Neutrophils, from marrow to microbes

Autophagy mediates the delivery of thrombogenic tissue factor to neutrophil extracellular traps in human sepsis

Background

Sepsis is associated with systemic inflammatory responses and induction of coagulation system. Neutrophil extracellular traps (NETs) constitute an antimicrobial mechanism, recently implicated in thrombosis via platelet entrapment and aggregation.

Methodology/Principal Findings

In this study, we demonstrate for the first time the localization of thrombogenic tissue factor (TF) in NETs released by neutrophils derived from patients with gram-negative sepsis and normal neutrophils treated with either serum from septic patients or inflammatory mediators involved in the pathogenesis of sepsis. Localization of TF in acidified autophagosomes was observed during this process, as indicated by positive LC3B and LysoTracker staining. Moreover, phosphatidylinositol 3-kinase inhibition with 3-MA or inhibition of endosomal acidification with bafilomycin A1 hindered the release of TF-bearing NETs. TF present in NETs induced thrombin generation in culture supernatants, which further resulted in protease activated receptor-1 signaling.

Conclusions/Significance

This study demonstrates the involvement of autophagic machinery in the extracellular delivery of TF in NETs and the subsequent activation of coagulation cascade, providing evidence for the implication of this process in coagulopathy and inflammatory response in sepsis.

Neutrophil extracellular traps: double-edged swords of innate immunity

Spectacular images of neutrophils ejecting nuclear chromatin and bactericidal proteins, in response to microbes, were first reported in 2004. As externalized chromatin could entangle bacteria, these structures were named neutrophil extracellular traps (NETs). Subsequent studies identified microorganisms and sterile conditions that stimulate NETs, as well as additional cell types that release extracellular chromatin. The release of NETs is the most dramatic stage in a cell death process called NETosis. Experimental evidence suggests that NETs participate in pathogenesis of autoimmune and inflammatory disorders, with proposed involvement in glomerulonephritis, chronic lung disease, sepsis, and vascular disorders. Exaggerated NETosis or diminished NET clearance likely increases risk of autoreactivity to NET components. The biological significance of NETs is just beginning to be explored. A more complete integration of NETosis within immunology and pathophysiology will require better understanding of NET properties associated with specific disease states and microbial infections. This may lead to the identification of important therapeutic targets.

Neutrophil-delivered myeloperoxidase dampens the hydrogen peroxide burst after tissue wounding in zebrafish

Prompt neutrophil arrival is critical for host defense immediately after injury [1-3]. Following wounding, a hydrogen peroxide (H(2)O(2)) burst generated in injured tissues is the earliest known leukocyte chemoattractant [4]. Generating this tissue-scale H(2)O(2) gradient uses dual oxidase [4] and neutrophils sense H(2)O(2) by a mechanism involving the LYN Src-family kinase [5], but the molecular mechanisms responsible for H(2)O(2) clearance are unknown [6]. Neutrophils carry abundant amounts of myeloperoxidase, an enzyme catalyzing an H(2)O(2)-consuming reaction [7, 8]. We hypothesized that this neutrophil-delivered myeloperoxidase downregulates the high tissue H(2)O(2) concentrations that follow wounding. This was tested in zebrafish using simultaneous fluorophore-based imaging of H(2)O(2) concentrations and leukocytes [4, 9-11] and a new neutrophil-replete but myeloperoxidase-deficient mutant (durif). Leukocyte-depleted zebrafish had an abnormally sustained wound H(2)O(2) burst, indicating that leukocytes themselves were required for H(2)O(2) downregulation. Myeloperoxidase-deficient zebrafish also had abnormally sustained high wound H(2)O(2) concentrations despite similar numbers of arriving neutrophils. A local H(2)O(2)/myeloperoxidase interaction within wound-recruited neutrophils was demonstrated. These data demonstrate that leukocyte-delivered myeloperoxidase cell-autonomously downregulates tissue-generated wound H(2)O(2) gradients in vivo, defining a new requirement for myeloperoxidase during inflammation. Durif provides a new animal model of myeloperoxidase deficiency closely phenocopying the prevalent human disorder [7, 12, 13], offering unique possibilities for investigating its clinical consequences.

p40phox expression regulates neutrophil recruitment and function during the resolution phase of intestinal inflammation

NADPH oxidase is a multisubunit complex that assembles during phagocytosis to generate reactive oxygen species. Several components of this complex have been implicated in chronic granulomatous disease and Crohn's disease, highlighting the importance of reactive oxygen species in regulating host immune response. In this study, we use genetically deficient mice to elucidate how p40(phox), one subunit of the NADPH oxidase complex, functions during intestinal inflammation. We show that p40(phox) deficiency enhances inflammation in both dextran sulfate sodium-induced and innate immune-mediated murine colitis models. This inflammation is characterized by severe colonic tissue injury, increased proinflammatory cytokines, and increased neutrophil recruitment. We demonstrate that neutrophils are essential during the recovery phase of intestinal inflammation and that p40(phox) expression is necessary for this restitution. Lastly, using an integrative bioinformatic approach, we show that p40(phox) deficiency leads to upregulation of chemokine receptor 1 and downregulation of enzymes involved in glycan modifications, including fucosyltransferases and sialyltransferases, during inflammation. We propose that p40(phox) deficiency enhances intestinal inflammation through the dysregulation of these two pathways in neutrophils.

Neuroimmunoendocrine regulation of the prion protein in neutrophils

The prion protein (PrP(C)) is a cell surface protein expressed mainly in the nervous system. In addition to the role of its abnormal conformer in transmissible spongiform encephalopathies, normal PrP(C) may be implicated in other degenerative conditions often associated with inflammation. PrP(C) is also present in cells of hematopoietic origin, including T cells, dendritic cells, and macrophages, and it has been shown to modulate their functions. Here, we investigated the impact of inflammation and stress on the expression and function of PrP(C) in neutrophils, a cell type critically involved in both acute and chronic inflammation. We found that systemic injection of LPS induced transcription and translation of PrP(C) in mouse neutrophils. Up-regulation of PrP(C) was dependent on the serum content of TGF-β and glucocorticoids (GC), which, in turn, are contingent on the activation of the hypothalamic-pituitary-adrenal axis in response to systemic inflammation. GC and TGF-β, either alone or in combination, directly up-regulated PrP(C) in neutrophils, and accordingly, the blockade of GC receptors in vivo curtailed the LPS-induced increase in the content of PrP(C). Moreover, GC also mediated up-regulation of PrP(C) in neutrophils following noninflammatory restraint stress. Finally, neutrophils with up-regulated PrP(C) presented enhanced peroxide-dependent cytotoxicity to endothelial cells. The data demonstrate a novel interplay of the nervous, endocrine, and immune systems upon both the expression and function of PrP(C) in neutrophils, which may have a broad impact upon the physiology and pathology of various organs and systems.

