Complement-induced expression of cryptic receptors on the neutrophil surface: a mechanism for regulation of acute inflammation in trauma

We explored the hypothesis that identified changes in neutrophil function in patients with acute injury result from in vivo exposure to C5a. To evaluate this hypothesis, we performed a battery of tests on 26 trauma patients (14 with blunt injury, 12 with penetrating injury). Measured were plasma levels of the complement activation products C3a and C5a; neutrophil chemotaxis to C5a and N-formyl-methionyl-leucyl-phenylalanine (FMLP); neutrophil receptors for FMLP and C3b; and superoxide response to FMLP and serum-opsonized zymosan. Patient responses measured within 48 hours of admission were divided into two groups based on neutrophil migratory response to C5a. Patients unresponsive to C5a (but responsive to FMLP) showed elevated plasma C3a levels (248 +/- 6 ng/ml) compared with patients with normal C5a migratory response (104 +/- 8 ng/ml). FMLP receptor number was markedly increased in the chemotactically deactivated group (group I: 155,680 +/- 100; group II: 51,200 +/- 200) and receptor affinity was diminished. Binding activity of C3b increased in the C5a-unresponsive cells to 126% that of controls versus 94% for normally responsive patient cells. Superoxide production was found to be significantly increased in patient cells with increased receptor numbers. These results support the concept that a subgroup of trauma patients manifest plasma and neutrophil changes compatible with complement activation. The neutrophil changes identified demonstrate a state of cellular activation. The clinical significance of these results may reside in a risk of pulmonary microvascular injury if activated cells are marginated and then subsequently stimulated.     

Complement-mediated neutrophil activation in sepsis- and trauma-related adult respiratory distress syndrome. Clarification with radioaerosol lung scans

Complement-mediated neutrophil activation (CMNA) has been proposed as an important pathogenic mechanism causing acute microvascular lung injury in the adult respiratory distress syndrome (ARDS). To clarify the relationship between CMNA and evolving lung injury, we studied 26 patients with multiple trauma and sepsis within 24 hours of risk establishment for ARDS. Pulmonary alveolar-capillary permeability (PACP) was quantified as the clearance rate of a particulate radioaerosol. Seventeen patients (65%) had increased PACP (six developed ARDS) while nine (35%) had normal PACP (none developed ARDS; clearance rates of 3.4%/min and 1.5%/min, respectively). These patients, regardless of evidence of early lung injury, had elevated plasma C3adesArg levels and neutrophil chemotactic desensitization to C5a/C5adesArg. Plasma C3adesArg levels correlated weakly, but significantly, with PACP. Thus, CMNA may be a necessary, but not a sufficient, pathogenic mechanism in the evolution of ARDS.     

Complement activation and clearance in acute illness and injury: evidence for C5a as a cell-directed mediator of the adult respiratory distress syndrome in man

The appearance of the adult respiratory distress syndrome (ARDS) during the course of acute illness is believed to result, in part, from intrapulmonary neutrophil sequestration and degranulation induced by circulating inflammatory mediators. To evaluate the role of complement-neutrophil interactions in the pathogenesis of ARDS in man, 34 patients suffering from intra-abdominal sepsis (seven), multisystem trauma (15), or acute pancreatitis (12) were serially studied with regard to neutrophil migratory responses to C5a and F-Met-Leu-Phe, lysosomal content of beta-glucuronidase and lysozyme, and simultaneously obtained plasma levels of immunoreactive C3adesArg and C5adesArg. Nineteen patients developed ARDS. In these patients, plasma C3adesArg levels obtained within 72 hours of admission to the hospital were elevated to 305 +/- 35 ng/ml compared with 145 +/- 16 ng/ml for patients who did not develop ARDS (p less than 0.0005). C5adesArg levels were not elevated in either group. In vitro studies showed that neutrophils from normal persons were able to clear all of the C5a/C5adesArg generated in up to 5% zymosan-activated serum, while no clearance of C3adesArg was identified. Patient migratory responses could be divided into three groups based on their initial (less than 72 hour) samples: (1) hyperresponsive to both N = formyl-methionyl-leucyl-phenylalanine (FMLP) and C5a, (2) specifically deactivated to C5a, and (3) deactivated to both C5a and FMLP. Patients in the latter two groups developed ARDS. Enzyme content of neutrophils from patients who developed ARDS showed a substantial fall in beta-glucuronidase and lysozyme levels. The finding of elevated plasma C3a levels and deactivation of migratory response to C5a support the contention that complement activation had occurred in these patients and that their neutrophils had been exposed to C5a/C5adesArg in vivo. The finding of nonspecific migratory dysfunction associated with lysozymal enzyme loss, a circumstance not reproducible in vitro by C5a exposure, suggests that other stimuli produced degranulation of neutrophils made hyperresponsive by prior exposure to C5a.     

