Identification of a thermolabile component of the human neutrophil NADPH oxidase. A model for chronic granulomatous disease caused by deficiency of the p67-phox cytosolic component

The physicochemical properties of membranes correlate with the NADPH oxidase activity

BACKGROUND

Phagocytes kill ingested microbes by exposure to high concentrations of toxic reactive species generated by NADPH-oxidases. This membrane-bound electron-transferring enzyme is tightly regulated by cellular signaling cascades. So far, molecular and biophysical studies of the NADPH-oxidase were performed over limited temperature ranges, which weaken our understanding of immune response or inflammatory events. In this work, we have inspected the influence of temperature and lipid membrane properties on the NADPH-oxidase activity using a system free of cell complexity.

METHODS

We have extended the experimental conditions of the accepted model for NADPH-oxidase activity, the so-called cell-free assay, to a large temperature range (10-40°C) using different membrane compositions (subcellular compartments or liposomes).

RESULTS

A remarkable increase of superoxide production rate was observed with rising temperature. Synchrotron radiation circular dichroism data showed that this is not correlated with protein secondary structure changes. When lipid bilayers are in fluid phase, Arrhenius plots of the oxidase activity showed linear relationships with small activation energy (Ea), while when in solid phase, high Ea was found. The sterol content modulates kinetic and thermodynamic parameters.

CONCLUSION

High temperature promotes the rate of superoxide production. The key element of this enhancement is related to membrane properties such as thickness and viscosity and not to protein structural changes. Membrane viscosity that can be driven by sterols is a paramount parameter of Ea of NADPH oxidase activity. The membrane bilayer state modulated by its sterol content may be considered locally as an enzyme regulator. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

Differential activation of RAGE by HMGB1 modulates neutrophil-associated NADPH oxidase activity and bacterial killing

The receptor for advanced glycation end products (RAGE) plays an important role in host defense against bacterial infection. In the present experiments, we investigated the mechanisms by which RAGE contributes to the ability of neutrophils to eradicate bacteria. Wild-type (RAGE(+/+)) neutrophils demonstrated significantly greater ability to kill Escherichia coli compared with RAGE(-/-) neutrophils. After intraperitoneal injection of E. coli, increased numbers of bacteria were found in the peritoneal fluid from RAGE(-/-) as compared with RAGE(+/+) mice. Exposure of neutrophils to the protypical RAGE ligand AGE resulted in activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and enhanced killing of E. coli, and intraperitoneal injection of AGE enhanced bacterial clearance during peritonitis. However, incubation of neutrophils with high mobility group box 1 protein (HMGB1), which also binds to RAGE, diminished E. coli-induced activation of NADPH oxidase in neutrophils and bacterial killing both in vitro and in vivo. Deletion of the COOH-terminal tail of HMGB1, a region necessary for binding to RAGE, abrogated the ability of HMGB1 to inhibit bacterial killing. Incubation of neutrophils with HMGB1 diminished bacterial or AGE-dependent activation of NADPH oxidase. The increase in phosphorylation of the p40(phox) subunit of NADPH oxidase that occurred after culture of neutrophils with E. coli was inhibited by exposure of the cells to HMGB1. These results showing that HMGB1, through RAGE-dependent mechanisms, diminishes bacterial killing by neutrophils as well as NADPH oxidase activation provide a novel mechanism by which HMGB1 can potentiate sepsis-associated organ dysfunction and mortality.

Cryopreservable neutrophil surrogates: Granule-poor, motile cytoplasts from polymorphonuclear leukocytes home to inflammatory lesions in vivo

Cytokineplasts (CKP) are anucleate, motile, granule-poor fragments induced from polymorphonuclear leukocytes on surfaces by the brief application of heat. Derived from the peripheral cytoplasm and membranes of PMN, they retain the sensing, transducing, and effector mechanisms necessary for chemotaxis and phagocytosis, and appear to represent a functional, self-purification of the motile apparatus. Unlike their parent PMN, CKP are cryopreservable. We have shown that they can adhere to endothelial cell monolayers, open interendothelial cell junctions, and migrate to the abluminal side when stimulated by a chemoattractant. Employing an animal model, we now show that, given intravenously, they can home to an inflammatory target lesion in vivo.

