Diverse novel functions of neutrophils in immunity, inflammation, and beyond

Interferon Lambda's New Role as Regulator of Neutrophil Function

Neutrophils are increasingly appreciated as multifaceted regulators of innate immunity and inflammation. Historically, these important innate cells have been considered suicidal phagocytes with a primary role in the destruction of extracellular pathogens. Recent studies have significantly altered this simplistic view of neutrophils and have instead presented extensive evidence for a complex role for neutrophils in the control of diverse inflammatory conditions. It is now appreciated that neutrophils are crucial not only for efficient clearance of various pathogens but also in the development and control of inflammatory states such as autoimmunity, cancer, and tissue repair. Mounting evidence also suggests that neutrophils are capable of differential activation giving rise to distinctly polarized cells with diverse effector functions. Interferon lambda (IFN-λ) (also known as type III IFN) has emerged as an unexpected regulator of neutrophil function. IFN-λs are the newest members of the IFN family of antiviral cytokines and although initial studies suggested identical biological activities to type I IFNs, it is now apparent that type III IFN has distinct functions in vivo. In this article, I summarize recent evidence linking type III IFNs to the regulation and potential tailoring of neutrophil responses. These exciting observations might have important implications for the development of IFN-λs as novel therapeutic cytokines for the treatment of a diversity of inflammatory states where neutrophils are crucial players.

DNA Damaging Effects, Oxidative Stress Responses and Cholinesterase Activity in Blood and Brain of Wistar Rats Exposed to Δ9-Tetrahydrocannabinol

Currently we are faced with an ever-growing use of Δ9-tetrahydrocannabinol (THC) preparations, often used as supportive therapies for various malignancies and neurological disorders. As some of illegally distributed forms of such preparations, like cannabis oils and butane hash oil, might contain over 80% of THC, their consumers can become intoxicated or experience various detrimental effects. This fact motivated us for the assessments of THC toxicity in vivo on a Wistar rat model, at a daily oral dose of 7 mg/kg which is comparable to those found in illicit preparations. The main objective of the present study was to establish the magnitude and dynamics of DNA breakage associated with THC exposure in white blood and brain cells of treated rats using the alkaline comet assay. The extent of oxidative stress after acute 24 h exposure to THC was also determined as well as changes in activities of plasma and brain cholinesterases (ChE) in THC-treated and control rats. The DNA of brain cells was more prone to breakage after THC treatment compared to DNA in white blood cells. Even though DNA damage quantified by the alkaline comet assay is subject to repair, its elevated level detected in the brain cells of THC-treated rats was reason for concern. Since neurons do not proliferate, increased levels of DNA damage present threats to these cells in terms of both viability and genome stability, while inefficient DNA repair might lead to their progressive loss. The present study contributes to existing knowledge with evidence that acute exposure to a high THC dose led to low-level DNA damage in white blood cells and brain cells of rats and induced oxidative stress in brain, but did not disturb ChE activities.

The Pivotal Role of Regulatory T Cells in the Regulation of Innate Immune Cells

The distinction between innate and adaptive immunity is one of the basic tenets of immunology. The co-operation between these two arms of the immune system is a major determinant of the resistance or susceptibility of the host following pathogen invasion. Hence, this interactive co-operation between cells of the innate and adaptive immunity is of significant interest to immunologists. The sub-population of CD4⁺ T cells with regulatory phenotype (regulatory T cells; Tregs), which constitute a part of the adaptive immune system, have been widely implicated in the regulation of the immune system and maintenance of immune homeostasis. In the last two decades, there has been an explosion in research describing the role of Tregs and their relevance in several immunopathologies ranging from inflammation to cancer. The majority of these studies focus on the role of Tregs on the cells of the adaptive immune system. Recently, there is significant interest in the role of Tregs on cells of the innate immune system. In this review, we examine the literature on the role of Tregs in immunology. Specifically, we focus on the emerging knowledge of Treg interaction with dendritic cells, macrophages, neutrophils, and γδ T cells. We highlight this interaction as an important link between innate and adaptive immune systems which also indicate the far-reaching role of Tregs in the regulation of immune responses and maintenance of self-tolerance and immune homeostasis.

Immune-endocrine interactions related to a high risk of infections in chronic metabolic diseases: The role of PPAR gamma

Diverse disturbances in immune-endocrine circuitries are involved in the development and aggravation of several chronic metabolic diseases (CMDs), including obesity, diabetes, and metabolic syndrome. The chronic inflammatory syndrome observed in CMDs culminates in dysregulated immune responses with low microbial killing efficiency, by means low host innate immune response, and loss of ability to eliminate the pathogens, which results in a high prevalence of infectious diseases, including pneumonia, tuberculosis, and sepsis. Herein, we review evidence pointing out PPARγ as a putative player in immune-endocrine disturbances related to increased risk of infections in CMDs. Cumulated evidence indicates that PPARγ activation modulates host cells to control inflammation during CMDs because of PPARγ agonists have anti-inflammatory and pro-resolutive properties, increasing host ability to eliminate pathogen, modulating hormone production, and restoring glucose and lipid homeostasis. As such, we propose PPARγ as a putative therapeutic adjuvant for patients with CMDs to favor a better infection control.

iTRAQ analysis of liver immune-related proteins from darkbarbel catfish (Pelteobagrus vachelli) infected with Edwardsiella ictaluri

Edwardsiella ictaluri causes enteric septicemia of catfish (ESC), a major disease occurring in these siluriform fish. As the liver is an important organ for defending against bacterial pathogens in fish, this study aimed to determine the liver immune response at the protein level. The differential proteomes of the darkbarbel catfish liver in response to E. ictaluri infection were identified with isobaric tags for relative and absolute quantitation (iTRAQ) labeling followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Using a 1.2-fold change in expression as a physiologically significant benchmark, a total of 819 differentially expressed proteins were reliably quantified using iTRAQ analysis, including 6 up-regulated proteins and 813 down-regulated proteins. GO enrichment analysis indicated that the "complement activation, alternative pathway" and "complement activation, classical pathway" were significantly enriched. KEGG enrichment analysis indicated the "antigen processing and presentation" and "bacterial secretion system" were significantly enriched. We selected the 6 up-regulated proteins and 10 immune-related down-regulated proteins for validation using real-time PCR. The 10 immune-related proteins included complement component C1r, C3, C5, C7, and C9 and plasma protease C1 inhibitor (C1-INH), signal recognition particle 54 kDa protein (SRP54), SRP receptor, proteasome activator complex subunit 1 (PSME1) and major histocompatibility complex class I (MHC class I) were selected from the GO clusters and KEGG pathways. The variations in mRNA expression for these genes were similar to the results of iTRAQ. This is the first report detailing the proteome response in the darkbarbel catfish liver during E. ictaluri infection and markedly contributes to our understanding of the defense mechanisms in the livers of darkbarbel catfish.

