Platelet-leukocyte activation and modulation of adhesion receptors in pediatric patients with congenital heart disease undergoing cardiopulmonary bypass

Flow cytometry for evaluating platelet immunophenotyping and function in patients with thrombocytopenia

Platelets play an essential role in primary hemostasis through bleeding and thromboembolism. Thus, the diagnosis or evaluation of impaired hereditary, acquired, and drug-related platelet dysfunction has become imperative. The assessment of the platelet function is too complex for routine platelet function study. The major methods involved in platelet function study include platelet function analyzer testing, thromboelastography, thromboelastometry, light transmission aggregometry, and flow cytometry. The current review article focuses on the methods with flow cytometry for immunophenotyping of platelet and evaluating platelet function for platelet disorders, especially in patients with thrombocytopenia. According to the consensus published by the International Society on Thrombosis and Haemostasis, for inherited and acquired platelet disorders, the two major measures by which flow cytometry determines platelet function are glycoprotein IIb/IIIa/P-selectin (CD62p) expression and percentage of leukocyte-platelet aggregates. Using flow cytometry to determine platelet function has several advantages, including good sensitivity to low platelet counts, small blood volume required, and the nonnecessity of centrifugation. However, flow cytometry has still many limitations and challenges, with standardization for routine laboratory testing also proving difficult. Although flow cytometry is available for multipurpose and sensitive study of platelet functions at the same time, the challenging analysis gradually increases and needs to be addressed before reality.

Inflammation and Oxidative Stress in the Context of Extracorporeal Cardiac and Pulmonary Support

Extracorporeal circulation (ECC) systems, including cardiopulmonary bypass, and extracorporeal membrane oxygenation have been an irreplaceable part of the cardiothoracic surgeries, and treatment of critically ill patients with respiratory and/or cardiac failure for more than half a century. During the recent decades, the concept of extracorporeal circulation has been extended to isolated machine perfusion of the donor organ including thoracic organs (ex-situ organ perfusion, ESOP) as a method for dynamic, semi-physiologic preservation, and potential improvement of the donor organs. The extracorporeal life support systems (ECLS) have been lifesaving and facilitating complex cardiothoracic surgeries, and the ESOP technology has the potential to increase the number of the transplantable donor organs, and to improve the outcomes of transplantation. However, these artificial circulation systems in general have been associated with activation of the inflammatory and oxidative stress responses in patients and/or in the exposed tissues and organs. The activation of these responses can negatively affect patient outcomes in ECLS, and may as well jeopardize the reliability of the organ viability assessment, and the outcomes of thoracic organ preservation and transplantation in ESOP. Both ECLS and ESOP consist of artificial circuit materials and components, which play a key role in the induction of these responses. However, while ECLS can lead to systemic inflammatory and oxidative stress responses negatively affecting various organs/systems of the body, in ESOP, the absence of the organs that play an important role in oxidant scavenging/antioxidative replenishment of the body, such as liver, may make the perfused organ more susceptible to inflammation and oxidative stress during extracorporeal circulation. In the present manuscript, we will review the activation of the inflammatory and oxidative stress responses during ECLP and ESOP, mechanisms involved, clinical implications, and the interventions for attenuating these responses in ECC.

Post-operative blood loss is higher among African American neonates undergoing open-heart surgery with cardiopulmonary bypass for CHD

BACKGROUND

Neonates are at high risk of bleeding after open-heart surgery. We sought to determine pre-operative and intra-operative risk factors for increased bleeding after neonatal open-heart surgery with cardiopulmonary bypass.

METHODS

We conducted a retrospective cohort study of neonates (0-30 days old) who underwent open-heart surgery with cardiopulmonary bypass from January, 2009, to March, 2013. Cardiac diagnosis; demographic and surgical data; and blood products, haemostatic agents, and anti-thrombotic agents administered before, during, and within 24 hours after surgery were abstracted from the electronic health record and anaesthesia records. The outcome of interest was chest tube output (in ml/kg body weight) within 24 hours. Relationships between chest tube output and putative associated factors were evaluated by unadjusted and adjusted linear regression.