Oxidase activity in cord blood neutrophils: a balance between increased membrane associated cytochrome b558 and deficient cytosolic components

INTRODUCTION

Newborn infants are prone to develop life-threatening pyogenic infections. Alterations in the function of neonatal phagocytes, including the activity of the neutrophil NADPH oxidase, have been suggested as one cause of increased susceptibility to such infections.

METHODS

In the present study, comprehensive analysis of NADPH oxidase enzyme system was performed in cord blood neutrophils from vaginally and cesarean section (CS) delivered, healthy, full-term infants.

RESULTS

Superoxide anion (O(2) (-)) production by intact neutrophils from cord blood in response to soluble stimuli was equal to or increased compared to levels generated by cells from adult controls. In the sodium dodecyl sulfate (SDS) cell-free system, cytosol and plasma membrane from cord blood neutrophils generated O(2) (-) at comparable rates to subcellular fractions from healthy adults. However, mixing experiments demonstrated higher O(2) (-) generation with combination of cytosol from adult controls and membrane from cord blood neutrophils and lower O(2) (-) production with combination of cytosol from cord blood neutrophils and membrane from adult controls. Kinetic parameters for cord blood specimens were no different from those obtained for fractions from adult controls. Quantitative analysis of cytosolic components showed moderately reduced amount of p40-phox, p47-phox, and p67-phox in neutrophils from cord blood. In contrast, cytochrome b(558) content of plasma membrane of cord blood neutrophils was approximately 2-fold higher compared to adult controls.

CONCLUSION

The normal to increased respiratory burst of intact cord blood neutrophils is the result of alterations to oxidase components: increased content of cytochrome b(558) in the plasma membrane and decreased levels of cytosolic components p47-phox, p67-phox, and p40-phox.

Another biological effect of tosylphenylalanylchloromethane (TPCK): it prevents p47phox phosphorylation and translocation upon neutrophil stimulation

TPCK (tosylphenylalanylchloromethane), first discovered as a serine protease inhibitor, has been described to affect in diverse systems a number of physiological events probably unrelated to its antiprotease effect, such as proliferation, apoptosis and tumour formation. In the present study, we focus on its inhibition of the neutrophil respiratory burst, an important element of non-specific immunological defence. The superoxide anion-producing enzyme, NADPH oxidase, is quiescent in resting cells. Upon cell stimulation, the redox component, membrane-bound flavocytochrome b558, is activated when the cytosolic factors (p47phox, p67phox and p40phox, as well as the small GTPase Rac) associate with it after translocating to the membrane. This requires the phosphorylation of several p47phox serine residues. The signal transduction events leading to enzyme activation are not completely understood. In the past, the use of diverse protease inhibitors suggested that proteases were involved in NADPH oxidase activation. We suggested previously that TPCK could prevent enzyme activation by the phorbol ester PMA, not due to inhibition of a protease, but possibly to inhibition of the cytosolic factor translocation [Chollet-Przednowed and Lederer (1993) Eur. J. Biochem. 218, 83-93]. In the present work, we show that TPCK, when added to cells before PMA, prevents p47phox phosphorylation and hence its translocation; moreover, when PMA-stimulated cells are incubated with TPCK, p47phox is dephosphorylated and dissociates from the membrane. These results are in line with previous suggestions that the respiratory burst is the result of a series of continuous phosphorylation and dephosphorylation events. They suggest that TPCK leads indirectly to activation of a phosphatase or inactivation of a kinase, and provide the first clue towards understanding the steps leading to its inhibition of NADPH oxidase activation.

