Role of complement activation in a model of adult respiratory distress syndrome

Inhibition of human polymorphonuclear leukocyte functions by ibuprofen

We have found that pretreatment of human neutrophils with ibuprofen (0.10-1.0 mg/ml) results in an irreversible, concentration-dependent inhibition of superoxide anion generation and release of lysosomal enzymes (myeloperoxidase, lysozyme) stimulated by the synthetic peptide, N-formyl-methionyl-leucyl-phenylalanine (FMLP), the complement fragment C5a, and to a lesser extent by serum opsonized zymosan. Inhibition of granule exocytosis and oxygen radical generation at ibuprofen concentrations less than 5 mg/ml was not due to drug cytotoxicity since release of the cytoplasmic enzyme lactate dehydrogenase was not affected by ibuprofen. In contrast to neutrophil responses mediated by C5a or FMLP, ibuprofen did not inhibit either enzyme release or superoxide anion generation by neutrophils stimulated with phorbol myristate acetate. Ibuprofen did not function as an oxygen radical scavenger in a cell-free system in which superoxide anion was generated by the aerobic action of xanthine oxidase on hypoxanthine. Ibuprofen also inhibited in a concentration-dependent fashion both directed migration (chemotaxis) and stimulated random migration (chemokinesis) of neutrophils exposed to either FMLP or C5a. Inhibition of neutrophil adherence to plastic surfaces and bovine pulmonary artery endothelial cells was equally effective when the neutrophils were treated with ibuprofen before stimulation with FMLP or phorbol myristate acetate. The inhibitory effects of ibuprofen pretreatment of neutrophils could not be overcome by addition of prostaglandins E1 or E2 (0.3-300 nM). These results demonstrate that ibuprofen is capable of suppressing many functions thought to be important in neutrophil-mediated acute pulmonary inflammatory processes. Results of these experiments further suggest that ibuprofen may inhibit neutrophil functions by acting on cellular components separate from membrane receptors or by blockade of cyclo-oxygenase products which may be involved in these neutrophil functions.

Current perspectives on septic shock

Although septic shock may be initiated by invading microbes, it is the metabolic and immunologic host responses that determine the true pathophysiology of this common critical care illness. Currently, septic shock therapeutics emphasize empiric and symptomatic treatment. Biochemical elucidation of the septic process will ultimately result in specific interventions for this ominous intensive care syndrome.

Evaluation of low dose anaphylatoxic peptides in the pathogenesis of the adult respiratory distress syndrome (ARDS). Monitoring of early C5a effects in a guinea-pig in vivo model after i.v. application

A guinea-pig in vivo model is presented that allows the infusion of purified C5a via a central vein catheter and the monitoring of its effects on granulocytes and platelets, the most important cells in the pathogenesis of several lung disorders, e.g. shock lung. After the infusion of C5a, which was adjusted to a quantity that caused slight and transient alterations of lung physiology, granulocytes disappeared from circulation within 1 min. Simultaneously the granulocyte content of the lung increased about three-fold as judged by histological evaluations. Morphologic destructions were not observed. After the drop a rebound of circulating Polymorpho-nuclear leucocytes (PMN) occurred, which was significantly higher than control values and the appearance of banded cells indicated a mobilization from bone marrow stores. Studies with 51-chromium labelled PMNs revealed that most, but not all, of the granulocytes returned to circulation after transient sequestration. The number of platelets also decreased after C5a infusion, but the rebound was delayed compared with the PMNs and did not exceed control values. The changes in circulating cells, lung histology, and lung physiology are comparable to those occurring during the onset of shock lung and thus strengthen the supposed importance of C5a concerning the pathogenesis of that syndrome.

The effect of enkephalins and prostaglandins on O-2 release by neutrophils

Derivatives of superoxide (O-2), produced by phagocytic cells, are thought to play a role in the adult respiratory distress syndrome (ARDS) and other disease states. Control of the release of O-2 may prove beneficial. Using human neutrophils as a source of O-2, and an assay for O-2 based upon the reduction of cytochrome C, we found that prostaglandin D2 (PGD2), leucine enkephalin (LE), and methionine enkephalin (ME) inhibited O-2 release. The Escherichia coli product, N-formyl methionyl leucyl phenylalanine (FMLP), was employed to stimulate O-2 release. PGD2 was most potent while there was no significant difference between LE and ME. Another peptide, thyrotropin releasing hormone (TRH), had no effect on O-2 release. There was no correlation between the potency of the inhibitory effect on O-2 release and the effect of these agents on the binding of [3H] FMLP to human neutrophils. Comparison of different but structurally related prostaglandins (PGD2, PGE2, and PGF2 alpha) revealed that PGD2 was more potent than PGE2 in inhibiting O-2 and that PGF2 alpha had no effect. This result suggested that the presence and position of the carbonyl group was an important determinant of the magnitude of inhibition.

Bacteriology of the closed duodenal loop model of acute pancreatitis and ultrastructural changes induced in the lungs

Injection of infected human bile into a closed duodenal loop in the rat consistently produces lethal pancreatitis with severe pulmonary damage. Lung abnormalities, resembling the human adult respiratory distress syndrome (ARDS) are frequently seen in this model and are usually ascribed to the pancreatitis. Similar pulmonary problems are seen in the human form of acute pancreatitis. Recently, it has been suggested, that the lung changes in the experimental animal are more likely to be due to bacteremia than to the pancreatitis. The aim of this study was to determine whether bacteremia occurred in this model, and if so, to determine whether bacteremia alone, in the absence of pancreatitis could produce this lung damage. A group of rats underwent induction of acute pancreatitis by a closed duodenal loop method and were compared to two groups comprising a closed small bowel loop bile infusion preparation, isolated from the pancreas, and a control group of rats undergoing a "sham" gastrotomy. Both pancreatitis and closed small bowel groups of animals were found to be bacteremic when sacrificed at 6 hr. The lungs from the animals with pancreatitis were significantly heavier than those in the other groups and scanning electron micrographs of the lungs in pancreatitis showed gross abnormalities, with marked increases in the alveolar wall thickness. The lungs in the closed small bowel loop preparation were indistinguishable from a control sham gastrotomy group of non-bacteremic rats. These results indicate that although the closed duodenal loop model of pancreatitis produces bacteremia, pancreatitis is necessary for development of pulmonary abnormalities.

