Role of neutrophils in systemic autoimmune diseases

The role for neutrophil extracellular traps in cystic fibrosis autoimmunity

While respiratory failure in cystic fibrosis (CF) frequently associates with chronic infection by Pseudomonas aeruginosa, no single factor predicts the extent of lung damage in CF. To elucidate other causes, we studied the autoantibody profile in CF and rheumatoid arthritis (RA) patients, given the similar association of airway inflammation and autoimmunity in RA. Even though we observed that bactericidal permeability-increasing protein (BPI), carbamylated proteins, and citrullinated proteins all localized to the neutrophil extracellular traps (NETs), which are implicated in the development of autoimmunity, our study demonstrates striking autoantibody specificity in CF. Particularly, CF patients developed anti-BPI autoantibodies but hardly any anti-citrullinated protein autoantibodies (ACPA). In contrast, ACPA-positive RA patients exhibited no reactivity with BPI. Interestingly, anti-carbamylated protein autoantibodies (ACarPA) were found in both cohorts but did not cross-react with BPI. Contrary to ACPA and ACarPA, anti-BPI autoantibodies recognized the BPI C-terminus in the absence of posttranslational modifications. In fact, we discovered that P. aeruginosa-mediated NET formation results in BPI cleavage by P. aeruginosa elastase, which suggests a novel mechanism in the development of autoimmunity to BPI. In accordance with this model, autoantibodies associated with presence of P. aeruginosa on sputum culture. Finally, our results provide a role for autoimmunity in CF disease severity, as autoantibody levels associate with diminished lung function.

The transcriptional repressor Gfi1 prevents lupus autoimmunity by restraining TLR7 signaling

The transcriptional repressor growth factor independence 1 (Gfi1) is important in myeloid and lymphoid differentiation. In the current study we evaluated the involvement of Gfi1 in systemic lupus erythematosus (SLE). We found that Genista mice, which carry a hypomorphic mutation in the gfi1 gene or Gfi1-deficient (Gfi1^-/- ) mice develop signs of spontaneous lupus autoimmunity, including increased serum levels of IgM and IgG2a, autoantibodies against RNA and DNA, glomerular immunodeposits and increased frequencies of plasmablasts, germinal center (GC) B cells and age-associated B cells (ABCs). On the contrary, Genista mice deprived of TLR7 did not show any of these phenotypes, suggesting that the observed lupus autoimmunity in Genista mice is TLR7-dependent. Moreover, Genista mice showed an increased activation of dendritic cells (DCs), B and T cells that was dependent on TLR7 for DCs and B cells, but not for T cells. Upon TLR7 or TLR4 stimulation Genista DCs produced increased amounts of TNF, IL-6 and IFN-β and showed increased NF-κB phosphorylation and IRF7 nuclear translocation, suggesting that Gfi1 controls the NF-κB and type I IFN signaling pathway downstream of TLRs. Our data reveal that Gfi1 plays a critical role in the prevention of spontaneous lupus autoimmunity by negatively regulating TLR7 signaling.

Fine-tuning neutrophil activation: Strategies and consequences

In spite of their important role in host defense, neutrophils can also cause severe morbidity and mortality. Neutrophils have an extensive armory necessary to eradicate pathogens, but neutrophil infiltration and activation also induces major tissue injury associated with acute and chronic inflammatory disorders. Here, we review neutrophil anti-microbial functions and discuss their individual contribution to disease pathogenesis. Furthermore, we provide an overview of the anti-inflammatory drugs that can dampen neutrophil transmigration, elastase activity, and the production of reactive oxygen species which are already in clinical trials. The discovery of potential inhibitors of the release of neutrophil extracellular trap is still in its infancy. Here, we discuss small molecule inhibitors and inhibitory receptors that show promising results in reducing neutrophil extracellular trap formation in vitro and in vivo and discuss the advantages and drawbacks of inhibiting the release of neutrophil extracellular traps as a therapeutic treatment. Specific suppression of neutrophil extracellular trap formation, preferably while other antimicrobial functions are preserved, would be an ideal approach to treat neutrophilic inflammation, since it prevents acute as well as chronic neutrophil-associated pathology.

Protective Effect of High Molecular Weight Protein Sub-fraction of Calotropis procera Latex in Monoarthritic Rats

Background:

Proteins present in the latex of Calotropis procera have been shown to produce anti-inflammatory effect and to afford protection in various disease models.