Activation of oxidative burst and degranulation of porcine neutrophils by a homologous spleen galectin-1 compared to N-formyl-l-methionyl-l-leucyl-l-phenylalanine and phorbol 12-myristate 13-acetate

Galectins are a family of animal lectins defined by their beta-galactoside-binding activities and a consensus sequence in their carbohydrate-recognizing domain (CRD). Relevant roles of galectins are described in adaptive immune response, innate immunity and modulation of the acute inflammatory response. We have extended our previous studies on a porcine spleen galectin-1 in relation to its functional roles such as polymorphonuclear neutrophils (PMNs) stimulation compared to well known PMN activators e.g. N-formyl-L-methionyl-L leucyl-L-phenylalanine (fMLP) and phorbol 12-myristate 13-acetate (PMA). Relative to activation of NADPH-oxidase fMLP and PMA are stronger than galectin-1 plus cytochalasin B (CB) when the lectin is employed at low concentrations (gal-1 1 microM, 3.6+0.8 nm O(2)(-)/min/10(7) PMN). Higher doses of galectin-1 (10 microM) plus CB produced a significant activation of NADPH-oxidase (27.9+14.8 nm O(2)(-)/min/10(7) PMN) and stimulated PMN degranulation up to 50%. We propose that local galectin-1 concentrations under physiological conditions might reach suitable levels for pig PMN stimulation, and might be a natural inducer of O(2)(-) formation or degranulation. Porcine galectins might produce enhanced responses in vivo when they stimulate neutrophils in combination with some other stimuli.

Temperature dependence of NADPH oxidase in human eosinophils

The phagocyte NADPH oxidase helps kill pathogens by producing superoxide anion, O2-. This enzyme is electrogenic because it translocates electrons across the membrane, generating an electron current, Ie. Using the permeabilized patch voltage-clamp technique, we studied the temperature dependence of Ie in human eosinophils stimulated by phorbol myristate acetate (PMA) from room temperature to >37 degrees C. For comparison, NADPH oxidase activity was assessed by cytochrome c reduction. The intrinsic temperature dependence of the assembled, functioning NADPH oxidase complex measured during rapid temperature increases to 37 degrees C was surprisingly weak: the Arrhenius activation energy Ea was only 14 kcal mol(-1) (Q10, 2.2). In contrast, steady-state NADPH oxidase activity was strongly temperature dependent at 20-30 degrees C, with Ea 25.1 kcal mol(-1) (Q10, 4.2). The maximum Ie measured at 34 degrees C was -30.5 pA. Above 30 degrees C, the temperature dependence of both Ie and O2- production was less pronounced. Above 37 degrees C, Ie was inhibited reversibly. After rapid temperature increases, a secondary increase in Ie ensued, suggesting that high temperature promotes assembly of additional NADPH oxidase complexes. Evidently, about twice as many NADPH oxidase complexes are active near 37 degrees C than at 20 degrees C. Thus, the higher Q10 of steady-state Ie reflects both increased activity of each NADPH oxidase complex and preferential assembly of NADPH oxidase complexes at high temperature. In summary, NADPH oxidase activity in intact human eosinophils is maximal precisely at 37 degrees C.

Activated polymorphonuclear cells increase sickle red blood cell retention in lung: role of phospholipids

This study investigates the role of the activated polymorphonuclear cell (APMN) products on sickle red blood cell (SRBC) retention/adherence in the pulmonary circulation. Isolated rat lungs were perfused with (51)Cr-labeled normal RBCs (NRBC) or SRBCs (10% hematocrit) suspensions +/- PMNs. Specific activities of lung and perfusate were measured and retention (the number of SRBC/g lung) was calculated. SRBC retention was 3.5 times greater than NRBC retention. PMN activation was required to increase SRBC retention. Supernatants from APMN increased SRBC retention, which suggested soluble products such as oxidants, PAF, and/or leukotriene (LTB(4)) are involved. Heat inactivation of PMN NADPH oxidase had no effect on retention. Whereas neither platelet-activating factor (PAF) nor LTB(4) (secreted by APMN) increased SRBC retention, PAF+LTB(4) did. The PAF antagonist, WEB-2170, attenuated SRBC retention mediated by PAF+LTB(4) and APMNs. Similarly, zileuton (5-lipoxygenase inhibitor) attenuated APMN-mediated SRBC retention. We conclude the concomitant release of PAF and LTB(4) from APMN is involved in the initiation of microvascular occlusion by SRBCs in the perfused rat lung.