Effect of aprotinin in adult respiratory distress syndrome

The possible beneficial effect of aprotinin, a broad protease inhibitor, on the incidence and outcome of ARDS was examined in two complementary studies. In the first study, the effect of aprotinin was assessed in 147 patients admitted with multiple trauma or shock. In the 57 patients who developed ARDS, mortality was significantly less in those who had previously received aprotinin (8/20, 40%) than in those who had not (26/37, 70%). Although both treatment groups were well matched, this was a retrospective study and a second prospective, randomised, controlled study was therefore carried out. In 78 patients at risk of ARDS, there was no significant difference between treated and control patients in the incidence, duration or severity of ARDS, or in mortality or other major complications. It is concluded that aprotinin is not effective in improving any aspect of ARDS or its outcome in seriously ill patients.

Effects of ibuprofen on chemotactic peptide-receptor binding and granulocyte response

Inhibition of complement-mediated granulocyte aggregation has been proposed recently as a mechanism of action of high-dose corticosteroids and ibuprofen in shock states. Such inhibition by corticosteroids may be effected through alteration of receptor function, and we have therefore examined the effect of ibuprofen on the extent and kinetics of binding of the synthetic chemotactic peptide formylmethionine-leucine-phenylalanine (FMLP) to its specific receptor on the granulocyte surface. Dose-dependent inhibition of binding was observed at ibuprofen concentrations paralleling plasma levels achieved with 30 mg/kg intravenous bolus therapy, and also at concentrations achieved with oral therapy. Ibuprofen did not affect the receptor number, but did decrease the association rate constant for the FMLP-receptor interaction (30% of normal for 0.125 mg/ml ibuprofen), leading to a decrease in receptor affinity for ligand. Dissociation kinetics, as determined by cold chase experiments, were unaltered by ibuprofen. We conclude that ibuprofen, like corticosteroids, can slow the rate of association of FMLP with its receptor on the granulocyte surface while allowing dissociation to proceed; altered kinetics of receptor-FMLP interaction may explain the inhibition of granulocyte aggregation. Blockade of granulocyte surface receptors for inflammatory stimuli may be important in the clinical effects of very high-dose corticosteroids and ibuprofen such as are administered in shock; such effects are seen at blood levels of ibuprofen that occur with oral therapy. Similar observations may hold for other physiologic stimuli.

Continuous intravenous infusion of elastase in normal and agranulocytic minipigs--effects on the lungs and the blood coagulation system

In order to investigate the acute effects on lung morphology, lung function, hemodynamic and blood coagulation system, elastase (330 units (U) kg-1 h-1) was continuously infused into 16 anesthetized and mechanically ventilated minipigs. Elastase infusion induced a disturbance of blood coagulation leading to hypocoagulability, a pulmonary leukostasis, interstitial edema, a progressive respiratory failure with prompt increase in pulmonary vascular resistance, decrease in systemic vascular resistance, increased venous admixture, and increased dead space ventilation. Agranulocytosis prevented interstitial edema but not disturbances in pulmonary or hemodynamic function or hypocoagulability. The results clearly indicate that elastase may be involved in the pathophysiology of acute lung failure and defects in the blood coagulation system.

Adult respiratory distress syndrome in patients with severe neutropenia

Most investigators believe that the pulmonary endothelial damage that is characteristic of the adult respiratory distress syndrome (ARDS) requires the action of neutrophils. In a retrospective review of patients with ARDS, we looked for cases that had developed in patients who already had neutropenia. Four clinical criteria were required for the diagnosis of ARDS: the occurrence of a precipitating event, diffuse bilateral pulmonary infiltrates on a chest x-ray film, a normal intravascular volume (as reflected by a wedge pressure of less than 18 mm Hg), and arterial hypoxemia. During 2 1/2 years, 11 patients fulfilled these clinical criteria, had severe neutropenia that antedated the onset of ARDS, and had pulmonary histologic specimens obtained during the early stages (less than seven days) of clinical respiratory distress. Five of these specimens showed diffuse alveolar damage without evidence of infectious pneumonitis (the histopathological finding characteristic of ARDS), and none had a neutrophil infiltrate. We conclude that ARDS can occur in the setting of severe neutropenia, without pulmonary neutrophil infiltration.

Effects of anti-C5a antibodies on the adult respiratory distress syndrome in septic primates

In vitro and in vivo studies have suggested that human complement component C5a plays a key role in neutrophil injury in the adult respiratory distress syndrome (ARDS). First, using leukocyte aggregometry, we demonstrated that the addition of a recently developed rabbit anti-human polyclonal antibody to C5a des arg to endotoxin-activated plasma prevented leukocyte aggregation in vitro. We then administered the anti-C5a des arg antibody to septic primates (Macaca fascicularis). Three groups of primates, control, septic, and anti-C5a antibody treated septic, were studied (n = 4 in each group). A 30-min infusion of Escherichia coli (1 X 10(10)/kg) resulted in severe sepsis and ARDS. Primates were killed 4 h after completion of the E. coli infusion. Septic animals not treated with anti-C5a antibody had 75% mortality (3/4), decreased oxygenation, severe pulmonary edema, and profound hypotension. Septic primates treated with anti-C5a antibodies did not die and did not develop decreased oxygenation (P less than 0.05) or increased extravascular lung water (P less than 0.05). They also had a marked recovery in their mean arterial blood pressure (P less than 0.05). This study demonstrates that treatment with rabbit anti-human C5a des arg antibodies attenuates ARDS and some of the systemic manifestations of sepsis in nonhuman primates.

