Lipopolysaccharide binding protein and CD14 interaction induces tumor necrosis factor-alpha generation and neutrophil sequestration in lungs after intratracheal endotoxin

A synthetic lipid A analog, B464, provides significant protection against the cardiopulmonary derangements in porcine Gram-negative sepsis

Many of the cardiopulmonary derangements associated with Gram-negative sepsis result from the activation of monocytes and macrophages by endotoxin with the resultant release of humoral mediators such as TNFα. Lipid A has been shown to retain the majority of endotoxin toxicity, however lipid A from nontoxic organisms has been shown, in vitro, to antagonize the action of other toxic endotoxin species. We examined the effects of a synthetic analog of lipid A (B464), on the evolution of hemodynamic derangements and acute lung injury following experimental Gram-negative sepsis. Anesthetized, ventilated swine were made septic with a 1 h intravenous infusion of live Pseudomonas aeruginosa and studied for 5 h. A treatment group received a bolus of B464 (100 μg/kg) prior to sepsis and a 1 h infusion (100 μg/kg/h) during the P. aeruginosa induction. A control group received simply 0.9% saline. All animals were studied for 5 h. B464 treatment failed to alter septic pulmonary hypertension or the decline in cardiac output. Late recovery from systemic hypotension was associated with reversal of arterial acidosis. Septic neutropenia was unaltered and was associated with increased lung neutrophil (PMN) sequestration measured by lung myeloperoxidase activity. However, decreased bronchoalveolar lavage protein content and improved arterial oxygen tension indicated attenuated acute lung injury in B464 treated animals. These preliminary data indicate that B464 may prove to be an effective tool in the treatment of human sepsis.

Current understanding of sepsis: criticism and a proposal

The failure to improve outcome of septic patients may reflect flawed hypotheses pertaining to the pathogenesis of sepsis. Alternatively, it may represent the use of clinically irrelevant experimental animal models. To address these issues, an alternative hypothesis is proposed. It is suggested that leukocyte activation in sepsis is initiated by a priming effect of minuscule doses of endotoxin on leukocytes for enhanced responsiveness to minute doses of inflammatory mediators (or vice versa) as opposed to activation by overwhelming doses of endotoxin per se. The experimental impetus of this hypothesis has been provided by a novel rat model of sepsis precipitated by the co-administration of PAF and LPS at doses 1/1000 lower than those previously used to elicit sepsis in the same species.

Time-resolved fluoroimmunoassay for bactericidal/permeability-increasing protein

Bactericidal/permeability-increasing protein (BPI) is a cationic antimicrobial protein produced by polymorphonuclear leukocytes, that specifically interacts with and kills Gram-negative bacteria. BPl competes with lipopolysaccharide-binding protein (LBP) secreted by liver cells into blood plasma for binding to lipopolysaccharide (LPS) and thus reduces the proinflammatory effects of LPS. We have developed a time-resolved fluoroimmunoassay for BPI and measured the concentration of BPI in human serum and plasma samples. The assay is based on a rabbit antibody against recombinant BPI. This antibody specifically adheres to polymorphonuclear leukocytes in immunostained human tissues. The difference in the serum concentration of BPI between unselected hospitalized patients with and without an infection was statistically significant. The mean concentration of BPI in serum samples was 28.3 μg/l (range 1.64–132, S.D. 26.8, n = 83). In contrast, there was no difference between the two groups in the BPI levels in plasma samples. For all individuals tested, BPI levels were consistently higher in plasma samples compared to the matched serum samples. The mean concentration of BPI in plasma samples was 52.3 μg/l (range 0.9–403, S.D. 60.6, n = 90). There was a positive correlation between the concentration of BPI and the white blood cell count as well as between the BPI concentration and C-reactive protein (CRP) in serum samples. In conclusion, the present study demonstrates that BPI can be quantified reliably by time-resolved fluoroimmunoassay in human serum samples.

Galectin-9 attenuates acute lung injury by expanding CD14- plasmacytoid dendritic cell-like macrophages

RATIONALE

Galectin (Gal)-9 plays a crucial role in the modulation of innate and adaptive immunity.