Localization of a constitutively active, phagocyte-like NADPH oxidase in rabbit aortic adventitia: enhancement by angiotensin II

Superoxide anion (O2-) plays a key role in the endogenous suppression of endothelium-derived nitric oxide (NO) bioactivity and has been implicated in the development of hypertension. In previous studies, we found that O2- is produced predominantly in the adventitia of isolated rabbit aorta and acts as a barrier to NO. In the present studies, we characterize the enzyme responsible for O2- production in the adventitia and show that this enzyme is a constitutively active NADPH oxidase with similar composition as the phagocyte NADPH oxidase. Constitutive O2--generating activity was localized to aortic adventitial fibroblasts and was enhanced by the potent vasoconstrictor angiotensin II. Immunohistochemistry of aortic sections demonstrated the presence of p22(phox), gp91(phox), p47(phox), and p67(phox) localized exclusively in rabbit aortic adventitia, coincident with the site of staining for O2- production. Furthermore, immunodepletion of p67(phox) from adventitial fibroblast particulates resulted in the loss of NADPH oxidase activity, which could be restored by the addition of recombinant p67(phox). Further study into the regulation of this adventitial source of O2- is important in elucidating the mechanisms regulating the bioactivity of NO and may contribute to our understanding of the pathogenesis of hypertension.

Analysis of activation-induced conformational changes in p47phox using tryptophan fluorescence spectroscopy

Activation of the neutrophil NADPH oxidase requires translocation of cytosolic proteins p47(phox), p67(phox), and Rac to the plasma membrane or phagosomal membrane, where they assemble with membrane-bound flavocytochrome b. During this process, it appears that p47(phox) undergoes conformational changes, resulting in the exposure of binding sites involved in assembly and activation of the oxidase. In the present study, we have directly evaluated activation-induced conformational changes in p47(phox) using tryptophan fluorescence and circular dichroism spectroscopy. Treatment of p47(phox) with amphiphilic agents known to activate the NADPH oxidase (SDS and arachidonic acid) caused a dose-dependent quenching in the intrinsic tryptophan fluorescence of p47(phox), whereas treatment with a number of other amphiphilic agents that failed to activate the oxidase had no effect on p47(phox) fluorescence. In addition, the concentration range of activating agents required to induce changes in fluorescence correlated with the concentration range of these agents that induced maximal NADPH oxidase activity in a cell-free assay system. We next determined if activation by phosphorylation caused the same type of conformational changes in p47(phox). Protein kinase C phosphorylation of p47(phox) in vitro resulted in comparable quenching of fluorescence, which also correlated directly with NADPH oxidase activity. Finally, the circular dichroism (CD) spectrum of p47(phox) was significantly changed by the addition of SDS, whereas treatment with a non-activating detergent had no effect on the CD spectrum. These results support the conclusion that activation by amphiphilic agents results in changes in the secondary structure of p47(phox). Thus, our studies provide direct evidence linking conformational changes in p47(phox) to the NADPH oxidase activation/assembly process and also further support the hypothesis that amphiphile-mediated activation of the NADPH oxidase induces changes in p47(phox) that are similar to those mediated by phosphorylation in vivo.

Phosphorylation of the respiratory burst oxidase subunit p67(phox) during human neutrophil activation. Regulation by protein kinase C-dependent and independent pathways

