Death receptors mediate the adverse effects of febrile-range hyperthermia on the outcome of lipopolysaccharide-induced lung injury

We have shown that febrile-range hyperthermia enhances lung injury and mortality in mice exposed to inhaled LPS and is associated with increased TNF-α receptor activity, suppression of NF-κB activity in vitro, and increased apoptosis of alveolar epithelial cells in vivo. We hypothesized that hyperthermia enhances lung injury and mortality in vivo by a mechanism dependent on TNF receptor signaling. To test this, we exposed mice lacking the TNF-receptor family members TNFR1/R2 or Fas (TNFR1/R2(-/-) and lpr) to inhaled LPS with or without febrile-range hyperthermia. For comparison, we studied mice lacking IL-1 receptor activity (IL-1R(-/-)) to determine the role of inflammation on the effect of hyperthermia in vivo. TNFR1/R2(-/-) and lpr mice were protected from augmented alveolar permeability and mortality associated with hyperthermia, whereas IL-1R(-/-) mice were susceptible to augmented alveolar permeability but protected from mortality associated with hyperthermia. Hyperthermia decreased pulmonary concentrations of TNF-α and keratinocyte-derived chemokine after LPS in C57BL/6 mice and did not affect pulmonary inflammation but enhanced circulating markers of oxidative injury and nitric oxide metabolites. The data suggest that hyperthermia enhances lung injury by a mechanism that requires death receptor activity and is not directly associated with changes in inflammation mediated by hyperthermia. In addition, hyperthermia appears to enhance mortality by generating a systemic inflammatory response and not by a mechanism directly associated with respiratory failure. Finally, we observed that exposure to febrile-range hyperthermia converts a modest, survivable model of lung injury into a fatal syndrome associated with oxidative and nitrosative stress, similar to the systemic inflammatory response syndrome.     

Depletion of resident alveolar macrophages does not prevent Fas-mediated lung injury in mice

Activation of the Fas/Fas ligand (FasL) system in the lungs results in a form of injury characterized by alveolar epithelial apoptosis and neutrophilic inflammation. Studies in vitro show that Fas activation induces apoptosis in alveolar epithelial cells and cytokine production in alveolar macrophages. The main goal of this study was to determine the contribution of alveolar macrophages to Fas-induced lung inflammation in mice, by depleting alveolar macrophages using clodronate-containing liposomes. Liposomes containing clodronate or PBS were instilled by intratracheal instillation. After 24 h, the mice received intratracheal instillations of the Fas-activating monoclonal antibody Jo2 or an isotype control antibody and were studied 18 h later. The Jo2 MAb induced increases in bronchoalveolar lavage fluid (BALF) total neutrophils, lung caspase-3 activity, and BALF total protein and worsened histological lung injury in the macrophage-depleted mice. Studies in vitro showed that Fas activation induced the release of the cytokine KC in a mouse lung epithelial cell line, MLE-12. These results suggest that the lung inflammatory response to Fas activation is not primarily dependent on resident alveolar macrophages and may instead depend on cytokine release by alveolar epithelial cells.     

Electron microscopic studies of the lung of the frog

Summary Scanning and transmission electron microscopy were used to study the inner architecture of the frog lung. In some specimens the alveolar surface mucus layer was removed to permit the examination of underlying features. The inner surface of the frog's lung is covered by a layer of microvilli belonging to only one type of epithelial cells. The boundaries of these epithelial cells are demarcated by small ridges. Different degrees of lung expansion cause variations of the surface topography. The morphology of certain surface features is examined in detail. Several methods of drying the specimens are compared.The author wishes to thank Dr. I. E. Richter, Institut für allgemeine und experimentelle Pathologie der Bundeswehr, Mainz, for the opportunity to do these investigations and for helpful discussions.     

An electron microscopic study of the acid mucosubstance lining the alveoli of hamster lung

Synopsis Hamster lung has been investigated by electron microscopy using colloidal iron oxide and Ruthenium Red stains. A continuous layer of acid mucosubstance has been demonstrated on the surface of the alveolar epithelial cells. The lining layer associated with the membranous pneumonocytes has been found to be consistently thinner than that covering the granular pneumonocytes and alveolar macrophages. Strong binding of stain has also been observed in osmiophilic membranous material which is thought to represent fragments of pulmonary surfactant. The susceptibility of the alveolar lining material to digestion by neuramidase suggests that it consists mainly of a sialomucin.     