Objectives:

To determine the efficacy of high molecular weight protein sub-fraction (LP_PI) of latex of C. procera in ameliorating joint inflammation and hyperalgesia in a preclinical model of arthritis.

Materials and Methods:

Monoarthritis was induced in rats by intra-articular injection of Freund's complete adjuvant (FCA) and the effect of two doses of LP_PI (5 and 25 mg/kg) and diclofenac (5 mg/kg) was evaluated on joint swelling, stair climbing ability, motility, and dorsal flexion pain on day 3. The rats were sacrificed on day 3 to measure tissue levels of reduced glutathione (GSH) and thiobarbituric acid reactive substances (TBARS). Evaluation of joint histology was also made.

Results:

Intra-articular injection of FCA produced joint swelling and difficulty in stair climbing ability, motility, and pain on flexion of the joint as revealed by scores obtained for these functional parameters. LP_PI produced a dose-dependent decrease in joint swelling and improved joint functions. Arthritic rats also revealed altered oxidative homeostasis where joint tissue GSH levels were decreased and TBARS levels were increased as compared to normal rats. The levels of these oxidative stress markers were near normal in arthritic rats treated with LP_PI. Moreover, treatment with LP_PI also maintained the structural integrity of the joint. The protective effect of LP_PI was comparable to the standard anti-inflammatory drug, diclofenac.

Conclusion:

The findings of the present study show that LP_PI fraction comprising high molecular weight proteins could be used for the alleviation of arthritic symptoms.

SUMMARY

High molecular weight protein sub-fraction of latex of Calotropis procera (LP_PI) reduced joint swelling and hyperalgesia in arthritic rats

LP_PI produced a significant improvement in stair climbing ability and motility in arthritic rats

LP_PI normalized the levels of oxidative stress markers in the arthritic joints

Treatment with LP_PI reduced neutrophil influx and edema in the arthritic joints

Abbreviations used: FCA: Freund's complete adjuvant, GSH: Glutathione, TBARS: Thiobarbituric acid reactive substances, TBA: Thiobarbituric acid, MDA: Malondialdehyde, LP_PI: Latex protein fraction PI.

Feedback Amplification of Neutrophil Function

As the first line of innate immune defense, neutrophils need to mount a rapid and robust antimicrobial response. Recent studies implicate various positive feedback amplification processes in achieving that goal. Feedback amplification ensures effective migration of neutrophils in shallow chemotactic gradients, multiple waves of neutrophil recruitment to the site of inflammation, and the augmentation of various effector functions of the cells. We review here such positive feedback loops including intracellular and autocrine processes, paracrine effects mediated by lipid (LTB4), chemokine, and cytokine mediators, and bidirectional interactions with the complement system and with other immune and non-immune cells. These amplification mechanisms are not only involved in antimicrobial immunity but also contribute to neutrophil-mediated tissue damage under pathological conditions.

Effects of budlein A on human neutrophils and lymphocytes

OBJECTIVE

In this study, we evaluated whether budlein A modulates the activation of innate and adaptive immune cells such as neutrophils and lymphocytes.

MATERIAL AND METHODS

Our research group has investigated several plant species and several compounds have been isolated, identified, and their medical potential evaluated. Budlein A is a SL isolated from the species Aldama buddlejiformis and A. robusta (Asteraceae) and shows anti-inflammatory and anti-nociceptive activities. Advances in understanding how plant-derived substances modulate the activation of innate and adaptive immune cells have led to the development of new therapies for human diseases.

RESULTS

Budlein A inhibited MPO activity, IL-6, CXCL8, IL-10, and IL-12 production and induces neutrophil apoptosis. In contrast, budlein A inhibited lymphocyte proliferation and IL-2, IL-10, TGF-β, and IFN-γ production, but it did not lead to cell death.

CONCLUSIONS

Collectively, our results indicate that budlein A shows distinct immunomodulatory effects on immune cells.

