How neutrophils kill microbes

A specific p47phox -serine phosphorylated by convergent MAPKs mediates neutrophil NADPH oxidase priming at inflammatory sites

Neutrophil NADPH oxidase plays a key role in host defense and in inflammation by releasing large amounts of superoxide and other ROSs. Proinflammatory cytokines such as GM-CSF and TNF-alpha prime ROS production by neutrophils through unknown mechanisms. Here we used peptide sequencing by tandem mass spectrometry to show that GM-CSF and TNF-alpha induce phosphorylation of Ser345 on p47phox, a cytosolic component of NADPH oxidase, in human neutrophils. As Ser345 is located in the MAPK consensus sequence, we tested the effects of MAPK inhibitors. Inhibitors of the ERK1/2 pathway abrogated GM-CSF-induced phosphorylation of Ser345, while p38 MAPK inhibitor abrogated TNF-alpha-induced phosphorylation of Ser345. Transfection of HL-60 cells with a mutated p47phox (S345A) inhibited GM-CSF- and TNF-alpha-induced priming of ROS production. This event was also inhibited in neutrophils by a cell-permeable peptide containing a TAT-p47phox-Ser345 sequence. Furthermore, ROS generation, p47phox-Ser345 phosphorylation, and ERK1/2 and p38 MAPK phosphorylation were increased in synovial neutrophils from rheumatoid arthritis (RA) patients, and TAT-Ser345 peptide inhibited ROS production by these primed neutrophils. This study therefore identifies convergent MAPK pathways on Ser345 that are involved in GM-CSF- and TNF-alpha-induced priming of neutrophils and are activated in RA. Inhibition of the point of convergence of these pathways might serve as a novel antiinflammatory strategy.

The tripeptide feG regulates the production of intracellular reactive oxygen species by neutrophils

BACKGROUND

The D-isomeric form of the tripeptide FEG (feG) is a potent anti-inflammatory agent that suppresses type I hypersensitivity (IgE-mediated allergic) reactions in several animal species. One of feG's primary actions is to inhibit leukocyte activation resulting in loss of their adhesive and migratory properties. Since activation of neutrophils is often associated with an increase in respiratory burst with the generation of reactive oxygen species (ROS), we examined the effect of feG on the respiratory burst in neutrophils of antigen-sensitized rats. A role for protein kinase C (PKC) in the actions of feG was evaluated by using selective isoform inhibitors for PKC.

RESULTS

At 18 h after antigen (ovalbumin) challenge of sensitized Sprague-Dawley rats a pronounced neutrophilia occurred; a response that was reduced in animals treated with feG (100 microg/kg). With antigen-challenged animals the protein kinase C (PKC) activator, PMA, significantly increased intracellular ROS of circulating neutrophils, as determined by flow cytometry using the fluorescent probe dihydrorhodamine-123. This increase was prevented by treatment with feG at the time of antigen challenge. The inhibitor of PKCdelta, rottlerin, which effectively prevented intracellular ROS production by circulating neutrophils of animals receiving a naïve antigen, failed to inhibit PMA-stimulated ROS production if the animals were challenged with antigen. feG treatment, however, re-established the inhibitory effects of the PKCdelta inhibitor on intracellular ROS production. The extracellular release of superoxide anion, evaluated by measuring the oxidative reduction of cytochrome C, was neither modified by antigen challenge nor feG treatment. However, hispidin, an inhibitor of PKCbeta, inhibited the release of superoxide anion from circulating leukocytes in all groups of animals. feG prevented the increased expression of the beta1-integrin CD49d on the circulating neutrophils elicited by antigen challenge.

CONCLUSION

feG reduces the capacity of circulating neutrophils to generate intracellular ROS consequent to an allergic reaction by preventing the deregulation of PKCdelta. This action of feG may be related to the reduction in antigen-induced up-regulation of CD49d expression on circulating neutrophils.