OBJECTIVES

To investigate whether Gal-9 plays a role in a murine acute lung injury (ALI) model.

METHODS

C57BL/6 mice were pretreated with Gal-9 by subcutaneous injection 24 and 48 hours before intranasal LPS inoculation.

MEASUREMENTS AND MAIN RESULTS

Gal-9 suppressed pathological changes of ALI induced by LPS. Gal-9 reduced levels of proinflammatory cytokines and chemokines, such as tumor necrosis factor (TNF)-α, IL-1β, IL-6, and keratinocyte-derived cytokine; decreased neutrophils; and increased IL-10 and CD11b(+)Gr-1(+) macrophages in the bronchoalveolar lavage fluid of ALI mice. In Gal-9-deficient mice, pathological changes of ALI were exaggerated, and the number of neutrophils and the TNF-α level were increased. CD11b(+)Gr-1(+) cells were increased in the spleen of both Gal-9-treated and phosphate-buffered saline (PBS)-treated ALI mice, but only Gal-9 increased the ability of CCR2-expressing macrophages to migrate toward monocyte chemoattractant protein-1. Transfer of CD11b(+)Gr-1(+) macrophages obtained from Gal-9-treated mice ameliorated ALI. CD11b(+)Gr-1(+) macrophages obtained from Gal-9-treated but not PBS-treated mice suppressed TNF-α and keratinocyte-derived cytokine production from LPS-stimulated macrophages, and down-regulated Toll-like receptor-4 (TLR4) and TLR2 expression on thioglycollate-elicited macrophages. Fluorescence-activated cell-sorting analysis revealed that CD14 is negligible on CD11b(+)Gr-1(+) macrophages obtained from Gal-9-treated mice, although those from both groups resembled plasmacytoid dendritic cells (pDCs). Gal-9 down-regulated CD14 on pDC-like macrophages from PBS-treated mice independently of Gal-9/Tim-3 (T-cell immunoglobulin- and mucin domain-containing molecule-3) interaction, resulting in the acquisition of suppressive function, suggesting that the loss of CD14 by Gal-9 is critical for the suppression of pDC-like macrophages.

CONCLUSIONS

Gal-9 attenuates ALI by expanding CD14(-)CD11b(+)Gr-1(+) pDC-like macrophages by preferentially suppressing macrophage functions to release proinflammatory cytokines through TLR4 and TLR2 down-regulation.

Role of CD14 in lung inflammation and infection

This article is one of ten reviews selected from the Yearbook of Intensive Care and Emergency Medicine 2010 (Springer Verlag) and co-published as a series in Critical Care. Other articles in the series can be found online at http://ccforum.com/series/yearbook. Further information about the Yearbook of Intensive Care and Emergency Medicine is available from http://www.springer.com/series/2855.

Role of CD14 in Lung Inflammation and Infection

Toll-like receptors (TLR) on the surface of cells of the respiratory tract play an essential role in sensing the presence of microorganisms in the airways and lungs. These receptors trigger inflammatory responses, activate innate immune responses, and prime adaptive immune responses to eradicate invading microbes [1]. TLR are members of a family of pattern-recognition receptors, which recognize molecular structures of bacteria, viruses, fungi and protozoa (pathogen-associated molecular patterns or PAMPs), as well as endogenous structures and proteins released during inflammation (damage/danger-associated molecular patterns or DAMPs). To date, ten different TLR have been identified in humans and twelve in mice. TLR are expressed on all cells of the immune system, but also on parenchymal cells of many organs and tissues. The binding of a PAMP to a TLR results in cellular activation and initiates a variety of effector functions, including cytokine secretion, proliferation’ co-stimulation or phagocyte maturation. To facilitate microbial recognition and to amplify cellular responses, certain TLR require additional proteins, such as lipopolysaccharide (LPS) binding protein (LBP), CD14, CD36 and high mobility group box-l protein (HMGB-l). In this chapter, the role of CD14 as an accessory receptor for TLR in lung inflammation and infection is discussed. The central role of CD14 in the recognition of various PAMPs and amplification of immune and inflammatory responses in the lung is depicted in Fig. 1.

