Neutrophils at work

Hantavirus-induced disruption of the endothelial barrier: neutrophils are on the payroll

Viral hemorrhagic fever caused by hantaviruses is an emerging infectious disease for which suitable treatments are not available. In order to improve this situation a better understanding of hantaviral pathogenesis is urgently required. Hantaviruses infect endothelial cell layers in vitro without causing any cytopathogenic effect and without increasing permeability. This implies that the mechanisms underlying vascular hyperpermeability in hantavirus-associated disease are more complex and that immune mechanisms play an important role. In this review we highlight the latest developments in hantavirus-induced immunopathogenesis. A possible contribution of neutrophils has been neglected so far. For this reason, we place special emphasis on the pathogenic role of neutrophils in disrupting the endothelial barrier.

Inflammation in cystic fibrosis lung disease: Pathogenesis and therapy

Lung disease is the major cause of morbidity and mortality in patients with cystic fibrosis (CF). Although CF lung disease is primarily an infectious disorder, the associated inflammation is both intense and ineffective at clearing pathogens. Persistent high-intensity inflammation leads to permanent structural damage of the CF airways and impaired lung function that eventually results in respiratory failure and death. Several defective inflammatory responses have been linked to cystic fibrosis transmembrane conductance regulator (CFTR) deficiency including innate and acquired immunity dysregulation, cell membrane lipid abnormalities, various transcription factor signaling defects, as well as altered kinase and toll-like receptor responses. The inflammation of the CF lung is dominated by neutrophils that release oxidants and proteases, particularly elastase. Neutrophil elastase in the CF airway secretions precedes the appearance of bronchiectasis, and correlates with lung function deterioration and respiratory exacerbations. Anti-inflammatory therapies are therefore of particular interest for CF lung disease but must be carefully studied to avoid suppressing critical elements of the inflammatory response and thus worsening infection. This review examines the role of inflammation in the pathogenesis of CF lung disease, summarizes the results of past clinical trials and explores promising new anti-inflammatory options.

ADAM9 disintegrin domain activates human neutrophils through an autocrine circuit involving integrins and CXCR2

ADAM9 is a member of the ADAM family whose expression positively correlates with tumor progression. Besides the metalloprotease activity, ADAM9D interacts with different integrins, modulating cell-adhesion events. Previous studies pointed to an important role for neutrophils in tumor development, as the inhibition of neutrophil migration or depletion of this immune cell impairs tumor growth. However, our understanding of the molecular mechanisms involved in this process, as well as the main key players acting on neutrophils, is very limited. Here, we investigated the possible modulatory effects of ADAM9D on human neutrophil functions. Our results show that ADAM9D promotes neutrophil activation and chemotaxis in a process that depends on the engagement of α_vβ₃ and α₉β₁ integrins and on the activation of PI3K/Akt and MAPK signaling pathway. ADAM9D impairs migration of neutrophils toward fMLP, LTB₄, and IL-8 as classic chemoattractants. This effect is blocked by PTX, a G(i)PCR inhibitor. Furthermore, CXCR2 antagonists RPTX and SB225002 also impaired neutrophil chemotaxis in response to ADAM9D, suggesting a hierarchical cross-talk of integrins with CXCR2. Our results indicate that ADAM9D activates neutrophil functions and may be implicated in the inflammatory events associated with cancer and other disorders.

Free Light Chains in patients with acute coronary syndromes: Relationships to inflammation and renal function

AIMS

We assessed changes of serum combined free immunoglobulin light chains (cFLC) levels, which are associated with increased all-cause mortality, in ST-elevation myocardial infarction (STEMI) in relation to inflammation and renal function indices.

METHODS

cFLC were measured in 48 patients with STEMI on days 1, 3, 7 and 30 with assessment of their relationships with monocyte subsets, high sensitivity C-reactive protein (hsCRP), and cystatin C. Day 1 levels in STEMI patients were compared to 40 patients with stable coronary artery disease, and 37 healthy controls.

RESULTS

There were no significant differences in cFLC levels between the study groups. In STEMI patients, cFLC values peaked on day 7 post-MI and remained elevated on day 30 (p<0.001 vs. day 1 for both). hsCRP concentrations peaked on day 3 of STEMI followed by their gradual reduction to the levels seen in the controls (p<0.001). In STEMI cFLC correlated with cystatin C (r=0.55, p<0.001), and negatively correlated with counts of CD14++CD16- monocytes (r=-0.55, p<0.001). On multivariate Cox regression analysis, cFLC concentrations were associated with increased need for future percutaneous coronary intervention (PCI) (p=0.019).