Gene expression in splenic CD4 and CD8 cells from BALB/c mice immunized with Porphyromonas gingivalis

BACKGROUND

T cells are fundamental in the pathogenesis of periodontal disease. Suppression of cell-mediated responses is associated with disease progression together with the concomitant increase in plaque pathogens including Porphyromonas gingivalis. The aim of the present study was to examine gene expression in T cells in response to P. gingivalis in mice.

METHODS

BALB/c mice were given weekly intraperitoneal injections of P. gingivalis outer-membrane antigens with Freund's incomplete adjuvant for 3 weeks, whereas control mice received phosphate buffered saline (PBS) and adjuvant only. Splenic CD4 and CD8 subpopulations were isolated by magnetic cell separation and their responses investigated using microarray analysis.

RESULTS

Most genes coded for enzymes concerned with metabolic pathways. Only five and 28 genes, respectively, were upregulated in CD4 and CD8 cells extracted from P. gingivalis-immunized mice, including immunoglobulin (Ig) heavy-chain genes for IgG1 and IgG2a in CD4 cells. In contrast, 1,141 and 1,175 genes, respectively, were downregulated. A total of 60 and 65 genes, respectively, coded for immune response proteins or those relevant to periodontal disease pathogenesis. The overlap of genes in the two subsets was 21%. One of the major effects, apart from T-cell function suppression, was the shift away from Th1 responses, although there was also a downregulation of two genes and upregulation of one Th2-response gene. Genes downregulated included those encoding cytokines, proteins involved in Ig binding, antigen presentation, innate immunity, extracellular matrix, and cell adhesion molecules that could result in dysregulation in the progressive periodontal lesion.

CONCLUSIONS

Early findings in humans demonstrated that periodontopathic bacteria induce immunosuppressive effects on T cells. The present study has shown that P. gingivalis had a predominant downregulatory effect on gene expression in CD4 and CD8 T cells in mice.

DNase expression allows the pathogen group A Streptococcus to escape killing in neutrophil extracellular traps

The innate immune response plays a crucial role in satisfactory host resolution of bacterial infection. In response to chemotactic signals, neutrophils are early responding cells that migrate in large numbers to sites of infection. The recent discovery of secreted neutrophil extracellular traps (NETs) composed of DNA and histones opened a novel dimension in our understanding of the microbial killing capacity of these specialized leukocytes. M1 serotype strains of the pathogen Group A Streptococcus (GAS) are associated with invasive infections including necrotizing fasciitis (NF) and express a potent DNase (Sda1). Here we apply a molecular genetic approach of allelic replacement mutagenesis, single gene complementation, and heterologous expression to demonstrate that DNase Sda1 is both necessary and sufficient to promote GAS neutrophil resistance and virulence in a murine model of NF. Live fluorescent microscopic cell imaging and histopathological analysis are used to establish for the first time a direct linkage between NET degradation and bacterial pathogenicity. Inhibition of GAS DNase activity with G-actin enhanced neutrophil clearance of the pathogen in vitro and reduced virulence in vivo. The results demonstrate a significant role for NETs in neutrophil-mediated innate immunity, and at the same time identify a novel therapeutic target against invasive GAS infection.

Fibrin structure and wound healing

Fibrinogen and fibrin play an important role in blood clotting, fibrinolysis, cellular and matrix interactions, inflammation, wound healing, angiogenesis, and neoplasia. The contribution of fibrin(ogen) to these processes largely depends not only on the characteristics of the fibrin(ogen) itself, but also on interactions between specific-binding sites on fibrin(ogen), pro-enzymes, clotting factors, enzyme inhibitors, and cell receptors. In this review, the molecular and cellular biology of fibrin(ogen) is reviewed in the context of cutaneous wound repair. The outcome of wound healing depends largely on the fibrin structure, such as the thickness of the fibers, the number of branch points, the porosity, and the permeability. The binding of fibrin(ogen) to hemostasis proteins and platelets as well as to several different cells such as endothelial cells, smooth muscle cells, fibroblasts, leukocytes, and keratinocytes is indispensable during the process of wound repair. High-molecular-weight and low-molecular-weight fibrinogen, two naturally occurring variants of fibrin, are important determinants of angiogenesis and differ in their cell growth stimulation, clotting rate, and fibrin polymerization characteristics. Fibrin sealants have been investigated as matrices to promote wound healing. These sealants may also be an ideal delivery vehicle to deliver extra cells for the treatment of chronic wounds.