Fig. 1.

Role of CD14 in Lung Inflammation and Infection

Toll-like receptors (TLR) on the surface of cells of the respiratory tract play an essential role in sensing the presence of microorganisms in the airways and lungs. These receptors trigger inflammatory responses, activate innate immune responses, and prime adaptive immune responses to eradicate invading microbes [1]. TLR are members of a family of pattern-recognition receptors, which recognize molecular structures of bacteria, viruses, fungi and protozoa (pathogen-associated molecular patterns or PAMPs), as well as endogenous structures and proteins released during inflammation (damage/danger-associated molecular patterns or DAMPs). To date, ten different TLR have been identified in humans and twelve in mice. TLR are expressed on all cells of the immune system, but also on parenchymal cells of many organs and tissues. The binding of a PAMP to a TLR results in cellular activation and initiates a variety of effector functions, including cytokine secretion, proliferation, co-stimulation or phagocyte maturation. To facilitate microbial recognition and to amplify cellular responses, certain TLR require additional proteins, such as lipopolysaccharide (LPS) binding protein (LBP), CD14, CD36 and high mobility group box-1 protein (HMGB-1). In this chapter, the role of CD14 as an accessory receptor for TLR in lung inflammation and infection is discussed. The central role of CD14 in the recognition of various PAMPs and amplification of immune and inflammatory responses in the lung is depicted in Figure 1. Fig. 1.

Signaling Mechanisms Regulating Endothelial Permeability

The microvascular endothelial cell monolayer localized at the critical interface between the blood and vessel wall has the vital functions of regulating tissue fluid balance and supplying the essential nutrients needed for the survival of the organism. The endothelial cell is an exquisite “sensor” that responds to diverse signals generated in the blood, subendothelium, and interacting cells. The endothelial cell is able to dynamically regulate its paracellular and transcellular pathways for transport of plasma proteins, solutes, and liquid. The semipermeable characteristic of the endothelium (which distinguishes it from the epithelium) is crucial for establishing the transendothelial protein gradient (the colloid osmotic gradient) required for tissue fluid homeostasis. Interendothelial junctions comprise a complex array of proteins in series with the extracellular matrix constituents and serve to limit the transport of albumin and other plasma proteins by the paracellular pathway. This pathway is highly regulated by the activation of specific extrinsic and intrinsic signaling pathways. Recent evidence has also highlighted the importance of the heretofore enigmatic transcellular pathway in mediating albumin transport via transcytosis. Caveolae, the vesicular carriers filled with receptor-bound and unbound free solutes, have been shown to shuttle between the vascular and extravascular spaces depositing their contents outside the cell. This review summarizes and analyzes the recent data from genetic, physiological, cellular, and morphological studies that have addressed the signaling mechanisms involved in the regulation of both the paracellular and transcellular transport pathways.

Porcine reproductive and respiratory syndrome virus infection increases CD14 expression and lipopolysaccharide-binding protein in the lungs of pigs

Porcine reproductive and respiratory syndrome virus (PRRSV) is a respiratory virus of swine that plays an important role in multifactorial respiratory disease. European strains of PRRSV cause mild or no respiratory signs on their own, but can sensitize the lungs for the production of proinflammatory cytokines and respiratory signs upon exposure to bacterial lipopolysaccharides (LPS). The inflammatory effect of LPS depends on the binding to the LPS receptor complex. Therefore, we quantified the levels of CD14 expression and LPS-binding protein (LBP) in the lungs of pigs throughout a PRRSV infection. Twenty-four gnotobiotic pigs were inoculated intranasally with PRRSV (10(6) 50% tissue culture infectious doses per pig, Lelystad strain) or phosphate-buffered saline (PBS), and euthanized 1-52 days later. Lungs were examined for CD14 expression (immunofluorescence and image analysis), LBP (ELISA), and virus replication. PRRSV infection caused a clear increase of CD14 expression from 3 to 40 days post-inoculation (DPI) and LBP from 7 to 14 DPI. Both parameters peaked at 9-10 DPI (40 and 14 times higher than PBS control pigs, respectively) and were correlated tightly with virus replication in the lungs. Double immunofluorescence labelings demonstrated that resident macrophages expressed little CD14 and that the increase of CD14 expression in the PRRSV-infected lungs was probably due to infiltration of highly CD14-positive monocytes in the interstitium. As both CD14 and LBP potentiate the inflammatory effects of LPS, their increase in the lungs could explain why PRRSV sensitizes the lungs for the production of proinflammatory cytokines and respiratory signs upon exposure to LPS.

