Cell-bound albumin is the 70-kDa peptidoglycan-, lipopolysaccharide-, and lipoteichoic acid-binding protein on lymphocytes and macrophages

The dangerous liaisons in innate immunity involving recombinant proteins and endotoxins: Examples from the literature and the Leptospira field

Endotoxins, also known as lipopolysaccharides (LPS), are essential components of cell walls of diderm bacteria such as Escherichia coli. LPS are microbe-associated molecular patterns that can activate pattern recognition receptors. While trying to investigate the interactions between proteins and host innate immunity, some studies using recombinant proteins expressed in E. coli reported interaction and activation of immune cells. Here, we set out to provide information on endotoxins that are highly toxic to humans and bind to numerous molecules, including recombinant proteins. We begin by outlining the history of the discovery of endotoxins, their receptors and the associated signaling pathways that confer extreme sensitivity to immune cells, acting alone or in synergy with other microbe-associated molecular patterns. We list the various places where endotoxins have been found. Additionally, we warn against the risk of data misinterpretation due to endotoxin contamination in recombinant proteins, which is difficult to estimate with the Limulus amebocyte lysate assay, and cannot be completely neutralized (e.g., treatment with polymyxin B or heating). We further illustrate our point with examples of recombinant heat-shock proteins and viral proteins from severe acute respiratory syndrome coronavirus 2, dengue and HIV, for which endotoxin contamination has eventually been shown to be responsible for the inflammatory roles previously ascribed. We also critically appraised studies on recombinant Leptospira proteins regarding their putative inflammatory roles. Finally, to avoid these issues, we propose alternatives to express recombinant proteins in nonmicrobial systems. Microbiologists wishing to undertake innate immunity studies with their favorite pathogens should be aware of these difficulties.

MAMPs: A devil tamed becomes an angel

Symbiotic microorganisms modulate systemic immunity with unclear mechanisms. In this issue of Cell Host & Microbe, Clarke and colleagues uncover a coherent mechanism where the systemic spread of Firmicutes cell wall glycoconjugates enhances global immune fitness while simultaneously being delicately controlled to prevent systemic inflammation.

Evaluation of Antibacterial Activity of Selenium Nanoparticles against Food-Borne Pathogens

Selenium is an essential micronutrient for all mammals and plays an important role in maintaining human physiological functions. Selenium nanoparticles (SeNPs) have been shown to demonstrate antioxidant and antimicrobial activity. The objective of this study was to explore whether SeNPs have the potential to be used as food preservatives with which to reduce food spoilage. SeNPs were synthesized through ascorbic acid reduction of sodium selenite (Na₂SeO₃) in the presence of bovine serum albumin (BSA) as a capping and stabilizing agent. The chemically synthesized SeNPs had a spherical conformation with an average diameter of 22.8 ± 4.7 nm. FTIR analysis confirmed that the nanoparticles were covered with BSA. We further tested the antibacterial activity of these SeNPs against ten common food-borne bacteria. A colony-forming unit assay showed that SeNPs exhibited inhibition on the growth of Listeria Monocytogens (ATCC15313) and Staphylococcus epidermidis (ATCC 700583) starting at 0.5 µg/mL, but higher concentrations were required to slow down the growth of Staphylococcus aureus (ATCC12600), Vibrio alginolyticus (ATCC 33787), and Salmonella enterica (ATCC19585). No inhibition was observed on the growth of the other five test bacteria in our study. Our data suggested that the chemically synthesized SeNPs were able to inhibit the growth of some food-borne bacteria. The size and shape of SeNPs, method of synthesis, and combination of SeNPs with other food preservatives should be considered when SeNPs are to be used for the prevention of bacteria-mediated food spoilage.

Albumin infusion may decrease the incidence and severity of overt hepatic encephalopathy in liver cirrhosis

BACKGROUND

The role of human albumin infusion for the prevention and treatment of overt hepatic encephalopathy (HE) in liver cirrhosis remains unclear.

RESULTS

Among the 708 patients without pre-existing overt HE, albumin infusion significantly decreased the incidence of overt HE (4.20% versus 12.70%, P<0.001) and in-hospital mortality (1.70% versus 5.40%, P=0.008). Among the 182 patients with overt HE at admission or during hospitalization, albumin infusion significantly improved overt HE (84.60% versus 68.10%, P=0.009) and decreased in-hospital mortality (7.70% versus 19.80%, P=0.018). Meta-analysis of 6 studies found that albumin infusion might decrease the risk of overt HE (OR=1.63, P=0.07), but the difference was not statistically significant. Meta-analysis of 3 studies found that albumin infusion significantly improved overt HE (OR=2.40, P=0.04).

CONCLUSIONS

Based on the results of our retrospective study and meta-analysis, albumin infusion might prevent from the occurrence of overt HE and improve the severity of overt HE in cirrhosis. Our retrospective study also suggested that albumin infusion improved the outcomes of cirrhotic patients regardless of overt HE.

METHODS

Cirrhotic patients consecutively admitted between January 2010 and June 2014 were considered in a retrospective study. A 1:1 propensity score matching analysis was performed. Additionally, publications regarding albumin infusion for the management of overt HE were systematically searched. Meta-analyses were performed by random-effect model. Odds ratio (OR) was calculated.

Regulation of interactions of endotoxin with host cells

Potent Toll-like receptor 4 (TLR4)-dependent cell activation by endotoxin requires lipopolysaccharide-binding protein (LBP) and CD14-dependent delivery of endotoxin to cells containing MD-2 and TLR4. We have used metabolically labeled [14C] meningococcal lipooligosaccharide (LOS), purified recombinant endotoxin-binding proteins, and cultured endothelial cells to better define protein: endotoxin intermediates key in cell activation in the absence of functional membrane (m) CD14. Protein:endotoxin complexes or aggregates ( agg) were purified by gel sieving and characterized by immunocapture and bio-assays. Cell activation closely correlated with LBP, albumin and soluble (s) CD14-dependent conversion of endotoxin agg (Mr≥ 20 × 106) to monomeric (M ~55 × 103) endotoxin:sCD14 complexes. Ordered interaction of LBP (+ albumin) and sCD14 withrLOS agg was required for the efficient formation of a bioactive endotoxin:sCD14 complex and potent cell activation. Increasing the ratio of LBP/sCD14 or addition of bactericidal/permeability-increasing protein (BPI) reduced accumulation of endotoxin:sCD14 complexes and instead yielded aggregates of endotoxin (Mr~1—20 × 106) containing LBP or BPI that were taken up by cells in a CD14- and TLR4-independent manner without inducing pro-inflammatory responses. These findings strongly suggest that host machinery linked to TLR4-dependent cellular activation or TLR4-independent cellular clearance of endotoxin selectively recognizes different protein:endotoxin complexes. At the outset of infection, the low concentrations of LBP present and absence of extracellular BPI favor formation of pro-inflammatory endotoxin:CD14 complexes. The mobilization of LBP and BPI that is triggered by inflammation directs endotoxin for clearance and hence resolution of endotoxin-triggered inflammation.

Role of albumin in diseases associated with severe systemic inflammation: Pathophysiologic and clinical evidence in sepsis and in decompensated cirrhosis

The metabolism of albumin in inflammatory states such as sepsis or major surgery is complex and still not well characterized. Nevertheless, in inflammatory states, albumin synthesis has been observed to increase. By contrast, in decompensated cirrhosis, a disease characterized by systemic inflammation, albumin synthesis by the liver may decrease to 30% to 50% of normal values. Furthermore, in these conditions, there are high capillary leakage and altered albumin kinetics. The discussion regarding the effect of exogenous albumin administration on intravascular volume in inflammatory states should therefore address albumin turnover. To add complexity to our understanding of the effects of albumin, there are many data indicating that the therapeutic action of albumin is mediated not only through the impact on plasma volume expansion but also through a modulatory effect on inflammation and oxidative stress. All these characteristics are relevant to diseases associated with systemic inflammation including sepsis and decompensated cirrhosis.

