SEARCH · PubMed Health

Results for “LIPOPOLYSACCHARIDES”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources

PubMed1966

Chemical and biological properties of an extracellular lipopolysaccharide from Escherichia coli grown under lysine-limiting conditions.

Lipopolysaccharide was prepared from the extracellular lipoglycopeptide produced by the lysine-requiring mutant Escherichia coli A.T.C.C. 12408 grown under lysine-limiting conditions. The lipid moiety, containing glucosamine phosphate and four fatty acids (lauric acid, myristic acid, beta-hydroxymyristic acid and palmitic acid) corresponded in composition to lipid A of known bacterial lipopolysaccharides. The components of the polysaccharide moiety were d-glucose, d-galactose, l-glycero-d-manno-heptose, 3-deoxy-2-oxo-octonic acid, ethanolamine and phosphate. These are the constituents of the polysaccharide of the cell-wall antigens from rough strains of E. coli. Lipopolysaccharides were also prepared from whole cells of E. coli 12408 grown with excess or limited amounts of lysine; they were identical in carbohydrate composition with the extracellular lipopolysaccharide. The biological properties of this material also resembled those of known lipopolysaccharides; it was antigenic, pyrogenic, toxic and had adjuvant activity.

Animals↗

PubMed1966

The relation of 3-deoxy-2-oxo-octonate to the serological and physical properties of a lipopolysaccharide from a rough strain of Escherichia coli.

1. A water-soluble preparation of lipopolysaccharide was isolated from the extracellular lipopolysaccharide-phospholipid-protein complex formed by Escherichia coli A.T.C.C. 12408. 2. Heating at 100 degrees and pH4.6 caused a rapid decrease in serological activity concomitant with the release of 3-deoxy-2-oxo-octonate; aggregation of the molecules also occurred. 3. Further evidence that the release of 3-deoxy-2-oxo-octonate is related to loss of serological activity was obtained by comparing the effects of heating for 1hr. at 100 degrees and pH values between 5.0 and 9.0; detectable changes still occurred at pH7.5. 4. 3-Deoxy-2-oxo-octonate was isolated from the products of hydrolysis of lipopolysaccharide and shown to be an effective inhibitor of the precipitin reaction between lipopolysaccharide and homologous antiserum. 5. The possibility that 3-deoxy-2-oxo-octonate is joined to the lipopolysaccharide through a phosphodiester linkage is discussed.

Alkaline Phosphatase↗

PubMed1996

Differential regulation of cyclo-oxygenase-1 and cyclo-oxygenase-2 gene expression by lipopolysaccharide treatment in vivo in the rat.

1. Prostaglandins are important regulatory mediators of cardiovascular and pulmonary functions which may become disordered in patients with sepsis. The mechanisms controlling their synthesis and release under these circumstances remain unclear. Cyclo-oxygenase (COX, prostaglandin G/H synthase) is a key enzyme in prostaglandin synthesis and has two isoforms (COX-1 and COX-2). COX-1 is constitutively expressed and is probably responsible for prostaglandin release under physiological conditions, whereas COX-2 is expressed at high levels upon induction. 2. We investigated the effect of lipopolysaccharide treatment in vivo on differential COX-1 and COX-2 mRNA expression in the rat. 3. The 2.8 kb COX-1 message was detected in all lungs and seven hearts of eight control rats. In lipopolysaccharide-treated animals, COX-1 expression was reduced by approximately 5-fold in lungs and 2-fold in hearts as quantified by densitometry. In parallel, a marked upregulation of COX-2 mRNA expression was observed. The 4.4 kb COX-2 transcript was absent or expressed at low level in control lungs and hearts, but was increased by approximately 7- and 12-fold in lipopolysaccharide-treated lungs and hearts respectively. Neither the down-regulation of COX-1 nor the upregulation of COX-2 mRNA induced by lipopolysaccharide was significantly affected by pretreatment with dexamethasone in lung and heart, although expression of inducible nitric oxide synthase, induced by lipopolysaccharide, was markedly inhibited in the same tissues. 4. The down-regulation of COX-1 and upregulation of COX-2 may contribute to the multi-organ failure seen in sepsis.

Animals↗

PubMed1999

Structural analysis of the lipopolysaccharide oligosaccharide epitopes expressed by Haemophilus influenzae strain RM.118-26.

