of neutrophil extracellular traps in protozoan and helminthic infections

A major Toxoplasma serine protease inhibitor protects the parasite against gut-derived serine proteases and NETosis damage

Toxoplasmosis is a life-threatening opportunistic infection in immunocompromised patients, caused by the parasite Toxoplasma gondii. Infection is initiated through oral ingestion of Toxoplasma cysts that must survive the harsh environment of the gut to undergo excystation. Released parasites invade intestinal epithelial cells and then disseminate throughout tissues for encystation, mainly in the brain. How Toxoplasma escapes destruction mediated by gastrointestinal proteases is poorly understood. T. gondii has nine genes encoding serine protease inhibitor proteins (TgPIs). TgPI-1 is highly expressed across all Toxoplasma strains and developmental stages and contains three domains for binding to various serine proteases. Here, we explore the role of TgPI-1 in protecting Toxoplasma against serine proteases in the gut and neutrophil-derived proteases in the lamina propria. TgPI-1 localizes to the parasite plasma membrane and cyst wall. We generated ΔTgPI-1 parasites, and the mutant is more sensitive to neutrophil elastase (NE), trypsin and chymotrypsin than WT. Neutrophils exposed to Toxoplasma release neutrophil extracellular traps (NET) with strain-dependent morphologies, ranging from spiky to extended cloudy. TgPI-1 was detected on NET containing NE, and ΔTgPI-1 parasites are more susceptible to destruction by NETosis. In mice, ΔTgPI-1 parasites exhibit reduced infectivity, poor dissemination to abdominal organs, and lower cyst burden in the brain. These findings shed light on a strategy employed by Toxoplasma to counteract enzymatic antimicrobial defenses in gut tissues, highlighting potential avenues for controlling tissue dissemination of this medically significant parasite.

Cellular immune responses of bovine polymorphonuclear neutrophils to Calicophoron daubneyi

Calicophoron daubneyi infections have increased in Europe, being more frequent than fasciolosis in some areas. Infection occurs once definitive hosts ingest encysted metacercariae present on vegetation. Following excystation, juvenile flukes penetrate the small intestinal mucosa and migrate into the rumen where adults mature. Throughout the somatic migration, juveniles come across different microenvironments and tissues and encounter host leukocytes. Besides phagocytosis, production of reactive oxygen species (ROS) and degranulation, polymorphonuclear neutrophils also cast neutrophil extracellular traps (NETs), which can entrap several parasite species, including the closely related liver fluke Fasciola hepatica. In this study, we analyzed whether in vitro exposure of bovine neutrophils to C. daubneyi antigen (CdAg) and eggs triggered neutrophils activation and NET formation. Results on scanning electron microscopy (SEM) and immunofluorescence analyses show weak formation of short spread NETs upon CdAg stimulation, corroborated by increased extracellular DNA measurements. Likewise, early NETosis was confirmed via nuclear area expansion assays. Bovine neutrophil stimulation with CdAg 100 µg/mL concentration led to a significant increase in oxygen consumption rates (p = 0.0152) and extracellular acidification rates (p = 0.0022), while lower concentrations of CdAg (10 µg/mL) failed to induce neutrophil activation, suggesting a dose dependent response. Both intra- and extracellular ROS production was not affected by any CdAg concentration here studied. Bovine neutrophil total adenosine triphosphate concentration significantly decreased after exposure to CdAg 100 µg/mL, in line to the observed with the positive control (phorbol myristate acetate/ionomycin). In summary, C. daubneyi activates bovine neutrophils with rather weak responses, which might suggest that the release of C. daubneyi-specific molecules (i.e. excretory-secretory antigens, proteases, or nucleases) could interfere with neutrophil-related effector mechanisms. Further ex vivo analyses will clarify if such mechanisms are also involved in pathogenesis of paramphistomosis by demonstrating neutrophil recruitment into affected intestinal mucosa.

Anti-Inflammatory Effects of Helminth-Derived Products: Potential Applications and Challenges in Diabetes Mellitus Management

The global rise in diabetes mellitus (DM), particularly type 2 diabetes (T2D), has become a major public health challenge. According to the "hygiene hypothesis", helminth infections may offer therapeutic benefits for DM. These infections are known to modulate immune responses, reduce inflammation, and improve insulin sensitivity. However, they also carry risks, such as malnutrition, anemia, and intestinal obstruction. Importantly, helminth excretory/secretory products, which include small molecules and proteins, have shown therapeutic potential in treating various inflammatory diseases with minimal side effects. This review explores the anti-inflammatory properties of helminth derivatives and their potential to alleviate chronic inflammation in both type 1 diabetes and T2D, highlighting their promise as future drug candidates. Additionally, it discusses the possible applications of these derivatives in DM management and the challenges involved in translating these findings into clinical practice.

Entamoeba histolytica-induced NETs are highly cytotoxic on hepatic and colonic cells due to serine proteases and myeloperoxidase activities

During intestinal and liver invasion by the protozoan parasite Entamoeba histolytica, extensive tissue destruction linked to large neutrophil infiltrates is observed. It has been proposed that microbicidal components of neutrophils are responsible for the damage, however, the mechanism by which they are released and act in the extracellular space remains unknown. In previous studies, we have shown that E. histolytica trophozoites induce NET formation, leading to the release of neutrophil granule content into extruded DNA. In this work, we evaluate the possible participation of NETs in the development of amoeba-associated pathology and analyze the contribution of anti-microbial components of the associated granules. E. histolytica-induced NETs were isolated and their effect on the viability and integrity of HCT 116 colonic and Hep G2 liver cultures were evaluated. The results showed that simple incubation of cell monolayers with purified NETs for 24 h resulted in cell detachment and death in a dose-dependent manner. The effect was thermolabile and correlated with the amount of DNA and protein present in NETs. Pretreatment of NETs with specific inhibitors of some microbicidal components suggested that serine proteases, are mostly responsible for the damage caused by NETs on HCT 116 cells, while the MPO activity was the most related to Hep G2 cells damage. Our study also points to a very important role of DNA as a scaffold for the activity of these proteins. We show evidence of the development of NETs in amoebic liver abscesses in hamsters as a preamble to evaluate their participation in tissue damage. In conclusion, these studies demonstrate that amoebic-induced NETs have potent cytotoxic effects on target cells and, therefore, may be responsible for the intense damage associated with tissue invasion by this parasite.

Neutrophil extracellular traps in homeostasis and disease

Neutrophil extracellular traps (NETs), crucial in immune defense mechanisms, are renowned for their propensity to expel decondensed chromatin embedded with inflammatory proteins. Our comprehension of NETs in pathogen clearance, immune regulation and disease pathogenesis, has grown significantly in recent years. NETs are not only pivotal in the context of infections but also exhibit significant involvement in sterile inflammation. Evidence suggests that excessive accumulation of NETs can result in vessel occlusion, tissue damage, and prolonged inflammatory responses, thereby contributing to the progression and exacerbation of various pathological states. Nevertheless, NETs exhibit dual functionalities in certain pathological contexts. While NETs may act as autoantigens, aggregated NET complexes can function as inflammatory mediators by degrading proinflammatory cytokines and chemokines. The delineation of molecules and signaling pathways governing NET formation aids in refining our appreciation of NETs' role in immune homeostasis, inflammation, autoimmune diseases, metabolic dysregulation, and cancer. In this comprehensive review, we delve into the multifaceted roles of NETs in both homeostasis and disease, whilst discussing their potential as therapeutic targets. Our aim is to enhance the understanding of the intricate functions of NETs across the spectrum from physiology to pathology.

