Role of CD11b in focal acid-induced pneumonia and contralateral lung injury in rats

Role of Positive End-Expiratory Pressure and Regional Transpulmonary Pressure in Asymmetrical Lung Injury

Rationale: Asymmetrical lung injury is a frequent clinical presentation. Regional distribution of Vt and positive end-expiratory pressure (PEEP) could result in hyperinflation of the less-injured lung. The validity of esophageal pressure (Pes) is unknown.Objectives: To compare, in asymmetrical lung injury, Pes with directly measured pleural pressures (Ppl) of both sides and investigate how PEEP impacts ventilation distribution and the regional driving transpulmonary pressure (inspiratory - expiratory).Methods: Fourteen mechanically ventilated pigs with lung injury were studied. One lung was blocked while the contralateral one underwent surfactant lavage and injurious ventilation. Airway pressure and Pes were measured, as was Ppl in the dorsal and ventral pleural space adjacent to each lung. Distribution of ventilation was assessed by electrical impedance tomography. PEEP was studied through decremental steps.Measurements and Results: Ventral and dorsal Ppl were similar between the injured and the noninjured lung across all PEEP levels. Dorsal Ppl and Pes were similar. The driving transpulmonary pressure was similar in the two lungs. Vt distribution between lungs was different at zero end-expiratory pressure (≈70% of Vt going in noninjured lung) owing to different respiratory system compliance (8.3 ml/cm H₂O noninjured lung vs. 3.7 ml/cm H₂O injured lung). PEEP at 10 cm H₂O with transpulmonary pressure around zero homogenized Vt distribution opening the lungs. PEEP ≥16 cm H₂O equalized distribution of Vt but with overdistension for both lungs.Conclusions: Despite asymmetrical lung injury, Ppl between injured and noninjured lungs is equalized and esophageal pressure is a reliable estimate of dorsal Ppl. Driving transpulmonary pressure is similar for both lungs. Vt distribution results from regional respiratory system compliance. Moderate PEEP homogenizes Vt distribution between lungs without generating hyperinflation.

Regulatory mechanisms of neutrophil migration from the circulation to the airspace

The neutrophil, a short-lived effector leukocyte of the innate immune system best known for its proteases and other degradative cargo, has unique, reciprocal physiological interactions with the lung. During health, large numbers of ‘marginated’ neutrophils reside within the pulmonary vasculature, where they patrol the endothelial surface for pathogens and complete their life cycle. Upon respiratory infection, rapid and sustained recruitment of neutrophils through the endothelial barrier, across the extravascular pulmonary interstitium, and again through the respiratory epithelium into the airspace lumen, is required for pathogen killing. Overexuberant neutrophil trafficking to the lung, however, causes bystander tissue injury and underlies several acute and chronic lung diseases. Due in part to the unique architecture of the lung’s capillary network, the neutrophil follows a microanatomic passage into the distal airspace unlike that observed in other end-organs that it infiltrates. Several of the regulatory mechanisms underlying the stepwise recruitment of circulating neutrophils to the infected lung have been defined over the past few decades; however, fundamental questions remain. In this article, we provide an updated review and perspective on emerging roles for the neutrophil in lung biology, on the molecular mechanisms that control the trafficking of neutrophils to the lung, and on past and ongoing efforts to design therapeutics to intervene upon pulmonary neutrophilia in lung disease.

Characterization of the seven-day course of pulmonary response following unilateral lung acid injury in rats

BACKGROUND

Aspiration of gastric acid is an important cause of acute lung injury. The time course of the pulmonary response to such an insult beyond the initial 48 hours is incompletely characterized. The purpose of this study was to comprehensively describe the pulmonary effects of focal lung acid injury over a seven day period in both directly injured and not directly injured lung tissue.

METHODS

Male Wistar rats underwent left-endobronchial instillation with hydrochloric acid and were sacrificed at 4, 24, 48, 96 or 168 h after the insult. Healthy non-injured animals served as controls. We assessed inflammatory cell counts and cytokine levels in right and left lung lavage fluid and blood, arterial oxygen tension, alterations in lung histology, lung wet-to-dry weight ratio and differential lung perfusion.

RESULTS

Lung acid instillation induced an early strong inflammatory response in the directly affected lung, peaking at 4-24 hours, with only partial resolution after 7 days. A less severe response with complete resolution after 4 days was seen in the opposite lung. Alveolar cytokine levels, with exception of IL-6, only partially reflected the localization of lung injury and the time course of the functional and histologic alterations. Alveolar leucocyte subpopulations exhibited different time courses in the acid injured lung with persistent elevation of alveolar lymphocytes and macrophages. After acid instillation there was an early transient decrease in arterial oxygen tension and lung perfusion was preferentially distributed to the non-injured lung.

CONCLUSION

These findings provide a basis for further research in the field of lung acid injury and for studies exploring effects of mechanical ventilation on injured lungs. Incomplete recovery in the directly injured lung 7 days after acid instillation suggests that increased vulnerability and susceptibility to further noxious stimuli are still present at that time.