Innate immune cells in liver inflammation

Innate immune system is the first line of defence against invading pathogens that is critical for the overall survival of the host. Human liver is characterised by a dual blood supply, with 80% of blood entering through the portal vein carrying nutrients and bacterial endotoxin from the gastrointestinal tract. The liver is thus constantly exposed to antigenic loads. Therefore, pathogenic microorganism must be efficiently eliminated whilst harmless antigens derived from the gastrointestinal tract need to be tolerized in the liver. In order to achieve this, the liver innate immune system is equipped with multiple cellular components; monocytes, macrophages, granulocytes, natural killer cells, and dendritic cells which coordinate to exert tolerogenic environment at the same time detect, respond, and eliminate invading pathogens, infected or transformed self to mount immunity. This paper will discuss the innate immune cells that take part in human liver inflammation, and their roles in both resolution of inflammation and tissue repair.

Granulocytes and vascularization regulate uterine bleeding and tissue remodeling in a mouse menstruation model

Menstruation-associated disorders negatively interfere with the quality of life of many women. However, mechanisms underlying pathogenesis of menstrual disorders remain poorly investigated up to date. Among others, this is based on a lack of appropriate pre-clinical animal models. We here employ a mouse menstruation model induced by priming mice with gonadal hormones and application of a physical stimulus into the uterus followed by progesterone removal. As in women, these events are accompanied by menstrual-like bleeding and tissue remodeling processes, i.e. disintegration of decidualized endometrium, as well as subsequent repair. We demonstrate that the onset of bleeding coincides with strong upregulation of inflammatory mediators and massive granulocyte influx into the uterus. Uterine granulocytes play a central role in regulating local tissue remodeling since depletion of these cells results in dysregulated expression of matrix modifying enzymes. As described here for the first time, uterine blood loss can be quantified by help of tampon-like cotton pads. Using this novel technique, we reveal that blood loss is strongly reduced upon inhibition of endometrial vascularization and thus, is a key regulator of menstrual bleeding. Taken together, we here identify angiogenesis and infiltrating granulocytes as critical determinants of uterine bleeding and tissue remodeling in a mouse menstruation model. Importantly, our study provides a technical and scientific basis allowing quantification of uterine blood loss in mice and thus, assessment of therapeutic intervention, proving great potential for future use in basic research and drug discovery.

A role for Toll-like receptor mediated signals in neutrophils in the pathogenesis of the anti-phospholipid syndrome

The anti-phospholipid syndrome (APS) is characterized by recurrent thrombosis and occurrence of anti-phospholipid antibodies (aPL). aPL are necessary, but not sufficient for the clinical manifestations of APS. Growing evidence suggests a role of innate immune cells, in particular polymorphonuclear neutrophils (PMN) and Toll-like receptors (TLR) to be additionally involved. aPL activate endothelial cells and monocytes through a TLR4-dependent signalling pathway. Whether this is also relevant for PMN in a similar way is currently not known. To address this issue, we used purified PMN from healthy donors and stimulated them in the presence or absence of human monoclonal aPL and the TLR4 agonist LPS monitoring neutrophil effector functions, namely the oxidative burst, phagocytosis, L-Selectin shedding and IL-8 production. aPL alone were only able to induce minor activation of PMN effector functions at high concentrations. However, in the additional presence of LPS the activation threshold was markedly lower indicating a synergistic activation pathway of aPL and TLR in PMN. In summary, our results indicate that PMN effector functions are directly activated by aPL and boosted by the additional presence of microbial products. This highlights a role for PMN as important innate immune effector cells that contribute to the pathophysiology of APS.

Cell recruitment and cytokines in skin mice sensitized with the vaccine adjuvants: saponin, incomplete Freund's adjuvant, and monophosphoryl lipid A

Vaccine adjuvants are substances associated with antigens that are fundamental to the formation of an intense, durable, and fast immune response. In this context, the use of vaccine adjuvants to generate an effective cellular immune response is crucial for the design and development of vaccines against visceral leishmaniasis. The objective of this study was to evaluate innate inflammatory response induced by the vaccine adjuvants saponin (SAP), incomplete Freund’s adjuvant (IFA), and monophosphoryl lipid A (MPL). After a single dose of adjuvant was injected into the skin of mice, we analyzed inflammatory reaction, selective cell migration, and cytokine production at the injection site, and inflammatory cell influx in the peripheral blood. We found that all vaccine adjuvants were able to promote cell recruitment to the site without tissue damage. In addition, they induced selective migration of neutrophils, macrophages, and lymphocytes. The influx of neutrophils was notable at 12 h in all groups, but at other time points it was most evident after inoculation with SAP. With regard to cytokines, the SAP led to production of interleukin (IL)-2, IL-6, and IL-4. IFA promoted production of tumor necrosis factor (TNF)-α, interferon (IFN)-γ, IL-6, IL-17, IL-4, and IL-10. We also observed that MPL induced high production of IL-2, TNF-α, and IFN-γ, in addition to IL-6, IL-17, and IL-10. In peripheral blood, values of certain cell populations in the local response changed after stimulation. Our data demonstrate that the three vaccine adjuvants stimulate the early events of innate immune response at the injection site, suggesting their ability to increase the immunogenicity of co-administered antigens. Moreover, this work provides relevant information about elements of innate and acquired immune response induced by vaccine adjuvants administered alone.

The pattern recognition receptors expressed on neutrophils and the associated cytokine profile from different aged patients with Candida-related denture stomatitis

This study evaluated the expression of pattern recognition receptors (PRRs) and activation factors associated with salivary and blood neutrophils from different aged patients diagnosed with Candida-related denture stomatitis (DS). Expression of neutrophil PRRs was determined by flow cytometry and immunofluorescence, and the levels of selected cytokines that influence immune activation were determined by ELISA. The salivary (but not the serum derived) neutrophils of individuals with DS were found to have an increased expression of CD69 regardless of the age of the patient compared to patients without DS. However, these salivary neutrophils had a lower expression of CD66b and CD64. Expression of TLR2 was lower on the salivary- and serum-derived neutrophils from elderly individuals compared to the neutrophils of younger subjects, regardless of whether the individual had DS. Salivary interleukin (IL)-4 was elevated in both of the elderly subject groups (with or without DS). Only elderly DS patients were observed to have increased serum IL-4 levels and reduced salivary IL-12 levels. Younger DS patients showed an increase in salivary IL-10 levels, and both the saliva and the serum levels of IFN-γ were increased in all of the younger subjects. Our data demonstrated that changes in both the oral immune cells and the protein components could be associated with DS. Furthermore, changes in the blood-derived factors were more associated with age than DS status.

Neutrophil reverse migration becomes transparent with zebrafish

The precise control of neutrophil-mediated inflammation is critical for both host defense and the prevention of immunopathology. In vivo imaging studies in zebrafish, and more recently in mice, have made the novel observation that neutrophils leave a site of inflammation through a process called neutrophil reverse migration. The application of advanced imaging techniques to the genetically tractable, optically transparent zebrafish larvae was critical for these advances. Still, the mechanisms underlying neutrophil reverse migration and its effects on the resolution or priming of immune responses remain unclear. Here, we review the current knowledge of neutrophil reverse migration, its potential roles in host immunity, and the live imaging tools that make zebrafish a valuable model for increasing our knowledge of neutrophil behavior in vivo.