Characterization of extracellular trap production and release by equine neutrophils in response to different stimuli

This study explores Neutrophil Extracellular Trap (NET) formation in equine neutrophils, which is crucial for eliminating infections and is implicated in various equine inflammatory diseases. We investigated the molecular pathways involved in NET release by equine neutrophils in response to stimuli. We use PMA, A23187, LPS, PAF, OZ, and cytokines, observing NET release in response to PMA, PAF, and A23187. In contrast, LPS, OZ, and the cytokines tested did not induce DNA release or did not consistently induce citrullination of histone 4. Peptidyl-arginine deiminase inhibition completely halted NET release, while NADPH oxidase and mitochondrial reactive oxygen species only played a role in PMA-induced NETs. Neutrophil elastase inhibition modestly affected PAF-induced NET liberation but not in PMA or A23187-induced NET, while myeloperoxidase did not contribute to NET release. We expect to provide a foundation for future investigations into the role of NETs in equine health and disease and the search for potential therapeutic targets.

Extracellular traps development in canine neutrophils induced by infective stage Toxocara canis larvae

Neutrophils, a crucial element of the host defense system, develop extracellular traps against helminth parasites. Neutrophils accumulate around the larvae of Toxocara canis (T. canis) in the tissues of the organism. This study aimed to determine the reaction in canine neutrophils after incubation with infective stage T. canis larvae (L3) in vitro. Most L3 were still active and moved between the extracellular traps (NETs) after 60-min incubation. NETs were not disintegrated by L3 movement. The L3 was only immobilized by NETs, entrapped larvae were still motile between the traps at the 24 h incubation. NETs were observed not only to accumulate around the mouth, excretory pole or anus but also the entire body of live L3. The extracellular DNA amount released from the canine neutrophils after being induced with phorbol 12-myristate 13-acetate was not affected by T. canis excretory/secretory products obtained from 250 L3. To the Authors'knowledge, the extracellular trap structures was firstly observed in canine neutrophils against T. canis L3 in vitro. NETs decorated with myeloperoxidase, neutrophil elastase and histone (H3) were observed under fluorescence microscope. There were not significant differences in the amount of extracellular DNA (P > 0.05), but the morphological structure of NETs was different in the live and head-inactivated T. canis larvae.

Immunomodulatory effects of hydatid antigens on mesenchymal stem cells: gene expression alterations and functional consequences

Background

Cystic echinococcosis, caused by the larval stage of Echinococcus granulosus, remains a global health challenge. Mesenchymal stem cells (MSCs) are renowned for their regenerative and immunomodulatory properties. Given the parasite's mode of establishment, we postulate that MSCs likely play a pivotal role in the interaction between the parasite and the host. This study aims to explore the response of MSCs to antigens derived from Echinococcus granulosus, the etiological agent of hydatid disease, with the hypothesis that exposure to these antigens may alter MSC function and impact the host's immune response to the parasite.

Methods

MSCs were isolated from mouse bone marrow and co-cultured with ESPs, HCF, or pLL antigens. We conducted high-throughput sequencing to examine changes in the MSCs' mRNA expression profile. Additionally, cell cycle, migration, and secretory functions were assessed using various assays, including CCK8, flow cytometry, real-time PCR, Western blot, and ELISA.

Results

Our analysis revealed that hydatid antigens significantly modulate the mRNA expression of genes related to cytokine and chemokine activity, impacting MSC proliferation, migration, and cytokine secretion. Specifically, there was a downregulation of chemokines (MCP-1, CXCL1) and pro-inflammatory cytokines (IL-6, NOS2/NO), alongside an upregulation of anti-inflammatory mediators (COX2/PGE2). Furthermore, all antigens reduced MSC migration, and significant alterations in cellular metabolism-related pathways were observed.

Conclusion

Hydatid disease antigens induce a distinct immunomodulatory response in MSCs, characterized by a shift towards an anti-inflammatory phenotype and reduced cell migration. These changes may contribute to the parasite's ability to evade host defenses and persist within the host, highlighting the complex interplay between MSCs and hydatid disease antigens. This study provides valuable insights into the pathophysiology of hydatid disease and may inform the development of novel therapeutic strategies.

A Putative Role for TRPC6 in Immune-Mediated Kidney Injury

Excessive activation of the immune system is the cause of a wide variety of renal diseases. However, the pathogenic mechanisms underlying the aberrant activation of the immune system in the kidneys often remain unknown. TRPC6, a member of the Ca2+-permeant family of TRPC channels, is important in glomerular epithelial cells or podocytes for the process of glomerular filtration. In addition, TRPC6 plays a crucial role in the development of kidney injuries by inducing podocyte injury. However, an increasing number of studies suggest that TRPC6 is also responsible for tightly regulating the immune cell functions. It remains elusive whether the role of TRPC6 in the immune system and the pathogenesis of renal inflammation are intertwined. In this review, we present an overview of the current knowledge of how TRPC6 coordinates the immune cell functions and propose the hypothesis that TRPC6 might play a pivotal role in the development of kidney injury via its role in the immune system.

Role of Neutrophil Extracellular Traps in Health and Disease Pathophysiology: Recent Insights and Advances

Neutrophils are the principal trouper of the innate immune system. Activated neutrophils undergo a noble cell death termed NETosis and release a mesh-like structure called neutrophil extracellular traps (NETs) as a part of their defensive strategy against microbial pathogen attack. This web-like architecture includes a DNA backbone embedded with antimicrobial proteins like myeloperoxidase (MPO), neutrophil elastase (NE), histones and deploys in the entrapment and clearance of encountered pathogens. Thus NETs play an inevitable beneficial role in the host's protection. However, recent accumulated evidence shows that dysregulated and enhanced NET formation has various pathological aspects including the promotion of sepsis, pulmonary, cardiovascular, hepatic, nephrological, thrombotic, autoimmune, pregnancy, and cancer diseases, and the list is increasing gradually. In this review, we summarize the NET-mediated pathophysiology of different diseases and focus on some updated potential therapeutic approaches against NETs.

Besnoitia besnoiti-induced neutrophil clustering and neutrophil extracellular trap formation depend on P2X1 purinergic receptor signaling

Bovine besnoitiosis is a re-emerging cattle disease caused by the cyst-forming apicomplexan parasite Besnoitia besnoiti. Neutrophil extracellular trap (NET) formation represents an efficient innate immune mechanism of polymorphonuclear neutrophils (PMN) against apicomplexan parasites, including B. besnoiti. PMN purinergic signaling was proposed as a critical factor for NET formation. One important purinergic ligand is ATP, which is recognized as a danger signal and released into the extracellular space acting as an autocrine/paracrine signaling molecule. ATP-driven effects on PMN via the nucleotide P2 receptor family include chemotaxis, reactive oxygen species (ROS) production, and NET formation. So far, data on both PMN ATP concentrations and the role of ATP as a key modulator of purinergic signaling in B. besnoiti tachyzoite-triggered bovine NETosis is scarce. Current data showed that B. besnoiti tachyzoite exposure to bovine PMN neither changed total PMN ATP nor extracellular ATP quantities even though it significantly triggered NET formation. Moreover, B. besnoiti tachyzoite-exposed PMN revealed enhanced oxygen consumption rates (OCR) as quantified by the Seahorse metabolic analyzer. Exogenous supplementation of ATP or non-hydrolizable ATP (ATPγS) led to increased extracellular acidification rates (ECAR) but failed to alter tachyzoite-induced oxidative responses (OCR) in exposed PMN. In addition, exogenous supplementation of ATPγS, but not of ATP, boosted B. besnoiti tachyzoite-induced anchored NET formation. Referring to purinergic signaling, B. besnoiti tachyzoite-triggered anchored NET formation revealed P2X1 purinergic as receptor-dependent since it was blocked by the P2X1 inhibitor NF449 at an IC50 of 1.27 µM. In contrast, antagonists of P2Y2, P2Y6, P2X4, and P2X7 purinergic receptors all failed to affect parasite-driven NETosis. As an interesting finding, we additionally observed that B. besnoiti tachyzoite exposure induced PMN clustering in a P2X1-dependent manner. Thus, we identified P2X1 purinergic receptor as a pivotal molecule for both B. besnoiti tachyzoite-induced PMN clustering and anchored NET formation.

