Neutrophil activation by bacterial lipoprotein versus lipopolysaccharide: differential requirements for serum and CD14

The differential formation and composition of leukocyte-platelet aggregates induced by various cellular stimulants

BACKGROUND

Leukocyte-platelet aggregates comprise a pathogenic link between hemostasis and immunity, but the prerequisites and mechanisms of their formation remain not understood.

AIMS

To quantify the formation, composition, and morphology of leukocyte-platelet aggregates in vitro under the influence of various cellular activators.

METHODS

Phorbol-12-myristate-13-acetate (PMA), lipopolysaccharide (LPS), thrombin receptor-activating peptide (TRAP-6), and adenosine diphosphate (ADP) were used as cellular activators. Flow cytometry was utilized to identify and quantify aggregates in whole human blood and platelet-rich plasma. Cell types and cellular aggregates were identified using fluorescently labeled antibodies against the appropriate cellular markers, and cell activation was assessed by the expression of appropriate surface markers. For confocal fluorescent microscopy, cell membranes and nuclei were labeled. Neutrophil-platelet aggregates were studied using scanning electron microscopy.

RESULTS

In the presence of PMA, ADP or TRAP-6, about 17-38 % of neutrophils and 61-77 % of monocytes formed aggregates with platelets in whole blood, whereas LPS did not induce platelet aggregation with either neutrophils or monocytes due the inability to activate platelets. Similar results were obtained when isolated neutrophils were added to platelet-rich plasma. All the cell types involved in the heterotypic aggregation expressed molecular markers of activation. Fluorescent and electron microscopy of the aggregates showed that the predominant platelet/leukocyte ratios were 1:1 and 2:1.

CONCLUSIONS

Formation of leukocyte-platelet aggregates depends on the nature of the cellular activator and the spectrum of its cell-activating ability. An indispensable condition for formation of leukocyte-platelet aggregates is activation of all cell types including platelets, which is the restrictive step.

Neutrophils in Inflammatory Diseases: Unraveling the Impact of Their Derived Molecules and Heterogeneity

Inflammatory diseases involve numerous disorders and medical conditions defined by an insufficient level of self-tolerance. These diseases evolve over the course of a multi-step process through which environmental variables play a crucial role in the emergence of aberrant innate and adaptive immunological responses. According to experimental data accumulated over the past decade, neutrophils play a significant role as effector cells in innate immunity. However, neutrophils are also involved in the progression of numerous diseases through participation in the onset and maintenance of immune-mediated dysregulation by releasing neutrophil-derived molecules and forming neutrophil extracellular traps, ultimately causing destruction of tissues. Additionally, neutrophils have a wide variety of functional heterogeneity with adverse effects on inflammatory diseases. However, the complicated role of neutrophil biology and its heterogeneity in inflammatory diseases remains unclear. Moreover, neutrophils are considered an intriguing target of interventional therapies due to their multifaceted role in a number of diseases. Several approaches have been developed to therapeutically target neutrophils, involving strategies to improve neutrophil function, with various compounds and inhibitors currently undergoing clinical trials, although challenges and contradictions in the field persist. This review outlines the current literature on roles of neutrophils, neutrophil-derived molecules, and neutrophil heterogeneity in the pathogenesis of autoimmune and inflammatory diseases with potential future therapeutic strategies.

Comparative effects of dietary methionine and cysteine supplementation on redox status and intestinal integrity in immunologically challenged-weaned pigs

Sulfur-containing amino acids such as methionine and cysteine play critical roles in immune system and redox status. A body of evidence shows that metabolic aspects of supplemented Met and Cys may differ in the body. Therefore, the study aimed to investigate the effects of dietary Met and Cys supplementation in immunologically challenged weaned pigs. Forty weaned piglets (6.5 ± 0.3 kg) were randomly allocated to five treatment groups. The treatment included: (1) sham-challenged control (SCC), (2) challenged control (CC), (3) MET (CC + 0.1% _DL-Met), (4) CYS (CC + 0.1% _L-Cys), and (5) MET + CYS (CC + 0.1% _DL-Met + 0.1% _L-Cys). On day 7, all pigs were intramuscularly injected with either Escherichia coli O55:B5 lipopolysaccharides (LPS) or phosphate-buffered saline. Blood, liver, and jejunum samples were analyzed for immune response and redox status. The CC group had lower (P < 0.05) villus surface area and higher (P < 0.05) flux of 4-kDa fluorescein isothiocyanate dextran (FD4) than the SCC group. A lower (P < 0.05) glutathione (GSH) concentration was observed in the jejunum of pigs in the CC group than those in the SCC group. Dietary Cys supplementation increased (P < 0.05) villus surface area, GSH levels, and reduced (P < 0.05) the flux of FD4 in the jejunum of LPS-challenged pigs. Dietary Met supplementation enhanced (P < 0.05) hepatic GSH content. Pigs challenged with LPS in the MET group had lower serum IL-8 concentration than those in the CC group. There was a Met × Cys interaction (P < 0.05) in serum IL-4 and IL-8 concentrations, and Trolox equivalent antioxidant capacity. Dietary _L-Cys supplementation restored intestinal integrity and GSH levels that were damaged by lipopolysaccharides administration. Dietary _DL-Met supplementation improved hepatic GSH and reduced systemic inflammatory response, but antagonistic interaction with dietary _L-Cys supplementation was observed in the inflammatory response and redox status.

Early mechanisms of neutrophil activation and transmigration in acute lung injury

Introduction:Neutrophil transmigration is multifactorial and primarily driven by selectins and β₂-integrins (CD11b/CD18), whose expression are dependent on the underlying stimulus. Ventilator-induced lung injury (VILI) results in a predominantly CD18-independent mechanism of neutrophil recruitment, while direct endotoxin-induced lung injury results from a CD18-dependent mechanism. We previously observed that lack of NADPH oxidases DUOX1 and DUOX2 resulted in reduced neutrophil influx in a VILI model of lung injury but had no influence on neutrophil influx after LPS exposure. Based on these observations, we hypothesized that DUOX1/DUOX2 are an important component of CD18-independent mechanisms of neutrophil recruitment in the lung. Methods:We exposed Duoxa ^-/- (KO) mice and Duoxa ^+/+ (WT) mice to either an intratracheal exposure of lipopolysaccharide (LPS/endotoxin)-or high tidal volume ventilation and compared expression of neutrophil markers between groups. WT mice (129S6/SvEvTac) were obtained from Taconic Biosciences (One Discovery Drive Suite 304; Rensselaer, NY 1244) and were allowed to acclimatize for one week prior to study enrollment. KO mice were generated as previously described [Grasberger 2012] and bred in-house on a 129S6 background. We provided positive-pressure ventilation at a tidal volume of 10 ml/kg with 2 cmH20 positive end-expiratory pressure (PEEP). Mice were assigned to groups consisting of KO (n = 5) and WT (n = 5) in each group and divided into non-ventilated, positive-pressure ventilation, or LPS IT exposure groups. Positive-pressure ventilation was instituted for 4-h using a FlexiVent (Flexiware 8.1, Scireq, Montreal, QC, Canada). Lipopolysaccharide (Salmonella enterica serotype tryphimurium L6143, Millipore Sigma) was administered via an intratracheal (IT) route at a dose of 0.1 mg/kg. Mice were humanely euthanized at 4-h post-injection consistent with the UC Davis IAUCAC-approved protocol. Results:As previously observed, neutrophilic influx into the airways was significantly impaired in the Duoxa ^-/- (KO) mice after VILI, but not after LPS exposure. LPS-induced lung injury resulted in upregulation of CD11b⁺ neutrophils and shedding of CD62L and CD162 regardless of DUOX expression, whereas VILI resulted in upregulation of CD49⁺ neutrophils in the Duoxa ^+/+ (WT) mice but not the Duoxa ^-/- (KO) mice. Conclusion:Our data suggest DUOX is required for CD18-independent mechanisms of neutrophil recruitment in the lung induced by acute lung injury, but not for canonical CD18depedent mechanisms after LPS exposure.