Neutrophils and macrophages: the main partners of phagocyte cell systems

Biological cellular systems are groups of cells sharing a set of characteristics, mainly key function and origin. Phagocytes are crucial in the host defense against microbial infection. The previously proposed phagocyte cell systems including the most recent and presently prevailing one, the mononuclear phagocyte system (MPS), grouped mononuclear cells but excluded neutrophils, creating an unacceptable situation. As neutrophils are archetypical phagocytes that must be members of comprehensive phagocyte systems, Silva recently proposed the creation of a myeloid phagocyte system (MYPS) that adds neutrophils to the MPS. The phagocytes grouped in the MYPS include the leukocytes neutrophils, inflammatory monocytes, macrophages, and immature myeloid DCs. Here the justifications behind the inclusion of neutrophils in a phagocyte system is expanded and the MYPS are further characterized as a group of dedicated phagocytic cells that function in an interacting and cooperative way in the host defense against microbial infection. Neutrophils and macrophages are considered the main arms of this system.

Janus-like effects of type I interferon in autoimmune diseases

In multiple sclerosis, type I interferon (IFN) is considered immune-modulatory, and recombinant forms of IFN-β are the most prescribed treatment for this disease. This is in contrast to most other autoimmune disorders, because type I IFN contributes to the pathologies. Even within the relapsing-remitting multiple sclerosis (RRMS) population, 30-50% of MS patients are non-responsive to this treatment, and it consistently worsens neuromyelitis optica, a disease similar to RRMS. In this article, we discuss the recent advances in the field of autoimmunity and introduce the theory explain how type I IFNs can be pro-inflammatory in disease that is predominantly driven by a Th17 response and are therapeutic when disease is predominantly Th1.

The role of neutrophils during intestinal inflammation

Polymorphonuclear leukocytes or neutrophils play a critical role in the maintenance of intestinal homeostasis. They have elegant defense mechanisms to eliminate microbes that have translocated across a single layer of mucosal epithelial cells that form a critical barrier between the gut lumen and the underlying tissue. During the inflammatory response, neutrophils also contribute to the recruitment of other immune cells and facilitate mucosal healing by releasing mediators necessary for the resolution of inflammation. Although the above responses are clearly beneficial, excessive recruitment and accumulation of activated neutrophils in the intestine under pathological conditions such as inflammatory bowel disease is associated with mucosal injury and debilitating disease symptoms. Thus, depending on the circumstances, neutrophils can be viewed as either good or bad. In this article, we summarize the beneficial and deleterious roles of neutrophils in the intestine during health and disease and provide an overview of what is known about neutrophil function in the gut.

The cellular cancer resistance of the SR/CR mouse

The SR/CR mouse phenotype, first described in 1999 in BALB/c and later bred into C57BL/6 mice, is resistant to cancer formation following high doses of cancer cells administered intraperitoneally. The tumor cell targeting and destruction mechanisms have not been identified. By fluorescence-activated cell sorting analysis, the immune response of SR/CR mice after intraperitoneal injection of cancer cells was investigated and compared with parent strain mice. A massive influx of leukocytes into the peritoneal cavity was found. A large fraction of these leukocytes were polymorphonuclear granulocytes, macrophages and natural killer cells. A relative decrease in influx of B-cells compared with controls was demonstrated. Increased proportions of leukocytes belonging to the innate immune system were also demonstrated in splenocytes of SR/CR mice. Cytospins of peritoneal fluid from SR/CR mice after cancer cell injection showed formations of immune cells morphologically resembling polymorphonuclear granulocytes and macrophages adjoining the cancer cells. The results point to the potential involvement of innate immune cells in cancer immunology. Our data support migration of polymorphonuclear granulocytes, macrophages and NK cells into the peritoneum of the SR/CR mouse in response to intraperitoneal injection of S180 cancer cells. The cell composition of spleens of SR/CR mice reflected the differential regulation of the innate immune cells in peritoneal exudates. Both peritoneal exudates and the spleens of SR/CR mice contained decreased proportions of B-cells compared with BALB/c and C57BL/6 mice. We reproduce important aspects of previous published data and further extend them by showing differentially regulated populations of splenocytes including B-lymphocytes in SR/CR mice compared with parent strain controls. Importantly, this differentially regulated immune response of SR/CR mice could not be found in response to challenge with the lymphoma cell line EL-4.

Identification of novel peptides that stimulate human neutrophils

Neutrophils play a key role in innate immunity, and the identification of new stimuli that stimulate neutrophil activity is a very important issue. In this study, we identified three novel peptides by screening a synthetic hexapeptide combinatorial library. The identified peptides GMMWAI, MMHWAM, and MMHWFM caused an increase in intracellular Ca2+ in a concentration-dependent manner via phospholipase C activity in human neutrophils. The three peptides acted specifically on neutrophils and monocytes and not on other non-leukocytic cells. As a physiological characteristic of the peptides, we observed that the three peptides induced chemotactic migration of neutrophils as well as stimulated superoxide anion production. Studying receptor specificity, we observed that two of the peptides (GMMWAI and MMHWFM) acted on formyl peptide receptor (FPR)1 while the other peptide (MMHWAM) acted on FPR2. Since the three novel peptides were specific agonists for FPR1 or FPR2, they might be useful tools to study FPR1- or FPR2-mediated immune response and signaling.

Inflection points in sepsis biology: from local defense to systemic organ injury

Sepsis and septic shock lead to considerable morbidity and mortality in developed and developing countries. Despite advances in understanding the innate immune events that lead to septic shock, molecular therapies based on these advances have failed to improve sepsis mortality. The clinical failure of laboratory-derived therapies may be, in part, due to the pleiotropic consequences of the acute inflammatory response, which is the focus of this review. A brisk response to infecting organism is essential for pathogen containment and eradication. However, systemic spread of inflammation beyond a single focus leads to organ injury and higher mortality. The primary goal of this article is to discuss recent animal- and human-based scientific advances in understanding the host response to infection and to highlight how these defense mechanisms can be locally beneficial but systemically detrimental. There are other factors that determine the severity of sepsis that are beyond the scope of this review, including the virulence of the pathogen and regulation by Toll-like receptors. Specifically, this review focuses on how the effector mechanisms of platelets, mast cells, neutrophil extracellular traps (NETs), and the endothelium participate in combating local infections yet can induce organ injury during systemic infection.

In vivo hydroquinone exposure impairs MCP-1 secretion and monocyte recruitment into the inflamed lung

Alveolar macrophages (AMs) are important cells in the resolution of the inflammatory process and they come into direct contact with inhaled pollutants. Hydroquinone (HQ) is an environmental pollutant and a component of cigarette smoke that causes immunosuppressive effects. In the present work, we showed that mice exposed to low levels of aerosolized HQ (25 ppm; 1 h/day/5 days) presented impaired mononuclear cell migration to the lipopolysaccharide (LPS)-inflamed lung. This may have been due to reduced monocyte chemoattractant protein-1 (MCP-1) secretion into bronchoalveolar lavage fluid (BALF), and it was not related to alterations to mononuclear cell mobilization into the blood or adhesion molecules expression on mononuclear cell membranes. Corroborating the actions of HQ on MCP-1 secretion, reduced MCP-1 concentrations were also found in the supernatant of ex vivo AM and tracheal tissue collected from HQ-exposed mice. A direct action of HQ on MCP-1 secretion, resulting from impaired gene synthesis, was verified by in vitro incubation of naive AMs or tracheal tissue with HQ. The role of reduced levels of MCP-1 in the BALF on monocyte migration was analysed in the human monocytic lineage THP-1 in in vitro chemotaxis assays, which showed that the reduced concentrations of MCP-1 found in the BALF or cell supernatants from HQ-exposed mice impaired cell migration. Considering the fact that MCP-1 presents a broad spectrum of actions on pathophysiological conditions and that resident mononuclear cells are involved in lung tissue homeostasis and in immune host defence, the mechanism of HQ toxicity presented herein might be relevant to the genesis of infectious lung diseases in smokers and in inhabitants of polluted areas.

