Role of alveolar macrophages in endotoxin-induced neutrophilic alveolitis in rats

Although bacterial endotoxins have potent effects on blood monocytes and tissue macrophages, the role of alveolar macrophages in regulating intrapulmonary neutrophil traffic following endotoxemia has not been studied previously. We have previously reported that a single intraperitoneal injection of endotoxin from Escherichia coli serotype 055B5 causes acute lung inflammation by neutrophils (PMN) in rats. The factors which influence the migration of PMN in the lung in this model are unknown. To determine whether macrophage-derived products could play a role in directing migration, we enumerated neutrophils in histologic sections and employed electron microscopy to document the location of neutrophils in the lung in vivo following endotoxin. We also cultured the alveolar macrophages recovered by lung lavage to measure the effect of their culture supernatants on neutrophil migration in vitro. In the first 6 hr following endotoxin, and also 24 hr later, there was an increase in the number of PMN enumerated in the lung parenchyma by light microscopy. Electron microscopy showed the location of the neutrophils to be exclusively intravascular at 6 hr. By contrast, neutrophils were observed in both interstitial and bronchoalveolar spaces at 24 hr, confirming that transvascular migration was active at that time. The pulmonary macrophages which were recovered by lung lavage from groups of rats sacrificed at 4 and at 15 hr following the administration of endotoxin were assayed for the release into culture media of migration-stimulatory activity for neutrophils. Macrophages from animals sacrificed 4 hr following endotoxin released less migration-stimulating activity into media than macrophages from controls. These macrophages could be stimulated to release migration-stimulating activity into culture media at levels comparable to macrophages from controls by the addition of opsonized Zymosan to the culture media. By contrast, macrophages from animals sacrificed 15 hr after endotoxin spontaneously released more migration-stimulating activity for neutrophils than did macrophages from controls. Thus, in this model, a specific increase in the synthesis or release by alveolar macrophages of factors which stimulate the migration of neutrophils in vitro coincided with a transition from intravascular to extravascular alveolar inflammation by neutrophils in vivo. These observations are consistent with the hypothesis that pulmonary alveolar macrophages may contribute to the regulation of alveolar inflammation following endotoxemia by releasing factors which influence the migration of neutrophils.     

Host defense deficiency in newborn nonhuman primate lungs

We have investigated two major aspects of the pulmonary host defense mechanism--alveolar macrophage function as a "first line of bacterial defense" and induced neutrophil migration into the lung as a "back-up defense." Chemotactic and phagocytic/killing assays revealed a functional deficiency in the alveolar macrophages of newborn primates. Serial bronchoalveolar lavage investigations revealed diminished neutrophil migration into the newborn primate lung. The overall pulmonary host defense capability in newborn primates was deficient. The results of this investigation may have direct clinical relevance to the susceptibility of newborns to infections and pneumonia.     

糖皮质激素对肺泡巨噬细胞趋化活性的影响

采用测定肺泡巨噬细胞(AM)趋化性和AM产生中性粒细胞趋化因子的实验技术。观察到糖皮质激素体外直接作用于大鼠AM悬液或大鼠皮下注射7d都可抑制AM的趋化性,并且肺灌洗液中的AM数量明显减少;但注射3d组无上述效应。以糖皮质激素处理AM 16h可使AM产生的中性粒细胞趋化因子强度明显降低。结果表明糖皮质激素可抑制AM的趋化性和抑制AM产生中性粒细胞趋化因子。提示这可能是较长期应用糖皮质激素抑制免疫和炎症反应、降低肺部防御能力的部分机理。     

Glycolipid accumulation in bronchoalveolar space in adult respiratory distress syndrome

Surfactant lipids in the alveolar space are believed to play an important role in normal respiratory function. Although the surface-active phospholipids have been extensively studied, the possible role of glycolipids in the surfactant remains to be explored. We have studied the glycolipid composition of cell-free bronchoalveolar lavage from healthy subjects and from adult patients with respiratory distress syndrome. Glycolipids were barely detectable in bronchoalveolar lavage from healthy subjects. However, in adult respiratory distress syndrome, the amount of glycolipid relative to phospholipid was increased by more than twenty times. These lipids, identified as lactosylceramide (galactose-glucose-ceramide) and paragloboside (galactose-N-acetylglucosamine-galactose-glucose-ceramide), may prove to be sensitive markers of lung injury. Since the glycolipids decreased the surface activity of surfactant in vitro, their potential role in the pathogenesis of adult respiratory distress syndrome should be considered.     

