Bronchoalveolar lavage in the assessment of pulmonary Hodgkin's disease

Abnormal chest radiographs in patients with Hodgkin's disease are occasionally due to pulmonary Hodgkin's disease. The fluids recovered from bronchoalveolar lavages (BALs) from 50 patients prior to autologous bone marrow transplantation for advanced Hodgkin's disease were examined. Abnormal chest roentgenograms were present in 24 patients (48%); 4 (17%) of these had Reed-Sternberg cells or their mononucleated variants in the lavage fluid and an alveolar lymphocytosis averaging 31.4% (normal: 11.5%). The lymphocytes were small and monotonous. Of the 20 patients with abnormal chest roentgenograms but no Reed-Sternberg cells in the lavage fluid, the lymphocyte count was 10.88%, with only 3 patients exceeding 17%. Two patients with normal chest roentgenograms had Reed-Sternberg-like cells in their lavage fluids and averaged 23% lymphocytes in their lavage differential count. Eosinophils averaged 1% or less of the lavage differential and were not predictive of pulmonary Hodgkin's disease. This experience suggests that pulmonary Hodgkin's disease can be diagnosed by BAL. Reed-Sternberg cells and their mononucleated variants can be recognized by their characteristic cytomorphologic features, although care must be taken not to misinterpret reactive binucleated macrophages as neoplastic cells. In patients with Hodgkin's disease, Reed-Sternberg cells should be sought when an alveolar lymphocytosis is present.     

Radioautographic study of DNA synthesis in bronchoalveolar lavage macrophages during chronic inflammatory processes in the lungs

The cells obtained by broncho-alveolar lavage from patients with chronic pulmonary inflammations were investigated using light and electron microscopy and radioautography. Proliferative activity of lavage alveolar macrophages was studied by 3H-thymidine in vitro incorporation. The labelling index of alveolar macrophages was up to 0.2% in chronic bronchitis and 1.25-3.33% in chronic destructive inflammation. The enhancement of human alveolar macrophage proliferation in chronic pulmonary destructive inflammation is of great importance for the maintenance of the number of mononuclear phagocytes responsible for cellular protection of respiratory lung structures.     

Phagocytic activity of alveolar macrophages in patients with bronchogenic carcinoma

Summary Human bronchoalveolar cells were obtained by lavage during diagnostic fiberoptic bronchoscopy of 21 patients suspected of having lung malignancies. Of these patients 11 were diagnosed as having primary lung cancer (Group I) and included individuals with squamous cell carcinoma, adenocarcinoma, undifferentiated large and oat cell carcinoma at varying locations and TNM stages, 4 patients demonstrated nonprimary metastatic carcinoma (Group II), and 6 patients did not reveal detectable tumors by bronchoscopy or follow-up (Group III) and were included as study controls. We examined the ability of pulmonary alveolar macrophages (PAMs) lavaged from patients in each of the three study groups to phagocytose opsonized sheep red blood cells. Phagocytic activity varied among patients in the same and different study groups; however, no significant differences were observed in the phagocytic or tumoristatic activities of PAMs recovered from tumor-bearing and nontumor-bearing lung regions of the same patient. Moreover, lavage fluids collected from tumor-bearing regions did not suppress the phagocytic activity of PAMs collected from control lungs nor lung regions contralateral to the tumor-bearing lung. The data do not support the view that bronchial neoplasms or their secreted products suppress phagocytic functions of alveolar macrophages.     

Partial purification and characterization of a gelatin-specific protease from the culture media of human pulmonary alveolar macrophages

A gelatin-specific protease from the culture media of human pulmonary alveolar macrophages has been partial purified by gel filtration and characterized. The macrophages were obtained by bronchopulmonary lavage from the lungs of disease-free smoking volunteers. The gelatin-specific protease initially requires trypsin activation. After chromatographing the culture media on a Sephadex G-200 column, trypsin is no longer required for activation. The gelatin-specific protease reported here shares many properties of previously reported gelatinases. It is inhibited by EDTA, cysteine, dithiothreitol and serum. It is unaffected by other protease inhibitors: phenylmethylsulfonyl fluoride, tosyllysine chloromethyl ketone and p-chloromercuribenzoate. Of all substrates tested activity was observed only with gelatin. It was inactive toward collagen, elastin and methemoglobin. This enzyme may have a role in the digestion of collagen which has been cleaved by a mammalian collagenase.     