The structure of the lipopolysaccharide of Haemophilus influenzae mutant strain, RM.118-26, was investigated. Electrospray ionization-mass spectrometry on intact lipopolysaccharide, O-deacylated lipopolysaccharide and core oligosaccharides obtained from lipopolysaccharide after mild acid hydrolysis provided information on the composition and relative abundance of the glycoforms. Oligosaccharide samples were studied in detail using high-field NMR techniques. The structure of the major glycoform containing phosphocholine is identical to the Hex2 glycoform described for H. influenzae RM.118-28 [Risberg, A., Schweda, E.K.H. & Jansson, P.-E. (1997) Eur. J. Biochem. 243, 701-707]. A second major glycoform, containing three hexose residues (Hex3), in which a lactose unit, beta-D-Galp-(1-->4)-beta-D-Glcp, is attached at the O-2 position of the terminal heptose of the inner core element, L-alpha-D-Hepp-(1-->2)-L-alpha-D-Hepp-(1-->3)-[beta-D-Glcp-( 1-->4)-]- L-alpha-D-Hepp-(1-->5)-alpha-Kdo, carries no phosphocholine. Instead this lipopolysaccharide glycoform is partly (40%) substituted by an O-acetyl group linked to the 6-position of the glucose residue in the lactose unit and has the following structure:

Antigens, Bacterial↗

PubMed1996

Interferon-gamma and nitric oxide down-regulate lipopolysaccharide-induced prostanoid production in cultured rat microglial cells by inhibiting cyclooxygenase-2 expression.

We have used purified microglial cultures obtained from neonatal rat brains to study some aspects of the regulation of prostanoid production in these cells. We found that nitric oxide, which is released into the culture medium along with prostanoids when the cells are exposed to lipo-polysaccharide (1-100 ng/ml), can down-regulate prostanoid biosynthesis. Indeed, the abrogation of endogenous nitric oxide production, obtained by depleting the medium of the precursor L-arginine or by blocking the activity of nitric oxide synthase by the specific inhibitor NG-monomethyl-L-arginine, led to a remarkable increase in lipopolysaccharide-induced prostanoid release. Moreover, the nitric oxide-generating compound 3-morpholinosydnonimine caused a substantial reduction of prostanoid formation, in the absence of endogenous nitric oxide, suggesting that both endogenous and exogenous nitric oxide may inhibit the induced prostanoid production. We also found that interferon-gamma potentiated the effect of lipopolysaccharide on nitrite accumulation as previously described by others and depressed the lipopolysaccharide-evoked production of prostaglandin E2, prostaglandin D2, and thromboxane. It is interesting that the inhibitory effect of interferon-gamma on prostanoid production did not appear to depend on the potentiation of NO release, as it was present also when the endogenous synthesis of nitric oxide was abrogated. Additional experiments showed that interferon-gamma and nitric oxide act mainly by down-regulating the lipopolysaccharide-induced enzymatic activity and expression (analyzed by western blot) of cyclooxygenase-2. Our data indicate that microglial prostanoid biosynthesis induced by proinflammatory stimuli, such as lipopolysaccharide, is tightly regulated by nitric oxide. Interferon-gamma appears to affect the balance between these local mediators by favoring nitric oxide production and inhibiting the prostanoid cascade and may thus contribute to the modulation of inflammation, local immune reactivity, and neuronal damage.

Animals↗

PubMed2003

Mevastatin suppresses lipopolysaccharide-induced Rac activation in the human monocyte cell line THP-1.

BACKGROUND: Rac is a member of the Rho family of small guanosine triphosphatases that regulate the actin cytoskeleton. Activation of Rac requires lipid modification that can be blocked by statins. Lipopolysaccharide-induced rearrangements in the actin cytoskeleton lead to changes in cell adhesion and motility that play a role in the cellular response to infection. The lipid products of phosphatidylinositol-3 kinase (PI3K) modulate Rac effector pathways and have been linked to the activation of the Rac-guanosine triphosphatase. We hypothesize that lipopolysaccharide stimulation leads to Rac activation and that this may be inhibited by statin pretreatment. Furthermore, signaling downstream of Rac is linked to PI3K; therefore, we hypothesize that a signaling complex between PI3K and Rac may be involved. METHODS: THP-1 cells were maintained in 1% fetal calf serum with or without 20 micromol/L mevastatin for 24 hours, followed by lipopolysaccharide stimulation. Active Rac was precipitated from THP-1 total cell lysate and then detected by immunoblotting. The PI3K-Rac complex was immunoprecipitated from total cell lysate, and the p85 regulatory subunit of PI3K was detected by immunoblotting. RESULTS: Lipopolysaccharide stimulation activated Rac. Rac activation was suppressed by pretreatment with mevastatin. The p85 subunit of PI3K was associated with Rac. CONCLUSIONS: Lipopolysaccharide stimulation leads to Rac activation in THP-1 cells, which may be suppressed with mevastatin pretreatment. There is an association between Rac and PI3K that demonstrates a role for PI3K in the activation of downstream Rac effector pathways.