The role of the neutrophil in inflammatory diseases of the lung

Under certain circumstances, the neutrophil has been implicated in causing disease by damaging normal host tissue. This may occur in the adult respiratory distress syndrome (ARDS). The neutrophil has been implicated since a) substances that activate neutrophils are produced in association with the predisposing risks that lead to ARDS; b) activated neutrophils migrate into the alveolar spaces and their toxic products can be found in lung lavage fluid and in the breath of patients with ARDS; and c) the magnitude of the physiologic alterations correlate with the number of neutrophils in the alveolar space. Additionally, the neutrophils may be primed by substances which are released by activated platelets within the confines of the lung. Both platelet adenine nucleotides and the platelet-derived extracellular matrix protein (ECM), thrombospondin, can prime the neutrophil for subsequent O2- generation following activation of the cells with the chemotactic peptide, F-met-leu-phe (FMLP). Furthermore, neutrophils can be primed or O2- generation by the basement membrane ECM protein, laminin. Since neutrophils express receptors for both laminin and thrombospondin, these constituents may serve to modulate neutrophil behavior for subsequent oxidative metabolism and contribute to exacerbating pulmonary disease.     

Role of complement in endotoxin/platelet-activating factor-induced lung injury.

C receptor-1 is a protein involved in the regulation of C3 and C5-convertases. Recombinant human soluble C receptor-1 has recently been produced and shown to reduce infarct size in a rat model of myocardial ischemia/reperfusion injury. The present study aimed to investigate whether recombinant human soluble C receptor-1 exerts any protective effect on pulmonary injury produced in a rodent model of adult respiratory distress syndrome. In this model, Escherichia coli endotoxin (LPS, 0.1 microgram/kg) combined with platelet-activating factor (1 pmol/kg/min over 60 min, n = 10) caused microvascular lung injury characterized by elevation of myeloperoxidase activity, deposition of C3 and C5b-9 on the endothelium of pulmonary vessels, and pulmonary edema. Furthermore, bronchoalveolar lavage revealed increased neutrophil count and elevated protein concentration. These pulmonary responses were associated with elevated serum TNF-alpha. Pretreatment (10 min, i.v.) with recombinant human soluble C receptor-1 at 10 mg/kg (n = 13), but not at 1 mg/kg, prevented the LPS/platelet-activating factor-induced pulmonary edema (p less than 0.01) and changes in the bronchoalveolar lavage fluid cell count (p less than 0.01) and protein concentration (p less than 0.05), and attenuated the deposition of C3 and C5b-9 to lung vessels. There was no effect on lung myeloperoxidase activity and serum TNF-alpha. Also, C depletion by cobra venom factor (500 U/kg, i.v.) eliminated the pulmonary edema and elevated leukocyte count in bronchoalveolar lavage fluid, but had no effect on lung myeloperoxidase activity and serum TNF-alpha. These data suggest that C factors may play an important role in the pathophysiology of adult respiratory distress syndrome.     

Endogenous Tumor Necrosis Factor (TNF) α Mediates Neutrophil Accumulation at the Mid-Phase of a Murine Model of Pseudomonas aeruginosa Pneumonia

To determine the role of endogenous tumor necrosis factor (TNF) α on neutrophil influx into the lungs in acute Pseudomonas aeruginosa pneumonia, we evaluated TNF α activity, inflammatory cell response and neutrophil chemotactic activity in the bronchoalveolar lavage fluids (BALFs) of P. aeruginosa-infected mice. In the case of fatal pneumonia, the TNF α activity in the BALFs appeared within 3 hr, peaked at 6–12 hr and attenuated within 24 hr after intratracheal challenging, while no TNF α activity was detected in the plasma. The elevation of TNF α activity in the BALFs was closely associated with neutrophil accumulation. Mirroring the TNF α activity response and the influx of neutrophils into the murine airway, the number of neutrophils in the BALFs increased within 3 hr, peaked at 6–12 hr and remained elevated up to 24 hr after challenging. Neutralization of the TNF α activity in the BALFs with anti-murine TNF antiserum decreased the level of neutrophil migration by BALF 45.0–49.7% at 6 hr and 49.3–54.2% at 12 hr, while the neutralizing antiserum had no effect on the level of neutrophil migration by BALFs at 3 and 24 hr. Furthermore, the intravenous administration of anti-murine TNF antiserum 2 hr before challenging significantly inhibited neutrophil migration into the lungs of mice with sublethal pneumonia (P < 0.05; compared with mice receiving pre-immune serum). These data suggest that intra-alveolar TNF α plays an important role in causing lung neutrophil accumulation at the mid-phase of murine P. aeruginosa pneumonia.     