Recent advances in cirrhotic cardiomyopathy

Cirrhotic cardiomyopathy, a cardiac dysfunction presented in patients with cirrhosis, represents a recently recognized clinical entity. It is characterized by altered diastolic relaxation, impaired contractility, and electrophysiological abnormalities, in particular prolongation of the QT interval. Several mechanisms seem to be involved in the pathogenesis of cirrhotic cardiomyopathy, including impaired function of beta-receptors, altered transmembrane currents, and overproduction of cardiodepressant factors, like nitric oxide, tumor necrosis factor α, and endogenous cannabinoids. Diastolic dysfunction is the first manifestation of cirrhotic cardiomyopathy and reflects the increased stiffness of the cardiac mass, which leads to delayed left ventricular filling. On the other hand, systolic incompetence is presented later, is usually unmasked during pharmacological or physical stress, and predisposes to the development of hepatorenal syndrome. The prolongation of QT is found in about 50 % of cirrhotic patients, but rarely leads to fatal arrhythmias. Cirrhotics with blunted cardiac function seem to have poorer survival rates compared to those without, and the risk is particularly increased during the insertion of transjugular intrahepatic portosystemic shunt or liver transplantation. Till now, there is no specific treatment for the management of cirrhotic cardiomyopathy. New agents, targeting to its pathogenetical mechanisms, may play some role as future therapeutic options.

Human serum albumin, systemic inflammation, and cirrhosis

Human serum albumin (HSA) is one of the most frequent treatments in patients with decompensated cirrhosis. Prevention of paracentesis-induced circulatory dysfunction, prevention of type-1 HRS associated with bacterial infections, and treatment of type-1 hepatorenal syndrome are the main indications. In these indications treatment with HSA is associated with improvement in survival. Albumin is a stable and very flexible molecule with a heart shape, 585 residues, and three domains of similar size, each one containing two sub-domains. Many of the physiological functions of HSA rely on its ability to bind an extremely wide range of endogenous and exogenous ligands, to increase their solubility in plasma, to transport them to specific tissues and organs, or to dispose of them when they are toxic. The chemical structure of albumin can be altered by some specific processes (oxidation, glycation) leading to rapid clearance and catabolism. An outstanding feature of HSA is its capacity to bind lipopolysaccharide and other bacterial products (lipoteichoic acid and peptidoglycan), reactive oxygen species, nitric oxide and other nitrogen reactive species, and prostaglandins. Binding to NO and prostaglandins are reversible, so they can be transferred to other molecules at different sites from their synthesis. Through these functions, HSA modulates the inflammatory reaction. Decompensated cirrhosis is a disease associated systemic inflammation, which plays an important role in the pathogenesis of organ or system dysfunction/failure. Although, the beneficial effects of HAS have been traditionally attributed to plasma volume expansion, they could also relate to its effects modulating systemic and organ inflammation.

Interaction of peptide-bound beads with lipopolysaccharide and lipoproteins

We previously reported the generation of lipopolysaccharide (LPS)-binding peptides by phage display and chemical modification. Among them, a dodecapeptide designated Li5-025 (K'YSSSISSIRAC'; K' and C' denote d-lysine and d-cysteine, respectively) showed a high binding affinity for LPS and was resistant to protease digestion (Suzuki et al., 2010). In the current study, Li5-025-bound silica beads, hereafter referred to as P-beads, were generated and found to be devoid of LPS-neutralizing activity. Thus, LPS bound to the P-beads could be directly used in the Limulus amebocyte lysate (LAL) assay. P-beads bound LPS dissolved in solutions of ethanol, pH4, pH10, and 0.5M NaCl and LPS bound to the P-beads was quantitatively assayed. The sensitivity of this assay was observed to be approximately 0.1pg/mL LPS. P-beads bound LPS dissolved in antithrombin III (AT III) solution which is a strong inhibitor of activated factors C and B as well as the clotting enzyme in the LAL assay; the inhibitory effect of AT III was completely reversed upon washing the P-beads with 25% acetonitrile. This was employed as the first step for the detection of free LPS in plasma using the LAL assay. LPS added to human plasma at 0°C followed by application to the P-beads and subsequent washing with 25% acetonitrile resulted in low LPS activity as detected by the LAL assay. However, further washing of the P-beads with 0.1% Triton X100 in 25% acetonitrile resulted in high LPS activity. This is the first instance of quantitative detection of free LPS in plasma using the LAL assay, and the sensitivity of this method was observed to be 1pg/mL of LPS. The proteins eluted in the 0.1% Triton X-100 wash were analyzed using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Two protein bands of 28kDa and 18kDa were predominantly observed. Mass spectrometry analysis revealed that the 28kDa and 18kDa bands corresponded to apolipoprotein A-I (apoA-I) and apolipoprotein A-II (apoA-II), respectively. ApoA-I and apoA-II are components of high density lipoprotein (HDL). Thus, it is likely that the P-beads-bound LPS was sequestered by HDL, resulting in neutralization of its toxicity. This study showed that by using P-beads, free LPS in plasma can be quantitatively measured by the LAL assay at a concentration of 1pg/mL.

Azacytidine induces necrosis of multiple myeloma cells through oxidative stress

Azacytidine is an inhibitor of DNA methyltransferase and is known to be an anti-leukemic agent to induce cancer cell apoptosis. In the present study, multiple myeloma cells were treated with azacytidine at clinically relevant concentrations to induce necrosis through oxidative stress. Necrotic myeloma cells exhibit unique characteristics, including enrichment of the cell-bound albumin and overexpression of endoplasmic reticulum (ER)- and mitochondrial-specific chaperones, which were not observed in other necrotic cells, including HUH-7, A2780, A549, and Hoc1a. Proteomic analysis shows that HSP60 is the most abundant up-regulated mitochondrial specific chaperone, and azacytidine-induced overexpression of HSP60 is confirmed by western blot analysis. In contrast, expression levels of cytosolic chaperones such as HSP90 and HSP71 were down-regulated in azacytidine-treated myeloma cells, concomitant with an increase of these chaperones in the cell culture medium, suggesting that mitochondrial chaperones and cytosolic chaperones behave differently in necrotic myeloma cells; ER- and mitochondrial-chaperones being retained, and cytosolic chaperones being released into the cell culture medium through the ruptured cell membrane. Our data suggest that HSP60 is potentially a new target for multiple myeloma chemotherapy.

Oxidative stress induces monocyte necrosis with enrichment of cell-bound albumin and overexpression of endoplasmic reticulum and mitochondrial chaperones

In the present study, monocytes were treated with 5-azacytidine (azacytidine), gossypol or hydrogen peroxide to induce cell death through oxidative stress. A shift from apoptotic to necrotic cell death occurred when monocytes were treated with 100 µM azacytidine for more than 12 hours. Necrotic monocytes exhibited characteristics, including enrichment of cell-bound albumin and up-regulation of endoplasmic reticulum (ER)- and mitochondrial-specific chaperones to protect mitochondrial integrity, which were not observed in other necrotic cells, including HUH-7, A2780, A549 and HOC1a. Our results show that the cell-bound albumin originates in the culture medium rather than from monocyte-derived hepatocytes, and that HSP60 is a potential binding partner of the cell-bound albumin. Proteomic analysis shows that HSP60 and protein disulfide isomerase are the most abundant up-regulated mitochondrial and ER-chaperones, and that both HSP60 and calreticulin are ubiquitinated in necrotic monocytes. In contrast, expression levels of the cytosolic chaperones HSP90 and HSP71 were down-regulated in the azacytidine-treated monocytes, concomitant with an increase in the levels of these chaperones in the cell culture medium. Collectively, our results demonstrates that chaperones from different organelles behave differently in necrotic monocytes, ER- and mitochondrial chaperones being retained and cytosolic and nuclear chaperones being released into the cell culture medium through the ruptured cell membrane. HSP60 may serve as a new target for development of myeloid leukemia treatment.