Adhesion Molecules: Master Controllers of the Circulatory System

This manuscript will review our current understanding of cellular adhesion molecules (CAMs) relevant to the circulatory system, their physiological role in control of vascular homeostasis, innate and adaptive immune responses, and their importance in pathophysiological (disease) processes such as acute lung injury, atherosclerosis, and pulmonary hypertension. This is a complex and rapidly changing area of research that is incompletely understood. By design, we will begin with a brief overview of the structure and classification of the major groups of adhesion molecules and their physiological functions including cellular adhesion and signaling. The role of specific CAMs in the process of platelet aggregation and hemostasis and leukocyte adhesion and transendothelial migration will be reviewed as examples of the complex and cooperative interplay between CAMs during physiological and pathophysiological processes. The role of the endothelial glycocalyx and the glycobiology of this complex system related to inflammatory states such as sepsis will be reviewed. We will then focus on the role of adhesion molecules in the pathogenesis of specific disease processes involving the lungs and cardiovascular system. The potential of targeting adhesion molecules in the treatment of immune and inflammatory diseases will be highlighted in the relevant sections throughout the manuscript.

Lung mechanical changes following bronchoaspiration in a porcine model: differentiation of direct and indirect mechanisms

Bronchoaspiration results in local deterioration of lung function through direct damage and/or indirect systemic effects related to neurohumoral pathways. We distinguished these effects by selectively intubating the two main bronchi in pigs while a PEEP of 4 or 10cm H2O was maintained. Gastric juice was instilled only into the right lung. Lung mechanical and ventilation defects were assessed by measuring unilateral pulmonary input impedance (ZL,s) and the third phase slope of the capnogram (SIII) for each lung side separately before the aspiration and for 120min thereafter. Marked transient elevations in ZL,s parameters and SIII were observed in the affected lung after aspiration. Elevating PEEP did not affect these responses in the ZL,s parameters, whereas it prevented the SIII increases. None of these indices changed in the intact left lung. These findings furnish evidence of the predominance of the local direct damage over the indirect systemic effects in the development of the deterioration of lung function, and demonstrate the benefit of an initially elevated PEEP following aspiration.

Unilateral acid aspiration augments the effects of ventilator lung injury in the contralateral lung

BACKGROUND

Mechanical ventilation is necessary during acute respiratory distress syndrome, but it promotes lung injury because of the excessive stretch applied to the aerated parenchyma. The authors' hypothesis was that after a regional lung injury, the noxious effect of mechanical ventilation on the remaining aerated parenchyma would be more pronounced.

METHODS

Mice, instilled with hydrochloric acid (HCl) in the right lung, was assigned to one of the following groups: mechanical ventilation with tidal volumes (VT) 25 ml/kg (HCl-VILI25, n = 12), or VT 15 ml/kg (HCl-VILI15, n = 9), or spontaneous breathing (HCl-SB, n = 14). Healthy mice were ventilated with VT 25 ml/kg (VILI25, n = 11). Arterial oxygenation, lung compliance, bronchoalveolar lavage inflammatory cells, albumin, and cytokines concentration were measured.

RESULTS

After 7 h, oxygenation and lung compliance resulted lower in HCl-VILI25 than in VILI25 (P < 0.05, 210 ± 54 vs. 479 ± 83 mmHg, and 32 ± 3.5 vs. 45 ± 4.1 µl/cm H2O, mean ± SD, respectively). After right lung injury, the left lung of HCl-VILI25 group received a greater fraction of the VT than the VILI25 group, despite an identical global VT. The number of total and polymorphonuclear cells in bronchoalveolar lavage resulted significantly higher in HCl-VILI25, compared with the other groups, in not only the right lung, but also in the left lung. The albumin content in the left lung resulted higher in HCl-VILI25 than in VILI25 (224 ± 85 vs. 33 ± 6 µg/ml; P < 0.05). Cytokines levels did not differ between groups.

CONCLUSION

Aggressive mechanical ventilation aggravates the preexisting lung injury, which is noxious for the contralateral, not previously injured lung, possibly because of a regional redistribution of VT.

Special article: the endothelial glycocalyx: emerging concepts in pulmonary edema and acute lung injury

The endothelial glycocalyx is a dynamic layer of macromolecules at the luminal surface of vascular endothelium that is involved in fluid homeostasis and regulation. Its role in vascular permeability and edema formation is emerging but is still not well understood. In this special article, we highlight key concepts of endothelial dysfunction with regards to the glycocalyx and provide new insights into the glycocalyx as a mediator of processes central to the development of pulmonary edema and lung injury.

Increased expression levels of integrin α9β1 and CD11b on circulating neutrophils and elevated serum IL-17A in elderly aspiration pneumonia

BACKGROUND

Repeated aspiration pneumonia is a serious problem in the elderly. In aspiration pneumonia, neutrophils play an important role in acute lung injury, while CD18-independent neutrophil transmigration pathways have also been reported in acid-aspiration pneumonia animal models. However, the involvement of IL-17A and β1 integrin still remains unclear. The β1 integrin subfamily integrin α9β1 has been shown to be expressed on human neutrophils and to mediate adhesion to extracellular matrix proteins including the vascular cell adhesion molecule-1.