Polysalicylic Acid Polymer Microparticle Decoys Therapeutically Treat Acute Respiratory Distress Syndrome

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) remain problematic due to high mortality rates and lack of effective treatments. Neutrophilic injury contributes to mortality in ALI/ARDS. Here, technology for rapid ARDS intervention is developed and evaluated, where intravenous salicylic acid-based polymer microparticles, i.e., Poly-Aspirin (Poly-A), interfere with neutrophils in blood, reducing lung neutrophil infiltration and injury in vivo in mouse models of ALI/ARDS. Importantly, Poly-A particles reduce multiple inflammatory cytokines in the airway and bacterial load in the bloodstream in a live bacteria lung infection model of ARDS, drastically improving survival. It is observed that phagocytosis of the Poly-A microparticles, with salicylic acid in the polymer backbone, alters the neutrophil surface expression of adhesion molecules, potentially contributing to their added therapeutic benefits. Given the proven safety profile of the microparticle degradation products-salicylic acid and adipic acid-it is anticipated that the Poly-A particles represent a therapeutic strategy in ARDS with a rare opportunity for rapid clinical translation.

Protocol for analysis of mouse neutrophil NETosis by flow cytometry

Studies involving neutrophils are steadily increasing, thus creating a need for more optimized and thorough protocols for studying neutrophil function. Here, we present our protocol for extracting mouse bone marrow neutrophils, estimating the purity of isolated neutrophils, and assessing their ability to induce NETosis upon an external cue. We test two isolation protocols that can be used to attain neutrophils to assess NETosis induction. This approach allows for the parallel assessment of NETosis induction in cohorts larger than 10 samples. For complete details on the use and execution of this protocol, please refer to Lu et al., 2021.

Dissecting the microenvironment around biosynthetic scaffolds in murine skin wound healing

The structural properties of biomaterials play crucial roles in guiding cell behavior and influencing immune responses against the material. We fabricated electrospun membranes with three types of surface topography (random, aligned, and latticed), introduced them to dorsal skin excisional wounds in mice and rats, and evaluated their effects on wound healing and immunomodulatory properties. An overview of different immune cells in the microenvironment with the help of single-cell RNA sequencing revealed diverse cellular heterogeneity in vivo. The time course of immune response was advanced toward an adaptive immunity–dominant stage by the aligned scaffold. In mice without mature T lymphocytes, lack of wound-induced hair neogenesis indicated a regulatory role of T cells on hair follicle regeneration. The microenvironment around scaffolds involved an intricate interplay of immune and cutaneous cells.

Monoclonal Antibody to CD14, TLR4, or CD11b: Impact of Epitope and Isotype Specificity on ROS Generation by Human Granulocytes and Monocytes

Lipopolysaccharides (LPSs or endotoxins) from Gram-negative bacteria represent pathogen-associated molecular patterns (PAMPs) that are recognized by CD14 and Toll-like receptor 4 (TLR4). Lipopolysaccharides prime polymorphonuclear leukocytes (PMNs) for substantial production of reactive oxygen species (ROS) during its response to secondary stimuli such as chemoattractants or pathogens. The excessive ROS production can damage surrounding host tissues, thereby amplifying the inflammatory reaction caused by pathogens. Today, specific antibodies against CD14, TLR4, and CD11b are being used as the essential tools to elucidate the role of these receptors in acute inflammation and some of these antibodies have advised as therapeutic agents for clinical use. Because each antibody has two antigen-binding arms [F(ab′)₂] and one Fc arm, its effect on cellular response is much more complicated rather than simple blockage of target receptor. In fact, IgG antibody, once bound to target receptor, engages Fc receptors γ (FcγRs) and thereby is able to activate the adaptive immune system. The consequences of antibody-dependent binary heterotypic association of CD14, TLR4, or CD11b with FcγRs as well as homotypic one on ROS production are not well elucidated. Moreover, the consequences of antigenic recognition of CD14, TLR4, or CD11b by specific F(ab′)₂ fragments are not always investigated. In this review, we will discuss known mechanisms underlying the therapeutic efficiency of CD14, TLR4, and CD11b/CD18 antibodies with a focus on LPS-dependent ROS or cytokine production by PMNs or monocytes. The impacts of F(ab′)₂ as well as antibody IgG subclasses (isotypes) in therapeutic efficiency or agonistic potency of known antibodies against abovementioned receptors are presented. We also pay attention to how the efficiency of different IgG antibody subclasses is modulated during LPS-induced inflammation and by production of priming agents such as interferon γ (IFN-γ). Our review reinforces the molecular targets and therapeutic approaches to amelioration of harmful consequences of excessive activation of human pattern recognition receptors.

Effects of bacterial lipopolysaccharides on platelet function: inhibition of weak platelet activation

Platelets are anucleate blood cells with reported roles in hemostasis and immune responses, which possess a functional receptor for bacterial lipopolysaccharides (LPSs), the well-known inducers of inflammation. However, LPSs effects on platelets are contradictory. Here we aim to investigate mechanisms of platelet functioning in the presence of LPS and to find the cause of the discrepancy in the previously published data. Cell activity was analyzed by flow cytometry, western blotting, and aggregometry. Thrombus growth was assessed by fluorescent microscopy. LPS' activity was checked by their capability to induce PMN activation. However, LPSs did not substantially affect either thrombus growth in flow chambers, irreversible platelet aggregation, or platelet responses to strong activation. Platelet aggregation in response to 1 μM of ADP was significantly inhibited by LPSs. Flow cytometry analysis revealed that platelet activation responses to weak stimulation were also diminished by LPSs, while VASP phosphorylation was weakly increased. Additionally, LPSs were capable of inhibition of ADP-induced P2-receptor desensitization. Incubation of platelets with a pan-PDE inhibitor IBMX significantly enhanced the LPSs-induced platelet inhibition, implying cAMP/cGMP dependent mechanism. The discrepancy in the previously published data could be explained by LPS-induced weak inhibition of platelet activation and the prevention of platelet desensitization.

Heightened Levels of Antimicrobial Response Factors in Patients With Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic progressive autoimmune disease leading to considerable disability over time. The disease can be characterized by the presence of multiple autoantibodies in the serum and synovial fluid. Microbial dysbiosis is proposed to play a role in the pathogenesis of RA. Increased systemic bacterial exposure leads to elevated levels of antimicrobial response factors (ARFs) in the circulation. In the present study, we tested whether RA patients have increased levels of ARFs by analyzing the levels of multiple ARFs in serum from RA patients and healthy age and sex-matched controls. The levels of soluble CD14 (sCD14), lysozyme, and CXCL16 were significantly elevated in RA patients compared to healthy controls. Lipopolysaccharide binding protein (LBP) levels remained unchanged in RA patients compared to healthy controls. A positive correlation of LBP with rheumatoid factor (RF) was also found in RA subjects. Interestingly, the levels of anti-endotoxin core antibodies (EndoCAb) IgM, total IgM, EndoCAb IgA, and total IgA were significantly elevated in RA patients compared to healthy controls. No significant changes in the levels of EndoCAb IgG and total IgG were observed in RA patients compared to healthy controls. Furthermore, lysozyme and CXCL16 levels were positively correlated with disease severity among RA subjects. Increases in the levels of several ARFs and their correlations with clinical indices suggest systemic microbial exposure in the RA cohort. Modulation of microbial exposure may play an important role in disease pathogenesis in individuals with RA.

Prenatal inflammation suppresses blood Th1 polarization and gene clusters related to cellular energy metabolism in preterm newborns

Chorioamnionitis (CA, fetal membrane inflammation) predisposes to preterm birth and is associated with increased neonatal infection risk, but the separate effects of prematurity, CA, and postnatal adaptations on this risk are unclear. Using pigs as models for infants, we examined the systemic immune-metabolic status in cesarean-delivered preterm pigs, with and without CA induced by intra-amniotic (IA) LPS exposure. At birth, cord blood of preterm pigs showed neutropenia and low expressions of innate and adaptive immune genes, relative to term pigs. IA LPS induced CA and fetal systemic innate immune activation via complement and neutrophil-related pathways. These were mainly modulated via cellular regulations rather than granulopoiesis, as validated by the in vitro LPS stimulation of cord blood. After birth, IA LPS-exposed preterm pigs did not follow normal immune-metabolic ontogenies found in fetuses or newborns without prenatal insults, but showed consistently high levels of Treg, impaired Th1 polarization, and reduced expressions of multiple genes related to cellular oxidative phosphorylation and ribosomal activities. In conclusion, our results provide cellular and molecular evidence for CA-induced distinct neonatal immune-metabolic status with increased disease tolerance strategy, suggesting mechanisms for the clinical observation of elevated sepsis risks in immune-compromised preterm infants born with CA.

