lipid-a and Bacteremia

Bacterial sepsis and septic shock result from the overproduction of inflammatory mediators as a consequence of the interaction of the immune system with bacteria and bacterial wall constituents in the body. Bacterial cell wall constituents such as lipopolysaccharide, peptidoglycans, and lipoteichoic acid are particularly responsible for the deleterious effects of bacteria. These constituents interact in the body with a large number of proteins and receptors, and this interaction determines the eventual inflammatory effect of the compounds. Within the circulation bacterial constituents interact with proteins such as plasma lipoproteins and lipopolysaccharide binding protein. The interaction of the bacterial constituents with receptors on the surface of mononuclear cells is mainly responsible for the induction of proinflammatory mediators by the bacterial constituents. The role of individual receptors such as the toll-like receptors and CD14 in the induction of proinflammatory cytokines and adhesion molecules is discussed in detail. In addition, the roles of a number of other receptors that bind bacterial compounds such as scavenger receptors and their modulating role in inflammation are described. Finally, the therapies for the treatment of bacterial sepsis and septic shock are discussed in relation to the action of the aforementioned receptors and proteins.

Topics: Acute-Phase Proteins; Bacteremia; Carrier Proteins; CD18 Antigens; Cytokines; Humans; Immune Tolerance; Kupffer Cells; Lipid A; Lipopolysaccharide Receptors; Lipopolysaccharides; Lipoproteins; Membrane Glycoproteins; Shock, Septic

The activation of leukocytes by bacterial cell wall lipopolysaccharide (LPS) contributes to the pathogenesis of septic shock. It is well established that, in the presence of plasma LPS-binding protein (LBP), LPS binds with high affinity to CD14. The binding of LPS to CD14 has been associated with the activation of cells, although available evidence indicates that CD14 itself does not transduce intracellular signalling. The physiological function of this interaction is to promote host defense mechanisms of cells to combat the infection and clear LPS from the circulation. At higher concentrations of LPS, however, the activation of cells can take place in the absence of LBP and CD14, presumably through a distinct low-affinity signalling LPS receptor. On the evidence published by us and others, we propose that in neutrophils, and possibly other leukocytes, L-selectin can act as a low-affinity LPS receptor.

Topics: Animals; Bacteremia; Carbohydrate Sequence; Humans; L-Selectin; Lipid A; Lipopolysaccharide Receptors; Lipopolysaccharides; Models, Biological; Molecular Sequence Data; Shock, Septic

Septic shock remains a major cause of morbidity and mortality, especially in the intensive care setting. A vast array of treatment strategies is under investigation; despite success in animal models, no effective adjunctive therapy has yet been approved for clinical use. This paper reviews the development of experimental therapies for sepsis and discusses those treatments that show promise for application in humans. Approaches to treatment fall into three broad categories: strategies directed against bacterial components, those directed against host-derived inflammatory mediators, and those designed to limit tissue damage. Because septic shock is a dynamic and evolving condition, different strategies may be needed at different stages in the pathogenesis of sepsis. Through carefully performed trials and thoughtful selection of combination therapy aimed at different points in the pathological process, it may be possible in the future to modify the course of this serious condition.

Topics: Acute-Phase Proteins; Animals; Antibodies, Bacterial; Bacteremia; Carrier Proteins; Combined Modality Therapy; Cytokines; Endotoxins; Humans; Lipid A; Lipopolysaccharides; Membrane Glycoproteins; Shock, Septic

Topics: Antibodies, Monoclonal; Antibodies, Monoclonal, Humanized; Antimicrobial Cationic Peptides; Bacteremia; Blood Proteins; Cell Adhesion Molecules; Child; Cytokines; Endotoxins; Genetic Therapy; Humans; Immunotherapy, Adoptive; Lipid A; Membrane Proteins; Multiple Organ Failure; Neutrophils; Shock, Septic