Adult respiratory distress syndrome in neutropenic patients

The precise pathophysiologic mechanisms that cause the adult respiratory distress syndrome are unknown. Indirect evidence from human studies and extrapolations from animal models have suggested that phagocytic neutrophils are important in the pathogenesis of this disease. To further evaluate the role of neutrophils, the frequency of neutropenia in 18 bacteremic patients who had the adult respiratory distress syndrome was compared with that in a control group who had bacteremia alone. Three of 18 patients in the group with the adult respiratory distress syndrome were neutropenic as opposed to one of 18 in the control group (p greater than 0.6). Histologic examination of the lungs from two patients with the adult respiratory distress syndrome and neutropenia demonstrated the absence of neutrophils. It is likely that there are many pathways that lead to the adult respiratory distress syndrome. Although neutrophils may be involved in some of these processes, this study demonstrates that neutrophils are not required for the development of the syndrome. In the appropriate clinical setting, the diagnosis of the adult respiratory distress syndrome should not be excluded solely because of neutropenia.

Oxidant activity in expired breath of patients with adult respiratory distress syndrome

Hydrogen peroxide levels were measured in the breath condensate of 43 patients receiving mechanical ventilation. In 16 patients the mean breath condensate peroxide level was 1.68 +/- 0.35 mumol/l on the day they met diagnostic criteria for adult respiratory distress syndrome (ARDS). The peak breath condensate peroxide level in the 27 patients in whom ARDS did not develop was significantly lower (0.34 +/- 0.08 mumol/l). Plasma lysozyme, a measure of in-vivo neutrophil turnover, was significantly higher in ARDS than in non-ARDS patients (9.2 +/- 2.2 U/ml v 3.4 +/- 1.1 U/ml). These findings support the hypothesis that neutrophil activation and oxidant production are involved in the pathogenesis of ARDS.

Complement levels and C3 breakdown products in open-heart surgery: association of C3 conversion with the postpericardiotomy syndrome

The role of the complement system in the pathogenesis of the post-pericardiotomy syndrome (PPS) was evaluated in a prospective study by measuring the levels of complement (C) components, total haemolytic complement activity and circulating C3 breakdown products in serial plasma and serum samples of 45 patients undergoing open-heart surgery. A consistent reduction in the levels of C3 and C4 but not of factor B was seen on the second post-operative day. During the second post-operative week the antigenic levels of each C component increased significantly. At this time six patients developed the post-pericardiotomy syndrome. Circulating C3 conversion products (C3bi and C3c) were demonstrated in the plasma samples from five of these patients by the immunofixation technique, the mean conversion percentage being 14.3 +/- 10.6. The samples from 15 of the 39 other patients also showed C3 conversion, but the mean percentage was significantly lower (4.5 +/- 6.1%, P less than 0.05). Before the second post-operative week C3 conversion was rare in both groups. The C3d levels of plasma samples, as detected by rocket immunoelectrophoresis, followed a similar pattern. Reduced total haemolytic complement activity was found in three patients suffering from the PPS. These results suggest a role for complement in the non-infectious, inflammatory response during the late post-operative period after open heart surgery, and especially in the post-pericardiotomy syndrome.

Contribution of complement component C5 to the pathogenesis of experimental murine cryptococcosis

C5-deficient (C5-) mice succumb much sooner after intravenous inoculation with Cryptococcus neoformans than do C5-sufficient (C5+) mice. The C5- mice developed acute, fatal cryptococcal pneumonia, whereas the C5+ mice did not. The pneumonia was characterized by lung viable counts in C5- mice up to 1000-fold higher than in C5+, initial sequestration of twice as much 59Fe-labeled C. neoformans, and subsequent development of pulmonary edema. Chemotaxis of heterophils (PMNs) and mononuclear cells in response to C. neoformans was markedly greater in C5+ mice than in C5- animals. The effect of C5 on localization and growth of C. neoformans in the lung appeared to account for the disparate survival times of C5+ and C5+ mice after intravenous inoculation with C. neoformans.

Leukocyte complement: interleukin-like properties of factor Bb

It has been previously shown that the activated form of Factor B (Factor Bb) of the alternative pathway of complement activation stimulates monocyte spreading and killing of xenogenic erythrocytes and staphylococci. Factor Bb also stimulates lymphocyte blastogenesis in vitro, and native (uncleaved) Factor B is a major constitutive product of murine macrophages. To evaluate the possible "monokine" or "lymphokine"-like properties of Factor Bb, a radioimmunoassay was developed to measure the quantities of Factor B in phytohemagglutinin (PHA)-mitogen-stimulated cultures of human peripheral blood mononuclear cells. Nonstimulated mononuclear cell cultures from human peripheral blood (containing 10-14% monocytes and greater than 85% lymphocytes) at a density of 3 X 10(6) cells/ml (in serum-free medium) released less than 7 X 10(-10) M/liter (60 ng/ml) of Factor B antigen in 24 hr at 37 degrees C, and when mononuclear cells were stimulated with PHA mitogen in serum-free medium, the levels of Factor B antigen in media at 24 hr were significantly higher 1-3 X 10(-8) M/liter (0.9-2.8 micrograms/ml). The molecular size of Factor B in these media was 50-65 kDa by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a size appropriate for Factor Bb (60 kDa). Since pathological effects of macrophages in autoimmune disease may result from the release of lysosomal hydrolases, the effects of purified Factor Bb on mononuclear phagocytes were investigated in an in vitro system of murine peritoneal exudate macrophages. Factor Bb induced secretion of marker lysosomal hydrolases N-acetyl-beta-D-glucosaminidase (hexosaminidase) and beta-glucuronidase from thioglycollate-elicited murine peritoneal exudate macrophages in a dose-response and kinetic manner. Hydrolase release was induced in serum-free medium without a known particulate activator at a concentration of 80-200 nM (5-13 micrograms/ml) Factor Bb. Maximal release occurred in 3-5 hr at 37 degrees C and extracellular enzyme activity of hexosaminidase and glucuronidase increased as intracellular enzyme levels decreased, suggesting that Factor Bb triggers release of these enzymes from intracellular lysosomal pools. These results provide an example of a complement protein which is synthesized, released, and activated during mononuclear cell culture and which induces release of lysosomal enzymes from macrophages. In conventional terminology, Factor B or Factor Bb might be termed a "lymphokine," "monokine," or "interleukin".