Cell density plays a critical role in ex vivo expansion of T cells for adoptive immunotherapy

The successful ex vivo expansion of a large numbers of T cells is a prerequisite for adoptive immunotherapy. In this study, we found that cell density had important effects on the process of expansion of T cells in vitro. Resting T cells were activated to expand at high cell density but failed to be activated at low cell density. Activated T cells (ATCs) expanded rapidly at high cell density but underwent apoptosis at low cell density. Our studies indicated that low-cell-density related ATC death is mediated by oxidative stress. Antioxidants N-acetylcysteine, catalase, and albumin suppressed elevated reactive oxygen species (ROS) levels in low-density cultures and protected ATCs from apoptosis. The viability of ATCs at low density was preserved by conditioned medium from high-density cultures of ATCs in which the autocrine survival factor was identified as catalase. We also found that costimulatory signal CD28 increases T cell activation at lower cell density, paralleled by an increase in catalase secretion. Our findings highlight the importance of cell density in T cell activation, proliferation, survival and apoptosis and support the importance of maintaining T cells at high density for their successful expansion in vitro.

Stabilization of gammaretroviral and lentiviral vectors: from production to gene transfer

BACKGROUND

The low stability of gammaretroviral and lentiviral vectors affects their production, making high quality clinical preparations a difficult goal to achieve. Recently, our laboratory has shown that the main inactivation mechanism for both these vectors is the loss of their capacity to perform reverse transcription. The present study aimed to increase the stability of gammaretroviral and lentiviral at 37 degrees C and at 4 degrees C.

METHODS

Inactivation studies were performed with gammaretroviral and lentiviral vectors at 37 and 4 degrees C, with and without several stabilizing compounds. The residual viral infectivity and reverse transcription capacity of these samples were tested.

RESULTS

The results obtained demonstrate that it is possible to increase the stability of reverse transcription and the infectivity stability of purified gammaretroviral vectors by adding recombinant human albumin (rHSA) to the storage buffer, both at 37 degrees C and at 4 degrees C. For lentiviral vectors, it was observed that further protection was needed. This was achieved by adding lipids to the storage buffer, using a mixture of lipoproteins and rHSA. The difference of stabilization between gammaretroviral and lentiviral vectors was validated by performing stabilization tests with vectors possessing different envelope proteins and produced by different cell lines.

CONCLUSIONS

The presented study reveals that it is possible to increase the half-life of purified gammaretroviral and lentiviral vectors at 37 degrees C and at 4 degrees C, but the two vectors have different stabilization requirements: for retroviral vectors, the addition of rHSA is enough and, for lentiviral vectors, it is necessary to add both lipoproteins and rHSA. The increase of the stability of the reverse transcription process was shown to have a high impact with respect to the increase of the stability of infectivity.

Human microglial cells synthesize albumin in brain

Albumin, an abundant plasma protein with multifunctional properties, is mainly synthesized in the liver. Albumin has been implicated in Alzheimer's disease (AD) since it can bind to and transport amyloid beta (Aβ), the causative agent of AD; albumin is also a potent inhibitor of Aβ polymerization. Despite evidence of non-hepatic transcription of albumin in many tissues including kidney and pancreas, non-hepatic synthesis of albumin at the protein level has been rarely confirmed. In a pilot phase study of Human Brain Proteome Project, we found evidence that microglial cells in brain may synthesize albumin. Here we report, for the first time, the de novo synthesis of albumin in human microglial cells in brain. Furtherore, we demonstrate that the synthesis and secretion of albumin from microglial cells is enhanced upon microgial activation by Aβ_1–42- or lipopolysaccharide (LPS)-treatment. These data indicate that microglial cells may play a beneficial role in AD by secreting albumin that not only inhibits Aβ polymerization but also increases its clearance.

The recognition of adsorbed and denatured proteins of different topographies by β2 integrins and effects on leukocyte adhesion and activation

Leukocyte beta2 integrins Mac-1 and p150,95 are promiscuous cell-surface receptors that recognise and mediate cell adhesion to a variety of adsorbed and denatured proteins. We used albumin as a model protein to study whether leukocyte adhesion and activation depended on the nm-scale topography of a protein adlayer. Albumin adsorbed from the native conformation gave rise to different adlayer topographies and different amounts of adsorbed protein on hydrophobic and relatively hydrophilic polystyrene and silanised silicon-wafer surfaces, whereas adsorption of pre-denatured Alb resulted in similar adlayer topographies and similar amounts of adsorbed protein on these surfaces. All three distinct protein-adlayer topographies supported adhesion of in vitro differentiated, macrophage-like U937 and THP-1 cells, but did not support adhesion of their promonocytic precursors. Human monocytes freshly isolated from peripheral blood did not adhere to adsorbed albumin, not even in the presence of monocyte chemoattractant protein-1 and macrophage inflammatory protein-1alpha chemokines. Adhesion of the macrophage-like cells to albumin in any of the three topographies was inhibited by antibodies against beta2 integrins, but not by antibodies against beta1 integrins, and did not induce secretion of the proinflammatory cytokine tumour necrosis factor-alpha.

Removal of lipopolysaccharides from protein–lipopolysaccharide complexes by nonflammable solvents

During the recovery of recombinant proteins from gram negative bacteria, many of the methods used to extract proteins from cells release lipopolysaccharides (LPS, endotoxin) along with the protein of interest. In many instances, LPS will co-purify with the target protein due to specific or non-specific protein-LPS interactions. We have investigated the ability of alkanediols to effect the separation of LPS from protein-LPS complexes while the complexes are immobilized on ion exchange chromatographic resins. Proteins were complexed with fluorescently labeled LPS and bound to ion exchange resin. Alkanediol washes of the resins were preformed and the proteins eluted. Column eluates were monitored for LPS and protein by fluorescence and UV spectroscopy, respectively. Alkanediols were effective agents for dissociating LPS from protein-LPS complexes. The efficiency of LPS removal increased with increasing alkanediol chain length. The 1,2-alkanediol isomers were more effective than terminal alkanediol isomers in the separation of LPS from protein-LPS complexes, while the separation of LPS from protein-LPS complexes was more efficient on cation exchangers than on anion exchangers. In addition, it was noted during these investigations that the 1,2-alkanediols increased the retention time of the proteins on the ion exchange resins. Alkanediols provide a safer alternative to the use of other organics such as alcohols or acetonitrile for the separation of LPS from protein due to their lower toxicity and decreased inflammability. In addition, they are less costly than many of the detergents that have been used for similar purposes.