CONCLUSION

cFLC levels increase during STEMI with peak values on day 7 after presentation and predict the need for future PCI.

Myeloperoxidase scavenges peroxynitrite: A novel anti-inflammatory action of the heme enzyme

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Ferric myeloperoxidase accelerates the decomposition of peroxynitrite.

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Compound I of myeloperoxidase does not promote this removal of peroxynitrite.

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Peroxynitrite removal is enhanced by substances reacting well with myeloperoxidase Compound II.

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In the presence of H₂O₂, peroxynitrite diminishes the chlorinating activity of myeloperoxidase.

Peroxynitrite, a potent pro-inflammatory and cytotoxic species, interacts with a variety of heme containing proteins. We addressed the question whether (i) the interaction of myeloperoxidase (MPO, an enzyme generating hypochlorous acid from hydrogen peroxide and chloride ions) with peroxynitrite affects the clearance of peroxynitrite, and (ii) if peroxynitrite could modulate the chlorinating activity of MPO. Our results show that this interaction promotes the decomposition of the highly reactive pro-inflammatory oxidant, whereby MPO Compound II (but not Compound I) is formed. The efficiency of MPO to remove peroxynitrite was enhanced by l-tyrosine, nitrite and (−)-epicatechin, substances known to reduce Compound II with high reaction rate. Next, peroxynitrite (added as reagent) diminished the chlorinating activity of MPO in the presence of hydrogen peroxide. Alternatively, SIN-1, a peroxynitrite donor, reduced hypochlorous acid formation by MPO, as measured by aminophenyl fluorescein oxidation (time kinetics) and taurine chloramine formation (end point measurement). At inflammatory loci, scavenging of peroxynitrite by MPO may overcome the uncontrolled peroxynitrite decomposition and formation of reactive species, which lead to cell/tissue damage.

Neutrophils and inflammatory metabolism in antimicrobial functions of the mucosa

In this mini-review, we will discuss recent findings that implicate neutrophil infiltration and function in establishing a metabolic environment to facilitate efficient pathogen clearance. For decades, neutrophils have been regarded as short lived, nonspecific granulocytes, equipped with toxic antimicrobial factors and a respiratory burst generating ROS. Recent findings demonstrate the importance of HIF signaling in leukocytes and surrounding tissues during inflammation. Here, we will review the potential mechanisms and outcomes of HIF stabilization within the intestinal mucosa.

The α2,3-sialyltransferase encoded by myxoma virus is a virulence factor that contributes to immunosuppression

Myxoma virus (MYXV) induces a lethal disease called Myxomatosis in European rabbits. MYXV is one of the rare viruses that encodes an α2,3-sialyltransferase through its M138L gene. In this study, we showed that although the absence of the enzyme was not associated with any in vitro deficit, the M138L deficient strains are highly attenuated in vivo. Indeed, while all rabbits infected with the parental and the revertant strains died within 9 days post-infection from severe myxomatosis, all but one rabbit inoculated with the M138L deficient strains survived the infection. In primary lesions, this resistance to the infection was associated with an increased ability of innate immune cells, mostly neutrophils, to migrate to the site of virus replication at 4 days post-infection. This was followed by the development of a better specific immune response against MYXV. Indeed, at day 9 post-infection, we observed an important proliferation of lymphocytes and an intense congestion of blood vessels in lymph nodes after M138L knockouts infection. Accordingly, in these rabbits, we observed an intense mononuclear cell infiltration throughout the dermis in primary lesions and higher titers of neutralizing antibodies. Finally, this adaptive immune response provided protection to these surviving rabbits against a challenge with the MYXV WT strain. Altogether, these results show that expression of the M138L gene contributes directly or indirectly to immune evasion by MYXV. In the future, these results could help us to better understand the pathogenesis of myxomatosis but also the importance of glycans in regulation of immune responses.