Neutrophils in animal models of autoimmune disease

Neutrophils have traditionally been thought to play only a peripheral role in the genesis of many autoimmune and inflammatory diseases. However, recent studies in a variety of animal models suggest that these cells are central to the initiation and propagation of autoimmunity. The use of mouse models, which allow either deletion of neutrophils or the targeting of specific neutrophil functions, has revealed the many complex ways these cells contribute to autoimmune/inflammatory processes. This includes generation of self antigens through the process of NETosis, regulation of T-cell and dendritic cell activation, production of cytokines such as BAFF that stimulate self-reactive B-cells, as well as indirect effects on epithelial cell stability. In comparing the many different autoimmune models in which neutrophils have been examined, a number of common underlying themes emerge - such as a role for neutrophils in stimulating vascular permeability in arthritis, encephalitis and colitis. The use of animal models has also stimulated the development of new therapeutics that target neutrophil functions, such as NETosis, that may prove beneficial in human disease. This review will summarize neutrophil contributions in a number of murine autoimmune/inflammatory disease models.

Immunoreceptors on neutrophils

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Neutrophil activities must be tightly controlled to maintain immune homeostasis.

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Activating and inhibitory receptors balance the outcome of immune cell activation.

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Immunoreceptors contain Ig-like extracellular domains and signal via ITAMs or ITIMs.

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Syk or SHP/SHIP mediate downstream signaling after immunoreceptor activation.

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Targeting immunoreceptors provides opportunities for therapeutic interventions.

Neutrophils play a critical role in the host defense against infection, and they are able to perform a variety of effector mechanisms for this purpose. However, there are also a number of pathological conditions, including autoimmunity and cancer, in which the activities of neutrophils can be harmful to the host. Thus the activities of neutrophils need to be tightly controlled. As in the case of other immune cells, many of the neutrophil effector functions are regulated by a series of immunoreceptors on the plasma membrane. Here, we review what is currently known about the functions of the various individual immunoreceptors and their signaling in neutrophils. While these immunoreceptors allow for the recognition of a diverse range of extracellular ligands, such as cell surface structures (like proteins, glycans and lipids) and extracellular matrix components, they commonly signal via conserved ITAM or ITIM motifs and their associated downstream pathways that depend on the phosphorylation of tyrosine residues in proteins and/or inositol lipids. This allows for a balanced homeostatic regulation of neutrophil effector functions. Given the number of available immunoreceptors and their fundamental importance for neutrophil behavior, it is perhaps not surprising that pathogens have evolved means to evade immune responses through some of these pathways. Inversely, some of these receptors evolved to specifically recognize these pathogens. Finally, some interactions mediated by immunoreceptors in neutrophils have been identified as promising targets for therapeutic intervention.

Role of the neutrophil chemorepellent soluble dipeptidyl peptidase IV in decreasing inflammation in a murine model of arthritis

OBJECTIVE

To determine whether an intraarticular injection of the neutrophil chemorepellent dipeptidyl peptidase IV (DPPIV; CD26) can attenuate inflammation and decrease the severity of arthritis in a murine model.

METHODS

DBA/1 mice were immunized with type II collagen/Freund's complete adjuvant to produce collagen-induced arthritis (CIA). On day 25 postimmunization, recombinant human DPPIV (rhDPPIV) or phosphate buffered saline was injected intraarticularly, and arthritis severity scores were recorded 3 times per week. The hind legs of mice in both groups were fixed, decalcified, paraffin embedded, and sectioned. Pathologic scores for inflammation and neutrophil infiltration were recorded on a scale of 1-8, and the number of neutrophils was determined by morphometric cell counts. In addition, Mac-2-positive macrophages and articular damage were assessed using anti-Mac-2 antibodies and histologic staining, respectively.

RESULTS

Injection of rhDPPIV reduced the mean score of arthritis severity in mice with CIA. DPPIV treatment reduced the overall extent of inflammation and articular damage around the arthritic joint and periarticular tissue, and also decreased neutrophil and macrophage infiltration.

CONCLUSION

A localized injection of the neutrophil chemorepellent DPPIV reduces inflammation and the severity of the disease in a murine model of arthritis.