Pulmonary granulocyte influx and impaired alveolar macrophage adenylyl cyclase responsiveness in developing respiratory distress

Alveolar macrophages have recently been postulated as being involved in the aetiology of adult respiratory distress syndrome (ARDS). To evaluate their role, basal cyclic AMP levels and responsiveness of adenylyl cyclase alveolar macrophages were determined at four intermediate stages of developing respiratory distress in piglets using a protocol with repeated lung lavage. Examination of alveolar cells recovered from the subsequent lavages reveals an influx of granulocytes (neutrophils and eosinophils) within 1 h of two intensive lung lavages. During the developing respiratory distress the basal cyclic AMPlevel of alveolar macrophages increases and adenylyl cyclase responsiveness to prostaglandin E(2) (PGE(2)) and isoprelanaline diminishes. The previously observed impairment of macrophage activity can then be explained at a subcellular level.     

Contribution of neutrophil-derived myeloperoxidase in the early phase of fulminant acute respiratory distress syndrome induced by influenza virus infection

Because the pathogenesis of acute respiratory distress syndrome (ARDS) induced by influenza virus infection remains unknown, we can only improve on existing therapeutic interventions. To approach the subject, we investigated immunological etiology focused on cytokines and an acute lung damage factor in influenza-induced ARDS by using a PR-8 (A/H1N1)-infected mouse model. The infected mouse showed fulminant severe pneumonia with leukocyte infiltration, claudin alteration on tight junctions, and formation of hyaline membranes. In addition to interferon (IFN)-α, plenty of keratinocyte-derived chemokines (KC), macrophage inflammatory protein 2 (MIP-2), regulated on activation normal T-cell expressed and secreted (RANTES), and monocyte chemotactic protein 1 (MCP-1) were significantly released into bronchoalveolar lavage fluid (BALF) of the model. We focused on neutrophil myeloperoxidase (MPO) as a potent tissue damage factor and examined its contribution in influenza pneumonia by using mice genetically lacking in MPO. The absence of MPO reduced inflammatory damage with suppression of leakage of total BALF proteins associated with alteration of claudins in the lung. MPO(-/-) mice also suppressed viral load in the lung. The present study suggests that MPO-mediated OCl(-) generation affects claudin molecules and leads to protein leakage and viral spread as a damage factor in influenza-induced ARDS.     

Interleukin 8 (IL-8) in the bronchoalveolar lavage fluid from patients with the adult respiratory distress syndrome (ARDS) and patients at risk for ARDS.

A sensitive and specific radioimmunoassay was used to measure interleukin 8 (IL-8) in bronchoalveolar lavage fluids from control subjects, patients with the adult respiratory distress syndrome (ARDS) and patients undergoing coronary bypass surgery, a risk factor for developing ARDS. Concentrations of IL-8, albumin, total protein and numbers of neutrophils were higher in both patient groups than in controls. Levels of IL-8 were significantly correlated with the influx of neutrophils, plasma protein extravasation and with the PaO2/FiO2 ratio. These data suggest that IL-8 may mediate the recruitment of neutrophils from the vascular compartment into the alveolar space and may therefore be an important determinant in neutrophil-mediated lung injury. Since increased levels of IL-8 were also found in BAL fluid from patients at risk in whom ARDS did not develop, other factors are likely to be involved and IL-8, as well as other markers of inflammation, are of little prognostic use.     

E. coli pneumonia induces CD18-independent airway neutrophil migration in the absence of increased lung vascular permeability

We examined the relationship between neutrophil [polymorphonuclear leukocyte (PMN)] influx and lung vascular injury in response to Escherichia coli pneumonia. We assessed lung tissue PMN uptake by measuring myeloperoxidase and transvascular PMN migration by determining PMN counts in lung interstitium and bronchoalveolar lavage fluid (BALF) in mice challenged intratracheally with E. coli. Lung vascular injury was quantified by determining microvessel filtration coefficient (Kf,c), a measure of vascular permeability. We addressed the role of CD18 integrin in the mechanism of PMN migration and lung vascular injury by inducing the expression of neutrophil inhibitory factor, a CD11/CD18 antagonist. In control animals, we observed a time-dependent sixfold increase in PMN uptake, a fivefold increase in airway PMN migration, and a 20-fold increase in interstitial PMN uptake at 6 h after challenge. Interestingly, Kf,c increased minimally during this period of PMN extravasation. CD11/CD18 blockade reduced lung tissue PMN uptake consistent with the role of CD18 in mediating PMN adhesion to the endothelium but failed to alter PMN migration in the tissue. Moreover, CD11/CD18 blockade did not affect Kf,c. Analysis of BALF leukocytes demonstrated diminished oxidative burst compared with leukocytes from bacteremic mice, suggesting a basis for lack of vascular injury. The massive CD11/CD18-independent airway PMN influx occurring in the absence of lung vascular injury is indicative of an efficient host-defense response elicited by E. coli pneumonia.     