Lipopolysaccharide (LPS), a major component of the meningococcal outer membrane, is sensed by the host through activation of Toll-like receptor 4 (TLR4). Recently, we demonstrated that a surprisingly large fraction of Neisseria meningitidis disease isolates are lipid A mutants, due to inactivating mutations in the lpxL1 gene. The lpxL1 mutants activate human TLR4 much less efficiently than wild-type bacteria, which may be advantageous by allowing them to escape from the innate immune system. Here we investigated the influence of lipid A structure on virulence in a mouse model of meningococcal sepsis. One limitation, however, is that murine TLR4 recognizes lpxL1 mutant bacteria much better than human TLR4. We show that an lpxL2 mutant, another lipid A mutant lacking an acyl chain at a different position, activates murine TLR4 less efficiently than the lpxL1 mutant. Therefore, the lpxL2 mutant in mice might be a better model for infections with lpxL1 mutants in humans. Interestingly, we found that the lpxL2 mutant is more virulent in mice than the wild-type strain, whereas the lpxL1 mutant is actually much less virulent than the wild-type strain. These results demonstrate the crucial role of N. meningitidis lipid A structure in virulence.

Topics: Animals; Bacteremia; Bacterial Outer Membrane Proteins; Cell Line; Cytokines; Disease Models, Animal; Enzyme-Linked Immunosorbent Assay; Female; Immunity, Innate; Lipid A; Meningococcal Infections; Mice; Mice, Inbred C57BL; Mutation; Neisseria meningitidis; Toll-Like Receptor 4

Stenotrophomonas maltophilia is a multiple-antibiotic-resistant opportunistic pathogen that is being isolated with increasing frequency from patients with health-care-associated infections and especially from patients with cystic fibrosis (CF). While clinicians feel compelled to treat infections involving this organism, its potential for virulence is not well established. We evaluated the immunostimulatory properties and overall virulence of clinical isolates of S. maltophilia using the well-characterized opportunistic pathogen Pseudomonas aeruginosa PAO1 as a control. The properties of CF isolates were examined specifically to see if they have a common phenotype. The immunostimulatory properties of S. maltophilia were studied in vitro by stimulating airway epithelial and macrophage cell lines. A neonatal mouse model of pneumonia was used to determine the rates of pneumonia, bacteremia, and mortality, as well as the inflammatory response elicited by S. maltophilia infection. Respiratory and nonrespiratory S. maltophilia isolates were highly immunostimulatory and elicited significant interleukin-8 expression by airway epithelial cells, as well as tumor necrosis factor alpha (TNF-alpha) expression by macrophages. TNF-alpha signaling appears to be important in the pathogenesis of S. maltophilia infection as less than 20% of TNFR1 null mice (compared with 100% of wild-type mice) developed pneumonia and bacteremia following intranasal inoculation. The S. maltophilia isolates were weakly invasive, and low-level bacteremia with no mortality was observed. Despite the lack of invasiveness of S. maltophilia, the immunostimulatory properties of this organism and its induction of TNF-alpha expression specifically indicate that it is likely to contribute significantly to airway inflammation.

Topics: Animals; Bacteremia; Cell Line; Cystic Fibrosis; Epithelial Cells; Gram-Negative Bacterial Infections; Humans; Interleukin-8; Lipid A; Macrophages; Mice; Mice, Inbred C57BL; Mice, Transgenic; Phagocytosis; Pneumonia, Bacterial; Pseudomonas aeruginosa; Receptors, Tumor Necrosis Factor, Type I; Respiratory Mucosa; Respiratory Tract Infections; Stenotrophomonas maltophilia; Tumor Necrosis Factor-alpha