Role of mitogen- and stress-activated kinases in inflammatory arthritis

Lysophosphatidic acid (LPA) is a pleiotropic lipid mediator that promotes motility, survival, and the synthesis of chemokines/cytokines in human fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis. LPA activates several proteins within the mitogen activated protein (MAP) kinase signaling network, including extracellular signal-regulated kinases (ERK) 1/2 and p38 MAP kinase (MAPK). Upon docking to mitogen- and stress-activated kinases (MSKs), ERK1/2 and p38 MAPK phosphorylate serine and threonine residues within its C-terminal domain and cause autophosphorylation of MSKs. Activated MSKs can then directly phosphorylate cAMP response element-binding protein (CREB) at Ser133 in FLS. Phosphorylation of CREB by MSKs is essential for the production of pro-inflammatory and anti-inflammatory cytokines. However, other downstream effectors of MSK1/2 such as nuclear factor-kappa B, histone H3, and high mobility group nucleosome binding domain 1 may also regulate gene expression in immune cells involved in disease pathogenesis. MSKs are master regulators of cell function that integrate signals induced by growth factors, pro-inflammatory cytokines, and cellular stresses, as well as those induced by LPA.

Assessment of murine collagen-induced arthritis by longitudinal non-invasive duplexed molecular optical imaging

OBJECTIVE

In the present study we evaluated the use of four commercially available fluorescent probes to monitor disease activity in murine CIA and its suppression during glucocorticoid therapy.

METHODS

Arthritis was induced in male DBA/1 mice by immunization with type II collagen in Complete Freund's Adjuvant, followed by a boost of collagen in PBS. Four fluorescent probes from PerkinElmer in combination [ProSense 750 fluorescent activatable sensor technology (FAST) with Neutrophil Elastase 680 FAST and MMPSense 750 FAST with CatK 680 FAST] were used to monitor disease development from day 5 through to day 40 post-immunization. Fluorescence generated in vivo by the probes was correlated with clinical and histological score and paw measurements.

RESULTS

The fluorescence intensity emitted by each probe was shown to correlate with the conventional measurements of disease. The highest degree of correlation was observed with ProSense 750 FAST in combination with Neutrophil Elastase 680 FAST; these probes were then used to successfully assess CIA suppression during dexamethasone treatment.

CONCLUSION

We have demonstrated that longitudinal non-invasive duplexed optical fluorescence imaging provides a simple assessment of arthritic disease activity within the joints of mice following the induction of CIA and may represent a powerful tool to monitor the efficacy of drug treatments in preclinical studies.

Potent and Selective Human Neutrophil Elastase Inhibitors with Novel Equatorial Ring Topology: in vivo Efficacy of the Polar Pyrimidopyridazine BAY-8040 in a Pulmonary Arterial Hypertension Rat Model

Human neutrophil elastase (HNE) is a key driver of inflammation in many cardiopulmonary and systemic inflammatory and autoimmune conditions. Overshooting high HNE activity is the consequence of a disrupted protease-antiprotease balance. Accordingly, there has been an intensive search for potent and selective HNE inhibitors with suitable pharmacokinetics that would allowing oral administration in patients. Based on the chemical probe BAY-678 and the clinical candidate BAY 85-8501 we explored further ring topologies along the equator of the parent pyrimidinone lead series. Novel ring systems were annulated in the east, yielding imidazolo-, triazolo-, and tetrazolopyrimidines in order to ensure additional inhibitor-HNE contacts beyond the S1 and the S2 pocket of HNE. The western annulation of pyridazines led to the polar pyrimidopyridazine BAY-8040, which combines excellent potency and selectivity with a promising pharmacokinetic profile. In vivo efficacy with regard to decreasing cardiac remodeling and amelioration of cardiac function was shown in a monocrotaline-induced rat model for pulmonary arterial hypertension. This demonstrated in vivo proof of concept in animals.

IRF5 controls both acute and chronic inflammation

Whereas the importance of macrophages in chronic inflammatory diseases is well recognized, there is an increasing awareness that neutrophils may also play an important role. In addition to the well-documented heterogeneity of macrophage phenotypes and functions, neutrophils also show remarkable phenotypic diversity among tissues. Understanding the molecular pathways that control this heterogeneity should provide abundant scope for the generation of more specific and effective therapeutics. We have shown that the transcription factor IFN regulatory factor 5 (IRF5) polarizes macrophages toward an inflammatory phenotype. IRF5 is also expressed in other myeloid cells, including neutrophils, where it was linked to neutrophil function. In this study we explored the role of IRF5 in models of acute inflammation, including antigen-induced inflammatory arthritis and lung injury, both involving an extensive influx of neutrophils. Mice lacking IRF5 accumulate far fewer neutrophils at the site of inflammation due to the reduced levels of chemokines important for neutrophil recruitment, such as the chemokine (C-X-C motif) ligand 1. Furthermore we found that neutrophils express little IRF5 in the joints and that their migratory properties are not affected by the IRF5 deficiency. These studies extend prior ones suggesting that inhibiting IRF5 might be useful for chronic macrophage-induced inflammation and suggest that IRF5 blockade would ameliorate more acute forms of inflammation, including lung injury.

