A peptide from alveolar macrophages that releases neutrophil enzymes into the lungs in patients with the adult respiratory distress syndrome

The Pathogenic Involvement of Neutrophils in Acute Respiratory Distress Syndrome and Transfusion-Related Acute Lung Injury

The acute respiratory distress syndrome (ARDS) is a serious and common complication of multiple medical and surgical interventions, with sepsis, pneumonia, and aspiration of gastric contents being common risk factors. ARDS develops within 1 week of a known clinical insult or presents with new/worsening respiratory symptoms if the clinical insult is unknown. Approximately 40% of the ARDS cases have a fatal outcome. Transfusion-related acute lung injury (TRALI), on the other hand, is characterized by the occurrence of respiratory distress and acute lung injury, which presents within 6 h after administration of a blood transfusion. In contrast to ARDS, acute lung injury in TRALI is not attributable to another risk factor for acute lung injury. 'Possible TRALI', however, may have a clear temporal relationship to an alternative risk factor for acute lung injury. Risk factors for TRALI include chronic alcohol abuse and systemic inflammation. TRALI is the leading cause of transfusion-related fatalities. There are no specific therapies available for ARDS or TRALI as both have a complex and incompletely understood pathogenesis. Neutrophils (polymorphonuclear leukocytes; PMNs) have been suggested to be key effector cells in the pathogenesis of both syndromes. In the present paper, we summarize the literature with regard to PMN involvement in the pathogenesis of both ARDS and TRALI based on both human data as well as on animal models. The evidence generally supports a strong role for PMNs in both ARDS and TRALI. More research is required to shed light on the pathogenesis of these respiratory syndromes and to more thoroughly establish the nature of the PMN involvement, especially considering the heterogeneous etiologies of ARDS.

Multiple System Organ Failure in the Adult Respiratory Distress Syndrome

Recently completed studies suggest that patients with the adult respiratory distress syndrome (ARDS) manifest early evidence of multiple-site endothelial injury. Ex trapulmonary disease is usually the cause of death in these patients. Furthermore, prognosis in individual cases of ARDS is strongly influenced by specific organ failures (e.g., hepatic and renal failure). The mechanisms by which ARDS and extrapulmonary organ system fail ure interact, however, are poorly delineated. We ad dress three aspects of the multisystemic nature of ARDS. First, we analyze evidence that suggests ARDS is a mul tisystem disorder fron the outset, involving panendothe lial injury mediated by cellular interactions and humoral substances that act similarly at many vascular target sites. Second, we discuss the role of three extrapulmo nary organs in the modulation of ARDS: the liver, the gastrointestinal mucosa, and the kidneys. Third, we ad dress the unifying hypothesis that uncontrolled ongoing inflammation, which is often but not always caused by infection, is the essential link between ARDS and its progression to multiple system organ failure.

Interleukin-8 (IL-8) is a major neutrophil chemotaxin from human alveolar macrophages stimulated with staphylococcal enterotoxin A (SEA)

Since Staphylococcus aureus is an important human pathogen, and infection of the lungs is characterized by neutrophil infiltration we studied the role of a staphylococcal toxin, enterotoxin A (SEA) on the synthesis and secretion of IL-8 by human alveolar macrophages. As SEA concentration was increased, the IL-8 accumulation in the macrophage conditioned medium increased. The concentration of mRNA encoding IL-8 was also elevated in the macrophage in response to increases in SEA concentration. Although the monocytic cell line U937 was able to respond to SEA and secrete IL-8, treatment with PMA prior to SEA stimulation increased the IL-8 accumulation around fifty fold indicating that maturation of the undifferentiated cell to a more macrophage-like cell facilitated IL-8 accumulation. Stimulating human alveolar macrophages with high concentrations of SEA caused an increase in IL-1 accumulation. However, when the cells were incubated with SEA in the presence of IL-1 receptor antagonist, there was no decrease in IL-8 accumulation. Addition of a neutralizing anti-IL-8 monoclonal antibody to the culture medium of SEA-stimulated macrophages significantly reduced the neutrophil chemotactic activity of the medium. These studies showed that IL-8 is a major neutrophil chemotaxin from human alveolar macrophages stimulated with SEA.