The role of polymorphonuclear leucocytes in the pulmonary dysfunction induced by complement activation

To determine the role of polymorphonuclear leucocytes (PMNs) in the pulmonary reaction induced by complement activation, pigs were infused with complement-activated plasma (CAP), cell-free supernatant from PMNs activated in vitro, or washed PMN aggregates produced in vitro. Infusion of CAP resulted in transient peripheral leucopenia, a reversible rise in pulmonary vascular resistance (PVR) and decreased arterial oxygen tension (PaO2). Indomethacin did not influence the CAP-induced drop in PMN count or the accumulation of PMNs in the lung, but significantly counteracted the rise in PVR and fall in PaO2. Antihistamines did not prevent the cellular or pulmonary reactions to CAP infusion. Methylprednisolone did not inhibit the decrease in PMN count, but modified the pulmonary reaction to CAP, although it did not prevent the rise in PVR to the same extent as indomethacin; it counteracted the fall in PaO2. Infusion of supernatant from activated PMNs did not influence the PMN count, but caused a reversible increase in PVR and a drop in PaO2. Indomethacin counteracted the pulmonary reaction to this infusion. Infusion of washed PMN aggregates did not result in any cellular or physiological changes. These findings suggest that the pulmonary reaction induced by complement activation is mediated by humoral components generated and/or released during activation of PMNs. Arachidonic acid metabolites play an important role and it is likely that substance(s) released from activated PMNs trigger prostanoid synthesis in other cells. It is conceivable, however, that PMNs exposed to activated complement factors also directly synthesize and release arachidonic acid metabolites.

The adult respiratory distress syndrome

The adult respiratory distress syndrome (ARDS) is a common form of acute respiratory failure that has been increasingly reported as associated with a wide variety of medical conditions. Unlike other identifiable pathological events causing severe lung injury, it is now recognized that ARDS is not a single disease, but a complex interaction of pathophysiological events that result in diffuse injury to lung parenchyma. Only through a thorough understanding of ARDS pathophysiology, pathogenesis, and clinical course can medical intervention be instituted in a judicious and timely manner. This review article is intended to provide an overview of the suspected precipitating causes, discrete pathophysiologic changes, and monitorable clinical events associated with ARDS. With mortality from ARDS high, significant attention is being given to improving therapeutic intervention with such conventional measures as mechanical ventilation, positive end-expiratory pressure, and fluid management, along with corticosteroids and several new experimental pharmacologic approaches.

Interactions of granulocytes with the lungs

Under normal conditions, there is a sizeable pool of marginated granulocytes in the lung circulation which is in dynamic equilibrium with the circulating granulocyte pool. The number of granulocytes in the lungs' microcirculation may depend on pulmonary blood flow or biochemical interactions between granulocytes and pulmonary vascular endothelium, or both. There is some evidence that normal lung function may be affected by granulocytes. Several acute and chronic diseases may result, at least in part, from interactions of granulocytes with the lungs. Acute diffuse lung injury (adult respiratory distress syndrome) is characterized by diffuse pulmonary inflammation, and, in animal models, some of the lung dysfunction depends on the presence of granulocytes. Bronchoconstriction and airway hyperreactivity, characteristic of asthma, may be influenced by granulocyte-generated products of arachidonic acid. Granulocyte-derived proteases and oxidants may contribute to the pathogenesis of pulmonary emphysema and may affect connective tissue synthesis in interstitial pulmonary fibrosis. There is some evidence suggesting a connection between granulocytes and chronic pulmonary hypertension. The fact that some interventions which cause pulmonary leukostasis do not cause severe, persistent lung injury indicates that as yet unknown factors may determine whether interactions of granulocytes with the lungs are benign or pathological. Such factors could include the generation of humoral substances, and metabolites of arachidonic acid are particularly interesting in this regard. Research related to interactions of granulocytes with the lungs suggests strongly that such interactions are integral to the pathogenesis of several lung diseases. Understanding those diseases will require further basic studies of granulocyte behavior and the modes of communication between cells intrinsic to the lung and granulocytes.

Complement and endotoxin-induced lung injury in sheep

Intravenous infusions of endotoxin in sheep cause lung injury characterized by edema due to increased microvascular permeability. Similar increases in pulmonary microvascular permeability are seen in septic patients with the adult respiratory distress syndrome. Since endotoxin-induced lung injury may be mediated by interactions between products of complement activation and polymorphonuclear leukocytes, plasma and lung lymph from six unanesthetized sheep infused with Escherichia coli endotoxin (1.0 micrograms/kg over 30 min) were examined for complement-derived chemotactic activity. By 2-3 hr following infusion of endotoxin, all animals had the increased lung lymph fluid and protein flows characteristic of permeability edema. Preinfusion samples of plasma and lung lymph did not contain chemotactic activity for polymorphonuclear leukocytes. Following infusion of endotoxin, however, significant chemotactic activity was detected in plasma at 0.5-3.5 hr (P less than 0.05) and in lymph at 1.5-6.5 hr (P less than 0.025). The chemotactic activity was heat stable (56 degrees C for 30 min) but was abolished by treatment with antibodies to C5. These data indicate that infusions of endotoxin lead to the generation in plasma, and the appearance in lung lymph, of C5-derived peptides with chemotactic activity for polymorphonuclear leukocytes. C5-derived peptides may account for the pulmonary microvascular leukostasis and endothelial injury that lead to increased permeability edema after infusions of endotoxin.