Advances in understanding the role of type I interferons in systemic lupus erythematosus

PURPOSE OF REVIEW

Advances in understanding the genetic and molecular basis of innate immune system activation and function have supported the hypothesis that type I interferons (IFN-I), the essential mediators of antiviral host defense, are central contributors to the pathogenesis of systemic lupus erythematosus (SLE). This review addresses the recent data that support the rationale for therapeutic targeting of the IFN-I pathway in SLE.

RECENT FINDINGS

New insights into the mechanisms of cell-intrinsic innate immune system activation, driven by endogenous virus-like nucleic acids and potentially modified by environmental stressors, provide a model for the induction of IFN-I that may precede the clinically apparent autoimmunity in patients with lupus. Further amplification of IFN-α production, induced by nucleic-acid-containing immune complexes that activate endosomal Toll-like receptors, augments and sustains immune system activation, autoimmunity and tissue damage.

SUMMARY

As demonstrated in the murine studies of persistent virus infection accompanied by sustained production of IFN-I, blockade of the IFN-I pathway may reverse the immune dysregulation and tissue damage that are the essential features of the immunopathogenesis of SLE. Recent research progress has identified numerous therapeutic targets, and specific candidate therapeutics relevant to the IFN-I pathway are under investigation.

Inhibition of the lymphocyte metabolic switch by the oxidative burst of human neutrophils

Activation of the phagocytic NADPH oxidase-2 (NOX-2) in neutrophils is a critical process in the innate immune system and is associated with elevated local concentrations of superoxide, hydrogen peroxide (H2O2) and hypochlorous acid. Under pathological conditions, NOX-2 activity has been implicated in the development of autoimmunity, indicating a role in modulating lymphocyte effector function. Notably, T-cell clonal expansion and subsequent cytokine production requires a metabolic switch from mitochondrial respiration to aerobic glycolysis. Previous studies demonstrate that H2O2 generated from activated neutrophils suppresses lymphocyte activation but the mechanism is unknown. We hypothesized that activated neutrophils would prevent the metabolic switch and suppress the effector functions of T-cells through a H2O2-dependent mechanism. To test this, we developed a model co-culture system using freshly isolated neutrophils and lymphocytes from healthy human donors. Extracellular flux analysis was used to assess mitochondrial and glycolytic activity and FACS analysis to assess immune function. The neutrophil oxidative burst significantly inhibited the induction of lymphocyte aerobic glycolysis, caused inhibition of oxidative phosphorylation and suppressed lymphocyte activation through a H2O2-dependent mechanism. Hydrogen peroxide and a redox cycling agent, DMNQ, were used to confirm the impact of H2O2 on lymphocyte bioenergetics. In summary, we have shown that the lymphocyte metabolic switch from mitochondrial respiration to glycolysis is prevented by the oxidative burst of neutrophils. This direct inhibition of the metabolic switch is then a likely mechanism underlying the neutrophil-dependent suppression of T-cell effector function.

Sjögren's Syndrome Antigen B Acts as an Endogenous Danger Molecule to Induce Interleukin-8 Gene Expression in Polymorphonuclear Neutrophils

BACKGROUND

Sjögren's syndrome antigen B is expressed in the nucleus and surface membrane of human polymorphonuclear neutrophils and is released after cell death. However, its biological role is not clear. This study is aimed to investigate the effect of Sjögren's syndrome antigen B on human polymorphonuclear neutrophils.

METHODS

Human recombinant Sjögren's syndrome antigen B (rSSB) purified from E. coli was incubated with human polymorphonuclear neutrophils as well as retinoid acid-induced granulocytic differentiated HL-60 cells, HL-60 (RA). Interleukin (IL)-8 protein production and mRNA expressions were measured by enzyme-linked immunosorbent assay and quantitative-polymerase chain reaction, respectively. Uptake of fluorescein isothiocyanate (FITC)-rSSB was assessed by flow cytometry and fluorescence microscopy. Moreover, mitogen-activated protein kinase (MAPK) pathways and nuclear factor-kappaB activation were investigated.