Ly6G ligation blocks recruitment of neutrophils via a β2-integrin-dependent mechanism

Ly6G is a glycosylphosphatidylinositol (GPI)-anchored protein of unknown function that is commonly targeted to induce experimental neutrophil depletion in mice. In the present study, we found that doses of anti-Ly6G Abs too low to produce sustained neutropenia remained capable of inhibiting experimental arthritis, leaving joint tissues free of infiltrating neutrophils. Thioglycollate-stimulated peritonitis was also attenuated. No alteration in neutrophil apoptosis was observed, implicating impaired recruitment. Indeed, Ly6G ligation abrogated neutrophil migration toward LTB(4) and other chemoattractants in a transwell system. Exploring the basis for this blockade, we identified colocalization of Ly6G and β2-integrins by confocal microscopy and confirmed close association by both coimmunoprecipitation and fluorescence lifetime imaging microscopy. Anti-Ly6G Ab impaired surface expression of β2-integrins in LTB(4)-stimulated neutrophils and mimicked CD11a blockade in inhibiting both ICAM-1 binding and firm adhesion to activated endothelium under flow conditions. Correspondingly, migration of β2-integrin-deficient neutrophils was no longer inhibited by anti-Ly6G. These results demonstrate that experimental targeting of Ly6G has functional effects on the neutrophil population and identify a previously unappreciated role for Ly6G as a modulator of neutrophil migration to sites of inflammation via a β2-integrin-dependent mechanism.

Cell type-specific targeting dissociates the therapeutic from the adverse effects of protein kinase inhibition in allergic skin disease

The kinase p38α, originally identified because of its endotoxin- and cytokine-inducible activity and affinity for antiinflammatory compounds, has been posited as a promising therapeutic target for various immune-mediated disorders. In clinical trials, however, p38α inhibitors produced adverse skin reactions and other toxic effects that often outweighed their benefits. Such toxicity may arise from a perturbation of physiological functions unrelated to or even protective against the disease being treated. Here, we show that the effect of interfering with p38α signaling can be therapeutic or adverse depending on the targeted cell type. Using a panel of mutant mice devoid of p38α in distinct cell types and an experimental model of allergic skin disease, we find that dendritic cell (DC)-intrinsic p38α function is crucial for both antigen-specific T-cell priming and T-cell-mediated skin inflammation, two independent processes essential for the immunopathogenesis. By contrast, p38α in other cell types serves to prevent excessive inflammation or maintain naïve T-cell pools in the peripheral lymphoid tissues. These findings highlight a dilemma in the clinical use of p38α inhibitors, yet also suggest cell-selective targeting as a potential solution for improving their therapeutic index.

Chemokine receptor CXCR2: physiology regulator and neuroinflammation controller?

The innate immune system is a crucial component of inflammatory reactions, while the central nervous system (CNS) is the most vulnerable site of the body to inflammatory tissue injury. Neuroinflammatory brain pathologies are disorders in which the CNS is threatened by its own immune system. Chemokine receptor CXCR2 and its ligands have been implicated in several neuroinflammatory brain pathologies, as well as in neutrophil recruitment and in the developmental positioning of neural cells. This review focuses on the basics of CXCR2, its regulating role in bone marrow neutrophil recruitment, oligodendrocyte progenitor cell positioning and neural repair mechanisms, as well as its diverse roles in neuroinflammatory brain pathologies.

Interactions between polymorphonuclear leukocytes and Pseudomonas aeruginosa biofilms on silicone implants in vivo

Chronic infections with Pseudomonas aeruginosa persist because the bacterium forms biofilms that are tolerant to antibiotic treatment and the host immune response. Scanning electron microscopy and confocal laser scanning microscopy were used to visualize biofilm development in vivo following intraperitoneal inoculation of mice with bacteria growing on hollow silicone tubes, as well as to examine the interaction between these bacteria and the host innate immune response. Wild-type P. aeruginosa developed biofilms within 1 day that trapped and caused visible cavities in polymorphonuclear leukocytes (PMNs). In contrast, the number of cells of a P. aeruginosa rhlA mutant that cannot produce rhamnolipids was significantly reduced on the implants by day 1, and the bacteria were actively phagocytosed by infiltrating PMNs. In addition, we identified extracellular wire-like structures around the bacteria and PMNs, which we found to consist of DNA and other polymers. Here we present a novel method to study a pathogen-host interaction in detail. The data presented provide the first direct, high-resolution visualization of the failure of PMNs to protect against bacterial biofilms.

Multiple roles for neutrophils in atherosclerosis

Because of their rare detection in atherosclerotic lesions, the involvement of neutrophils in the pathophysiology of atherosclerosis has been largely denied. However, over the past couple of years, studies have provided convincing evidence for the presence of neutrophils in atherosclerotic plaques and further revealed the causal contribution of neutrophils during various stages of atherosclerosis. This review describes mechanisms underlying hyperlipidemia-mediated neutrophilia and how neutrophils may enter atherosclerotic lesions. It also highlights possible mechanisms of neutrophil-driven atherogenesis and plaque destabilization. Knowledge of the contribution of neutrophils to atherosclerosis will allow for exploration of new avenues in the treatment of atherogenesis and atherothrombosis.

Deciphering mechanisms of staphylococcal biofilm evasion of host immunity

Biofilms are adherent communities of bacteria contained within a complex matrix. Although host immune responses to planktonic staphylococcal species have been relatively well-characterized, less is known regarding immunity to staphylococcal biofilms and how they modulate anti-bacterial effector mechanisms when organized in this protective milieu. Previously, staphylococcal biofilms were thought to escape immune recognition on the basis of their chronic and indolent nature. Instead, we have proposed that staphylococcal biofilms skew the host immune response away from a proinflammatory bactericidal phenotype toward an anti-inflammatory, pro-fibrotic response that favors bacterial persistence. This possibility is supported by recent studies from our laboratory using a mouse model of catheter-associated biofilm infection, where S. aureus biofilms led to the accumulation of alternatively activated M2 macrophages that exhibit anti-inflammatory and pro-fibrotic properties. In addition, relatively few neutrophils were recruited into S. aureus biofilms, representing another mechanism that deviates from planktonic infections. However, it is important to recognize the diversity of biofilm infections, in that studies by others have demonstrated the induction of distinct immune responses during staphylococcal biofilm growth in other models, suggesting influences from the local tissue microenvironment. This review will discuss the immune defenses that staphylococcal biofilms evade as well as conceptual issues that remain to be resolved. An improved understanding of why the host immune response is unable to clear biofilm infections could lead to targeted therapies to reverse these defects and expedite biofilm clearance.