Neutrophil Effector Functions Are Not Impaired in Duffy Antigen Receptor for Chemokines (DARC)-Null Black South Africans

Neutrophils are well-recognized for their pathogen killing mechanisms and disorders of neutrophil count and function are associated with recurrent infections. The Duffy Antigen Receptor for Chemokines (DARC)-null genotype is predominant in sub-Saharan African ancestry populations and is the major genetic determinant of benign ethnic neutropenia which has been associated with increased risk of Human Immunodeficiency Virus (HIV)-1 acquisition and mother-to-child transmission. However, the impact of DARC-null-linked neutropenia on HIV disease progression remains controversial. While the DARC-null genotype is associated with low numbers of circulating neutrophils, the effects of the polymorphism on neutrophil functions is unknown. We investigated the impact of the DARC-null trait and lower absolute neutrophil counts (ANCs) on key neutrophil effector functions [proteolytic activity within the phagosome following Fc receptor-mediated phagocytosis, reactive oxygen species (ROS) production, and neutrophil extracellular trap (NET) formation] in 20 HIV negative and 22 HIV-1 chronically infected black South Africans. Phagosome maturation was measured by flow cytometry following Fc-mediated uptake of IgG opsonized beads; ROS production was measured by chemi-luminescence after activation of neutrophils with phorbol 12-myristate 13-acetate (PMA). Activated neutrophils were also visualized by fluorescent microscopy for NET quantification. Study subjects were genotyped for the DARC trait using TaqMan allelic discrimination assays and ANCs were measured by full blood count. As expected, the DARC-null polymorphism was highly prevalent in our participant cohort (69%) and was strongly associated with lower ANCs in uninfected (p = 0.0007) and HIV-1 infected (p = 0.03) subjects. We observed enhanced proteolytic activity within the phagosome in the absence of DARC at 10 min (p = 0.05 and p = 0.009) and 60 min (p = 0.05 and p = 0.07) in uninfected and HIV-1 infected subjects, respectively. ROS was unaffected by DARC trait irrespective of HIV status. Furthermore, formation of NETs was reduced in neutrophils from DARC-null subjects (p = 0.04) following prolonged in vitro stimulation, but only in HIV-1 infected subjects. The data indicate differential neutrophil function in the absence of DARC that may be moderately modulated by HIV-1 infection but overall, the data suggest that DARC-null trait is not deleterious to neutrophil effector functions in African populations.

Neutrophil Activation During Septic Shock

In addition to their well-known role as the cellular mediators of immunity, key other roles have been identified for neutrophils during septic shock. Importantly, neutrophils indeed play a critical role in the recently described immunothrombosis concept and in septic shock-induced coagulopathy. Septic shock is one of the most severe forms of infection, characterized by an inadequate host response to the pathogenic organism. This host response involves numerous defense mechanisms with an intense cellular activation, including neutrophil activation. Neutrophils are key cells of innate immunity through complex interactions with vascular cells and their activation may participate in systemic tissue damages. Their activation also leads to the emission of neutrophil extracellular traps, which take part in both pathogen circumscription and phagocytosis, but also in coagulation activation. Neutrophils thus stand at the interface between hemostasis and immunity, called immunothrombosis.The present review will develop a cellular approach of septic shock pathophysiology focusing on neutrophils as key players of septic shock-induced vascular cell dysfunction and of the host response, associating immunity and hemostasis. We will therefore first develop the role of neutrophils in the interplay between innate and adaptive immunity, and will then highlight recent advances in our understanding of immunothrombosis septic shock-induced coagulopathy.

Targeting immune cells for cancer therapy

Recent years have seen a renaissance in the research linking inflammation and cancer with immune cells playing a central role in smouldering inflammation in the tumor microenvironment. Diverse immune cell types infiltrate the tumor microenvironment, and the dynamic tumor-immune cell interplay gives rise to a rich milieu of cytokines and growth factors. Fundamentally, this intricate cross-talk creates the conducive condition for tumor cell proliferation, survival and metastasis. Interestingly, the prominent impact of immune cells is expounded in their contrary pro-tumoral role, as well as their potential anti-cancer cellular weaponry. The latter is known as immunotherapy, a concept born out of evidence that tumors are susceptible to immune defence and that by manipulating the immune system, tumor growth can be successfully restrained. Naturally, a deeper understanding of the multifaceted roles of various immune cell types thus contributes toward developing innovative anti-cancer strategies. Therefore, in this review we first outline the roles played by the major immune cell types, such as macrophages, neutrophils, natural killer cells, T cells and B cells. We then explain the recently-explored strategies of immunomodulation and discuss some important approaches via an immunology perspective.

Extra-Neutralizing FcR-Mediated Antibody Functions for a Universal Influenza Vaccine

While neutralizing antibody titers measured by hemagglutination inhibition have been proposed as a correlate of protection following influenza vaccination, neutralization alone is a modest predictor of protection against seasonal influenza. Instead, emerging data point to a critical role for additional extra-neutralizing functions of antibodies in protection from infection. Specifically, beyond binding and neutralization, antibodies mediate a variety of additional immune functions via their ability to recruit and deploy innate immune effector function. Along these lines, antibody-dependent cellular cytotoxicity, antibody-mediated macrophage phagocytosis and activation, antibody-driven neutrophil activation, antibody-dependent complement deposition, and non-classical Fc-receptor antibody trafficking have all been implicated in protection from influenza infection. However, the precise mechanism(s) by which the immune system actively tunes antibody functionality to drive protective immunity has been poorly characterized. Here we review the data related to Fc-effector functional protection from influenza and discuss prospects to leverage this humoral immune activity for the development of a universal influenza vaccine.

The role of neutrophil activation in determining the outcome of pregnancy and modulation by hormones and/or cytokines

Neutrophils are often exclusively considered as a first-line innate immune defence, able to rapidly kill or trap pathogens and causing in case of over-activation tissue damage. In the female reproductive tract, however, the presence and activity of neutrophils seems to be tightly regulated. Major players in orchestrating this regulation are cyclical steroid sex hormones present during the menstrual cycle and pregnancy. This review describes the role of sex hormones in regulating directly or indirectly the functionality of neutrophils, the role of neutrophils during fertilization and pregnancy and in controlling viral, fungal and bacterial infection. This review also discusses the consequence of overt neutrophil activation in pregnancy pathologies.

Monocytes Latently Infected with Human Cytomegalovirus Evade Neutrophil Killing

One site of latency of human cytomegalovirus (HCMV) in vivo is in undifferentiated cells of the myeloid lineage. Although latently infected cells are known to evade host T cell responses by suppression of T cell effector functions, it is not known if they must also evade surveillance by other host immune cells. Here we show that cells latently infected with HCMV can, indeed, be killed by host neutrophils but only in a serum-dependent manner. Specifically, antibodies to the viral latency-associated US28 protein mediate neutrophil killing of latently infected cells. To address this mechanistically, a full proteomic screen was carried out on latently infected monocytes. This showed that latent infection downregulates the neutrophil chemoattractants S100A8/A9, thus suppressing neutrophil recruitment to latently infected cells. The ability of latently infected cells to inhibit neutrophil recruitment represents an immune evasion strategy of this persistent human pathogen, helping to prevent clearance of the latent viral reservoir.

The type III intermediate filament vimentin regulates organelle distribution and modulates autophagy

The cytoskeletal protein vimentin plays a key role in positioning of organelles within the cytosol and has been linked to the regulation of numerous cellular processes including autophagy, however, how vimentin regulates autophagy remains relatively unexplored. Here we report that inhibition of vimentin using the steroidal lactone Withaferin A (WFA) causes vimentin to aggregate, and this is associated with the relocalisation of organelles including autophagosomes and lysosomes from the cytosol to a juxtanuclear location. Vimentin inhibition causes autophagosomes to accumulate, and we demonstrate this results from modulation of mechanistic target of rapamycin (mTORC1) activity, and disruption of autophagosome-lysosome fusion. We suggest that vimentin plays a physiological role in autophagosome and lysosome positioning, thus identifying vimentin as a key factor in the regulation of mTORC1 and autophagy.