Inert gas analysis of ventilation-perfusion matching during hemodialysis

The mechanism of hypoxemia during hemodialysis was investigated by the multiple inert gas elimination technique in anesthetized, paralyzed, mechanically ventilated dogs. Profound leukopenia occurred in the first hour of a 2-h hemodialysis with a cuprophan membrane and dialysate that contained acetate. Arterial partial pressure of O2 and CO2 and oxygen consumption remained unchanged during dialysis. Pulmonary carbon dioxide elimination and lung respiratory exchange ratio decreased with the initiation of dialysis, remained depressed throughout the duration of dialysis, and returned to predialysis levels after the cessation of dialysis. Cardiac output diminished during dialysis but did not return to base-line levels after dialysis. Multiple indices calculated from inert gas analysis revealed no ventilation-perfusion mismatching during dialysis. The shunt and perfusion to regions of low alveolar ventilation-to-perfusion ratio (VA/Q) were unchanged during dialysis. There was no change in the mean or standard deviation of the profile of the percentage of total perfusion to regions of the lung that had VA/Q near 1.0; nor was there any increase in the directly calculated arterial-alveolar partial pressure differences for the inert gases during dialysis. Dead space became mildly elevated during dialysis. These results show that during dialysis with controlled ventilation there is no ventilation-perfusion mismatching that leads to hypoxemia. During spontaneous ventilation any hypoxemia must occur due to hypoventilation secondary to the CO2 exchange by the dialyzer and subsequent reduction in pulmonary CO2 exchange.

Complement activation and its relationship to adult respiratory distress syndrome. An experimental study in pigs

Pulmonary leucostasis induced by complement activation has been considered an important pathogenic factor in adult respiratory distress syndrome (ARDS). To determine whether complement activation per se could evoke pulmonary dysfunction similar to ARDS, pigs were repeatedly infused with complement-activated plasma (CAP). Complement activation was produced by incubation of plasma with zymosan. Three groups of animals were investigated. Control animals received non-activated plasma. Nine animals (Group II) were given four infusions of CAP at a rate of 7 ml X min-1, and another nine animals (Group III) received two CAP infusions at a rate of 7 ml X min-1 followed by two at a rate of 14 ml X min-1. In the control animals there were no changes in gas exchange or haemodynamic variables and the leucocyte counts gradually increased. Infusion of CAP resulted in transient peripheral leucopenia and a dose-rate-dependent reversible increase in pulmonary vascular resistance in all animals. In one animal of Group II and in six of Group III there was a significant infusion-related decrease in Pao2 due to increased venous admixture. These animals were characterized by an enhanced pulmonary vascular tone before the start of the first CAP infusion. They also displayed a more pronounced pulmonary vascular response to infusion of CAP. The changes in gas exchange variables and pulmonary haemodynamics showed no relation to the degree of leucopenia or decrease in platelet count. The increased venous admixture was caused by "dry" ventilation/perfusion mismatching and not by oedema. These results suggest that additional factors besides complement activation and pulmonary leucostasis are required for the development of increased microvascular permeability and the pulmonary oedema characterizing ARDS.

Cardiopulmonary abnormalities in severe acute respiratory failure

Serial cardiopulmonary variables were recorded over 4 days in 23 children with severe acute respiratory failure. In all patients, pulmonary artery catheters were inserted within 24 hours of the diagnosis of respiratory failure, and all required greater than 10 cm H2O positive end-expiratory pressure to achieve adequate oxygenation. Eight patients died (35% mortality). Evaluation of systemic hemodynamic variables indicated that survivors had higher blood pressures than nonsurvivors, although neither group was in the hypotensive range. Systemic vascular resistance was lower in the nonsurvivors. Cardiac function as evaluated by cardiac index, right ventricular stroke work index, and left ventricular stroke work index was similar in both groups. Survivors demonstrated elevations in mean pulmonary artery pressure and pulmonary vascular resistance during the first 36 hours, with gradual improvement thereafter. In contrast, pulmonary artery pressure and resistance increased progressively in patients who died. Intrapulmonary shunt fractions remained high in the nonsurvivors despite the use of up to 25 cm H2O PEEP. Cardiac function and oxygen delivery were well maintained in both groups despite the high levels of PEEP.

Differential effects of complement activation induced by cobra venom factor on pulmonary transvascular fluid and protein exchange

Sheep were prepared with lung lymph fistulas for assessment of the effects of complement activation on pulmonary transvascular fluid and protein exchange in the intact animal. Cobra venom factor (CVF 200 +/- 46 U/kg) was injected intravenously for activation of the complement system. In some animals (n = 6), pulmonary lymph flow (Qlym) and pulmonary arterial pressure (Ppa) increased without a change in the lymph-to-plasma protein concentration ratio (L/P) or in pulmonary blood flow (QL), indicating an increase in pulmonary vascular permeability to proteins. In another group (n = 6), Qlym and the L/P did not change, and there were also no changes in Ppa and QL following a similar injection of CVF. Morphologic evidence showed that leukocytes were trapped in pulmonary vessels and interstitium of both groups. Pulmonary edema was also present in both groups. Complement activation does not uniformly increase pulmonary lymph flow despite pathologic evidence of leukocyte sequestration and pulmonary edema. The lack of change in lymph flow in some animals may be due to lymphatic insufficiency, or lack of generation of humoral mediators, and/or a decrease in pulmonary capillary pressure.

Chemotaxis of granulocytes across bovine pulmonary artery intimal explants without endothelial cell injury

Emigration of granulocytes from vessel lumen to a site of injury is a hallmark of acute inflammation but whether this migration is necessarily associated with vascular damage is not clear. To follow the structural changes associated with granulocyte migration across an intact endothelial cell layer and to assess changes in vascular permeability, an in vitro technique was developed in which intimal explants were stripped from bovine pulmonary artery and mounted in chemotaxis chambers. All explants studied had granulocytes and trace amounts of 3H-water, 14C-sucrose and 125I-albumin in the upper well of the chambers. Experimental explants had zymosan-activated plasma in the lower well and control explants had either serum in the lower well or zymosan-activated plasma in the upper well. Explants were incubated at 37 degrees C for periods from 15 min to 3 hr. When the chemoattractant was added to the lower well, granulocytes migrated into the explants. Transmission and scanning electron microscopy showed an orderly sequence of granulocyte--endothelial interactions throughout which the two cell types maintained close opposition--granulocyte adherence to and exploration of the endothelial surface; penetration and migration through the interendothelial cell junction; reapposition and reformation of the luminal 'tight' junctions and finally passage of granulocytes through the endothelial basal lamina. After 60 min incubation, the majority of granulocytes seen in each section was through the endothelial cell layer and after 2 hr, they were through the basal lamina. Structural evidence of granulocyte or endothelial cell damage was not found at any of the times examined, neither was there any demonstrable increase in intimal permeability. In control explants, granulocyte migration was strikingly less frequent at 2 hr (approximately 10% of that seen towards the chemoattractant). Thus, granulocyte migration across an endothelial cell layer towards a chemoattractant is not necessarily associated with structural evidence of endothelial cell injury or increased vascular permeability.