Arguments against and alternatives for an extracellular surfactant layer in the alveoli of mammalian lung

It is generally believed that lung alveoli contain an extracellular aqueous layer of surfactant material, which is allegedly required to prevent alveolar collapse at small lung volume; the surfactant's major constituent is a fully saturated phospholipid, referred to as dipalmitoyl lecithin or DPL. I herein demonstrate that the surfactant hypothesis of alveolar stability is fundamentally wrong. Although DPL is synthesized inside type II epithelial cells and stored in the typical inclusion bodies therein and lowers surface tension to zero in the surface balance, there is no evidence to the effect that type II cells secrete the DPL surfactant into the aqueous intra-alveolar layer which is shown by electron microscopy in support of the surfactant theory. To the contrary, all the evidence indicates that, when seen, such an extracellular layer is an artifact. This is probably upon the damage glutaraldehyde inflicts onto alveolar structures during fixation of air-inflated lung tissue. Furthermore, several cogent arguments invalidate the belief that an extracellular layer of DPL and serum proteins is present in the alveoli of normal lung. In light of these arguments, a surface tension role of DPL in alveolar stability is excluded. Three hypotheses for an alternative role of DPL in respiration mechanics are proposed. They are: (a) alveolar clearance by viscolytic and surfactant action (bubble or foam formation) on the aqueous systems which are present in lung alveoli during edema and in prenatal life and which would otherwise be impervious to air; (b) homeostasis of blood palmitate in normal lung; (c) modulation of the elasticity of terminal lung tissue by the intact inclusion bodies and parts thereof inside type II cells in normal lung.     

Evaluation of two-way protein fluxes across the alveolo-capillary membrane by scintigraphy in rats: effect of lung inflation.

Pulmonary microvascular and alveolar epithelial permeability were evaluated in vivo by scintigraphic imaging during lung distension. A zone of alveolar flooding was made by instilling a solution containing 99mTc-albumin in a bronchus. Alveolar epithelial permeability was estimated from the rate at which this tracer left the lungs. Microvascular permeability was simultaneously estimated measuring the accumulation of (111)In-transferrin in lungs. Four levels of lung distension (corresponding to 15, 20, 25, and 30 cmH2O end-inspiratory airway pressure) were studied during mechanical ventilation. Computed tomography scans showed that the zone of alveolar flooding underwent the same distension as the contralateral lung during inflation with gas. Increasing lung tissue stretch by ventilation at high airway pressure immediately increased microvascular, but also alveolar epithelial, permeability to proteins. The same end-inspiratory pressure threshold (between 20 and 25 cmH2O) was observed for epithelial and endothelial permeability changes, which corresponded to a tidal volume between 13.7 +/- 4.69 and 22.2 +/- 2.12 ml/kg body wt. Whereas protein flux from plasma to alveolar space ((111)In-transferrin lung-to-heart ratio slope) was constant over 120 min, the rate at which 99mTc-albumin left air spaces decreased with time. This pattern can be explained by changes in alveolar permeability with time or by a compartment model including an intermediate interstitial space.     

Type I cell-like morphology in tight alveolar epithelial monolayers

The pulmonary alveolar epithelium separates air spaces from a fluid-filled interstitium and might be expected to exhibit high resistance to fluid and solute movement. Previous studies of alveolar epithelial barrier properties have been limited due to the complex anatomy of adult mammalian lung. In this study, we characterized a model of isolated alveolar epithelium with respect to barrier transport properties and cell morphology. Alveolar epithelial cells were isolated from rat lungs and grown as monolayers on tissue culture-treated Nuclepore filters. On Days 2-6 in primary culture, monolayers were analyzed for transepithelial resistance (Rt) and processed for electron microscopy. Mean cell surface area and arithmetic mean thickness (AMT) were determined using morphometric techniques. By Day 5, alveolar epithelial cells in vitro exhibited morphologic characteristics of type I alveolar pneumocytes, with thin cytoplasmic extensions and protruding nuclei. Morphometric data demonstrated that alveolar pneumocytes in vitro develop increased surface area and decreased cytoplasmic AMT similar to young type I cells in vivo. Concurrent with the appearance of type I cell-like morphology, monolayers exhibited high Rt (greater than 1000 omega.cm2), consistent with the development of tight barrier properties. These monolayers of isolated alveolar epithelial cells may reflect the physiological and morphological properties of the alveolar epithelium in vivo.     

Thrombin-induced contraction in alveolar epithelial cells probed by traction microscopy.