Immune Checkpoint Inhibitors, Small-Molecule Immunotherapies and the Emerging Role of Neutrophil Extracellular Traps in Therapeutic Strategies for Head and Neck Cancer

Immune checkpoint inhibitor (ICI) therapy has revolutionized the treatment of many cancer types, including head and neck cancers (HNC). When checkpoint and partner proteins bind, these send an "off" signal to T cells, which prevents the immune system from destroying tumor cells. However, in HNC, and indeed many other cancers, more people do not respond and/or suffer from toxic effects than those who do respond. Hence, newer, more effective approaches are needed. The challenge to durable therapy lies in a deeper understanding of the complex interactions between immune cells, tumor cells and the tumor microenvironment. This will help develop therapies that promote lasting tumorlysis by overcoming T-cell exhaustion. Here we explore the strengths and limitations of current ICI therapy in head and neck squamous cell carcinoma (HNSCC). We also review emerging small-molecule immunotherapies and the growing promise of neutrophil extracellular traps in controlling tumor progression and metastasis.

Neutrophil sub-types in maintaining immune homeostasis during steady state, infections and sterile inflammation

INTRODUCTION

Neutrophils are component of innate immune system and a) eliminate pathogens b) maintain immune homeostasis by regulating other immune cells and c) contribute to the resolution of inflammation. Neutrophil mediated inflammation has been described in pathogenesis of various diseases. This indicates neutrophils do not represent homogeneous population but perform multiple functions through confined subsets. Hence, in the present review we summarize various studies describing the heterogeneous nature of neutrophils and associated functions during steady state and pathological conditions.

METHODOLOGY

We performed extensive literature review with key words 'Neutrophil subpopulations' 'Neutrophil subsets', Neutrophil and infections', 'Neutrophil and metabolic disorders', 'Neutrophil heterogeneity' in PUBMED.

RESULTS

Neutrophil subtypes are characterized based on buoyancy, cell surface markers, localization and maturity. Recent advances in high throughput technologies indicate the existence of functionally diverse subsets of neutrophils in bone marrow, blood and tissues in both steady state and pathological conditions. Further, we found proportions of these subsets significantly vary in pathological conditions. Interestingly, stimulus specific activation of signalling pathways in neutrophils have been demonstrated.

CONCLUSION

Neutrophil sub-populations differ among diseases and hence, mechanisms regulating formation, sustenance, proportions and functions of these sub-types vary between physiological and pathological conditions. Hence, mechanistic insights of neutrophil subsets in disease specific manner may facilitate development of neutrophil-targeted therapies.

NETosis in Parasitic Infections: A Puzzle That Remains Unsolved

Neutrophils are the key players in the innate immune system, being weaponized with numerous strategies to eliminate pathogens. The production of extracellular traps is one of the effector mechanisms operated by neutrophils in a process called NETosis. Neutrophil extracellular traps (NETs) are complex webs of extracellular DNA studded with histones and cytoplasmic granular proteins. Since their first description in 2004, NETs have been widely investigated in different infectious processes. Bacteria, viruses, and fungi have been shown to induce the generation of NETs. Knowledge is only beginning to emerge about the participation of DNA webs in the host's battle against parasitic infections. Referring to helminthic infections, we ought to look beyond the scope of confining the roles of NETs solely to parasitic ensnarement or immobilization. Hence, this review provides detailed insights into the less-explored activities of NETs against invading helminths. In addition, most of the studies that have addressed the implications of NETs in protozoan infections have chiefly focused on their protective side, either through trapping or killing. Challenging this belief, we propose several limitations regarding protozoan-NETs interaction. One of many is the duality in the functional responses of NETs, in which both the positive and pathological aspects seem to be closely intertwined.

Entamoeba histolytica induced NETosis and the dual role of NETs in amoebiasis

Entamoeba histolytica (Eh), a microaerophilic parasite, causes deadly enteric infections that result in Amoebiasis. Every year, the count of invasive infections reaches 50 million approximately and 40,000 to 1,00,000 deaths occurring due to amoebiasis are reported globally. Profound inflammation is the hallmark of severe amoebiasis which is facilitated by immune first defenders, neutrophils. Due to size incompatibility, neutrophils are unable to phagocytose Eh and thus, came up with the miraculous antiparasitic mechanism of neutrophil extracellular traps (NETs). This review provides an in-depth analysis of NETosis induced by Eh including the antigens involved in the recognition of Eh and the biochemistry of NET formation. Additionally, it underscores its novelty by describing the dual role of NETs in amoebiasis where it acts as a double-edged sword in terms of both clearing and exacerbating amoebiasis. It also provides a comprehensive account of the virulence factors discovered to date that are implicated directly and indirectly in the pathophysiology of Eh infections through the lens of NETs and can be interesting drug targets.

Microbes and the fate of neutrophils

Neutrophils or polymorphonuclear neutrophils (PMNs) are an important component of innate host defense. These phagocytic leukocytes are recruited to infected tissues and kill invading microbes. There are several general characteristics of neutrophils that make them highly effective as antimicrobial cells. First, there is tremendous daily production and turnover of granulocytes in healthy adults-typically 1011 per day. The vast majority (~95%) of these cells are neutrophils. In addition, neutrophils are mobilized rapidly in response to chemotactic factors and are among the first leukocytes recruited to infected tissues. Most notably, neutrophils contain and/or produce an abundance of antimicrobial molecules. Many of these antimicrobial molecules are toxic to host cells and can destroy host tissues. Thus, neutrophil activation and turnover are highly regulated processes. To that end, aged neutrophils undergo apoptosis constitutively, a process that contains antimicrobial function and proinflammatory capacity. Importantly, apoptosis facilitates nonphlogistic turnover of neutrophils and removal by macrophages. This homeostatic process is altered by interaction with microbes and their products, as well as host proinflammatory molecules. Microbial pathogens can delay neutrophil apoptosis, accelerate apoptosis following phagocytosis, or cause neutrophil cytolysis. Here, we review these processes and provide perspective on recent studies that have potential to impact this paradigm.

Crosslinking of membrane CD13 in human neutrophils mediates phagocytosis and production of reactive oxygen species, neutrophil extracellular traps and proinflammatory cytokines

Aminopeptidase N, or CD13, is a cell membrane ectopeptidase highly expressed in myeloid cells. Through its enzymatic activity, CD13 regulates the activity of several bioactive peptides, such as endorphins and enkephalins, chemotactic peptides like MCP-1 and IL-8, angiotensin III, bradikinin, etc. In recent years, it has been appreciated that independently of its peptidase activity, CD13 can activate signal transduction pathways and mediate effector functions such as phagocytosis and cytokine secretion in monocytes and macrophages. Although neutrophils are known to express CD13 on its membrane, it is currently unknown if CD13 can mediate effector functions in these cells. Here, we show that in human neutrophils CD13 can mediate phagocytosis, which is dependent on a signaling pathway that involves Syk, and PI3-K. Phagocytosis mediated by CD13 is associated with production of reactive oxygen species (ROS). The level of phagocytosis and ROS production mediated by CD13 are similar to those through FcγRIII (CD16b), a widely studied receptor of human neutrophils. Also, CD13 ligation induces the release of neutrophil extracellular traps (NETs) as well as cytokine secretion from neutrophils. These results support the hypothesis that CD13 is a membrane receptor able to activate effector functions in human neutrophils.