Human neutrophils secrete bioactive paucimannosidic proteins from azurophilic granules into pathogen-infected sputum

Unlike plants and invertebrates, mammals reportedly lack proteins displaying asparagine (N)-linked paucimannosylation (mannose(1-3)fucose(0-1)N-acetylglucosamine(2)Asn). Enabled by technology advancements in system-wide biomolecular characterization, we document that protein paucimannosylation is a significant host-derived molecular signature of neutrophil-rich sputum from pathogen-infected human lungs and is negligible in pathogen-free sputum. Five types of paucimannosidic N-glycans were carried by compartment-specific and inflammation-associated proteins of the azurophilic granules of human neutrophils including myeloperoxidase (MPO), azurocidin, and neutrophil elastase. The timely expressed human azurophilic granule-resident β-hexosaminidase A displayed the capacity to generate paucimannosidic N-glycans by trimming hybrid/complex type N-glycan intermediates with relative broad substrate specificity. Paucimannosidic N-glycoepitopes showed significant co-localization with β-hexosaminidase A and the azurophilic marker MPO in human neutrophils using immunocytochemistry. Furthermore, promyelocyte stage-specific expression of genes coding for paucimannosidic proteins and biosynthetic enzymes indicated a novel spatio-temporal biosynthetic route in early neutrophil maturation. The absence of bacterial exoglycosidase activities and paucimannosidic N-glycans excluded exogenous origins of paucimannosylation. Paucimannosidic proteins from isolated and sputum neutrophils were preferentially secreted upon inoculation with virulent Pseudomonas aeruginosa. Finally, paucimannosidic proteins displayed affinities to mannose-binding lectin, suggesting immune-related functions of paucimannosylation in activated human neutrophils. In conclusion, we are the first to document that human neutrophils produce, store and, upon activation, selectively secrete bioactive paucimannosidic proteins into sputum of lungs undergoing pathogen-based inflammation.

Molecular control of PtdIns(3,4,5)P3 signaling in neutrophils

Neutrophils play critical roles in innate immunity and host defense. However, excessive neutrophil accumulation or hyper-responsiveness of neutrophils can be detrimental to the host system. Thus, the response of neutrophils to inflammatory stimuli needs to be tightly controlled. Many cellular processes in neutrophils are mediated by localized formation of an inositol phospholipid, phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3), at the plasma membrane. The PtdIns(3,4,5)P3 signaling pathway is negatively regulated by lipid phosphatases and inositol phosphates, which consequently play a critical role in controlling neutrophil function and would be expected to act as ideal therapeutic targets for enhancing or suppressing innate immune responses. Here, we comprehensively review current understanding about the action of lipid phosphatases and inositol phosphates in the control of neutrophil function in infection and inflammation.

Complement inhibition in a xenogeneic model of interactions between human whole blood and porcine endothelium

Xenotransplantation (xeno-Tx) is considered as an alternative solution to overcome the shortage of human donor organs. However, the success of xeno-Tx is hindered by immune reactions against xenogeneic cells (e. g. of porcine origin). More specifically, activation of innate immune mechanisms such as complement and triggering of the coagulation cascade occur shortly after xeno-Tx, and adhesion of human leukocytes to porcine endothelium is another early critical step mediating the immune attack. To investigate the therapeutic potential of complement inhibition in the context of xenogeneic interactions, we have employed a whole-blood model in the present study. Incubation of human blood with porcine endothelial cells (PAECs) led to activation of complement and coagulation as well as to increased leukocyte adhesion. The observed responses can be attributed to the pig-to-human xenogeneicity, since the presence of human endothelium induced a minor cellular and plasmatic inflammatory response. Importantly, complement inhibition using a potent complement C3 inhibitor, compstatin analogue Cp40, abrogated the adhesion of leukocytes and, more specifically, the attachment of neutrophils to porcine endothelium. Moreover, Cp40 inhibited the activation of PAECs and leukocytes, since the levels of the adhesion molecules E-selectin, ICAM-1, ICAM-2, and VCAM-1 on PAECs and the surface expression of integrin CD11b on neutrophils were significantly decreased. Along the same line, inhibition of CD11b resulted in decreased leukocyte adhesion. Taken together, our findings provide a better understanding of the mechanisms regulating the acute innate immune complications in the context of xeno-Tx and could pave the way for complement-targeting therapeutic interventions.