The effects of methylprednisolone on complement, immunoglobulins and pulmonary neutrophil sequestration during cardiopulmonary bypass.

In this study, the authors administered high dose (30 mg/kg body weight i.v.) methylprednisolone before cardiopulmonary bypass to observe the effects on complement, immunoglobulins and pulmonary neutrophil sequestration. Fifty patients undergoing valve replacements were included in this study. Patients were divided into two groups: group I (20 patients) served as control and did not receive methylprednisolone, group II (30 patients) received methylprednisolone. Blood samples for complements (C3c and C4) were taken, before cardiopulmonary bypass, at 5, 10 and 30 min intervals from the end of cardiopulmonary bypass, after reversal of heparin with protamine infusion, and after skin closure. Blood samples for immunoglobulins were taken before cardiopulmonary bypass, 30 min after onset of cardiopulmonary bypass and after skin closure. After onset of cardiopulmonary bypass, all C3c and C4 levels decreased in both groups. There was a significant decrease in C4 levels at end of cardiopulmonary bypass and after protamine infusion in group I compared with group II (P < 0.05). C3c levels in group I decreased significantly compared with group II after 30 min of cardiopulmonary bypass and after protamine infusion (P < 0.05). All immunoglobulin (IgG, IgM, IgA) levels were decreased in both groups, but the decrease in IgG was statistically significant after skin closure in group I compared with group II (P < 0.05). Pulmonary neutrophil sequestration was higher in the control group compared with the methyl-prednisolone group (P < 0.05). In conclusion, methylprednisolone administration before cardiopulmonary bypass may prevent the harmful effects of complement activation, immunoglobulin denaturation and neutrophil sequestration in the pulmonary capillary system.     

Leukocyte depletion ameliorates free radical-mediated lung injury after cardiopulmonary bypass

Activated leukocytes and oxygen free radicals have been implicated in the pathogenesis of lung injury associated with cardiopulmonary bypass. To determine whether leukocyte depletion could prevent this injury, we used a dog model simulating routine cardiac operations. Mongrel dogs (11 to 17 kg) were subjected to cardiopulmonary bypass with a bubble oxygenator and cooled to 27 degrees C. After aortic crossclamping and cardioplegic arrest for 90 minutes, control animals (n = 5) were rewarmed and weaned from bypass, and their condition was then stabilized for 90 minutes. Leukocyte-depleted animals (n = 5) had a leukocyte filter incorporated in the bypass circuit. During bypass, circulating leukocyte counts decreased by 60% in control dogs, and by 97% in leukocyte-depleted animals. Free radical generation (estimated by spectrophotometric assay of plasma conjugated dienes) was significantly reduced by leukocyte depletion during and after bypass. Total hemolytic complement activity and the titer of C5 decreased markedly immediately after the onset of bypass in both the control and leukocyte-depleted animals. Pulmonary function after bypass was better preserved in leukocyte-depleted animals. These data suggest that depletion of circulating leukocytes contributes to lung injury during cardiopulmonary bypass and is associated with increased oxygen radical activity, pulmonary edema, and vasoconstriction. Leukocyte depletion substantially reduced the pulmonary injury seen after cardiopulmonary bypass.     