Immunomodulatory effect of extracellular vesicles from Entamoeba histolytica trophozoites: Regulation of NETs and respiratory burst during confrontation with human neutrophils

Parasites release extracellular vesicles (EVs) which, in some cases, modulate the host's immune response contributing to the establishment of the infection. In this work we have isolated and characterized the EVs released by trophozoites of the human protozoan parasite Entamoeba histolytica, the causal agent of amoebiasis, when alone or in coculture with human neutrophils, and determined their effect on neutrophil NETs and ROS production. Nanoparticle tracking analysis showed that amoebic EVs are variable in size, ranging from less than 50 nm to nearly 600 nm in diameter (average of 167 nm), whereas neutrophil EVs are more uniform in size, with an average of 136 nm. In cocultures amoeba:neutrophil (1:100) most EVs are 98 nm in size, which is the typical size of exosomes. EVs from amoebae and neutrophils showed almost equal levels of ROS, which were considerably increased in EVs from cocultures. Uptake of amoebic EVs by neutrophils was demonstrated by fluorescence and resulted in a significant reduction in the oxidative burst and NET release triggered by PMA, ionophore A23187, or the amoebae itself used as stimuli. Interestingly, uptake of EVs from cocultures did not affect ROS production, but instead caused a greater delay in the onset of NETs release and in their quantity. A comparative proteomic analysis between the EVs of amoebae and neutrophils separately vs the cocultures showed a similar distribution of protein categories in the GO analysis, but differences in the expression and abundance of proteins such as the N-acetyl-D-galactosamine (GalNAc) inhibitable surface lectin and calreticulin in amoeba EVs, and various antimicrobial molecules in neutrophil EVs, such as lactoferrin and myeloperoxidase. These results highlight the importance of EVs in the immunomodulatory effects exerted by amoeba on human neutrophils.

Serine protease inhibitor derived from Trichinella spiralis (TsSERP) inhibits neutrophil elastase and impairs human neutrophil functions

During early infection with Trichinella spiralis, host neutrophils destroy newborn larvae migrating in the bloodstream, preventing infection. However, parasites secrete various immunomodulatory molecules to escape the host’s defense mechanisms, allowing them to infect the host and live for long periods. T. spiralis secretes serine protease inhibitors (TsSERPs), which are key inhibitory molecules that regulate serine proteases involved in digestion and inflammation. However, the modulatory roles of TsSERP in the inhibition of neutrophil serine proteases (NSPs) and neutrophil functions are unknown. Therefore, the immunomodulatory properties of recombinant TsSERP1 (rTsSERP1) on NSPs and neutrophil functions were investigated in this study. rTsSERP1 preferentially inhibited human neutrophil elastase (hNE). In addition, incubation of rTsSERP1 with fMLP-induced neutrophils impaired their phagocytic ability. The formation of neutrophil extracellular traps (NETs) was activated with phorbol myristate acetate (PMA), and NETs were dramatically reduced when treated with rTsSERP1. Furthermore, rTsSERP1 suppressed the production of proinflammatory cytokines and chemokines during neutrophil activation, which are essential for neutrophil-mediated local or systemic inflammation regulation. In conclusion, T. spiralis immune evasion mechanisms are promoted by the inhibitory properties of TsSERP1 against neutrophil elastase and neutrophil defense functions, and these might be promising alternative treatment targets for inflammatory disorders.

Unweaving the NET: Microbial strategies for neutrophil extracellular trap evasion

Circa 20 years ago, a new type of defense mechanism was described in neutrophils. At the time, this mechanism corresponded to the extrusion of DNA, associated with histones, granular and cytosolic proteins from the cell and it was produced in response to exposure to pathogens or interleukins. The resulting NET-like structure was described as to entrap and/or kill microbes. However, shortly after the discovery the so-called Neutrophil Extracellular Traps, it was soon noticed and often mentioned in the literature that certain microbes are able to evade NET-mediated entrapment and/or death, to the point where its antimicrobial capacities were questioned, depending on the infection context. In this review, we summarize the diversity of strategies published thus far that viruses, fungi, bacteria and protists employ as to prevent or endure NETs. Moreover, we point to a few perspectives on the matter and a few evolutionary speculations on NETs evasion.

Glycolysis, monocarboxylate transport, and purinergic signaling are key events in Eimeria bovis-induced NETosis

The protozoan parasite Eimeria bovis is the causative agent of bovine coccidiosis, an enteric disease of global importance that significantly affects cattle productivity. Previous studies showed that bovine NETosis—an important early host innate effector mechanism of polymorphonuclear neutrophil (PMN)—is elicited by E. bovis stages. So far, the metabolic requirements of E. bovis-triggered NET formation are unknown. We here studied early glycolytic and mitochondrial responses of PMN as well as the role of pH, distinct metabolic pathways, P2 receptor-mediated purinergic signaling, and monocarboxylate transporters 1 and 2 (MCT1, MCT2) in E. bovis sporozoite-induced NET formation. Seahorse-based experiments revealed a rapid induction of both neutrophil oxygen consumption rate (OCR) and early glycolytic responses, thereby reflecting immediate PMN activation and metabolic changes upon confrontation with sporozoites. The impact of these metabolic changes on NET formation was studied via chemical inhibition experiments targeting glycolysis and energy generation by the use of 2-fluor-2-deoxy-D-glucose (FDG), 6-diazo-5-oxo-L-norleucin (DON), sodium dichloroacetate (DCA), oxythiamine (OT), sodium oxamate (OXA), and oligomycin A (OmA) to block glycolysis, glutaminolysis, pyruvate dehydrogenase kinase, pyruvate dehydrogenase, lactate dehydrogenase, and mitochondrial ATP-synthase, respectively. Overall, sporozoite-induced NET formation was significantly diminished via PMN pretreatments with OmA and OXA, thereby indicating a key role of ATP- and lactate-mediated metabolic pathways. Consequently, we additionally studied the effects of extracellular pH, MCT1, MCT2, and purinergic receptor inhibitors (AR-C141900, AR-C155858, theobromine, and NF449, respectively). Pretreatment with the latter inhibitors led to blockage of sporozoite-triggered DNA release from exposed bovine PMN. This report provides first evidence on the pivotal role of carbohydrate-related metabolic pathways and purinergic receptors being involved in E. bovis sporozoite-induced NETosis.

Neutrophil Extracellular Traps and Neutrophil-Derived Extracellular Vesicles: Common Players in Neutrophil Effector Functions

Neutrophil granulocytes are a central component of the innate immune system. In recent years, they have gained considerable attention due to newly discovered biological effector functions and their involvement in various pathological conditions. They have been shown to trigger mechanisms that can either promote or inhibit the development of autoimmunity, thrombosis, and cancer. One mechanism for their modulatory effect is the release of extracellular vesicles (EVs), that trigger appropriate signaling pathways in immune cells and other target cells. In addition, activated neutrophils can release bactericidal DNA fibers decorated with proteins from neutrophil granules (neutrophil extracellular traps, NETs). While NETs are very effective in limiting pathogens, they can also cause severe damage if released in excess or cleared inefficiently. Since NETs and EVs share a variety of neutrophil molecules and initially act in the same microenvironment, differential biochemical and functional analysis is particularly challenging. This review focuses on the biochemical and functional parallels and the extent to which the overlapping spectrum of effector molecules has an impact on biological and pathological effects.