IL-8 in pleural effusion

Interleukin-8 (IL-8) is a recently described potent chemotactic factor that may be involved in the pathogenesis of pleural effusions. To understand the actual mechanisms mediating the inflammatory response, changes in cellular components and IL-8 level in pleural fluid of different aetiologies were evaluated. Thirty-four patients (19 male, 15 female) with a mean age of 46 +/- 22 years (range 16-92) were included in the study. Of these, 13 had tuberculous pleural effusion, seven had empyema/parapneumonic pleural effusion, and 14 had malignant pleural effusion (seven adenocarcinoma, three ovarian carcinoma, two lymphoma, one chronic myeloid leukaemia, and one small cell carcinoma) with positive cytology. Differential cell counts in the pleural fluid were obtained using cytocentrifuge preparations. The concentrations of IL-8 in pleural fluid were measured by the ELISA method. Interleukin-8 was detected in all 34 pleural fluid samples. The serum IL-8 level was analysed only in the empyema/parapneumonic pleural effusion group. The mean IL-8 levels of tuberculous, empyema/parapneumonic, and malignant pleural effusions were 1420 +/- 1049 pg ml-1, 4737 +/- 2297 pg ml-1, and 1574 +/- 1079 pg ml-1, respectively. The IL-8 levels in the empyema/parapneumonic group were significantly raised over malignant and tuberculous groups (P < 0.02). The mean pleural fluid neutrophil counts in tuberculous, empyema/parapneumonic and malignant pleural effusions were 315 +/- 575 cells mm-3, 11,136 +/- 12,452 cells mm-3, and 635 +/- 847 cells mm-3, respectively (P < 0.003). There was a significant positive correlation between pleural IL-8 levels and neutrophil counts (r = 0.46, P < 0.006). The levels of IL-8 in paired samples of serum and pleural fluid in the empyema/parapneumonic effusion group were compared, and the concentration of IL-8 was higher in the pleural effusion than serum (means, 4737 +/- 2297 pg ml-1 and 130.0 +/- 62.5 pg ml-1, respectively, P < 0.03). There was a significant negative correlation between IL-8 concentrations in serum and pleural fluid (r = -0.80, P < 0.03). This data suggests that production of IL-8 in pleural effusion may play a key role in initiation and maintenance of inflammatory reactions, especially in empyema/parapneumonic pleural effusions. It may offer the basis for introduction of novel anti-inflammatory agents in treatment.

A synthetic peptide which specifically inhibits heat-treated interleukin-8 binding and chemotaxis for neutrophils

Interleukin-8 (IL-8) is a peptide which is secreted by stimulated human monocytes and which is chemotactic for human neutrophils. We synthesized three overlapping peptides spanning the amino-terminal region of the IL-8 sequence. None of the peptides retained the chemotactic activity of the native molecule. One of the peptides, IL-8(3-25), inhibited the neutrophil chemotactic activity of recombinant IL-8 (rIL-8) which had been preheated to 40 degrees C but did not reduce neutrophil chemokinesis, or the chemotactic activity of unheated rIL-8, FMLP, C5a or LTB4. Interleukin-8 exhibited similar binding kinetics and chemotaxis for neutrophils regardless of whether it had been pretreated at 40 degrees C. In addition, IL-8(3-25) was also able to decrease the binding of preheated IL-8 to neutrophils. IL-8(3-25), which can self-associate, binds directly to receptors on the neutrophil. The data suggest that heat-treated, but not untreated, IL-8 causes the IL-8(3-25) multimers to disaggregate, allowing the monomeric peptide to directly bind to the IL-8 receptor and thus inhibiting IL-8/receptor binding.