Cardiopulmonary effects of cuprophane-activated plasma in the swine

Hemodialysis with cuprophane membrane is associated with complement activation and the formation of anaphylatoxins. Frequently, it is also complicated by various adverse reactions which include hypoxemia and hemodynamic changes. This study examined the cardiopulmonary effects of cuprophane membrane on experimental animals. To support the hypothesis that these effects were mediated by complement activation products, the effects of zymosan-activated plasma and C5adesArg challenge on the same variables were compared. We showed that intravenous infusion of autologous cuprophane-activated plasma into swine produced severe pulmonary hypertension, hypoxemia and leukopenia. In addition, mean systemic arterial pressure fluctuated and cardiac output fell. Infusion of zymosan-activated plasma produced similar results, suggesting that complement activation products are responsible for these alterations. Similar responses to porcine C5adesArg infusion suggested further that this polypeptide was the mediator. When swine were subjected to extracorporeal circulation using cuprophane membrane but without dialysis, acute pulmonary hypertension was seen preceding the onset of significant leukopenia. These data suggest that blood contact with cuprophane membrane produces both pulmonary and systemic hemodynamic changes, which are mediated by complement activation products. Furthermore, these products and/or other humoral factors, but not leukoagglutination, cause the pulmonary hypertension.     

Continuous pulmonary perfusion during cardiopulmonary bypass prevents lung injury in infants

BACKGROUND: Lung injury after cardiopulmonary bypass is a serious complication for infants with congenital heart disease and pulmonary hypertension. Excessive neutrophil sequestration in the lung occurring after reestablishment of pulmonary circulation implies that interaction between neutrophils and pulmonary endothelium is the major cause of lung injury. METHODS: Thirty infants with either ventricular septal defect or atrioventricular septal defect and with pulmonary hypertension were enrolled in this study. We performed continuous pulmonary perfusion during total cardiopulmonary bypass on 16 patients (perfused group) and conventional cardiopulmonary bypass on 14 patients (control group). PaO2/FiO2 and neutrophil counts were assessed from immediately before surgery to 24 hours after termination of cardiopulmonary bypass. RESULTS: PaO2/FiO2 was higher in the perfused group than in the control group, and the difference was significant throughout the study period. Neutrophil counts decreased below prebypass values in both groups at 30 minutes after aortic unclamping, and the difference was significant in the control group but was not in the perfused group. Duration of postoperative ventilatory support was significantly less in the perfused group. CONCLUSIONS: Our study demonstrates that arrested pulmonary circulation during cardiopulmonary bypass is the major risk factor of lung injury and that continuous pulmonary perfusion is effective in preventing lung injury.     

Complement activation during cardiopulmonary bypass: mechanism and prevention

The mechanism of complement activation during cardiopulmonary bypass was studied for the prevention. In ten patients undergoing open-heart procedures, the serum levels of complement fractions (C3, C4, and C3 activator) were measured by a single radial immune diffusion method. In four of ten patients, the plasma levels of C3a, C4a, and C5a fractions were studied by the radioimmunoassay 2 antibodies method. The serum levels of C3, C4, and C3 activator decreased after cardiopulmonary bypass. The plasma levels of C3a, C4a, and C5a increased after bypass. The lower level of C3 activator shows that C3 activator was not excessively produced during cardiopulmonary bypass. Therefore it can be thought that much C4b2a from classical pathway as well as C3a over-production localizing extra-corporeal circuits and little inhibitors on alternative pathway resulted in increased complement activation. The prevention should be done from these etiologies.     

The effects of methylprednisolone on complement-mediated neutrophil activation during cardiopulmonary bypass

Complement-mediated neutrophil activation (CMNA) has been implicated as an important pathophysiologic mechanism contributing to acute microvascular lung injury in the adult respiratory distress syndrome (ARDS). Using cardiopulmonary bypass (CPB) as a clinical model for complement-mediated microvascular injury, we studied the effects of methylprednisolone (MPSS) pretreatment on manifestations of CMNA in 28 pediatric patients undergoing CPB. Six patients not receiving MPSS served as controls. Results demonstrated that MPSS did not prevent complement activation as noted by 4.5- and 7.7-fold increases in plasma C3a des Arg levels during and immediately after CPB, respectively. However, detectable in vivo and in vitro manifestations of CMNA were altered. Neutropenia during CPB was attenuated to 65% of prebypass values compared with 47% in the control group. Neutrophil selective chemotactic desensitization toward C5a/C5a des Arg during the on bypass and postbypass periods was evident in the control group (0.41 and 0.76 cm specific migration, respectively) and prevented in the MPSS group (1.55 and 2.00 cm specific migration, respectively). We conclude that CMNA during CPB is ameliorated and/or prevented by MPSS pretreatment. These findings suggest that MPSS pretreatment may ameliorate complement-mediated microvascular (lung) injury in CPB and ARDS.     