OBJECTIVES

To elucidate the possible involvement of β1 integrin subfamily and IL-17A in aspiration pneumonia.

METHODS

We analyzed the expression levels of CD11b, CD18 and integrin α9β1 in circulating neutrophils and serum concentration of IL-17A, IL-22 and IL-23 in elderly aspiration pneumonia patients (n = 32, 14 males and 18 females, 78.8 ± 3.9 years old) at 2 time points (on the day of admission before starting antibiotics and the day after finishing antibiotics) and compared the results with those of a control group (n = 30, 13 males and 17 females, 76.1 ± 3.4 years old).

RESULTS

Recombinant IL-17A stimulated integrin α9β1 and CD11b expression levels in healthy human neutrophils in vitro. The expression levels of integrin α9β1 and CD11b in circulating neutrophils were significantly higher in pneumonia patients compared with the controls. In addition, serum IL-17A concentration was significantly increased in pneumonia patients. Integrin α9β1 levels positively correlated with serum IL-17A and CD18 expression levels.

CONCLUSIONS

These findings suggest a potential role of integrin α9β1 expressed in neutrophils and elevated serum IL-17A in extravasation of neutrophils in cases of aspiration pneumonia.

Models and mechanisms of acute lung injury caused by direct insults

Acute lung injury (ALI) and its more severe form acute respiratory distress syndrome (ARDS) are life-threatening diseases that are characterized by acute onset, pulmonary inflammation, oedema due to increased vascular permeability and severe hypoxemia. Clinically, ARDS can be divided into ARDS due to direct causes such as pneumonia, aspiration or injurious ventilation, and due to extrapulmonary indirect causes such as sepsis, severe burns or pancreatitis. In order to identify potential therapeutic targets, we asked here whether common molecular mechanisms can be identified that are relevant in different models of the direct form of ALI/ARDS. To this end, we reviewed three widely used models: (a) one based on a biological insult, i.e. instillation of bacterial endotoxins; (b) one based on a chemical insult, i.e. instillation of acid; and (c) one based on a mechanical insult, i.e. injurious ventilation. Studies were included only if the mediator or mechanism of interest was studied in at least two of the three animal models listed above. As endpoints, we selected neutrophil sequestration, permeability, hypoxemia (physiological dysfunction) and survival. Our analysis showed that most studies have focused on mechanisms of pulmonary neutrophil sequestration and models with moderate forms of oedema. The underlying mechanisms that involve canonical inflammatory pathways such as MAP kinases, CXCR2 chemokines, PAF, leukotrienes, adhesions molecules (CD18, ICAM-1) and elastase have been defined relatively well. Further mechanisms including TNF, DARC, HMGB1, PARP, GADD45 and collagenase are under investigation. Such mechanisms that are shared between the three ALI models may represent viable therapeutic targets. However, only few studies have linked these pathways to hypoxemia, the most important clinical aspect of ALI/ARDS. Since moderate oedema does not necessarily lead to hypoxemia, we suggest that the clinical relevance of experimental studies can be further improved by putting greater emphasis on gas exchange.

Low-dose carbon monoxide treatment attenuates early pulmonary neutrophil recruitment after acid aspiration

Exogenous carbon monoxide (CO) has anti-inflammatory and cytoprotective properties that show promise in the treatment of numerous pulmonary diseases. However, the effectiveness of CO in acute pulmonary injury associated with direct lung insult has not been shown conclusively. The purpose of this study was to determine if exogenous CO would modulate the pulmonary inflammation and lung injury that develops after acid aspiration. Groups of mice were given intratracheal (IT) injections of either saline or an acidic solution. After the IT injection, some of the mice in each group were allowed to spontaneously inhale CO (500 ppm). Mice exposed to CO for 6 h after IT acid had a significant decrease in bronchoalveolar lavage (BAL) fluid neutrophil counts and in histological evidence of lung injury. These results could not be explained by changes in BAL fluid chemokine levels or altered CXCR2 expression. The reduced neutrophil recruitment was associated with a decrease in the percentage of peripheral blood neutrophils expressing CD11b protein. However, within 24 h, the BAL neutrophil counts increased and were not different from animals without CO exposure. In addition, indices of vascular integrity were not different between animals with acid aspiration regardless of CO exposure at the later time point. These results showed that CO can modulate the early development of acute lung inflammation in this model of acid aspiration. Although these effects were eventually overwhelmed, the results suggest that CO may have efficacy during the initial treatment of aspiration lung injury.

Effects of a catecholamine-induced increase in cardiac output on lung injury after experimental unilateral pulmonary acid instillation

OBJECTIVES

Increasing pulmonary blood flow aggravated ventilation-associated lung injury in ex vivo animal experiments, but data were less consistent in an in vivo animal model and do not reflect redistributed lung perfusion seen in clinical acute lung injury. We sought to determine the effects of increased cardiac output on markers of lung injury in an in vivo model of inhomogeneous lung perfusion and injury.

DESIGN

Prospective, controlled animal study.

SETTING

Experimental research laboratory of a university hospital.