Multi-walled carbon nanotube oxidation dependent keratinocyte cytotoxicity and skin inflammation

BACKGROUND

The effects of carbon nanotubes on skin toxicity have not been extensively studied; however, our lab has previously shown that a carboxylated multi-walled carbon nanotube (MWCNT) exacerbates the 2, 4-dinitrofluorobenzene induced contact hypersensitivity response in mice. Here we examine the role of carboxylation in MWCNT skin toxicity.

RESULTS

MWCNTs were analyzed by transmission electron microscopy, zetasizer, and x-ray photoelectron spectroscopy to fully characterize the physical properties. Two MWCNTs with different levels of surface carboxylation were chosen for further testing. The MWCNTs with a high level of carboxylation displayed increased cytotoxicity in a HaCaT keratinocyte cell line, compared to the MWCNTs with intermediate levels of carboxylation. However, neither functionalized MWCNT increased the level of in vitro reactive oxygen species suggesting an alternative mechanism of cytotoxicity. Each MWCNT was tested in the contact hypersensitivity model, and only the MWCNTs with greater than 20% surface carboxylation exacerbated the ear swelling responses. Analysis of the skin after MWCNT exposure reveals that the same MWCNTs with a high level of carboxylation increase epidermal thickness, mast cell and basophil degranulation, and lead to increases in polymorphonuclear cell recruitment when co-administered with 2, 4-dinitrofluorobenzene.

CONCLUSIONS

The data presented here suggest that acute, topical application of low doses of MWCNTs can induce keratinocyte cytotoxicity and exacerbation of allergic skin conditions in a carboxylation dependent manner.

Neutrophil Cathepsin G Regulates Dendritic Cell Production of IL-12 during Development of CD4 T Cell Responses to Antigens in the Skin

Contact hypersensitivity (CHS) is a CD8 T cell-mediated response to hapten skin sensitization and challenge. Sensitization of wild-type (WT) mice induces hapten-reactive effector CD8 T cells producing IFN-γ and IL-17- and IL-4-producing CD4 T cells that cannot mediate CHS. Although CXCR2-dependent Ly6G⁺ (neutrophil) cell recruitment into hapten-challenged skin is required to direct effector CD8 T cell infiltration into the challenge site to elicit CHS, 2,4-dinitrofluorobenezene (DNFB) sensitization of CXCR2^-/- mice and neutrophil-depleted WT mice induced both hapten-reactive CD4 and CD8 T cells producing IFN-γ and IL-17. CD4 T cell-mediated CHS responses were not generated during DNFB sensitization of neutrophil-depleted WT mice treated with anti-IL-12 mAb or neutrophil-depleted IL-12^-/- mice. Neutrophil depletion during DNFB sensitization of WT mice markedly increased IL-12-producing hapten-primed dendritic cell numbers in the skin-draining lymph nodes. Sensitization of mice lacking the neutrophil serine protease cathepsin G (CG)-induced hapten-reactive CD4 and CD8 T cells producing IFN-γ and IL-17 with elevated and elongated CHS responses to DNFB challenge. Induction of CHS effector CD4 T cells producing IFN-γ in neutrophil-depleted WT mice was eliminated by s.c. injection of active, but not inactivated, CG during sensitization. Thus, hapten skin sensitization induces neutrophil release of CG that systemically inhibits hapten-presenting dendritic cell production of IL-12 and the development of hapten-reactive CD4 T cells to IFN-γ-producing CHS effector cells.

Monitoring of Neutrophil Recruitment to Mice Lungs During Pneumonic Plague

Early sensing of bacterial infection and the immediate recruitment of neutrophils to the lung is a major and decisive stage of the innate immune response to pulmonary bacterial infections. This chapter details the preparation of lung tissue suspensions from mice infected intra-nasally (I.N.) with the plague bacterium Yersinia pestis to study in vivo neutrophil responses to the infection. The samples were used for the quantification of neutrophil levels and for the characterization of the pro-inflammatory response required for neutrophil recruitment to the lung. The specific requirements for performing the procedures under Biosafety Level 3 containment and the proper handling and sterilization of the samples are discussed.

The Antidepressant Mirtazapine Inhibits Hepatic Innate Immune Networks to Attenuate Immune-Mediated Liver Injury in Mice

Activation of the innate immune system, including tissue macrophages and associated neutrophil infiltration, is an important driver of subsequent adaptive immune responses in many autoimmune diseases, including autoimmune hepatitis (AIH). The antidepressant mirtazapine has a unique complex pharmacology, altering signaling through a number of serotonin and histamine receptors that can impact macrophage function; an effect potentially influencing AIH outcome. In the mouse model of concanavalin A (Con A) induced liver injury (mimics many aspects of human AIH), in which early innate immune activation (i.e., stimulated hepatic macrophages/monocytes recruit neutrophils and additional monocytes to the liver) critically drives immune-mediated hepatitis induction, mirtazapine strikingly and dose-dependently inhibited Con A-induced liver injury. This inflammation-suppressing effect of mirtazapine was linked to an attenuation of Con A-stimulated early innate immune responses within the liver, including inhibition of hepatic macrophage/monocyte activation, decreased hepatic macrophage/monocyte-derived pro-inflammatory cytokine (e.g., TNFα) and chemokine (e.g., CXCL1 and CXCL2) production, suppression of Con A-induced increases in the hepatic expression of the neutrophil relevant endothelial cell adhesion molecule ICAM-1, with the resultant significant reduction in neutrophil recruitment into the liver. Consistent with our findings in the Con A model, mirtazapine also significantly reduced activation-induced release of cytokine/chemokine mediators from human CD14⁺ monocytes in vitro. Conclusion: Our data suggest that mirtazapine can attenuate hepatic innate immune responses that critically regulate the subsequent development of autoimmune liver injury. Therefore, given that it is a safe and widely used medication, mirtazapine may represent a novel therapeutic approach to autoimmune liver disease.

The Vitamin D Binding Protein and Inflammatory Injury: A Mediator or Sentinel of Tissue Damage?

Neutrophils are the most abundant type of white blood cell in most mammals including humans. The primary role of these cells is host defense against microbes and clearance of tissue debris in order to facilitate wound healing and tissue regeneration. The recruitment of neutrophils from blood into tissues is a key step in this process and is mediated by numerous different chemoattractants. The neutrophil migratory response is essential for host defense and survival, but excessive tissue accumulation of neutrophils is observed in many inflammatory disorders and strongly correlates with disease pathology. The vitamin D binding protein (DBP) is a circulating multifunctional plasma protein that can significantly enhance the chemotactic activity of neutrophil chemoattractants both in vitro and in vivo. Recent in vivo studies using DBP deficient mice showed that DBP plays a larger and more central role during inflammation since it induces selective recruitment of neutrophils, and this cofactor function is not restricted to C5a, as prior in vitro studies indicated, but can enhance chemotaxis to many chemoattractants. DBP also is an extracellular scavenger for actin released from damaged/dead cells and formation of DBP-actin complexes is an immediate host response to tissue injury. Recent in vitro evidence indicates that DBP bound to G-actin, and not free DBP, functions as an indirect but essential cofactor for neutrophil migration. DBP-actin complexes always will be formed regardless of what initiated an inflammation, since release of actin from damaged cells is a common feature in all types of injury and DBP is abundant and ubiquitous in all extracellular fluids. Indeed, these complexes have been detected in blood and tissue fluids from both humans and experimental animals following various forms of injury. The published data strongly supports the premise that DBP-actin complexes are the functional neutrophil chemotactic cofactor that enhances neutrophil chemotaxis in vitro and augments neutrophilic inflammation in vivo. This review will assess the fundamental role of DBP in neutrophilic inflammation and injury.