Different activation patterns in the plasma kallikrein-kinin and complement systems during coronary bypass surgery

Components of the plasma kallikrein-kinin and complement systems were determined in patients undergoing open heart surgery with cardiopulmonary bypass. Spontaneous kallikrein activity (KK), plasma prekallikrein (PKK), functional kallikrein inhibition capacity (KKI), C3 activation products (C3-act), and the terminal complement complex (TCC) were measured. A marked, transitory increase in KK and a decrease in PKK were found prior to cardiopulmonary bypass just after heparin injection. An additional decline in PKK and KKI during bypass with a return to near control levels in the postoperative period was observed. C3-act increased in all patients during bypass, reaching a peak value at wound closure. The TCC concentration also increased significantly during cardiopulmonary bypass, returned to control levels in the early postoperative period, and then increased again in the late postoperative period. It is concluded that activation of the kallikrein-kinin system started after injection of heparin, prior to cardiopulmonary bypass. Activation of both the initial and the terminal complement cascade, however, started only after onset of cardiopulmonary bypass.     

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.     

Soluble tumor necrosis factor receptor prevents post-pump syndrome.

Post-pump syndrome is an acute lung injury following cardiopulmonary bypass (CPB) which is indistinguishable from the adult respiratory distress syndrome (ARDS). Tumor necrosis factor (TNF) is central to the inflammatory process and is capable of triggering the entire pathophysiologic response leading to ARDS. We hypothesized that treatment with a soluble TNF receptor-binding protein (TNFbp) would reduce the increase in serum TNF and prevent acute lung injury in our sequential insult model of ARDS following CPB. Anesthetized pigs were randomized to one of three groups: Control (n = 3), surgical preparation only; CPB + LPS (n = 6), femoral-femoral hypothermic bypass for 1 h followed by infusion of low dose Escherichia coli lipopolysaccharide (LPS; 1 microg/kg); and TNFbp + CPB + LPS (n = 4), pretreatment with intravenous TNFbp (2 mg/kg) followed immediately by both insults. CPB + LPS caused severe lung injury demonstrated by a significant fall in PaO2 and an increase in both intrapulmonary shunt and peak airway pressure as compared to all groups (P < 0.05). These changes were associated with a significant increase in plasma TNF level and pulmonary neutrophil sequestration. TNFbp significantly reduced plasma levels of TNF and prevented the lung injury typically observed with this ARDS model, but did not reduce pulmonary neutrophil sequestration. Thus, elevated serum TNF is not responsible for neutrophil sequestration but does play a role in neutrophil activation which causes lung injury. Prophylactic use of TNFbp in CPB patients may prevent neutrophil activation and reduce the incidence of post-pump ARDS.     

Regulation of neutrophil migratory function in burn injury by complement activation products.

Polymorphonuclear neutrophils were isolated from patients with burn injury and random mobility, chemotaxis in response to C5adesArg (as agarose-activated control serum) and to N-formyl-methionyl-leucyl-phenylalanine (F-Met-Leu-Phe) were assessed. For a group of eight patients identified as not experiencing systemic infection, all three neutrophil migratory functions were observed to fall below control levels, beginning 4 to 6 days following burn injury, and to return to control levels after 21 to 30 days of hospitalization. Over this time the chemotactic differential (distance chemotactic migration-distance random migration) for F-Met-Leu-Phe remained positive, while the chemotactic differential for activated serum became nil after postburn day 4. This temporal, specific loss of a chemotactic response to activated serum was associated with rises in immunoreactive plasma C3a and C5a. This pattern of loss of chemotactic function was associated with a selective loss of C5a but not F-Met-Leu-Phe binding activity. These results demonstrate that burn injury can alter neutrophil migratory functions generally, and specifically depress chemotactic responsiveness to activated serum. The mechanism of the latter phenomenon appears to be related to desensitization of circulating neutrophils to C5a due to complement activation.     