SUBJECTS

A total of 50 anesthetized, mechanically ventilated, male Wistar rats.

INTERVENTIONS

Unilateral lung injury was induced in rats by left lung acid instillation. After 24 hrs, animals were anesthetized and subjected to mechanical ventilation (tidal volume, 8 mL/kg; positive end-expiratory pressure, 7 cm H2O; FIO2, 0.4) and continuous infusion of either 10 microg x kg x min dobutamine or isotonic saline (control) for 4 hrs.

MEASUREMENTS AND MAIN RESULTS

Cardiac output and differential lung perfusion were recorded throughout the ventilation period. Right and left lung wet-to-dry weight ratio, cytokines and inflammatory cells in lung lavage, and histologic lung injury were measured postmortem. After acid injury, lung perfusion was preferentially distributed to the noninjured lung. Dobutamine increased baseline cardiac output (>70%) and perfusion of both lungs (left, acid-instilled lung: from 16 +/- 2 to 29 +/- 6 mL/min; right, non-acid-instilled lung: from 54 +/- 3 to 98 +/- 7 mL/min). There was no difference in left lung injury between dobutamine- and saline-infused animals, but right lung injury was aggravated in dobutamine-infused animals, as indicated by increased lung edema, histologic lung injury, and cell counts in lavage.

CONCLUSIONS

In the setting of unilateral lung injury and uneven lung perfusion, a dobutamine-induced increase in cardiac output has potentially detrimental effects on the opposite lung.

A novel model of selective lung ventilation to investigate the long-term effects of ventilation-induced lung injury

Mechanical ventilation (MV) with large tidal volumes (V(T)) causes ventilator induced lung injury. Whereas immediate effects of short-term injurious ventilation are well studied, little is known about its long-term effects. We aimed to establish an animal model of selective injurious MV, permitting assessment of the long-term course of ventilation-induced lung injury. In anesthetized and instrumented rats (n = 26), laryngoscopy was performed, and one cannula for MV was placed in the left main bronchus and a second one in the trachea. Two ventilators were used to ventilate the left lung with high (20 mL/kg) and the right lung with low (4 mL/kg) V(T). In control animals, both lungs received low V(T). After 2 h of MV, animals were extubated and observed for 24 h and then killed. Left and right lungs were excised and sampled for further investigations. Survival in animals ventilated with the high V(T) was 90%. Twenty-four hours after MV, alveolar levels of humoral (tumor necrosis factor alpha, interleukin 6) and cellular (polymorphonuclear leukocytes) inflammatory markers were increased, and histological alterations were present in lungs ventilated with high V(T). A delayed decrease in PaO2 was noted 24 h after MV, with high V(T) delivered to one lung as compared with low V(T) delivered to both lungs. This animal model permits assessment of the long-term course of ventilation-induced lung injury and shows that pulmonary inflammation and histological alterations are present 24 h after unilateral injurious ventilation.

Neutrophil cytoskeletal rearrangements during capillary sequestration in bacterial pneumonia in rats

RATIONALE

Neutrophils accumulate in pulmonary capillaries during acute inflammation. Initial events in injury recognition and sequestration do not occur through selectin-mediated rolling. Cytoskeletal rearrangements, as assessed by submembrane F-actin rims, result in poorly deformable neutrophils that may not pass through capillaries.

OBJECTIVE

To test the hypothesis that neutrophils sequestering during pneumonia contain F-actin rims and to determine the roles of CD11/CD18, L-selectin expression, and neutrophil-platelet adhesion in neutrophil sequestration.

METHODS

Neutrophils were compared in blood obtained simultaneously from venous and arterial sites before and 4 h after instillation of Streptococcus pneumoniae or Escherichia coli in rats.

MEASUREMENTS AND MAIN RESULTS

At 4 h of pneumonia, the number of neutrophils was greater in the venous blood entering the lungs than in the arterial blood leaving the lungs, indicating that neutrophil sequestration was occurring. More neutrophils entering the lungs contained F-actin rims than did neutrophils exiting, and the venous-arterial difference in F-actin-rimmed neutrophil counts completely accounted for sequestration. In E. coli pneumonia, in which neutrophil adhesion is mediated by CD11/CD18, CD18 blockade 15 min before blood samples were obtained did not prevent this sequestration of F-actin-rimmed neutrophils. Neutrophils expressing high or low levels of L-selectin or of neutrophils that bound platelets while circulating did not preferentially sequester.

CONCLUSIONS

Neutrophils with cytoskeletal rearrangements preferentially sequester within the lungs during pneumonia, and this sequestration is not due to CD11/CD18-mediated adhesion, L-selectin expression, or platelet adhesion to neutrophils, suggesting that cytoskeletal rearrangements result in sequestration of neutrophils.

PEEP has beneficial effects on inflammation in the injured and no deleterious effects on the noninjured lung after unilateral lung acid instillation

OBJECTIVE

In clinical lung injury areas of inflammation and structural alveolar alteration are unevenly distributed and interspaced between healthy or less injured lung areas. Positive end-expiratory pressure (PEEP) applied with mechanical ventilation (MV) may affect injured and healthy lung areas differently. We compared the effects of PEEP on the inflammatory response in injured and noninjured regions of the lung in an animal model of unilateral lung acid instillation.