Enhancing Effect on Radical Scavenging Activity of Edible Brown Alga, Laminaria japonica (Ma-konbu) by Roasting Treatment

Various edible algae have been traditionally consumed as healthy food stuffs in Asian countries such as China, Korea and Japan, and roasting treatments have been carried out on some of these edible algae for the improvement of their taste and flavor. In the present paper, we analyzed the effect of roasting treatments on the radical scavenging activity of a typical Japanese edible brown alga, Laminaria japonica (L. japonica, Ma-konbu). The effect was estimated by a stable radical compound, diphenylpicrylhydrazyl (DPPH) and a chemiluminescence assay of superoxide anion generation using hypoxanthine (HPX) and xanthine oxidase (XOD) system. Weak but significant radical scavenging activities against the DPPH radical and superoxide anion were observed in the water extract of L. japonica when it was roasted at 130-150ºC. Very strong radical-scavenging activities were detected under much higher temperature conditions (180-200ºC). The enhancing effect of the roasting treatment on the radical scavenging activity was highly associated with the roasting-induced increase of polyphenol and tannin in the L. japonica extract. The sugar concentrations in the L. japonica extracts under different roasting conditions were significantly, but not strongly associated with their radical scavenging activities. The protein concentrations in the L. japonica extracts, however, were not associated with their radical scavenging activities under different roasting conditions. Furthermore, the extracts of L. japonica roasted under higher temperature conditions (180-200ºC) caused strong radical scavenging effects on the generation of opsonized zymosan (Opz)-induced reactive oxygen species (ROS) generation in human blood neutrophils, which was measured by chemiluminescence assay. These experimental results suggest that the roasting treatment of L. japonica causes an enhancing effect on the radical scavenging activity in the extract of this alga, and is associated with the increase in various radical scavenging substances in the extract. The significance of this finding is discussed from the viewpoint of healthy food science.

Itraconazole in combination with neutrophil depletion reduces the expression of genes related to pulmonary fibrosis in an experimental model of paracoccidioidomycosis

Itraconazole (ITC) is the drug of choice for treating paracoccidioidomycosis (PCM); nonetheless, patients with the chronic form of this mycosis develop fibrosis, a residual pulmonary abnormality, even after treatment. Recently, we observed that the depletion of neutrophils with a specific monoclonal antibody (mAb-anti-Ly6G) during the chronic stages of PCM was associated with a decrease in the fungal burden, the inflammatory response and a reduction of fibrosis. Herein, we aimed to evaluate the effect of ITC in combination with the mAb-anti-Ly6G in an experimental model of pulmonary PCM. BALB/c male mice were challenged with Paracoccidioides brasiliensis yeasts and treated with the mAb-anti-Ly6G and/or ITC at 4th week post-infection (p.i.) and then sacrificed at 12th week p.i. to assess neutrophil subpopulations, fungal load, collagen, expression of fibrosis- and pro-inflammatory-related genes and histopathology. We observed that combination of ITC/mAb-anti-Ly6G favored the control of infection and diminished the inflammatory response. Of note, such therapeutic strategy reduced the expression of IL-1β, IL-6, IL-17, IL-10, TNF-α, TGF-β1, TGF-β3, GATA-3, RORc, Ahr, MMP-1α, MMP-8 MMP-15, TIMP-1, and TIMP-2 genes in an additive manner compared to those mice treated with the mAb or ITC alone. Interestingly, ITC induced an increase of type-II neutrophils even in those mice treated with the mAb-anti-Ly6G. These results indicate that combination ITC/mAb-anti-Ly6G reduced the infection and pulmonary fibrosis through down-regulation of inflammatory and pro-fibrotic genes. Additionally, we confirmed the immunomodulatory properties of this antifungal in vivo. This work emphasizes the importance of exploring new potential combination treatments to treat fungal infections.

Myeloid-Specific Deletion of Mcl-1 Yields Severely Neutropenic Mice That Survive and Breed in Homozygous Form

Mouse strains with specific deficiency of given hematopoietic lineages provide invaluable tools for understanding blood cell function in health and disease. Whereas neutrophils are dominant leukocytes in humans and mice, there are no widely useful genetic models of neutrophil deficiency in mice. In this study, we show that myeloid-specific deletion of the Mcl-1 antiapoptotic protein in Lyz2^Cre/CreMcl1^flox/flox (Mcl1^ΔMyelo) mice leads to dramatic reduction of circulating and tissue neutrophil counts without affecting circulating lymphocyte, monocyte, or eosinophil numbers. Surprisingly, Mcl1^ΔMyelo mice appeared normally, and their survival was mostly normal both under specific pathogen-free and conventional housing conditions. Mcl1^ΔMyelo mice were also able to breed in homozygous form, making them highly useful for in vivo experimental studies. The functional relevance of neutropenia was confirmed by the complete protection of Mcl1^ΔMyelo mice from arthritis development in the K/B×N serum-transfer model and from skin inflammation in an autoantibody-induced mouse model of epidermolysis bullosa acquisita. Mcl1^ΔMyelo mice were also highly susceptible to systemic Staphylococcus aureus or Candida albicans infection, due to defective clearance of the invading pathogens. Although neutrophil-specific deletion of Mcl-1 in MRP8-CreMcl1^flox/flox (Mcl1^ΔPMN) mice also led to severe neutropenia, those mice showed an overt wasting phenotype and strongly reduced survival and breeding, limiting their use as an experimental model of neutrophil deficiency. Taken together, our results with the Mcl1^ΔMyelo mice indicate that severe neutropenia does not abrogate the viability and fertility of mice, and they provide a useful genetic mouse model for the analysis of the role of neutrophils in health and disease.

Omega-9 Oleic Acid, the Main Compound of Olive Oil, Mitigates Inflammation during Experimental Sepsis

The Mediterranean diet, rich in olive oil, is beneficial, reducing the risk of cardiovascular diseases and cancer. Olive oil is mostly composed of the monounsaturated fatty acid omega-9. We showed omega-9 protects septic mice modulating lipid metabolism. Sepsis is initiated by the host response to infection with organ damage, increased plasma free fatty acids, high levels of cortisol, massive cytokine production, leukocyte activation, and endothelial dysfunction. We aimed to analyze the effect of omega-9 supplementation on corticosteroid unbalance, inflammation, bacterial elimination, and peroxisome proliferator-activated receptor (PPAR) gamma expression, an omega-9 receptor and inflammatory modulator. We treated mice for 14 days with omega-9 and induced sepsis by cecal ligation and puncture (CLP). We measured systemic corticosterone levels, cytokine production, leukocyte and bacterial counts in the peritoneum, and the expression of PPAR gamma in both liver and adipose tissues during experimental sepsis. We further studied omega-9 effects on leukocyte rolling in mouse cremaster muscle-inflamed postcapillary venules and in the cerebral microcirculation of septic mice. Here, we demonstrate that omega-9 treatment is associated with increased levels of the anti-inflammatory cytokine IL-10 and decreased levels of the proinflammatory cytokines TNF-α and IL-1β in peritoneal lavage fluid of mice with sepsis. Omega-9 treatment also decreased systemic corticosterone levels. Neutrophil migration from circulation to the peritoneal cavity and leukocyte rolling on the endothelium were decreased by omega-9 treatment. Omega-9 also decreased bacterial load in the peritoneal lavage and restored liver and adipose tissue PPAR gamma expression in septic animals. Our data suggest a beneficial anti-inflammatory role of omega-9 in sepsis, mitigating leukocyte rolling and leukocyte influx, balancing cytokine production, and controlling bacterial growth possibly through a PPAR gamma expression-dependent mechanism. The significant reduction of inflammation detected after omega-9 enteral injection can further contribute to the already known beneficial properties facilitated by unsaturated fatty acid-enriched diets.