Heparin-coated circuits reduce occult myocardial damage during CPB: a randomized, single blind clinical trial.

OBJECTIVES: Cardiopulmonary bypass is associated with a diffuse systemic inflammatory response that can cause considerable morbidity, including organ dysfunction and bleeding. Heparin-coated circuits have been shown to give a reduced inflammatory response with clinical benefits during open-heart surgery. However, the effects on lipid peroxidation, neutrophil activation and myocardial ischemic damage in the human have remained unknown. METHODS: In a randomized single blind trial, complement activation, neutrophil counts, malondialdehyde, and cardiac enzymes were studied in 39 patients undergoing open-heart surgery. Two groups were perfused with cardiopulmonary bypass circuits with (n=20) or without heparin-coating (n=19). RESULTS: The different complement factors (C3, C4, C3d, C3d/C3 and the C-function), neutrophil levels, MDA and the cardiac enzyme levels were comparable before CPB was started and significantly increased in both groups during bypass. There were significant intergroup differences in the neutrophil levels and MDA after reperfusion (P<0.0001). Furthermore, significant positive correlations between the lipid peroxidation, expressed as MDA levels, and the levels of neutrofils and the cardiac enzyme, CK-MB were seen within the groups. CONCLUSIONS: Heparin coated circuits did lead to a decreased neutrophil response and MDA level. The correlations between CK-MB and neutrophil and MDA levels suggest neutrophil activation leading to lipid peroxidation that may influence myocardial damage. Heparin coating improved biocompatibility and was associated with less occult myocardial ischemic damage in patients undergoing open heart surgery.     

Anaphylatoxins and terminal complement complexes in pancreatitis. Evidence of complement activation in plasma and ascites fluid of patients with acute pancreatitis

Complement activation has been proposed as a mediator of remote complications of acute pancreatitis. Thirty-seven patients with acute pancreatitis were studied with respect to the formation of anaphylatoxins (C3a/C3adesArg, C5a/C5adesArg) and terminal complement complexes (TCC) in plasma and ascites fluid. The patients were classified according to Ranson's criteria. Eighteen patients with moderate or severe pancreatitis had higher maximum plasma C3a/C3adesArg and TCC concentrations than 19 patients with mild pancreatitis. During convalescence, the concentrations had returned to normal. High concentrations of C5a/C5adesArg and TCC were also found in ascites and pancreatic cyst fluid, drawn from patients with moderate or severe pancreatitis. As the terminal complement pathway activation is involved in reactive lysis and anaphylatoxins increase vascular permeability, anemia and impaired respiration in these patients may be influenced by complement activation.     

Effects of cardiopulmonary bypass on pulmonary leukostasis and complement activation

We measured white blood cell counts and complement component (C3a, C4a, and C5a) and prostacyclin levels, and studied lung biopsy specimens, in 16 patients undergoing cardiopulmonary bypass and compared them with four patients undergoing other pulmonary procedures. Bypass caused no significant elevation in peripheral venous white blood cell counts. Higher counts were present in the right atrium compared with the left atrium. Patients who underwent bypass had elevated complement component and prostacyclin concentrations before operation and these levels increased further during operation. Trapping of polymorphonuclear leukocytes occurred in pulmonary alveolar capillaries and venules after bypass. We conclude that bypass activates complement components primarily of the alternative pathway and leads to increased blood prostacyclin levels. These changes are accompanied by polymorphonuclear leukocyte accumulation in the lungs and may be important in initiation of the adult respiratory distress syndrome in these patients.     

Reduction of complement activation during bypass by prime manipulation

Complement activation is believed to be of importance in the development of complications arising after cardiopulmonary bypass. The effect on complement activation of priming the extracorporeal circuit with crystalloid alone, crystalloid plus albumin, or crystalloid plus the plasma expander polygeline was assessed in 36 patients undergoing coronary artery operations with cardiopulmonary bypass using a bubble oxygenator. Activation of the alternative and common complement pathways was monitored before, during, and after the bypass period by measuring concentrations of factor B and its fragment Ba and C3 and its fragment C3d. Complement activation occurred in all three groups of patients, with no difference between the crystalloid and crystalloid-albumin groups. In contrast, Ba fragment concentrations were persistently and significantly lower during and after bypass in the polygeline group, denoting reduced complement activation. C3d levels also showed a tendency to be lower in this group. Our results indicate that addition of polygeline to the priming solution reduces complement activation. Because complement activation is associated with morbidity after cardiopulmonary bypass, addition of polygeline to the priming solution may offer an inexpensive method of reducing morbidity after cardiopulmonary bypass.     