RESULTS

The cohort consisted of 107 neonates, of whom 79% had a Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery (STAT) Mortality Category of 4 or 5. Median chest tube output was 37 ml/kg (range 9-655 ml/kg). Age, African-American race, and longer durations of surgery and cardiopulmonary bypass each had statistically significant associations with increased chest tube output in unadjusted analyses. In multivariable analysis, African-American race retained an independent, statistically significant association with increased chest tube output; the geometric mean of chest tube output among African-American neonates was 71% higher than that of Caucasians (95% confidence interval, 29-125%; p = 0.001).

CONCLUSION

Among neonates with CHD undergoing open-heart surgery with cardiopulmonary bypass, African-American race is independently associated with greater chest tube output over the first 24 hours post-operatively.

Platelet-leukocyte aggregate is associated with adverse events after surgical intervention for rheumatic heart disease

Platelet-leukocyte aggregate (PLA) is implicated in the etiology of both vascular lesions and cardiovascular events. This prospective cohort study aimed to examine the prognostic value of PLA for major adverse cardiac and cerebrovascular events (MACCE) and perioperative adverse events (AEs) in patients with rheumatic heart disease undergoing surgical intervention by Cox proportional hazard regression and logistic regression. A total of 244 patients were included, of whom 7 were lost to follow-up. Among the analyzed 237 subjects who completed 3-year follow-up, 30 experienced MACCE and 38 experienced perioperative AEs. Preoperative PLA was higher in subjects who developed MACCE (13.32%) than in those who did not (8.69%, p = 0.040). In multivariate regression, elevated PLA was associated with increased MACCE (hazard ratio 1.51 for each quartile, 95% CI 1.07-2.13; p = 0.020), and perioperative AEs (odds ratio 1.61, 95% CI 1.14-2.26; p = 0.007). The optimal PLA cut-off for predicting MACCE was 6.8%. Subjects with PLA > 6.8% had a higher prevalence of MACCE (17.1% vs. 5.5%, p = 0.009) and perioperative AEs (19.9% vs. 8.6%, p = 0.018). Kaplan-Meier analysis showed shorter MACCE-free survival in patients with PLA > 6.8% (p = 0.007, log rank). Elevated preoperative PLA is associated with increased MACCE and perioperative AEs in patients with rheumatic valve disease undergoing surgical intervention.

Blood Platelet Activation and Membrane Glycoprotein Changes during Extracorporeal Life Support (Ecls). In Vitro Studies

The aim of this study was to evaluate an in vitro model for investigation of platelet function parameters in an extracorporeal system. Two different perfusion pumps were compared, a roller pump (Polystan) and a centrifugal pump (Biomedicus). A continuous increase in glycoprotein (GP)1b-negative platelets was observed in both circuits. A marked increase of plasma β-thromboglobulin thromboglobulin concentration and a decrease of the intracellular pool of serotonin was observed, indicating a marked release of alpha as well as of dense granules. The plasma concentration of glycocalicin increased in parallel with a reduced platelet surface expression of GP1b, suggesting that the loss of GP1b is caused by proteolysis rather than by a downregulation of this receptor protein. It is concluded that ECLS results in a pronounced platelet degranulation and causes changes of important membrane receptors which might explain some of the bleeding problems observed in patients treated with ECLS. No significant difference was noted between the roller pump and the centrifugal pump. Trial of strategies, e.g. protease inhibitors and nitric oxide to revert this untoward effect of ECLS are highly warranted.