Identification of two neutrophil chemotactic peptides produced by porcine alveolar macrophages.

We have purified to homogeneity two distinct 10-kDa proteins with potent chemotactic activity for neutrophils from porcine alveolar macrophages incubated for 24 h with Escherichia coli endotoxin (lipopolysaccharide (LPS), 10 micrograms/ml). Neutrophil chemotactic activity in alveolar macrophage supernatants was concentrated by adsorption to SP-Sephadex, and purified by cation exchange and reversed phase high performance liquid chromatography. The first peptide, alveolar macrophage chemotactic factor (AMCF)-I, had chemotactic activity for both porcine and human neutrophils. The chemotactic activity for porcine neutrophils was detectable at 3 x 10(-10) M, peaked at 3 x 10(-8) M, and was comparable to that of zymosan-activated porcine serum. Segmental instillation of AMCF-I into porcine lungs caused marked neutrophil accumulation at 4 h in both bronchoalveolar lavage fluid and in lung tissue. The second peptide, AMCF-II, was active at 1.4 x 10(-9) M for porcine neutrophils, but it was less active for human polymorphonuclear neutrophils than was AMCF-I. Oligonucleotide probes to regions of the N-terminal sequences of AMCF-I and AMCF-II hybridized to mRNA recovered from LPS-stimulated alveolar macrophages. The N-terminal sequences and amino acid compositions indicate that AMCF-I and AMCF-II are distinct proteins, but that both have homologies with a family of peptide chemoattractants produced by human blood monocytes and platelets. Thus, alveolar macrophages stimulated with LPS produce two distinct 10-kDa cytokines with potent chemotactic activity for neutrophils. This indicates that there are two different peptide pathways by which alveolar macrophages can recruit neutrophils into the lung.     

Induction of acute respiratory distress syndrome in rats by lipopolysaccharide and its effect on oxidative stress and antioxidant status in lung

Acute lung injury (ALI) or its severe form, acute respiratory distress syndrome (ARDS) is an important cause of mortality in the human population. Despite significant advances made, the mortality associated with ALI remains unchanged. The objective of the present study was to evaluate the role of oxidative stress, alveolar antioxidant status and multiple organ injury in ARDS induced by lipopolysaccharide (LPS) in rats. Rats were divided into 4 groups, group I control rats were given saline intraperitoneally, whereas groups II, III and IV (LPS-treated) rats received an intraperitoneal injection of LPS (10 mg/kg body weight) and sacrificed after various time intervals. In LPS-treated rats, we observed increased levels of oxidative products, decreased levels of antioxidants in lung tissues and increased levels of serum marker enzymes, suggesting multiple organ injury. Bronchoalveolar lavage fluid (BALF) neutrophil content and protein concentration in LPS-treated rats were significantly elevated in a time-dependent manner. Histological studies revealed neutrophil influx and diffused alveolar damage in LPS-administered rats. These results clearly suggested that increased oxidant levels led to oxidative stress, antioxidant deficiency attenuating lung inflammation and tissue damage. LPS administration resulted in multiple organ failure, leading to increased mortality.     

Soluble Vascular Cell Adhesion Molecule-1 (sVCAM-1) Is Elevated in Bronchoalveolar Lavage Fluid of Patients with Acute Respiratory Distress Syndrome

Introduction

Pulmonary vascular endothelial activation has been implicated in acute respiratory distress syndrome (ARDS), yet little is known about the presence and role of endothelial activation markers in the alveolar space in ARDS. We hypothesized that endothelial activation biomarkers would be differentially expressed in bronchoalveolar lavage fluid from patients with ARDS compared with healthy volunteers, and that biomarker concentrations would be associated with ARDS severity.