The proteasome as a lipopolysaccharide-binding protein in macrophages: differential effects of proteasome inhibition on lipopolysaccharide-induced signaling events

We have developed a novel LPS probe using a highly purified and homogenous preparation of [(3)H] Escherichia coli LPS from the deep rough mutant, which contains a covalently linked, photoactivable 4-p-(azidosalicylamido)-butylamine group. This cross-linker was used to identify the LPS-binding proteins in membranes of the murine-macrophage-like cell line RAW 264.7. The alpha-subunit (PSMA1 C2, 29.5 kDa) and the beta-subunit (PSMB4 N3, 24.36 kDa) of the 20S proteasome complex were identified as LPS-binding proteins. This is the first report demonstrating LPS binding to enzymes such as the proteasome subunits. Functionally, LPS enhanced the chymotrypsin-like activity of the proteasome to degrade synthetic peptides in vitro and, conversely, the proteasome inhibitor lactacystin completely blocked the LPS-induced proteasome's chymotrypsin activity as well as macrophage TNF-alpha secretion and the expression of multiple inflammatory mediator genes. Lactacystin also completely blocked the LPS-induced expression of Toll-like receptor 2 mRNA. In addition, lactacystin dysregulated mitogen-activated protein kinase phosphorylation in LPS-stimulated macrophages, but failed to inhibit IL-1 receptor-associated kinase-1 activity. Importantly, lactacystin also prevented LPS-induced shock in mice. These data strongly suggest that the proteasome complex regulates the LPS-induced signal transduction and that it may be an important therapeutic target in Gram-negative sepsis.

Heparin inhibits lipopolysaccharide (LPS) binding to leukocytes and LPS-induced cytokine production

The glycosaminoglycan heparin is known to exhibit anti-inflammatory properties unrelated to its anticoagulant activity. However, in a generalized inflammatory response with implanted or extracorporeal devices, the beneficial effect of heparin coating and/or systemic administration is still unclear as well as the precise mechanisms of action. In the present study, we have first studied the effect of heparin on lipopolysaccharide (LPS)-induced cytokine production by human blood monocytes. Our results indicated that the production of interleukin-1alpha, tumor necrosis factor-alpha, and interleukin-8 was significantly decreased when heparin was simultaneously incubated with Escherichia coli LPS. Because the modulation of heparin on monocyte activation could be mediated by its binding via CD14, the main LPS receptor on monocytes, we then studied the binding of LPS and heparin to leukocytes from human blood and to Chinese hamster ovary cells transfected with the human CD14 gene. The data by flow cytometry showed the binding of biotinylated heparin to leukocytes. Moreover, the experiments performed on leukocytes and on CD14-positive Chinese hamster ovary cells indicated that heparin inhibited LPS binding. From our results, we conclude that: 1. heparin is an effective inhibitor of LPS-induced monocyte activation, and 2. heparin inhibits the binding of LPS to cells via a CD14-independent pathway. This study suggests a potentially important therapeutic application for heparin or heparin analogs to prevent inflammation with biomaterials.

An essential role for albumin in the interaction of endotoxin with lipopolysaccharide-binding protein and sCD14 and resultant cell activation

Experiments utilizing endotoxin aggregates, lipooligosaccharides (LOS) isolated from metabolically labeled Neisseria meningitidis serotype group B, demonstrate that albumin is an essential component of lipopolysaccharide binding protein- (LBP) and sCD14-dependent 1) disaggregation of LOS and 2) LOS activation of human umbilical vein endothelial cells (HUVEC). Aggregates of LOS (LOS(agg)) with an apparent M(r) >or= 2 x 10(7) were isolated by gel sieving on Sephacryl HR S500 in buffered balanced salts solution plus albumin. Incubation of LOS(agg) with LBP and sCD14 promoted LOS(agg) disaggregation in an albumin-dependent fashion to complexes that contain LOS and sCD14, but no LBP, with an apparent M(r) approximately 60,000 (LOS:sCD14) as determined by Sephacryl S200 chromatography. Isolation by gel filtration of LOS(agg):protein aggregates formed by the interaction of LOS(agg) with either LBP or sCD14 alone revealed that the sequence of LOS-protein interactions as well as the step(s) at which albumin is necessary for the production of bioactive LOS:sCD14 were specific. Efficient generation of LOS:sCD14 required 1) interaction of LOS(agg) with LBP before interaction with CD14 and 2) the presence of albumin during the interaction of LBP with LOS(agg). Activation of HUVEC by LOS(agg), as measured by IL-8 production, required both LBP and sCD14 and was thirty times more potent in the presence of albumin. In contrast, LOS:sCD14 did not require additional LBP, sCD14, or albumin to activate HUVEC but depended on the presence of albumin for optimal solubility/stability once formed. The albumin effect is apparently specific, because neither ovalbumin nor gelatin substituted for albumin in facilitating LBP:sCD14-dependent disaggregation of LOS(agg) or activation of endothelial cells. These results indicate that albumin is an essential facilitator of LBP/sCD14-induced LOS disaggregation that is required for activation of endothelial cells by LOS(agg).

Interactions of bacterial lipopolysaccharide and peptidoglycan with a 70 kDa and an 80 kDa protein on the cell surface of CD14+ and CD14- cells

Bacterial cell wall components, lipopolysaccharide (LPS), lipoteichoic acid (LTA), and peptidoglycan (PGN) are known to stimulate cells of the immune, inflammatory and vascular systems contributing to septic shock. CD14 has been identified as the main LPS receptor, a process that is accelerated by the serum protein LPS-binding protein (LBP). CD14 has also been found to bind LTA and PGN from the cell wall of gram positive bacteria. Recently, toll-like receptor proteins TLR-2 and TLR-4 have been shown to be required for LPS and LTA-induced intracellular signalling. Although CD14 functions as either a glycosylphosphatidylinositol (GPI)-anchored molecule that does not transverse the cell membrane or as a soluble serum protein, the mechanisms by which the CD14-LPS/LTA complex interacts with the TLRs remains to be elucidated. We have looked directly for cell surface protein(s) that bind LPS or LTA in a CD14-dependent manner. Using biochemical approaches we have identified two proteins of molecular weight 70 kDa (LAP-1) and 80 kDa (LAP-2) that can be precipitated from both CD14(+) and CD14(-) cells with LPS- or LTA-specific antibodies. Binding of LPS and LTA to LAP-1 and -2 required serum. While soluble CD14 (sCD14) was sufficient to allow precipitation of these two proteins from CD14(-) cells, serum could not be replaced by purified sCD14 and/or LBP when mCD14-expressing cells were used.

Analysis of lipopolysaccharide (LPS)-binding characteristics of serum components using gel filtration of FITC-labeled LPS

Lipopolysaccharide (LPS)-binding components in serum play an important role in modifying LPS toxicity. We analyzed the binding characteristics of LPS in the presence of serum using gel filtration of FITC-labeled LPS (FITC-LPS) with on line detection of optical density and fluorescence. FITC-LPS separately behaves as an aggregate resulting in a low, dequenched, fluorescence. Binding of single LPS molecules, segregated from the aggregate, to serum components results in an increase in the fluorescence due to dequenching, and a comigration of fluorescence and optical density signals using gel filtration. This method, in combination with the use of specific antibodies inducing additional shifts, demonstrated that in serum high-density lipoproteins (HDL), albumin and low-density lipoproteins (LDL) were able to monomerize LPS. An ELISA on collected fractions of the gel filtration revealed binding of the recently identified LPS-binding protein, serum amyloid P component (SAP), to the high molecular weight LPS aggregate. In serum, binding of soluble CD14 (sCD14) and LPS-binding protein (LBP) to LPS could not be detected. However, this was probably due to an overshadowing effect of albumin, as an extra addition of recombinant sCD14 to serum clearly monomerized FITC-LPS. Biosensor technology revealed that, of all LPS-binding components tested, only SAP clearly bound to the LPS-coated sensor chip. These results show that gel filtration of FITC-LPS is a quick and reliable method to study the binding characteristics of LPS-binding components.