Contractile tension of alveolar epithelial cells plays a major role in the force balance that regulates the structural integrity of the alveolar barrier. The aim of this work was to study thrombin-induced contractile forces of alveolar epithelial cells. A549 alveolar epithelial cells were challenged with thrombin, and time course of contractile forces was measured by traction microscopy. The cells exhibited basal contraction with total force magnitude 55.0 +/- 12.0 nN (mean +/- SE, n = 12). Traction forces were exerted predominantly at the cell periphery and pointed to the cell center. Thrombin (1 U/ml) induced a fast and sustained 2.5-fold increase in traction forces, which maintained peripheral and centripetal distribution. Actin fluorescent staining revealed F-actin polymerization and enhancement of peripheral actin rim. Disruption of actin cytoskeleton with cytochalasin D (5 microM, 30 min) and inhibition of myosin light chain kinase with ML-7 (10 microM, 30 min) and Rho kinase with Y-27632 (10 microM, 30 min) markedly depressed basal contractile tone and abolished thrombin-induced cell contraction. Therefore, the contractile response of alveolar epithelial cells to the inflammatory agonist thrombin was mediated by actin cytoskeleton remodeling and actomyosin activation through myosin light chain kinase and Rho kinase signaling pathways. Thrombin-induced contractile tension might further impair alveolar epithelial barrier integrity in the injured lung.     

Altered expression of tight junction molecules in alveolar septa in lung injury and fibrosis

The dysfunction of alveolar barriers is a critical factor in the development of lung injury and subsequent fibrosis, but the underlying molecular mechanisms remain poorly understood. To clarify the pathogenic roles of tight junctions in lung injury and fibrosis, we examined the altered expression of claudins, the major components of tight junctions, in the lungs of disease models with pulmonary fibrosis. Among the 24 known claudins, claudin-1, claudin-3, claudin-4, claudin-7, and claudin-10 were identified as components of airway tight junctions. Claudin-5 and claudin-18 were identified as components of alveolar tight junctions and were expressed in endothelial and alveolar epithelial cells, respectively. In experimental bleomycin-induced lung injury, the levels of mRNA encoding tight junction proteins were reduced, particularly those of claudin-18. The integrity of the epithelial tight junctions was disturbed in the fibrotic lesions 14 days after the intraperitoneal instillation of bleomycin. These results suggest that bleomycin mainly injured alveolar epithelial cells and impaired alveolar barrier function. In addition, we analyzed the influence of transforming growth factor-β (TGF-β), a critical mediator of pulmonary fibrosis that is upregulated after bleomycin-induced lung injury, on tight junctions in vitro. The addition of TGF-β decreased the expression of claudin-5 in human umbilical vein endothelial cells and disrupted the tight junctions of epithelial cells (A549). These results suggest that bleomycin-induced lung injury causes pathogenic alterations in tight junctions and that such alterations seem to be induced by TGF-β.     

Administration of keratinocyte growth factor down-regulates the pulmonary capacity of acetylcholine production

Keratinocyte growth factor protects the lung against various injurious stimuli. The protective mechanisms, however, are not yet fully understood. The aim of this study is to determine the influence of keratinocyte growth factor on the pulmonary capacity to synthesize acetylcholine, a potent regulator of pulmonary functions which is potentially involved in lung damage. Rats were treated twice (days 1 and 2) intratracheally with keratinocyte growth factor and analyzed at day 4. The mRNA expression of choline acetyltransferase - the acetylcholine synthesizing enzyme - was analyzed by real-time RT-PCR in the lung and in isolated alveolar epithelial type II cells. Choline acetyltransferase protein was assessed by immunoblotting and immunohistochemistry. Finally, pulmonary acetylcholine content was assessed biochemically. Keratinocyte growth factor-treatment led to decreased levels of choline acetyltransferase mRNA in the lung and in isolated alveolar epithelial type II cells. Accordingly, pulmonary choline acetyltransferase protein levels were reduced and pulmonary acetylcholine content declined from 2.8 nmol (control) to 0.4 nmol acetylcholine per gram of wet weight. In conclusion, the present data show that the potent regulator of pulmonary functions, acetylcholine, is produced by the major pulmonary target cell of keratinocyte growth factor, that is alveolar epithelial type II cells. Acetylcholine synthesis is down-regulated by keratinocyte growth factor administration which might contribute to lung protection and to harmonize surfactant homeostasis under conditions of keratinocyte growth factor-induced alveolar epithelial type II cell hyperplasia.     