Innate immunosenescence: effect of aging on cells and receptors of the innate immune system in humans

Components of the innate immune response, including neutrophils and macrophages, are the first line of defense against infections. Their role is to initiate an inflammatory response, phagocyte and kill pathogens, recruit natural killer cells (NK), and facilitate the maturation and migration of dendritic cells that will initiate the adaptive immune response. Extraordinary advances have been made in the last decade on the knowledge of the receptors and mechanisms used by cells of the innate immunity not only to sense and eliminate the pathogen but also to communicate each other and collaborate with cells of adaptive immunity to mount an effective immune response. The analysis of innate immunity in elderly humans has evidenced that aging has a profound impact on the phenotype and functions of these cells. Thus altered expression and/or function of innate immunity receptors and signal transduction leading to defective activation and decreased chemotaxis, phagocytosis and intracellular killing of pathogens have been described. The phenotype and function of NK cells from elderly individuals show significant changes that are compatible with remodeling of the different NK subsets, with a decrease in the CD56bright subpopulation and accumulation of the CD56dim cells, in particular those differentiated NK cells that co-express CD57, as well as a decreased expression of activating natural cytotoxicity receptors. These alterations can be responsible of the decreased production of cytokines and the lower per-cell cytotoxicity observed in the elderly. Considering the relevance of these cells in the initiation of the immune response, the possibility to reactivate the function of innate immune cells should be considered in order to improve the response to pathogens and to vaccination in the elderly.

PAD4 is not essential for disease in the K/BxN murine autoantibody-mediated model of arthritis

Introduction

Both murine and human genome-wide association studies have implicated peptidyl arginine deiminase (PAD4) as a susceptibility gene in rheumatoid arthritis (RA). In addition, patients with RA commonly have autoantibodies which recognize PAD4 or and/or citrullinated peptides. This study aims to evaluate the role of PAD4 in the effector phase of arthritis.

Methods

PAD4 knock out (KO) and wild type (WT) C57BL/6J mice were injected with K/BxN sera to induce disease. Progression of disease was monitored by measuring paw and ankle swelling and clinical indexes of disease, and pathogenesis was assessed by indexing of clinical progression on paws collected from WT and PAD4 KO mice injected with K/BxN serum. PAD4 activity was determined by visualization of neutrophil extracellular traps (NETs) and immunohistological analysis of histone citrullination.

Results

PAD4 activity is readily detectable in the inflamed synovium of WT but not PAD4 deficient animals, as demonstrated by histone citrullination and NET formation. However, PAD4 WT and KO animals develop K/BxN serum transfer disease with comparable severity and kinetics, with no statistically significant differences noted in clinical scores, swelling, joint erosion or joint invasion.

Conclusions

PAD4 WT and KO mice develop disease in the K/BxN serum transfer model of arthritis with similar severity and kinetics, indicating that PAD4 is dispensable in this effector phase model of disease.

Matrix metalloprotease 9 mediates neutrophil migration into the airways in response to influenza virus-induced toll-like receptor signaling

The early inflammatory response to influenza virus infection contributes to severe lung disease and continues to pose a serious threat to human health. The mechanisms by which neutrophils gain entry to the respiratory tract and their role during pathogenesis remain unclear. Here, we report that neutrophils significantly contributed to morbidity in a pathological mouse model of influenza virus infection. Using extensive immunohistochemistry, bone marrow transfers, and depletion studies, we identified neutrophils as the predominant pulmonary cellular source of the gelatinase matrix metalloprotease (MMP) 9, which is capable of digesting the extracellular matrix. Furthermore, infection of MMP9-deficient mice showed that MMP9 was functionally required for neutrophil migration and control of viral replication in the respiratory tract. Although MMP9 release was toll-like receptor (TLR) signaling-dependent, MyD88-mediated signals in non-hematopoietic cells, rather than neutrophil TLRs themselves, were important for neutrophil migration. These results were extended using multiplex analyses of inflammatory mediators to show that neutrophil chemotactic factor, CCL3, and TNFα were reduced in the Myd88^−/− airways. Furthermore, TNFα induced MMP9 secretion by neutrophils and blocking TNFα in vivo reduced neutrophil recruitment after infection. Innate recognition of influenza virus therefore provides the mechanisms to induce recruitment of neutrophils through chemokines and to enable their motility within the tissue via MMP9-mediated cleavage of the basement membrane. Our results demonstrate a previously unknown contribution of MMP9 to influenza virus pathogenesis by mediating excessive neutrophil migration into the respiratory tract in response to viral replication that could be exploited for therapeutic purposes.

Influenza-associated morbidity and mortality due to yearly epidemics and sporadic, devastating pandemics are a significant health and economic burden. Severe complications arising from highly virulent viruses are associated with rapid, massive inflammatory cell infiltration. Although neutrophils are the predominant cell population recruited to the lung in response to pandemic influenza viruses, the mechanisms by which they gain entry to the respiratory tract remain unclear. In this study, we show a previously unknown contribution of MMP9 to influenza pathogenesis by mediating excessive neutrophil migration into the lung, which not only controls viral replication, but also contributes to morbidity. The in vivo relevance of MMP9-derived enzymatic activity in neutrophils is controversial and understudied, but our data provide new evidence that innate recognition of influenza virus attracts neutrophils that secrete MMP9, which enables them to traverse the basement membrane of the lung by digesting the extracellular matrix. The dichotomy of MMP9 function in immunity versus pathology provides real challenges for targeting MMP9 for therapeutic purposes. Nevertheless, finding the balance to modulate neutrophil numbers following influenza virus infection will allow for innate immunity to be boosted whilst preventing pathology associated with pandemic strains.

Innate immunity in the central nervous system

Immune responses in the CNS are common, despite its perception as a site of immune privilege. These responses can be mediated by resident microglia and astrocytes, which are innate immune cells without direct counterparts in the periphery. Furthermore, CNS immune reactions often take place in virtual isolation from the innate/adaptive immune interplay that characterizes peripheral immunity. However, microglia and astrocytes also engage in significant cross-talk with CNS-infiltrating T cells and other components of the innate immune system. Here we review the cellular and molecular basis of innate immunity in the CNS and discuss what is known about how outcomes of these interactions can lead to resolution of infection, neurodegeneration, or neural repair depending on the context.