Anti-CD14 monoclonal antibodies inhibit the production of tumor necrosis factor alpha and interleukin-10 by human monocytes stimulated with killed and live Haemophilus influenzae or Streptococcus pneumoniae organisms

In previous studies, we have shown that intact, heat-killed, gram-negative bacteria (GNB) and gram-positive bacteria (GPB) can stimulate the production of various proinflammatory and anti-inflammatory cytokines. The objective of the present study was to investigate whether the production of tumor necrosis factor alpha (TNF) and interleukin-10 (IL-10) by human monocytes stimulated by intact heat-killed or live Haemophilus influenzae or Streptococcus pneumoniae is mediated by CD14. Two anti-CD14 monoclonal antibodies (MAbs) were used to study the interaction between human monocytes and bacteria; lipopolysaccharide (LPS) was used to validate the effect of anti-CD14 MAb. MAb 18E12 decreased significantly TNF and IL-10 production upon stimulation with LPS or heat-killed bacteria and TNF production during stimulation by live bacteria. MAb My-4 decreased production of TNF and IL-10 by monocytes stimulated with LPS, IL-10 but not TNF production upon stimulation with heat-killed H. influenzae, and production of neither TNF nor IL-10 upon stimulation with S. pneumoniae. Together, these results led to the conclusion that CD14 is involved in the recognition and stimulation of human monocytes by intact GNB and GPB. Consequentially, the option for adjunctive treatment of severe infections with anti-CD14 MAb is postulated.

Use of a Photoactivatable Taxol Analogue to Identify Unique Cellular Targets in Murine Macrophages: Identification of Murine CD18 as a Major Taxol-Binding Protein and a Role for Mac-1 in Taxol-Induced Gene Expression

Taxol, a potent antitumor agent that binds β-tubulin and promotes microtubule assembly, results in mitotic arrest at the G2/M phase of the cell cycle. More recently, Taxol was shown to be a potent LPS mimetic in murine, but not in human macrophages, stimulating signaling pathways and gene expression indistinguishably from LPS. Although structurally unrelated to LPS, Taxol’s LPS-mimetic activities are blocked by inactive structural analogues of LPS, indicating that despite the species-restricted effects of Taxol, LPS and Taxol share a common receptor/signaling complex that might be important in LPS-induced human diseases. To identify components of the putatively shared Taxol/LPS receptor, a novel, photoactivatable Taxol analogue was employed to identify unique Taxol-binding proteins in murine macrophage membranes. Seven major Taxol-binding proteins, ranging from ∼50 to 200 kDa, were detected. Although photoactivatable Taxol analogue failed to bind to CD14, the prominent Taxol-binding protein was identified as CD18, the ∼96-kDa common component of the β2 integrin family. This finding was supported by the concomitant failure of macrophage membranes from Mac-1 knockout mice to express immunoreactive CD18 and the major Taxol-binding protein. In addition, Taxol-induced IL-12 p40 mRNA was markedly reduced in Mac-1 knockout macrophages and anti-Mac-1 Ab blocked secretion of IL-12 p70 in Taxol- and LPS-stimulated macrophages. Since CD18 has been described as a participant in LPS-induced binding and signal transduction, these data support the hypothesis that the interaction of murine CD18 with Taxol is involved in its proinflammatory activity.

Gram-positive sepsis. Mechanisms and differences from gram-negative sepsis

This article has reviewed the mechanisms by which gram-positive bacteria lead to septic shock, with regard to bacterial structure and toxicology and the host responses elicited both in animal models and in the clinical setting. Gram-positive organisms are better suited to invade host tissues and elicit, in general, a brisker phagocytic response than gram-negative organisms. The lack of endotoxin in the outer cell wall is compensated for by the presence of exposed peptidoglycan and a range of other toxic secreted products. It appears that cell wall components of gram-positive bacteria may signal via the same receptor as gram-negative endotoxin, although the type of signal and coreceptor may differ. Both animal and clinical data suggest that, unlike endotoxin-mediated shock, gram-positive infection produces a modest TNF response only and does not respond well to anti-TNF therapies. This leads one to conclude that the mechanisms leading to shock in gram-positive infection may be multifactorial and perhaps more difficult to treat. A thorough review of gram-positive mechanisms of sepsis is hampered by a lack of basic research in this field. Understanding of gram-negative bacterial structure and the regulation of virulence genes is at an advanced stage, yet the molecular tools to analyse virulence factors in the gram-positive genome have only recently become available. There is a paucity of good animal models of gram-positive infection and a lack of microbiologic data from some of the major trials in sepsis that might have given greater insight into the mechanisms leading to shock in various infections.

A lipoteichoic acid fraction of Enterococcus hirae activates cultured human monocytic cells via a CD14-independent pathway to promote cytokine production, and the activity is inhibited by serum components

To elucidate the cellular activation mechanisms of lipoteichoic acid (LTA) compared with those of lipopolysaccharide (LPS), a quantitatively major LTA fraction, QM-1M, was prepared from hot phenol-water extracts of Enterococcus hirae (ATCC 9790) by hydrophobic octyl-Sepharose chromatography and by ion-exchange membrane (QMA-Mem Sep 1010) chromatography as a 60% 1-propanol- and 1 M NaCl-eluted fraction. Unlike the reference Escherichia coli LPS, QM-1M did not demonstrate any ability to induce cytokines in a human whole blood culture system in this study, whereas QM-1M induced a few cytokines such as interleukin (IL)-8 and tumor necrosis factor-alpha in human monocytic THP-1 cell and human peripheral mononuclear cell (PBMC) cultures in the absence of serum. Fetal calf and human sera decreased the above cytokine induction by QM-1M in THP-1 and PBMC cultures, whereas sera increased activities of the reference LPS. IL-8 induction in the absence of serum in response to QM-1M was demonstrated to proceed through a CD14-independent pathway unlike the reference LPS.

Binding of bacterial peptidoglycan to CD14

The hypothesis that soluble peptidoglycan (sPGN, a macrophage-activator from Gram-positive bacteria) binds to CD14 (a lipopolysaccharide (LPS) receptor) was tested. sPGN specifically bound to CD14 in the following three assays: binding of soluble 32P-CD14 (sCD14) to agarose-immobilized sPGN, enzyme-linked immunosorbent assay, and photoaffinity cross-linking. sCD14 also specifically bound to agarose-immobilized muramyl dipeptide or GlcNAc-muramyl dipeptide but not to PGN pentapeptide. Binding of sCD14 to both sPGN and ReLPS (where ReLPS is LPS from Salmonella minnesota Re 595) was competitively inhibited by unlabeled sCD14, 1-152 N-terminal fragment of sCD14, sPGN, smooth LPS, ReLPS, lipid A, and lipoteichoic acid but not by dextran, dextran sulfate, heparin, ribitol teichoic acid, or soluble low molecular weight PGN fragments. Binding of sCD14 to sPGN was slower than to ReLPS but of higher affinity (KD = 25 nM versus 41 nM). LPS-binding protein (LBP) increased the binding of sCD14 to sPGN by adding another lower affinity KD and another higher Bmax, but for ReLPS, LBP increased the affinity of binding by yielding two KD with significantly higher affinity (7.1 and 27 nM). LBP also enhanced inhibition of sCD14 binding by LPS, ReLPS, and lipid A. Binding of sCD14 to both sPGN and ReLPS was inhibited by anti-CD14 MEM-18 mAb, but other anti-CD14 mAbs showed differential inhibition, suggesting conformational binding sites on CD14 for sPGN and LPS, that are partially identical and partially different.