Several studies have shown that lipopolysaccharide and lipid A impair red blood cell deformability and. However, it is unclear whether impaired red blood cell deformability is associated with binding of lipopolysaccharide to the red blood cell membrane.. Analysis of hydroxymyristic acid content in red blood cell membranes and red blood cell deformation in patients with Gram-negative septicemia and after incubation of red blood cells from healthy adults with 100 microg of lipid A or 1 mg of lipopolysaccharide per milliliter of red blood cell in buffer solution and in whole blood. Hydroxymyristic acid is a fatty acid of the lipid A part of lipopolysaccharide in most Gram-negative bacteria.. University research laboratories.. Ten healthy adults and four patients with clinical and laboratory signs of septicemia.. Blood sampling.. Red blood cell deformation was measured with a laser-diffraction shearing device (Rheodyn) and a computerized micropore filtration system (CTA). Lipopolysaccharide and lipid A binding to red blood cell membranes was studied by measuring the amide-linked hydroxymyristic acid by gas chromatography. The detection rates of hydroxymyristic acid were 82% for lipopolysaccharide and 79% for lipid A in buffer solution. In membranes of washed red blood cell, the detection rates of lipopolysaccharide and lipid A were 0.26 +/- 0.03% (2.6 +/- 0.3 microg/mL) and 1.3 +/- 0.5% (1.3 +/- 0.5 microg/mL), and in red blood cell membranes of whole blood the detection rates were 2.6% (25.5 microg/mL) and 4.1% (4.1 microg/mL), respectively. The lipopolysaccharide content in red blood cell membranes of septic patients ranged from 47 to 103 microg/mL of red blood cell. Red blood cell deformation in the Rheodyn and in the CTA were not influenced by lipopolysaccharide incubated with washed red blood cells. In the Rheodyn, red blood cell deformation was significantly decreased by 18% after lipid A incubation in washed red blood cells, by 26% after lipopolysaccharide incubation in whole blood, and by 31% in septic patients. Similar effects were observed when we used the CTA.. Red blood cell deformation is decreased in septic patients, after incubation of washed red blood cells with lipid A and of whole blood with lipopolysaccharide. Lipopolysaccharide did not influence red blood cell deformation after incubation with washed red blood cells. The decrease of red blood cell deformation was related to the amount of hydroxymyristic acid measured in red blood cell membranes, suggesting that endotoxin binding directly affects mechanical properties of red blood cells.

Topics: Adult; Bacteremia; Bacterial Proteins; Binding Sites; Biomarkers; Case-Control Studies; Chromatography, Gas; Cytochrome P-450 Enzyme System; Endotoxins; Erythrocyte Deformability; Erythrocyte Membrane; Gram-Negative Bacterial Infections; Humans; Laser-Doppler Flowmetry; Lipid A; Lipopolysaccharides; Microcirculation; Micropore Filters; Mixed Function Oxygenases; NADPH-Ferrihemoprotein Reductase

Topics: Bacteremia; Carbohydrate Sequence; Chemical Phenomena; Chemistry, Physical; Cytokines; Female; Humans; Lipid A; Lipopolysaccharides; Male; Meningitis, Meningococcal; Meningococcal Infections; Molecular Sequence Data; Molecular Structure; Neisseria meningitidis; Shock, Septic

Monophosphoryl lipid A (MPL) is a less toxic derivative of lipid A that enhances survival from endotoxemia. This study examined whether MPL induced resistance to Gram-positive sepsis and cytokines. Mice were administered MPL or saline (phosphate-buffered saline) and challenged 24 h later with live Staphylococcus aureus (SA), staphylococcus enterotoxin B (SEB), toxic shock syndrome toxin (TSST-1), and tumor necrosis factor (TNF). Survival was determined at 72 h. A separate set of animals was phlebotomized for determination of cytokines. MPL increased survival from S. aureus bacteremia from 20 to 87% (p < .05). Interleukin-6 (IL-6) and interleukin-1 (IL-1) and TNF were also significantly decreased. SEB and TSST survival were enhanced from 10 to 90% (p < .05). In SEB-treated animals, TNF and IL-6 levels were significantly decreased. Survival from TNF infusion was increased from 20 to 100% with MPL, however, no significant differences in cytokines were observed. These data suggest that MPL induces resistance to Gram-positive sepsis and cytokine-mediated activity.