Global and Extended Coagulation Monitoring during Extracorporeal Lung Assist with Heparin-Coated Systems in ARDS Patients

Heparin-coated systems for extracorporeal lung-assist (ECLA) were developed to reduce hemorrhagic risk by lowering the systemic heparinization, monitored by global tests, e.g. activated coagulation time (ACT) and activated partial thromboplastin time (APTT). Since this strategy gives no insight into procoagulant states, five ARDS patients receiving ECLA with heparin-coated systems were investivated for changes in coagulation using both global and extended tests. During ECLA onset the APTT and ACT were within or near normal ranges, platelets decreased 76.5% within 48h, fibrinogen decreased 28.7%, thrombin-antithrombin-III complexes were elevated before ECLA (53 μg/L), but demonstrated an additional peak (238 μg/L), plasminogen-activator-inhibitor-1 increased 12-fold, and the C1-inhibitor dropped 14.1%. In conclusion, after the onset of ECLA from a previous prethrombotic state, the precoagulant, anticoagulant, fibrinolytic and complement systems were activated in a similar way to that reported for non-heparinized systems with high-dose heparin. This was however only monitored by an extended test panel which was unable to predict thromboembolic events during ECLA.

Endotoxin Removal from Whole Blood by a Novel Adsorption Resin: Efficiency and Hemocompatibility

The structural component of Gram- bacteria, endotoxin (ET), induces the release of endogenous mediators of sepsis. Attempts to remove these downstream molecules in vivo, have not improved survival. However, extracorporeal strategies such as continuous renal replacement therapy or therapeutic plasmapheresis have shown benefit. We are presenting an affinity-based extracorporeal technology for the removal of ET from whole blood. The small-scale device contains an adsorbent that removed 75% of ET present in whole blood. This affinity resin displayed good hemocompatibility regarding the coagulation pathway. Minimal platelet, neutrophil and complement activation were observed. There was also no evidence of consumption of coagulation factors or cell loss. In as much as ET participates in both the inflammatory and coagulation abnormalities in sepsis, this method represents an efficient and hemocompatible way to remove ET from whole blood, which, in an extracorporeal setting, may improve the outcome of sepsis.

Use of Confidex to control perioperative bleeding in pediatric heart surgery: prospective cohort study

Bleeding during and after cardiac surgery is a major issue in pediatric patients. A prospective cohort study was conducted to evaluate the effect of a commercially available prothrombin complex (Confidex) administered in cardiac surgery after weaning from cardiopulmonary bypass of infants with nonsurgical bleeding. In this study, 14 patients younger than 1 year received a Confidex bolus and were matched with 11 patients of a similar age who did not receive the drug. The preoperative coagulation profile was similar in the two groups. No side effects, including anaphylaxis or thrombotic events, were observed. The numbers of units of packed red blood cells and fresh frozen plasma administered both intra- and postoperatively were similar. The postoperative coagulation examination results and thromboelastographic parameters did not differ significantly between the two groups. However, the Confidex patients bled significantly less than the control subjects during the first 24 postoperative hours. The median volume of drained blood was 0.0 ml/kg h (range 0-1.9 ml/kg h) compared with 1.9 ml/kg h (range 1-3 ml/kg h) (p = 0.009). At least one unit of packed red blood cells in the postoperative phase was required by 2 patients (14 %) in the Confidex group and six patients (54 %) in the control group (odds ratio [OR], 0.13; 95 % confidence interval [CI], 0.02-0.9; p = 0.03). The median duration of mechanical ventilation was 3 days (range 2-4 days) in the Confidex group and 4 days (range 0-8 days) in the control group (p = 0.66). The median stay in the intensive care unit was 6 days (range 5-9 days) in the Confidex group and 7 days (range 4-12 days) in the control group (p = 0.88). The use of Confidex for infants undergoing cardiac surgery was safe and effective. It reduced postoperative bleeding and allowed fewer units of packed red blood cells to be infused in the postoperative phase without major side effects.