Apolipoprotein A-I attenuates ovalbumin-induced neutrophilic airway inflammation via a granulocyte colony-stimulating factor-dependent mechanism

Apolipoprotein A-I (apoA-I) is a key component of high-density lipoproteins that mediates reverse cholesterol transport from cells and reduces vascular inflammation. We investigated whether endogenous apoA-I modulates ovalbumin (OVA)-induced airway inflammation in mice. We found that apoA-I expression was significantly reduced in the lungs of OVA-challenged, compared with saline-challenged, wild-type (WT) mice. Next, to investigate the role of endogenous apoA-I in the pathogenesis of OVA-induced airway inflammation, WT and apoA-I(-/-) mice were sensitized by intraperitoneal injections of OVA and aluminum hydroxide, followed by multiple nasal OVA challenges for 4 weeks. OVA-challenged apoA-I(-/-) mice exhibited a phenotype of increased airway neutrophils compared with WT mice, which could be rescued by an administration of a 5A apoA-I mimetic peptide. Multiple pathways promoted neutrophilic inflammation in OVA-challenged apoA-I(-/-) mice, including the up-regulated expression of (1) proinflammatory cytokines (IL-17A and TNF-α), (2) CXC chemokines (CXCL5), (3) vascular adhesion molecules (i.e., vascular cell adhesion molecule-1), and (4) granulocyte colony-stimulating factors (G-CSF). Because concentrations of G-CSF in bronchoalveolar lavage fluid (BALF) were markedly increased in OVA-challenged apoA-I(-/-) mice, we hypothesized that enhanced G-CSF expression may represent the predominant pathway mediating increased neutrophilic inflammation. This was confirmed by the intranasal administration of a neutralizing anti-G-CSF antibody, which significantly reduced BALF neutrophilia by 72% in OVA-challenged apoA-I(-/-) mice, compared with mice that received a control antibody. We conclude that endogenous apoA-I negatively regulates OVA-induced neutrophilic airway inflammation, primarily via a G-CSF-dependent mechanism. Furthermore, these findings suggest that apoA-I may play an important role in modulating the severity of neutrophilic airway inflammation in asthma.

Anionic lipid-induced conformational changes in human phagocyte flavocytochrome b precede assembly and activation of the NADPH oxidase complex

Phagocyte NADPH oxidases generate superoxide at high rates in defense against infectious agents, a process regulated by second messenger anionic lipids using incompletely understood mechanisms. We reconstituted the catalytic core of the human neutrophil NADPH oxidase, flavocytochrome b (Cyt b) in 99% phosphatidylcholine vesicles in order to correlate anionic lipid-dependent conformational changes in membrane-bound Cyt b and oxidase activity. The anionic lipid 10:0 phosphatidic acid (10:0 PA) specifically induced conformational changes in Cyt b as measured by a combination of fluorescence resonance energy transfer methods and size exclusion chromatography. The fluorescence lifetime of a complex between Cyt b and Cascade Blue-derivatized anti-p22(phox) antibody (CCB-CS9), increased after exposure to 10:PA by ∼50% of the change observed when the complex is dissociated, indicating a structural rearrangement of p22(phox) and/or the Cyt b heme prosthetic groups. Half of the quenching relaxation occurred at 10:0 PA concentrations permissive to less than 10% full NADPH oxidase activity, but saturated near the saturation in activity in a matched cell-free oxidase assay. We conclude that anionic lipids modulate the conformation of Cyt b in the membrane and suggest they may serve to modulate the structure of Cyt b as a control mechanism for the NADPH oxidase.

Platelet-rich plasma: a milieu of bioactive factors

Platelet concentrates such as platelet-rich plasma (PRP) have gained popularity in sports medicine and orthopaedics to promote accelerated physiologic healing and return to function. Each PRP product varies depending on patient factors and the system used to generate it. Blood from some patients may fail to make PRP, and most clinicians use PRP without performing cell counts on either the blood or the preparation to confirm that the solution is truly PRP. Components in this milieu have bioactive functions that affect musculoskeletal tissue regeneration and healing. Platelets are activated by collagen or other molecules and release growth factors from alpha granules. Additional substances are released from dense bodies and lysosomes. Soluble proteins also present in PRP function in hemostasis, whereas others serve as biomarkers of musculoskeletal injury. Electrolytes and soluble plasma hormones are required for cellular signaling and regulation. Leukocytes and erythrocytes are present in PRP and function in inflammation, immunity, and additional cellular signaling pathways. This article supports the emerging paradigm that more than just platelets are playing a role in clinical responses to PRP. Depending on the specific constituents of a PRP preparation, the clinical use can theoretically be matched to the pathology being treated in an effort to improve clinical efficacy.

ETosis: A Microbicidal Mechanism beyond Cell Death

Netosis is a recently described type of neutrophil death occurring with the release to the extracellular milieu of a lattice composed of DNA associated with histones and granular and cytoplasmic proteins. These webs, initially named neutrophil extracellular traps (NETs), ensnare and kill microorganisms. Similarly, other cell types, such as eosinophils, mast cells, and macrophages, can also dye by this mechanism; thus, it was renamed as ETosis, meaning death with release of extracellular traps (ETs). Here, we review the mechanism of NETosis/etosis, emphasizing its role in diseases caused by protozoan parasites, fungi, and viruses.

Depletion of dendritic cells enhances innate anti-bacterial host defense through modulation of phagocyte homeostasis

Dendritic cells (DCs) as professional antigen-presenting cells play an important role in the initiation and modulation of the adaptive immune response. However, their role in the innate immune response against bacterial infections is not completely defined. Here we have analyzed the role of DCs and their impact on the innate anti-bacterial host defense in an experimental infection model of Yersinia enterocolitica (Ye). We used CD11c-diphtheria toxin (DT) mice to deplete DCs prior to severe infection with Ye. DC depletion significantly increased animal survival after Ye infection. The bacterial load in the spleen of DC-depleted mice was significantly lower than that of control mice throughout the infection. DC depletion was accompanied by an increase in the serum levels of CXCL1, G-CSF, IL-1α, and CCL2 and an increase in the numbers of splenic phagocytes. Functionally, splenocytes from DC-depleted mice exhibited an increased bacterial killing capacity compared to splenocytes from control mice. Cellular studies further showed that this was due to an increased production of reactive oxygen species (ROS) by neutrophils. Adoptive transfer of neutrophils from DC-depleted mice into control mice prior to Ye infection reduced the bacterial load to the level of Ye-infected DC-depleted mice, suggesting that the increased number of phagocytes with additional ROS production account for the decreased bacterial load. Furthermore, after incubation with serum from DC-depleted mice splenocytes from control mice increased their bacterial killing capacity, most likely due to enhanced ROS production by neutrophils, indicating that serum factors from DC-depleted mice account for this effect. In summary, we could show that DC depletion triggers phagocyte accumulation in the spleen and enhances their anti-bacterial killing capacity upon bacterial infection.

CpsY influences Streptococcus iniae cell wall adaptations important for neutrophil intracellular survival

The ability of a pathogen to evade neutrophil phagocytic killing mechanisms is critically important for dissemination and establishment of a systemic infection. Understanding how pathogens overcome these innate defenses is essential for the development of optimal therapeutic strategies for invasive infections. CpsY is a conserved transcriptional regulator previously identified as an important virulence determinant for systemic infection of Streptococcus iniae. While orthologs of CpsY have been associated with the regulation of methionine metabolism and uptake pathways, CpsY additionally functions in protection from neutrophil-mediated killing. S. iniae does not alter neutrophil phagosomal maturation but instead is able to adapt to the extreme bactericidal environment of a mature neutrophil phagosome, a property dependent upon CpsY. This CpsY-dependent adaptation appears to involve stabilization of the cell wall through peptidoglycan O-acetylation and repression of cellular autolysins. Furthermore, S. iniae continues to be a powerful model for investigation of bacterial adaptations during systemic streptococcal infection.