Cell Line↗

PubMed1973

Isolation and characterization of lipopolysaccharide protein from Escherichia coli.

Extraction of the cell envelope of E. coli with 1% sodium dodecyl sulfate yielded a lipopolysaccharide protein that was purified to homogeneity by conventional techniques. Analysis of the pure protein indicated that it is a complex lipopolysaccharide protein with the following molar ratios of constitutents: 3-deoxyoctulosonate, 1.0; glucosamine, 1.3; neutral sugar (glucose + heptose), 1.0; organic phosphate, 2.3; and amino acid, 21. On a quantitative basis, all of the 3-deoxyoctulosonate present in the cell envelope preparation was solubilized in hot sodium dodecyl sulfate and subsequently accounted for in its entirely in the isolated protein component. After incubation of the cell-wall particulate fraction of cells grown on [(3)H]glucosamine with UDP-[(14)C]galactose under conditions designed to measure galactosyl transferase activity, the isolated lipopolysaccharide protein contained all of the [(14)C]galactose that was incorporated during the incubation. We concluded that the lipopolysaccharide of this organism occurs in the outer cellenvelope membrane exclusively in the form of lipopolysaccharide protein.

Autoradiography↗

PubMed1977

Domains involving nonrandom distribution of lipopolysaccharide in the outer membrane of Escherichia coli.

The present data demonstrate that the outer membrane of Escherichia coli contains domains of lipopolysaccharide that do not intermix freely with each other. A strain of E. coli lacking galactose epimerase was grown with galactose, for varying periods of time, which permits formation of a long polysaccharide, and without galactose, which results in a short polysaccharide. Such cultures yielded outer membrane fragments that were heterogeneous in lipopolysaccharide composition, some containing more long- than short-chain lipopolysaccharide, and vice versa. The kinetics of formation of these fragments suggest that lipopolysaccharide initially enters the membrane at points from which it can diffuse but ultimately is organized into domains that do not mix with each other, at least when lipopolysaccharides or different composition are present in the same organism.

Cell Membrane↗

PubMed1998

Relative contribution of transcription and translation to the induction of tumor necrosis factor-alpha by lipopolysaccharide.

The synthesis of tumor necrosis factor-alpha has been suggested to be regulated at both the transcriptional and translational levels in response to stimulation by bacterial lipopolysaccharide, although the relative contribution of these two mechanisms has not been quantitatively evaluated. Here, using the murine monocytic cell line RAW 264.7 as a model system, we show that steady-state TNF-alpha mRNA levels increase approximately 77-fold following treatment with lipopolysaccharide for 2 h and to a maximum of 164-fold after 8 h as measured by an RNase protection assay. The TNF-alpha gene transcription rate increases approximately 5-fold following exposure to lipopolysaccharide for 2 h as measured by a nuclear run-on assay. TNF-alpha mRNA stability did not change in the presence of lipopolysaccharide. A ribosomal sedimentation assay and an RNA transfection assay revealed that the translation rate of endogenous as well as transiently transfected TNF-alpha mRNAs increases only approximately 2-3-fold after stimulation with lipopolysaccharide for 2 h. Taken together, these results suggest that the large increase in the level of secreted TNF-alpha protein in RAW 264.7 cells is due primarily to activation of TNF-alpha gene transcription.

Animals↗

PubMed1999

Activation of p38 mitogen-activated protein kinase by lipopolysaccharide in human neutrophils requires nitric oxide-dependent cGMP accumulation.