The methyltransferase Setdb2 mediates virus-induced susceptibility to bacterial superinfection

Immune responses are tightly regulated to ensure efficient pathogen clearance while avoiding tissue damage. Here we report that Setdb2 was the only protein lysine methyltransferase induced during infection with influenza virus. Setdb2 expression depended on signaling via type I interferons, and Setdb2 repressed expression of the gene encoding the neutrophil attractant CXCL1 and other genes that are targets of the transcription factor NF-κB. This coincided with occupancy by Setdb2 at the Cxcl1 promoter, which in the absence of Setdb2 displayed diminished trimethylation of histone H3 Lys9 (H3K9me3). Mice with a hypomorphic gene-trap construct of Setdb2 exhibited increased infiltration of neutrophils during sterile lung inflammation and were less sensitive to bacterial superinfection after infection with influenza virus. This suggested that a Setdb2-mediated regulatory crosstalk between the type I interferons and NF-κB pathways represents an important mechanism for virus-induced susceptibility to bacterial superinfection.

Enzymatic 'stripping' and degradation of PEGylated carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) coated or functionalized with PEG chains of different molecular weight were assessed for their propensity to undergo biodegradation under in vitro conditions using recombinant myeloperoxidase (MPO) or ex vivo using freshly isolated primary human neutrophils. Our findings suggest that under natural conditions, a combined process of 'stripping' (i.e., defunctionalization) and biodegradation of PEG-SWCNTs might occur and that PEG-SWCNTs are a promising--and degradable--nanomedicine vector.

Neutrophil priming occurs in a sequential manner and can be visualized in living animals by monitoring IL-1β promoter activation

Rapid enhancement of phagocyte functionality is a hallmark of neutrophil priming. GeneChip analyses unveiled elevated CD54, dectin-2, and IL-1β mRNA expression by neutrophils isolated from inflammatory sites. In fact, CD54 and dectin-2 protein expression was detected on neutrophils recovered from skin, peritoneal, and lung inflammation lesions but not on those in bone marrow or peripheral blood. Neutrophils increased CD54 and dectin-2 mRNA during migration in Boyden chambers and acquired CD54 and dectin-2 surface expression after subsequent exposure to GM-CSF. Neutrophils purified from IL-1β promoter-driven DsRed-transgenic mice acquired DsRed signals during cell migration or exposure to GM-CSF. CD54 and dectin-2 were expressed by DsRed(+) (but not DsRed(-)) neutrophils in GM-CSF-supplemented cultures, and neutrophils recovered from inflammatory sites exhibited strong DsRed signals. The dynamic process of neutrophil priming was studied in chemically induced inflammatory skin lesions by monitoring DsRed expression using confocal microscopy. A majority (>80%) of Ly6G(+) neutrophils expressed DsRed, and those DsRed(+)/Ly6G(+) cells exhibited crawling motion with a higher velocity compared with their DsRed(-)/Ly6G(+) counterparts. This report unveils motile behaviors of primed neutrophils in living animals. We propose that neutrophil priming occurs in a sequential manner with rapid enhancement of phagocyte functionality, followed by CD54 and dectin-2 mRNA and protein expression, IL-1β promoter activation, and accelerated motility. Not only do these findings provide a new conceptual framework for our understanding of the process of neutrophil priming, they also unveil new insights into the pathophysiology of many inflammatory disorders that are characterized by neutrophil infiltration.

Anti-inflammatory effects of secondary metabolites of marine Pseudomonas sp. in human neutrophils are through inhibiting P38 MAPK, JNK, and calcium pathways

Activated neutrophils play a significant role in the pathogenesis of many inflammatory diseases. The metabolites of marine microorganisms are increasingly employed as sources for developing new drugs; however, very few marine drugs have been studied in human neutrophils. Herein, we showed that secondary metabolites of marine Pseudomonas sp. (N11) significantly inhibited superoxide anion generation and elastase release in formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP)-activated human neutrophils, with IC50 values of 0.67±0.38 µg/ml and 0.84±0.12 µg/ml, respectively. In cell-free systems, neither superoxide anion-scavenging effect nor inhibition of elastase activity was associated with the suppressive effects of N11. N11 inhibited the phosphorylation of p38 MAP kinase and JNK, but not Erk and Akt, in FMLP-induced human neutrophils. Also, N11 dose-dependently attenuated the transient elevation of intracellular calcium concentration in activated neutrophils. In contrast, N11 failed to alter phorbol myristate acetate-induced superoxide anion generation, and the inhibitory effects of N11 were not reversed by protein kinase A inhibitor. In conclusion, the anti-inflammatory effects of N11 on superoxide anion generation and elastase release in activated human neutrophils are through inhibiting p38 MAP kinase, JNK, and calcium pathways. Our results suggest that N11 has the potential to be developed to treat neutrophil-mediated inflammatory diseases.