Methods

We performed a cross-sectional analysis of data from 26 intubated patients with ARDS undergoing evaluation for clinically suspected ventilator-associated pneumonia and five healthy volunteers. Patients underwent bronchoalveolar lavage a median of five days after intubation. Healthy volunteers also underwent bronchoalveolar lavage. Endothelial activation biomarkers (soluble vascular cell adhesion molecule-1 [sVCAM-1], soluble endothelial selectin [sESEL], angiopoietin-1 [Ang-1] and angiopoietin-2 [Ang-2]) were measured in bronchoalveolar lavage fluid. Clinically suspected ventilator-associated pneumonia was confirmed with microbiologic culture data.

Results

Patients with ARDS had significantly higher median sVCAM-1 concentrations in the bronchoalveolar lavage fluid compared with healthy volunteers (985 vs 119 pg/mL, p = 0.03). Additionally, there was a trend toward greater bronchoalveolar lavage fluid sVCAM-1 concentrations among patients with moderate/severe compared to mild ARDS (1395 vs 209 pg/mL, p = 0.06). We did not detect significant differences in bronchoalveolar lavage fluid levels of sESEL, Ang-1 or Ang-2 between patients with ARDS and healthy volunteers. Median bronchoalveolar lavage fluid biomarker levels did not differ between patients with and without microbiologically-confirmed ventilator-associated pneumonia.

Conclusions

sVCAM-1 concentrations were significantly higher in the bronchoalveolar lavage fluid of patients with ARDS compared to healthy controls, and tended to be higher in moderate/severe ARDS compared to mild ARDS. Our findings add to the growing evidence supporting the concept that endothelial activation plays an important mechanistic role in the pathogenesis of ARDS. Further studies are necessary to characterize the role and/or clinical significance of sVCAM-1 and other endothelial activation markers present in the alveolar space in ARDS.     

Reduction of neutrophil influx diminishes lung injury and mortality following phosgene inhalation.

Phosgene inhalation causes a severe noncardiogenic pulmonary edema characterized by an influx of neutrophils into the lung. To study the role of neutrophils in lung injury and mortality after phosgene, we investigated the effects of leukocyte depletion with cyclophosphamide, inhibiting the generation of the chemotaxin leukotriene B4 with the 5-lipoxygenase inhibitor AA861 and impairing neutrophil migration with the microtubular poison colchicine. Cyclophosphamide, AA861, and colchicine injected before exposure significantly reduced percent neutrophils, protein, and thiobarbituric acid-reactive products in bronchoalveolar lavage fluid of rats exposed to phosgene (0.5 ppm X 60 min). Cyclophosphamide, AA861, and colchicine also significantly decreased mortality from phosgene (2.0 ppm X 90 min) in mice. Colchicine significantly reduced neutrophil influx, lung injury, and mortality even when given 30 min after phosgene exposure. We conclude that lung injury and mortality after phosgene exposure are associated with an influx of neutrophils into the lung. Prevention of neutrophil migration with colchicine may hold therapeutic potential in phosgene poisoning.     

MCTR1 enhances the resolution of lipopolysaccharide‐induced lung injury through STAT6‐mediated resident M2 alveolar macrophage polarization in mice

Acute respiratory distress syndrome (ARDS) is a fatal disease characterized by excessive infiltration of inflammatory cells. MCTR1 is an endogenously pro‐resolution lipid mediator. We tested the hypothesis that MCTR1 accelerates inflammation resolution through resident M2 alveolar macrophage polarization. The mice received MCTR1 via intraperitoneal administration 3 days after LPS stimulation, and then, the bronchoalveolar lavage (BAL) fluid was collected 24 hours later to measure the neutrophil numbers. Flow cytometry was used to sort the resident and recruited macrophages. Post‐treatment with MCTR1 offered dramatic benefits in the resolution phase of LPS‐induced lung injury, including decreased neutrophil numbers, reduced BAL fluid protein and albumin concentrations and reduced histological injury. In addition, the expression of the M2 markers Arg1, FIZZ1, Remlα, CD206 and Dectin‐1 was increased on resident macrophages in the LPS + MCTR1 group. Resident macrophage depletion abrogated the therapeutic effects of MCTR1, and reinjection of the sorted resident macrophages into the lung decreased neutrophil numbers. Finally, treatment with MCTR1 increased STAT6 phosphorylation. The STAT6 inhibitor AS1517499 abolished the beneficial effects of MCTR1. In conclusion, MCTR1 promotes resident M2 alveolar macrophage polarization via the STAT6 pathway to accelerate resolution of LPS‐induced lung injury.     