This study examined the signal transduction pathway(s) leading to phosphorylation of p38 in human neutrophils stimulated with lipopolysaccharide and formyl peptides. Blockade of the nitric oxide (NO) pathway in neutrophils with the NO synthase inhibitor N-nitro-L-arginine methyl ester or by treatment with the NO scavenger 2-phenyl-tetramethylimidazoline-1-oxyl-3-oxide attenuated phosphorylation of the mitogen-activated protein kinase p38 in response to lipopolysaccharide but not fMet-Leu-Phe. Using the NO releasing agents S-nitroso-N-acetylpenicillamine and sodium nitroprusside it was determined that nitric oxide is sufficient to cause an increase in phosphorylation of p38. Increasing cellular cGMP with phosphodiesterase inhibitors, by stimulation of soluble guanylyl cyclase with YC-1 or with exogenous dibutyryl cGMP resulted in mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 3,6 (MEK3,6) activation and phosphorylation of p38. This phenomenon was specific for MEK3,6, because these agents had no effect on the phosphorylation state of MEK1,2. A role for protein kinase G but not protein kinase A downstream of lipopolysaccharide but not formylmethionylleucylphenylalanine was shown using the specific inhibitors KT5823 and H89, respectively. These data indicate that activation of p38 by fMet-Leu-Phe and lipopolysaccharide involve different mechanisms, and that activation of protein kinase G by NO-dependent stimulation of guanylyl cyclase is necessary and sufficient for phosphorylation of p38 downstream of lipopolysaccharide.

Calcium-Calmodulin-Dependent Protein Kinases↗

PubMed2000

Immulectin-2, a lipopolysaccharide-specific lectin from an insect, Manduca sexta, is induced in response to gram-negative bacteria.

A lipopolysaccharide-specific lectin, immulectin-2, was isolated from plasma of the tobacco hornworm, Manduca sexta. Immulectin-2 has specificity for xylose, glucose, lipopolysaccharide, and mannan. A cDNA clone encoding immulectin-2 was isolated from an Escherichia coli-induced M. sexta larval fat body cDNA library. The cDNA is 1253 base pairs long, with an open reading frame of 981 base pairs, encoding a 327-residue polypeptide. Immulectin-2 is a member of the C-type lectin superfamily. It consists of two carbohydrate recognition domains, which is similar to the organization of M. sexta immulectin-1. Immulectin-2 was present at a constitutively low level in plasma of control larvae and increased 3-4-fold after injection of Gram-negative bacteria or lipopolysaccharide. Immulectin-2 mRNA was detected in fat body of control larvae, and its level increased dramatically after injection of E. coli. The concentration of immulectin-2 in plasma did not change significantly after injection of Gram-positive bacteria or yeast, even though its mRNA level was increased by these treatments. Compared with immulectin-1, immulectin-2 has a more restricted specificity for binding to Gram-negative bacteria. Immulectin-2 at low physiological concentrations agglutinated E. coli in a calcium-dependent manner. It also bound to immobilized lipopolysaccharide from E. coli. Binding of immulectin-2 to lipopolysaccharide stimulated phenol oxidase activation in plasma. The properties of immulectin-2 are consistent with its function as a pattern recognition receptor for detection and defense against Gram-negative bacterial infection in M. sexta.

Agglutination Tests↗

PubMed2001

P2Y(6) nucleotide receptor mediates monocyte interleukin-8 production in response to UDP or lipopolysaccharide.

Extracellular nucleotides are autocrine and paracrine cellular mediators that signal through P2 nucleotide receptors. Monocytic cells express several P2Y receptors but the role of these G protein-coupled receptors in monocytes is not known. Here, we present evidence that P2Y(6) regulates chemokine production and release in monocytes. We find that UDP, a selective P2Y(6) agonist, stimulates interleukin (IL)-8 release in human THP-1 monocytic cells whereas other nucleotides are relatively inactive. P2 receptor antagonists or P2Y(6) antisense oligonucleotides inhibit IL-8 release induced by UDP. Furthermore, UDP specifically activated IL-8 production in astrocytoma 1321N1 cells transfected with human P2Y(6). Since lipopolysaccharide has been suggested to activate P2 receptors via nucleotide release, we tested whether IL-8 production stimulated by lipopolysaccharide might result from P2Y(6) activation. P2 antagonists or apyrase, an enzyme which hydrolyzes nucleotides including UDP, inhibit IL-8 production induced by lipopolysaccharide but not by other stimuli. Furthermore, IL-8 gene expression activated by lipopolysaccharide is enhanced by P2Y(6) overexpression and inhibited by P2Y(6) antisense oligonucleotides. Thus, UDP activates IL-8 production via P2Y(6) in monocytic cells. Furthermore, lipopolysaccharide mediates IL-8 production at least in part by autocrine P2Y(6) activation. These findings indicate a novel role for P2Y(6) in innate immune defenses.