SUBJECTS

Anesthetized, paralyzed, and ventilated rats.

INTERVENTIONS

Rats underwent left-endobronchial instillation with either hydrochloric acid or isotonic saline and were randomized 24 h later to MV using constant tidal volume (16 ml/kg) with either ZEEP, PEEP at 5 mmHg, or PEEP at 10 mmHg. After 4 h of MV the animals (n=9 or 10 per group) were killed and inflammatory markers assessed in left- and right-lung lavage fluid samples. In four additional animals per group differential lung perfusion was assessed.

RESULTS

Unilateral acid injury alone worsened oxygenation, decreased left-lung perfusion, and increased left-lung lavage neutrophil and macrophage counts and cytokine levels. MV with ZEEP further impaired oxygenation and further decreased left-lung perfusion in acid-injured animals. MV with high PEEP preserved oxygenation and significantly decreased left-lung lavage protein content and cell counts in acid-injured animals and had no deleterious effect on the right (noninjured) lung.

CONCLUSION

In this model of unilateral lung acid injury high PEEP attenuates the inflammatory cell response in the acid-injured lung, preserved oxygenation and has no deleterious effects in the opposite lung.

Sampling-dependent up-regulation of gene expression in sequential samples of human airway epithelial cells

As part of a study of in vivo gene expression levels in the human airway epithelium in response to chronic cigarette smoking, we have identified a number of genes whose expression levels are altered in a time-dependent fashion resulting from the procedure used to sample epithelial cells. Fiberoptic bronchoscopy and airway epithelium brushing were used to obtain independent samples from a single individual, 1st from the right lung, followed by sampling of the left lung. We observed that a specific subset of early response genes encoding proteins involved in transcription, signal transduction, cell cycle/growth, and apoptosis were significantly up-regulated in the left lung samples (the 2nd region to be sampled) compared with the right lung samples (the 1st region to be sampled). This response was due to the temporal nature of the sampling procedure and not to inherent gene expression differences between airway epithelium of the right and left lungs. When the order of sampling was reversed, with the left airway epithelium sampled 1st, the same subset of genes were up-regulated in the samples obtained from the right airway epithelium. The time-dependent up-regulation of these genes was likely in response to the stress of the procedure and/or the anesthesia used. Sampling-dependent uncertainty of gene expression is likely a general phenomenon relevant to the procedures used for obtaining biological samples, particularly in humans where the sampling procedures are dependent on ensuring comfort and safety.

Bench-to-bedside review: acute respiratory distress syndrome - how neutrophils migrate into the lung

Acute lung injury and its more severe form, acute respiratory distress syndrome, are major challenges in critically ill patients. Activation of circulating neutrophils and transmigration into the alveolar airspace are associated with development of acute lung injury, and inhibitors of neutrophil recruitment attenuate lung damage in many experimental models. The molecular mechanisms of neutrophil recruitment in the lung differ fundamentally from those in other tissues. Distinct signals appear to regulate neutrophil passage from the intravascular into the interstitial and alveolar compartments. Entry into the alveolar compartment is under the control of CXC chemokine receptor (CXCR)2 and its ligands (CXC chemokine ligand [CXCL]1–8). The mechanisms that govern neutrophil sequestration into the vascular compartment of the lung involve changes in the actin cytoskeleton and adhesion molecules, including selectins, β₂ integrins and intercellular adhesion molecule-1. The mechanisms of neutrophil entry into the lung interstitial space are currently unknown. This review summarizes mechanisms of neutrophil trafficking in the inflamed lung and their relevance to lung injury.

Proinflammatory effects of copper deficiency on neutrophils and lung endothelial cells

Dietary copper deficiency increases the accumulation of circulating neutrophils in the rat lung microcirculation. This process includes neutrophil adhesion to, migration along, and emigration though the vascular endothelium. The current study was designed to examine the role of copper in each of these steps. Neutrophils were isolated from rats fed either a copper-adequate (CuA, 6.1 microg Cu/g diet) or copper-deficient diet (CuD, 0.3 microg Cu/g diet) for 4 weeks. First, transient and firm adhesion of neutrophils to P-selectin in a flow chamber showed there were more adhered CuD neutrophils than CuA ones. This effect is probably caused by the increased expression of CD11b that was observed in the current study. Second, the evaluation of neutrophil migration under agarose showed that the CuD neutrophils moved farther than the CuA group in response to IL-8 but not fMLP; this suggests an increased sensitivity to a CD11/CD18-independent signalling pathway. Third, the contractile mechanism of endothelial cells was studied. Elevated F-actin formation in Cu-chelated lung microvascular endothelial cells suggests that neutrophil emigration may be promoted by enhanced cytoskeletal reorganization of the endothelium during copper deficiency. Combined, these results support the theory that dietary copper deficiency has proinflammatory effects on both neutrophils and the microvascular endothelium that promote neutrophil-endothelial interactions.

