Killing activity of neutrophils is mediated through activation of proteases by K+ flux

Effect of interleukin-8 and granulocyte colony-stimulating factor on priming and activation of bovine neutrophils

Neutrophils are important effector cells in innate and acquired immunity, but the magnitude and character of their phagocytic and bactericidal responses depend on cues derived from mediators in the local microenvironment. This study investigated the effect of bovine interleukin-8 (IL-8) and granulocyte colony-stimulating factor (G-CSF) on priming and activation of bovine neutrophils in vitro and in vivo. Neutrophils were isolated from blood and cultured for up to 18 h, with or without cytokines, and then Mannheimia haemolytica-induced oxidative burst and phagocytosis of Staphylococcus aureus were measured by flow cytometry. Neither IL-8 nor G-CSF directly triggered an oxidative burst, but incubation with these cytokines for 18 h primed neutrophils for a greater oxidative burst triggered by M. haemolytica and for enhanced uptake of S. aureus. The maximal response was observed when neutrophils were incubated with both cytokines together, at concentrations of 200 ng/ml for G-CSF and 400 ng/ml for IL-8. The IL-8-induced priming effect was reduced by treatment with a neutralizing antibody to IL-8, and was not attributed to endotoxin contamination. Instillation of IL-8 into the lung using a bronchoscope induced neutrophil recruitment within 18 h. Neutrophils from IL-8-treated lung showed dose-dependent enhancement of the oxidative burst triggered by M. haemolytica. Histologically, neutrophils filled alveoli and bronchioles, and scattered macrophages contained neutrophils with morphological features of apoptosis. Thus, prolonged in vitro or in vivo exposure to IL-8 and/or G-CSF enhances the subsequent oxidative burst and phagocytic responses of bovine neutrophils.

Voltage-gated proton channels and other proton transfer pathways

Proton channels exist in a wide variety of membrane proteins where they transport protons rapidly and efficiently. Usually the proton pathway is formed mainly by water molecules present in the protein, but its function is regulated by titratable groups on critical amino acid residues in the pathway. All proton channels conduct protons by a hydrogen-bonded chain mechanism in which the proton hops from one water or titratable group to the next. Voltage-gated proton channels represent a specific subset of proton channels that have voltage- and time-dependent gating like other ion channels. However, they differ from most ion channels in their extraordinarily high selectivity, tiny conductance, strong temperature and deuterium isotope effects on conductance and gating kinetics, and insensitivity to block by steric occlusion. Gating of H(+) channels is regulated tightly by pH and voltage, ensuring that they open only when the electrochemical gradient is outward. Thus they function to extrude acid from cells. H(+) channels are expressed in many cells. During the respiratory burst in phagocytes, H(+) current compensates for electron extrusion by NADPH oxidase. Most evidence indicates that the H(+) channel is not part of the NADPH oxidase complex, but rather is a distinct and as yet unidentified molecule.

Sympathoadrenal and immune system activation during the periparturient period and their association with bovine coliform mastitis. A review

Increased incidence of clinical mastitis in high-yielding cows during early lactation has been attributed to a depressed functional capacity of the immune system. Sympathoadrenal factors are known to play an important role in modulating the host susceptibility and resistance to infectious diseases. Of primary importance in combating acute intramammary infections are polymorphonuclear leukocytes (PMN), as they represent one of the early lines of immunological defense. The release of stress hormones at parturition and during the first weeks of lactation has been proposed to partly contribute to the impaired function of PMN. Here, we summarize the current understanding of the stress-induced peripheral effectors, i.e. the limbs of the sympathetic system and the hypothalamic-pituitary-adrenal axis, on PMN function around parturition and during coliform mastitis. The questions as to whether and how stress induced secretion of glucocorticoids and catecholamines might affect the lactating dairy cow's udder health will be addressed.