THE ULTRASTRUCTURE OF MOUSE LUNG GENERAL ARCHITECTURE OF CAPILLARY AND ALVEOLAR WALLS

The general architecture of capillary and alveolar walls of the mouse lung was studied by means of the electron microscope. In order to minimize tissue damage and to improve the cutting properties of embeddings, several modifications in the tissue processing methods were adopted. These modifications were: fixation by infusion, a prolonged time of dehydration, of impregnation, and of polymerization, the use of acetone for dehydration, ammonium sulfide treatment of the fixed and washed tissue, and an elevated (80°C.) polymerization temperature combined with the use of prepolymerized methacrylate. The generally favorable effects of these modified methods upon preservation and cutting properties of embedded tissue are discussed. Both capillary endothelium and alveolar epithelium were found continuous and without pores. The endothelium was seen to be thinnest in those portions that were adjacent to alveolar air spaces. Two morphological "types" of alveolar epithelial cells were found. One protruded into the alveolar lumen with its thick portion containing the nucleus. The other was often located in a niche of the alveolar wall, and contained peculiar dark inclusions amidst numerous mitochondria. Both were attenuated at their periphery to form the thin epithelial layer. The layer between endothelium and epithelium was designated as basement membrane. It was seen to be generally thin and structureless, but was found thickened in some areas where it also contained collagen fibrils.     

Immunological study of lung development in the mouse embryo. II. First appearance of the great alveolar cell, as shown by immunofluorescence microscopy.

An antiserum that specifically recognizes a lung-specific antigen present in the great alveolar cell in the adult mouse lung was used in immunofluorescence studies to detect the first appearance of this antigen in the embryo. Cellular fluorescence was found to occur in the lung tissue from about Day 14.2 onward and to be due to the presence of the lung-specific or a related antigen. The simultaneous appearance of this antigen (ca. Day 14.2) and the cuboidal type of epithelial cell in which it occurs (ca. Day 14) means that the great alveolar cell—or its precursor—is first detectable around Day 14.2. Since the great alveolar cell—or its precursor—is the first and only type of alveolar epithelial cell to occur in the embryonic lung, it must be the stem cell from which the small alveolar cell derives. The persistent sharp demarcation between the prospective alveolar and bronchial epithelia indicates that the respiratory and the conducting portions of the lung originate from different parts of the tubular system in the prenatal lung.     

Scanning electron microscope study of the lung epithelium of the rabbit during ontogenesis

The development of the bronchial and alveolar epithelium was observed in rabbits from the 15th day post conception until the time of birth with the scanning electron microscope. In the pseudoglandular phase, primitive bronchi proliferate in the mesenchyme. The epithelial cells are not differentiated and have single cilia. After retraction of these single cilia cell differentiation begins. Flat cells densely populated with cytopodia can be recognized on the 22nd day, ciliated cells on the 23rd day post conception. Both are located in the bronchi near the hilus. In the canalicular phase of development, the differentiation of the mucoid cells and the Clara-cells begins. The interstitial connective tissue develops more and more capillaries. The alveolar phase begins around the 26th day p. c. The lung capillaries reach the alveolar epithelial cells and arrange themselves directly beneath the epithelial basement membrane. This "alveolarization" of the lung tissue starts in the centre of the lung lobules and proceeds to the periphery. After the 26th day post conception the alveolar epithelial cells retract their single cilium and at the same time become type I or type II pneumocytes. The undifferentiated entodermal stem cell of the alveolar epithelium is the pneumoblast.     

The ultrastructure of mouse lung; general architecture of capillary and alveolar walls

The general architecture of capillary and alveolar walls of the mouse lung was studied by means of the electron microscope. In order to minimize tissue damage and to improve the cutting properties of embeddings, several modifications in the tissue processing methods were adopted. These modifications were: fixation by infusion, a prolonged time of dehydration, of impregnation, and of polymerization, the use of acetone for dehydration, ammonium sulfide treatment of the fixed and washed tissue, and an elevated (80 degrees C.) polymerization temperature combined with the use of prepolymerized methacrylate. The generally favorable effects of these modified methods upon preservation and cutting properties of embedded tissue are discussed. Both capillary endothelium and alveolar epithelium were found continuous and without pores. The endothelium was seen to be thinnest in those portions that were adjacent to alveolar air spaces. Two morphological "types" of alveolar epithelial cells were found. One protruded into the alveolar lumen with its thick portion containing the nucleus. The other was often located in a niche of the alveolar wall, and contained peculiar dark inclusions amidst numerous mitochondria. Both were attenuated at their periphery to form the thin epithelial layer. The layer between endothelium and epithelium was designated as basement membrane. It was seen to be generally thin and structureless, but was found thickened in some areas where it also contained collagen fibrils.     