Development and application of an enzyme-linked immunosorbent assay for the quantitation of alternative complement pathway activation in human serum

We have developed a new, specific, and highly sensitive enzyme-linked immunosorbent assay (ELISA) which quantitates activation of the alternative pathway in human serum, plasma, or on the surface of activators. The ELISA detects the third component of complement (C3b), proteolytic fragment of complement Factor B (Bb), and properdin (P) complex or its derivative product, C3b,P. In the method, activator-plasma mixtures, plasma containing an activated alternative pathway, or other samples are added to the wells of microtitration plates precoated with antibody to P. C3b, Bb,P or C3b,P complexes which become bound are quantitated by subsequently added, enzyme-labeled, anti-C3. The resulting hydrolysis of the chromogenic substrate is expressed as nanograms of C3b by reference to a C3 standard curve. In addition to absolute specificity for activation of the pathway because of the nature of the complex detected by the assay, the ELISA is highly sensitive and able to reproducibly detect 10-20 ng/ml of C3b,P complexes in serum. This value corresponds to 0.0015% of the C3 in serum. In a series of studies to validate the parameters of the ELISA, reactivity was found to be dependent on the presence of alternative pathway proteins, the functional integrity of the pathway, and on the presence of magnesium. Sheep erythrocytes were converted to activators by treatment with neuraminidase. By using a variety of activators, the kinetics of activation and the numbers of bound C3b molecules quantitated by the ELISA were very similar to those measured by C3b deposition. The ELISA also detected identical activation kinetics when MgEGTA-serum and a mixture of the purified alternative pathway proteins were used as sources of the pathway. ELISA reaction kinetics also correlated with the restriction index, a measure of alternative pathway-activating ability. These studies cumulatively validate the ELISA as a direct and quantitative assay for alternative pathway activation. The sensitivity of the ELISA has permitted its use to detect direct alternative pathway activation by several viruses. The ELISA has also shown that certain classical pathway activators trigger the amplification loop of the alternative pathway while others do not. In addition, stable ELISA reactive complexes appeared in the supernatant of mixtures of serum with certain, but not other activators. The ability of the ELISA to detect activation which has already occurred and the stability of the reactive complexes permits studies of clinical sera. Normal human sera (20) contained low levels (5-20 ng/ml) of ELISA-reactive complexes. A proportion of sera from individuals with the adult respiratory distress syndrome (9-10), typhoid fever (8-10), malaria (3-5), gram-negative sepsis (9 of 47), acute trauma and shock (6 f 25), and systemic lupus erythematosus (3 of 29) showed elevated levels of complexes reactive in the alternative pathway ELISA. In contrast, nine sera from patients with circulating C3 nephritic factor were not reactive in the ELISA.

Immunoreactive trypsin in the adult respiratory distress syndrome

With the purpose of studying the role of proteinases in the development of ARDS, plasma levels of immunoreactive trypsin (IRT) and amylase were measured in 43 intensive care patients at risk of developing ARDS (22 polytrauma, seven abdominal surgery, four burns, two DIC and eight pancreatitis). Twenty four of these 43 patients developed ARDS and 31 presented abnormal IRT values (above 70 micrograms/L). Twenty-one of these 31 patients had ARDS; a significant correlation thus appeared between ARDS and abnormal IRT values. In nine patients, IRT values were higher than 800 micrograms/L and remained high for 3 to 4 days. A statistically significant correlation also appeared between abnormal IRT and septic phenomena: 20 patients with high IRT values presented septic problems. When IRT values were high, amylase values were often also abnormal: 12 of 23 patients with high IRT had abnormal amylase levels (the eight patients with documented pancreatitis were excluded); no other clinical signs or symptoms of pancreatitis were present in these patients. IRT could be one of the mediators of ARDS in septic patients. It is not clear that the pancreas is the origin of IRT in all cases.

Role of complement and polymorphonuclear cells in demethylchlortetracycline-induced phototoxicity in guinea pigs. Inhibition by decomplementation in vivo

In this study, demethylchlortetracycline was used as a prototype of exogenous phototoxic substances. In vitro, exposure of serum containing demethylchlortetracycline to ultraviolet-A irradiation resulted in the diminution of total complement hemolytic activity and C4, C2, C3, and C5 activities. In addition, chemotactic activity for human polymorphonuclear cells was generated, which was thermostable and antigenically related to human C5 but not human C3. In vivo, phototoxic lesions were induced in guinea pigs upon intradermal injections of demethylchlortetracycline solution, followed by ultraviolet-A irradiation. On a scale of 0-3+, the animals developed a maximal response of 2.5 at 20 h. This clinical response was associated with cellular infiltrate in the dermis, consisting of 29 +/- 2% of neutrophils at 24 h. The participation of the polymorphonuclear cells was evaluated in guinea pigs rendered neutropenic by treatment with cyclophosphamide. In these guinea pigs, demethylchlortetracycline and ultraviolet-A induced a maximal response of 0.75 +/- 0.5, which was associated histologically with 1.2 +/- 0.5% neutrophils in the dermis. The role of complement in this process was studied in guinea pigs congenitally deficient in C4, and in guinea pigs decomplemented by treatment with cobra venom factor. In contrast to normal guinea pigs, C4-deficient animals exhibited a maximal reaction of 0.83 +/- 0.16 at 6 h, which subsided within 24 h. Cobra venom factor-treated guinea pigs developed a maximal response of 0.5 at 0.5 and at 6 h. These clinical changes were associated with the development of an increased vascular permeability, as demonstrated by studies using guinea pigs injected intravenously with Evans blue solution. In animals with a normal complement system, there was intense localized bluing at the sites of phototoxic lesion. In contrast, only minimal bluing was observed in decomplemented guinea pigs. These data indicate that a normal number of polymorphonuclear cells and an intact complement system are required for the full development of demethylchlortetracycline-induced phototoxic lesions.

