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D C Morrison

Publications and source records attributed to D C Morrison.

At least 37 records · Page 2Linked to original sources
PubMed1998

Mechanisms involved in the pathogenesis of sepsis are not necessarily reflected by in vitro cell activation studies.

It is thought that lipopolysaccharide (LPS) from gram-negative bacteria contributes significantly to the pathogenesis of septic shock. In vitro studies to address the mechanisms involved in this process have often investigated human monocytes or mouse macrophages, since these cells produce many of the mediators found in septic patients. Targeting of these mediators, especially tumor necrosis factor alpha (TNF-alpha), has been pursued as a means of reducing mortality in sepsis. Two experimental approaches were designed to test the assumption that in vitro studies with macrophages accurately predict in vivo mechanisms of LPS pathogenesis. In the first approach, advantage was taken of the fact that on consecutive days after injection of thioglycolate into mice, increased numbers of macrophages could be harvested from the peritoneum. These cells manifested markedly enhanced levels of in vitro TNF-alpha, interleukin 6 (IL-6), and nitric oxide production in response to LPS. In D-galactosamine-sensitized mice, however, thioglycolate treatment significantly decreased mortality due to LPS, as well as levels of circulating TNF-alpha and IL-6. Anti-TNF-alpha treatment confirmed this cytokine's role in the observed lethality. In a second experimental approach, we compared the mouse macrophage-stimulating potencies of different LPS preparations with their lethalities to mice. In these studies, the in vitro macrophage-stimulating profiles presented by rough-LPS and smooth-LPS preparations were the reverse of their relative lethal potencies in vivo. In conclusion, peritoneal macrophages appear not to be the major cells responsible for the overall host response during endotoxic shock. These findings underscore the importance of verifying the correlation of in vivo systems with in vitro systems when attributing specific functions to a cell type.

Animals↗
PubMed1998

Antibiotic-mediated release of endotoxin and the pathogenesis of gram-negative sepsis.

Since the earliest days of antibiotic chemotherapy to treat infection with Gram-negative microbes, investigators have recognized that such treatments may result in the release of microbial constituents that might, in turn, exacerbate the pathophysiological manifestations of disease. Both in vitro studies and in vivo animal experiments have over the years provided evidence in support of this concept; however, the actual clinical importance of this phenomenon to patients with Gram-negative sepsis is unclear. Recently published reports from a number of laboratories have shown that cell wall-active antibiotics that differ in their fundamental mechanisms of action in disrupting microbial growth (via selective interactions with various penicillin binding proteins) also differ in their relative ability to induce the release of biologically active endotoxin both in vitro and in vivo. Further, quantitative differences in total endotoxin release correlate well with antibiotic-initiated morphological changes in the microbe. Of potential significance is the finding that these differences are also reflected in differential production of cytokines from endotoxin-stimulated mononuclear phagocytes and other host target cells, including 11-6 and TNF. Since these immunologic hormones have been strongly implicated as contributing factors to the pathogenesis of Gram-negative sepsis, interest in the potential use of this chemotherapeutic approach as a means of controlling the host immunopathologic response has increased. Carefully controlled clinical trials in which different antibiotic treatments are correlated with production of cytokines will be of significant potential value in evaluating the actual significance of this phenomenon in the Gram-negative septic patient.

Animals↗
PubMed1997

Two functionally independent pathways for lipopolysaccharide-dependent activation of mouse peritoneal macrophages.

We have investigated the effects of human LPS-binding protein (LBP) and human bactericidal/permeability-increasing protein (BPI) on LPS-dependent activation of mouse thioglycolate-elicited peritoneal macrophages in vitro, in comparison with human PBMCs. Confirming earlier published studies, BPI inhibited, and LBP enhanced, the ability of LPS to stimulate PBMC production of the cytokines TNF-alpha and IL-6. In marked contrast to these results, under identical conditions of in vitro culture, both LBP and BPI suppressed, in a dose-dependent manner, the ability of LPS to stimulate cytokine production in mouse macrophages. Further, while human BPI also suppressed LPS-dependent NO secretion in mouse macrophages, human LBP had no inhibitory effect on NO secretion under conditions that inhibited TNF-alpha secretion. These data provide the first direct evidence that mouse macrophages may utilize two independent pathways in response to LPS, thus leading to different phenotypic responses.

Acute-Phase Proteins↗
PubMed1997

An interferon-gamma-activated site (GAS) is necessary for full expression of the mouse iNOS gene in response to interferon-gamma and lipopolysaccharide.