High levels of interleukin-8 in the blood and alveolar spaces of patients with pneumonia and adult respiratory distress syndrome

There is ample experimental evidence that polymorphonuclear neutrophils (PMN) play a critical role in the pathogenesis of the adult respiratory distress syndrome (ARDS). Since interleukin-8 (IL-8) is a strong chemotactic factor for PMN, we measured IL-8 levels in plasma and bronchoalveolar lavage (BAL) fluid of 18 patients, 12 with ARDS and 6 with severe pneumonia uncomplicated by ARDS, all of whom had an increased number of PMN in BAL fluid. Seven healthy subjects served as controls. We found elevated levels of IL-8 in the alveolar spaces of all patients tested. Elevated BAL IL-8 levels were related to a fatal outcome and the presence of shock and correlated with a general clinical severity index (simplified acute physiological score). BAL fluid levels of IL-8 were significantly higher in patients with ARDS than in patients with pneumonia. In plasma, IL-8 levels were increased similarly in all patients and did not correlate with survival or the presence of shock. The BAL fluid-to-plasma ratio of IL-8 was significantly greater than that of tumor necrosis factor alpha, indicating higher local production of IL-8. Moreover, the presence of a primed subpopulation of blood PMN with respect to H2O2 production indicates that IL-8 may contribute to the neutrophil-mediated process in the pathogenesis of ARDS and pneumonia.

New perspectives on basic mechanisms in lung disease. 6. Proteinase imbalance: its role in lung disease

The hypothesis, some 30 years ago, that NE was the sole proteolytic agent responsible for the development of emphysema seems naive in retrospect. The availability of technology to measure NE facilitated the early research into the relationship between NE and lung disease. Despite an abundance of information on the activity of NE in the lung, it will probably require prospective studies in man with specific NE inhibitors or control at the gene level to establish a causal relationship between NE and lung disease. Parallel research has resulted in the isolation and characterisation of NE inhibitors other than PI and, indeed, alternative proteolytic enzymes that might contribute to lung disease. It is perhaps impossible now to think that a single proteinase, however omnipotent it may be, causes lung diseases as diverse as emphysema and fibrosis. An important aspect that is emerging is the interrelationship between proteolytic enzymes produced by different, or sometimes the same, cells that could potentiate tissue proteolysis. The evidence suggests that there is likely to be coordinated action between neutrophils, macrophages, and possibly mesenchymal proteinases which can activate or inactivate each other. In addition, one class of proteinases often appears able to proteolytically inactivate inhibitors of the opposite class, which presumably could amplify proteolysis if it occurred in vivo. Although the work on this aspect of proteinase activity is in its infancy, one suspects that part of the normal regulation of proteinase activity might include compartmentalisation. For example, the neutrophil stores proteinases before appropriate release and can inactivate PI to enable proteolytic action pericellularly, whereas degradation of extracellular matrix by macrophages requires interaction between the cell and matrix which is facilitated by cell receptor bound uPA. Disintegration of these "compartments" due to oedema, proteolysis, or for mechanical reasons could, firstly, expose further extracellular matrix substrates to inflammatory and damaged cell proteinases but, secondly, might enhance proteinase potential by the cooperative action of these enzymes. It seems increasingly likely that, where proteinases play a part, there is a cocktail of proteinases that is characteristic of the injury that develops (fig). What remains unclear is why only a proportion of those susceptible, such as smokers or those with acute lung injury, develop irreversible lung disease. This suggests that there are other factors acquired or inherited that need to be considered.

Immunologic therapy for ARDS, septic shock, and multiple-organ failure

Advances in cytokine biology and molecular biology have led to the development of novel immunologic approaches to the treatment of septic shock, ARDS, and MOF. These advances are necessary since improvements in supportive care clearly fall short of the hoped-for reductions in mortality associated with these disorders. As noted in this review, these new therapies are directed at three distinct levels of the inflammatory cascade: (1) the inciting event or insult (eg, endotoxin); (2) the mediators (eg, TNF, IL-1); and (3) the effector cells (eg, neutrophils). The current status of these treatments has been reviewed; and while each individual therapy has shown potential, it is likely that combinations of these agents may be necessary to substantially impact on survival. That is, due to the complexity and redundancy of the inflammatory network, it is doubtful that a "magic bullet" will be found. However, it is also clear that advances in our understanding of the pathogenesis of ARDS, septic shock, and MOF at the molecular level have provided clinicians with powerful weapons with which to do battle. It remains to be seen which ones will work the best.