Unique structural features that influence neutrophil emigration into the lung

Neutrophil emigration in the lung differs substantially from that in systemic vascular beds where extravasation occurs primarily through postcapillary venules. Migration into the alveolus occurs directly from alveolar capillaries and appears to progress through a sequence of steps uniquely influenced by the cellular anatomy and organization of the alveolar wall. The cascade of adhesive and stimulatory events so critical to the extravasation of neutrophils from postcapillary venules in many tissues is not evident in this setting. Compelling evidence exists for unique cascades of biophysical, adhesive, stimulatory, and guidance factors that arrest neutrophils in the alveolar capillary bed and direct their movement through the endothelium, interstitial space, and alveolar epithelium. A prominent path accessible to the neutrophil appears to be determined by the structural interactions of endothelial cells, interstitial fibroblasts, as well as type I and type II alveolar epithelial cells.

Exacerbation with granulocyte colony-stimulating factor of prior acute lung injury during neutropenia recovery in rats

OBJECTIVE

Neutropenia recovery may be associated with an increased risk of respiratory function deterioration. A history of pneumonia complicating neutropenia has been identified as the leading cause of adult respiratory distress syndrome during neutropenia recovery in patients receiving anticancer chemotherapy, suggesting that neutropenia recovery may worsen prior lung injury.

DESIGN

Controlled animal study.

SETTING

Research laboratory of an academic institution.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

We studied the effect of recovery from cyclophosphamide-induced neutropenia on endotoxin (lipopolysaccharide)- or hydrochloric acid-induced acute lung injury in rats. We also studied the effects of adding granulocyte colony-stimulating factor.

MEASUREMENTS AND MAIN RESULTS

Compared with noncyclophosphamide-treated rats, rats undergoing neutropenia recovery had a higher wet/dry lung weight ratio after hydrochloric acid-induced but not lipopolysaccharide-induced acute lung injury. Granulocyte colony-stimulating factor significantly increased both alveolar cell recruitment (bronchoalveolar lavage fluid counts) and pulmonary edema (wet/dry lung ratio) in both acute lung injury models during neutropenia recovery. Furthermore, in an experiment in hydrochloric acid-instilled rats, exacerbation by granulocyte colony-stimulating factor of hydrochloric acid-induced acute lung injury was inhibited by lidocaine, which prevents adhesion of neutrophils to endothelial cells. Tumor necrosis factor-alpha and interleukin-1 beta concentrations in supernatants of lipopolysaccharide-stimulated alveolar macrophages from rats undergoing neutropenia recovery with granulocyte colony-stimulating factor treatment were significantly increased compared with rats undergoing neutropenia recovery without granulocyte colony-stimulating factor.

CONCLUSION

Neutropenia recovery can worsen acute lung injury, and this effect is exacerbated by granulocyte colony-stimulating factor.

Severely reduced neutrophil adhesion and impaired host defense against fecal and commensal bacteria in CD18-/-P-selectin-/- double null mice

Leukocyte recruitment to sites of inflammation requires the functions of selectins and integrins. P-selectin null (CD62P-/-) mice show a mild and CD18 null (CD18-/-) mice a more severe neutrophil recruitment defect in some inflammatory models. To investigate the possible cooperative interactions between CD18 integrins and P-selectin in mediating neutrophil recruitment, we generated CD18-/-CD62P-/- double null mice. CD18-/-CD62P-/- mice were apparently normal at weaning and fertile but later failed to gain weight, showed increased susceptibility to infection by fecal and commensal bacteria, and survived only 5-6 months. Some CD18-/-CD62P-/- mice showed severe spontaneous skin lesions; most showed neutrophil infiltration in the lungs and liver, and positive bacterial cultures from internal organs. The number and velocity of rolling leukocytes in tumor necrosis factor alpha treated venules of CD18-/-CD62P-/- mice was similar to those in wild-type mice, but neutrophil adhesion was severely reduced. Only 25% of adhered leukocytes were neutrophils in CD18-/-CD62P-/- mice vs. >90% in wild-type, CD62P-/-, and CD18-/- single mutants. Our data show that removing both P-selectin and CD18 integrins from mice leads to severe neutrophil recruitment defects and spontaneous pathology.

Neutrophil proteinases in hydrochloric acid- and endotoxin-induced acute lung injury: evaluation of interstitial protease activity by in situ zymography

We investigated the role of polymorphonuclear neutrophil (PMN) proteinases, elastase, and gelatinase B in rat models of acute lung injury. Three groups of rats were studied 6 hours after unilateral instillation of hydrochloric acid (HCl; 0.1 N), lipopolysaccharide (LPS) (4 microg), or saline. The results demonstrated that HCl-induced lung injury, as compared with LPS-induced lung injury, was associated with an increase in permeability (wet/dry weight ratio and proteins in bronchoalveolar lavage fluid). In contrast, there was similar PMN recruitment (in bronchoalveolar lavage fluid and myeloperoxidase activity in lung homogenates) and similar proteinase exocytosis (residual alveolar PMN content of elastase and gelatinase B) in both types of lung injury. In situ zymography, evaluating interstitial protease/inhibitor balance, demonstrated a decrease in gelatinolytic activity in both HCl- and LPS-injured lungs compared with normal lung. The increase in interleukin 6 concentration in lung homogenates, which is observed after both injuries compared with saline-instilled animals, could be involved in up-regulation of tissue inhibitor of matrix metalloproteinase-1, shown by immunocytochemistry to participate in antiproteinase excess. Neither inhibition of alveolar neutrophil influx using a leukocyte elastase inhibitor (EPI-hNE-4) nor inhibition of gelatinase activities by recombinant adenovirus for the human tissue inhibitor of matrix metalloproteinase 1 gene transfer decreased lung edema in HCl-induced injury. These data suggest that PMN proteinases do not contribute to HCl-induced acute lung injury in rats.