Elemental analysis of the Mycobacterium avium phagosome in Balb/c mouse macrophages

Using a hard X-ray microprobe, we showed recently that in unstimulated peritoneal macrophages from C57BL/6 mice, the phagosome of pathogenic mycobacteria (Mycobacterium tuberculosis and Mycobacterium avium) can accumulate iron. We expanded our studies to the M. avium infection of peritoneal macrophages of Balb/c mice that show a similar degree of M. tuberculosis and M. avium-related chronic disease, but a higher susceptibility towards other intracellular pathogens such as Listeria monocytogenes, Leishmania major, or Brucella abortus as compared to C57BL/6 mice. Similar to C57BL/6 macrophages, the iron concentration in Balb/c macrophages increased significantly after 24 h of infection. A significant increase of the chlorine and potassium concentrations was observed in the Balb/c phagosomes between 1 and 24 h, in contrast with macrophages from C57BL/6 mice. The absolute elemental concentrations of calcium and zinc were higher in the mycobacterial phagosomes of Balb/c mice. We hypothesize that a potassium channel is abundant in the phagosome in macrophages that may be related to microbiocidal killing, similar to the requirement of potassium channels for microbiocidal function in neutrophils.

Copy number polymorphisms are not a common feature of innate immune genes

Extensive copy number polymorphism was recently reported for innate immunity-related alpha-defensin genes DEFA1 and DEFA3 and beta-defensin genes DEFB4, DEFB103, and DEFB104. To establish whether such polymorphisms are a common feature of innate immune genes we used quantitative real-time PCR to determine the copy numbers of seven genes whose products have important innate immune functions. The genes encoding lysozyme, lactoferrin, cathelicidin antimicrobial peptide (hCAP18/LL-37), cathepsin G, bactericidal/permeability-increasing protein, azurocidin (CAP37/heparin-binding protein), and neutrophil elastase were each found to be single copy per haploid genome. These findings, along with the recent observation that defensin genes DEFA4, DEFA5, DEFA6, and DEFB1 are single copy, suggest that copy number polymorphisms are not a common feature of the innate immune genome but are restricted to a small subset of innate immunity-related genes.

A splice-supporting intronic mutation in the last bp position of a cryptic exon within intron 6 of the CYBB gene induces its incorporation into the mRNA causing chronic granulomatous disease (CGD)

Chronic granulomatous disease (CGD) is caused by a defect in both the host's defenses and its regulation of inflammation normally provided by phagocytes and other leukocytes. As in the case described here, it is not uncommon that CGD patients are diagnosed late, only after organ-damaging manifestations have already progressed. In this patient, we found that CGD arose due to a splice-supporting mutation in the last position of a cryptic exon towards the middle of intron 6 of the CYBB (gp91-phox) gene. The mutation led to the insertion of 56 bp into most of the CYBB mRNA of leukocytes causing a frame shift and a premature stop codon. The normal cryptic exon was also found to be mildly active in some tissues other than leukocytes in healthy donors, to be conserved in many primates, and to a lesser degree in other mammals. Some sequence similarity suggests that the cryptic exon may have originated from a mammalian interspersed repetitive (MIR) element. Taken together, we clarify an unusual disease-causing mutation, indicate its evolutionary background and emphasize the importance of a timely diagnosis of CGD.