Consequences of unbalanced protease in the lung: protease involvement in destruction and local defense mechanisms of the lung

Complex mechanisms regulate sequestration, retention and migration of neutrophils in the lung. Neutrophils can migrate into the lung without producing significant damage under some circumstances, whereas at other times great structural alteration occurs. A potential explanation lies in the phenomenon of priming, a state of altered responsivity of neutrophils. A wide variety of molecules are able to induce this higher degree of responsiveness including PAF, TNF, GM-CSF, and IL-1. Enhanced cellular responses include secretion, adhesion and synthetic function. Unprimed neutrophils can migrate through lung tissues, secreting but little of their contents, in the context of "normal" inflammatory response. On the other hand neutrophils primed before the emigration phase, injury to the tissue they are migrating through would be likely by virtue of releasing toxic mediators. One of these mediators is neutrophil elastase, a potent protease. It is the purpose of this review to highlight the duality function of neutrophils as (i) one of the bodies highly effective host defense weapons and (ii) mediator of destruction and host defense impairment in the lung by releasing mediators such as neutrophil elastase.

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

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

Interleukin-8 in sepsis: relation to shock and inflammatory mediators

Because of its neutrophil-activating properties, interleukin-8 (IL-8) may play an important role in the pathophysiology of sepsis. We measured circulating IL-8 levels in 47 patients with clinical sepsis. Levels on admission were elevated in 42 of the 47 patients (89%) and were comparable in patients with gram-positive or gram-negative infections. Patients with shock had significantly higher IL-8 levels than normotensive patients (P = 0.0014, Wilcoxon-Mann-Whitney test), whereas no differences in IL-8 levels were found between patients with or without adult respiratory distress syndrome. Patients who died had higher IL-8 levels on admission than the patients who survived. The largest differences in IL-8 levels between survivors and nonsurvivors was found when only patients with positive cultures were considered (P = 0.0342). IL-8 levels appeared to correlate significantly with lactate levels and inversely with leukocyte and platelet numbers and mean arterial pressure. In addition, the IL-8 level in the sepsis patients was found to correlate significantly with levels of IL-6, elastase-alpha 1-antitrypsin, and C3a. Serial observations revealed that in most patients IL-8 levels decreased, irrespective of the outcome. Thus, our results demonstrate that IL-8 levels are increased in most patients with sepsis and correlate with some important clinical, biochemical, and inflammatory parameters. These findings suggest a role for IL-8 in the pathophysiology of sepsis.

Sandwich ELISA for detection of picogram quantities of interleukin-8

A sensitive sandwich enzyme-linked immunosorbent assay (ELISA) was developed for interleukin-8 (IL-8), a neutrophil chemoattractant and activator. A polyclonal antibody to recombinant human IL-8 was raised in rabbits, and the IgG was isolated from the antisera using a protein A column. Native and biotinylated forms of this antibody served as the capture antibody and developing antibody for the ELISA, respectively, and avidin-conjugated horse radish peroxidase provided the means for enzymatic color development. The lower limit of sensitivity for the assay was found to be 84 +/- 20 pg/ml IL-8 (mean +/- SD for 10 determinations). An inter-assay variability of 15-29% and an intra-assay variability of 12% were observed. The assay was able to detect IL-8 when the samples were prepared in either normal saline, RPMI, or human plasma. The development of this rapid, sensitive assay should provide a means to more fully evaluate the role of this cytokine in diverse disease states.

Synthesis and secretion of high- and low-molecular-weight forms of the enzyme-releasing peptide (ERP) from the macrophage-like cell line THP-1

Neutrophil enzymes have been implicated as a source of lung injury in patients with the adult respiratory distress syndrome (ARDS) and with emphysema. We studied a human alveolar macrophage-derived peptide messenger, the enzyme-releasing peptide (ERP), which causes neutrophils to secrete their enzymes. The secretion and synthesis of ERP was studied in human alveolar macrophages and in the macrophage-like cell lines THP-1, HL-60, and U937. All four cell types secrete an ERP-like peptide. THP-1 cells secrete a higher concentration of the peptide than do macrophages. The secretion of ERP by THP-1 is suppressed by the protein synthesis inhibitors actinomycin D and cycloheximide. While the macrophages secrete ERP, they do not synthesize it. These studies suggest that ERP is synthesized by an alveolar macrophage precursor and stored in the mature macrophage for later release. 12-O-tetradecanoylphorbol-13-acetate (TPA) suppresses ERP secretion by THP-1 cells, but it does not modify secretion in macrophages. Escherichia coli-derived lipopolysaccharide and dimethyl sulfoxide do not modify secretion in either cell type. The THP-1 cells secrete a high- and low-mass-ratio (Mr) form of ERP-like proteins. The low Mr but not the high Mr form stimulates neutrophils to secrete their granule enzymes. We conclude that human alveolar macrophages secrete ERP but do not synthesize it. It is likely that ERP is made by an alveolar macrophage precursor in a high Mr form that is cleaved prior to secretion by the macrophages.