Distinct roles of pattern recognition receptors CD14 and Toll-like receptor 4 in acute lung injury

Acute lung injury (ALI) induced by lipopolysaccharide (LPS) is a major cause of mortality among humans. ALI is characterized by microvascular protein leakage, neutrophil influx, and expression of proinflammatory mediators, followed by severe lung damage. LPS binding to its receptors is the crucial step in the causation of these multistep events. LPS binding and signaling involves CD14 and Toll-like receptor 4 (TLR4). However, the relative contributions of CD14 and TLR4 in the induction of ALI and their therapeutic potentials are not clear in vivo. Therefore, the aim of the present study was to compare the roles of CD14 and TLR4 in LPS-induced ALI to determine which of these molecules is the more critical target for attenuating ALI in a mouse model. Our results show that CD14 and TLR4 are necessary for low-dose (300-microg/ml) LPS-induced microvascular leakage, NF-kappaB activation, neutrophil influx, cytokine and chemokine (KC, macrophage inflammatory protein 2, tumor necrosis factor alpha, interleukin-6) expression, and subsequent lung damage. On the other hand, when a 10-fold-higher dose of LPS (3 mg/ml) was used, these responses were only partially dependent on CD14 and they were totally dependent on TLR4. The CD14-independent LPS response was dependent on CD11b. A TLR4 blocking antibody abolished microvascular leakage, neutrophil accumulation, cytokine responses, and lung pathology with a low dose of LPS but only attenuated the responses with a high dose of LPS. These data are the first to demonstrate that LPS-induced CD14-dependent and -independent (CD11b-dependent) signaling pathways in the lung are entirely dependent on TLR4 and that blocking TLR4 might be beneficial in lung diseases caused by LPS from gram-negative pathogens.

Cellular antiendotoxin activities of lung surfactant protein C in lipid vesicles

The respiratory system is continuously exposed to airborne particles containing lipopolysaccharide. Our laboratory established previously that the hydrophobic surfactant protein C (SP-C) binds to lipopolysaccharide and to one of its cellular receptors, CD14. Here we examined the influence of SP-C, and of a synthetic analog, on some cellular in vitro effects of lipopolysaccharide. When associated with vesicles of dipalmitoylphosphatidylcholine, SP-C inhibits the binding of a tritium-labeled lipopolysaccharide to the macrophage cell line RAW 264.7. Under similar conditions of presentation, SP-C inhibits the mitogenic effect of lipopolysaccharide on mouse splenocytes, and inhibits the lipopolysaccharide-induced production of tumor necrosis factor-alpha by peritoneal and alveolar macrophages, and of nitric oxide by RAW 264.7 cells. In contrast, tumor necrosis factor-alpha production induced by a lipopeptide, and nitric oxide production induced by picolinic acid, were not affected by SP-C. The lipopolysaccharide-binding capacity of SP-C is resistant to peroxynitrite, a known mediator of acute lung injury formed by reaction of nitric oxide with superoxide anions. These results indicate that SP-C may play a role in lung defense; SP-C resists degradation under inflammatory conditions and traps lipopolysaccharide, preventing it from inducing production of noxious mediators in alveolar cells.