Plasma membrane depolarization reduces nitric oxide (NO) production in P388D.1 macrophage-like cells during Leishmania major infection

In the present study, we compare changes in host cell plasma membrane potential (V(m)), K(+) fluxes, and NO production during K(+) channel blockade with those changes that occur during infection with Leishmania major. Infection of P388D.1 cells with L. major promastigotes or treatment with K(+) channel blockers (either 1mM 4-AP, 10mM TEA, or 200 microM quinine) suppressed NO production. Inhibition of NO production correlated with depolarization of the P388D.1 cell V(m). Infection of P388D.1 cells with L. major increased the unidirectional influx of rubidium (86Rb), a tracer for K(+) flux, that was comparable to that induced by K(+) channel blockade by 1mM 4-AP. The similar effects of K(+) channel blockers and L. major on NO production, K(+) influx, and V(m) suggest that K(+) channel activity and the maintenance of V(m) is important for NO production in these cells. We suggest that intracellular parasites employ a strategy to inhibit NO production by disrupting V(m) during the invasion/infection process by altering host cell K(+) channel activity.

Severe impairment in early host defense against Listeria monocytogenes in mice deficient in acid sphingomyelinase

The phagolysosomal compartment is crucial for the defense against infection with intracellular pathogens. Within this compartment, the TNF- and IFN-gamma-responsive acid sphingomyelinase (ASMase) generates the signaling molecule ceramide, resulting in the activation of proteases like cathepsin D. To investigate the possible role of ASMase as a mediator of the antibacterial effects of TNF and IFN-gamma, ASMase(-/-) mice were infected with Listeria monocytogenes. ASMase(-/-) mice showed a dramatically increased susceptibility to L. monocytogenes (LD(50) approximately 100 CFU) when compared with syngeneic wild-type mice (LD(50) approximately 10,000 CFU). In L. monocytogenes-challenged ASMase(-/-) mice, IFN-gamma serum levels as well as IL-1 beta and IL-6 secretion by macrophages were similar to those observed in wild-type C57BL/6 mice. Although macrophages and granulocytes from ASMase(-/-) mice showed intact production of reactive nitrogen intermediates and oxidative burst, ASMase(-/-) macrophages proved completely incapable of restricting the growth of L. monocytogenes in vitro. The results of this study suggest that ASMase is crucially required for the intracellular control of L. monocytogenes in macrophages and granulocytes by nonoxidative mechanisms.

Granulocyte colony-stimulating factor induces the release in the bone marrow of proteases that cleave c-KIT receptor (CD117) from the surface of hematopoietic progenitor cells

OBJECTIVE

Administration of granulocyte colony-stimulating factor (G-CSF) results in the mobilization of hematopoietic progenitor and stem cells from the bone marrow into the peripheral blood. Although the mechanisms leading to the mobilization of primitive hematopoietic cells is not fully understood, it has been noted that the yield of mobilization in humans is correlated to the down-regulation of c-KIT/CD117 expression on mobilized cells. We sought to determine the mechanisms responsible for the reduced expression of c-KIT on mobilized hematopoietic progenitor cells.

MATERIALS AND METHODS

Mice were mobilized with G-CSF and primitive hematopoietic cells were collected from bone marrow and blood to analyze c-KIT expression. Using cell lines expressing mouse and human c-KIT and a recombinant protein comprising the entire extracellular domain of human c-KIT, we analyzed by flow cytometry and immunoblotting the proteolytic cleavage of c-KIT by proteases released in bone marrow extracellular fluids extracted from mobilized mice.

RESULTS

Administration of G-CSF into mice results in the reduction of c-KIT expression on primitive hematopoietic cells in bone marrow and peripheral blood. Bone marrow extracellular fluids isolated from G-CSF-mobilized mice contain serine proteases that cleave c-KIT into discrete fragments. Proteases capable of cleaving c-KIT include neutrophil elastase, cathepsin G, proteinase-3 and matrix metalloproteinase-9.

CONCLUSIONS

In addition to transcriptional controls, exocytosis, and ligand-induced internalization, the direct proteolytic cleavage of c-KIT by neutrophil and macrophage proteases represents a novel pathway to regulate the levels of c-KIT expression at the surface of hematopoietic cells and may be responsible in part for the down-regulation of c-KIT expression on mobilized hematopoietic progenitors in vivo.