Association of chlorphentermine with phospholipids in rat alveolar lavage materials, alveolar macrophages and type II cells

Administration of chlorphentermine to rats leads to an increase in the phospholipid content of pulmonary surfactant materials and alveolar macrophages. It is known that this drug binds to pure phospholipids and prevents their degradation by phospholipases. Therefore, experiments were carried out to determine if chlorphentermine binds to surfactant phospholipids in vitro and to measure the in vivo association of drug with phospholipids in alveolar lavage materials from rats injected with [14C]chlorphentermine. The presence of chlorphentermine in alveolar macrophages, type II cells and other small pneumocytes (a population of lung cells which does not include alveolar macrophages or type II cells) from treated animals was also assessed. Binding of the drug to surfactant phospholipids, as measured with the fluorescent probe, 1-anilino-8-naphthalene sulfonate, occurs in vitro and does not differ in various subfractions of alveolar lavage materials isolated by differential centrifugation. Following daily administration of chlorphentermine to rats for 3 days, the drug appears to be associated with surfactant phospholipids such that the molar ratio is 1:100 (chlorphentermine/phospholipid). Chlorphentermine is also associated with alveolar macrophages (molar ratio, 1:18) and type II cells (molar ratio, 1:33). Not much drug is associated with the population of other lung cells (molar ratio, 1:333). In alveolar macrophages, approx. 70% of the drug seems to be bound to phospholipid and/or sequestered in subcellular organelles. However, only 20% of the chlorphentermine is bound and/or sequestered in type II cells. The results of these experiments suggest that following chlorphentermine administration, the drug is associated with phospholipids in acellular pulmonary lavage materials, alveolar macrophages and type II cells. This drug-phospholipid interaction may impair phospholipid degradation and lead to a phospholipidosis in surfactant materials and alveolar macrophages.     

Quantitative Differences In Phagocytosis and Degradation of Pneumocystis By Alveolar Macrophages In Aids and Non-Hiv Patients In Vivo

Broncholaveolar lavage (BAL) specimens (n= 213) from AIDS and non-HIV immunosuppressed patients were investigated for the presence of Pneumocystis carinii infection by fluorescence microscopy of Papanicolaou-stained slides. Alveolar casts, extracellular pneumocysts and phagocytosed cysts and their degradation products in pulmonary alveolar macrophages were identified. the number of phagocytosed pneumocysts within human pulmonary alveolar macrophages was recorded and correlated with the number of extracellular cysts and alveolar casts, in both groups of patients. Both phagocytic and degradation capacity were depressed in AIDS patients. This observation may explain the large number of extracellular organisms found in BAL specimens of AIDS patients compared with non-HIV-positive immunocompromised individuals.     

Cytology of Bronchoalveolar Lavage In Some Rare Pulmonary Disorders: Pulmonary Alveolar Proteinosis and Amiodarone Pulmonary Toxicity

Cytological patterns of bronchoalveolar lavage (BAL) in pulmonary alveolar proteinosis (PAP) and amiodarone pulmonary toxicity (APT) are presented together with light and electron microscopy (EM). the differential cell count of BAL in both diseases is similar in that alveolar macrophages predominate. However, the cytology of PAP is characterized by scanty macrophages and alveolar epithelial cells in abundant periodic acid-Schiff (PAS)-positive extracellular material. the gross appearance of the BAL fluid is therefore opaque. In contrast, the cytology of APT is characterized by foamy alveolar macrophages with numerous lamellar bodies in their cytoplasm, and the BAL fluid is clear.     

Lung Collagens Perpetuate Pulmonary Fibrosis via CD204 and M2 Macrophage Activation