RESULTS

Human rSSB stimulated IL-8 production from normal human neutrophils and HL-60 (RA) cells in a time- and dose-dependent manner. This IL-8-stimulated activity was blocked by chloroquine and NH4Cl, indicating that endosomal acidification is important for this effect. We found rSSB activated both MAPK pathway and nuclear factor-kappaB signaling to transcribe the IL-8 gene expression of cells. Furthermore, tumor necrosis factor-α exerted an additive effect and rSSB-anti-SSB immune complex exhibited a synergistic effect on rSSB-induced IL-8 production.

CONCLUSIONS

Sjögren's syndrome antigen B might act as an endogenous danger molecule to enhance IL-8 gene expression in human polymorphonuclear neutrophils.

Two new inflammatory markers associated with Disease Activity Score-28 in patients with rheumatoid arthritis: neutrophil-lymphocyte ratio and platelet-lymphocyte ratio

AIM

Rheumatoid arthritis (RA) is an inflammatory autoimmune disease with unknown etiology and systemic involvement. Neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR) are two new inflammatory markers used in the assessment of systemic inflammation. The aim here is to study NLR and PLR in patients with RA to investigate their relation with Disease Activity Score of 28 joints (DAS-28).

METHODS

The study included 104 patients with RA and a control group of 51 age- and gender-matched healthy subjects. We divided the patients into two groups according to the DAS-28 score. Group 1 included patients with a score of lower than 2.6 by the DAS-28 (patients in remission) and Group 2 included patients with a score of 2.6 and higher (patients with active disease).

RESULTS

NLR was 2.12 ± 0.83 in the patient group and 1.58 ± 0.57 in the control group. PLR was 136.50 ± 53.52 in the patient group and 114.84 ± 29.41 in the control group. There was a statistically significant difference in NLR and PLR between the patient and control groups (P ≤ 0.0001 and P = 0.001, respectively). Patients in Group 1 had an NLR of 1.84 ± 0.61 and a PLR of 119.25 ± 41.77. Patients in Group 2 had an NLR of 2.29 ± 0.90 and a PLR of 147.28 ± 56.96. There was a statistically significant difference in NLR and PLR between the two groups (P = 0.003 and P = 0.005 respectively). A correlation was observed between NLR and PLR by DAS-28 (r = 0.345, P ≤ 0.0001 and r = 0.352, P ≤ 0.0001, respectively).

CONCLUSIONS

The present study showed us that NLR and PLR were two new inflammatory markers which could be used to assess disease activity in patients with RA.

Parietal and intravascular innate mechanisms of vascular inflammation

Sustained inflammation of the vessel walls occurs in a large number of systemic diseases (ranging from atherosclerosis to systemic vasculitides, thrombotic microangiopathies and connective tissue diseases), which are ultimately characterized by ischemia and end-organ failure. Cellular and humoral innate immunity contribute to a common pathogenic background and comprise several potential targets for therapeutic intervention. Here we discuss some recent advances in the effector and regulatory action of neutrophils and in the outcome of their interaction with circulating platelets. In parallel, we discuss novel insights into the role of humoral innate immunity in vascular inflammation. All these topics are discussed in light of potential clinical and therapeutic implications in the near future.

Peroxisomal lipid synthesis regulates inflammation by sustaining neutrophil membrane phospholipid composition and viability

Fatty acid synthase (FAS) is altered in metabolic disorders and cancer. Conventional FAS null mice die in utero, so effects of whole-body inhibition of lipogenesis following development are unknown. Inducible global knockout of FAS (iFASKO) in mice was lethal due to a disrupted intestinal barrier and leukopenia. Conditional loss of FAS was associated with the selective suppression of granulopoiesis without disrupting granulocytic differentiation. Transplantation of iFASKO bone marrow into wild-type mice followed by Cre induction resulted in selective neutrophil depletion, but not death. Impaired lipogenesis increased ER stress and apoptosis in neutrophils by preferentially decreasing peroxisome-derived membrane phospholipids containing ether bonds. Inducible global knockout of PexRAP, a peroxisomal enzyme required for ether lipid synthesis, also produced neutropenia. FAS knockdown in neutrophil-like HL-60 cells caused cell loss that was partially rescued by ether lipids. Inhibiting ether lipid synthesis selectively constrains neutrophil development, revealing an unrecognized pathway in immunometabolism.