Neutrophil extracellular traps capture and kill Candida albicans yeast and hyphal forms

Neutrophils phagocytose and kill microbes upon phagolysosomal fusion. Recently we found that activated neutrophils form extracellular fibres that consist of granule proteins and chromatin. These neutrophil extracellular traps (NETs) degrade virulence factors and kill Gram positive and negative bacteria. Here we show for the first time that Candida albicans, a eukaryotic pathogen, induces NET-formation and is susceptible to NET-mediated killing. C. albicans is the predominant aetiologic agent of fungal infections in humans, particularly in immunocompromised hosts. One major virulence trait of C. albicans is its ability to reversibly switch from singular budding cells to filamentous hyphae. We demonstrate that NETs kill both yeast-form and hyphal cells, and that granule components mediate fungal killing. Taken together our data indicate that neutrophils trap and kill ascomycetous yeasts by forming NETs.

Regulation of SUMOylation by reversible oxidation of SUMO conjugating enzymes

Posttranslational modification with small ubiquitin-related modifier (SUMO) has emerged as a central regulatory mechanism of protein function. However, little is known about the regulation of sumoylation itself. It has been reported that it is increased after exposure to various stresses including strong oxidative stress. Conversely, we report that ROS (reactive oxygen species), at low concentrations, result in the rapid disappearance of most SUMO conjugates, including those of key transcription factors. This is due to direct and reversible inhibition of SUMO conjugating enzymes through the formation of (a) disulfide bond(s) involving the catalytic cysteines of the SUMO E1 subunit Uba2 and the E2-conjugating enzyme Ubc9. The same phenomenon is also observed in a physiological scenario of endogenous ROS production, the respiratory burst in macrophages. Thus, our findings add SUMO conjugating enzymes to the small list of specific direct effectors of H(2)O(2) and implicate ROS as key regulators of the sumoylation-desumoylation equilibrium.

Defective acute inflammation in Crohn's disease: a clinical investigation

BACKGROUND

The cause of Crohn's disease has not been mechanistically proven. We tested the hypothesis that the disease is a form of immunodeficiency caused by impaired innate immunity.

METHODS

We investigated inflammatory responses in patients and controls by quantifying neutrophil recruitment and cytokine production after acute trauma, interleukin 8 secretion by cultured monocyte-derived macrophages after exposure to inflammatory mediators, and local inflammatory and vascular changes in response to subcutaneous injection of heat-killed Escherichia coli.

FINDINGS

In patients with Crohn's disease, trauma to rectum, ileum, or skin led to abnormally low neutrophil accumulation (differences from healthy individuals of 79%, n=8, p=0.0003; 57%, n=3, p=0.05; 50%, n=13, p<0.0001, respectively) and lower production of proinflammatory interleukin 8 (63%, n=7, p=0.003; 63%, n=3, p=0.05; 45%, n=8, p<0.0001) and interleukin 1beta (50%, n=8, p=0.0005). Interleukin 8 secretion by cultured macrophages was reduced after exposure to acute wound fluid (38%, n=50, p<0.0001), C5a (48%, n=41, p=0.0005), or tumour necrosis factor alpha (52%, n=27, p<0.0001). Local inflammatory reaction to inoculation with E coli was attenuated, as quantified by changes in bloodflow (ileal disease 50%, n=6, p=0.01; colonic disease 77%, n=6, p=0.0003). This response was mediated by nitric oxide in controls, was increased by sildenafil in patients, and was not related to CARD15 genotype.

INTERPRETATION

In Crohn's disease, a constitutionally weak immune response predisposes to accumulation of intestinal contents that breach the mucosal barrier of the bowel wall, resulting in granuloma formation and chronic inflammation. Polymorphisms in CARD15 do not underlie this phenotype, but incapacitate the NOD2 pathway that can compensate for impairment of innate inflammation. Current treatment of secondary chronic inflammation might exaggerate the underlying lesion and promote chronic disease.