Mouse macrophages can be stimulated by interferon (IFN)-gamma and bacterial lipopolysaccharide (LPS) to produce nitric oxide (NO) as the result of expression of the inducible NO synthase (iNOS; EC 1.14.13.39) gene. The iNOS gene promoter contains a candidate gamma-interferon-activated site (GAS). In transfection studies reported here, it was demonstrated that a luciferase reporter-gene construct, containing four synthetic copies of the iNOS GAS, was inducible when transfected macrophages were stimulated with either IFN-gamma, LPS, or a combination of the two. Consistent with this finding were other transfection analyses, which showed that responsiveness of the intact iNOS promoter to these same agents was significantly reduced when two conserved nucleotide positions within the GAS were mutated. Oligonucleotide probes, which mimicked the iNOS GAS, formed a complex with proteins that appeared in the nuclei of IFN-gamma or IFN-gamma + LPS-treated macrophages within 30 min of stimulation, as shown by electrophoretic mobility shift assay. LPS alone also caused the the appearance of a nuclear protein capable of binding the iNOS GAS-containing oligonucleotide; however, in contrast to binding induced by IFN-gamma, approximately 2 h of stimulation with LPS were required. The protein bound to the iNOS GAS-containing oligonucleotide reacted specifically with an antibody raised against Stat1a, regardless of the stimulus used. These data collectively support the conclusion that binding of Stat1 alpha to the iNOS promoter's GAS is required for optimal induction of the iNOS gene by IFN-gamma and LPS.

Animals↗
PubMed1996

Bacteremia versus endotoxemia in experimental mouse leukopenia--role of antibiotic chemotherapy.

Imipenem and ceftazidime have different specificities for penicillin-binding proteins and cause a differential release of lipopolysaccharide (LPS) from gram-negative bacteria in vitro. In studies in mice made leukopenic by the administration of cyclophosphamide, the innate relative resistance to the lethal effects of LPS was not significantly changed, but these animals became highly sensitized to bacterial infection. When leukopenic mice were challenged with graded doses of Escherichia coli O111:B4, an LD50 was achieved at a dose of approximately 10(6) cfu. Administration of either antibiotic resulted in a shift in the LD50 of approximately 500-fold, in contrast to D-galactosamine-treated LPS-sensitized mice, in which a < 10-fold increase in the LD50 was observed with antibiotic therapy. Further, if mice were made LPS-sensitive with D-galactosamine, no differences between leukopenic and normal mice were noted with antibiotic therapy.

Animals↗
PubMed1996

Altered regulation of inducible nitric oxide synthase expression in macrophages from senescent mice.

We investigated the capacity of mouse macrophages obtained from senescent animals to respond in vitro to microbial stimuli. Significant hypersecretion of nitric oxide (NO) was observed in thioglycolate-elicited macrophages from senescent mice compared with those obtained from young mice in response to lipopolysaccharide (LPS). In contrast, both cell populations manifested equivalent responses to LPS with respect to tumor necrosis factor alpha secretion. Further, macrophages from senescent animals also showed potentiated responses to both zymosan and heat-killed Staphylococcus aureus, as assessed by NO production. Both cell populations were equivalently inhibited by a competitive inhibitor of NO synthase NG-monomethyl-L-arginine. Since endogenous beta interferon (IFN-beta) is recognized as an essential cofactor for LPS-induced NO production by macrophages, we investigated the role of IFN-beta in enhancing the capacity of both macrophage populations for LPS-induced NO production. Macrophages from young mice were minimally activated by LPS alone to express inducible NO synthase (iNOS), and the response was significantly potentiated by the addition of IFN-beta. These findings were confirmed by immunocytochemical staining of iNOS in which the frequency of iNOS-positive cells in response to LPS was enhanced in the presence of IFN-beta. Reverse transcription-PCR analyses revealed that macrophages from senescent animals produced larger amounts of iNOS mRNA in response to LPS. Further, exogenous IFN-beta potentiated iNOS mRNA expression in macrophages from young mice. In contrast, the frequency of LPS-activated macrophages for iNOS expression was markedly increased during senescence and addition of IFN-beta did not significantly change this frequency. These results correlated with reverse transcription PCR data showing high levels of iNOS mRNA in LPS-stimulated macrophages from senescent mice. LPS-induced NO production in macrophages from both young and senescent mice was inhibited by neutralizing antibody to either IFN-beta or IFN-gamma. Mixed cultures of macrophages from young and senescent mice stimulated with LPS manifested significantly enhanced NO production relative to that which would be predicted from an additive response of the two macrophage populations stimulated separately. The differential responsiveness of NO production observed with thioglycolate-elicited macrophages from young and senescent mice was also observed in resident macrophages but, interestingly, not in bone marrow culture-derived macrophages. These results suggest that environmental factors may be responsible for the potentiated NO responses of macrophages from senescent mice. Collectively, these data suggest that macrophages from senescent animals manifest an altered mechanism for regulation of macrophage function in NO production and iNOS expression by constitutive and/or induced expression of autoregulatory cytokines.