Enhancement of lipopolysaccharide-induced neutrophil oxygen radical production by tumor necrosis factor alpha

Although tissues become exposed to both exogenous and endogenous cell-activating mediators during infection, there is little appreciation of the effects of subjecting cells to multiple mediators. We examined the hypothesis that the response of neutrophils to bacterial lipopolysaccharide (LPS) is significantly altered in the presence of the endogenous mediator tumor necrosis factor alpha (TNF). The data showed that human neutrophils pretreated with TNF for 10 to 30 min, displayed significantly enhanced superoxide production in response to LPS (from either Escherichia coli K-235 or E. coli O127:B8), measured as lucigenin-dependent chemiluminescence (CL), seen as an increase in the initial peak rate as well as the total CL accumulated over the incubation period. TNF amplified the response to LPS at 1 to 100 U of TNF/10(6) neutrophils and was able to enhance the response to a wide range of concentrations of LPS (0.01 to 1,000 ng/ml). The TNF-induced increase in the LPS response was paralleled by an increase in LPS binding to the neutrophils, which could be abrogated by an anti-CD14 monoclonal antibody. The results demonstrate that TNF significantly increases the LPS-induced release of oxygen radicals in neutrophils through the upregulation of cell surface CD14.

Detection of lipopolysaccharide (LPS)-binding membrane proteins by immuno-coprecipitation with LPS and anti-LPS antibodies

In this study we describe a general method for the detection and characterization of endotoxin-(lipopolysaccharide, LPS)-binding membrane proteins. In the past, experimental procedures to detect LPS-binding sites on cells were generally performed with chemically modified LPS derivates. Since any modification of a ligand may lead to a modification of its binding characteristics, the results of those studies are controversial. In our assay, cell membrane preparations are treated with free lipid A, the endotoxic center of LPS, in the presence of normal human serum. After binding of lipid A, membrane proteins are solubilized by mild detergent treatment without disruption of the lipid A-protein complexes. Addition of anti-(lipid A) mAbs and subsequent adding of protein A agarose lead to the precipitation of complexes of lipid A and its binding proteins. By SDS/PAGE and western blot, these precipitates can be screened for the presence of LPS/lipid A-binding proteins. We describe the use of this method for the immuno-coprecipitation of lipid A (or LPS) with an 80-kDa LPS-binding membrane protein (LMP80), which we have previously identified on several human cells. In addition, CD14, the well-known functional LPS receptor on monocytes and macrophages, can be detected. By means of this immuno-coprecipitation approach we could demonstrate binding of either purified LPS preparations or synthetic lipid A to these LPS/lipid A-binding membrane proteins at physiological pH under conditions in which the proteins are in their natural membranous environment.

Cellular binding of soluble CD14 requires lipopolysaccharide (LPS) and LPS-binding protein

The stimulation of nonmyeloid cells by lipopolysaccharide (LPS) is mediated by the serum protein, soluble CD14 (sCD14). We have examined the interaction of sCD14 with whole cells using a biologically active radiolabeled sCD14 molecule as a ligand. Specific binding of sCD14 to nonmyeloid cells is detected only when it is first incubated with both LPS and the serum LPS-binding protein (LBP). Through the use of an anti-CD14 monoclonal antibody, we demonstrate that sCD14 must interact with LPS in order for cellular binding to occur. Although LBP is traditionally known to function as a catalyst in the transfer of LPS to sCD14, our results reveal that LBP is actually a physical part of sCD14-containing, cell-associating complexes. The LPS- and LBP-dependent cell surface binding of sCD14 appears to be distinct from events leading to cell stimulation, since certain anti-CD14 and anti-LBP monoclonal antibodies have different effects on cellular binding versus cellular activation. Bound sCD14 is internalized, indicating that the LBP- and LPS-dependent binding of sCD14 may represent a novel general mechanism by which nonmyeloid cells clear LPS.

Heparin-induced structural modifications and oxidative cleavage of human serum albumin in the absence and presence of glucose--implications for transcapillary leakage of albumin in hyperglycaemia

Both unfractionated and fractionated, low-molecular-mass heparins were tested on human serum albumin in the absence and presence of glucose at concentrations similar to those frequently found in diabetic hyperglycaemic patients, to ascertain whether heparin and glucose interfered with each other in affecting the conformation of albumin. Reproducible results were obtained with both heparins when used at equal masses, but not when used at equal molar concentrations, suggesting a crucial role of the amount of the saccharide units in determining the observed effects. Spectroscopic studies showed that the binding sites of glucose and heparin on albumin do not overlap and that changes in protein structure depend on complex and mutual interference of glucose and heparin with the protein, although the effects of heparin in modifying the chromophore environment and increasing the ordered structure of the protein also prevailed in the presence of glucose. Heparin binding to albumin rapidly gave rise to oxidative reactions, which were responsible for the increase in the carbonyl content of the protein together with its higher susceptibility to tryptic digestion. Glucose enhanced and prolonged the production of heparin-induced oxidants. Oxidation caused peptide bond cleavage at Lys323 in the primary structure of albumin, yielding two large fragments of 27.5 kDa and 35 kDa which aggregated to form disulphide-linked homodimers visible in SDS/PAGE as two new bands of 54 kDa and 74 kDa, respectively. This was accompanied with a reduction in Val, Glu, and Gly residues, only partially counterbalanced by an increase in Thr and Ser residues. While only a small percentage of albumin molecules underwent fragmentation in the presence of heparin with glucose, albumin turned out to display in an even higher proportion structural modifications consistent with a higher degree of ordered structure. The mechanism(s) underlying this heparin-driven effect and possible physiopathological implications in vivo are discussed.

Pseudomonas aeruginosa lipopolysaccharide binds galectin-3 and other human corneal epithelial proteins

The aim of this study was to test whether galectin-3 is present in human corneal epithelium and whether lipopolysaccharide (LPS) purified from Pseudomonas aeruginosa ATCC 19660 binds to this animal lectin and/or to another human corneal epithelial protein(s) (HCEP) and to confirm which component of LPS (inner or outer core or lipid A) is important in bacterial binding by using the eye in organ culture. LPS isolated and purified from P. aeruginosa ATCC 19660 and a commercial LPS (serotype 10) differed in polyacrylamide gel analysis but bound similarly to blotted HCEP. Binding was determined to be a receptor-ligand type of interaction by the solid-phase assay, because it was both specific and saturable. Several LPS binding proteins in HCEP were identified by an overlay method. Western blotting with antibody against galectin-3 revealed the presence of this protein in both freshly isolated and cultured transformed human corneal epithelium. Binding inhibition assays showed that antibody specific for the outer core region of LPS and an anti-galectin antibody significantly inhibited bacterial binding in vitro. These data provide further evidence that LPS is an important adhesin of P. aeruginosa, that it binds to protein receptor molecules in HCEP, that one of the LPS binding proteins is galectin-3, and that the outer core portion of the molecule appears to be critical for LPS binding to the eye.