Effect of CD14 blockade on endotoxin-induced acute lung injury in mice

CD14 functions as a cell surface receptor for endotoxin (lipopolysaccharide [LPS]) and is thought to have an essential role in innate immune responses to infection. Previous studies have revealed attenuation of the systemic response after sepsis by blocking CD14. In this study, we tested the hypothesis that CD14 blockade protects against inflammatory responses associated with LPS pneumonia. We examined the effect of an anti-murine CD14 monoclonal antibody (4C1) on the development of acute lung injury induced by intratracheal LPS in mice. We also measured the production of cytokines (tumor necrosis factor-alpha, interleukin-6, and macrophage inflammatory protein-2) and nitric oxide by murine peritoneal macrophages exposed to LPS in vitro. Nuclear factor (NF)-kappa B translocation was evaluated in nuclear extracts from lung homogenates. 4C1 significantly attenuated pulmonary edema and neutrophil emigration after LPS administration. The production of cytokines and nitric oxide by LPS-stimulated macrophages was significantly decreased by 4C1 treatment. NF-kappa B translocation induced by LPS instillation was also suppressed by 4C1. These results suggest that blockade of CD14 might attenuate acute lung injury after intratracheal instillation of LPS through the suppression of NF-kappa B translocation. The inhibitory effect of CD14 blockade on cytokine production and nitric oxide release of macrophages might contribute to the attenuation of lung injury.

Activation of rho is involved in the mechanism of hydrogen-peroxide-induced lung edema in isolated perfused rabbit lung

Acute lung injury is attributed primarily to increased vascular permeability caused by reactive oxygen species derived from neutrophils, such as hydrogen peroxide (H2O2). Increased permeability is accompanied by the contraction and cytoskeleton reorganization of endothelial cells, resulting in intercellular gap formation. The Rho family of Ras-like GTPases is implicated in the regulation of the cytoskeleton and cell contraction. We examined the role of Rho in H2O2-induced pulmonary edema with the use of isolated perfused rabbit lungs. To our knowledge, this is the first study to examine the role of Rho in increased vascular permeability induced by H2O2 in perfused lungs. Vascular permeability was evaluated on the basis of the capillary filtration coefficient (Kfc, ml/min/cm H2O/100 g). We found that H2O2 (300 microM) increased lung weight, Kfc, and pulmonary capillary pressure. These effects of H2O2 were abolished by treatment with Y-27632 (50 microM), an inhibitor of the Rho effector p160 ROCK. In contrast, the muscular relaxant papaverine inhibited the H2O2-induced rise in pulmonary capillary pressure, but did not suppress the increases in lung weight and Kfc. These findings indicate that H2O2 causes pulmonary edema by elevating hydrostatic pressure and increasing vascular permeability. Y-27632 inhibited the formation of pulmonary edema by blocking both of these H2O2-induced effects. Our results suggest that Rho-related pathways have a part in the mechanism of H2O2-induced pulmonary edema.

Protective role of lung surfactant protein D in a murine model of invasive pulmonary aspergillosis

The protective effects of intranasal administration of amphotericin B (AmB), human SP-A, SP-D and a 60-kDa fragment of SP-D (rSP-D) were examined in a murine model of invasive pulmonary aspergillosis (IPA). The untreated group of IPA mice showed no survival at 7 days postinfection. Treatment with AmB, SP-D, and rSP-D increased the survival rate to 80, 60, and 80%, respectively, suggesting that SP-D (and rSP-D) can protect immunosuppressed mice from an otherwise fatal challenge with Aspergillus fumigatus conidia.

Differential anti-inflammatory and anti-oxidative effects of dexamethasone and N-acetylcysteine in endotoxin-induced lung inflammation