Aging↗
PubMed1996

Low-dose lipopolysaccharide (LPS) pretreatment of mouse macrophages modulates LPS-dependent interleukin-6 production in vitro.

Lipopolysaccharide (LPS) can induce mouse macrophages to produce a number of cytokines and other inflammatory mediators. Our laboratory previously reported that LPS-dependent macrophage-derived tumor necrosis factor alpha (TNF-alpha) production could be significantly potentiated by pretreatment with LPS at substimulatory LPS priming doses. The observed potentiation was shown to be coincident with a down-regulation of LPS-dependent nitric oxide (NO) production (X. Zhang and D. C. Morrison, J. Exp. Med. 177: 511-516, 1993). In order to determine whether these LPS reprogramming effects in mouse macrophages were selective for these two macrophage-derived mediators, we have examined the effects of LPS pretreatment on LPS-dependent interleukin 6 (IL-6) production. Thioglycolate-elicited mouse peritoneal macrophages were pretreated with various subthreshold stimulatory concentrations of LPS for 6 h, washed three times, and then stimulated with an effective stimulatory concentration of smooth LPS for 18 h. In confirmation of earlier studies, pretreatment of mouse macrophages with substimulatory doses of LPS inhibited the subsequent LPS-dependent NO production. This down-regulation was accompanied by a coordinate up-regulation of LPS-dependent IL-6 production, similar to what was shown earlier for TNF-alpha production. These priming effects with the substimulatory dose of smooth LPS are shown to be independent of doses of LPS used for subsequent activation and are not restricted to specific LPS stimulation. Moreover, the enhancement of the IL-6 response by LPS pretreatment is still observed in the presence of neutralizing antibody to TNF-alpha. These findings, therefore, provide further support for the conclusion that LPS-dependent macrophage reprogramming is likely to involve common regulatory pathways that control the secretion of both IL-6 and TNF-alpha.

Animals↗
PubMed1996

Evidence for antibiotic-mediated endotoxin release as a contributing factor to lethality in experimental gram-negative sepsis.

Endotoxic lipopolysaccharide (LPS) is a major constituent of the outer membrane of the Gram-negative microbe. Following its release from the bacterium, LPS serves as a potent proinflammatory stimulus by interacting with humoral and cellular mediator systems to stimulate production of an array of inflammatory molecules. Cell-wall active antibiotics are known to promote endotoxin release. To assess the contribution of antibiotic-induced endotoxin release in the pathogenesis of Gram-negative sepsis, we have developed several experimental models in which mice have been pretreated with various agents to make them sensitive to Gram-negative (E. coli, pseudomonas) infection and/or the lethal effects of endotoxin. For the former, both cyclophosphamide (which renders mice neutropenic) and the reversible hepatotoxin D-galactosamine (D-gal) have been used. D-gal also sensitized mice to the lethal effects of LPS. Infected mice treated with cell-wall active antibiotics are protected approximately five- to 10-fold (as assessed by increases in LD50) if they are sensitive to LPS lethality (D-gal treatment) but 500-fold if they are resistant to LPS lethality. Importantly, different antibiotics that have been documented to cause different amounts of endotoxin release in vitro also differ in their protective efficacy in vivo. Thus, imipenem, which causes relatively low endotoxin release, is significantly more protective (8-fold) than ceftazidime or meropenem (3-fold, P < 0.005) under conditions of equivalent MICs. Lethality data correlate well with circulating levels of interleukin-6 (Il-6) in vivo and with induction of Il-6 in ex vivo studies in which anticoagulated mouse blood is incubated with bacteria and antibiotics. Finally, antiendotoxin agents manifest additional levels of protection in vivo under conditions in which antibiotics alone are not protective. Collectively, these results strongly implicate antibiotic-induced endotoxin release as a significant contributing factor in experimental Gram-negative sepsis.