Quantitative phosphoproteomics reveals diverse stimuli activate distinct signaling pathways during neutrophil activation

Neutrophils display functional heterogeneity upon responding diversely to physiological and pathological stimulations. During type 2 diabetes (T2D), hyperglycemia constitutively activates neutrophils, leading to reduced response to infections and on the other hand, elevated metabolic intermediates such as homocysteine induce bidirectional activation of platelets and neutrophils leading to thrombosis. Hence, in the context of T2D-associated complications, we examined the influence of high glucose, homocysteine, and LPS representing effector molecules of hyperglycemia, thrombosis, and infection, respectively, on human neutrophil activation to identify distinct signaling pathways by quantitative phosphoproteomics approach. High glucose activated C-Jun-N-Terminal Kinase, NTRK1, SYK, and PRKACA kinases associated with Rho GTPase signaling and phagocytosis, whereas LPS induced AKT1, SRPK2, CSNK2A1, and TTN kinases involved in cytokine signaling and inflammatory response. Homocysteine treatment led to activatation of  LRRK2, FGR, MAPK3, and PRKCD kinases which are associated with neutrophil degranulation and cytoskeletal remodeling. Diverse inducers differentially modulated phosphorylation of proteins associated with neutrophil functions such as oxidative burst, degranulation, extracellular traps, and phagocytosis. Further validation of phosphoproteomics data on selected kinases revealed neutrophils pre-cultured under high glucose showed impeded response to LPS to phosphorylate p-ERK1/2^{Thr202/Tyr204}, p-AKT^Ser473, and C-Jun-N-Terminal Kinase^Ser63 kinases. Our study provides novel phosphoproteome signatures that may be explored to understand neutrophil biology in T2D-associated complications.

Autoimmunity in human CE: Correlative with the fertility status of the CE cyst

Cystic echinococcosis is speculated to exert several immune-evasion strategies involving autoimmune-phenomena. We evaluated the hypothesizes that the prevalence of autoantibodies increases in the sera of CE patients that may evidence the association between the parasite and autoimmune diseases. Sera from 63 subjects at distinct types of CE cyst fertility were investigated for antinuclear antibodies (ANA), and anti-CCP antibodies. Plasma levels and cellular production of IL-17A cytokine were specifically defined as being assumed to prime for autoimmunity. Healthy-controls were age and gender-matched to test sera. ANA expressions inside the surgically removed metacestode and adventitial layer were also assayed. Out of 63 patients, 35 % had fertile highly viable cysts (group-1), 41 % had fertile low viable cysts (group-2) and 24 % had non-fertile cysts (group-3). A four-fold increase in ANA sera-levels was detected in group-1 compared with their controls (p-value 0.001) while anti-CCP levels were of insignificant differences. In group-2 and group-3, no significant differences were detected between ANA and anti-CCP sera-levels in CE patients and their controls. IL-17A sera-levels in group-1 and group- 2 were significantly higher than their healthy-controls while being of insignificant differences in group-3, p-value= 0.300. No association was detected between sera-levels of IL-17A and ANA as well as anti-CCP antibodies. Interestingly, relative IL-17A cellular expression associated positive ANA deposition in the parasite cells and adventitial layer. Collectively, based on the parasite fertility, IL-17A and ANA seemed to be involved in the host immune defenses against CE. There is no association between CE and anti-CCP antibodies.

Hookworm infections: Reappraising the evidence for a role of Neutrophils in light of NETosis

In Hookworm infection, neutrophils have long had the image of the villain, being recruited to the site of larval migration because of damage but participating themselves in tissue injury. With recent developments in neutrophil biology, there is an increasing body of evidence for the role of neutrophils as effector cells in hookworm immunity. In particular, their ability to release extracellular traps, or neutrophil extracellular traps (NETs), confer neutrophils a larvicidal activity. Here, we review recent evidence in this nascent field and discuss the avenue for future research on NETs/hookworm interactions.

Exploring the paradox of defense between host and Leishmania parasite

Leishmaniasis, a neglected tropical disease, still remains a global concern for the healthcare sector. The primary causative agents of the disease comprise diverse leishmanial species, leading to recurring failures in disease diagnosis and delaying the initiation of appropriate chemotherapy. Various species of the Leishmania parasite cause diverse clinical manifestations ranging from skin ulcers to systemic infections. Therefore, host immunity in response to different forms of infecting species of Leishmania becomes pivotal in disease progression or regression. Thus, understanding the paradox of immune arsenals during host and parasite interface becomes crucial to eliminate this deadly disease. In the present review, we have elaborated on the immunological perspectives of the disease and discussed primary host immune cells that form a defense line to counteract parasite infection. Furthermore, we also have shed light on the immune cells and effector molecules responsible for parasite survival in host lethal milieu/ environment. Next, we have highlighted recent molecules/compounds showing potent leishmanicidal activities pertaining to their pro-oxidant and immuno-modulatory mechanisms. This review addresses an immuno-biological overview of the factors influencing the parasitic disease, as this knowledge can aid in the unraveling/ identification of potential biomarkers, novel therapeutics, and vaccine candidates against leishmaniasis.

Histological and immunological insights to hydatid disease in camels

PURPOSE

To investigate the immuno-histological evidences in viable and non-viable hydatid cysts obtained from naturally infected camels.

METHODS

A cohort study (February 2018-December 2019), a total of 15 hydatidosis-infected camels from slaughter houses in Cairo were involved. Specimens were investigated for parasite viability, liver histological changes, IL-17A cytokine immunohistochemical expressions in the adventitial layer, and the anti-nuclear antibodies (ANAs) immunofluorescent expression in the metacestode's structures. Real-Time Quantitative -Morphocytometry and SPSS were utilized.

RESULTS

Multi-focal lesions and high viability were found in 60% of the cases. Overall accumulation of collagen associated the parasite establishment that involved infiltrations of mononuclear cells with significantly increased IL-17A expression. Interestingly, the ANAs appeared to have a role in the immune-defense against the metacestode showing different patterns. ANAs production correlated with IL-17A expression and the viability of the parasite.

CONCLUSION

IL-17A responses in hydatidosis is associated with collagen deposition and ANA production as a sort of anti-parasite immunity in a viability dependent manner.

Lessons in type 2 immunity: Neutrophils in Helminth infections

Neutrophils constitute the body's first line of defense against invading pathogens. Equipped with a large array of tools, these immune cells are highly efficient in eliminating bacterial and viral infections, yet their activity can at the same time be detrimental to the host itself - this is the broad consensus on these granulocytes. However, the last decade has proven that neutrophils are a much more sophisticated cell type with unexpected and underappreciated functions in health and disease. In this review, we look at the latest discoveries in neutrophil biology with a focus on their role during the hallmark setting of type 2 immunity - helminth infection. We discuss the involvement of neutrophils in various helminth infection models and summarize the latest findings regarding neutrophil regulation and effector function. We will show that neutrophils have much more to offer than previously thought and while studies of neutrophils in helminth infections are still in its infancy, recent discoveries highlight more than ever that these cells are a key cog of the immune system, even during type 2 responses.