Preferential activation and depletion of the alternative complement pathway by burn injury

Complement levels of eight adult burn patients (25% to 90% body surface area) were studied upon admission to a burn unit and sequentially for one week. Mean classical pathway titers (CH50) were 49% below the normal mean, while hemolytic C4 titers were reduced by 53% and C3 by 43%. However, the alternative pathway titer was reduced by more than 90%, suggesting preferential depletion of this pathway. This depletion was associated with sepsis, pneumonia, and "shock lung." Alternative pathway deficiency was still present one week postburn, and may contribute to the susceptibility of burn patients to bacterial sepsis.

Adult respiratory distress syndrome as a cause of death in pneumococcal pneumonia. Report of ten cases

The Pneumococcus continues to be a common cause of infectious pneumonia; however, the cause of death in pneumococcal disease remains obscure. Ten patients are described who developed the adult respiratory distress syndrome (ARDS) secondary to pneumococcal pneumonia. The patients are young (median age, 33 years) and leukopenic (median white blood cell count, 2.1 cells/cu mm) and have a mortality of 50 percent (five patients). It is postulated that pulmonary sequestration of leukocytes may play a role in the pathogenesis of ARDS secondary to pneumococcal disease. Four different pneumococcal capsular subtypes (9V [68]; 9A [33]; 4; 3) were found capable of causing ARDS. The currently available pneumococcal vaccine does not contain two of the capsular subtypes associated with ARDS.

Aggregation, chemotaxis, and chemiluminescence of canine granulocytes. Studies utilizing improved cell preparation techniques

Wishing to extrapolate in vitro observations of granulocyte function and pharmacology made with human cells to animal models of diseases in which we believe granulocyte stimulation to play a major role, we examined techniques for preparation of canine granulocytes and conducted a survey of the function and pharmacology of those cells. Isotonic density gradients of Percoll proved a simple and highly satisfactory method of preparation. Canine granulocytes in most respects paralleled human cells in function and pharmacology, except that canine cells lacked receptors for formylated oligopeptides and resisted them as stimuli; canine plasma contained a heat-labile inhibitor of canine PMN aggregation, oxidative metabolism, and myeloperoxidase release; canine PMNs were not inhibited in aggregation by protease inhibitors such as aprotinin; canine response to ibuprofen and steroids was more variable than that of human cells, and synergy between those agents was less readily demonstrated; heterologous stimulation (canine cells by human C5a or vice versa) led to a different time course and maximum response from those observed in the homologous systems. Canine granulocytes were readily marked with indium-111, and functioned normally in vitro and survived well in vivo after marking. We conclude that the dog is a suitable animal for studying the role of stimulated PMNs in disease, as long as the observed differences are taken into account in experimental design and data interpretation.

Lung injury secondary to chemotactic factor-induced leukocyte activation

Intravascular complement activation in rats following thermal injury or vascular infusion of cobra venom factor results in acute lung injury as determined morphologically and measured by increases in lung vascular permeability. The acute lung injury is associated with the early appearance of C5-derived chemotactic activity in the circulation coincident with the development of neutropenia. The lung injury is closely linked to availability of complement and neutrophils and can be prevented by systemic treatment of animals with a combination of superoxide dismutase and catalase, specific inhibitors of toxic oxygen metabolites. These data suggest that intravascular complement activation leads to activation of neutrophils and their intrapulmonary capillary sequestration, and subsequent acute lung injury, which is associated with production and release of oxygen-derived free radicals by C5a-activated blood neutrophils.

Alterations in activities of anaphylatoxin inactivator and chemotactic factor inactivator during hemodialysis

The systemic infusion of complement-derived anaphylatoxin ane chemotaxins during hemodialysis results in profound transient neutropenia and may be associated with subtle pulmonary dysfunction. The fact that these potent inflammatory peptides do not usually produce serious ill effects may be due in part to their rapid inactivation by the serum regulatory proteins anaphylatoxin inactivator (AI) and chemotactic factor inactivator (CFI). Accordingly, the authors investigated the effect of hemodialysis on circulating neutrophil counts and serum levels of AI and CFI activity in 10 patients. In all patients, circulating neutrophil counts plummeted by more than 50% within 5 minutes of the onset of dialysis and rose beyond control levels by 1 hour. AI activity significantly fell from 65 +/- 16 mU/ml before dialysis to 18.7 +/- 7.8 mU/ml within 5 minutes of its initiation; levels remained depressed throughout the procedure. In contrast, CFI gradually increased, achieving a level significantly different from the predialysis value by 15 minutes. These events contrasted with the observation that activation of the complement system in vitro results in a significant decline in both CFI and AI activities. We suggest that the maintenance of or increase in CFI activity in patients undergoing hemodialysis enhances the clearance of circulating chemotactins, preventing the persistent activation of neutrophils during the procedure and subsequent organ dysfunction.

Alternative complement pathway activation increases mortality in a model of burn injury in mice

We have studied the role of the complement system in burn injury in an experimental model in mice. A 25% body surface area, full-thickness scald wound was produced in anesthetized animals. Massive activation of the alternative complement pathway, but not the classical pathway, was seen. This activation was associated with the generation of neutrophil aggregating activity in the plasma, neutrophil aggregates in the lungs, increased pulmonary vascular permeability, and increased lung edema formation. Decomplementation with cobra venom factor (CVF) or genetic C5 deficiency diminished these pathologic changes, and CVF pretreatment substantially reduced burn mortality in the first 24 h. Preliminary data show that human burn patients have a similar pattern of complement activation involving predominantly the alternative pathway, indicating the possible relevance of the murine model to human disease.