Structural analysis of a tumor-produced sulfated glycoprotein capable of initiating muscle protein degradation

A material of Mr 24,000 has been isolated from a cachexia-inducing mouse tumor (MAC16) and shown to initiate protein degradation in isolated gastrocnemius muscle. Biological activity was destroyed by preincubation with peptide N-glycosidase F (PNGase F) and endo-alpha-N-acetylgalactosaminidase (O-glycosidase) but not by neuraminidase or trypsin. Antibody reactivity was destroyed by treatment with periodate, indicating carbohydrate moieties to be the antigenic determinants. Antigenic activity was also reduced by treatment with PNGase F and O-glycosidase and was completely destroyed by treatment with chondroitinase ABC but was unaffected by treatment with either trypsin or chymotrypsin, confirming that the N- and O-linked sulfated oligosaccharide chains were both the antigenic and biological determinants. Biosynthetic labeling of MAC16 cells using a combination of [35S]sulfate and [6-3H]GlcN gave a single component of Mr 24,000 containing both radiolabels. Similar material could not be isolated from a cell line (MAC13) originating from a tumor that does not cause cachexia in vivo. Digestion of 3H/35S material with PNGase F produced two fragments of Mr 14,000 and 10,000 containing both radiolabels, and digestion with O-glycosidase produced three fragments of Mr 14,000, 6,000, and 4, 000, the first two contained both radiolabels and the third contained only 3H. Digestion of the fragment of Mr 14,000 released by PNGase F with O-glycosidase also gave fragments of Mr 6,000 and 4, 000. The products from both digestions were acidic as determined by anion exchange chromatography on DEAE-cellulose. The negative charge on the fragment of Mr 4,000 was removed by treatment with alkaline phosphatase. This suggests that the charge originated from phosphate residues, and this has been confirmed by biosynthetic labeling of MAC16 cells with [32P]orthophosphate, where radiolabel was incorporated into material of Mr 24,000 and into the fragment of Mr 4,000 after treatment with O-glycosidase. To determine the size of the polypeptide core MAC16 cells were biosynthetically labeled with L-[2,5-3H]His which after chemical deglycosylation produced a major component of Mr 4,000. These results suggest a model for the Mr 24, 000 material consisting of a central polypeptide chain of Mr 4,000 and with phosphate residues that may be attached to the polypeptide or a short oligosaccharide chain containing GlcN, one O-linked sulfated oligosaccharide chain containing GlcN, and of Mr 6,000 and one N-linked sulfated oligosaccharide chain of Mr 10,000 also containing GlcN. Neither chain was cleaved into disaccharides with chondroitinase ABC, suggesting that the material is a sulfated glycoprotein.

Specific binding of soluble peptidoglycan and muramyldipeptide to CD14 on human monocytes

Previously, we were able to show that soluble peptidoglycan (sPG)-induced monokine production in human peripheral monocytes is inhibited by anti-CD14 monoclonal antibodies and by lipid A partial structures. This suggested but did not prove that monocytic surface protein CD14 is involved in the activation of human monocytes not only by cell wall components of gram-negative bacteria such as lipopolysaccharide (LPS) but also by cell wall components of gram-positive bacteria such as sPG. In the present study, we provide experimental evidence that CD14 indeed constitutes a binding site for sPG recognition and activation of human monocytes. The results show that fluorescein isothiocyanate-sPG (FITC-sPG) binds to human monocytes in a saturable, dose-dependent, and specific manner. For maximal binding, 2 to 3 microg of FITC-sPG per ml was sufficient, and this binding is completed within 90 min; about 40% of the binding is completed within the first 3 min. The FITC-sPG binding is considered specific because unlabeled sPG and also muramyldipeptide (MDP), the minimal bioactive structure of sPG, inhibit the binding of sPG to monocytes in a dose-dependent manner. This specific binding was also inhibited by an anti-CD14 monoclonal antibody, LPS, and lipid A partial structure compound 406. Direct evidence for an interaction of sPG with CD14 is provided by experiments involving native polyacrylamide gel electrophoresis that showed a shift of the electrophoretic mobility of CD14 by LPS as well as by sPG. These results allow the conclusion that sPG binds directly to CD14, that MDP represents the active substructure of sPG, and that CD14 may be a lectin-like receptor which plays a key role in cellular stimulation by bioactive components of not only gram-negative but also gram-positive bacteria.

Different binding of 125I-LPS to plasma proteins from persons with high or low HDL

In severe trauma, sepsis or during surgery, bacterial lipopolysaccharide (LPS) frequently enters the circulation. Persons with high levels of high-density lipoprotein (HDL) have previously demonstrated higher monocyte procoagulant activity (PCA) when whole blood is challenged with LPS. The aim of the study was to investigate the distribution of radiolabelled LPS (125I-LPS) in plasma from six persons with high (2.14-2.82 mmol l-1) and six persons with low (0.54-1.04 nmol l-1) HDL, subjecting plasma to fast protein liquid chromatography (FPLC), or agarose electrophoresis followed by quantitative autoradiography. In heparin plasma 125I-LPS was located mainly in parts of plasma containing low-density lipoprotein (LDL) or very low-density lipoprotein (VLDL) and the immunoglobulins, and located to a lesser extent in HDL. However, persons with high HDL showed significantly higher binding of 125I-LPS to HDL and the immunoglobulins, probably to IgG, and significantly lower binding to LDL/VLDL. In calcium-depleted plasma (EDTA) 125I-LPS demonstrated a sharp increase in the binding to HDL, combined with a persistently high binding to LDL/VLDL and binding to the immunoglobulins was almost eliminated in all subjects investigated. Likewise, the binding of 125I-LPS to HDL in EDTA plasma was also significantly higher and to LDL/VLDL significantly lower in persons with high HDL. This study demonstrates that the distribution of 125I-LPS in heparin and EDTA plasma from persons with high or low HDL is different, which is presumed to be of importance concerning the various bioactivities of LPS.

CD14 is a cell-activating receptor for bacterial peptidoglycan

The hypothesis that CD14 (an endotoxin receptor present on macrophages and neutrophils) acts as a cell-activating receptor for bacterial peptidoglycan was tested using mouse 70Z/3 cells transfected with human CD14. 70Z/3 cells transfected with an empty vector were unresponsive to insoluble and soluble peptidoglycan, as well as to low concentrations of endotoxin. 70Z/3-CD14 cells were responsive to both insoluble and soluble peptidoglycan, as well as to low concentrations of endotoxin, as measured by the expression of surface IgM, activation of NF-kappaB, and degradation of IkappaB-alpha. Peptidoglycan also induced activation of NF-kappaB and degradation of IkappaB-alpha in macrophage RAW264.7 cells. These peptidoglycan-induced effects (in contrast to endotoxin-induced effects) were not inhibited by polymyxin B. Both peptidoglycan- and endotoxin-induced activation of NF-kappaB were inhibited by anti-CD14 mAb. The N-terminal 151 amino acids of CD14 were sufficient for acquisition of full responsiveness to both peptidoglycan and endotoxin, but CD14 deletion mutants lacking four small regions within the N-terminal 65 amino acids showed differentially diminished responses to peptidoglycan and endotoxin. These results identify CD14 as the functional receptor for peptidoglycan and demonstrate that similar, but not identical sequences in the N-terminal 65-amino acid region of CD14 are critical for the NF-kappaB and IgM responses to both peptidoglycan and endotoxin.

CD14 expression in injured patients correlates with outcome

OBJECTIVE

The authors determined the correlation between monocyte CD14 expression and outcome in severely injured patients.

SUMMARY BACKGROUND DATA

Human leukocyte antigen-DR (HLA-DR) expression CD14 positive monocytes correlates with the development of major infection and subsequent death in severely injured patients. Recent studies show that CD14 is not only a marker for mature monocytes, but also is an important endotoxin/lipopolysaccharide receptor.

METHODS

Flow cytometry data obtained by dual staining techniques (CD14 and HLA-DR) of monocytes in 213 severely injured patients were analyzed over a 30-day period. Outcome criteria included survival and the development of both major and minor infections.