Idiopathic pulmonary fibrosis is characterized by abundant collagen production and accumulation of alternatively activated macrophages (M2) in the lower respiratory tract. Mechanisms as to how alveolar macrophages are activated by collagen breakdown products are unknown. Alveolar macrophages were obtained by bronchoalveolar lavage from 30 patients with idiopathic pulmonary fibrosis (IPF) and 37 healthy donors (HD). Alveolar macrophages were cultured in the presence of collagen type I, III, IV and V monomers w/wo a neutralizing antibody against scavenger receptor I class A (CD204). Culture supernatants were assayed for the M2 markers CCL18, CCL2, and interleukin-1 receptor antagonist (IL-1ra) by ELISA. Furthermore, expression of phospho-Akt was measured using ELISA and expression of CD204 by RT-PCR and flow cytometry. Stimulation with collagen type I and III monomers significantly up-regulated CCL18, IL-1ra production of alveolar macrophages. Furthermore, expression of CCL2 and CD204 were up-regulated by collagen type I exposure. In addition, collagen type I stimulation increased pospho-Akt expression. Collagen type I effects were abrogated by neutralizing antiCD204 and a non-selective Phosphatidylinositide 3-kinase inhibitor (LY294002). Spontaneous CD204 expression of alveolar macrophages was significantly increased in patients with IPF. In conclusion, our findings demonstrate that monomeric collagen type I via CD204 induces phospho-Akt expression shifting alveolar macrophages to the profibrotic M2 type. Innate immune responses induced by collagen monomers might perpetuate pulmonary fibrosis.     

Electron microscopy and autoradiography study of bronchoalveolar lavage cells in nonspecific pneumonia

Cells obtained by bronchoalveolar lavage from patients with chronic nonspecific pulmonary inflammatory diseases were studied using light and electron microscopy and radioautography. Five morphological forms of alveolar macrophages, distinct in their structure and 3H-uridine content were described. A higher level of RNA synthesis has been revealed in alveolar macrophage forms 2 and 3 than in forms 1, 4 and 5; with it being lower in polymorphonuclear leukocytes and lymphocytes. It was shown that changes in the number of lavage cells and the structure-to-function characteristics in each cellular population depended on the phase of the inflammatory process. It was postulated that structural and metabolic heterogeneity of alveolar macrophages reflected the successive stages of cellular development from cell-precursors (through activation of protein synthesis) to cells with complete lysosomal cycle and the following phagocytosis.     

PU.1 regulation of human alveolar macrophage differentiation requires granulocyte-macrophage colony-stimulating factor

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is critically implicated in lung homeostasis in the GM-CSF knockout mouse model. These animals develop an isolated lung lesion reminiscent of pulmonary alveolar proteinosis (PAP) seen in humans. The development of the adult form of human alveolar proteinosis is not due to the absence of a GM-CSF gene or receptor defect but to the development of an anti-GM-CSF autoimmunity. The role of GM-CSF in the development of PAP is unknown. Studies in the GM-CSF knockout mouse have shown that lack of PU.1 protein expression in alveolar macrophages is correlated with decreased maturation, differentiation, and surfactant catabolism. This study investigates PU.1 expression in vitro and in vivo in human PAP alveolar macrophages as well as the regulation of PU.1 by GM-CSF. We show for the first time that PU.1 mRNA expression in PAP bronchoalveolar lavage cells is deficient compared with healthy controls. PU.1-dependent terminal differentiation markers CD32 (FCgammaII), mannose receptor, and macrophage colony-stimulating factor receptor (M-CSFR) are decreased in PAP alveolar macrophages. In vitro studies demonstrate that exogenous GMCSF treatment upregulated PU.1 and M-CSFR gene expression in PAP alveolar macrophages. Finally, in vivo studies showed that PAP patients treated with GM-CSF therapy have higher levels of PU.1 and M-CSFR expression in alveolar macrophages compared with healthy control and PAP patients before GM-CSF therapy. These observations suggest that PU.1 is critical in the terminal differentiation of human alveolar macrophages.     

Haemosiderin-Laden Sputum Macrophages for Diagnosis in Pulmonary Veno-Occlusive Disease

Aims

Pulmonary veno-occlusive disease (PVOD) is a rare condition of pulmonary arterial hypertension (PAH), in which post-capillary veins are affected. Since the therapeutic approach in PVOD differs from other forms of PAH, it is crucial to establish the diagnosis. Due to the fact that affected patients are often hemodynamically unstable, minimal invasive procedures are necessary for the diagnostic work-up. Chronic alveolar haemorrhage has been observed during bronchoalveolar lavage in PVOD cases. This study therefore investigates whether signs of alveolar haemorrhage can also be found in the sputum of these patients.