Granulocyte function in grancalcin-deficient mice

Grancalcin, one of the penta-EF-hand Ca(2+) binding proteins, is expressed at high levels in polymorphonuclear granulocytes (neutrophils). EF-hand proteins are implicated in the regulation of diverse processes including cell migration, apoptosis, and mobilization of neutrophil effector functions. To determine the role of grancalcin in vivo, we inactivated the gene encoding grancalcin (Gca) in embryonic stem cells and generated grancalcin-deficient mice. Homozygous Gca mutants appeared healthy and reproduced normally. Leukocyte recruitment into the peritoneal cavity upon induction of inflammation was not significantly affected by the absence of grancalcin. The mutants also resisted systemic fungal infection similarly to wild-type mice, and in vitro killing of Staphylococcus aureus by inflammatory cells was not significantly impaired. While marginally increased survival rates of mutants faced with endotoxic shock may indicate a contribution of grancalcin to immunopathogenesis, it is not essential for vital leukocyte effector functions required to control microbial infections.

Interaction of the sensor module of Mycobacterium tuberculosis H37Rv KdpD with members of the Lpr family

The genetic and biochemical mechanisms by which Mycobacterium tuberculosis senses and responds to the complex environment that it encounters during infection and persistence within the host remain unknown. In a number of bacterial species, the Kdp signal transduction pathway appears to be the primary response to environmental osmotic stress, which is primarily mediated by K+ concentration in bacteria. We show that kdp encodes for components of a mycobacterial signalling pathway by demonstrating the K+ dependence of kdpFABC expression in both M. tuberculosis H37Rv and Mycobacterium smegmatis. To identify proteins of M. tuberculosis that participate in this signalling pathway, we used the N-terminal sensing module of the histidine kinase KdpD as bait in a yeast two-hybrid screen. We show that the sensing domain of KdpD interacts specifically with two membrane lipoproteins, LprJ (Rv1690) and LprF (Rv1368). Overexpression of lprF and lprJ alleles in mycobacterial kdpF-lacZ reporter strains enabled us to identify alleles that modulate kdpFABC expression. By exploiting the yeast three-hybrid system, we have found that the histidine kinase domain of KdpD forms ternary complexes with LprF and LprJ and the sensing module of KdpD. Our results establish a role for membrane proteins in the Kdp signalling pathway and suggest that LprF and LprJ function as accessory or ligand-binding proteins that communicate directly with the sensing domain of KdpD to modulate kdp expression.

The interplay between Salmonella typhimurium and its macrophage host--what can it teach us about innate immunity?

Salmonella enterica sv. Typhimurium (S. typhimurium) is a genetically tractable, facultative intracellular pathogen, whose capacity to cause systemic disease in mice depends upon its ability to survive and replicate within macrophages. The identification of Salmonella mutants that lack this activity, has provided a tool with which to dissect the mechanisms used by Salmonella to establish a permissive niche, and identify host activities which it must overcome in order to achieve this. Salmonella actively maintains itself within an intracellular vacuole, thereby shielding itself from an antibacterial activity of host macrophage cytosol. Salmonella controls the maturation of its vacuole, segregating itself from the macrophage degradative pathway. Like several other pathogens, Salmonella reduces the effectiveness of bacteriocidal and bacteriostatic free radicals generated by macrophages, by synthesising enzymes and products that counteract them. Recent evidence indicates that Salmonella also avoids free radical-dependent macrophage antimicrobial mechanisms by more novel means. Here, we review recent studies of the interplay between pathogen and host, with particular emphasis on those areas that suggest new facets to the cell biology of macrophages, and their innate immune functions.

The increased bactericidal activity of a fatty acid-modified synthetic antimicrobial peptide of human cathepsin G correlates with its enhanced capacity to interact with model membranes