Diphosphatidylglycerol in experimental acute alveolar injury in the dog

Acute alveolar injury closely resembling that seen in humans was induced in dogs by subcutaneous injection of N-nitroso-N-methylurethane. Necrosis of alveolar epithelial cells was observed during early injury. Proliferation of immature epithelial cells which began during early injury and became massive after peak injury was followed by their differentiation to mature type II cells during recovery. Quantities of diphosphatidylglycerol (DPG) and of phosphatidylglycerol (PG) in alveolar lavage and in post-lavage lung tissue were measured. An increase in tissue DPG coincided with a sharp decrease in tissue and lavage PG during early injury. DPG was not detectable in the lavage. During late recovery, tissue DPG increased threefold over controls. This increase was accompanied by persistence of a 50% decrease in tissue PG and 83% decrease in lavage PG. Biosynthesis of DPG and PG in isolated lung mitochondria demonstrated that DPG was formed from PG in the presence of CDP-diglyceride. These findings suggest that the low level of PG in the surfactant complex during acute alveolar injury is due to increased turnover of PG to DPG in the lung.     

In vitro and in vivo regulation of transepithelial lung alveolar sodium transport by serine proteases

The amiloride-sensitive epithelial sodium channel (ENaC) constitutes a rate-limiting step for sodium (Na+) and water absorption across lung alveolar epithelium. Recent reports suggested that ENaC is regulated by membrane-bound extracellular serine proteases, such as channel-activating proteases (CAPs). The objectives of this study were to examine the role of serine proteases in the regulation of transepithelial alveolar Na+ and water transport in vitro and in vivo and the expression of CAPs in rodent distal lung. In vitro experiments showed that inhibition of endogenous serine proteases by apical aprotinin 1) decreased ENaC-mediated currents in primary cultures of rat and mouse alveolar epithelial cells without affecting the abundance nor the electrophoretic migration pattern of biotinylated alpha- and beta-ENaC expressed at the cell surface and 2) suppressed the increase in amiloride-sensitive short-circuit current induced by the beta2-agonist terbutaline. RT-PCR experiments indicated that CAP1, CAP2, and CAP3 mRNAs were expressed in mouse alveolar epithelial cells, whereas CAP1 was also expressed in alveolar macrophages recovered by bronchoalveolar lavage. CAP1 protein was detected by Western blotting in rat and mouse alveolar epithelial cells, alveolar macrophages and bronchoalveolar lavage fluid. Finally, in vivo experiments revealed that intra-alveolar treatment with aprotinin abolished the increase in Na+-driven alveolar fluid clearance (AFC) induced by terbutaline in an in situ mouse lung model, whereas trypsin potentiated it. These results show that endogenous membrane-bound and/or secreted serine proteases such as CAPs regulate alveolar Na+ and fluid transport in vitro and in vivo in rodent lung.     

Histopathological Features and Viral Antigen Distribution in the Lung of Fatal Patients with <Emphasis Type="Italic">Enterovirus</Emphasis> 71 Infection

Enterovirus 71 (EV71) infection causes hand-foot-and-mouth disease (HFMD) in children and might be accompanied by severe neurological complications. It has become one of the most important pathogens of central nervous system infection. To explore the causes of lung injury by EV71, the distribution of EV71 receptors, SCARB2 and PSGL-1, in human lung tissues was examined. Our results revealed that SCARB2 was positively distributed in the bronchial and bronchiolar epithelial cells, alveolar cells and macrophages, while PSGL-1 was positively scattered in bronchial and bronchiolar epithelial cells and macrophages, and negatively distributed in alveolar cells. The pathological changes of fatal lung with EV71 infection demonstrated intrapulmonary bronchitis and bronchiolitis, diffuse or focal infiltration of inflammatory cells, such as T cells and B cells in the wall and surrounding tissues, widened alveolar septum, capillaries in the septum with highly dilated and congested, and infiltrated inflammatory cells, showing different degrees of protein edema with fibrin exudation in the alveolar cavity, as well as obvious hyaline membrane formation in some alveolar cavities. The EV71 antigen in lung tissues was detected, and the viral antigen was positive in lung bronchial and bronchiolar epithelial cells, and positively scattered in the alveolar cells and macrophages. Therefore, in addition to the complications of central nervous system injury, the lung remains the main target organ for virus attack in severe EV71 infected patients. Lung injury was mainly caused by neurogenic damage and/or direct invasion of the virus into the lungs in critically serious children, and the lesions were mainly pulmonary edema and interstitial pneumonia.     