Tick Immunobiology and Extracellular Traps: An Integrative Vision to Control of Vectors

Ticks are hematophagous ectoparasites that infest a diverse number of vertebrate hosts. The tick immunobiology plays a significant role in establishing and transmitting many pathogens to their hosts. To control tick infestations, the acaricide application is a commonly used method with severe environmental consequences and the selection of tick-resistant populations. With these drawbacks, new tick control methods need to be developed, and the immune system of ticks contains a plethora of potential candidates for vaccine design. Additionally, tick immunity is based on an orchestrated action of humoral and cellular immune responses. Therefore, the actors of these responses are the object of our study in this review since they are new targets in anti-tick vaccine design. We present their role in the immune response that positions them as feasible targets that can be blocked, inhibited, interfered with, and overexpressed, and then elucidate a new method to control tick infestations through the development of vaccines. We also propose Extracellular Traps Formation (ETosis) in ticks as a process to eliminate their natural enemies and those pathogens they transmit (vectorial capacity), which results attractive since they are a source of acting molecules with potential use as vaccines.

A Review of Neutrophil Extracellular Traps (NETs) in Disease: Potential Anti-NETs Therapeutics

Activated neutrophils release neutrophil extracellular traps (NETs) in response to a variety of stimuli. NETosis is driven by protein-arginine deiminase type 4, with the release of intracellular granule components that function by capturing and destroying microbes, including viral, fungal, bacterial, and protozoal pathogens. The positive effects of pathogen control are countered by pro-inflammatory effects as demonstrated in a variety of diseases. Components of NETS are non-specific, and other than controlling microbes, they cause injury to surrounding tissue by themselves or by increasing the pro-inflammatory response. NETs can play a role in enhancement of the inflammation seen in autoimmune diseases including psoriasis, rheumatoid arthritis, and systemic lupus erythematosis. In addition, autoinflammatory diseases such as gout have been associated with NETosis. Inhibition of NETs may decrease the severity of many diseases improving survival. Herein, we describe NETosis in different diseases focusing on the detrimental effect of NETs and outline possible therapeutics that can be used to mitigate netosis. There is a need for more studies and clinical trials on these and other compounds that could prevent or destroy NETs, thereby decreasing damage to patients.

Neutrophil extracellular traps (NETs) in a randomized controlled trial of a combination of antiviral and nonsteroidal anti-inflammatory treatment in a bovine model of respiratory syncytial virus infection

The function of neutrophils in viral infections has long been established and studies have been done to examine the role of neutrophil extracellular traps (NETs). Further study and analysis of NETs in viral infections may reveal a new therapeutic target. Administration of ibuprofen and GS-561937, a fusion protein inhibitor (FPI), have been experimentally shown to decrease the severity of bovine respiratory syncytial virus (BRSV) infection. Our aims were to determine the effect of ibuprofen and FPI on NETs after BRSV infection as a monotherapy or combined therapy.

METHODS

We conducted a randomized placebo-controlled trial of ibuprofen, FPI, or as a dual therapy initiated at 3 or 5 days after experimental infection with BRSV in 36 five to six-week-old Holstein calves (Bos Taurus). Lung tissue samples were collected and stained with antibodies conjugated with fluorescence dyes to visualize and quantify the NETs in situ. We estimated the average NETs in the sample lung tissue slides and compared the areas occupied by NETS within and between the treatment groups.

RESULTS

There were significantly fewer NETs in the lung tissue from calves that were given ibuprofen and both ibuprofen and fusion protein inhibitor from day 3 post infection compared to the placebo group. Calves administered with ibuprofen, fusion protein inhibitor or both from day five had visually fewer NETs than the placebo but the difference was not significant.

CONCLUSION

BRSV can induce NET formation in vitro and in vivo. A combination of both drugs (Ibuprofen and FPI) resulted in less NETs observed in lung tissue of BRSV infected calves compared to the placebo or monotherapy groups.

Mitochondria are essential for antibacterial extracellular trap formation mediated by zymosan in hemocytes of Ruditapes philippinarum

The formation of extracellular traps (ETs) is an important innate immune mechanism that serves to combat different invading pathogens. In this study, zymosan significantly induced the formation of ETs in the hemocytes of Ruditapes philippinarum, and this effect was accompanied by translocation of the mitochondria to the cell surface. Zymosan stimulation clearly induced an increase in intracellular ROS and MPO production and an overexpression of ROS-related genes (PI3K, AKT and HIF). In response to the ROS burst, the mitochondrial membrane potential decreased, and the mitochondrial permeability transition pore opened. Conversely, mitochondrial superoxide inhibitor (Mito-TEMPO) significantly inhibited the formation of ETs, suggesting that mitochondrial ROS were necessary for the formation of ETs. In addition, we found that zymosan-induced ETs showed antibacterial activities against gram-negative and gram-positive bacteria, such as Vibrio anguillarum, Vibrio harveyi, Escherichia coli and Micrococcus luteus. Taken together, these findings elucidated a new antibacterial approach for R. philippinarum and highlighted the role of mitochondria in the formation of zymosan-induced ETs.

A Review of the Neutrophil Extracellular Traps (NETs) from Cow, Sheep and Goat Models

This review provides insight into the importance of understanding NETosis in cows, sheep, and goats in light of the importance to their health, welfare and use as animal models. Neutrophils are essential to innate immunity, pathogen infection, and inflammatory diseases. The relevance of NETosis as a conserved innate immune response mechanism and the translational implications for public health are presented. Increased understanding of NETosis in ruminants will contribute to the prediction of pathologies and design of strategic interventions targeting NETs. This will help to control pathogens such as coronaviruses and inflammatory diseases such as mastitis that impact all mammals, including humans. Definition of unique attributes of NETosis in ruminants, in comparison to what has been observed in humans, has significant translational implications for one health and global food security, and thus warrants further study.

Neutrophil extracellular traps in cancer

Beyond their well-known functions in the acute phases of the immune response, neutrophils play important roles in the various phases of tumor initiation and progression, through the release of their stored or newly synthesized mediators. In addition to reactive oxygen species, cytokines, chemokines, granule proteins and lipid mediators, neutrophil extracellular traps (NETs) can also be released upon neutrophil activation. NET formation can be achieved through a cell-death process or in association with the release of mitochondrial DNA from viable neutrophils. NETs are described as extracellular fibers of DNA and decorating proteins responsible for trapping and killing extracellular pathogens, playing a protective role in the antimicrobial defense. There is increasing evidence, however, that NETs play multiple roles in the scenario of cancer-related inflammation. For instance, NETs directly or indirectly promote tumor growth and progression, fostering tumor spread at distant sites and shielding cancer cells thus preventing the effects of cytotoxic lymphocytes. NETs can also promote tumor angiogenesis and cancer-associated thrombosis. On the other hand, there is some evidence that NETs may play anti-inflammatory and anti-tumorigenic roles. In this review, we focus on the main mechanisms underlying the emerging effects of NETs in cancer initiation and progression.

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.

Piscirickettsia salmonis-Triggered Extracellular Traps Formation as an Innate Immune Response of Atlantic Salmon-Derived Polymorphonuclear Neutrophils

Simple Summary

Within innate immunity, polymorphonuclear neutrophils (PMN) are the most abundant leukocyte population. Alongside PMN, monocytes, eosinophils, and basophils are also known to exist. All of them can release extracellular traps (ETs), a complex web-like structure composed of chromatin decorated with nuclear histones, granular enzymes, peptides, and proteins, to firmly entrap invasive pathogens, thereby slowing dissemination and helping to develop proper immune responses against bacteria, fungi, viruses, and parasites. Here, we showed for the first time that Atlantic salmon-derived PMN released ETs-like structures in vitro, in response to highly pathogenic facultative intracellular rickettsial bacteria Piscirickettsia salmonis. The release of ET-like structures from PMN could be a new alternative to improve farmed salmon’s defense against pathogens.