Lung inflammatory responses

Inflammation is an important manifestation of respiratory disease in domestic animals. The respiratory system is mucosal in nature and has specific defense mechanisms used to control invasion by microbes and environmental elements. Inflammation can be beneficial or detrimental to the host. This article broadly discusses the primary mediators and mechanisms of inflammation within the respiratory tract of domestic animals. The role of cells, chemokines, cytokines and mediators in both acute and chronic inflammation are addressed. The pathogenesis of the initial insult determines the type of inflammation that will be induced, whether it is acute, chronic or allergic in origin. Maintenance of the microenvironment of cytokines and chemokines is critical for pulmonary homeostasis. Uncontrolled inflammation in the respiratory tract can be life threatening to the animal. The understanding of the mechanisms of inflammation, whether due to microbes or through inappropriate immune activation such as those occurring with allergies, is required to develop successful intervention strategies and control respiratory disease in animals.

Effect of arachidonic acid reacylation on leukotriene biosynthesis in human neutrophils stimulated with granulocyte-macrophage colony-stimulating factor and formyl-methionyl-leucyl-phenylalanine

Priming of human neutrophils with granulocyte-macrophage colony-stimulating factor (GM-CSF) followed by treatment with formyl-methionyl-leucyl-phenylalanine (fMLP) stimulates cells in a physiologically relevant manner with modest 5-lipoxygenase activation and formation of leukotrienes. However, pretreatment of neutrophils with thimerosal, an organomercury thiosalicylic acid derivative, led to a dramatic increase (>50-fold) in the production of leukotriene B(4) and 5-hydroxyeicosatetraenoic acid, significantly higher than that observed after stimulation with calcium ionophore A23187. Little or no effect was observed with thimerosal alone or in combination with either GM-CSF or fMLP. Elevation of [Ca(2+)](i) induced by thimerosal in neutrophils stimulated with GM-CSF/fMLP was similar but more sustained compared with samples where thimerosal was absent. However, [Ca(2+)](i) was significantly lower compared with calcium ionophore-treated cells, suggesting that a sustained calcium rise was necessary but not sufficient to explain the effects of this compound on the GM-CSF/fMLP-stimulated neutrophil. Thimerosal was found to directly inhibit neutrophil lysophospholipid:acyl-CoA acyltransferase activity at the doses that stimulate leukotriene production, and analysis of lysates from neutrophil preparations stimulated in the presence of thimerosal showed a marked increase in free arachidonic acid, supporting the inhibition of the reincorporation of this fatty acid into the membrane phospholipids as a mechanism of action for this compound. The dramatic increase in production of leukotrienes by neutrophils when a physiological stimulus such as GM-CSF/fMLP is employed in the presence of thimerosal suggests a critical regulatory role of arachidonate reacylation that limits leukotriene biosynthesis in concert with 5-lipoxygenase and cytosolic phospholipase A(2)alpha activation.

Mechanisms of evasion of neutrophil killing by Anaplasma phagocytophilum

PURPOSE OF REVIEW

This review summarizes recent knowledge regarding the strategies employed by Anaplasma phagocytophilum to evade or subvert neutrophil killing mechanisms and modify other neutrophil pathways to promote its survival.

RECENT FINDINGS

A. phagocytophilum evades neutrophil oxidative killing by preventing fusion of cytochrome b558-carrying specific granules and secretory vesicles with the membrane of its cytoplasmic compartment. It also directly detoxifies superoxide anion. Additionally, the bacterium alters the interaction of transcription factors with the CYYB promoter, which results in greatly reduced gp91phox levels and a consequent decline in respiratory burst capability. A. phagocytophilum not only fails to activate the normal neutrophil apoptosis differentiation program stimulated by bacterial uptake, but also delays spontaneous apoptosis by manipulating the expression of pro and antiapoptotic genes. Maintenance of the proapoptotic factor Bfl-1 contributes, at least in part, to the preservation of mitochondrial membrane integrity and inhibition of caspase 3 activation.