Ibuprofen in canine endotoxin shock

The participation of prostaglandins in the physiologic alterations of endotoxin shock has been well established with the aid of prostaglandin synthetase inhibitors. Our study was designed to investigate the potential of ibuprofen, a highly specific cyclooxygenase inhibitor, to reverse the hemodynamic and acid base abnormalities of canine endotoxin shock. Mean blood pressure fell to 49.8 +/- 6.6 mm Hg in dogs given endotoxin by 5 min after injection, and remained below 83 mm Hg for the duration of the 120-min observation period. In animals given endotoxin followed by ibuprofen, a similar initial drop of systemic blood pressure was seen, but it subsequently recovered to 150.2 +/- 4.1 mm Hg by 120 min (P less than 0.001). Cardiac index increased in animals given ibuprofen (2.3 +/- 0.28 liter/m2 per min) compared with animals given endotoxin alone (1.0 +/- 0.09 liter/m2 per min) by termination of the experiment. The arterial pH dropped in endotoxin treated animals to 7.18 +/- 0.03 by 120 min. Ibuprofen prevented the acidosis, the final pH in ibuprofen and endotoxin treated animals measuring 7.36 +/- 0.01. We conclude that ibuprofen protects against the hypotension, acidosis, and depression of cardiac index of canine endotoxin shock.

Another look at ARDS

ARDA is a common clinical problem resulting in acute respiratory failure in many and death in the majority of patients with a wide variety of direct and indirect pulmonary insults. ARDS is widely recognized and appropriately treated by empiric supportive care. Pharmacologic approaches to support the circulation are established. The use of corticosteroids remains controversial. The future depends upon unraveling the biologic mysteries which lead to the cascade of events which result in ARDA. This will establish a basis for further improvements in management.

Gram-positive bacteria-induced granulocytopenia and pulmonary leukostasis in rabbits

Pneumococci have been shown to induce granulocytopenia and pulmonary leukostasis which might contribute to morbidity and mortality in pneumococcal sepsis. We studied whether other gram-positive species (groups A and B streptococci, Staphylococcus aureus, Bacillus cereus, and Clostridium perfringens) could also induce these phenomena. Rabbits were challenged with nonviable preparations of each species, and all five species induced profound granulocytopenia (mean decrease of 90%) and pulmonary leukostasis. In vitro studies of serum incubated with these species of bacteria showed a mean consumption of total hemolytic complement of 90%, a mean increase of chemotactic activity for granulocytes of 204%, and a mean augmentation of granulocyte adherence of 45% (compared with 18% for the control). Infusion of sonicate-exposed sera induced granulocytopenia in recipient rabbits. Thus, several nonviable gram-positive species can interact with serum to activate the complement system, generate C5a bioactivity, augment granulocyte adherence, and generate a neutropenia-inducing factor. These alterations may contribute to granulocytopenia or pulmonary leukostasis, which may play a role in the morbidity and mortality associated with gram-positive bacterial infections.

Synergy among agents inhibiting granulocyte aggregation

Recent evidence suggests complement (C) -stimulated granulocytes (PMNs) are important in a variety of diseases, including shock and myocardial infarction (MI). Corticosteroids inhibit PMN response to C and show promise in some studies of shock and MI, but their use has not become routine for several reasons. Synergy was sought among agents inhibiting PMN aggregation in vitro in response to activated C: methylprednisolone (MP), with a 50% inhibitory dose (AD50) of 0.6 mg/ml; ibuprofen (IBU), with AD50 of 1.0 mg/ml, and betahistine (BH), with AD50 of 1.6 mg/ml. Simultaneous use of all three agents produced 3.4-fold synergy; 3-fold synergy obtained between IBU + MP and IBU + BH, while 1.5-fold synergy was noted between MP + BH. Further, MP and IBU were at least additive in inhibiting .O2- generation by FMLP-stimulated PMNs and in blocking directed migration. In a preliminary in vivo test of this finding, cats were given MP and IBU--in known individually ineffective doses--immediately prior to coronary artery ligation. Neither MP nor the low dose of IBU chosen limited the size of the resultant MI, while both agents together reduced MI size by 42%. Synergy among these agents suggests that they inhibit PMN function of distinct cellular mechanisms (as yet not elucidated). Further, early in vivo results encourage speculation that such synergy might ultimately be exploited clinically, although such speculation must presently be regarded as preliminary.

Intravascular activation of complement and acute lung injury. Dependency on neutrophils and toxic oxygen metabolites

Intravascular activation of the complement system with cobra venom factor results in acute lung injury, which has been quantitated by increases in lung vascular permeability. Cobra venom factor preparations devoid of phospholipase A2 activity retain full lung-damaging capacity. The lung injury is associated with the preceding appearance of chemotactic activity in the serum coincident with the development of a profound neutropenia. The chemotactic activity is immunochemically related to human C5a. Morphologic studies have revealed discontinuities in the endothelial cell lining of lung alveolar capillaries, damage and/or destruction of endothelial cells in these areas, plugging of pulmonary capillaries with neutrophils that are in direct contact with vascular basement membrane, the presence of fibrin in alveolar spaces and in areas adjacent to damaged endothelial cells, and intraalveolar hemorrhage. Lung injury is dramatically attenuated in animals that have been previously neutrophil depleted. Teh intravenous injection of superoxide dismutase or catalase also provides significant protection from the pulmonary damage. Very little protection from the pulmonary damage. Very little protection is afforded by pretreatment of rats with antihistamine. These studies suggest that intravascular activation of the complement system leads to neutrophil aggregation and activation, intrapulmonary capillary sequestration of neutrophils, and vascular injury, which may be related to production of toxic oxygen metabolites by complement-activated neutrophils.