The bactericidal potency of a synthetic peptide (CG 117-136) of human lysosomal cathepsin G (cat G) can be substantially increased by covalent attachment to its N- or C-termini, of saturated, linear fatty acids (FAs), namely those with C-8, C-10 and C-12 hydrocarbon chains. In order to understand better the mechanism by which FA moieties increase the bactericidal activity of CG 117-136, the interaction of N-terminally FA-modified peptides with artificial membranes was studied. First, the content of secondary structure motifs in the modified and unmodified peptides was determined by circular dichroism (CD). A marked increase in the propensity of FA-modified CG 117-136 to form an alpha-helix structure was observed for the C-8, C-10 and C-12 derivatives compared with unmodified/short-chain and long-chain (C-14, C-16, C-18) derivatives. These effects were observed both in the presence of large unilamellar liposomes or in trifuluoroethanol, a membrane-stimulating agent. Second, the capacity of peptides to insert into large unilamellar liposomes as a function of FA length was determined by their ability to release a trapped fluorescent dye. FA derivatives with the highest alpha-helical content were found to be the most effective in releasing a fluorescent dye, compared with an unmodified peptide and/or derivatives having a low alpha-helical content. The ability of the peptides to attain alpha-helical structure in the membrane-like environment and the ability to disrupt the liposomal membrane, therefore correlate remarkably well with their increased ability to kill bacteria. A plausible explanation for improved bactericidal action of the modified peptide is that the FA moiety facilitates formation of the peptide with an alpha-helical structure formation in membranes, which is essential for disrupting the integrity of the bacterial cytoplasmic membrane.

A novel assay system implicates PtdIns(3,4)P(2), PtdIns(3)P, and PKC delta in intracellular production of reactive oxygen species by the NADPH oxidase

Activated neutrophils assemble an NADPH oxidase enzyme complex to produce superoxide for microbial killing. Much of the initial oxidase assembly occurs on intracellular granules, followed by movement of the oxidase to phagolysosomes and the plasma membrane. We have developed a novel assay system using Streptolysin-O permeabilized neutrophils that recapitulates the initial intracellular activation process while maintaining the ultrastructural features of this granulocytic cell type. Using this system, we biochemically dissect molecular events and signaling pathways involved in NADPH oxidase assembly and demonstrate specific roles for PKC delta, PI(3,4)P(2)/PI(3,4,5)P(3), and PI(3)P in the PMA-dependent intracellular activation process. This system should be of great utility for the study of cell signaling events that regulate the intracellular production of reactive oxygen species by neutrophils.

Redox signaling and the MAP kinase pathways

The mitogen-activated protein (MAP) kinases are a large family of proline-directed, serine/threonine kinases that require tyrosine and threonine phosphorylation of a TxY motif in the activation loop for activation through a phosphorylation cascade involving a MAPKKK, MAPKK and MAPK, often referred to as the MAP kinase module. Three separate such modules have been identified, based on the TxY motif of the MAP kinase and the dual-specificity kinases that strictly phosphorylate their specific TxY sequence. They are the extracellular signal regulated kinases (ERKs), c-jun N-terminal kinases (JNKs) and p38 MAPKs. The ERKs are mainly associated with proliferation and differentiation while the JNKs and p38MAP kinases regulate responses to cellular stresses. Redox homeostasis is critical for proper cellular function. While reactive oxygen species (ROS) and oxidative stress have been implicated in injury, a rapidly growing literature suggests that a transient increase in ROS levels is an important mediator of proliferation and results in activation of various signaling molecules and pathways, among which the MAP kinases. This review will summarize the role of ROS in MAP kinase activation in various systems, including in macrophages, cells of myeloid origin that play an essential role in inflammation and express a multi-component NADPH oxidase that catalyzes the receptor-regulated production of ROS.

Unravelling the biology of macrophage infection by gene expression profiling of intracellular Salmonella enterica

For intracellular pathogens such as Salmonellae, Mycobacteriae and Brucellae, infection requires adaptation to the intracellular environment of the phagocytic cell. The transition from extracellular to intravacuolar environment has been expected to involve a global modulation of bacterial gene expression, but the precise events have been difficult to determine. We now report the complete transcriptional profile of intracellular Salmonella enterica sv. Typhimurium following macrophage infection. During replication in murine macrophage-like J774-A.1 cells, 919 of 4451 S. Typhimurium genes showed significant changes in transcription. The expression profile identified alterations in numerous virulence and SOS response genes and revealed unexpected findings concerning the biology of the Salmonella-macrophage interaction. We observed that intracellular Salmonella are not starved for amino acids or iron (Fe2+), and that the intravacuolar environment is low in phosphate and magnesium but high in potassium. S. Typhimurium appears to be using the Entner-Douderoff pathway to use gluconate and related sugars as a carbon source within macrophages. Almost half the in vivo-regulated genes were of unknown function, suggesting that intracellular growth involves novel macrophage-associated functions. This is the first report that identifies the whole set of in vivo-regulated genes for any bacterial pathogen during infection of mammalian cells.