Protective effect of an elastase inhibitor in a neuromyelitis optica-like disease driven by a peptide of myelin oligodendroglial glycoprotein

BACKGROUND

The pathology of neuromyelitis optica (NMO), in contrast to multiple sclerosis, comprises granulocyte infiltrates along extensive lengths of spinal cord, as well as optic nerve. Furthermore, IFN-β treatment worsens NMO. We recently found that experimental autoimmune encephalomyelitis (EAE) induced with Th17 cells is exacerbated by IFN-β, in contrast to disease induced with Th1 where treatment attenuated symptoms.

OBJECTIVE

This study demonstrates the similarities between NMO and Th17 EAE and how neutrophils mediate pathology in Th17 disease.

METHODS

Levels of blood biomarkers in NMO were assessed by Luminex and ELISA. Effects of IFN-β on neutrophils were assessed by culture assays and immunofluorescence. EAE was induced by transfer of myelin-specific Th1 or Th17 cells and treated with Sivelestat sodium hydrate, a neutrophil elastase inhibitor.

RESULTS

We show Th17 cytokines, granulocyte chemokines, type 1 interferon and neutrophil elastase are elevated in patients with definitive NMO. In culture, we find that IFN-β stimulates neutrophils to release neutrophil elastase. In Th17 EAE, we demonstrate neutrophilic infiltration in the optic nerve and spinal cord which was not present in Th1 EAE. Blockade of neutrophil elastase with Sivelestat had efficacy in Th17 EAE but not Th1 EAE.

CONCLUSIONS

The similarities between Th17 EAE and NMO indicate that this model represents several aspects of NMO. Neutrophils are critical in the pathologies of both Th17-EAE and NMO, and therefore blockade of neutrophil elastase is a promising target in treating NMO.

Phosphoinositide lipid phosphatase SHIP1 and PTEN coordinate to regulate cell migration and adhesion

SHIP1 regulates PtdIns(3,4,5)P3 production in response to cell adhesion. Loss of SHIP1 leads to elevated PtdIns(3,4,5)P3 and Akt activation upon adhesion. SHIP1^−/− neutrophils lose polarity upon cell adhesion. They are extremely adherent, which impairs chemotaxis. Chemotaxis in SHIP1^−/− neutrophils can be rescued by reducing cell adhesion.

The second messenger phosphatidylinositol(3,4,5)P₃ (PtdIns(3,4,5)P₃) is formed by stimulation of various receptors, including G protein–coupled receptors and integrins. The lipid phosphatases PTEN and SHIP1 are critical in regulating the level of PtdIns(3,4,5)P₃ during chemotaxis. Observations that loss of PTEN had minor and loss of SHIP1 resulted in a severe chemotaxis defect in neutrophils led to the belief that SHIP1 rather than PTEN acts as a predominant phospholipid phosphatase in establishing a PtdIns(3,4,5)P₃ compass. In this study, we show that SHIP1 regulates PtdIns(3,4,5)P₃ production in response to cell adhesion and plays a limited role when cells are in suspension. SHIP1^−/− neutrophils lose their polarity upon cell adhesion and are extremely adherent, which impairs chemotaxis. However, chemo­taxis can be restored by reducing adhesion. Loss of SHIP1 elevates Akt activation following cell adhesion due to increased PtdIns(3,4,5)P₃ production. From our observations, we conclude that SHIP1 prevents formation of top-down PtdIns(3,4,5)P₃ polarity to facilitate proper cell attachment and detachment during chemotaxis.

Persistence of Bartonella spp. stealth pathogens: from subclinical infections to vasoproliferative tumor formation

Bartonella spp. are facultative intracellular bacteria that typically cause a long-lasting intraerythrocytic bacteremia in their mammalian reservoir hosts, thereby favoring transmission by blood-sucking arthropods. In most cases, natural reservoir host infections are subclinical and the relapsing intraerythrocytic bacteremia may last weeks, months, or even years. In this review, we will follow the infection cycle of Bartonella spp. in a reservoir host, which typically starts with an intradermal inoculation of bacteria that are superficially scratched into the skin from arthropod feces and terminates with the pathogen exit by the blood-sucking arthropod. The current knowledge of bacterial countermeasures against mammalian immune response will be presented for each critical step of the pathogenesis. The prevailing models of the still-enigmatic primary niche and the anatomical location where bacteria reside, persist, and are periodically seeded into the bloodstream to cause the typical relapsing Bartonella spp. bacteremia will also be critically discussed. The review will end up with a discussion of the ability of Bartonella spp., namely Bartonella henselae, Bartonella quintana, and Bartonella bacilliformis, to induce tumor-like vascular deformations in humans having compromised immune response such as in patients with AIDS.

Recurrent infections and immune evasion strategies of Staphylococcus aureus

Staphylococcus aureus causes purulent skin and soft tissue infections (SSTIs) that frequently reoccur. Staphylococal SSTIs can lead to invasive disease and sepsis, which are among the most significant causes of infectious disease mortality in both developed and developing countries. Human or animal infections with S. aureus do not elicit protective immunity against staphylococcal diseases. Here we review what is known about the immune evasive strategies of S. aureus that enable the pathogen's escape from protective immune responses. Three secreted products are discussed in detail, staphylococcal protein A (SpA), staphylococcal binder of immunoglobulin (Sbi) and adenosine synthase A (AdsA). By forming a complex with V(H)3-type IgM on the surface of B cells, SpA functions as a superantigen to modulate antibody responses to staphylococcal infection. SpA also captures pathogen-specific antibodies by binding their Fcγ portion. The latter activity of SpA is shared by Sbi, which also associates with complement factors 3d and factor H to promote the depletion of complement. AdsA synthesizes the immune signaling molecule adenosine, thereby dampening innate and adaptive immune responses during infection. We discuss strategies how the three secreted products of staphylococci may be exploited for the development of vaccines and therapeutics.

Inflammatory response in acute chorioamnionitis

Acute chorioamnionitis is the principal antecedent of premature birth and an important contributor to specific neonatal and other complications that may extend throughout subsequent life. A large number of studies have addressed surrogate markers of in-utero inflammation including cytokines, chemokines, pathogen-associated molecular patterns, and elicited host proteins. However, chorioamnionitis means inflammation occurring within the chorioamnion and the only practical direct measure available to assess this finding in most placentas is histopathology. The maternal and fetal inflammatory response to the presence of organisms within the placental membranes, so-called histologic chorioamnionitis, is the focus of this review. The issues addressed are the nature and origin of the eliciting antigen, mode of spread to the placenta, general characteristics of placental immunity, and a specific characterization of the spectrum of pathologic lesions observed in placentas with membrane infection.

CXCL1 can be regulated by IL-6 and promotes granulocyte adhesion to brain capillaries during bacterial toxin exposure and encephalomyelitis

Background

Granulocytes generally exert protective roles in the central nervous system (CNS), but recent studies suggest that they can be detrimental in experimental autoimmune encephalomyelitis (EAE), the most common model of multiple sclerosis. While the cytokines and adhesion molecules involved in granulocyte adhesion to the brain vasculature have started to be elucidated, the required chemokines remain undetermined.