Inhalation of bacterial endotoxin induces an acute inflammation in the lower respiratory tract. In this study, the anti-inflammatory effects of the anti-oxidant N-acetylcysteine (NAC) and the glucocorticoid dexamethasone were investigated in mice exposed to aerosolized endotoxin (lipopolysaccharide (LPS)). Powerful reduction of neutrophils in bronchoalveolar lavage fluid (BALF) was obtained by a single i.p. injection of dexamethasone (10 mg/kg), whereas treatment with NAC only resulted in reduction of neutrophils when administered at a high dose (500 mg/kg). Measurement of cytokine and chemokine expression in lung tissue revealed a significant decrease of tumour necrosis factor-alpha, IL-1alpha, IL-1beta IL-6, IL- 12p40, and MIP-1alpha mRNA when mice where treated with dexamethasone but not when treated with NAC. Analysis of oxidative burst demonstrated a remarkable reduction of oxygen radicals in BALF neutrophils after treatment with dexamethasone, whereas the effect of NAC was not significantly different from that in untreated animals. In conclusion, dexamethasone exerted both anti-inflammatory and anti-oxidative effects in acute airway inflammation, probably by blocking early events in the inflammatory cascade. In contrast, treatment with NAC resulted in a weak reduction of the inflammatory response but no inhibition of proinflammatory cytokines or reduction of oxidative burst in neutrophils. These results demonstrate dramatic differences in efficiency and also indicate that the two drugs have different actions. Combined treatment with NAC and dexamethasone revealed an additive action but no synergy was observed.

Endotoxin priming of the cyclooxygenase-2-thromboxane axis in isolated rat lungs

Enhanced prostanoid generation has been implicated in vascular abnormalities occurring during endotoxemia and sepsis, and the lung is particularly prone to such events. Prostanoids are generated from arachidonic acid (AA) via cyclooxygenase (COX)-1 or -2, both isoenzymes recently demonstrated to be expressed in different lung cell types. Upregulation of COX may underlie the phenomenon that endotoxin [lipopolysaccharide (LPS)]-exposed lungs show markedly enhanced vasoconstrictor responses to secondarily applied stimuli (priming). Isolated rat lungs were perfused with a physiological salt buffer solution in the absence and presence of 1.5% rat plasma and exposed to different concentrations of LPS (1,000 or 10,000 ng/ml) during a 2-h priming period. No change in physiological variables was noted during this period, although enhanced baseline liberation of both thromboxane (Tx) A(2) and PGI(2) as well as of tumor necrosis factor (TNF)-alpha was evident compared with that in control lungs in the absence of LPS. LPS priming caused a significant elevation in AA-induced pulmonary arterial pressure, ventilation pressure, and lung weight gain. Concomitant increased levels of TxA(2) were found in the buffer perfusate. All changes were largely suppressed by three selective, structurally unrelated COX-2 inhibitors (NS-398, DUP-697, and SC-236) in both buffer- and buffer-plasma-perfused lungs. Anti-TNF-alpha neutralizing antibodies were ineffective under conditions of buffer perfusion. In the presence of plasma components, manyfold augmented TNF-alpha generation was noted, and anti-TNF-alpha antibodies significantly suppressed the increase in ventilation pressure but not in the vascular pressor response and lung edema formation. We conclude that the propensity of LPS-primed lungs to respond with enhanced vasoconstriction, edema formation, and bronchoconstriction to a secondarily applied stimulus proceeds nearly exclusively via COX-2 and increased Tx formation, with TNF-alpha generation being involved in the change in bronchomotor reactivity in the presence of plasma constituents. In context with recent immunohistological investigations, LPS-induced upregulation of the COX-2-thromboxane synthase axis in vascular and bronchial smooth muscle cells is suggested to underlie these events.

Surfactant-associated protein A inhibits LPS-induced cytokine and nitric oxide production in vivo

The role of surfactant-associated protein (SP) A in the mediation of pulmonary responses to bacterial lipopolysaccharide (LPS) was assessed in vivo with SP-A gene-targeted [SP-deficient; SP-A(-/-)] and wild-type [SP-A(+/+)] mice. Concentrations of tumor necrosis factor (TNF)-alpha, macrophage inflammatory protein-2, and nitric oxide were determined in recovered bronchoalveolar lavage fluid after intratracheal administration of LPS. SP-A(-/-) mice produced significantly more TNF-alpha and nitric oxide than SP-A(+/+) mice after LPS treatment. Intratracheal administration of human SP-A (1 mg/kg) to SP-A(-/-) mice restored regulation of TNF-alpha, macrophage inflammatory protein-2, and nitric oxide production to that of SP-A(+/+) mice. Other markers of lung injury including bronchoalveolar fluid protein, phospholipid content, and neutrophil numbers were not influenced by SP-A. Data from experiments designed to test possible mechanisms of SP-A-mediated suppression suggest that neither binding of LPS by SP-A nor enhanced LPS clearance are the primary means of inhibition. Our data and others suggest that SP-A acts directly on immune cells to suppress LPS-induced inflammation. These results demonstrate that endogenous or exogenous SP-A inhibits pulmonary LPS-induced cytokine and nitric oxide production in vivo.