Blood and milk neutrophil chemiluminescence and viability in primiparous and pluriparous dairy cows during late pregnancy, around parturition and early lactation

Extensive studies have shown the polymorphonuclear leukocytes (PMN) dysfunction inextricably links to parturition. To investigate the effect of parity on PMN function, phorbol 12-myristate 13-acetate (PMA) stimulated luminol-amplified chemiluminescence (CL) and viability of blood and milk PMN were investigated in primiparous and pluriparous dairy cows during periparturient period. The CL kinetics of blood and milk PMN and hematological profiles were also assessed. Milk PMN CL was always lower than blood PMN CL. Blood and milk PMN CL and milk PMN viability were significantly higher in primiparous cows throughout the study. Blood PMN CL in pluriparous cows showed a sharper decrease. Both in pluriparous and in primiparous cows, minimal blood PMN CL appeared at periparturient day (PPD) 2. After PPD 7, blood PMN CL recovery rate was faster in primiparous cows. Milk PMN CL was minimal at PPD 2 in both groups. Whereas no changes were observed in blood PMN viability, the viability of milk PMN in primiparous cows was substantially higher than in pluriparous cows. The number of circulating eosinophils and immature neutrophils was substantially higher in primiparous cows throughout the study. The CL kinetics of blood PMN at PPD -2 and 2 and of milk PMN at PPD 2 exhibited different responses to PMA, with higher intensity and durability, peaking and subsiding more slowly in primiparous dairy cows. The pronounced reduction in PMN CL and viability in milk PMN of pluriparous cows may be involved in the underlying mechanisms that make these animals more susceptible to periparturient infectious diseases.

Differential recognition of structural details of bacterial lipopeptides by toll-like receptors

The question which detailed structures of bacterial modulins determine their relative biological activity and respective host cell receptors was examined with synthetic variants of mycoplasmal lipopeptides as model compounds, as well as recombinant outer surface protein A (OspA) of Borrelia burgdorferi and lipoteichoic acid. Mouse fibroblasts bearing genetic deletions of various toll-like receptors (TLR) were the indicator cells to study receptor requirements, primary macrophages served to measure dose response. The following results were obtained: (i) the TLR system discriminates between modulins with three and those with two long-chain fatty acids in their lipid moiety, in that lipopeptides with three fatty acids were recognized by TLR2, whereas those with two long-chain fatty acids and lipoteichoic acid required the additional cooperation with TLR6; (ii) substitution of the free N terminus of mycoplasmal lipopeptides with an acetyl or palmitoyl group decreased the specific activity; (iii) removal of one or both ester-bound fatty acids lowered the specific activity by five orders of magnitude or deleted biological activity; (iv) oxidation of the thioether group lowered the specific activity by at least four orders of magnitude. The implications of these findings for physiological inactivation of lipopeptides and host-bacteria interactions in general are discussed.

Hydrogen peroxide as second messenger in lymphocyte activation

Oxidants such as H2O2 are connected to lymphocyte activation, but the molecular mechanisms behind this phenomenon are less clear. Here, I review data suggesting that by inhibiting protein tyrosine phosphatases, H2O2 plays an important role as a secondary messenger in the initiation and amplification of signaling at the antigen receptor. These findings explain why exposure of lymphocytes to H2O2 can mimic the effect of antigen. In addition, more recent data show that antigen receptors themselves are H2O2-generating enzymes and that the oxidative burst in macrophages seems to play a role not only in pathogen killing but also in the activation of these as well as neighboring cells. Thus, by controlling the activity of the negative regulatory phosphatases inside the cell, H2O2 can set and influence critical thresholds for lymphocyte activation.