Neutrophil progenitor populations of rhesus macaques

Captive-bred rhesus macaques of Indian origin represent one of the most important large animal models for infectious disease, solid organ transplantation, and stem cell research. There is a dearth of information defining hematopoietic development, including neutrophil leukocyte differentiation in this species using multicolor flow cytometry. In the current study, we sought to identify cell surface markers that delineate neutrophil progenitor populations with characteristic immunophenotypes. We defined four different postmitotic populations based on their CD11b and CD87 expression pattern, and further refined their immunophenotypes using CD32, CD64, lactoferrin, and myeloperoxidase as antigenic markers. The four subsets contained myelocyte, metamyelocyte, band, and segmented neutrophil populations. We compared our flow cytometry-based classification with the classical nuclear morphology-based classification. We found overlap of immunological phenotype between populations of different nuclear morphology and identified phenotypically different subsets within populations of similar nuclear morphology. We assessed the responsiveness of these populations to stimulatory signals, such as LPS, fMLP, or PMA, and demonstrated significant differences between human and rhesus macaque neutrophil progenitors. In this study, we provided evidence for species-specific features of granulopoiesis that ultimately manifested in the divergent immunophenotypes of the fully differentiated segmented neutrophils of humans and rhesus macaques. Additionally, we found functional markers that can be used to accurately quantify neutrophil progenitors by flow cytometry. Although these markers do not coincide with the classical nuclear-morphology-based grading, they enable us to perform functional studies monitoring immunophenotypic markers.

Changes in Neutrophil Metabolism upon Activation and Aging

Neutrophil activation is an important mechanism of host defense against pathogens. Chronic inflammation and autoimmunity are often associated with abnormalities in phenotype and functions of neutrophils. Since effector functions of immune cells during inflammation are tightly linked to their metabolic state, changes in neutrophil metabolome upon activation have been investigated in this study. Human neutrophils from healthy blood donors (n = 6) were treated either with tumor necrosis factor α (TNF-α) or lipopolysaccharide (LPS), whereas untreated neutrophils were used as control. Since apoptotic cells are abundant at sites of inflammation, the metabolome of aged, mainly apoptotic neutrophils was analyzed too. NMR spectroscopy of water-soluble metabolites revealed a clear distinction between aged neutrophils and neutrophils in control and activated samples. Higher levels of NAD⁺ (4- to 9-fold) and lower levels of ATP (0.3-fold), glutathione (0.8-fold), hypotaurine (0.8-fold), and phosphocholine (0.6-fold) were detected in aged neutrophils than in the other samples. Differences in metabolic profiles between LPS and TNF-α-stimulated cells as well as between stimulated and control neutrophils were statistically not significant. Replication with additional six blood donors confirmed increased NAD⁺ levels in aged cells compared to activated and control neutrophils.

Intestinal microbiota and the immune system in metabolic diseases

The intestinal microbiota is comprised of millions of microorganisms that reside in the gastrointestinal tract and consistently interact with the host. Host factors such as diet and disease status affect the composition of the microbiota, while the microbiota itself produces metabolites that can further manipulate host physiology. Dysbiosis of the intestinal microbiota has been characterized in patients with certain metabolic diseases, some of which involve damage to the host intestinal epithelial barrier and alterations in the immune system. In this review, we will discuss the consequences of dietdependent bacterial dysbiosis in the gastrointestinal tract, and how the associated interaction with epithelial and immune cells impacts metabolic diseases.

1-palmitoyl-2-linoleoyl-3-acetyl-rac-glycerol (PLAG) reduces hepatic injury in concanavalin A-treated mice

1-palmitoyl-2-linoleoyl-3-acetyl-rac-glycerol (PLAG), a chemically synthesized monoacetyldiaglyceride, is one of the constituents in Sika deer antlers and has been known traditionally as having immunomodulatory effects. However, the mechanism by which PLAG controls neutrophil migration, which evokes liver injury in the hepatitis animal model, remains largely unknown. This study was designed to evaluate the immunomodulatory effects of PLAG on cytokine secretion and neutrophil migration in vivo and in vitro. Concanavalin A (Con A) induced leukocyte infiltration in the liver and increased plasma cytokine levels. Pretreatment with PLAG reduced the levels of interleukin (IL)-4, IL-6, IL-10, and CXCL2, but maintained interferon (IFN)-γ levels and modulated neutrophil recruitment toward the liver. Furthermore, the mRNA and protein levels of IL-4 and CXCL2 in liver tissue were also decreased in the Con A-treated mice. Liver histology analyses showed that PLAG reduced Con A-induced hepatic necrosis, which was accompanied by leukocyte infiltration. The in vitro studies revealed that PLAG reduced IL-4 secretion in Con A stimulated T cell and blocked signal transducer and activator of transcription 6 (STAT6) Con A induced hepatocyte. PLAG attenuated IL-4 induced activation of atypical protein kinase C (PKC)/STAT6 in hepatocytes and inhibited neutrophil migration toward the liver tissue through suppression of IL-8/vascular cell adhesion molecule (VCAM) expression. These results suggest that PLAG could mitigate excess neutrophil migration into liver tissue and potentially have a therapeutic effect on immune-mediated liver injury.

Roles of serum in innate immune responses of human leukocytes to synthetic lipopeptide

Tripalmitoyl-S-glyceryl-l-Cys-Ser-(Lys)₄ (Pam₃CSK₄) is a highly conserved molecular motif found in various classes of lipoproteins. The requirement for leukocyte to respond to synthetic Pam₃CSK₄ were studied. Pam₃CSK₄ primed neutrophils for a respiratory burst in a serum-dependent manner. Pam₃CSK₄ upregulated CD11b, CD14, and cytochrome b₅₅₈, and downregulated Leu-8. Treatment of neutrophils with anti-CD14 antibodies and treatment of serum with anti-LPS binding protein (LBP) antibodies resulted in the inhibition of priming for respiratory burst by Pam₃CSK₄. It should be noted that LBP could not replicate the effects of serum in priming of neutrophils for respiratory burst by Pam₃CSK₄. Serum LBP bound to immobilized Pam₃CSK₄. Pam₃CSK₄ induced the interleukin-8 (IL-8) production by leukocytes in a serum-dependent manner. Further, Pam₃CSK₄-induced priming of neutrophils for respiratory burst was not inhibited by the LPS antagonists LA-14-PP, Rhodobacter sphaeroides LPS, or E5531, and Pam₃CSK₄-induced IL-8 production by leukocytes was not affected by LPS antagonist, E5531, indicating that Pam₃CSK₄ was recognized by a different receptor than LPS. Thus, Pam₃CSK₄ and LPS had similar biological activities and similar requirement to act on leukocytes, but were recognized by different receptors. Serum in the action of Pam₃CSK₄ on leukocytes was not replicated by LBP, suggesting that Pam₃CSK₄ might be disaggregated by serum to result in the activation of leukocytes.

Bruton Tyrosine Kinase Inhibition Attenuates Liver Damage in a Mouse Warm Ischemia and Reperfusion Model

BACKGROUND

Bruton tyrosine kinase (Btk) is a central player in multiple signaling pathways of lymphoid and myeloid cells. Myeloid cells are crucial early effectors in organ ischemia-reperfusion (IR) injury. BTKB66 is a selective, irreversible inhibitor of Btk. In this study, we hypothesized that Btk inhibition would reduce hepatocellular injury in a murine model of liver warm hepatic IR.

METHODS

First, BTKB66 was tested in in vitro models of lipopolysaccharide-mediated neutrophil and macrophage activation. Then, to assess its efficacy in vivo, BTKB66 was administered orally to mice for 7 days before subjecting them to 90 minutes of warm hepatic ischemia followed by reperfusion for 6 or 24 hours. Clinical and pathologic features in the livers, including AST, ALT, and a panel of cytokines and chemokines, were examined.

RESULTS

BTKB66 potently inhibited lipopolysaccharide-mediated activation of bone marrow-derived neutrophils and macrophages in vitro. It also reduced the severity of IR injury as determined by AST and ALT levels, as well as immune cell infiltrates. BTKB66 significantly decreased hepatic markers of sterile inflammation, such as C-X-C motif chemokine 1, C-X-C motif chemokine 2, and C-X-C motif chemokine 10, in parallel with depression of serum markers of the myeloid cell activation, such as CCL5, CCL11, and C-X-C motif chemokine 5.