Rac-GTPases and Rac-GEFs in neutrophil adhesion, migration and recruitment

Rac-GTPases and their Rac-GEF activators play important roles in the recruitment and host defence functions of neutrophils. These proteins control the activation of adhesion molecules and the cytoskeletal dynamics that enable the adhesion, migration and tissue recruitment of neutrophils. They also regulate the effector functions that allow neutrophils to kill bacterial and fungal pathogens, and to clear debris. This review focuses on the roles of Rac-GTPases and Rac-GEFs in neutrophil adhesion, migration and recruitment.

NADPH oxidase activation in neutrophils: Role of the phosphorylation of its subunits

Neutrophils are key cells of innate immunity and during inflammation. Upon activation, they produce large amounts of superoxide anion (O₂ ^-. ) and ensuing reactive oxygen species (ROS) to kill phagocytized microbes. The enzyme responsible for O₂ ^-. production is called the phagocyte NADPH oxidase. This is a multicomponent enzyme system that becomes active after assembly of four cytosolic proteins (p47^phox , p67^phox , p40^phox and Rac2) with the transmembrane proteins (p22^phox and gp91^phox , which form the cytochrome b₅₅₈ ). gp91^phox represents the catalytic subunit of the NADPH oxidase and is also called NOX2. NADPH oxidase-derived ROS are essential for microbial killing and innate immunity; however, excessive ROS production induces tissue injury and prolonged inflammatory reactions that contribute to inflammatory diseases. Thus, NADPH oxidase activation must be tightly regulated in time and space to limit ROS production. NADPH oxidase activation is regulated by several processes such as phosphorylation of its components, exchange of GDP/GTP on Rac2 and binding of p47^phox and p40^phox to phospholipids. This review aims to provide new insights into the role of the phosphorylation of the NADPH oxidase components, that is gp91^phox , p22^phox , p47^phox , p67^phox and p40^phox , in the activation of this enzyme.

Recent advances on the crosstalk between neutrophils and B or T lymphocytes

An increasing body of literature supports a role for neutrophils as players in the orchestration of adaptive immunity. During acute and chronic inflammatory conditions, neutrophils rapidly migrate not only to sites of inflammation, but also to draining lymph nodes and spleen, where they engage bidirectional interactions with B- and T-lymphocyte subsets. Accordingly, a relevant role of neutrophils in modulating B-cell responses under homeostatic conditions has recently emerged. Moreover, specialized immunoregulatory properties towards B or T cells acquired by distinct neutrophil populations, originating under pathological conditions, have been consistently described. In this article, we summarize the most recent data from human studies and murine models on the ability of neutrophils to modulate adaptive immune responses under physiological and pathological conditions and the mechanisms behind these processes.

The enigmatic role of the neutrophil in asthma: Friend, foe or indifferent?

Whilst severe asthma has classically been categorized as a predominantly Th2-driven pathology, there has in recent years been a paradigm shift with the realization that it is a heterogeneous disease that may manifest with quite disparate underlying inflammatory and remodelling profiles. A subset of asthmatics, particularly those with a severe, corticosteroid refractory disease, present with a prominent neutrophilic component. Given the potential of neutrophils to impart extensive tissue damage and promote inflammation, it has been anticipated that these cells are closely implicated in the underlying pathophysiology of severe asthma. However, uncertainty persists as to why the neutrophil is present in the asthmatic lung and what precisely it is doing there, with evidence supporting its role as a protagonist of pathology being primarily circumstantial. Furthermore, our view of the neutrophil as a primitive, indiscriminate killer has evolved with the realization that neutrophils can exhibit a marked anti-inflammatory, pro-resolving and wound healing capacity. We suggest that the neutrophil likely exhibits pleiotropic and potentially conflicting roles in defining asthma pathophysiology-some almost certainly detrimental and some potentially beneficial-with context, timing and location all critical confounders. Accordingly, indiscriminate blockade of neutrophils with a broad sword approach is unlikely to be the answer, but rather we should first seek to understand their complex and multifaceted roles in the disease state and then target them with the same subtleties and specificity that they themselves exhibit.

Neutrophil Vaccination Dynamics and Their Capacity To Mediate B Cell Help in Rhesus Macaques

Neutrophils are the most abundant leukocyte and play a critical role in the initial response to an Ag. Recently, their ability to contribute to adaptive immunity has been highlighted. We evaluated the ability of neutrophils from blood to contribute to the adaptive immune response in a preclinical rhesus macaque SIV vaccine trial. Replication-competent adenovirus-SIV recombinants induced neutrophil activation, B cell help markers, and enhanced ability to generate reactive oxygen species. Boosting with SIV vaccines (adjuvant together with ALVAC or DNA plus envelope protein) elicited significant neutrophil responses. Serum cytokine and chemokine levels induced correlated with the frequency of neutrophil subsets expressing IL-21, myeloperoxidase, and CD64. Post-SIV infection, neutrophils exhibited dysfunction, both phenotypically and functionally. B cells from protected and infected macaques cocultured with autologous polymorphonuclear cells, consisting primarily of neutrophils, were activated, underwent class switching, and produced Abs. This B cell help was not aided by addition of IL-10 and was largely contact dependent. Numerous genes associated with inflammation, Ab production, and chemotaxis were upregulated in the cocultured B cells. We conclude that immune stimulation by vaccination or antigenic exposure imparts a greater ability of neutrophils to contribute to the adaptive immune response. Harnessing this granulocytic response has the potential to improve vaccine efficacy.

The role of neutrophil granule proteins in neuroinflammation and Alzheimer's disease

Neutrophils are the innate immune system’s first line of defense. Neutrophils play a critical role in protecting the host against infectious pathogens, resolving sterile injuries, and mediating inflammatory responses. The granules of neutrophils and their constituent proteins are central to these functions. Although neutrophils may exert a protective role upon acute inflammatory conditions or insults, continued activity of neutrophils in chronic inflammatory diseases can contribute to tissue damage. Neutrophil granule proteins are involved in a number of chronic inflammatory conditions and diseases. However, the functions of these proteins in neuroinflammation and chronic neuroinflammatory diseases, including Alzheimer’s disease (AD), remain to be elucidated. In this review, we discuss recent findings from our lab and others that suggest possible functions for neutrophils and the neutrophil granule proteins, CAP37, neutrophil elastase, and cathepsin G, in neuroinflammation, with an emphasis on AD. These findings reveal that neutrophil granule proteins may exert both neuroprotective and neurotoxic effects. Further research should determine whether neutrophil granule proteins are valid targets for therapeutic interventions in chronic neuroinflammatory diseases.