Expression of 9E3 mRNA is associated with mitogenicity, phosphorylation, and morphological alteration in chicken embryo fibroblasts

Transformation of chicken embryo fibroblasts (CEF) with viruses encoding src, ros, yes, and fps as well as ras, mos, middle T, erbA and erbB, myc, and crk stimulated 9E3 mRNA expression. Treatment of CEF with agents that modulate cell shape or attachment to the substratum caused an increase in 9E3 mRNA without an increase in tyrosine phosphorylation. 9E3 mRNA was also increased in CEF in response to several agents which modulate phosphorylation, including phorbol myristic acetate, vanadate, and okadaic acid, which suggests that the rapid induction of 9E3 mRNA expression in CEF by the src protein occurs downstream of morphological or phosphorylation events.

Expression of 9E3 mRNA is associated with mitogenicity, phosphorylation, and morphological alteration in chicken embryo fibroblasts

Transformation of chicken embryo fibroblasts (CEF) with viruses encoding src, ros, yes, and fps as well as ras, mos, middle T, erbA and erbB, myc, and crk stimulated 9E3 mRNA expression. Treatment of CEF with agents that modulate cell shape or attachment to the substratum caused an increase in 9E3 mRNA without an increase in tyrosine phosphorylation. 9E3 mRNA was also increased in CEF in response to several agents which modulate phosphorylation, including phorbol myristic acetate, vanadate, and okadaic acid, which suggests that the rapid induction of 9E3 mRNA expression in CEF by the src protein occurs downstream of morphological or phosphorylation events.

Reactive type II pneumocytes in bronchoalveolar lavage fluid from adult respiratory distress syndrome can be mistaken for cells of adenocarcinoma

A growing body of literature illustrates that bronchoalveolar lavage is a reliable and efficient means of diagnosing primary and secondary malignancies in the lung. Its safety in severely compromised patients often makes it preferable to other biopsy procedures. However, a variety of reparative and degenerative pulmonary disorders may result in cytologic alterations so severe that pneumocytes resemble cells of malignancy. We describe four patients with the adult respiratory distress syndrome from whom lavage fluid showed gland-like groups of malignant-appearing cells morphologically consistent with adenocarcinoma. Transbronchial biopsy sections in one case and lavage fluid electron microscopy in another showed that these pseudomalignant cells were reactive Type II pneumocytes with surface microvilli, cell junctions, and numerous cytoplasmic myelin figures. Careful clinicopathologic correlation is the best way to ensure accurate diagnosis in these cases.

Search for drugs that may reduce the load of neutrophil azurophilic granule enzymes in the lungs of patients with emphysema

Neutrophil elastase and myeloperoxidase probably play an important role in the development of pulmonary emphysema. We have analyzed drugs from the major classes of agents that alter neutrophil function to determine if there are drugs in use today that can reduce the load of neutrophil elastase or myeloperoxidase in the lungs of smokers. Eleven representative drugs were tested for their ability to inhibit chemotaxis and degranulation. None of the drugs inhibited chemotaxis in a dose-response fashion at concentrations achievable in human plasma. Sulfinpyrazone, phenylbutazone, and auranofin completely inhibited the release of azurophilic granules (myeloperoxidase) and tertiary granules (beta-D-glucuronidase) when formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) was used as the stimulant, and inhibited azurophilic granule release by 69%, 19%, and 64% respectively, but not tertiary granule release when macrophage-conditioned media was used as the stimulus. In conclusion, none of the drugs tested are inhibitors of chemotaxis; however, three are excellent inhibitors of azurophilic granule enzyme release. Of these three, sulfinpyrazone, a drug that is not currently used clinically for its antiinflammatory effects, is the least toxic and should be considered as a potential drug to reduce the elastase and myeloperoxidase load in the lungs of smokers who are developing emphysema.