Cell Line↗

PubMed2002

Pore formation and function of phosphoporin PhoE of Escherichia coli are determined by the core sugar moiety of lipopolysaccharide.

The lipid matrix of the outer membrane of Gram-negative bacteria is an asymmetric bilayer composed of a phospholipid inner leaflet and a lipopolysaccharide outer leaflet. Incorporated into this lipid matrix are, among other macromolecules, the porins, which have a sieve-like function for the transport or exclusion of hydrophilic substances. It is known that a reduced amount of porins is found in the outer membrane of rough mutants as compared with wild-type bacteria. This observation was discussed to be caused by a reduced number of insertion sites in the former. We performed electrical measurements on reconstituted planar bilayers composed of lipopolysaccharide on one side and a phospholipid mixture on the other side using lipopolysaccharide from various rough mutant strains of Salmonella enterica serovar Minnesota. We found that pore formation by PhoE trimers that were added to the phospholipid side of the bilayers increased with the increasing length of the lipopolysaccharide core sugar moiety. These results allow us to conclude that the length of the sugar moiety of lipopolysaccharide is the parameter governing pore formation and that no particular insertion sites are required. Furthermore, we found that the voltage gating of the porin channels is strongly dependent on the composition of the lipid matrix.

Escherichia coli Proteins↗

PubMed2004

Chromosomal and plasmid-encoded enzymes are required for assembly of the R3-type core oligosaccharide in the lipopolysaccharide of Escherichia coli O157:H7.

The type R3 core oligosaccharide predominates in the lipopolysaccharides from enterohemorrhagic Escherichia coli isolates including O157:H7. The R3 core biosynthesis (waa) genetic locus contains two genes, waaD and waaJ, that are predicted to encode glycosyltransferases involved in completion of the outer core. Through determination of the structures of the lipopolysaccharide core in precise mutants and biochemical analyses of enzyme activities, WaaJ was shown to be a UDP-glucose:(galactosyl) lipopolysaccharide alpha-1,2-glucosyltransferase, and WaaD was shown to be a UDP-glucose:(glucosyl)lipopolysaccharide alpha-1,2-glucosyltransferase. The residue added by WaaJ was identified as the ligation site for O polysaccharide, and this was confirmed by determination of the structure of the linkage region in serotype O157 lipopolysaccharide. The initial O157 repeat unit begins with an N-acetylgalactosamine residue in a beta-anomeric configuration, whereas the biological repeat unit for O157 contains alpha-linked N-acetylgalactosamine residues. With the characterization of WaaJ and WaaD, the activities of all of the enzymes encoded by the R3 waa locus are either known or predicted from homology data with a high level of confidence. However, when core oligosaccharide structure is considered, the origin of an additional alpha-1,3-linked N-acetylglucosamine residue in the outer core is unknown. The gene responsible for a nonstoichiometric alpha-1,7-linked N-acetylglucosamine substituent in the heptose (inner core) region was identified on the large virulence plasmids of E. coli O157 and Shigella flexneri serotype 2a. This is the first plasmid-encoded core oligosaccharide biosynthesis enzyme reported in E. coli.

Base Sequence↗

PubMed2004

Kinome profiling for studying lipopolysaccharide signal transduction in human peripheral blood mononuclear cells.

The DNA array technique allows comprehensive analysis of the genome and transcriptome, but the high throughput array-based assessment of intracellular signal transduction remains troublesome. The goal of this study was to test a new peptide array technology for studying the activity of all kinases of whole cell lysates, the kinome. Cell lysates from human peripheral blood mononuclear cells before and after stimulation with lipopolysaccharide were used for in vitro phosphorylation with [gamma-33P]ATP arrays consisting of 192 peptides (substrates for kinases) spotted on glass. The usefulness of peptide arrays for studying signal transduction was demonstrated by the generation of the first comprehensive description of the temporal kinetics of phosphorylation events induced by lipopolysaccharide stimulation. Furthermore analysis of the signals obtained suggested activation of p21Ras by lipopolysaccharide, and this was confirmed by direct measurement of p21Ras GTP levels in lipopolysaccharide-stimulated human peripheral blood mononuclear cells, which represents the first direct demonstration of p21Ras activation by stimulation of a Toll receptor family member. Further confidence in the usefulness of peptide array technology for studying signal transduction came from Western blot analysis of lipopolysaccharide-stimulated cells, which corroborated the signals obtained using peptide arrays as well as from the demonstration that kinase inhibitors effected peptide array phosphorylation patterns consistent with the expected action of these inhibitors. We conclude that this first metabolic array is a useful method to determine the enzymatic activities of a large group of kinases, offering high throughput analysis of cellular metabolism and signal transduction.