SUMMARY

A. phagocytophilum combats neutrophil oxidative killing by scavenging O2, inhibiting NADPH oxidase assembly on its vacuolar membrane, and modifying promoter activity for a key NADPH oxidase component, gp91phox. Uptake of this unique pathogen fails to induce neutrophil apoptosis. Furthermore, A. phagocytophilum extends the life of its otherwise short-lived host cell by dysregulating neutrophil gene expression and molecular machinery to potentially maximize its survival and dissemination within its mammalian host.

Charge compensation during the phagocyte respiratory burst

The phagocyte NADPH oxidase produces superoxide anion (O(2)(.-)) by the electrogenic process of moving electrons across the cell membrane. This charge translocation must be compensated to prevent self-inhibition by extreme membrane depolarization. Examination of the mechanisms of charge compensation reveals that these mechanisms perform several other vital functions beyond simply supporting oxidase activity. Voltage-gated proton channels compensate most of the charge translocated by the phagocyte NADPH oxidase in human neutrophils and eosinophils. Quantitative modeling of NADPH oxidase in the plasma membrane supports this conclusion and shows that if any other conductance is present, it must be miniscule. In addition to charge compensation, proton flux from the cytoplasm into the phagosome (a) helps prevent large pH excursions both in the cytoplasm and in the phagosome, (b) minimizes osmotic disturbances, and (c) provides essential substrate protons for the conversion of O(2)(*-) to H(2)O(2) and then to HOCl. A small contribution by K+ or Cl- fluxes may offset the acidity of granule contents to keep the phagosome pH near neutral, facilitating release of bactericidal enzymes. In summary, the mechanisms used by phagocytes for charge compensation during the respiratory burst would still be essential to phagocyte function, even if NADPH oxidase were not electrogenic.

Disorders of Neutrophil Number and Function

This review of disorders of neutrophil number and function will discuss important research advances in the field and then provide a clinical diagnostic approach. The focus will be on two recent clinical developments in the field of phagocyte disorders. First, an important natural history study from the Severe Chronic Neutropenia International Registry has recently quantitated the incidence and risk factors for death from sepsis and for progression to myelodysplastic syndrome and acute myeloid leukemia in a large cohort of severe chronic neutropenia patients, many of whom were followed 10 or more years on treatment with granulocyte colony-stimulating factor. Second, in the past year, a multinational group has announced successful gene therapy of two adults with chronic granulomatous disease, the most common disorder of neutrophil function. However, monitoring of retroviral insertion sites revealed expansion of the multiclonal population of gene-modified cells, raising concerns about eventual leukemogenesis. The review also provides a pragmatic approach to the evaluation of a patient with a suspected disorder of neutrophil number or function.

Immunomodulatory effects of beta-glucan on neutrophil function in fathead minnows (Pimephales promelas Rafinesque, 1820)

Stimulatory effects of yeast beta-1,3-1,6-glucans on neutrophils have long been recognized, but effects of glucans on degranulation of primary granules in fish neutrophils have not been previously reported. Neutrophil function was monitored during in vitro and in vivo application of glucans to non- (NS), acute- (AS) and chronically stressed (CS) fish. beta-Glucan proved to be a strong and quick (80%, 2 min) stimulant of degranulation. Dietary glucan increased degranulation in NS fish, and prevented a decrease in AS fish. Degranulation in CS fish returned to NS levels 3 days after the glucan diet was fed. Fathead minnows appear to be a useful model to investigate neutrophil degranulation in fish exposed to different environmental conditions and immunomodulators. Use of beta-glucans in fish diets prior to AS and during chronic stress can enhance neutrophil function, potentially increasing disease resistance and survival rates after transportation or exposure to poor water quality.

Systems biology of neutrophil differentiation and immune response

Systems biology has emerged as a new scientific field, which aims at investigating biological processes at the genomic and proteomic levels. Recent studies have unravelled aspects of neutrophil differentiation and immune responses at the systems level using high-throughput technologies. These studies have identified a plethora of novel effector proteins stored in the granules of neutrophils. In addition, these studies provide evidence that neutrophil differentiation and immune response are governed by a highly coordinated transcriptional programme that regulates cellular fate and function in a context-dependent manner.