RESULTS

The percentage of cells expressing CD14 (%CD14) correlated with clinical outcome, reaching significance (p < 0.05) between noninfected survivors (n = 74) and nonsurvivors (n = 21) at days 3, 7, 11, 17, 24, and 30. At days 3, 7, and 17, the %CD14 also was different between noninfected and infected survivors. After 7 days, differences were only seen between survivors and nonsurvivors (p < 0.05). The mean fluorescence intensity (MC CD14) in monocytes of all patients was significantly reduced at day 3 compared with day 1 and remained low for 30 days (p < 0.05). The nonsurvivor group had consistently low MC CD14 values, which were significant at day 5 (p < 0.05).

CONCLUSIONS

In addition to HLA-DR expression, CD14 expression on monocytes is an indicator of clinical outcome after injury and could represent a more precise target for treatment.

Purification of a peptidoglycan recognition protein from hemolymph of the silkworm, Bombyx mori

A method was developed for obtaining a homogeneous silkworm hemolymph protein (peptidoglycan recognition protein, PGRP) which has affinity for peptidoglycan and the ability to trigger the prophenoloxidase cascade upon its binding to peptidoglycan. The purified PGRP had a molecular mass of about 19 kDa and is composed of a single polypeptide with an isoelectric point of 6.5. It bound to peptidoglycan in the absence of divalent cation, whereas its binding to beta1,3-glucan and chitin was not detected. N-Acetyl-D-glucosaminyl-(beta1-4)-N-acetylmuramyl-L-alanyl-D-isogluta mine did not inhibit purified PGRP to bind insoluble peptidoglycan, but fragmented soluble peptidoglycan did. PGRP seemed to require peptidoglycan as a possible ligand to keep its glycan portion consisting of at least two or more of the repeating unit. PGRP did not have any detectable lysozyme activity, and its amino acid composition and amino-terminal sequence of 20 amino acid residues were shown to be different from those of silkworm lysozyme. PGRP seems to be a hitherto unknown protein. In the absence of PGRP, the prophenoloxidase cascade in the plasma fraction of hemolymph could not be triggered by peptidoglycan, indicating that some type of activity, capable of activating the cascade, is generated upon their binding. However, the exact nature of this activity is not yet known. The purified PGRP bound to peptidoglycan did not hydrolyze significantly any of the 26 commercially available peptidyl-7-amino-4-methylcoumarins, substrates for various proteases.

Analysis of the signal transduction in the induction of nitric oxide synthase by lipoteichoic acid in macrophages

1. This study investigates the signal transduction mechanisms leading to the enhanced formation of nitric oxide (NO) due to the induction of NO synthase (iNOS) in murine J774.2 macrophages in culture activated with lipoteichoic acid (LTA), a cell wall component of the gram-positive bacterium Staphylococcus aureus. 2. LTA (10 microgram ml-1) caused within 24 h an enhanced accumulation of nitrite (an indicator of NO biosynthesis) in the supernatant of J774.2 macrophages which was prevented by the non-selective NOS inhibitor NG-monomethyl-L-arginine (L-NMMA; IC50: 35 microM) or by the iNOS-selective NOS inhibitor, aminoethyl-isothiourea (AE-ITU; IC50: 6 microM). The inhibition of nitrite formation afforded by these agents was prevented by excess L-arginine (3-30 mM), but not by D-arginine (3-30 mM). Furthermore, the degree of iNOS inhibition was similar when these NOS inhibitors were added to the macrophages 10 h after LTA. 3. Pretreatment of J774.2 macrophages with cyclohexamide or dexamethasone prevented the enhanced formation of nitrite caused by LTA. This inhibition did not occur when dexamethasone or cyclohexamide were added to the cells 10 h after LTA. The increase in nitrite formation stimulated by LTA (10 micrograms ml-1) was not affected by polymyxin B (0.05-0.5 microgram ml-1), an agent which binds and inactivates endotoxin. 4. A specific inhibitor of phosphatidylcholine-phospholipase C (PC-PLC), D609, prevented the increase in nitrite formation (IC50 = 20 micrograms ml-1) caused by LTA. The inhibition afforded by D609 was significantly smaller when this agent was added to the cells 10 h after LTA. 5. The structurally distinct tyrosine kinase inhibitors, erbstatin, genistein, and tyrphostin AG126 prevented the formation of nitrite caused by LTA. The inhibition afforded by these compounds was significantly attenuated when they were added to the cells 10 h after LTA. In contrast, daidzein or tyrphostin A-1, which are inactive analogues of genistein and tyrphostin (up to a concentration of 10 microM) did not affect the nitrite formation caused by LTA. 6. Inhibitors of the activation of the nuclear transcription factor NF-kappa B such as pyrrolidine dithiocarbamate (PDTC; an antioxidant and a metal chelator), butylated hydroxyanisole (BHA; an antioxidant), L-1-tosylamido-2-phenylethyl chloromethyl ketone (TPCK), calpain inhibitor I (both I kappa B-protease inhibitors), or rotenone (an antioxidant which inhibits electron transport) prevented the nitrite formation stimulated by LTA. The inhibition afforded by these agents was significantly smaller when they were added to the macrophages 10 h after LTA. 7. Incubation of J774.2 cells with LTA over 24 h resulted in the expression of iNOS protein (130 kDa) as identified by Western blot analysis. The expression of iNOS protein by LTA was significantly attenuated by cyclohexamide, D609, tyrphostin AG126, PDTC or by TPCK. 8. Thus, the signal transduction leading to the expression of iNOS protein and activity caused by LTA in murine J774.2 macrophages involves (i) the activation of PC-PLC, (ii) phosphorylation of tyrosine kinase, and (iii) the activation of the transcription factor NF-kappa B.

A lipooligosaccharide-binding site on HepG2 cells similar to the gonococcal opacity-associated surface protein Opa

The lacto-N-neotetraose-containing lipooligosaccharide (LOS) present on the surface of most Neisseria gonorrhoeae organisms may serve many important functions in gonococcal pathogenesis. This surface glycolipid contains the cross-reactive epitope to human paragloboside and can be sialylated by gonococci grown in the presence of CMP-N-acetylneuraminic acid. Another possible role for this glycolipid could be to mimic human asialocarbohydrates and act as a ligand for asialoglycoprotein receptors contained on numerous human cells. The most noted of this large family of receptors is that expressed on the surface of hepatic cells. In a model cell system, using the hepatoma tissue culture cell line HepG2, we wanted to investigate if the presence of this asialoglycoprotein receptor influenced the adherence and/or invasion of gonococci expressing the lacto-N-neotetraose structure. Piliated variants of the gonococcal wild-type strain 1291 and its isogeneic LOS mutant 1291E were used in adherence-invasion assays. This gonococcal strain is somewhat unusual in that it expresses large amounts of predominantly one species of LOS, thus reducing the complexity of interpreting the data. The data from these assays suggested that the Gal(beta 1-4)GlcNAc(beta 1-3)Gal(beta 1-4)Glc carbohydrate structure on the wild-type LOS affected the adherence-invasion of gonococci into the HepG2 cells. In studies to determine whether the major hepatic asialoglycoprotein receptor was involved in these interactions, we found that the HepG2 cells contained two receptors which bound gonococcal LOS. One of these was the asialoglycoprotein receptor, and the data concerning this receptor will be reported elsewhere. The data on the second receptor are reported here. Purified, 125I-labeled gonococcal LOS was used to identify specific high-affinity LOS-binding sites. These binding experiments revealed one major binding site corresponding to a protein with a molecular mass of 70 kDa (p70). Several lines of evidence in this study suggested that the oligosaccharide region of LOS played an important role in LOS binding to the p70 of HepG2 cells. In addition, we show that this human LOS receptor has some similarities to the gonococcal Opa proteins.