Animals↗
PubMed1995

Differences in therapeutic efficacy among cell wall-active antibiotics in a mouse model of gram-negative sepsis.

The in vivo efficacy of three cell wall-active antibiotics, imipenem, meropenem, and ceftazidime, was compared in mice rendered hypersusceptible to the pathophysiologic effects of lipopolysaccharide by treatment with D-galactosamine. When CF-1 mice were administered Escherichia coli, D-galactosamine, and saline intraperitoneally, an LD50 was achieved at an inoculum of approximately 2 x 10(4) cfu. Administration of antibiotic at 20 mg/kg resulted in significant but widely variable protective efficacy from E. coli lethality among the three antibiotics. At this dose, an approximately 3-fold increase in LD50 was observed with either meropenem or ceftazidime, whereas administration of imipenem resulted in an approximately 8-fold increase in LD50 (P = .0053). When the dose of antibiotic was decreased to 2 mg/kg, neither meropenem nor ceftazidime could provide measurable protection, whereas imipenem was almost fully protective (P < .002). These differences in protective efficacy were also noted with experimental Pseudomonas aeruginosa but not Staphylococcus aureus infection.

Animals↗
PubMed1995

Therapeutic efficacy of a polymyxin B-dextran 70 conjugate in experimental model of endotoxemia.

Numerous studies have suggested that lipopolysaccharide (LPS), a major component of the cell wall of gram-negative bacteria, is responsible for the initiation of gram-negative septic shock. Previously, others have designed therapeutic regimens to target the biologically active lipid A region of LPS by either neutralization of the biological properties of LPS or enhancement of clearance of this molecule. One such compound capable of neutralizing lipid A is the antibiotic polymyxin B. However, the clinical utility of polymyxin B is limited by its toxicity. We therefore covalently conjugated this antibiotic to the high-molecular-weight polysaccharide dextran 70, resulting in reduced toxicity of polymyxin B but retention of its endotoxin-neutralizing ability. The studies described in this report were designed to test the in vivo efficacy of this compound in an experimental animal model of gram-negative septic shock. Mice were administered graded doses of Escherichia coli or Pseudomonas aeruginosa along with D-galactosamine and the antibiotic imipenem. We had previously determined that antibiotic chemotherapy provides significant protection against E. coli-mediated lethality with smaller doses of bacteria; however, the antibiotic does not provide protection against larger doses of bacteria, but it is effective at killing the bacterial inoculum in vivo. Administration of the polymyxin B-dextran 70 conjugate provided significant protection when given with an antibiotic but was not effective by itself. A requirement for a pretreatment period prior to E. coli challenge was shown to depend upon the bacterial challenge dose. In other studies using this D-galactosamine sensitization model, we demonstrated that the lipid A-specific conjugate had no effect on lethality caused by staphylococcus aureus or tumor necrosis factor alpha. The results of these studies indicate that this compound is effective in preventing lethal gram-negative septic shock in mice and may be useful as a potential therapeutic agent in humans as well.

Animals↗
PubMed1995

CD14 is not involved in Rhodobacter sphaeroides diphosphoryl lipid A inhibition of tumor necrosis factor alpha and nitric oxide induction by taxol in murine macrophages.