CONCLUSIONS

BTKB66 treatment ameliorated hepatocellular injury in a well-established model of liver partial warm ischemia and in situ reperfusion. These findings confirm that neutrophil recruitment and activation play an essential role in IR stress, and that targeting Btk activity may provide a useful approach for preventing hepatocellular damage and improving outcomes in liver transplantation.

The dual role of LBP and CD14 in response to Gram-negative bacteria or Gram-negative compounds

Innate immunity initiates protection of the host organism against invasion of micro-organisms by specific recognition mechanisms. This article reviews the dual role of LBP/CD14 in innate immunity, focusing mostly on experiments performed in mice by the authors. LPS induces uncontrolled pro-inflammatory response that kills the host and is LBP- and CD14-dependent, as neutralization of LBP and CD14 prevents lethal shock. However, surprisingly, the synthetic Pam3CysSerLys4 bacterial lipoprotein from Escherichia coli (BLP), which is well tolerated in mice, kills the mice upon LBP or CD14 blockade. Furthermore, after blockade of LBP and CD14, the mice succumb to a challenge with virulent Klebsiella pneumoniae or Salmonella typhimurium. Therefore, host responses to Gram-negative bacteria are not identical to that of LPS or BLP. When the host is in the presence of virulent Gram-negative bacteria, the invading pathogens must be held in check by the innate immune system until a specific immune response is mounted. Under these conditions, LBP, CD14, and likely Toll-like receptors (TLRs) are a prerequisite to trigger a pro-inflammatory response of macrophages, which is crucial for keeping an infection under control. These studies indicate that we are very far from understanding how the innate system works and more work needs to be done concerning LBP, CD14 or TLRs. Therefore, caution should be the rule about the use of therapeutic approaches to block the pro-inflammatory response in Gram-negative infections.

Effect of the synthetic Toll-like receptor ligands LPS, Pam3CSK4, HKLM and FSL-1 in the function of bovine polymorphonuclear neutrophils

Toll-like receptors (TLR) are a family of pattern recognition receptors that sense microbial associated molecular patterns (MAMP) such as microbial membrane components and nucleic acids of bacterial origin. Polymorphonuclear neutrophils (PMN) are the first cell of the innate immune system to arrive at the site of infection or injury and elicit oxidative and non-oxidative microbicidal mechanisms. Observations in human and mouse suggest that TLR ligands can induce direct responses in PMN. So far, there is no information of the effect of synthetic TLR ligands on the response of bovine PMN. The objective of this study was to evaluate the functional response of bovine PMN incubated with four synthetic TLR ligands: ultrapure LPS (TLR4), Pam(3)CSK(4) (TLR2/1), HKLM (TLR2) and FSL-1 (TLR2/6). The results show that all the ligands increment cells size as identified by changes in the FSC-SSC as part of the flow cytometric analysis. Interestingly, only Pam(3)CSK(4) consistently induced a calcium influx, increased ROS production and secretion of gelatinase granules, whereas no response was seen using other ligands. Furthermore, exposure of bovine PMN to ultrapure LPS, Pam(3)CSK(4), HKLM or FSL-1 for 24 hours did not impact on apoptosis of these cells. Our data provide evidence for a selective response of bovine PMNs to TLR ligands.

Decreased expression of CD200R3 on mouse basophils as a novel marker for IgG1-mediated anaphylaxis

IgE-mediated mast cell activation is the trigger of anaphylaxis in humans, whereas it is known that not only IgE but also IgG can induce anaphylaxis in mice. In our preliminary experiments, the expression of a murine basophil identification marker, CD200R3, on antigen-sensitized basophils decreased following specific antigen challenge. Interestingly, this decrease did not always correspond with increased expression of the IgE-mediated basophil activation marker CD200R1. Since IgG as well as IgE plays a role in mouse anaphylaxis, we hypothesized that the observed decrease in CD200R3 on basophils was caused by IgG-mediated cell activation. We attempted to establish whether CD200R3 is a marker of IgG-mediated basophil activation and if its expression is correlated with anaphylaxis in a mouse model. Mouse basophils were stimulated via Fc∊Rs and/or FcγRs, and levels of CD200R1 and CD200R3 were analyzed by flow cytometry. Basophils derived from naive mice were challenged with a natural antigen, β-lactoglobulin, after passive sensitization with anti-β-LG serum or IgG/IgG subclass-depleted antiserum. Systemic anaphylaxis was induced by i.v. injection of anti-FcγRIII/II monoclonal antibody, and CD200R3 expression on peripheral basophils was assessed. Stimulation via Fc∊Rs induced a significant increase in CD200R1 expression but had only a small effect on that of CD200R3. However, anti-FcγRIII/II stimulation reduced CD200R3 expression markedly. In passive sensitization experiments, down-regulation of CD200R3 induced by antigen challenge was strongly negated by the depletion of IgG or IgG1 from antiserum. Intravenous injection of anti-FcγRIII/II induced CD200R3 down-regulation on peripheral basophils, together with a drop in rectal temperature. Lowered CD200R3 expression on basophils is induced by IgG-mediated stimulation via FcγRs. Use of CD200R1 and CD200R3 as activation markers enables the evaluation of murine basophil activation mediated by IgE and IgG, respectively.

Influence of particle size on the in vitro and in vivo anti-inflammatory and anti-allergic activities of a curcumin lipid nanoemulsion

The polyphenolic compound, curcumin, is a natural yellow pigment component of turmeric. It exerts various biological effects, such as anti-inflammatory effects, and we have previously demonstrated that curcumin is a specific inhibitor of DNA polymerase λ. Curcumin is characterized by poor bioavailability as it is water-insoluble, is poorly absorbed and is systemically eliminated. In order to increase the bioavailability of curcumin, in this study, we produced a curcumin-loaded lipid nanoemulsion of various particle sizes (50, 100 and 200 nm). The curcumin lipid nanoemulsion was prepared by a modified thin-film hydration method followed by sonication. To identify the optimal particle size which exhibits the strongest physiological activity, we investigated the inhibitory effects of the obtained nanoemulsions against inflammatory and allergic activities. In in vitro cell culture experiments, the 100-nm curcumin lipid nanoemulsion showed the most prominent inhibitory effect on the production of tumor necrosis factor-α (TNF-α) induced by lipopolysaccharide (LPS) in RAW264.7 murine macrophages, and on the release of β-hexosaminidase induced by the calcium ionophore, A23187, in rat basophilic leukemia RBL-2H3 cells. In an in vivo experiment, in which mice were administered the curcumin-loaded lipid nanoemulsion of various particle sizes, the 100-nm curcumin lipid nanoemulsion showed the most prominent anti-inflammatory and anti-allergic effects, inhibiting 12-O-tetradecanoylphorbol-13-acetate-induced inflammatory ear edema and immunoglobulin E (IgE)-induced passive cutaneous anaphylactic (PCA) reaction. The effects of particle size on serum curcumin absorption were also assessed in mice, and the 100-nm lipid nanoemulsion showed the greatest absorption. The results from our study suggest that the physiological activities of curcumin lipid nanoemulsions differ depending on particle size. Our data indicate that the curcumin lipid nanoemulsion with a particle size of 100 nm has potential for use in enhancing the bioavailability and medical value of curcumin.

Human filarial Wolbachia lipopeptide directly activates human neutrophils in vitro

The host inflammatory response to the Onchocerca volvulus endosymbiont, Wolbachia, is a major contributing factor in the development of chronic pathology in humans (onchocerciasis/river blindness). Recently, the toll-like pattern recognition receptor motif of the major inflammatory ligands of filarial Wolbachia, membrane-associated diacylated lipoproteins, was functionally defined in murine models of pathology, including mediation of neutrophil recruitment to the cornea. However, the extent to which human neutrophils can be activated in response to this Wolbachia pattern recognition motif is not known. Therefore, the responses of purified peripheral blood human neutrophils to a synthetic N-terminal diacylated lipopeptide (WoLP) of filarial Wolbachia peptidoglycan-associated lipoprotein (PAL) were characterized. WoLP exposure led to a dose-dependent activation of healthy, human neutrophils that included gross morphological alterations and modulation of surface expressed integrins involved in tethering, rolling and extravasation. WoLP exposure induced chemotaxis but not chemokinesis of neutrophils, and secretion of the major neutrophil chemokine, interleukin 8. WoLP also induced and primed the respiratory burst, and enhanced neutrophil survival by delay of apoptosis. These results indicate that the major inflammatory motif of filarial Wolbachia lipoproteins directly activates human neutrophils in vitro and promotes a molecular pathway by which human neutrophils are recruited to sites of Onchocerca parasitism.