Neutrophils sense microbe size and selectively release neutrophil extracellular traps in response to large pathogens

Neutrophils are critical for antifungal defense, but the mechanisms that clear hyphae and other pathogens that are too large to be phagocytosed remain unknown. We show that neutrophils sense microbial size and selectively release neutrophil extracellular traps (NETs) in response to large pathogens, such as Candida albicans hyphae and extracellular Mycobacterium bovis aggregates, but not small yeast and single bacteria. NETs are fundamental in countering large pathogens in vivo. Phagocytosis via dectin-1, acts as a sensor for microbial size preventing NETosis by downregulating neutrophil elastase (NE) translocation to the nucleus. Dectin-1 deficiency leads to aberrant NETosis and NET-mediated tissue damage during infection. Size-tailored neutrophil responses clear large microbes and minimize pathology when microbes are small enough to be phagocytosed.

Type I interferon in the pathogenesis of lupus

Investigations of patients with systemic lupus erythematosus have applied insights from studies of the innate immune response to define IFN-I, with IFN-α as the dominant mediator, as central to the pathogenesis of this prototype systemic autoimmune disease. Genetic association data identify regulators of nucleic acid degradation and components of TLR-independent, endosomal TLR-dependent, and IFN-I-signaling pathways as contributors to lupus disease susceptibility. Together with a gene expression signature characterized by IFN-I-induced gene transcripts in lupus blood and tissue, those data support the conclusion that many of the immunologic and pathologic features of this disease are a consequence of a persistent self-directed immune reaction driven by IFN-I and mimicking a sustained antivirus response. This expanding knowledge of the role of IFN-I and the innate immune response suggests candidate therapeutic targets that are being tested in lupus patients.

Neutrophils at work

In this Review we discuss data demonstrating recently recognized aspects of neutrophil homeostasis in the steady state, granulopoiesis in 'emergency' conditions and interactions of neutrophils with the adaptive immune system. We explore in vivo observations of the recruitment of neutrophils from blood to tissues in models of blood-borne infections versus bacterial invasion through epithelial linings. We examine data on novel aspects of the activation of NADPH oxidase and the heterogeneity of phagosomes and, finally, consider the importance of two neutrophil-derived biological agents: neutrophil extracellular traps and ectosomes.

Social networking of human neutrophils within the immune system

It is now widely recognized that neutrophils are highly versatile and sophisticated cells that display de novo synthetic capacity and may greatly extend their lifespan. In addition, concepts such as "neutrophil heterogeneity" and "neutrophil plasticity" have started to emerge, implying that, under pathological conditions, neutrophils may differentiate into discrete subsets defined by distinct phenotypic and functional profiles. A number of studies have shown that neutrophils act as effectors in both innate and adaptive immunoregulatory networks. In fact, once recruited into inflamed tissues, neutrophils engage into complex bidirectional interactions with macrophages, natural killer, dendritic and mesenchymal stem cells, B and T lymphocytes, or platelets. As a result of this cross-talk, mediated either by contact-dependent mechanisms or cell-derived soluble factors, neutrophils and target cells reciprocally modulate their survival and activation status. Altogether, these novel aspects of neutrophil biology have shed new light not only on the potential complex roles that neutrophils play during inflammation and immune responses, but also in the pathogenesis of several inflammatory disorders including infection, autoimmunity, and cancer.

Pivotal Functions of Plasmacytoid Dendritic Cells in Systemic Autoimmune Pathogenesis

Plasmacytoid dendritic cells (pDCs) were initially identified as the prominent natural type I interferon-producing cells during viral infection. Over the past decade, the aberrant production of interferon α/β by pDCs in response to self-derived molecular entities has been critically implicated in the pathogenesis of systemic lupus erythematosus and recognized as a general feature underlying other autoimmune diseases. On top of imperative studies on human pDCs, the functional involvement and mechanism by which the pDC-interferon α/β pathway facilitates the progression of autoimmunity have been unraveled recently from investigations with several experimental lupus models. This article reviews correlating information obtained from human in vitro characterization and murine in vivo studies and highlights the fundamental and multifaceted contribution of pDCs to the pathogenesis of systemic autoimmune manifestation.