Taxol, a microtubule stabilizer with anticancer activity, mimics the actions of lipopolysaccharide (LPS) on murine macrophages in vitro. Recently, it was shown that taxol-induced macrophage activation was inhibited by the LPS antagonist Rhodobacter sphaeroides diphosphoryl lipid A (RsDPLA). To investigate the mechanisms of taxol-induced macrophage activation, the present study focused on the interaction of LPS, RsDPLA, and taxol in the activation of and binding to macrophages. Taxol alone induced murine C3H/He macrophages to secrete tumor necrosis factor alpha (TNF) and to produce nitric oxide (NO) with kinetics similar to that of LPS. Macrophages from LPS-hyporesponsive C3H/HeJ mice, in contrast, did not yield any detectable TNF and NO production in response to LPS or taxol. RsDPLA inhibited taxol-induced TNF and NO production from C3H/He macrophages in a dose-dependent manner. The inhibition by RsDPLA was specific for LPS and taxol in that RsDPLA did not inhibit heat-killed Listeria monocytogenes- or zymosan-induced TNF production. Polymyxin B blocked the inhibitory effect of RsDPLA on taxol-induced TNF production. The inhibitory activity of RsDPLA appeared to be reversible since macrophages still responded to taxol in inducing TNF production after the RsDPLA was washed out with phosphate-buffered saline prior to the addition of taxol. Taxol-induced TNF production was not inhibited by colchicine, vinblastine, or 10-deacetylbaccatine III. A mutant cell line, J7.DEF3, defective in expression of a CD14 antigen, responded equally well to taxol by producing TNF as did the parent J774.1 cells. This suggested that the activation of macrophages by taxol does not require CD14. Taxol-induced TNF production by the mutant cells was also inhibited by RsDPLA. 125I-labeled LPS and 3H-labeled taxol was reported to bind to J774.1 cells predominantly via CD14 and microtubules, respectively. The binding of 125I-labeled LPS to J7.DEF3 cells was about 30 to 40% of that to J774.1 cells. The binding of 125I-LPS to J774.1 cells was inhibited by unlabeled LPS and RsDPLA but not by taxol. On the other hand, 3H-labeled taxol bound to both J774.1 cells and J7.DEF3 cells in similar time- and dose-dependent manners. The binding of [3H]taxol to these cells was inhibited by taxol but not by LPS or RsDPLA. Although the binding studies failed to examine cross competition for binding to macrophages, a possible explanation of these results is that LPS, RsDPLA, and taxol share the same molecule(s) on murine macrophages for their functional receptor(s), which is neither CD14 nor tubulin.

Animals↗
PubMed1994

Differential antibiotic-induced release of endotoxin from gram-negative bacteria.

Treatment of log phase cultures of Escherichia coli with cell wall active antibiotics results in increased exposure of immunologically reactive lipid A epitopes of lipopolysaccharide (LPS) and release of soluble LPS into culture supernatants. Comparison of the efficacy of two cell wall active antibiotics, ceftazidime, a penicillin-binding protein 3 selective antibiotic, and imipenem, a penicillin-binding protein 2 selective antibiotic, for their relative efficacy in mediating LPS release indicated quantitative but not qualitative differences, with the former antibiotic manifesting a significantly broader range of concentrations at which LPS release could be demonstrated. Comparison of the relative efficacy of these two antibiotics in a mouse bacteraemia model in which animals were made hypersensitive to the lethal effects of endotoxin by treatment with D-galactosamine indicated that the latter antibiotic may provide a greater level of protection. These studies suggest that the release of endotoxin mediated by antibiotic treatment may contribute to the pathogenesis of disease in infectious due to gram-negative organisms.

Animals↗
PubMed1994

Differential effects of serum on lipopolysaccharide receptor-directed macrophage activation for nitric oxide production.

In this manuscript, the effects of fetal bovine serum (FBS) on activation of mouse macrophages through the p73 lipopolysaccharide (LPS) receptor have been evaluated. In confirmation of earlier published studies, FBS will significantly potentiate the ability of LPS to activate macrophages to produce nitric oxide (NO). Evidence that this potentiating effect of FBS is mediated primarily by an interaction with LPS is provided by data showing that the stimulating effects of a hamster IgM monoclonal antibody to the p73 LPS receptor are significantly suppressed under identical conditions of FBS addition. The presence of FBS enhances both the kinetics of LPS-induced NO production and delays the induction of MAb5D3-induced NO production. The data establish that the ability of FBS to reduce MAb5D3-initiated NO production can only be manifest during the first 4-6 h following activation with antibody. Similarly, the ability of polymyxin B (which does not affect MAb5D3 activity) to inhibit LPS-dependent macrophage activation is also only effective during the first 4-6 h of stimulation, suggesting a parallel kinetic profile in the activation of the inducible NO synthase by these related activators. These studies provide data which suggest a dual role for serum factors in LPS-dependent macrophage activation, a direct effect of FBS on LPS which potentiates its immunostimulatory activity, and a secondary down-regulation effect which is manifest at the level of the macrophage.

Animals↗
PubMed1994

Induction of proinflammatory responses in human monocytes by particulate and soluble forms of lipopolysaccharide.