Abstract

Extracellular traps (ETs) are webs of DNA, citrullinated histones, anti-microbial peptides, and proteins that were not previously reported in Atlantic salmon (Salmo salar). ETs are mainly released from polymorphonuclear neutrophils (PMN) and are considered a novel PMN-derived effector mechanism against different invasive pathogens. Here, we showed that Atlantic salmon-derived PMN released ETs-like structures in vitro in response to highly pathogenic facultative intracellular rickettsial bacteria Piscirickettsia salmonis. PMN were isolated from pre-smolt Atlantic salmon and stimulated in vitro with oleic acid and P. salmonis. Extracellular DNA was measured using the PicoGreen™ dye, while immunofluorescence image analysis was used to confirm the classical components of salmonid-extruded ETs. Future studies are required to better understand the role of Atlantic salmon-derived ETs orchestrating innate/adaptive immunity and the knowledge on regulation pathways involved in this cell death process. Thus, comprehension of salmonid-derived ETs against P. salmonis might represent novel alternative strategies to improve host innate defense mechanisms of farmed salmon against closely related rickettsial bacteria, as a complement to disease prevention and control strategies.

Neutrophils: Many Ways to Die

Neutrophils or polymorphonuclear leukocytes (PMN) are key participants in the innate immune response for their ability to execute different effector functions. These cells express a vast array of membrane receptors that allow them to recognize and eliminate infectious agents effectively and respond appropriately to microenvironmental stimuli that regulate neutrophil functions, such as activation, migration, generation of reactive oxygen species, formation of neutrophil extracellular traps, and mediator secretion, among others. Currently, it has been realized that activated neutrophils can accomplish their effector functions and simultaneously activate mechanisms of cell death in response to different intracellular or extracellular factors. Although several studies have revealed similarities between the mechanisms of cell death of neutrophils and other cell types, neutrophils have distinctive properties, such as a high production of reactive oxygen species (ROS) and nitrogen species (RNS), that are important for their effector function in infections and pathologies such as cancer, autoimmune diseases, and immunodeficiencies, influencing their cell death mechanisms. The present work offers a synthesis of the conditions and molecules implicated in the regulation and activation of the processes of neutrophil death: apoptosis, autophagy, pyroptosis, necroptosis, NETosis, and necrosis. This information allows to understand the duality encountered by PMNs upon activation. The effector functions are carried out to eliminate invading pathogens, but in several instances, these functions involve activation of signaling cascades that culminate in the death of the neutrophil. This process guarantees the correct elimination of pathogenic agents, damaged or senescent cells, and the timely resolution of the inflammation that is essential for the maintenance of homeostasis in the organism. In addition, they alert the organism when the immunological system is being deregulated, promoting the activation of other cells of the immune system, such as B and T lymphocytes, which produce cytokines that potentiate the microbicide functions.

NETosis in Rheumatic Diseases

PURPOSE OF REVIEW

Neutrophils are the most numerous and the first responder cells of the innate immune system. Evidence suggests that neutrophils may play an essential role in the pathogenesis of multiple systemic diseases. A novel mechanism of neutrophil extracellular traps (NETs) leading to breaking of self-tolerance and generation of autoimmune responses in predisposed individuals has been described in various autoimmune conditions. The purpose of the review is to identify these important mechanisms of NETs leading to autoimmunity in various rheumatic diseases.

RECENT FINDINGS

NETs contain histone and chromatin, which contain important autoantigens. Many autoimmune conditions are associated with increased NET-generating capacity, unique low-density granulocyte population, and impaired NET degradation leading to persistent inflammation and tissue damage. NETs can also activate other immune cells, and their components may amplify the inflammatory response by activation of complement pathways and inflammasomes. NETs can also contribute to autoantibody formation in disorders such as rheumatoid arthritis, ANCA-associated vasculitis, and systemic lupus erythematosus by providing a constant source of autoantigens. NETs can also serve as biomarkers providing insights into disease diagnosis and therapeutics. NETs seem to play a primary role in inflammatory disease pathogenesis. Identification of different NET pathogenic pathways in various rheumatic conditions could provide new insights into disease pathogenesis and therapeutic targets could be developed towards the future treatment of inflammatory autoimmune diseases.

The Role of TLR2 and TLR4 in Recognition and Uptake of the Apicomplexan Parasite Eimeria bovis and Their Effects on NET Formation

BACKGROUND

Bovine polymorphonuclear neutrophils (PMN) constitutively express the Toll-like receptors (TLRs) TLR2 and TLR4 and have been shown to generate Neutrophil extracellular traps (NETs) upon exposure to Eimeria bovis. The present work investigated the role of TLR2 and TLR4 in the recognition and uptake of E. bovis sporozoites, IL-8 production and neutrophil extracellular trap (NET) formation.

METHODS

TLR expression was performed by flow cytometric analysis on PMN exposed to live carboxyfluorescein succinimidyl ester (CFSE)-stained sporozoites. Supernatants of PMN exposed to different E. bovis sporozoite preparations and antigens in the absence or presence of TLR antibodies were assessed for IL-8 secretion. Cells were exposed to sporozoite preparations and assessed for the activation of transcription factor NF-κB using a luciferase reporter assay. Immunofluorescence analysis was done to investigate TLR2 and TLR4 surface expression and NET formation on bovine PMN exposed to vital sporozoites.

RESULTS

we observed significantly increased TLR2 and TLR4 expression with a mean increase in expression that was greater for TLR2 than TLR4. This upregulation neither inhibited nor promoted sporozoite phagocytosis by bovine PMN. Live sporozoites together with anti-TLR2 mAb resulted in a significant enhancement of IL-8 production. NF-κB activation was more strongly induced in TLR2-HEK cells than in TLR4/MD2-HEK cells exposed to heat-killed sporozoites and antigens. Immunofluorescence analysis showed TLR-positive signals on the surface of PMN and concomitant NET formation.

CONCLUSIONS

This is the first report on E. bovis-induced concomitant TLR2 and TLR4 expression during bovine PMN-derived NETosis.

Understanding the immune responses involved in mediating protection or immunopathology during leishmaniasis

Leishmaniasis is a vector-borne Neglected Tropical Disease (NTD) transmitted by the sand fly and is a major public health problem worldwide. Infections caused by Leishmania clinically manifest as a wide range of diseases, such as cutaneous (CL), diffuse cutaneous (DCL), mucosal (MCL) and visceral leishmaniasis (VL). The host innate and adaptative immune responses play critical roles in the defense against leishmaniasis. However, Leishmania parasites also manipulate the host immune response for their survival and replication. In addition, other factors such as sand fly salivary proteins and microbiota also promote disease susceptibility and parasite spread by modulating local immune response. Thus, a complex interplay between parasite, sand fly and the host immunity governs disease severity and outcome. In this review, we discuss the host immune response during Leishmania infection and highlight the factors associated with resistance or susceptibility.