The respiratory burst oxidase of phagocytes and B lymphocytes catalyzes the reduction of oxygen to superoxide anion (O-2) at the expense of NADPH. This multicomponent enzyme is dormant in resting cells but is activated on exposure to an appropriate stimulus. The phosphorylation-dependent mechanisms regulating the activation of the respiratory burst oxidase are unclear, particularly the phosphorylation status of the cytosolic component p67(phox). In this study, we found that activation of human neutrophils with formyl-methionyl-leucyl-phenylalanine (fMLP), a chemotactic peptide, or phorbol myristate acetate (PMA), a stimulator of protein kinase C (PKC), resulted in the phosphorylation of p67(phox). Using an anti-p67(phox) antibody or an anti-p47(phox) antibody, we showed that phosphorylated p67(phox) and p47(phox) form a complex. Phosphoamino acid analysis of the phosphorylated p67(phox) revealed only 32P-labeled serine residues. Two-dimensional tryptic peptide mapping analysis showed that p67(phox) is phosphorylated at the same peptide whether fMLP or PMA is used as a stimulus. In addition, PKC induced the phosphorylation of recombinant GST-p67(phox) in vitro, at the same peptide as that phosphorylated in intact cells. PMA-induced phosphorylation of p67(phox) was strongly inhibited by the PKC inhibitor GF109203X. In contrast, fMLP-induced phosphorylation was minimally affected by this PKC inhibitor. Taken together, these results show that p67(phox) is phosphorylated in human neutrophils by different pathways, one of which involves protein kinase C.

The cytosolic subunit p67phox contains an NADPH-binding site that participates in catalysis by the leukocyte NADPH oxidase

The NADPH-dependent respiratory burst oxidase of human neutrophils catalyzes the reduction of oxygen to superoxide using NADPH as the electron donor and is essential for normal host defenses. To gain insight into the function of the various oxidase subunits that are required for the full expression of catalytic activity, we studied the interactions between the 2',3'-dialdehyde derivative of NADPH (NADPH dialdehyde) and neutrophil cytosol. NADPH dialdehyde treatment of cytosol resulted in the loss of the ability of the cytosol to participate in cell-free oxidase activation; this inactivation was blocked by NADPH but not by NAD, NADP, or GTP. Partial purification of neutrophil cytosol yielded a single peak which could restore the activity lost in cytosol treated with NADPH dialdehyde. This peak contained p67phox but not p47phox or Rac2. Purified recombinant p67phox was similarly able to restore the activity lost in NADPH dialdehyde-treated cytosol and bound [32P]NADPH dialdehyde in a specific fashion. The activity of recombinant p67phox in cell-free oxidase assays was lost on treatment with NADPH dialdehyde. Together, these data suggest p67phox contains the catalytic NADPH-binding site of the leukocyte NADPH oxidase.

Naphthalenesulphonamides block neutrophil superoxide production by intact cells and in a cell-free system: is myosin light chain kinase responsible for these effects?

Selective antagonists of myosin light chain kinase (MLCK) [e.g. ML-7; 1-(5-iodonaphthalene-1-sulphonyl)-1H-hexahydro-1,4-diazepine hydrochloride] were found to inhibit superoxide (O2-) release from stimulated neutrophils. The concentrations of ML-7 that were inhibitory were substantially lower than those reported for a selective antagonist of protein kinase C [i.e. H-7; 1-(5-isoquinolinesulphonyl)-2-methylpiperazine dihydrochloride]. ML-7 also reduced the phosphorylation of the 47 kDa subunit of the NADPH-oxidase system (p47-phox) and blocked translocation of this protein to the Triton X-100-insoluble fraction in stimulated cells. Interestingly, ML-7 also inhibited O2- production in a cell-free system derived from neutrophils at concentrations similar to those that were effective in vivo. This cell-free system does not require ATP and is insensitive to all other inhibitors of protein kinases tested, including some highly effective against MLCK (i.e. staurosporine). Thus, the data suggest that ML-7 does not block O2- release by inhibiting a protein kinase but instead may interact directly with a subunit of the oxidase. The binding site for ML-7 may provide a valuable target for inhibiting the inflammatory properties of phagocytic leucocytes by naphthalenesulphonamides designed to lack activity against protein kinases.