Complement (C3, C4) Consumption in Cardiopulmonary Bypass,Cardioplegia, and Protamine Administration

Anaphylatoxins produced by complement activation have been postulated to be responsible for postperfusion syndrome and protamine hypotension in patients undergoing cardiac surgical procedures. The consumption of serum complement components C3 and C4, which reflects the classic and alternate pathway activations of the complement system, was studied in 22 patients undergoing cardiac operations. Prior to the onset of cardiopulmonary bypass, the complement levels were within normal range. Rapid reduction in both C3 and C4 within minutes of cardiopulmonary bypass indicated rapid complement activation. Such a reduction in complement levels could not be accounted for by either hemodilution or transfusion of complement-poor blood. Aortic cross-clamping and cold potassium cardioplegia followed by myocardial reperfusion did not lead to further consumption of C3 and C4. Slow intravenous infusion of protamine sulfate after cardiopulmonary bypass did not change C3 and C4 levels significantly in our patients, although protamine and heparin-protamine complex have been shown to activate complement components in vitro.In another group of 9 similar cardiac surgical patients, C3 and C4 were found to return to normal levels within 24 hours after operation. This study thus confirms the rapid activation of the complement system by cardiopulmonary bypass but fails to demonstrate further activation of the complement system by cardioplegia or protamine administration.     

Activation of inflammatory systems during cardiopulmonary bypass

"Whole body inflammation" induced by cardiopulmonary bypass may play a role in the pathogenesis of postoperative complications after open-heart surgery. The inflammatory response, in terms of complement activation and release of granular proteins from neutrophil granulocytes, was investigated in six patients undergoing aortocoronary bypass surgery. Complement activation was demonstrated as well as substantially increased plasma levels of lactoferrin and myeloperoxidase--two granulocyte factors. The activation of inflammatory systems probably takes place on the artificial surfaces of the extracorporeal device. The biocompatibility of these components therefore should be further studied.     

Differential expression of neutrophil adhesion molecules during coronary artery surgery with cardiopulmonary bypass.

BACKGROUND: Activation of neutrophil adhesion molecules and subsequent neutrophil adhesion to vascular endothelium are key events initiating inflammatory organ dysfunction after cardiopulmonary bypass and ischemic reperfusion. OBJECTIVES: We sought to characterize neutrophil integrin CD11b and L-selectin activation associated with coronary artery bypass graft surgery and to determine whether neutrophil activation contributes to their sequestration on postbypass reperfusion. METHODS: Twenty patients undergoing routine coronary artery bypass were studied. Heparinized whole blood was simultaneously sampled from a central venous line, aorta, coronary sinus, and right and left atrium before, during, and up to 20 minutes after cardiopulmonary bypass. Neutrophil counts were obtained, and neutrophil CD11b and L-selectin expression was determined by flow cytometric analysis in whole blood. RESULTS: CD11b expression on circulating neutrophils increased during cardiopulmonary bypass, peaking at 145% of baseline level after release of the aortic clamp and then declined by 20 minutes after bypass (analysis of variance, P =.003). No change in neutrophil L-selectin expression was observed during cardiopulmonary bypass. Neutrophils responded to ex vivo stimulation by C5a and leukotriene B(4) during cardiopulmonary bypass but not at 24 hours after the operation. After reperfusion, neutrophil loss, but not local activation, was demonstrated in the coronary and pulmonary circulations. CONCLUSIONS: Upregulated CD11b expression on neutrophils is likely to contribute to neutrophil sequestration in the heart and lungs after bypass, but neutrophil activation may be limited by their reduced responsiveness to agonist stimulation. CD11b represents a potential therapeutic target for diminishing inflammation after cardiac operations.