Differential role of CD18 integrins in mediating lung neutrophil sequestration and increased microvascular permeability induced by Escherichia coli in mice

The in vivo contributions of CD18 integrin-dependent and -independent mechanisms in mediating the increases in lung neutrophil (polymorphonuclear leukocyte; PMN) sequestration and microvascular permeability are not well understood. We determined the time course of these responses to Gram-negative sepsis in the mouse lung and addressed the specific contributions of CD18 integrins and ICAM-1. PMN sequestration in the lung was assessed by morphometric analysis, and transalveolar PMN migration was assessed by bronchoalveolar lavage. Lung tissue PMN number increased by 6-fold within 1 h after i.p. Escherichia coli challenge; this value peaked at 3 h (7-fold above control) and decreased at 12 h (3.5-fold above control). PMN migration into the airspace was delayed; the value peaked at 6 h and remained elevated up to 12 h. Saturating concentrations of anti-CD18 and anti-ICAM-1 mAbs reduced lung tissue PMN sequestration and migration; however, peak responses at 3 and 6 h were inhibited by 40%, indicating that only a small component of PMN sequestration and migration was CD18 dependent at these times. In contrast to the time-dependent decreased role of CD18 integrins in mediating PMN sequestration and migration, CD18 and ICAM-1 blockade prevented the increase in lung microvascular permeability and edema formation at all times after E. coli challenge. Thus, Gram-negative sepsis engages CD18/ICAM-1-independent mechanisms capable of the time-dependent amplification of lung PMN sequestration and migration. The increased pulmonary microvascular permeability induced by E. coli is solely the result of engagement of CD18 integrins even when PMN accumulation and migration responses are significantly CD18 independent.

The alpha 4 beta 1 (very late antigen (VLA)-4, CD49d/CD29) and alpha 5 beta 1 (VLA-5, CD49e/CD29) integrins mediate beta 2 (CD11/CD18) integrin-independent neutrophil recruitment to endotoxin-induced lung inflammation

The beta(2) integrin cell adhesion molecules (CAM) mediate polymorphonuclear leukocyte (PMNL) emigration in most inflamed tissues, but, in the lung, other yet to be identified CAMs appear to be involved. In Lewis rats, the intratracheal injection of Escherichia coli-LPS induced acute (6-h) PMNL accumulation in the lung parenchyma (280 x 10(6) by myeloperoxidase assay; PBS control = 35 x 10(6)) and bronchoalveolar lavage fluid (BALF = 27 x 10(6); PBS = 0.1 x 10(6)). Parenchymal accumulation was not inhibited by a blocking Ab to beta(2) integrins and only minimally inhibited (20.5%; p < 0.05) in BALF. We examined the role of alpha(4)beta(1) and alpha(5)beta(1) integrins and of selectins in this PMNL recruitment. Treatment with mAbs to alpha(4)beta(1) or alpha(5)beta(1), even in combination, had no effect on PMNL accumulation induced by intratracheal LPS. However, anti-alpha(4) combined with anti-beta(2) mAbs inhibited PMNL recruitment to the parenchyma by 56% (p < 0.001) and to BALF by 58% (p < 0.01). The addition of anti-alpha(5) mAb to beta(2) plus alpha(4) blockade inhibited PMNL accumulation further (by 79%; p < 0.05). In contrast, blockade of L-, P-, and E-selectins in combination or together with beta(2), alpha(4), and alpha(5) integrins had no effect. LPS-induced BALF protein accumulation was not inhibited by treatment with anti-beta(2) plus alpha(4) mAbs, but was prevented when alpha(5)beta(1) was also blocked. Thus, while selectins appear to play no role, alpha(4)beta(1) and alpha(5)beta(1) function as major alternate CAMs to the beta(2) integrins in mediating PMNL migration to lung and to pulmonary vascular and epithelial permeability.