Dysregulated Calcium Homeostasis in Cystic Fibrosis Neutrophils Leads to Deficient Antimicrobial Responses

Cystic fibrosis (CF), one of the most common human genetic diseases worldwide, is caused by a defect in the CF transmembrane conductance regulator (CFTR). Patients with CF are highly susceptible to infections caused by opportunistic pathogens (including Burkholderia cenocepacia), which induce excessive lung inflammation and lead to the eventual loss of pulmonary function. Abundant neutrophil recruitment into the lung is a key characteristic of bacterial infections in CF patients. In response to infection, inflammatory neutrophils release reactive oxygen species and toxic proteins, leading to aggravated lung tissue damage in patients with CF. The present study shows a defect in reactive oxygen species production by mouse Cftr^-/- , human F508del-CFTR, and CF neutrophils; this results in reduced antimicrobial activity against B. cenocepacia Furthermore, dysregulated Ca²⁺ homeostasis led to increased intracellular concentrations of Ca²⁺ that correlated with significantly diminished NADPH oxidase response and impaired secretion of neutrophil extracellular traps in human CF neutrophils. Functionally deficient human CF neutrophils recovered their antimicrobial killing capacity following treatment with pharmacological inhibitors of Ca²⁺ channels and CFTR channel potentiators. Our findings suggest that regulation of neutrophil Ca²⁺ homeostasis (via CFTR potentiation or by the regulation of Ca²⁺ channels) can be used as a new therapeutic approach for reestablishing immune function in patients with CF.

Sex-specific differences in the regulation of inducible nitric oxide synthase by bisphenol A in neutrophils

The aim of the study was to evaluate the effect of bisphenol A (BPA) on nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) expression by neutrophils with regard to sex and nuclear factor-κB (NF-κB) pathway participation in this process. This study demonstrated that BPA intensifies the production of NO and the expression of iNOS in the cytoplasmic fraction of neutrophils of women as well as men. In addition, an enhanced expression of NF-κB in the cytoplasmic and nuclear fraction of neutrophils exposed to BPA was observed in the cells of both sexes. The lipopolysaccharide (LPS) stimulation of neutrophils of both sexes led to an intensification of NO production and expression of all tested proteins. However, simultaneous stimulation of neutrophils of both men and women with LPS and BPA decreased the production of NO and expression of iNOS and NF-κB in both fractions compared to the cells exposed only to xenoestrogen. Moreover, expression of iNOS and NF-κB was higher in female neutrophils than in male cells. This study demonstrated that BPA affects the production of NO with the participation of iNOS by human polymorphonuclear neutrophils. This process is associated with the activation of the NF-κB pathway. In addition, different activity of NF-κB in neutrophils, observed with respect to sex, indicates a different role of this pathway in female and male cells.

Differential Gene Expression Profile of Human Neutrophils Cultured with Plasmodium falciparum-Parasitized Erythrocytes

Neutrophils (PMNs) are the most abundant cellular component of our innate immune system, where they play central roles in the pathogenesis of and resistance to a broad range of diseases. However, their roles in malarial infection remain poorly understood. Therefore, we examined the transcriptional gene profile of human PMNs in response to Plasmodium falciparum-parasitized erythrocytes (iRBCs) by using oligonucleotide microarrays. Results revealed that PMNs induced a broad and vigorous set of changes in gene expression in response to malarial parasites, represented by 118 upregulated and 216 downregulated genes. The transcriptional response was characterized by the upregulation of numerous genes encoding multiple surface receptors, proteins involved in signal transduction pathways, and defense response proteins. This response included a number of genes which are known to be involved in the pathogenesis of malaria and other inflammatory diseases. Gene enrichment analysis suggested that the biological pathways involved in the PMN responses to the iRBCs included insulin receptor, Jak-STAT signaling pathway, mitogen-activated protein kinase (MAPK), and interleukin and interferon-gamma (IFN-γ) signaling pathways. The current study provides fundamental knowledge on the molecular responses of neutrophils to malarial parasites, which may aid in the discovery of novel therapeutic interventions.

Oxidant sensor cation channel TRPM2 regulates neutrophil extracellular trap formation and protects against pneumoseptic bacterial infection

Neutrophil extracellular trap (NET) formation constitutes an important extracellular antimicrobial function of neutrophils that plays a protective role in bacterial pneumonia. Formation of reactive oxygen species (ROS) such as highly diffusible hydrogen peroxide (H2O2) is a hallmark of oxidative stress during inflammatory lung conditions including pneumonia. However, the impact of exogenous ROS on NET formation and the signaling pathway involved in the process is not completely understood. Here we demonstrate that the ROS-sensing, nonselective, calcium-permeable channel transient receptor potential melastatin 2 (TRPM2) is required for NET formation in response to exogenous H2O2. This TRPM2-dependent H2O2-mediated NET formation involved components of autophagy and activation of AMPK and p38 MAPK, but not PI3K and AKT. Primary neutrophils from Trpm2-/- mice fail to activate this pathway with a block in NET release and a concomitant decrease in their antimicrobial capacity. Consequently, Trpm2-/- mice were highly susceptible to pneumonic infection with Klebsiella pneumoniae owing to an impaired NET formation and high bacterial burden despite increased neutrophil infiltration in their lungs. These results identify a key role of TRPM2 in regulating NET formation by exogenous ROS via AMPK/p38 activation and autophagy machinery, as well as a protective antimicrobial role of TRPM2 in pneumonic bacterial infection.-Tripathi, J. K., Sharma, A., Sukumaran, P., Sun, Y., Mishra, B. B., Singh, B. B., Sharma, J. Oxidant sensor cation channel TRPM2 regulates neutrophil extracellular trap formation and protects against pneumoseptic bacterial infection.

Near infrared laser irradiation induces NETosis via oxidative stress and autophagy

NETosis is a novel immune defense strategy in which neutrophil activation results in the formation of extracellular DNA/protein network which is able to kill microbial populations. NETosis can be induced in vitro by lipopolysaccharide (LPS) or phorbol myristate acetate (PMA). Due to the importance of NETosis in different physiological and pathological processes, photobiostimulation effect on this neutrophil activation mechanism has been investigated. Human granulocytes, isolated from venous blood of healthy donors, were stimulated with a diode laser emitting at 980 nm with an energy intensity ranging from 0 to 75 joules. After 3 h of laser stimulation, granulocytes were fixed and colored with crystal violet in order to assess the NETosis morphology while extracellular DNA produced has been quantified using Sytox Green fluorescent dye. To evaluate ROS production and autophagy role in photobiostimulation-induced NETosis, granulocytes were pre-treated with ROS scavengers (vitamin C, sodium pyruvate, L-NAME, sodium azide), and an autophagy inhibitor (wortmannin). Laser stimulation induced an energy-dependent neutrophil extracellular trap (NET) production in human granulocytes starting from 50-J laser intensity. ROS scavengers and the autophagy inhibitor were able to abrogate both morphological features of NETosis and extracellular DNA production without modifying the basal level of NETosis. Photobiostimulation induced an increase in NET production due to an increase in ROS levels and autophagy activation.

The antidiabetic drug metformin blunts NETosis in vitro and reduces circulating NETosis biomarkers in vivo

AIMS

Diabetes is associated with an excess release of neutrophil extracellular traps (NETs) and an enhanced NETosis, a neutrophil cell death programme instrumental to anti-microbial defences, but also involved in tissue damage. We herein investigated whether the antidiabetic drug metformin protects against NETosis.

METHODS

We measured NET components in the plasma of patients with pre-diabetes who were randomized to receive metformin or placebo for 2 months. To control for the effect on glucose, we also measured NET components in the plasma of patients with type 2 diabetes before and after treatment with insulin or dapagliflozin. In vitro, we used static and dynamic imaging with advanced live confocal two-photon microscopy to evaluate the effects of metformin on cellular events during NETosis. We examined putative molecular mechanisms by monitoring chromatin decondensation and DNA release in vitro.