Topics: Animals; Bacteremia; Bacterial Toxins; Dose-Response Relationship, Drug; Enterotoxins; Enzyme-Linked Immunosorbent Assay; Interleukin-1; Interleukin-6; Lipid A; Mice; Mice, Inbred ICR; Salmonella; Staphylococcal Infections; Superantigens; Tumor Necrosis Factor-alpha

Antibodies were raised in rabbits by immunization with the heat-killed J5 mutant of Escherichia coli O111 (Rc chemotype). Serum antibodies were separated into purified IgG and IgM by sequential affinity chromatography on protein G-Sepharose and anti-rabbit IgG-Sepharose columns. J5 lipopolysaccharide (LPS)-specific IgG was prepared by affinity chromatography of purified IgG on a J5 LPS-EAH Sepharose 4B affinity column. Purified IgM, IgG, and J5 LPS-specific IgG protected neutropenic rats against lethal challenge with Pseudomonas aeruginosa 12:4:4 (Fisher Devlin immunotype 6). Nine of 16 rats treated with the IgM fraction were protected (P < .001). Thirteen of 20 rats treated with the purified IgG and 6 of 8 treated with J5 LPS-specific IgG were protected compared with none of 25 treated with IgG made from the preimmune serum of the same rabbit (P < .001). These results demonstrate that purified J5 LPS-specific IgG protects against the lethal consequences of gram-negative bacteremia.

Topics: Animals; Antibody Specificity; Bacteremia; Bacterial Vaccines; Blotting, Western; Chromatography, Affinity; Enzyme-Linked Immunosorbent Assay; Escherichia coli; Female; Immunodiffusion; Immunoglobulin G; Lipid A; Lipopolysaccharides; Neutropenia; Pseudomonas aeruginosa; Pseudomonas Infections; Rabbits; Rats; Rats, Sprague-Dawley

A recombinant endotoxin-neutralizing protein (ENP) from Limulus polyphemus and a monoclonal IgM anti-lipid A antibody (HA-1A) were compared in a rat model of Escherichia coli sepsis. One hour after intraperitoneal challenge with 10(6) cfu of E. coli O18ac K1, animals were sensitized to endotoxin with lead acetate and treated with ENP, HA-1A, or saline, followed by ceftriaxone and gentamicin. Before treatment, 95% of rats had high-grade bacteremia and high serum endotoxin concentrations, which were similar in all treatment groups (P > .60). One hour after treatment, there was no bacterial growth in any blood sample, and endotoxin concentrations were significantly lower in the ENP group than in the HA-1A and saline groups (P < .01). At 24 h after challenge, survival in the ENP group was significantly higher than in the HA-1A saline group (P < .001). ENP improved survival in a rat model of E. coli sepsis with high mortality despite effective antibiotic therapy.

Topics: Animals; Antibodies, Monoclonal; Antimicrobial Cationic Peptides; Arthropod Proteins; Bacteremia; Endotoxins; Escherichia coli Infections; Galactosamine; Horseshoe Crabs; Immunoglobulin M; Invertebrate Hormones; Lipid A; Male; Organometallic Compounds; Rats; Rats, Wistar; Recombinant Proteins

Experiments were performed to test the ability of mouse antiidiotopic mAb, specific for an antilipid A mAb, to act as a vaccine against gram-negative bacterial infections. Lipid A is a conserved region of bacterial LPS. Immunization with the antiidiotopic antibodies, coupled to an immunogenic carrier protein (hemocyanin), specifically induced anti-LPS antibody responses in animals from different species. In a mouse model, this immunization resulted in protection against both lethal gram-negative bacteremia and endotoxemia. The antiidiotopic antibodies, however, did not stimulate endotoxin-associated bioactivities, such as induction of TNF and IL-1. These results support the hypothesis that an idiotope vaccine can stimulate beneficial protective immunity against gram-negative infections without the toxicity inherent in LPS.

Topics: Animals; Antibodies, Anti-Idiotypic; Antibodies, Bacterial; Bacteremia; Bacterial Infections; Bacterial Vaccines; Endotoxins; Female; Gram-Negative Bacteria; Immunoglobulin Idiotypes; Interleukin-1; Lipid A; Lipopolysaccharides; Mice; Mice, Inbred BALB C; Tumor Necrosis Factor-alpha