The transcriptome response of Neisseria gonorrhoeae to hydrogen peroxide reveals genes with previously uncharacterized roles in oxidative damage protection

Symptomatic gonococcal infection, caused by the pathogen Neisseria gonorrhoeae (Gc), is characterized by the influx of polymorphonuclear leukocytes (PMNs) to the site of infection. Although PMNs possess several mechanisms of oxidative killing, intact Gc can be found associated with PMNs, suggesting that gonococcal defences against oxidative stress are crucial for its ability to evade killing by PMNs. We used microarrays to identify genes that were differentially expressed after transient exposure of Gc to hydrogen peroxide (H2O2). Of the 75 genes found to be upregulated after H2O2 treatment, over one-quarter, including two of the most highly upregulated genes (NGO1686 and NGO554), were predicted to encode proteins with unknown functions. Further characterization of a subset of these upregulated genes demonstrated that NGO1686, a putative zinc metalloprotease, protects against oxidative damage caused by both H2O2 and cumene hydroperoxide, and that NGO554, a Gc-specific protein, acts to protect against damage caused by high levels of H2O2. Our current study also ascribes a role in H2O2 damage protection to recN, a gene previously characterized for its role in DNA repair. A PMN survival assay demonstrated that the recN and NGO1686 mutants were more susceptible to killing than the parent strain FA1090. These results define for the first time the robust transcriptional response to H2O2 by this strict human pathogen and underscore the importance of this system for survival to host defences.

NADPH oxidases in Eukaryotes: red algae provide new hints!

The red macro-alga Chondrus crispus is known to produce superoxide radicals in response to cell-free extracts of its green algal pathogenic endophyte Acrochaete operculata. So far, no enzymes involved in this metabolism have been isolated from red algae. We report here the isolation of a gene encoding a homologue of the respiratory burst oxidase gp91(phox) in C. crispus, named Ccrboh. This single copy gene encodes a polypeptide of 825 amino acids. Search performed in available genome and EST algal databases identified sequences showing common features of NADPH oxidases in other algae such as the red unicellular Cyanidioschyzon merolae, the economically valuable red macro-alga Porphyra yezoensis and the two diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana. Domain organization and phylogenetic relationships with plant, animal, fungal and algal NADPH oxidase homologues were analyzed. Transcription analysis of the C. crispus gene revealed that it was over-transcribed during infection of C. crispus gametophyte by the endophyte A. operculata, and after incubation in presence of atrazine, methyl jasmonate and hydroxyperoxides derived from C20 polyunsaturated fatty acids (PUFAs). These results also illustrate the interest of exploring the red algal lineage for gaining insight into the deep evolution of NADPH oxidases in Eukaryotes.

Why Is the Arg5-Glu13 Salt Bridge Conserved in Mammalian α-Defensins?

Mammalian alpha-defensins, expressed primarily in leukocytes and epithelia, kill a broad range of microbes, constituting one of the first lines of innate immune defense against infection. Nine amino acid residues, including six cysteines, one glycine, and a pair of oppositely charged residues Arg/Glu, are conserved in the otherwise diverse sequences of all known mammalian alpha-defensins. Structural analysis indicates that the two charged residues form a salt bridge, likely stabilizing a protruding loop in the molecule. To investigate the structural and functional roles of the conserved Arg5-Glu13 salt bridge in alpha-defensins, we chemically prepared human neutrophil alpha-defensin 2 (HNP2) and five HNP2 analogs, R5E/E13R, E13Q, E13R, R5T/E13Y, and R14A. In contrast to HNP2 and R14A-HNP2, none of the four salt bridge analogs was capable of folding into a native conformation in the context of isolated defensin domains. However, when covalently attached to the 45-residue pro-HNP2 propeptide, the salt bridge analogs of HNP2 in their pro-forms all folded productively, suggesting that the Arg5-Glu13 salt bridge is not required for correct pro-alpha-defensin folding. When assayed against both Escherichia coli and Staphylococcus aureus, the six alpha-defensins showed bactericidal activity that correlated with the number of net positive charges carried by individual molecules in the panel, irrespective of whether or not the Arg5-Glu13 salt bridge was decimated, suggesting that Arg5 and Glu13 are not functionally conserved. Proteolytic resistance analysis with human neutrophil elastase, one major protease contained in azurophils with HNPs, revealed that destabilization of the salt bridge dramatically accelerated defensin degradation by the enzyme. Thus, we propose that the Arg5-Glu13 salt bridge found in most mammalian alpha-defensins is conserved for defensin in vivo stability.