Effect of interleukin-10 (IL-10) on experimental LPS-induced acute lung injury

The purpose of this study was to clarify the role of interleukin-10 (IL-10) during the development of acute lung injury induced by lipopolysaccharide (LPS) in a mouse model. When LPS was given to nude mice, the mortality rate was 100% at 48 h of the observation period. However, mortality was reduced to 30% when IL-10 was added concomitantly (P < 0.01). In the IL-10 group, a significant reduction of inflammatory change in lung tissue was observed. It was also found that peripheral neutrophils increased when IL-10 was added. When LPS and IL-10 were given concomitantly, the level of tumor necrosis factor (TNF)-alpha in both serum and bronchoalveolar lavage fluid (BALF) decreased significantly (P < 0.05). In-vitro observations were made concerning the influence of human neutrophils. Both neutrophil superoxide (O2-) and elastase production were increased by TNF-alpha stimulation, while significant inhibition was seen with the concomitant dosing of IL-10 (P < 0.05). TNF-alpha stimulation increased the occurrence of adhesion molecules for neutrophil surface, lymphocyte function-associated antigen-1 (LFA-1), and macrophage antigen-1 (Mac-1). LPS stimulation greatly increased the occurrence of neutrophil surface 55-kDa TNF-receptor [TNF-R (p55)], when observation was made under laser microscopy. However, no significant occurrence was seen with IL-10 concomitant dosing. The above results suggested that IL-10 inhibited TNF-alpha production and neutrophil activity in LPS-induced acute lung injury, which led to a reduction of the lung tissue injury.

The Role of Leukocyte Emigration and IL-8 on the Development of Lipopolysaccharide-Induced Lung Injury in Rabbits

Leukocyte emigration and alveolar macrophage-derived cytokines may contribute to lung microvascular injury associated with adult respiratory distress syndrome. We have used mAbs against cell adhesion molecules on leukocytes (anti-CD18 and anti-CD49d) or against IL-8 to investigate these contributions. Intratracheal (i.t.) instillation of LPS (50 μg/kg) caused a significant increase in bronchoalveolar lavage polymorphonuclear leukocytes (PMNs) without an increase in mononuclear cells (MNCs) or an increase in lung permeability. Injection of LPS (10 μ/kg) i.v. at 24 h after i.t. LPS caused significant increases in bronchoalveolar lavage PMNs, MNCs, IL-8, and monocyte chemotactic protein-1, as well as increases in lung permeability. Rabbits that were administered i.t. LPS followed by i.v. LPS and treated with anti-CD18 mAb had a significantly lower lung permeability index and emigration of fewer PMNs but no change in MNC emigration compared with saline treatment. Anti-IL-8 mAb treatment resulted in a significantly lower lung permeability index with no change in PMN emigration compared with no treatment. These results suggest that PMN emigration is necessary but not sufficient for the development of LPS-induced lung injury, and that IL-8 plays a significant role in PMN-dependent lung injury, independent of PMN emigration.

Prophylaxis against lipopolysaccharide-induced acute lung injury by alpha-tocopherol liposomes

OBJECTIVE

To investigate whether intravenously administered liposomal alpha-tocopherol can protect the lung from the injurious action of Escherichia coli lipopolysaccharide (LPS).

DESIGN

Prospective, randomized animal study.

SETTING

Government research laboratory.

SUBJECTS

Twenty adult male Sprague-Dawley rats.