Keratinocyte growth factor protects against Pseudomonas aeruginosa-induced lung injury

We have previously reported that keratinocyte growth factor (KGF) attenuates alpha-naphthylthiourea-induced lung injury by upregulating alveolar fluid transport. The objective of this study was to determine the effect of KGF pretreatment in Pseudomonas aeruginosa pneumonia. A 5% bovine albumin solution with 1 microCi of (125)I-labeled human albumin was instilled into the air spaces 4 or 24 h after intratracheal instillation of P. aeruginosa, and the concentration of unlabeled and labeled proteins in the distal air spaces over 1 h was used as an index of net alveolar fluid clearance. Alveolocapillary barrier permeability was evaluated with an intravascular injection of 1 microCi of (131)I-albumin. In early pneumonia, KGF increased lung liquid clearance (LLC) compared with that in nonpretreated animals. In late pneumonia, LLC was significantly reduced in the absence of KGF but increased above the control value with KGF. KGF pretreatment increased the number of polymorphonuclear cells recovered in the bronchoalveolar lavage fluid and decreased bacterial pulmonary translocation. In conclusion, KGF restores normal alveolar epithelial fluid transport during the acute phase of P. aeruginosa pneumonia and LLC in early and late pneumonia. Host response is also improved as shown by the increase in the alveolar cellular response and the decrease in pulmonary translocation of bacteria.     

Cell population obtained by bronchoalveolar lavage in Pneumocystis carinii pneumonitis

In the course of bronchoalveolar lavages performed in 115 immunocompromised patients in order to investigate the occurrences of pneumonitis, Pneumocystis carinii pneumonia was diagnosed by demonstration of cysts in bronchoalveolar lavage specimens from 11 patients. The cellular phenomena associated with P. carinii infection at the level of the alveolar space were evaluated. Differential cell counts on bronchoalveolar lavage preparations stained by the May-Grünwald-Giemsa method were performed in immunocompromised patients and in ten nonimmunocompromised patients without any respiratory disease. A decrease in the alveolar macrophage count associated with an increase in the polymorphonuclear neutrophil count and the presence of plasma cells and/or immunoblasts was highly suggestive of P. carinii pneumonia. These cellular changes in bronchoalveolar lavage specimens are discussed in relation to the pathologic features usually described in P. carinii pneumonia.     

Matrilysin shedding of syndecan-1 regulates chemokine mobilization and transepithelial efflux of neutrophils in acute lung injury

The influx of inflammatory cells to sites of injury is largely directed by signals from the epithelium, but how these cells form chemotactic gradients is not known. In matrilysin null mice, neutrophils remained confined in the interstitium of injured lungs and did not advance into the alveolar space. Impaired transepithelial migration was accompanied by a lack of both shed syndecan-1, a heparan sulfate proteoglycan, and KC, a CXC chemokine, in the alveolar fluid. KC was bound to shed syndecan-1, and it was not detected in the lavage of syndecan-1 null mice. In vitro, matrilysin cleaved syndecan-1 from the surface of cells. Thus, matrilysin-mediated shedding of syndecan-1/KC complexes from the mucosal surface directs and confines neutrophil influx to sites of injury.     

Salmeterol, a beta2-receptor agonist, attenuates lipopolysaccharide-induced lung inflammation in mice

Lipopolysaccharide is ubiquitously present in the environment. To determine the effect of salmeterol, a long-acting beta(2)-receptor agonist, on lipopolysaccharide-induced lung inflammation, mice received lipopolysaccharide (10 microg) intranasally with or without salmeterol intraperitoneally (5 mg/kg) 30 min earlier and 12 h thereafter. Salmeterol dose- and time-dependently inhibited the lipopolysaccharide-induced influx of neutrophils into bronchoalveolar lavage fluid and lung tissue, and these pulmonary neutrophils displayed a reduced expression of CD11b at their surface. To determine the contribution of the salmeterol effect on neutrophil CD11b in the attenuated neutrophil recruitment, we treated mice intranasally exposed to lipopolysaccharide with salmeterol with or without a blocking anti-CD11b antibody. Anti-CD11b profoundly reduced lipopolysaccharide-induced neutrophil influx in bronchoalveolar lavage fluid, an effect that was modestly enhanced by concurrent salmeterol treatment. These data suggest that salmeterol inhibits lipopolysaccharide-induced neutrophil recruitment to the lungs by a mechanism that possibly in part is mediated by an effect on neutrophil CD11b.