Cutting edge: MyD88 controls phagocyte NADPH oxidase function and killing of gram-negative bacteria

MyD88 is an adaptor protein for the TLR family of proteins that has been implicated as a critical mediator of innate immune responses to pathogen detection. In this study, we report that MyD88 plays a crucial role in killing Gram-negative bacteria by primary macrophages via influencing NADPH oxidase function. Peritoneal macrophages from MyD88-/- mice exhibited a marked inability to kill Escherichia coli (F18) or an attenuated strain of Salmonella typhimurium (sseB) in vitro. This defect in killing was due to diminished NADPH oxidase-mediated production of superoxide anion in response to bacteria by MyD88-/- phagocytes as a consequence of defective NADPH oxidase assembly. Defective oxidase assembly in MyD88-deficient macrophages resulted from impaired p38 MAPK activation and subsequent phosphorylation of p47phox. Together these data demonstrate a pivotal role for MyD88 in killing Gram-negative bacteria via modulation of NADPH oxidase activity in phagocytic cells.

p40phox: The last NADPH oxidase subunit

The phagocytic NADPH-oxidase is a multiprotein system activated during the inflammatory response to produce superoxide anion (O2-), which is the substrate for formation of additional reactive oxygen species (ROS). The importance of this system for innate immunity is established by chronic granulomatous disease (CGD), a primary immunodeficiency caused by defects in the NADPH oxidase. In this review, we present and discuss recent knowledge about p40phox, the last NADPH oxidase component to be identified. Furthermore, its interaction with cellular pathways outside of the NADPH oxidase is discussed. Described in this review is evidence that p40phox participates in NADPH oxidase dynamics within cells, what is known about its role in the oxidase, the possibility that p40phox participates in non-NADPH oxidase processes in phagocytic and non-phagocytic cells and whether p40phox could mediate a similar function in other NADPH oxidases. An improved understanding of p40phox should provide new insights about NADPH oxidase, the physiology of phagocytic cells and the innate immune system.

[What is your diagnosis? (Cutaneous leishmaniasis)]

Neutrophils are the most abundant, short lived, and terminally differentiated leukocytes with distinct tiers of arsenals to counter pathogens. Neutrophils were traditionally considered transcriptionally inactive cells, but recent researches in the field led to a paradigm shift in neutrophil biology and revealed subpopulation heterogeneity, and functions pivotal to immunity and inflammation. Furthermore, recent unfolding of metabolic plasticity in neutrophils has challenged the long-standing concept of their sole dependence on glycolytic pathway. Metabolic adaptations and distinct regulations have been identified which are critical for neutrophil differentiation and functions. The metabolic reprogramming of neutrophils by inflammatory mediators or during pathologies such as sepsis, diabetes, glucose-6-phosphate dehydrogenase deficiency, glycogen storage diseases (GSDs), systemic lupus erythematosus (SLE), rheumatoid arthritis, and cancer are now being explored. In this review, we discuss recent developments in understanding of the metabolic regulation, that may provide clues for better management and newer therapeutic opportunities for neutrophil centric immuno-deficiencies and inflammatory disorders.