Proteinase 3 and Serpin B1: a novel pathway in the regulation of caspase-3 activation, neutrophil spontaneous apoptosis, and inflammation

Neutrophils are the first responders of the inflammatory response. They are characterized by their potent cytotoxic content but also by their limited lifetime. This short half-life is thought to be a self-protecting mechanism for the host, as highlighted by the numerous pathologies associated with imbalanced neutrophil survival. Neutrophil spontaneous death is the prototype of programmed cell death, harboring all the phenotypic hallmarks of apoptosis and dependent on the activation of the effector caspase-3. However, the pathways regulating neutrophil spontaneous death remain ill-defined. In a recent publication, we determined that in aging neutrophils, the cleavage and activation of caspase-3 was mediated by the serine protease Proteinase 3 (PR3), and was independent of the canonical extrinsic and intrinsic apoptosis pathways. In mature neutrophils, PR3 was stored in granules and progressively released to the cytosol during neutrophil aging. The release of PR3 was dependent on lysosomal membrane permeabilization (LMP). Once in the cytosol, PR3 cleaved procaspase-3 at a site upstream of the caspase-9 cleavage site, leading to caspase-3 activation. Inhibition, knockdown or knockout of PR3 delayed neutrophil apoptosis in vitro and in vivo. The adoptive transfer of both WT and PR3-deficient neutrophils to WT mice revealed that the delayed death of neutrophils lacking PR3 in vivo was due to an altered intrinsic apoptosis/survival pathway and not to difference in the inflammatory microenvironment. The cytosolic inhibitor of serine proteases serpin b1 counterbalanced the activity of PR3 in the cytosol of neutrophils, and the deletion of serpinb1 in neutrophils accelerated their spontaneous death. In summary, our results reveal that PR3 and serpinB1 are part of a newly characterized apoptosis pathway, regulating caspase-3 activation and neutrophil spontaneous death and the survival of neutrophils during inflammation.

Neutrophil serine proteases in antibacterial defense

Neutrophil serine proteases (NSPs) are critical for the effective functioning of neutrophils and greatly contribute to immune protection against bacterial infections. Thanks to their broad substrate specificity, these chymotrypsin-like proteases trigger multiple reactions that are detrimental to bacterial survival such as direct bacterial killing, generation of antimicrobial peptides, inactivation of bacterial virulence factors and formation of neutrophil extracellular traps. Recently, the importance of NSPs in antibacterial defenses has been further underscored by discoveries of unique bacterial evasion strategies to combat these proteases. Bacteria can indirectly disarm NSPs by protecting bacterial substrates against NSP cleavage, but also produce inhibitory molecules that potently block NSPs. Here we review recent insights in the functional contribution of NSPs in host protection against bacterial infections and the elegant strategies that bacteria use to counteract these responses.

Biologic scaffolds for regenerative medicine: mechanisms of in vivo remodeling

Successful regenerative medicine strategies for functional tissue reconstruction include the in situ placement of acellular materials composed of the extracellular matrix (ECM) or individual components of the ECM. The composition and ultrastructure of these materials vary depending on multiple factors including the tissue source and species from which the materials are harvested, the methods of manufacture, the efficiency of decellularization, post-processing modifications such as chemical cross-linking or solubilization, and the methods of terminal sterilization. Appropriately configured materials have the ability to modulate different stages of the healing response by inducing a shift from a process of inflammation and scar tissue formation to one of constructive remodeling and functional tissue restoration. The events that facilitate such a dramatic change during the biomaterial-host interaction are complex and necessarily involve both the immune system and mechanisms of stem cell recruitment, growth, and differentiation. The present manuscript reviews the composition of biologic scaffolds, the methods and recommendations for manufacture, the mechanisms of the biomaterial-host interaction, and the clinical application of this regenerative medicine approach.