Viscum album agglutinin-induced aggregation of blood cells and the lectin effects on neutrophil function

Extracts from mistletoe enjoy a large popularity in central Europe as an unconventional treatment modality for cancer, warranting scientific efforts with defined components to delineate any potential benefit. The galactose-specific lectin from Viscum album (VAA), known to exhibit immunomodulatory and ensuing antitumoral capacities in animal model systems, was shown to aggregate human blood cells in the following order: neutrophils, mononuclear cells--thrombocytes and erythrocytes. To contribute to the analysis of lectin effects on individual aspects of the host defence system, two parameters of neutrophils were quantitatively assessed, namely the aggregating activity of VAA as a measure of strength of interaction with cell surface ligands and the effect of lectin on oxidative metabolism (H2O2 release) of these cells. It was found that whole lectin and its carbohydrate-binding B-subunit possessed the capacity to induce cell aggregation and H2O2 release, which were blocked by D-galactose and lactose. Both effects displayed similar dependence on the lectin concentration in the range 0.1-25 micrograms/ml. The toxic A-subunit displayed detectable activity only in high doses (50 micrograms/ml) while the bovine heart galaptin (14 kDa; galectin-1) failed to affect neutrophils. The role of oxidative metabolism in regulation of neutrophil aggregation induced by VAA was studied using metabolic inhibitors and controlled heating at 46 degrees C leading to inhibition of plasma membrane NADPH-oxidase system. Trifluoperazine and menadione inhibited the neutrophil aggregation in a dose-dependent manner in comparison with such inhibitors as amiloride and theophylline.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of a H(+)-selective conductance during granulocytic differentiation of HL-60 cells

The NADPH oxidase is one of the main microbicidal systems of granulocytes. Stimulation of the oxidase during infection leads to a burst of metabolic acid generation. Potentially deleterious cytosolic acidification is prevented by the simultaneous activation of homeostatic H+ extrusion mechanisms, including a recently described H+ conductance. Studies in granulocytes from chronic granulomatous disease patients have suggested a relationship between the oxidase and the H+ conductive pathway. In this report we compared the expression of the H+ conductance and the NADPH oxidase during granulocytic differentiation of dimethyl sulfoxide-induced HL-60 cells. Patch-clamp determinations demonstrated that the H(+)-selective current detectable in differentiated HL-60 cells is virtually absent in uninduced cells. The H+ conductance was also estimated fluorimetrically, measuring changes in the cytosolic pH of suspended cells. Imposition of an inward protonmotive force failed to induce significant cytosolic acidification. In contrast, a sizable conductive H+ extrusion was detected in acid-loaded differentiated cells, consistent with the rectifying properties of the current measured electrophysiologically. By the spectroscopic method, the H+ conductance was not detectable in uninduced cells, developing gradually during granulocytic differentiation. Development of the conductive pathway was found to parallel the biochemical and functional appearance of the NADPH oxidase. These findings suggest that the H+ extrusion mechanisms required for the maintenance of the intracellular pH during granulocyte activation develop pari passu with the acid generating systems and suggest a functional and possibly structural association between the H+ conductance and the NADPH oxidase.

Activation of H+ conductance in neutrophils requires assembly of components of the respiratory burst oxidase but not its redox function

In phagocytes, superoxide generation by the NADPH oxidase is accompanied by metabolic acid production. Cytoplasmic acidification during this metabolic burst is prevented by a combination of H+ extrusion mechanisms, including a unique H+ conductance. NADPH oxidase is deficient in chronic granulomatous disease (CGD) patients. The burst of acid production is absent in CGD patients lacking the 47-kD (p47-phox) or the 91-kD (gp91-phox) subunits of the oxidase. Activation of the H+ conductance is also defective in these patients suggesting that (a) the oxidase itself undertakes H+ translocation or (b) oxidase assembly is required to stimulate a separate H+ conducting entity. To discern between these possibilities, three rare forms of CGD were studied. In neutrophils expressing nonfunctional cytochrome b, the conductance was activated to near-normal levels, implying that functional oxidase is not required to activate H+ extrusion. CGD cells expressing diminished amounts of cytochrome displayed H+ conductance approaching normal levels, suggesting that the oxidase itself does not translocate H+. Finally, the conductance was only partially inhibited in patients lacking the 67-kD subunit, indicating that this component is not essential for stimulation of H+ transport. We propose that normal assembly of the oxidase subunits is required for optimal activation of a closely associated but distinct H+ conducting entity.