Methods and Results

Six patients suffering from PVOD were included in this analysis. As controls, patients with idiopathic PAH (n = 11), chronic thromboembolic PH (n = 9) and with sclerodermia-associated PH (n = 10) were assessed. Sputum from every patient was obtained by a non-invasive manner. The amount of haemosiderin-laden macrophages was determined using the Golde score. There were statistically significant more haemosiderin-laden macrophages in the sputum of patients suffering from PVOD as compared to the other groups (P<0.05). Assuming a cut-off of 200 on the Golde score, all of the 6 PVOD patients surpassed this value compared with only 1 out of the 30 cases with precapillary PH. Thus, sensitivity and specificity with respect to the diagnosis of PVOD was 100% and 97%, respectively.

Conclusion

The content of haemosiderin-laden macrophages in the sputum of patients suffering from PVOD is significantly higher as compared to other forms of PH and may be useful in the non-invasive diagnostic work-up of these patients.     

Changes in the composition of canine respiratory cells obtained by bronchial lavage following irradiation or drug immunosuppression.

Canine respiratory cells, obtained by bronchial lavage, and blood leukocytes were monitored to observe cellular changes following acute and chronic immunosuppression. Irradiation (350 R) produced bone marrow suppression and prompt peripheral blood leukopenia, but did not affect recovery of pulmonary alveolar macrophages or lymphocytes for 12 days after. Treatment for 6 weeks with daily methylprednisolone (1 mg/kg) caused a progressive decrease in the number of recoverable respiratory lymphocytes, whereas alternate day methylprednisolone (2 mg/kg) had less effect. Cyclophosphamide in combination with steroids generally augmented the progressive loss of blood and respiratiory lymphocytes. Recovery of alveolar macrophages was not changed appreciably. Thus, the population of lung macrophages, sampled by pulmonary lavage, withstood acute and chronic forms of immunosuppression very well. In contrast, canine lymphocytes seem more susceptible to injury, especially to drug regimens containing steroids.     

Alveolar macrophages from subjects with chronic obstructive pulmonary disease are deficient in their ability to phagocytose apoptotic airway epithelial cells

Chronic obstructive pulmonary disease is a highly prevalent, complex disease, usually caused by cigarette smoke. It causes serious morbidity and mortality and costs the global community billions of dollars per year. While chronic inflammation, extracellular matrix destruction and increased airway epithelial cell apoptosis are reported in chronic obstructive pulmonary disease, the understanding of the basic pathogenesis of the disease is limited and there are no effective treatments. We hypothesized that the accumulation of apoptotic airway epithelial cells chronic obstructive pulmonary disease in could be due to defective phagocytic clearance by alveolar macrophages. There have been no previous studies of the phagocytic capacity of alveolar macrophages in chronic obstructive pulmonary disease using physiologically relevant apoptotic airway epithelial cells as phagocytic targets. We developed a phagocytosis assay whereby cultured 16HBE airway epithelial cells were induced to apoptosis with ultraviolet radiation and stained with mitotracker green. Alveolar macrophages from bronchoalveolar lavage from eight control and six chronic obstructive pulmonary disease subjects were analysed following 1.5 h incubation with apoptotic airway epithelial cells, then staining with macrophage marker anti CD33. CD33+/mitotracker green + events (i.e., alveolar macrophages which had phagocytosed apoptotic airway epithelial cells) were analysed using flow cytometry. Phagocytosis of polystyrene microbeads was investigated in parallel. A significantly reduced proportion of alveolar macrophages from chronic obstructive pulmonary disease subjects ingested apoptotic airway epithelial cells compared with controls (11.6 +/- 4.1% for chronic obstructive pulmonary disease versus 25.6 +/- 9.2% for control group). Importantly, the deficiency was not observed using polystyrene beads, suggesting that the failure to resolve epithelial damage in chronic obstructive pulmonary disease may result, at least partially, from specific defects in phagocytic ability of alveolar macrophages to ingest apoptotic airway epithelial cells.     

Hemosiderin-laden macrophages in bronchoalveolar lavage fluid.