WITHDRAWN: Neutrophil activation in Behçet's Disease

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.intimp.2013.07.017. The duplicate article has therefore been withdrawn.

Exploring the immunomodulatory potential of microbial-associated molecular patterns derived from the enteric bacterial microbiota

The human intestinal lumen represents one of the most densely populated microbial niches in the biological world and, as a result, the intestinal innate immune system exists in a constant state of stimulation. A key component in the innate defence system is the intestinal epithelial layer, which acts not only as a physical barrier, but also as an immune sensor. The expression of pattern recognition receptors, such as Toll-like receptors, in epithelial cells allows innate recognition of a wide range of highly conserved bacterial moieties, termed microbial-associated molecular patterns (MAMPs), from both pathogenic and non-pathogenic bacteria. To date, studies of epithelial immunity have largely concentrated on inflammatory pathogenic antigens; however, this review discusses the major types of MAMPs likely to be produced by the enteric bacterial microbiota and, using data from in vitro studies, animal model systems and clinical observations, speculates on their immunomodulatory potential.

Neutrophil-mediated oxidation of erythrocyte peroxiredoxin 2 as a potential marker of oxidative stress in inflammation

Peroxiredoxin 2 (Prx2) is an abundant thiol protein in erythrocytes. It is oxidized readily on exposure to hydrogen peroxide (H2O2) and provides antioxidant protection by cycling between its reduced and disulfide-bonded forms. To test whether Prx2 oxidation could occur in pathological situations where neutrophils are activated, we exposed human erythrocytes to stimulated neutrophils and measured Prx2 oxidation by immunoblotting of nonreducing gels. With phorbol myristate acetate, lipopolysaccharide or Staphylococcus aureus Prx2 dimer increased from <5% to up to 100% depending on neutrophil number and incubation time. Studies with inhibitors and myeloperoxidase-deficient neutrophils showed that H2O2 generated by the neutrophil NADPH oxidase was responsible. Prx2 oxidation was detected at erythrocyte:neutrophil ratios found in blood and reversed over time as the oxidative burst subsided. Acidotic conditions also increased erythrocyte Prx2 oxidation. In a mouse model of endotoxemia induced by lipopolysaccharide, oxidized Prx2 increased transiently from <1 to 15%, then reverted to baseline by 24 h. No increase was seen in mice lacking NADPH oxidase activity. These results indicate that erythrocyte Prx2 scavenges H2O2 produced during inflammation. Oxidized erythrocyte Prx2 could be a sensitive real-time marker of systemic neutrophil activation and an early indicator of inflammation and oxidative stress.

CD14 expression and Kupffer cell dysfunction in non-alcoholic steatohepatitis: superparamagnetic iron oxide-magnetic resonance image and pathologic correlation

BACKGROUND AND AIM

Kupffer cell (KC) function and CD14 expression contributes to pathogenesis of non-alcoholic steatohepatitis (NASH). However, these relationships remain unclear. We investigated the relationship of KC function with superparamagnetic iron oxide-enhanced magnetic resonance imaging (SPIO-MRI), histopathological severity of NASH, and number of CD14-positive KCs in NASH.

METHODS

This retrospective study included 32 patients (24 with NASH and eight with simple steatosis) who had previously undergone SPIO-MRI with T2-weighted gradient-recalled echo sequence. All subjects were diagnosed pathologically and were evaluated for necroinflammation grade, fibrosis stage, and number of CD14-positive KCs. Patients with NASH and simple steatosis were compared by using the Mann-Whitney test to determine differences in percent reduction of liver-to-muscle signal intensity ratio (reduction-%LMR), as a surrogate parameter of KC function, and number of CD14-positive KCs. Kruskal-Wallis test and Pearson's correlation coefficient were used to analyze relation among reduction-%LMR, histopathological severity and number of CD14-positive KCs.

RESULTS

There were statistically significant differences in reduction-%LMR and number of CD14-positive KCs between NASH and simple steatosis patients (Mann-Whitney test, P < 0.001 for all comparisons). Reduction-%LMR decreased with an increase in necroinflammation grade or fibrosis stage. The number of CD14-positive KCs increased with an increase in necroinflammation grade and fibrosis stage (Kruskal-Wallis test, both, P < 0.001). A high correlation was seen between number of CD14-positive KCs and reduction-%LMR (Pearson r = 0.81; P < 0.001).

CONCLUSIONS

KC phagocytic function evaluated with SPIO-MRI correlated with histopathological severity and number of CD14-positive KCs. These results support the concept that KC phagocytic dysfunction contributes to the pathogenesis of NASH.

Pretreatment with lipopolysaccharide modulates innate immunity in corneal fibroblasts challenged with Aspergillus fumigatus

Aspergillus fumigatus triggers inflammatory responses through Toll-like receptors (TLRs), particularly TLR2 and TLR4. In this study, we tested the hypothesis that lipopolysaccharide (LPS), a ligand of TLR4, can induce tolerance of A. fumigatus hyphae in telomerase-immortalized human stroma fibroblasts (THSFs). The THSFs were pretreated with low-dose LPS for various times and then challenged with A. fumigatus hyphae. We observed that pretreatment of THSFs with low-dose LPS resulted in diminished production of cytokines IL-8 and IL-6 and elevated expression of antimicrobial peptides, such as CC chemokine-ligand 20 (CCL20) and thymosin β4 (Tβ4), upon subsequent A. fumigatus challenge. Furthermore, LPS pretreatment also resulted in suppression of polymorphonuclear leukocyte (PMN) migration. Our results suggested that THSFs pretreated with LPS develop a state of A. fumigatus hyphae tolerance. This may induce protective mechanisms during fungal keratitis to prevent an excessive inflammatory response and to control infection of the cornea.

Priming effects of lipopolysaccharide and inflammatory cytokines on canine granulocytes

Granulocytes play a pivotal role in natural immunity. Under inflammatory conditions, granulocytes are universally primed by several agents, such as endotoxins and inflammatory cytokines. Primed granulocytes exert potent adhesiveness, chemotaxis, phagocytosis and reactive oxygen species (ROS) production, effectively eliminating invading agents. Reactivity against priming agents is known to vary with species; however, there have been few reports on the effects of priming agents on canine granulocytes. In the present study, we assayed the priming effects of lipopolysaccharide (LPS), recombinant canine tumor necrosis factor-alpha (rcTNF-alpha) and recombinant canine granulocyte macrophage colony-stimulating factor (rcGM-CSF) on canine granulocyte function in vitro. Isolated recombinant canine were primed with various concentrations of LPS, rcTNF-alpha and rcGM-CSF, and CD11b expression was assayed. Furthermore, actin polymerization, phagocytosis and ROS production were then assayed at primer concentrations where enhancement of CD11b expression was observed. LPS did not enhance canine granulocyte function. Phagocytosis and actin polymerization were not enhanced by priming agents; however, rcTNF-alpha and rcGM-CSF enhanced CD11b expression and ROS production in canine granulocytes. These results suggest that priming effects are mainly reflected in CD11b expression and ROS production, with rcGM-CSF and rcTNF-alpha having a priming effect similar to that observed in humans.

Intracellular Mycoplasma genitalium infection of human vaginal and cervical epithelial cells elicits distinct patterns of inflammatory cytokine secretion and provides a possible survival niche against macrophage-mediated killing

Background

Mycoplasma genitalium is an emerging sexually transmitted pathogen that has been associated with significant reproductive tract inflammatory syndromes in women. In addition, the strong association between severity of M. genitalium infection and Human Immunodeficiency Virus type 1 (HIV-1) shedding from the cervix suggests that innate responses to M. genitalium may influence pathogenesis of other sexually transmitted infections. Epithelial cells (ECs) of the reproductive mucosa are the first cells contacted by sexually transmitted pathogens. Therefore, we first characterized the dynamics of intracellular and extracellular localization and resultant innate immune responses from human vaginal, ecto- and endocervical ECs to M. genitalium type strain G37 and a low-pass contemporary isolate, M2300.