Voltage-activated proton currents in human lymphocytes

Voltage-activated proton currents are reported for the first time in human peripheral blood T and B lymphocytes and in the human leukaemic T cell line Jurkat E6-1. The properties of H(+) currents studied using tight-seal voltage-clamp recording techniques were similar in all cells. Changing the pH gradient by one unit caused a 47 mV shift in the reversal potential, demonstrating high selectivity of the channels for protons. H(+) current activation upon membrane depolarisation had a sigmoidal time course that could be fitted by a single exponential function after a brief delay. Increasing pH(o) shifted the activation threshold to more negative potentials, and increased both the H(+) current amplitude and the rate of activation. In lymphocytes studied at pH(i) 6.0, the activation threshold was more negative and the H(+) current density was three times larger than at pH(i) 7.0. Increasing the intracellular Ca(2+) concentration to 1 microM did not change H(+) current amplitude or kinetics detectably. Extracellularly applied Zn(2+) and Cd(2+) inhibited proton currents, slowing activation and shifting the voltage-activation curve to more positive potentials. The H(+) current amplitude was 100 times larger in CD19+ B lymphocytes and in Jurkat E6-1 cells than in CD3+ T lymphocytes. Following stimulation with the phorbol ester PMA, the H(+) current density in peripheral blood T lymphocytes and Jurkat T cells increased. In contrast, the H(+) current density of phorbol ester (PMA)-stimulated B lymphocytes was reduced and activation became slower. The pattern of expression of H(+) channels in lymphocytes appears well suited to their proposed role of charge compensation during the respiratory burst.

Characterization of four murine homologs of the human ov-serpin monocyte neutrophil elastase inhibitor MNEI (SERPINB1)

The human ov-serpin monocyte neutrophil elastase inhibitor (MNEI) is encoded by a single gene SERPINB1. It is a highly efficient inhibitor of neutrophil granule proteases. Four murine genes with high sequence identity with MNEI were identified and fully sequenced, and these were named EIA, EIB, EIC, and EID. EIA, EIB and EIC showed the same seven-exon gene structure as SERPINB1. However, EIC included an additional, alternatively spliced, exon due to the insertion of an endogenous retrovirus-like sequence. EID lacked several exons and is a pseudogene. Reverse transcriptase-PCR showed that EIA, like MNEI, is expressed at high levels in many tissues. EIB is mainly expressed in brain, and EIC was only expressed as splicing variants unlikely to encode a functional serpin. Upon incubation with serine proteases, EIA formed inhibitory covalent complexes with pancreatic and neutrophil elastases, cathepsin G, proteinase-3, and chymotrypsin, as previously shown for MNEI, whereas EIB was only able to do so with cathepsin G. According to the new serpin nomenclature, the genes encoding EIA, EIB, EIC, and EID will be called Serpinb1, Serpinb1b, Serpinb1c, and Serpinb1-ps1. These data demonstrate that the four murine homologs of MNEI have met different evolutionary fates, and that EIA is the mouse ortholog of MNEI.

Neutrophil elastase-mediated killing of bacteria: lessons from targeted mutagenesis

Engineering of mice deficient in neutrophil elastase (NE) has allowed us to demonstrate the role of this protease in host defense against bacteria and to begin to understand its killing mechanism. Strategies to inhibit NE because of its involvement in tissue-destructive diseases should be reconsidered, while preserving its beneficial properties.

Neutrophil elastase and secretory leukocyte protease inhibitor in prelabor rupture of membranes, parturition and intra-amniotic infection

OBJECTIVE

Neutrophil elastase (NE), a multifunctional serine protease stored in azurophilic granules of mature neutrophils, is capable of intracellular degradation of proteins during phagocytosis and extracellular degradation of connective tissue during an inflammatory process. Secretory leukocyte protease inhibitor (SLPI) is a natural NE inhibitor present in amniotic fluid, fetal membranes and cervical mucus. An imbalance between NE and SLPI has been implicated as a mechanism of abnormal tissue destruction in chronic inflammatory diseases. The purpose of this study was to determine if parturition, premature rupture of the membranes (PROM) and microbial invasion of the amniotic cavity are associated with changes in amniotic fluid concentrations of NE and SLPI.