Repopulation of a human alveolar matrix by adult rat type II pneumocytes in vitro : A novel system for type II pneumocyte culture

This paper describes the preparation of lung acellular alveolar matrix fragments and culture of rat type II pneumocytes directly on the alveolar epithelial basement membrane, thereby permitting study of the effect of lung basement membrane on the morphology and function of type II cells. Collagen types I, III, IV and V, laminin and fibronectin were located by immunofluorescence in the lung matrix with the same patterns as those described for the normal human lung. Transmission electron microscopy (TEM) of the fragments revealed intact epithelial and endothelial basement membranes. The matrix maintained the normal three-dimensional alveolar architecture. Glycosaminoglycans were still present by Alcian Blue staining. Isolated adult rat type II pneumocytes cultured on 150 micron thick fragments of acellular human alveolar extracellular matrix undergo gradual cytoplasmic flattening, with loss of lamellar bodies, mitochondria, and surface microvilli. These changes are similar to the in vivo differentiation of type II pneumocytes into type I pneumocytes. The type II pneumocyte behaviour on the lung epithelial basement membrane contrasted sharply with that of the same cell type cultured on a human amnionic basement membrane. On the latter surface the cells retained their cuboidal shape, lamellar bodies and surface microvilli for up to 8 days. These observations suggest that the basement membranes from different organ systems exert differing influences on the morphology and function of type II pneumocytes and that the alveolar and amnionic basement membranes may have differing three-dimensional organizations. The technique of direct culture of type II cells on the lung basement membrane provides a useful tool for studying the modulating effect of the basement membrane on alveolar epithelial cells.     

Intact alveolar epithelial permeability and transalveolar fluid absorption after thoracic irradiation in rats.

We have addressed the question of how the alveolar space stays relatively free of fluid when thoracic irradiation injures the pulmonary capillary endothelium and plasma fluid leaks into the interstitium. A single dose of 15 Gy to the thorax of rats significantly increased the pulmonary capillary filtration coefficient and the lung wet/dry weight ratio 2 h after irradiation. However, there was no significant increase in the release of lactose dehydrogenase or leaking of Evans blue dye into the alveolar space, indicating that alveolar epithelial permeability remained intact. We found no significant difference in the basal alveolar fluid clearance between control and irradiated animals. There was also no significant difference in blockage of alveolar fluid clearance by amiloride. This indicates that the function of the alveolar epithelial Na(+) channels is not impaired and that alveolar epithelium absorbs fluid normally. Examination of lung tissue by light microscopy demonstrated accumulation of fluid in the perivascular region but not in the alveolar space. Our data appear to indicate that the alveolar epithelial barrier function is more resistant to radiation than that of the pulmonary capillary endothelium. We conclude that intact alveolar epithelial permeability and normal transalveolar epithelial fluid absorption ability are of critical importance in keeping the alveolar space relatively free of fluid during acute radiation lung injury.     

Expression and functional implications of CCR2 expression on murine alveolar epithelial cells

Acute lung injury results in damage to the alveolar epithelium, leading to leak of proteins into the alveolar space and impaired gas exchange. Lung function can be restored only if the epithelial layer is restored. The process of reepithelialization requires migration of lung epithelial cells to cover denuded basement membranes. The factors that control the migration of lung epithelial cells are incompletely understood. We examined isolated murine type II alveolar epithelial cells (AECs) for expression of CC chemokine receptor 2 (CCR2) and functional consequences of the binding of the main CCR2 ligand monocyte chemoattractant protein-1 (MCP-1). We found that primary AECs bound MCP-1 and expressed CCR2 mRNA. These cells demonstrated functional consequences of CCR2 expression with migration in response to MCP-1 in chemotaxis/haptotaxis assays. Primary AECs cultured from mice lacking CCR2 did not respond to MCP-1. Monolayers of AECs lacking CCR2 demonstrated delayed closure of mechanical wounds compared with AEC monolayers expressing CCR2. Delayed closure of mechanical wounds of wild-type AECs was also demonstrated in the presence of anti-MCP-1 antibody. These data demonstrate for the first time that AECs express CCR2 and are capable of using this receptor for chemotaxis and healing of wounds. CCR2-MCP-1 interactions may be important in the process of reepithelialization after lung injury.