Lipopolysaccharide (LPS), a major constituent of the outer membrane of Gram-negative bacteria, is thought to be chiefly responsible for induction by these organisms of Gram-negative septic shock, an often fatal complication of Gram-negative septicemia. Accordingly, monocytes and macrophages, which are believed to be the primary cellular targets of LPS, have been shown to mount vigorous proinflammatory responses to highly purified, soluble LPS. Relatively less is known, however, about the ability of these cells to respond to native, insoluble forms of LPS, such as those represented by intact Gram-negative bacterial particles. Furthermore, the intact microbe would be expected to exhibit additional non-LPS components that are capable of stimulating proinflammatory responses, and the relative roles of these components and LPS in stimulating proinflammatory responses have not, to date, been fully defined. Therefore, experiments have been conducted to assess stimulation of human monocytes by highly purified, soluble LPS as well as by particulate forms of LPS, including Gram-negative bacterial particles and LPS-coated latex beads. As indicated by induction of procoagulant activity and production of tumor necrosis factor, LPS appears to be the Gram-negative bacterial component of primary importance for induction of monocytic proinflammatory responses. Furthermore, the presentation of LPS associated with the bacterial surface is also capable of eliciting such responses, albeit with less potency than that observed for soluble LPS. At least part of this reduction in potency appears attributable to the particulate nature of bacterium-bound LPS, since a reduction in potency is similarly observed for soluble LPS coated onto latex beads.

Animals↗
PubMed1994

Necessity and sufficiency of beta interferon for nitric oxide production in mouse peritoneal macrophages.

Bacterial lipopolysaccharide and some cytokines can activate macrophages to secrete nitric oxide. Macrophage-derived nitric oxide is a key cytotoxic factor for microbicidal and tumoricidal processes. We report here that a monoclonal antibody specific for beta interferon inhibited lipopolysaccharide-induced nitric oxide production in thioglycolate-elicited C3HeB/FeJ peritoneal macrophages and macrophage-like cell line RAW 264.7. In addition, exogenous added beta interferon enabled lipopolysaccharide-hyporesponsive thioglycolate-elicited C3H/HeJ peritoneal macrophages to produce nitric oxide in response to lipopolysaccharide. These data support the concept that beta interferon provides an essential signal(s) for lipopolysaccharide-triggered nitric oxide production by mouse macrophages. Heat-killed Staphylococcus aureus, a gram-positive bacterium which was unable to initiate nitric oxide production in thioglycolate-elicited C3HeB/FeJ peritoneal macrophages in vitro, promoted nitric oxide formation in the presence of beta interferon, suggesting that beta interferon may be a general cofactor necessary for bacterium-derived stimulus-induced nitric oxide production in these macrophages. However, neither beta interferon nor tumor necrosis factor alpha, alone or in combination, triggered nitric oxide production in thioglycolate-elicited mouse peritoneal macrophages, demonstrating that these macrophage-derived cytokines, while necessary, were not sufficient by themselves for the induction of nitric oxide production in these cells. On the other hand, gamma interferon and tumor necrosis factor alpha acted together to induce nitric oxide production in vitro in the absence of lipopolysaccharide in thioglycolate-elicited mouse peritoneal macrophages, indicating that these two types of interferons provided different signals during the activation of these macrophages.

Animals↗
PubMed1994

Evidence for lipopolysaccharide as the predominant proinflammatory mediator in supernatants of antibiotic-treated bacteria.

Lipopolysaccharide (LPS), purified from gram-negative bacteria, is well known to induce proinflammatory responses in monocytes and macrophages, and release of LPS from the microbial surface has been suggested to be an important initiating event in the sepsis syndrome. However, numerous studies have documented that a variety of constituents present in the outer cell membrane of gram-negative bacteria have the capacity to activate cells of the immune system. Given that the majority of immunotherapeutic approaches designed to intervene in gram-negative sepsis have to date targeted the LPS molecule, it would be of value to assess the relative proinflammatory properties of LPS and other gram-negative structures. Experiments were therefore undertaken to assess stimulation of human monocytes by components released from Escherichia coli following bacteriolysis by the cell wall-active antibiotic ceftazidime. As assessed by both induction of procoagulant activity and release of tumor necrosis factor, bacterial culture supernatants contain significant proinflammatory activity. When culture supernatants are fractionated via either velocity sedimentation in sucrose gradients or isopycnic density gradient ultracentrifugation in cesium chloride, the predominant monocyte-stimulating activity is identified in LPS-containing fractions. Further, such activity can be readily abrogated by the addition of polymyxin B. These results provide support for the hypothesis that LPS may be responsible for the majority of the proinflammatory activity released from E. coli following bacteriolysis in vitro.

Antigens, Bacterial↗