Results

Both M. genitalium strains rapidly attached to vaginal and cervical ECs by 2 h post-infection (PI). By 3 h PI, M. genitalium organisms also were found in intracellular membrane-bound vacuoles of which approximately 60% were adjacent to the nucleus. Egress of M. genitalium from infected ECs into the culture supernatant was observed but, after invasion, viable intracellular titers were significantly higher than extracellular titers at 24 and 48 h PI. All of the tested cell types responded by secreting significant levels of pro-inflammatory cytokines and chemokines in a pattern consistent with recruitment and stimulation of monocytes and macrophages. Based on the elaborated cytokines, we next investigated the cellular interaction of M. genitalium with human monocyte-derived macrophages and characterized the resultant cytokine responses. Macrophages rapidly phagocytosed M. genitalium resulting in a loss of bacterial viability and a potent pro-inflammatory response that included significant secretion of IL-6 and other cytokines associated with enhanced HIV-1 replication. The macrophage-stimulating capacity of M. genitalium was independent of bacterial viability but was sensitive to heat denaturation and proteinase-K digestion suggesting that M. genitalium protein components are the predominant mediators of inflammation.

Conclusion

Collectively, the data indicated that human genital ECs were susceptible and immunologically responsive to M. genitalium infection that likely induced cellular immune responses. Although macrophage phagocytosis was an effective method for M. genitalium killing, intracellular localization within vaginal and cervical ECs may provide M. genitalium a survival niche and protection from cellular immune responses thereby facilitating the establishment and maintenance of reproductive tract infection.

Malaria and bacterial sepsis: similar mechanisms of endothelial apoptosis and its prevention in vitro

OBJECTIVE AND DESIGN

Apoptotic endothelial damage contributes to multiorgan failure in Plasmodium falciparum malaria and in sepsis. In malaria, endothelial apoptosis is amplified by neutrophils and their secretory products, and reduced by inhibitors of neutrophil-derived substances in vitro. We compared the mechanisms of endothelial apoptosis in malaria and in sepsis, using the human umbilical vein endothelial cell as a model.

INTERVENTIONS

Endothelial cells were incubated with patient sera (P. falciparum malaria, Escherichia coli sepsis, Staphylococcus aureus sepsis) or culture supernatants of the respective organisms, with or without neutrophils. Ascorbic acid or ulinastatin was used to neutralize reactive oxygen species or elastase secreted by neutrophils. Transwell sieve inserts or antibodies against leukocyte function antigen 1 or intercellular adhesion molecule 1 was used to study the effect of direct interaction between neutrophils and endothelial cells. The rate of apoptotic endothelial cells was determined by TUNEL and annexin staining.

MEASUREMENTS AND MAIN RESULTS

Incubation of endothelial cells with patient sera or culture supernatants (P. falciparum, E. coli, S. aureus) lead to higher apoptosis rates, compared with incubation with control sera or control supernatants. Addition of neutrophils augmented the apoptosis rate further. Addition of ascorbic acid or ulinastatin reduced endothelial apoptosis in the presence of neutrophils. Separation of neutrophils from endothelial cells with Transwell sieve inserts, or addition of anti-leukocyte function antigen-1 antibodies also reduced endothelial cell apoptosis. However, addition of anti-intercellular adhesion molecule-1 antibodies restored high apoptosis rates that had been reduced by Transwell inserts.

CONCLUSIONS

These in vitro results show how neutrophils can contribute to endothelial damage in malaria and in sepsis, both by their secretory products and by binding to intercellular adhesion molecule-1 on endothelial cells. The presence of similar pathomechanisms suggests that similar antiapoptotic strategies may offer potential benefit in malaria and in sepsis.

Characterization of bacterial DNA binding to human neutrophil surface

Bacterial DNA activates neutrophils through a CpG- and TLR9-independent mechanism. Neutrophil activation does not require DNA internalization, suggesting that it results from the interaction of bacterial DNA with a neutrophil surface receptor. The aim of this study was to characterize the interaction of bacterial DNA with the neutrophil surface. Bacterial DNA binding showed saturation and was inhibited by unlabeled DNA but not by other polyanions like yeast tRNA and poly-A. Resembling the conditions under which bacterial DNA triggers neutrophil activation, binding was not modified in the presence or absence of calcium, magnesium or serum. Treatment of neutrophils with proteases not only dramatically reduced bacterial DNA binding but also inhibited neutrophil activation induced by bacterial DNA. Experiments performed with DNA samples of different lengths obtained after digestion of bacterial DNA with DNase showed that only DNA fragments greater than approximately 170-180 nucleotides competed bacterial DNA binding and retained the ability to trigger cell activation. Treatment of neutrophils with chemoattractants or conventional agonists significantly increased bacterial DNA binding. Moreover, neutrophils that underwent transmigration through human endothelial cell monolayers even in the absence of chemoattractants, exhibited higher binding levels of bacterial DNA. Together, our findings provide evidence that binding of bacterial DNA to neutrophils is a receptor-mediated process that conditions the ability of DNA to trigger cell activation. We speculate that neutrophil recognition of bacterial DNA might be modulated by the balance of agonists present at inflammatory foci. This effect might be relevant in bacterial infections with a biofilm etiology, in which extracellular DNA could function as a potent neutrophil agonist.

Apoptotic cells protect mice against lipopolysaccharide-induced shock

LPS is a main causative agent of septic shock. There is a lack of effective therapies. In vitro studies have shown that uptake of apoptotic cells actively inhibits the secretion by activated macrophages (Mphi) of proinflammatory mediators such as TNF-alpha and that such uptake increases the antiinflammatory and immunosuppressive cytokine TGF-beta. We therefore investigated the protective effect of apoptotic cells against LPS-induced endotoxic shock in mice. The current report is the first study to demonstrate that administration of apoptotic cells can protect mice from LPS-induced death, even when apoptotic cells were administered 24 h after LPS challenge. The beneficial effects of administration of apoptotic cells included 1) reduced circulating proinflammatory cytokines, 2) suppression of polymorphonuclear neutrophil infiltration in target organs, and 3) decreased serum LPS levels. LPS can quickly bind to apoptotic cells and these LPS-coated apoptotic cells can be recognized and cleared by Mphi in a CD14/thrombospondin/vitronectin receptor-dependent manner, accompanied with suppression of TNF-alpha and enhancement of IL-10 expression by LPS-activated Mphi. Apoptotic cells may therefore have therapeutic potential for the treatment of septic shock.

Escherichia coli isolated from a Crohn's disease patient adheres, invades, and induces inflammatory responses in polarized intestinal epithelial cells

Inflammatory diseases of the intestinal tract are a major health concern both in the United States and around the world. Evidence now suggests that a new category of Escherichia coli, designated Adherent Invasive E. coli (AIEC) is highly prevalent in Crohn's Disease (CD) patients. AIEC strains have been shown to colonize and adhere to intestinal epithelial cells (IEC). However, the role AIEC strains play in the induction of an inflammatory response is not known. Therefore, we examined several E. coli strains (designated LF82, O83:H1, 6604 and 6655) that were isolated from CD patients for their ability to induce inflammation in two IEC, Caco-2BBe and T-84 cells. Results showed that each strain had varying abilities to adhere to and invade IEC as well as induced cytokine secretion from polarized IEC. However, E. coli O83:H1 displayed the best characteristics of AIEC strains as compared to the prototype AIEC strain LF82, inducing cytokine secretion from IEC and promoting immune cell migration through IEC. Upon further analysis, E. coli O83:H1 did not harbor virulence genes present in known pathogenic intestinal organisms. Further characterization of E. coli O83:H1 virulence determinants showed that a non-flagellated O83:H1 strain significantly decreased the organism's ability to adhere to and invade both IEC and elicit IEC cytokine secretion compared to the wild type and complemented strains. These findings demonstrate that E. coli O83:H1 possesses the characteristics of the AIEC LF82 strain that may contribute to the low-grade, chronic inflammation observed in Crohn's disease.