The Role of Small Extracellular Vesicles in Viral-Protozoan Symbiosis: Lessons From Trichomonasvirus in an Isogenic Host Parasite Model

The protozoan parasite Trichomonas vaginalis (TV), exclusively adapted to the human genital tract, is one of the most common sexually transmitted pathogens. Adding to the complexity of the host-pathogen interactions, the parasite harbors TV-specific endosymbiont viruses (Trichomonasvirus, TVV). It was reported that small extracellular vesicles (sEVs) released by TV play a role in host immunity; however, the role of the viral endosymbiosis in this process remained unknown. We hypothesized that the virus may offer evolutionary benefit to its protozoan host at least in part by altering the immunomodulatory properties of sEVs spreading from the site of infection to non-infected immune effector cells. We infected human vaginal epithelial cells, the natural host of the parasite, with TV natively harboring TVV and an isogenic derivative of the parasite cured from the viral infection. sEVs were isolated from vaginal cell culture 24 h post TV infection and from medium where the isogenic TV strains were cultured in the absence of the human host. sEVs from TVV-negative but not TVV-positive parasites cultured alone caused NF-κB activation and increase of IL-8 and RANTES expression by uterine endocervical cells, which provide innate immune defense at the gate to the upper reproductive tract. Similarly, mononuclear leukocytes increased their IL-8, IL-6 and TNF-α output in response to sEVs from virus-negative, but not isogenic virus-positive parasites, the latter exosomes being immunosuppressive in comparison to TV medium control. The same phenomenon of suppressed immunity induced by the TVV-positive compared to TVV-negative phenotype was seen when stimulating the leukocytes with sEVs originating from infected vaginal cultures. In addition, the sEVs from the TVV-positive infection phenotype suppressed immune signaling of a toll-like receptor ligand derived from mycoplasma, another frequent TV symbiont. Quantitative comparative proteome analysis of the secreted sEVs from virus-positive versus virus-negative TV revealed differential expression of two functionally uncharacterized proteins and five proteins involved in Zn binding, protein binding, electron transfer, transferase and catalytic activities. These data support the concept that symbiosis with viruses may provide benefit to the protozoan parasite by exploiting sEVs as a vehicle for inter-cellular communications and modifying their protein cargo to suppress host immune activation.

Extracellular Traps Released by Neutrophils from Cats are Detrimental to Toxoplasma gondii Infectivity

Toxoplasma gondii is the causative agent of toxoplasmosis, an infectious disease that affects over 30% of the human world population, causing fatal infections in immunocompromised individuals and neonates. The life cycle of T. gondii is complex, and involves intermediate hosts (birds and mammals) and definitive hosts (felines, including domestic cats). The innate immune repertoire against the parasite involves the production of neutrophil extracellular traps (NET), and neutrophils from several intermediate hosts produce NET induced by T. gondii. However, the mechanisms underlying NET release in response to the parasite have been poorly explored. Therefore, the aims of this study were to investigate whether neutrophils from cats produce NET triggered by T. gondii and to understand the mechanisms thereby involved. Neutrophils from cats were stimulated with T. gondii tachyzoites and NET-derived DNA in the supernatant was quantified during the time. The presence of histone H1 and myeloperoxidase was detected by immunofluorescence. We observed that cat neutrophils produce both classical and rapid/early NET stimulated by T. gondii. Inhibition of elastase, intracellular calcium, and phosphatidylinositol 3-kinase (PI3K)-δ partially blocked classical NET release in response to the parasite. Electron microscopy revealed strands and networks of DNA in close contact or completely entrapping parasites. Live imaging showed that tachyzoites are killed by NET. We conclude that the production of NET is a conserved strategy to control infection by T. gondii amongst intermediate and definitive hosts.

Influence of the Host and Parasite Strain on the Immune Response During Toxoplasma Infection

Toxoplasma gondii is an exceptionally successful parasite that infects a very broad host range, including humans, across the globe. The outcome of infection differs remarkably between hosts, ranging from acute death to sterile infection. These differential disease patterns are strongly influenced by both host- and parasite-specific genetic factors. In this review, we discuss how the clinical outcome of toxoplasmosis varies between hosts and the role of different immune genes and parasite virulence factors, with a special emphasis on Toxoplasma-induced ileitis and encephalitis.

Hookworms Evade Host Immunity by Secreting a Deoxyribonuclease to Degrade Neutrophil Extracellular Traps

Hookworms cause a major neglected tropical disease, occurring after larvae penetrate the host skin. Neutrophils are phagocytes that kill large pathogens by releasing neutrophil extracellular traps (NETs), but whether they target hookworms during skin infection is unknown. Using a murine hookworm, Nippostrongylus brasiliensis, we observed neutrophils being rapidly recruited and deploying NETs around skin-penetrating larvae. Neutrophils depletion or NET inhibition altered larvae behavior and enhanced the number of adult worms following murine infection. Nevertheless, larvae were able to mitigate the effect of NETs by secreting a deoxyribonuclease (Nb-DNase II) to degrade the DNA backbone. Critically, neutrophils were able to kill larvae in vitro, which was enhanced by neutralizing Nb-DNase II. Homologs of Nb-DNase II are present in other nematodes, including the human hookworm, Necator americanus, which also evaded NETs in vitro. These findings highlight the importance of neutrophils in hookworm infection and a potential conserved mechanism of immune evasion.

Neutrophil extracellular traps and MPO in models of susceptibility and resistance against Entamoeba histolytica

The main effector mechanisms of neutrophils are the release of neutrophil extracellular traps (NETs) and myeloperoxidase (MPO). In this work, we evaluated the role of NETs and the activity of MPO in the interactions of rodent neutrophils with amoebae and in amoebic liver abscess (ALA)-resistant and ALA-susceptible models. We showed with in vitro assays that mice produced greater amounts of NETs and MPO than did hamsters, and the elastase activity was high in both models. However, the inhibition of NETs and MPO promoted an increase in amoeba viability in the mice. The mouse ALAs showed a more profound presence of NETs and MPO than did the hamster ALAs. We concluded that both effector mechanisms were essential for the amoebic damage and could prevent the formation of ALAs in the resistant model.

Chromatin extracellular trap release in rainbow trout, Oncorhynchus mykiss (Walbaum, 1792)

Neutrophils release nuclear chromatin decorated with antimicrobial proteins into the extracellular milieu as an innate immune defence mechanism to counter invading microbes. These chromatin structures, called extracellular traps (ETs) and released by a process called NETosis, have been detected in mammals, certain invertebrates and some fish species, including fathead minnow, zebrafish, common carp, turbot, sole and barramundi. However, there have been no previous studies of ETs in the Salmonidae. ETs are released in response to chemical and biological stimuli, but observations from different fish species are inconsistent, particularly regarding the potency of various inducers and inhibitors. Thus, this present study aimed to describe ET release in a salmonid (rainbow trout, Oncorhynchus mykiss (Walbaum, 1792)) and uncover the inducers and inhibitors that can control this response. Highly enriched suspensions of polymorphonuclear cells (PMNs; mainly neutrophils) were prepared from head kidney tissues by a triple-layer Percoll gradient technique. ET structures were visualised in PMN-enriched suspensions through staining of the chromatin with nucleic acid-specific dyes and immunocytochemical probing of characteristic proteins expected to decorate the structure. ET release was quantified after incubation with inducers and inhibitors known to affect this response in other organisms. Structures resembling ETs stained positively with SYTOX Green (a stain specific for nucleic acid) while immunocytochemistry was used to detect neutrophil elastase, myeloperoxidase and H2A histone in the structures, which are diagnostic proteinaceous markers of ETs. Consistent with other studies on mammals and some fish species, calcium ionophore and flagellin were potent inducers of ETs, while cytochalasin D inhibited NETosis. Phorbol 12-myristate 13-acetate (PMA), used commonly to induce ETs, exerted only weak stimulatory activity, while heat-killed bacteria and lipopolysaccharide did not induce ET release. Unexpectedly, the ET-inhibitor diphenyleneiodonium chloride acted as an inducer of ET release, an observation not reported elsewhere. Taken together, these data confirm for the first time that ETs are released by salmonid PMNs and compounds useful for manipulating NETosis were identified, thus providing a platform for further studies to explore the role of this mechanism in fish immunity. This new knowledge provides a foundation for translation to farm settings, since manipulation of the innate immune response offers a potential alternative to the use of antibiotics to mitigate against microbial infections, particularly for pathogens where protection by vaccination has yet to be realised.