Ventilator-induced lung injury is associated with neutrophil infiltration, macrophage activation, and TGF-beta 1 mRNA upregulation in rat lungs

Activated neutrophils contribute to the development of ventilator-induced lung injury (VILI) caused by high-pressure mechanical ventilation. However, exact cellular and molecular mechanisms have not been conclusively studied. Our investigation aimed to examine expression of adhesion molecules by both neutrophils and macrophages in lung lavage fluids of rats with VILI. Further, involvement of proinflammatory (tumor necrosis factor-alpha) and profibrogenetic (transforming growth factor-beta 1) mediators was analyzed at mRNA level in lung tissue. Wistar rats were ventilated by high pressure (45 cm H(2)O of peak inspiratory pressure, n = 23) or low pressure (7 cm H(2)O, n = 13) with 0 positive end-expiratory pressure. After 40 min of comparative ventilation, lung lavage was performed in 20 rats from the experimental group and 10 from the control for immunofluorescence analysis with anti-Mac-1 and anti-ICAM-1 monoclonal antibodies. The lung tissues from remaining rats were subjected to pathological and reverse transcription-polymerase chain reaction examinations. Although there was no significant change of PaO(2) in the low-pressure group, PaO(2) was decreased in the high-pressure group. The high-pressure group also had greater neutrophil infiltration into alveolar spaces, upregulation of CD54 and CD11b on alveolar macrophages, and more transforming growth factor-beta 1 mRNA in lung tissues. Tumor necrosis factor-alpha was not involved in the pathogenesis of the severe VILI observed. Histologic findings also demonstrated more infiltrating neutrophils, destructive change of the alveolar wall, and deposition of matrix in the high-pressure group. These results suggest that a series of proinflammatory reactions and profibrogenetic process may be involved in the course of VILI.

Pulmonary aspiration and lung injury

Lung injury after aspiration, although very rare, is a feared and potentially devastating sequela after anaesthesia. This paper summarizes the most recent studies in aspiration lung injury focusing on its clinical epidemiology, new insights in its pathophysiology and innovative concepts in its prevention and therapy.

Migration of CD18-deficient neutrophils in vitro: evidence for a CD18-independent pathway induced by IL-8

Neutrophils isolated from a child with severe leukocyte adhesion deficiency 1 (LAD1) had a complete absence of expression of the CD11/CD18 beta2 integrin family of adhesion molecules, and were shown to be deficient in the in vitro adhesion and migration properties. However, we found that interleukin-8 (IL8), a potent chemoattractant for neutrophils, and sputum sol phase induced these LAD1 neutrophils to migrate through an endothelial cell layer in vitro, and confirmed that this migration was CD18-independent. These findings add to evidence of CD18-independent mechanisms of neutrophil recruitment, in particular neutrophil infiltration into the lungs, where IL8 may be an important recruitment factor.

Neutrophil and endothelial cell interactions in sepsis. The role of adhesion molecules

Although adhesion molecules present on circulating neutrophils and endothelial cells are essential for normal host defense, generalized activation of these molecules has been implicated in the inflammatory tissue injury occurring during sepsis and septic shock. A review of both preclinical and clinical studies suggests, however, that although these molecules mediate tissue injury related to a variety of microbial and host inflammatory mediators, their predominant role during sepsis with infection is a protective one.

Inhibition of pulmonary neutrophil trafficking during endotoxemia is dependent on the stimulus for migration

In rat models of Gram-negative pneumonia, pulmonary emigration of neutrophils (polymorphonuclear leukocytes [PMNs]) is blocked when rats are made endotoxemic by an intravenous administration of endotoxin (lipopolysaccharide [LPS]). To test whether dysfunctional PMN migratory responses in the endotoxemic rat are specific for airway endotoxin, we gave rats intrapulmonary stimuli known to elicit different adhesion pathways for pulmonary PMN migration. Sprague-Dawley rats were treated intravenously with either saline or LPS and then instilled intratracheally with either sterile saline, LPS from Escherichia coli, interleukin (IL)-1, hydrochloric acid (HCl), zymosan-activated serum (ZAS), or lipoteichoic acid (LTA). Three hours later, accumulation of PMNs and protein in bronchoalveolar lavage fluid (BALF) were assessed. BALF PMN accumulation in response to intratracheal treatment with LPS (100%), IL-1 (100%), ZAS (40%), and LTA (58%) was inhibited by endotoxemia. In rats given intratracheal HCl, BALF PMN numbers were unaffected by intravenous LPS. The pattern of inhibition of migration suggests that intravenous LPS only inhibits migration in response to stimuli for which migration is CD18-dependent. In contrast to PMN migration, BALF protein accumulation was inhibited by intravenous LPS only when IL-1 or LPS was used as the intratracheal stimulus. To characterize further the differential responses to the various airway stimuli, the appearance in BALF of tumor necrosis factor-alpha (TNF-alpha) and the PMN chemokine macrophage inflammatory protein (MIP)-2 was measured. Accumulation of PMNs in BALF correlated with the BALF concentrations of MIP-2 (r = 0.846, P < 0.05) and TNF (r = 0.911; P < 0.05). The ability of intravenous LPS to inhibit pulmonary PMN migration correlated weakly with MIP-2 (r = 0.659; P < 0.05) and with TNF (r = 0.413; P > 0.05) concentrations in BALF. However, this correlation was strengthened for TNF (r = 0.752; P < 0.05) when data from IL-1-treated animals were excluded. Thus, the presence in BALF of inflammatory mediators that are known to promote CD18-mediated migration correlates with endotoxemia-related inhibition of PMN migration. Furthermore, the pattern of inhibition of pulmonary PMN migration during endotoxemia is consistent with the CD18 requirement of each migratory stimulus.