Methods

CXCR2 ligand expression was examined in the CNS of mice suffering from EAE or exposed to bacterial toxins by quantitative RT-PCR and in situ hybridization. CXCL1 expression was analyzed in IL-6-treated endothelial cell cultures by quantitative RT-PCR and ELISA. Granulocytes were counted in the brain vasculature after treatment with a neutralizing anti-CXCL1 antibody using stereological techniques.

Results

CXCL1 was the most highly expressed ligand of the granulocyte receptor CXCR2 in the CNS of mice subjected to EAE or infused with lipopolysaccharide (LPS) or pertussis toxin (PTX), the latter being commonly used to induce EAE. IL-6 upregulated CXCL1 expression in brain endothelial cells by acting transcriptionally and mediated the stimulatory effect of PTX on CXCL1 expression. The anti-CXCL1 antibody reduced granulocyte adhesion to brain capillaries in the three conditions under study. Importantly, it attenuated EAE severity when given daily for a week during the effector phase of the disease.

Conclusions

This study identifies CXCL1 not only as a key regulator of granulocyte recruitment into the CNS, but also as a new potential target for the treatment of neuroinflammatory diseases such as multiple sclerosis.

Distinct TLR adjuvants differentially stimulate systemic and local innate immune responses in nonhuman primates

TLR ligands (TLR-Ls) represent novel vaccine adjuvants, but their immunologic effects in humans remain poorly defined in vivo. In the present study, we analyzed the innate responses stimulated by different TLR-Ls in rhesus macaques. MPL (TLR4-L), R-848 (TLR7/8-L), or cytosine-phosphate-guanine oligodeoxynucleotide (TLR9-L) induced a rapid and robust expansion of blood neutrophils, with a concomitant reduction in PBMCs. Furthermore, all TLR-Ls induced rapid (3-8 hours) expansion of CD14(+) monocytes, but only TLR7/8-L and TLR9-L mobilized the CD14(+)CD16(+) and CD14(dim)CD16(++) monocytes, and only TLR7/8-L and TLR9-L induced activation of myeloid dendritic cells (mDCs) and plasmacytoid DCs (pDCs), production of IP-10 and type-I IFN, and expression of type-I IFN-related and chemokine genes in the blood. In the draining lymph nodes (LNs), consistent with the effects in blood, all TLR-Ls induced expansion of CD14(+) monocytes, but only TLR7/8-L and TLR9-L expanded the activated CD14(+)CD16(+) cells. TLR4-L and TLR9-L differentially induced the expansion of mDCs and pDCs (1-3 days), but did not activate DCs. In contrast, TLR7/8-L did not induce DC expansion, but did activate mDCs. Finally, both TLR9-L and TLR7/8-L induced the expression of genes related to chemokines and type-I IFNs in LNs. Thus different TLR-Ls mediate distinct signatures of early innate responses both locally and systemically.

Neutrophil function: from mechanisms to disease

Neutrophils are the most abundant white blood cells in circulation, and patients with congenital neutrophil deficiencies suffer from severe infections that are often fatal, underscoring the importance of these cells in immune defense. In spite of neutrophils' relevance in immunity, research on these cells has been hampered by their experimentally intractable nature. Here, we present a survey of basic neutrophil biology, with an emphasis on examples that highlight the function of neutrophils not only as professional killers, but also as instructors of the immune system in the context of infection and inflammatory disease. We focus on emerging issues in the field of neutrophil biology, address questions in this area that remain unanswered, and critically examine the experimental basis for common assumptions found in neutrophil literature.

Intracellular sensors of extracellular bacteria

Initial recognition of bacteria by the innate immune system is thought to occur primarily by germline-encoded pattern recognition receptors (PRRs). These receptors are present in multiple compartments of host cells and are thus capable of surveying both the intracellular and extracellular milieu for bacteria. It has generally been presumed that the cellular location of these receptors dictates what type of bacteria they respond to: extracellular bacteria being recognized by cell surface receptors, such as certain Toll-like receptors, and bacteria that are capable of breaching the plasma membrane and entering the cytoplasm, being sensed by cytoplasmic receptors, including the Nod-like receptors (NLRs). Increasingly, it is becoming apparent that this is a false dichotomy and that extracellular bacteria can be sensed by cytoplasmic PRRs and this is crucial for controlling the levels of these bacteria. In this review, we discuss the role of two NLRs, Nod1 and Nod2, in the recognition of and response to extracellular bacteria.

Dendritic cells take up and present antigens from viable and apoptotic polymorphonuclear leukocytes

Dendritic cells (DC) are endowed with the ability to cross-present antigens from other cell types to cognate T cells. DC are poised to meet polymorphonuclear leukocytes (PMNs) as a result of being co-attracted by interleukin-8 (IL-8), for instance as produced by tumor cells or infected tissue. Human monocyte-derived and mouse bone marrow-derived DC can readily internalize viable or UV-irradiated PMNs. Such internalization was abrogated at 4°C and partly inhibited by anti-CD18 mAb. In mice, DC which had internalized PMNs containing electroporated ovalbumin (OVA) protein, were able to cross-present the antigen to CD8 (OT-1) and CD4 (OT-2) TCR-transgenic T cells. Moreover, in humans, tumor cell debris is internalized by PMNs and the tumor-cell material can be subsequently taken up from the immunomagnetically re-isolated PMNs by DC. Importantly, if human neutrophils had endocytosed bacteria, they were able to trigger the maturation program of the DC. Moreover, when mouse PMNs with E. coli in their interior are co-injected in the foot pad with DC, many DC loaded with fluorescent material from the PMNs reach draining lymph nodes. Using CT26 (H-2(d)) mouse tumor cells, it was observed that if tumor cells are intracellularly loaded with OVA protein and UV-irradiated, they become phagocytic prey of H-2(d) PMNs. If such PMNs, that cannot present antigens to OT-1 T cells, are immunomagnetically re-isolated and phagocytosed by H-2(b) DC, such DC productively cross-present OVA antigen determinants to OT-1 T cells. Cross-presentation to adoptively transferred OT-1 lymphocytes at draining lymph nodes also take place when OVA-loaded PMNs (H-2(d)) are coinjected in the footpad of mice with autologous DC (H-2(b)). In summary, our results indicate that antigens phagocytosed by short-lived PMNs can be in turn internalized and productively cross-presented by DC.

The actin-bundling protein L-plastin: a critical regulator of immune cell function

L-plastin is a leukocyte-specific protein that cross-links actin filaments into tight bundles, increasing the stability of actin-based structures such as podosomes and lamellipodia. While first identified as an abundant cytoplasmic protein in hematopoietically derived cells over 25 years ago, the requirement for L-plastin in multiple functions critical for immunity, such as antigen receptor signaling, adhesion, and motility, has only recently become clear. L-plastin has been identified as an important component in cellular processes critical for neutrophil, macrophage, osteoclast, eosinophil, and T- and B-lymphocyte biology. Following a brief description of the structure and function of L-plastin, the regulation of immune cell functions by L-plastin will be reviewed in detail.