RESULTS

Metformin, as compared to placebo, significantly reduced the concentrations of NET components elastase, proteinase-3, histones and double strand DNA, whereas glucose control with insulin or dapagliflozin exerted no significant effect. In vitro, metformin prevented pathologic changes in nuclear dynamics and DNA release, resulting in a blunted NETosis in response to phorbol myristate acetate and calcium influx. Metformin prevented membrane translocation of PKC-βII and activation of NADPH oxidase in neutrophils, both of which diminished the NETosis response.

CONCLUSIONS

Metformin treatment reduced the concentrations of NET components independently from glucose control. This effect was reproducible in vitro and was related to the inhibitory effect exerted by metformin on the PKC-NADPH oxidase pathway.

Revisiting the Page & Schroeder model: the good, the bad and the unknowns in the periodontal host response 40 years later

In their classic 1976 paper, Page & Schroeder described the histopathologic events and the types of myeloid cells and lymphocytes involved in the initiation and progression of inflammatory periodontal disease. The staging of periodontal disease pathogenesis as 'initial', 'early', 'established' and 'advanced' lesions productively guided subsequent research in the field and remains fundamentally valid. However, major advances regarding the cellular and molecular mechanisms underlying the induction, regulation and effector functions of immune and inflammatory responses necessitate a reassessment of their work and its integration with emerging new concepts. We now know that each type of leukocyte is actually represented by functionally distinct subsets with different, or even conflicting, roles in immunity and inflammation. Unexpectedly, neutrophils, traditionally regarded as merely antimicrobial effectors in acute conditions and protagonists of the 'initial' lesion, are currently appreciated for their functional versatility and critical roles in chronic inflammation. Moreover, an entirely new field of study, osteoimmunology, has emerged and sheds light on the impact of immunoinflammatory events on the skeletal system. These developments and the molecular dissection of crosstalk interactions between innate and adaptive leukocytes, as well as between the immune system and local homeostatic mechanisms, offer a more nuanced understanding of the host response in periodontitis, with profound implications for treatment. At the same time, deeper insights have generated new questions, many of which remain unanswered. In this review, 40 years after Page & Schroeder proposed their model, we summarize enduring and emerging advances in periodontal disease pathogenesis.

Neutrophils are essential for induction of vaccine-like effects by antiviral monoclonal antibody immunotherapies

Using a mouse retroviral model, we have shown that mAb-based immunotherapy can induce life-long endogenous protective immunity (vaccine-like effects). This observation has potentially important consequences for treating life-threatening human viral infections. Here, we investigated the role of neutrophils in this effect. Neutrophils are innate immunity effector cells with well-established microbe-killing activities that are rapidly mobilized upon infection. They are also emerging as orchestrators of innate and adaptive immunities. However, their immunomodulatory activity during antiviral mAb immunotherapies has never been studied. Our data reveal that neutrophils have an essential role in immunotherapy-induced immune protection of infected mice. Unexpectedly, neutrophils have a limited effect in controlling viral propagation upon passive immunotherapy administration, which is mostly mediated by NK cells. Instead, neutrophils operate as essential inducers of a potent host humoral antiviral response. Thus, neutrophils play an unexpected key role in protective immunity induction by antiviral mAbs. Our work opens approaches to improve antiviral immunotherapies, as it suggests that preserving neutrophil functions and counts might be required for achieving mAb-induced protective immunity.

Innate and adaptive immunity in atherosclerosis

Atherosclerosis is a chronic inflammatory disorder of the large and medium-size arteries characterized by the subendothelial accumulation of cholesterol, immune cells, and extracellular matrix. At the early onset of atherogenesis, endothelial dysfunction takes place. Atherogenesis is further triggered by the accumulation of cholesterol-carrying low-density lipoproteins, which acquire properties of damage-associated molecular patterns and thereby trigger an inflammatory response. Following activation of the innate immune response, mainly governed by monocytes and macrophages, the adaptive immune response is started which further promotes atherosclerotic plaque formation. In this review, an overview is given describing the role of damage-associated molecular patterns, NLRP3 inflammasome activation, and innate and adaptive immune cells in the atherogenesis process.

Extracellular Sphingomyelinase Rv0888 of Mycobacterium tuberculosis Contributes to Pathological Lung Injury of Mycobacterium smegmatis in Mice via Inducing Formation of Neutrophil Extracellular Traps

Mycobacterium tuberculosis is the causative agent of tuberculosis (TB), which mainly causes pulmonary injury and tubercles. Although macrophages are generally considered to harbor the main cells of M. tuberculosis, new evidence suggests that neutrophils are rapidly recruited to the infected lung. M. tuberculosis itself, or its early secreted antigenic target protein 6 (ESAT-6), can induce formation of neutrophil extracellular traps (NETs). However, NETs trap mycobacteria but are unable to kill them. The role of NETs’ formation in the pathogenesis of mycobacteria remains unclear. Here, we report a new M. tuberculosis extracellular factor, bifunctional enzyme Rv0888, with both nuclease and sphingomyelinase activities. Rv0888 sphingomyelinase activity can induce NETs’ formation in vitro and in the lung of the mice and enhance the colonization ability of Mycobacterium smegmatis in the lungs of mice. Mice infected by M. smegmatis harboring Rv0888 sphingomyelinase induced pathological injury and inflammation of the lung, which was mainly mediated by NETs, induced by Rv0888 sphingomyelinase, associated protein (myeloperoxidase) triggered caspase-3. In summary, the study sheds new light on the pathogenesis of mycobacteria and reveals a novel target for TB treatment.

Idelalisib impairs TREM-1 mediated neutrophil inflammatory responses

Triggering receptor expressed on myeloid cells (TREM)-1 on polymorphonuclear neutrophils (PMN) regulates innate immune activation in infectious and non-infectious conditions. TREM-1 ligation activates phosphatidyl-inositol 3 kinase (PI3K) triggering all neutrophil effector functions. As idelalisib is a PI3K inhibitor in clinical use for the treatment of non-Hodgkin lymphomas, we asked whether this inhibitor affects PMN functionalities. We analyzed PMNs from healthy donors or lymphoma patients for oxidative burst, phagocytosis, activation markers and IL-8 release upon TREM-1 or TLR ligation ex vivo. In addition, we performed western blot analyses to characterize the signaling events inhibited by idelalisib and other PI3K inhibitors. Upon TREM-1 ligation, the oxidative burst, degranulation, L-selectin shedding and cytokine release were all strongly reduced in the presence of idelalisib along impaired phosphorylation of P38, AKT and ERK by western blot analyses. In line with this, PMNs from patients receiving idelalisib also displayed an impaired TREM-1 mediated PMN activation ex vivo. In conclusion, PI3K inhibitors might cause a neutropenia-like susceptibility to infections in patients by leading to impaired PMN functionality. This should be considered when evaluating patients for infections treated with such inhibitors in daily clinical routine.

Sex-based differences in phagocyte metabolic profile in rats with monosodium glutamate-induced obesity

The important component of obesity pathogenesis is inflammatory activation of innate immune cells within adipose tissue and in other body locations. Both the course of obesity and innate immune reactivity are characterized by sex-associated differences. The aim of the work was a comparative investigation of metabolic profiles of phagocytes from different locations in male and female rats with MSG-induced obesity. The administration of monosodium glutamate (MSG) caused obesity, with sex-associated differences, that was more severe in male rats. Obesity was associated with pro-inflammatory activation of CD14+ phagocytes from adipose tissue in female, but not in male rats, which was demonstrated by decreased phagocytosis activity along with increased ROS generation. Phagocytes from the peritoneal cavity and peripheral blood of obese female rats exhibited neutral metabolic profile, whereas those cells from obese male rats displayed a pro-inflammatory metabolic profile. Thus, the manifestation of obesity-induced inflammation was characterized by different patterns of metabolic profile of phagocytes in male and female rats. Identified immune cell characteristics expand our knowledge of obesity immunobiology and may help to develop more effective preventive and therapeutic interventions for obese patients of different sexes.