Diffuse pulmonary hemorrhage syndromes occasionally present diagnostic problems if the clinical picture is not very typical. The presence of hemosiderin-laden alveolar macrophages in bronchoalveolar lavage (BAL) fluid is a useful diagnostic criterion for this entity. However, in many diffuse interstitial pulmonary diseases (DIPD) there is a lesion at the alveolocapillary barrier, and an exit of red blood cells could occur from the blood vessels, leading to the appearance of siderophages. The aim of this work was dual: to evaluate the presence and number of siderophages in different types of interstitial pulmonary disease and to compare the diagnostic yield of two ways of quantifying hemosiderin-laden macrophages. Three groups of patients--controls (n = 5), DIPD (n = 32) and diffuse pulmonary hemorrhage (n = 3)--were subjected to BAL, and a differential count was made on cytocentrifuged Diff-Quik- and Perl-stained preparations. On the latter, two different measurements were made: the number of macrophages laden with hemosiderin and a quantitative "score." The results of a conventional count (percent of Perl-positive macrophages) showed significant differences between the three groups considered overall. Applying a cutoff value of 20%, the sensitivity of this method was 100% and the specificity, 91.6%. The results of the hemosiderin score showed significant differences between the three groups. Applying a value of 50 as a cutoff, the sensitivity and specificity of the method were 100%. In control patients and carriers of DIPD, the percentage of alveolar macrophages was higher than in healthy subjects. Quantification of the hemosiderin content of alveolar macrophages improved the specificity of the diagnosis of diffuse pulmonary hemorrhage by BAL.     

Alterations in rat alveolar surfactant phospholipids and proteins induced by administration of chlorphentermine

Chlorphentermine is a cationic amphiphilic drug which produces a phospholipid storage disorder in rat lungs. Experiments were carried out to characterize changes in the composition of acellular alveolar lavage materials and to study possible mechanisms by which pulmonary surfactant phospholipidosis is produced by administration of the drug. Following ten daily injections of chlorphentermine (25 mg/kg body weight), there are 12.2- and 13.6-fold increases of pulmonary lavage total phospholipids and disaturated phosphatidylcholines (disaturated PC), respectively. In addition, there is a 2.8-fold increase in total protein and a 12.7-fold increase in the surfactant apoprotein group with molecular weights from 28,000 to 32,000. We measured incorporation of labeled palmitate, choline and glycerol into disaturated PC in type II cells and alveolar macrophages isolated from control and chlorphentermine-treated animals. The drug does not affect the incorporation of labeled substrates into disaturated PC in either cell type. However, in alveolar macrophages there is a decrease in the rate of intracellular degradation of recently synthesized disaturated PC in chlorphentermine-treated animals. The drug also inhibits the phospholipase-induced catabolism of rat surfactant disaturated PC which occurs during incubation of alveolar lavage fluid in vitro at 37 degrees C. When the lavage fluid is divided into subfractions by differential centrifugation, a larger percentage of the phospholipid is distributed in the less sedimentable subfractions in chlorphentermine-treated animals relative to controls, suggesting the accumulation of older surfactant materials. These results suggest that chlorphentermine-induced phospholipidosis of pulmonary surfactant materials is due to decreased rates of phospholipid degradation.     

Rapid host defense against Aspergillus fumigatus involves alveolar macrophages with a predominance of alternatively activated phenotype

The ubiquitous fungus Aspergillus fumigatus is associated with chronic diseases such as invasive pulmonary aspergillosis in immunosuppressed patients and allergic bronchopulmonary aspergillosis (ABPA) in patients with cystic fibrosis or severe asthma. Because of constant exposure to this fungus, it is critical for the host to exercise an immediate and decisive immune response to clear fungal spores to ward off disease. In this study, we observed that rapidly after infection by A. fumigatus, alveolar macrophages predominantly express Arginase 1 (Arg1), a key marker of alternatively activated macrophages (AAMs). The macrophages were also found to express Ym1 and CD206 that are also expressed by AAMs but not NOS2, which is expressed by classically activated macrophages. The expression of Arg1 was reduced in the absence of the known signaling axis, IL-4Rα/STAT6, for AAM development. While both Dectin-1 and TLR expressed on the cell surface have been shown to sense A. fumigatus, fungus-induced Arg1 expression in CD11c(+) alveolar macrophages was not dependent on either Dectin-1 or the adaptor MyD88 that mediates intracellular signaling by most TLRs. Alveolar macrophages from WT mice efficiently phagocytosed fungal conidia, but those from mice deficient in Dectin-1 showed impaired fungal uptake. Depletion of macrophages with clodronate-filled liposomes increased fungal burden in infected mice. Collectively, our studies suggest that alveolar macrophages, which predominantly acquire an AAM phenotype following A. fumigatus infection, have a protective role in defense against this fungus.     