Vibrio vulnificus IlpA-induced cytokine production is mediated by Toll-like receptor 2

Vibrio vulnificus is a pathogenic bacterium causing primary septicemia, which follows a classical septic shock pathway, including an overwhelming inflammatory cytokine response. In this study, we identified a putative lipoprotein of V. vulnificus, encoded by the ilpA gene, as one of the surface proteins that specifically reacted with the antibodies raised against outer membrane proteins of V. vulnificus. Using a mutant V. vulnificus in which its ilpA gene was knocked out, we found that IlpA is important in the production of interferon-gamma in human peripheral blood mononuclear cells. Production of tumor necrosis factor-alpha and interleukin-6 is also induced by the recombinant IlpA (rIlpA) in human monocytes. Lipidation of the rIlpA was observed by in vivo labeling in Escherichia coli. Experiments using the mutant IlpA, which is unable to be modified by lipidation, indicate that the lipid moiety of this protein has an essential property for cytokine production in human cells. Pretreatment of monocytes with antibodies against Toll-like receptor 2 (TLR2) inhibited production of both tumor necrosis factor-alpha and interleukin-6. The role of TLR2 in IlpA-induced cytokine production was confirmed by an in vitro assay, in which only the TLR2-expressing cells showed a dramatic induction of nuclear factor-kappaB activity by rIlpA. In addition, rIlpA treatment resulted in induction of TLR2 transcription in human cells. In comparison with the wild type V. vulnificus, the ilpA mutant showed a reduced mortality in mice. These results demonstrate that IlpA of V. vulnificus functions as an immunostimulant to human cells via TLR2.

The role of Toll-like receptors in the regulation of neutrophil migration, activation, and apoptosis

Toll-like receptors (TLRs) play an essential role in the detection of invading pathogens and in the induction of host antimicrobial defenses. TLR4, the major endotoxin receptor, and TLR2, with agonists derived principally from gram-positive organisms, are likely to be important in the pathogenesis of sepsis. Both TLR2 and TLR4 agonists regulate important neutrophil functions, including adhesion, generation of reactive oxygen species, and release of chemokines, and activate major proinflammatory signaling pathways, including the nuclear factor- kappa B pathway. TLR stimulation produces only a modest direct inhibition of neutrophil apoptosis, although this signal is greatly amplified by the presence of monocytes, suggesting that regulation of the life span of neutrophils by TLR agonists may be principally mediated by responses of other endotoxin-responsive cells. We suggest that activation of neutrophils by TLRs is highly regulated, permitting acute neutrophil antimicrobial responses to TLR activation while providing a "brake" on inflammation by requiring the presence of mononuclear cells to significantly extend neutrophil survival.

Role of primary human alveolar epithelial cells in host defense against Francisella tularensis infection

Francisella tularensis, an intracellular pathogen, is highly virulent when inhaled. Alveolar epithelial type I (ATI) and type II (ATII) cells line the majority of the alveolar surface and respond to inhaled pathogenic bacteria via cytokine secretion. We hypothesized that these cells contribute to the lung innate immune response to F. tularensis. Results demonstrated that the live vaccine strain (LVS) contacted ATI and ATII cells by 2 h following intranasal inoculation of mice. In culture, primary human ATI or ATII cells, grown on transwell filters, were stimulated on the apical (AP) surface with virulent F. tularensis Schu 4 or LVS. Basolateral (BL) conditioned medium (CM), collected 6 and 24 h later, was added to the BL surfaces of transwell cultures of primary human pulmonary microvasculature endothelial cells (HPMEC) prior to the addition of polymorphonuclear leukocytes (PMNs) or dendritic cells (DCs) to the AP surface. HPMEC responded to S4- or LVS-stimulated ATII, but not ATI, CM as evidenced by PMN and DC migration. Analysis of the AP and BL ATII CM revealed that both F. tularensis strains induced various levels of a variety of cytokines via NF-kappaB activation. ATII cells pretreated with an NF-kappaB inhibitor prior to F. tularensis stimulation substantially decreased interleukin-8 secretion, which did not occur through Toll-like receptor 2, 2/6, 4, or 5 stimulation. These data indicate a crucial role for ATII cells in the innate immune response to F. tularensis.

The role of IFN-alpha as homeostatic agent in the inflammatory response: a balance between danger and response?

Interferon-alpha (IFN-alpha) is thought of by most immunologists as a fundamental component of the antiviral innate immune response, with other, accessory properties. Several lines of evidence point to a fundamental reappraisal of this conceptual framework because it may neglect other crucial functions of this cytokine under both health and disease conditions. Among these, a regulatory role in the inflammatory response is probably of paramount importance, as shown by in vivo and in vitro studies on humans, pets, and farm and laboratory animals. This role would not conflict with the main functions of IFN-alpha in the innate immune system and would complement these in line with major, evolution-based needs of the host. A hinge role of IFN-alpha between innate and adaptive immunity was recognized in the past on the basis of compelling evidence. This concept should now be widened; not only does IFN-alpha act to trigger, amplify, and sustain the different phases of the immune response, but it could also promote a substantial balance between danger and inflammatory response when an infectious challenge is either declining or completely over.

Direct stimulatory effects of the TLR2/6 ligand bacterial lipopeptide MALP-2 on neutrophil granulocytes

Bacterial lipopeptides represent a group of bacterial compounds able to trigger the functions of cells of the innate immune response. Whereas diacylated lipopeptides are recognized by TLR2/6 dimers, triacylated lipopeptides were shown to act via TLR2/1 dimers. Although several previous studies dealt with the effect of the TLR2/1 ligand Pam(3)CysSK(4) on neutrophil granulocytes (PMN), it is still not clear whether TLR2/6 ligand lipopeptides can directly influence PMN functions. In the present study we used highly purified human neutrophils to investigate the direct effects of the diacylated mycoplasmal macrophage activating lipopeptide-2 (MALP-2) on the function of neutrophil granulocytes. After exposure to 10 ng/ml MALP-2 neutrophils acquired activated cell shape, secreted IL-8 and MIP-1beta and their phagocytic capacity was enhanced. Analysis of cell surface activation markers confirmed the activating effect of MALP-2, the expression of CD62L was downregulated whereas CD11b was upregulated on PMN after exposure to MALP-2. The constitutive apoptosis of PMN was inhibited after exposure to MALP-2. However, MALP-2 exerted only a short-term effect on the apoptosis of resting neutrophils, a longer lasting effect was observed after transendothelial migration. MALP-2 did not directly induce the production of reactive oxygen intermediates but primed PMN for a fMLP-induced oxidative burst. The migration of neutrophils was enhanced after treatment with MALP-2. This was due, however, to a chemokinetic rather than to a chemotactic effect. Pam(3)CysSK(4) also activated PMN, but in comparison to MALP-2, at higher concentrations. These findings suggest that diacylated lipopeptides are important microbial structures recognized by and acting on neutrophil granulocytes.

Neutrophil Signaling Pathways Activated by Bacterial DNA Stimulation

We have previously shown that bacterial DNA activates human neutrophils in a CpG-independent manner. In this study, we have characterized the signaling pathways involved in the activation mechanism. We found that p38 MAPK, ERK1/2, and JNK pathways, as well as the PI3K/Akt pathway, are activated by bacterial DNA. We also determined that bacterial DNA induces NF-kappaB and AP-1 activation. When analyzing the role of these pathways on neutrophil functions, we observed that up-regulation of CD11b triggered by bacterial DNA was decreased by pharmacological inhibitors of the p38 MAPK, ERK1/2, and JNK, whereas stimulation of IL-8 release was dependent on p38, ERK1/2, and NF-kappaB. Moreover, we found that IL-8 production was markedly enhanced by inhibition of JNK, suggesting that this pathway negatively modulates NF-kappaB-dependent transcription. We also observed that bacterial DNA stimulated IL-1R-associated kinase-1 kinase activity and its partial degradation. Finally, we determined that bacterial DNA stimulated CD11b up-regulation in TLR9(-/-) but not in MyD88(-/-) mouse neutrophils, supporting that bacterial DNA induces neutrophil activation through a TLR9-independent and MyD88-dependent pathway.