A critical role for monocytes and CD14 in endotoxin-induced endothelial cell activation

Vascular endothelium activated by endotoxin (lipopolysaccharide [LPS]) and cytokines plays an important role in organ inflammation and blood leukocyte recruitment observed during sepsis. Endothelial cells can be activated by LPS directly, after its interaction with LPS-binding protein and soluble CD14 in plasma. LPS-LPS-binding protein complexes in blood also interact with monocytes and neutrophils bearing glycosyl-phosphatidylinositol (GPI) anchored membrane CD14 (mCD14), promoting the release of cytokines such as tumor necrosis factor and interleukin 1 (IL-1). These molecules, in turn, have the capacity to activate endothelial cells providing an indirect pathway for LPS-dependent endothelial cell activation. In this work, we address the relative importance of the direct and the indirect pathway of in vitro LPS-induced human umbilical vein endothelial cell (HUVEC) activation. Substituting whole blood for plasma resulted in a 1,000-fold enhancement of HUVEC sensitivity to LPS. Both blood- and plasma-dependent enhanced activation of HUVEC were blocked with an anti-CD14 monoclonal antibody. Blood from patients with paroxysmal nocturnal hemoglobinuria, whose cells lack mCD14 and other GPI anchored proteins, was unable to enhance LPS activation of HUVEC above the level observed with plasma alone. IL-10, an inhibitor of monocyte release of cytokines, decreased the blood-dependent enhancement of HUVEC activation by LPS. Blood adapted to small doses of LPS was also less efficient than nonadapted blood in producing this enhancement. Addition of purified mononuclear cells to HUVEC or the transfer of plasma from whole blood incubated with LPS to HUVEC, duplicated the enhancement effect observed when whole blood was incubated with HUVEC. Taken together, these data suggest that the indirect pathway of LPS activation of endothelial cell is mediated by monocytes and mCD14 through the secretion of a soluble mediator(s). The indirect pathway is far more efficient than the direct, plasma-dependent pathway.

Heat shock in human neutrophils: superoxide generation is inhibited by a mechanism distinct from heat-denaturation of NADPH oxidase and is protected by heat shock proteins in thermotolerant cells

Independently of the stimulating agent used, generation of O2- by human neutrophils is transiently inhibited when the cells have been exposed to elevated temperatures. This phenomenon is concomitant with the synthesis of heat shock proteins (HSPs). We have investigated a possible relationship between HSPs and modulation of NADPH oxidase activity in human neutrophils exposed to heat. HSPs were not involved in the inhibition of O2- generation since 1) in enucleated cytoplasts, which are unable to synthesize proteins, the generation of O2- was inhibited after exposure to 43 degrees C, 2) using actinomycin D (Act D) in intact cells, it was possible selectively to inhibit the synthesis of HSPs without modifying the inhibition of NADPH oxidase activity that followed HS. Furthermore, the recovery of NADPH oxidase activity was not under the control of HSPs because the enzyme recovered as well in Act D-treated neutrophils. The NADPH oxidase activity was reconstituted in a cell-free assay by combining the cytosol with the plasma membrane-enriched fraction in the presence of arachidonic acid (AA) and NADPH. Subcellular fractions obtained from control or heated neutrophils exhibited similar oxidase activities suggesting that heat exposure did not induce denaturation of the oxidase components but rather altered the mechanisms of translocation and/or assembly of these components with the plasma membrane. This hypothesis was supported by the inhibition of the granule release in heated cells, a process which also requires translocation and association fusion with the plasma membrane. On the other hand, preexposure of neutrophils to HS prevented the inhibition of O2- generation during a second challenging HS. This acquired thermotolerance was abolished when the synthesis of HSPs was inhibited during the first HS with Act D, indicating a direct relationship between protection of O2- generation and synthesis of HSP. Here we demonstrate that synthesis of HSPs and inhibition or recovery of NADPH oxidase activity are concomitant but unrelated phenomena. In contrast, accumulation of HSPs in thermotolerant neutrophils appeared to play an important role in the prevention of NADPH oxidase inhibition. These results provide further insights into the behavior of human neutrophils and NADPH oxidase upon heat injury.