STUDY DESIGN

Amniotic fluid was retrieved by amniocentesis from 380 patients in the following groups: (1) preterm labor and intact membranes without microbial invasion of the amniotic cavity who delivered at term (n = 13) or prematurely (n = 26), and preterm labor with microbial invasion of the amniotic cavity (n = 9); (2) preterm PROM with (n = 34) and without (n = 51) microbial invasion of the amniotic cavity; and (3) term gestation without microbial invasion of the amniotic cavity with intact membranes not in labor (n = 63), in labor (n = 158), and with rupture of membranes not in labor (n = 26). Microbial invasion of the amniotic cavity was determined by a positive amniotic fluid culture for micro-organisms including aerobic, anaerobic and Mycoplasma species. NE and SLPI amniotic fluid levels were determined by highly specific and sensitive immunoassays.

RESULTS

Preterm PROM was associated with a significant increase in the amniotic fluid concentration of NE. Microbial invasion of the amniotic cavity was associated with a significant increase in the amniotic fluid concentration of NE in women with preterm labor and intact membranes, as well as in women with preterm PROM. Term and preterm parturition was associated with a significant increase in the amniotic fluid concentration of NE. In the absence of microbial invasion of the amniotic cavity, preterm and term PROM were associated with a significant reduction in the amniotic fluid concentration of SLPI.

CONCLUSION

Preterm PROM, microbial invasion of the amniotic cavity, and parturition at term and preterm are associated with a significant increase in the amniotic fluid concentration of NE. PROM is associated with a reduced amniotic fluid concentration of SLPI.

Binding of the PX domain of p47(phox) to phosphatidylinositol 3,4-bisphosphate and phosphatidic acid is masked by an intramolecular interaction

p47(phox) is a key cytosolic subunit required for activation of phagocyte NADPH oxidase. The X-ray structure of the p47(phox) PX domain revealed two distinct basic pockets on the membrane-binding surface, each occupied by a sulfate. These two pockets have different specificities: one preferentially binds phosphatidylinositol 3,4-bisphosphate [PtdIns(3,4)P(2)] and is analogous to the phophatidylinositol 3-phosphate (PtdIns3P)-binding pocket of p40(phox), while the other binds anionic phospholipids such as phosphatidic acid (PtdOH) or phosphatidylserine. The preference of this second site for PtdOH may be related to previously observed activation of NADPH oxidase by PtdOH. Simultaneous occupancy of the two phospholipid-binding pockets radically increases membrane affinity. Strikingly, measurements for full-length p47(phox) show that membrane interaction by the PX domain is masked by an intramolecular association with the C-terminal SH3 domain (C-SH3). Either a site-specific mutation in C-SH3 (W263R) or a mimic of the phosphorylated form of p47(phox) [Ser(303, 304, 328, 359, 370)Glu] cause a transition from a closed to an open conformation that binds membranes with a greater affinity than the isolated PX domain.

Rac activation: P-Rex1 - a convergence point for PIP(3) and Gbetagamma?

P-Rex1, a novel Rac activator, has been identified in the first biochemical purification of a guanine nucleotide exchange factor for GTPases of the Rho family. P-Rex1 is synergistically activated by PIP(3) and Gbetagamma and may act as a coincidence detector for these signaling molecules.

Microbial killing: oxidants, proteases and ions

There is accumulating evidence that two aspects of the innate immune response, the respiratory burst and secretion of proteases, are intimately intertwined. A recent study suggests that K(+) may be the missing link. Is it time to merge signal transduction with biophysics?

Catalase negative Staphylococcus aureus retain virulence in mouse model of chronic granulomatous disease

Myeloperoxidase-mediated chlorination is thought to be a necessary microbicidal mechanism. The H2O2 required for this process is generated by the NADPH oxidase. Staphylococcus aureus can also produce H2O2, which is not broken down by catalase negative organisms. It has been thought that this bacterial H2O2 can substitute for cellular H2O2 in the halogenation reaction in chronic granulomatous disease (CGD) where neutrophils are lacking the NADPH oxidase. We have readdressed this issue in a mouse model of CGD using clinical isolates of catalase positive and negative strains of S. aureus. The results showed these organisms to be equally virulent and that the H2O2 they produced is insufficient to cause significant iodination, a marker for chlorination, thereby contradicting the accepted views on this subject.