Amino Acid Sequence↗

PubMed2006

Specific amino acids of the glycosyltransferase LpsA direct the addition of glucose or galactose to the terminal inner core heptose of Haemophilus influenzae lipopolysaccharide via alternative linkages.

Lipopolysaccharide is the major glycolipid of the cell wall of the bacterium Haemophilus influenzae, a Gram-negative commensal and pathogen of humans. Lipopolysaccharide is both a virulence determinant and a target for host immune responses. Glycosyltransferases have high donor and acceptor substrate specificities that are generally limited to catalysis of one unique glycosidic linkage. The H. influenzae glycosyltransferase LpsA is responsible for the addition of a hexose to the distal heptose of the inner core of the lipopolysaccharide molecule and belongs to the glycosyltransferase family 25. The hexose added can be either glucose or galactose and linkage to the heptose can be either beta1-2 or beta1-3. Each H. influenzae strain uniquely produces only one of the four possible combinations of linked sugar in its lipopolysaccharide. We show that, in any given strain, a specific allelic variant of LpsA directs the anomeric linkage and the added hexose, glucose, or galactose. Site-directed mutagenesis of a single key amino acid at position 151 changed the hexose added in vivo from glucose to galactose or vice versa. By constructing chimeric lpsA gene sequences, it was shown that the 3' end of the gene directs the anomeric linkage (beta1-2 or beta1-3) of the added hexose. The lpsA gene is the first known example where interstrain variation in lipopolysaccharide core structure is directed by the specific sequence of a genetic locus encoding enzymes directing one of four alternative possible sugar additions from the inner core.

Alleles↗

PubMed1978

Characterization of lipopolysaccharide of Haemophilus influenzae.

Lipopolysaccharide from strains of Haemophilus influenzae was extracted and isolated by the hot phenol-water procedure. The preparations were relatively insoluble in water but could be solubilized with surface-active agents. The preparations contained carbohydrate (30%), fatty acid (29%), and phosphate (4.7%); protein content was less than 1%. Thin-layer chromatography, gas-liquid chromatography, and colorimetric assays detected glucose, galactose, glucosamine, heptose, and a 2-keto-3-deoxy-octonate-like molecule (less than 1%). Neither methylpentose nor dideoxyhexose was detected. The lipid portion was composed of fatty acids common to lipopolysaccharide of Salmonella. The preparations provoked positive dermal Shwartzman reactions and biphasic febrile responses in rabbits, responses typical of endotoxic activity. The 50% lethal dose for mice was decreased from 16.5 microgram/g to 0.015 microgram/g by concomitant administration of actinomycin D. The preparations were shown to be polyclonal activators of bone marrow-derived (B) cells. Limulus lysate gelation was seen with 8.0 ng of lipopolysaccharide. Preliminary hemagglutination data suggested at least three different antigenic factors associated with the lipopolysaccharide of H. influenzae type b. The H. influenzae lipopolysaccharide appeared biologically similar to that of enterobacteria but chemically different.

Animals↗

PubMed1989

Polymyxin B prevents lipopolysaccharide-induced release of tumor necrosis factor-alpha from alveolar macrophages.

Polymyxin B (PmB) blocks many of the toxic effects of lipopolysaccharide by mechanisms that are not yet understood. The production of tumor necrosis factor-alpha (TNF-alpha) by isolated rat alveolar macrophages in response to lipopolysaccharide and macrophage-activating factor was blocked by PmB at concentrations of 100, 10, and 1 micrograms/ml. Gentamicin enhanced rather than inhibited TNF production at the 100-micrograms/ml concentrations and had no effect at low concentration. Similar inhibitory effects were induced by PmB in an in vivo model in which rat macrophage TNF production was stimulated by intratracheally injected lipopolysaccharide. Because many of the effects of lipopolysaccharide are mediated by TNF, this inhibition provides a mechanism to explain the protection afforded by PmB against lipopolysaccharide-induced toxicity.

Animals↗