INTERVENTIONS

Animals were intravenously pretreated with alpha-tocopherol liposomes (20 mg alpha-tocopherol/kg body weight), plain liposomes, or saline. Twenty-four hours later, pretreated animals were challenged with an intravenous injection of LPS (E. coli 0111:B4, 1 mg/kg body weight), and killed 2 hrs after LPS challenge.

MEASUREMENTS AND MAIN RESULTS

Challenge of saline-pretreated animals with LPS resulted in lung injuries as evidenced by an increase in wet lung weight and a reduction in pulmonary angiotensin converting enzyme (25%) and alkaline phosphatase (28%), injury markers of lung endothelial and epithelial type II cells, respectively. Also, LPS administration resulted in an increase in pulmonary myeloperoxidase and protease activities, indicative of a neutrophilic inflammatory response. Pretreatment of animals with liposomal alpha-tocopherol significantly attenuated the LPS-induced edematous lung weight response, and reduced the extent of injuries to the pulmonary endothelial and epithelial cells, demonstrated by a significantly smaller reduction in the corresponding enzyme marker activities.

CONCLUSION

These results suggest that augmentation of the pulmonary antioxidant status can ameliorate LPS-induced lung injuries mediated by oxidative stress mechanisms.

Plasma potentiates the priming effects of endotoxin on platelet activating factor-induced pulmonary hypertension in the rabbit lung

During Gram-negative sepsis, endotoxin lipopolysaccharide (LPS) may activate host inflammatory responses, resulting in the systemic inflammatory response syndrome and the adult respiratory distress syndrome. In cell culture systems, LPS activation of cellular responses may be potentiated by plasma proteins. In the isolated perfused rabbit lung, LPS administration markedly increases the pulmonary hypertensive response to subsequent administration of platelet activating factor (PAF). We examined whether plasma would potentiate the priming effects of LPS in this model. Male New Zealand White rabbits were used in a standard, isolated buffer-perfused rabbit lung preparation, and the pulmonary hypertensive response to 5 nM PAF was measured after 2 h of perfusion with different LPS doses (0, 1, and 10 ng/mL), with and without plasma (10% by volume). In the absence of plasma, 10 ng/mL LPS, but not 1 ng/mL LPS, increased the pulmonary hypertensive response to subsequent administration of 5 nM PAF. However, in the presence of plasma, 1 ng/mL LPS significantly increased the hypertensive response to subsequent administration of 5 nM PAF. We conclude that components of plasma--possibly LPS binding protein and soluble CD14--potentiate the priming effect of endotoxin, resulting in an augmented pulmonary hypertensive response to PAF. Thus, plasma proteins decrease the threshold at which endotoxin primes the lung and may have a critical role in the pathogenesis of endotoxin-induced acute lung injury.

Soluble CD14 in serum mediates LPS-induced increase in permeability of bovine pulmonary arterial endothelial cell monolayers in vitro

Lipopolysaccharide (LPS) is a mediator of septic shock and acute respiratory distress syndrome (ARDS), conditions which are characterized by high-permeability pulmonary edema. LPS increases endothelial permeability both directly and indirectly via the pro-inflammatory cytokines produced by monocytes and macrophages. We investigated the role of soluble CD14 in serum in the increased endothelial permeability induced by LPS. Bovine pulmonary artery endothelial cells were grown to confluence on a microporous filter and the 125I-albumin clearance rate across the monolayer was determined. Even a high concentration of LPS (1 microgram/ml) did not increase endothelial permeability under a serum-free condition. In the presence of more than 3% normal human serum, LPS increased endothelial permeability. The presence of neutralizing anti-CD14 monoclonal antibody eliminated the serum-dependent effect of LPS. The addition of recombinant sCD14 completely replaced the requirement for serum. LPS-binding protein (LBP) did not enhance the rsCD14-mediated LPS effect, and anti-LBP antibody did not attenuate the serum-dependent LPS effect. These findings suggest that sCD14 in serum mediates the permeability-increasing effect on LPS on endothelial cells but that LBP is not necessary for this effect.