Cadherin-11 contributes to pulmonary fibrosis: potential role in TGF-β production and epithelial to mesenchymal transition

Pulmonary fibrosis, characterized by excess deposition of extracellular matrix by myofibroblasts, is a serious component of chronic lung diseases. Cadherin-11 (CDH11) is increased in wound healing and fibrotic skin. We hypothesized that CDH11 is increased in pulmonary fibrosis and contributes its development. CDH11 expression was assessed in lung tissue from idiopathic pulmonary fibrosis patients. The role of CDH11 in lung fibrosis was determined using the bleomycin model of pulmonary fibrosis, and in vitro analyses were performed on A549 cells during the process of epithelial to mesenchymal transition (EMT). Immunohistochemical studies demonstrated CDH11 expression on fibroblasts, epithelial cells, and alveolar macrophages of patients with pulmonary fibrosis and mice given bleomycin. Interestingly, CDH11-deficient mice had decreased fibrotic endpoints in the bleomycin model of pulmonary fibrosis compared to wild-type mice. Furthermore, anti-CDH11-neutralizing monoclonal antibodies successfully treated established pulmonary fibrosis induced by bleomycin. TGF-β levels were reduced in bronchoalveolar lavage (BAL) fluid, BAL cells, and primary alveolar macrophages from CDH11-deficient mice. Mechanistic studies demonstrated that TGF-β up-regulated CDH11 expression on A549 cells, and inhibition of CDH11 expression using siRNA reduced TGF-β-induced EMT. Together, these results identify CDH11 as a novel therapeutic target for pulmonary fibrosis.     

The role of subcellular factors in pulmonary immune function: physicochemical characterization of two distinct species of lymphocyte-activating factor produced by rabbit alveolar macrophages

T cell stimulatory factors produced by rabbit alveolar macrophages were investigated. Physicochemical characterization revealed that alveolar macrophages (harvested by bronchopulmonary lavage and stimulated in tissue culture with bacterial lipopolysaccharide) released 2 predominant species of lymphocyte-activating factor (LAF) with isoelectric points of 4.6 and 7.4, and m.w. of 14,400 and 11,600 daltons, respectively, as calculated by the Svedberg equation. Using C3H/HeJ mouse thymocytes (and in some instances nylon wool-purified nonadherent rabbit spleen or lymph node cells) as target cells, rabbit LAF was found to induce proliferative responses directly, as well as enhance proliferative responses to phytomitogens. Both LAF species were inactivated by heating, treatment with trypsin, or at low (2.3) pH. The pI 7.4 LAF was also unstable at high pH (9.0). The thymocyte stimulatory activity of both LAF species was not inhibited by the anti-proteases alpha-1-anti-trypsin, Traysylol (aprotinin), leupeptin, or pepstatin.     

Alveolar macrophages contribute to alveolar barrier dysfunction in ventilator-induced lung injury

In patients requiring mechanical ventilation for acute lung injury or acute respiratory distress syndrome (ARDS), tidal volume reduction decreases mortality, but the mechanisms of the protective effect have not been fully explored. To test the hypothesis that alveolar macrophage activation is an early and critical event in the initiation of ventilator-induced lung injury (VILI), rats were ventilated with high tidal volume (HV(T)) for 10 min to 4 h. Alveolar macrophage counts in bronchoalveolar lavage (BAL) fluid decreased 45% by 20 min of HV(T) (P < 0.05) consistent with activation-associated adhesion. Depletion of alveolar macrophages in vivo with liposomal clodronate significantly decreased permeability and pulmonary edema following 4 h of HV(T) (P < 0.05). BAL fluid from rats exposed to 20 min of HV(T) increased nitric oxide synthase activity nearly threefold in na?ve primary alveolar macrophages (P < 0.05) indicating that soluble factors present in the air spaces contribute to macrophage activation in VILI. Media from cocultures of alveolar epithelial cell monolayers and alveolar macrophages exposed to 30 min of stretch in vitro also significantly increased nitrite production in na?ve macrophages (P < 0.05), but media from stretched alveolar epithelial cells or primary alveolar macrophages alone did not, suggesting alveolar epithelial cell-macrophage interaction was required for the subsequent macrophage activation observed. These data demonstrate that injurious mechanical ventilation rapidly activates alveolar macrophages and that alveolar macrophages play an important role in the initial pathogenesis of VILI.