Protective effect of paeoniflorin on immunological liver injury induced by bacillus Calmette-Guerin plus lipopolysaccharide: modulation of tumour necrosis factor-alpha and interleukin-6 MRNA

1. Paeoniflorin is one of the main effective components of the total glucosides of paeony (TGP) extracted from the root of Paeonia lactiflora which has been used for gynaecological problems and for cramp, pain and giddiness for over 1,500 years in Chinese medicine. Anti-inflammatory, antioxidative, antihepatic injury and immunoregulatory activities of TGP have been extensively proved in our laboratory for many years. Our present study investigates the effects and mechanisms of paeoniflorin on immunological liver injury in mice. 2. A model of immunological liver injury was induced by tail vein injection of bacillus Calmette-Guérin (BCG) and lipopolysaccharide (LPS) in mice. Activities of serum alanine aminotransferase (ALT) were measured by biochemical methods. Hepatic tissue sections were stained with haematoxylin and eosin and examined under a light microscope. Tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, lipopolysaccharide binding protein (LBP) and CD14 mRNA (messenger ribonucleic acid) expression in mouse liver were determined by semiquantitative reverse transcription polymerase chain reaction (RT-PCR) analysis. 3. Immunological liver injury induced by BCG plus LPS was successfully duplicated. Serum ALT activities were significantly decreased by paeoniflorin. (25, 50, 100 mg/kg). Histological examination demonstrated that paeoniflorin could attenuate the area and extent of necrosis and reduce the immigration of inflammatory cells. The increase in TNF-alpha, LBP and CD14 mRNA expression in mouse liver after BCG and LPS injection was significantly decreased by paeoniflorin (100 mg/kg) and was changed by paeoniflorin (25, 50 mg/kg) at different time-point. The augmentation of IL-6 mRNA in mouse liver was markedly increased by paeoniflorin at 1 h and 3 h after LPS injection. 4. Paeoniflorin could significantly protect against immunological liver injury in mice. TNF-alpha, IL-6, LBP and CD14 mRNA expression in mouse liver may be involved in BCG plus LPS induced liver injury. The protective mechanism of paeoniflorin might be partially related to modulation of TNF-alpha, IL-6, LBP and CD14 mRNA expressions in mouse liver.

Upregulation of TNF-alpha and IL-6 mRNA in mouse liver induced by bacille Calmette-Guerin plus lipopolysaccharide

AIM

To investigate the mechanism of immunological liver injury induced by bacille Calmette-Guerin (BCG) plus lipopolysaccharide (LPS).

METHODS

Mice were injected via the tail vein with 125 mg/kg BCG, and 12 d later, the mice were injected intravenously with different doses of LPS (125, 250, or 375 microg/kg). Serum alanine aminotransferase (ALT) activity and liver pathological changes were examined. The expression of tumor necrosis factor (TNF)- alpha, interleukin (IL)-6, lipopolysaccharide binding protein (LBP) and CD14 mRNA, and NF-kappaB and IkappaB-alpha protein in mouse liver at different time points after BCG and LPS injection were measured using RT-PCR, immunohistochemistry and Western blotting analysis, respectively.

RESULTS

The activity of serum ALT in mice treated with BCG and LPS was significantly increased. Different degrees of liver injury, such as inflammatory cell infiltration, spotty necrosis, piecemeal necrosis, even bridging necrosis, could be seen in liver sections from mice after BCG and LPS administration. Furthermore, the levels of TNF-alpha and IL-6 mRNA in mouse liver were significantly elevated after administration of BCG plus LPS (P<0.05). The levels of LBP and CD14 mRNA in mouse liver were markedly upregulated after treatment with BCG and LPS, and treatment with BCG alone led to an increase in CD14 mRNA in mouse liver. Finally, immunoreactivity for NF-kappaB p65 was predominantly detected in hepatocyte nuclei from mice treated with BCG plus LPS, compared with the normal group. Protein levels of IkappaB-alpha were strikingly decreased by LPS or BCG plus LPS treatment, compared with the normal group or BCG group.

CONCLUSION

TNF-alpha and IL-6 mRNA were partially involved in early immunological liver injury induced by challenge with small doses of LPS after BCG priming. Upregulation of TNF-alpha and IL-6 mRNA might be related to increases in LBP and CD14 mRNA expression and activation of NF-kappaB. Furthermore, BCG priming in immunological liver injury may occur via upregulation of CD14 mRNA expression in mononuclear cell infiltration into the liver.

CD14 expression on Kupffer cells during the course of carbon tetrachloride-mediated liver injury

OBJECTIVE

To investigate the expression of CD14 on Kupffer cells during the course of carbon tetrachloride (CCl(4))-mediated liver injury and its role in the activation of Kupffer cells.

METHODS

Rats were administered CCl(4) twice weekly for up to 8 weeks. Kupffer cells were isolated from normal and CCl(4)-treated rats by the combined 'collagenase-pronase' perfusion method, discontinuous density gradient centrifugation. On the day after isolation, the cells were incubated with RPMI-1640 containing varying doses of lipopolysaccharide (LPS) for 6 h. Supernatants were then collected for measuring the concentration of tumor necrosis factor-alpha (TNF-alpha) by enzyme-linked immunosorbent assay (ELISA). The expression of CD14 mRNA on Kupffer cells were determined by RT-PCR. The plasma concentrations of endotoxin were determined by chromogenic substrate Limulus amebocyte lysate assay.

RESULTS

Basic TNF-alpha production of Kupffer cells isolated from CCl(4)-treated rats at 4 and 6 weeks was significantly higher than that of normal (P < 0.05). Following LPS stimulation the production of TNF-alpha was markedly increased in Kupffer cells from the 2-, 4- and 6-week treatment groups (P < 0.05). Moreover, LPS-induced TNF-alpha production was dose-dependent. CD14 mRNA expression on Kupffer cells isolated from CCl(4)-treated rats was elevated following 2 weeks of CCl(4) administration and the maximum elevation occurred at 6 weeks. Gene expression was decreased in Kupffer cells after 8 weeks of CCl(4) treatment. CCl(4) administration elicited extensive changes in liver morphology, including steatosis, inflammation and necrosis. The plasma concentrations of endotoxin of CCl(4)-treated rats were increased during the time of liver injury.

CONCLUSION

Up-regulation of CD14 expression in Kupffer cells during CCl(4)-mediated chronic liver injury indicates cell activation and that they are more sensitive to LPS stimulation. Kupffer cells are critical effector cells in the early stage of liver injury.

Effects of IFN-α on the Inflammatory Response of Swine Leukocytes to Bacterial Endotoxin

Because low-dose interferon-alpha (IFN-alpha) treatment had proved effective in several models of chronic inflammation and autoimmune disease, a possible role of IFN-alpha in modulating the response of swine leukocytes to bacterial endotoxin was investigated in this study. Exposure of swine peripheral blood mononuclear cells (PBMC) to low concentrations of human IFN-alpha caused a strong, dose-dependent decrease in CD14 expression, the lowest level being observed at 5 U/ml IFN-alpha. This result was confirmed if PBMC were later exposed to purified lipopolysaccharide (LPS). A 10-fold lower IFN-alpha concentration (0.5 U/ml) caused the largest reduction of tumor necrosis factor-alpha (TNF-alpha) accumulation in the medium of pulmonary alveolar macrophages (PAM), stimulated with bacterial LPS. At 0.5 U/ml, the expression of the TNF-alpha gene in PAM was also strongly reduced, as opposed to cells pretreated with 50 U/ml IFN-alpha. In contrast, expression of the interleukin-1beta (IL- 1beta) gene was stimulated and that of the IL-6 gene was not significantly affected at both IFN-alpha concentrations. Results point to an important role of IFN-alpha in control of the inflammatory response to bacterial endotoxin in pigs.

The expression and roles of Toll-like receptors in the biology of the human neutrophil

Neutrophils are amongst the first immune cells to arrive at sites of infection, where they initiate antimicrobial and proinflammatory functions, which serve to contain infection. Sensing and defeating microbial infections are daunting tasks as a result of their molecular heterogeneity; however, Toll-like receptors (TLRs) have emerged as key components of the innate-immune system, activating multiple steps in the inflammatory reaction, eliminating invading pathogens, and coordinating systemic defenses. Activated neutrophils limit infection via the phagocytosis of pathogens and by releasing antimicrobial peptides and proinflammatory cytokines and generating reactive oxygen intermediates. Through the production of chemokines, they additionally recruit and activate other immune cells to aid the clearance of the microbes and infected cells and ultimately, mount an adaptive immune response. In acute inflammation, influx of neutrophils from the circulation leads to extremely high cell numbers within tissues, which is exacerbated by their delayed, constitutive apoptosis caused by local inflammatory mediators, potentially including TLR agonists. Neutrophil apoptosis and safe removal by phagocytic cells limit tissue damage caused by release of neutrophil cytotoxic granule contents. This review addresses what is currently known about the function of TLRs in the biology of the human neutrophil, including the regulation of TLR expression, their roles in cellular recruitment and activation, and their ability to delay apoptotic cell death.