Regulation of immune cell signaling by activated protein C

Innate immune cells are an essential part of the host defense response, promoting inflammation through release of proinflammatory cytokines or formation of neutrophil extracellular traps. While these processes are important for defense against infectious agents or injury, aberrant activation potentiates pathologic inflammatory disease. Thus, understanding regulatory mechanisms that limit neutrophil extracellular traps formation and cytokine release is of therapeutic interest for targeting pathologic diseases. Activated protein C is an endogenous serine protease with anticoagulant activity as well as anti-inflammatory and cytoprotective functions, the latter of which are mediated through binding cell surface receptors and inducing intracellular signaling. In this review, we discuss certain leukocyte functions, namely neutrophil extracellular traps formation and cytokine release, and the inhibition of these processes by activated protein C.

Neutrophils mediate HIV-specific antibody-dependent phagocytosis and ADCC

There is growing evidence to support the role of Fc-mediated effector functions, such as Antibody-Dependent Cellular cytotoxicity (ADCC) and Antibody-Dependent Phagocytosis (ADP) in the protection and control of HIV. The RV144 trial and other recent HIV vaccine studies have highlighted the importance of ADCC responses in protection against HIV. The role of neutrophils, the most abundant leukocyte in the blood, has not been thoroughly evaluated for Fc-mediated effector functions to HIV. We optimized HIV-specific neutrophil ADCC and Antibody-Dependent Neutrophil Phagocytosis (ADNP) assays using freshly isolated primary human neutrophils from blood. We also developed methods to study ADP using the neutrophil-like HL-60 cell line. We found that neutrophils mediate both HIV-specific ADP and ADCC responses. In vitro, neutrophil-mediated ADCC responses peaked at 4 h, much faster than primary NK cell or monocyte-mediated responses. We detected a wide range of responses in the ADNP, HL-60 mediated ADP and ADCC across a cohort of 41 viremic antiretroviral therapy naïve HIV positive subjects. HL-60 and Neutrophil-mediated ADP and ADCC responses correlated well with each other, suggesting that they measure overlapping functions. The ADNP and HL-60 ADP inversely correlated with HIV viral load, suggesting that these antibody-mediated neutrophil-based assays should prove useful in dissecting HIV-specific immunity.

Immune-Modulating Perspectives for Low Frequency Electromagnetic Fields in Innate Immunity

In recent years, the effects of electromagnetic fields (EMFs) on the immune system have received a considerable interest, not only to investigate possible negative health impact but also to explore the possibility to favorably modulate immune responses. To generate beneficial responses, the immune system should eradicate pathogens while “respecting” the organism and tolerating irrelevant antigens. According to the current view, damage-associated molecules released by infected or injured cells, or secreted by innate immune cells generate danger signals activating an immune response. These signals are also relevant to the subsequent activation of homeostatic mechanisms that control the immune response in pro- or anti-inflammatory reactions, a feature that allows modulation by therapeutic treatments. In the present review, we describe and discuss the effects of extremely low frequency (ELF)-EMF and pulsed EMF on cell signals and factors relevant to the activation of danger signals and innate immunity cells. By discussing the EMF modulating effects on cell functions, we envisage the use of EMF as a therapeutic agent to regulate immune responses associated with wound healing.

STAT6 Mediates Footpad Immunopathology in the Absence of IL-12p40 Following Infection of Susceptible BALB/c Mice With Leishmania major

Leishmania major (L. major) parasites are intracellular parasites belong to the Trypanosomatidae family and are the causative agent of cutaneous leishmaniasis. This disease affects approximately 1.5 million per year worldwide and there is currently no prophylactic vaccine available. L. major is transmitted by the bite of an infected sandfly and has been considered for decades now as a mouse model of choice to identify the factors implicated in T helper (Th)1 and Th2 polarization due to the natural resistance and susceptibility to infection of C57BL/6 and BALB/c mice, respectively. In this study, we refine the role of IL-12p40 cytokine, which is implicated the development of a protective Th1 response, and STAT6, a transcription factor involved in the signaling via detrimental interleukin (IL)-4 and IL-13 associated Th2 cytokines during L. major infection in the BALB/c model. In the absence of STAT6 and IL-12p40 signaling, double knockout (DKO) susceptible BALB/c mice displayed reduced footpad swelling and ulcerative lesion compared to IL-12p40^−/− mice upon L. major infection. Hence, they expressed slower upregulation of keratinocyte markers implicated in the inhibition of wound healing, such as keratin 6a (Krt6a) and Krt16. This coincides with the presence of neutrophils displaying an altered phenotype characterized by a lower expression of surface markers Ly6C, CD11b, and Ly6G. These neutrophils exhibited very lower levels of apoptosis similarly to neutrophils present in resistant STAT6^−/− mice. Interestingly, the reduced footpad swelling in DKO mice is associated with a high footpad parasite level similar to susceptible IL-12p40^−/− mice. In conclusion, this study demonstrate that in the absence of both STAT6 and IL-12p40 signaling, L. major-infected mice display smaller and less ulcerated lesions, which does, however, not correlate with reduced parasite load. In addition, the presence of neutrophils with an altered phenotype is associated with reduced apoptosis and delayed immunopathologies, demonstrating the detrimental role of STAT6 in infected susceptible BALB/c mice.

The influence of agents differentiating HL-60 cells toward granulocyte-like cells on their ability to release neutrophil extracellular traps

Studies on neutrophil extracellular traps (NETs) are challenging as neutrophils live shortly and easily become activated. Thus, availability of a cell line model closely resembling the functions of peripheral blood neutrophils would be advantageous. Our purpose was to find a compound that most effectively differentiates human promyelocytic leukemia (HL-60) cells toward granulocyte-like cells able to release NETs. HL-60 cells were differentiated with all-trans retinoic acid (ATRA), dimethyl sulfoxide (DMSO) or dimethylformamide (DMF) and stimulated with phorbol 12-myristate 13-acetate (PMA) or calcium ionophore A23187 (CI). Cell differentiation, phagocytosis and calcium influx were analyzed by flow cytometry. Reactive oxygen species production and NETs release were measured fluorometrically and analyzed microscopically. LC3-II accumulation and histone 3 citrullination were analyzed by western blot. ATRA most effectively differentiated HL-60 cells toward granulocyte-like cells. ATRA-dHL-60 cells released NETs only upon PMA stimulation, DMSO-dHL-60 cells only post CI stimulation, while DMF-dHL-60 cells formed NETs in response to both stimuli. Oxidative burst was induced in ATRA-, DMSO- and DMF-dHL-60 cells post PMA stimulation and only in DMF-dHL-60 cells post CI stimulation. Increased histone 3 citrullination was observed in stimulated DMSO- and DMF-, but not in ATRA-dHL-60 cells. The calcium influx was diminished in ATRA-dHL-60 cells. Significant increase in autophagosomes formation was observed only in PMA-stimulated DMF-dHL-60 cells. Phagocytic index was higher in ATRA-dHL-60 cells than in control, DMSO- and DMF-dHL-60 cells. We conclude that ATRA, DMSO and DMF differentiate HL-60 in different mechanisms. DMF is the best stimulus for HL-60 cell differentiation for NETs studies.