Abnormal whole blood thrombi in humans with inherited platelet receptor defects

To delineate the critical features of platelets required for formation and stability of thrombi, thromboelastography and platelet aggregation measurements were employed on whole blood of normal patients and of those with Bernard-Soulier Syndrome (BSS) and Glanzmann's Thrombasthenia (GT). We found that separation of platelet activation, as assessed by platelet aggregation, from that needed to form viscoelastic stable whole blood thrombi, occurred. In normal human blood, ristocetin and collagen aggregated platelets, but did not induce strong viscoelastic thrombi. However, ADP, arachidonic acid, thrombin, and protease-activated-receptor-1 and -4 agonists, stimulated both processes. During this study, we identified the genetic basis of a very rare double heterozygous GP1b deficiency in a BSS patient, along with a new homozygous GP1b inactivating mutation in another BSS patient. In BSS whole blood, ADP responsiveness, as measured by thrombus strength, was diminished, while ADP-induced platelet aggregation was normal. Further, the platelets of 3 additional GT patients showed very weak whole blood platelet aggregation toward the above agonists and provided whole blood thrombi of very low viscoelastic strength. These results indicate that measurements of platelet counts and platelet aggregability do not necessarily correlate with generation of stable thrombi, a potentially significant feature in patient clinical outcomes.

Platelet-Derived Microparticles and Platelet Function Profile in Children With Congenital Heart Disease

Platelet microparticles (PMPs) and function profile in children with congenital heart disease (CHD) have not been widely explored. We investigated platelet aggregation, flow cytometric platelet surface receptors (P-selectin and glycoprotein (GP) IIb/IIIa) and PMPs in 23 children with cyanotic CHD (CCHD), 30 children with acyanotic CHD (ACHD) and 30 healthy controls correlating these variables to hematological and coagulation parameters including von Willebrand factor antigen (vWF Ag) as a marker of endothelial dysfunction. Hemoglobin, hematocrit (HCT), d-dimer, and vWF Ag were significantly higher in CCHD than ACHD group. Platelet MPs and P-selectin expression were increased in patients than controls, particularly in CCHD and positively correlated to HCT, d-dimer, and vWF Ag while platelet count, aggregation, and GP IIb/IIIa expression were decreased in CCHD compared with ACHD group and negatively correlated to HCT. The overproduction of PMPs and platelet activation with suppressed aggregation may be implicated in the pathogenesis of coagulation/hemostatic abnormalities in children with CCHD.

Role of GPIIb-IIIa in platelet-monocyte and platelet-neutrophil conjugate formation in whole blood

Platelets in stirred whole blood can be induced to form aggregates and also to form heterotypic platelet-monocyte (P/M) and platelet-neutrophil (P/N) conjugates. Here we have investigated the effects of three GPIIb-IIIa antagonists (GR144053F, MK-852 and Reopro, a CD62P-blocking antibody, GA6, and EDTA on the conjugate formation that occurs on stirring whole blood and in response to adding ADP and PAF. We have confirmed the identities of the conjugates by light microscopy after cell sorting. Platelet aggregation was measured by platelet counting. Monocytes, neutrophils, P/M and P/N were detected and quantitated using immunofluorescence and flow cytometry. Stirring whole blood resulted in both platelet aggregation and formation of P/M but not P/N. Adding ADP or PAF to whole blood caused rapid platelet aggregation and generation of both P/M and P/N. All of the GPIIb-IIIa antagonists studied had similar effects: inhibition of stirring-induced platelet aggregation and P/M formation, and inhibition of ADP-induced platelet aggregation and P/N formation. In contrast, they accelerated ADP induced-P/M conjugate formation and PAF-induced formation of both P/M and P/N. Both EDTA and GA6 completely inhibited P/M and P/N, which is commensurate with CD62P being involved in platelet-leucocyte conjugate formation. The results of these investigations suggest that GPIIb-IIIa has a dual role in determining the interaction between platelets and leukocytes.

Platelet activation in the postoperative period after lung transplantation

OBJECTIVE

During lung transplantation, cells in the pulmonary parenchyma are subjected to ischemia, hypothermic storage, and reperfusion injury. Platelets, whose granular contents include adhesion receptors, chemokines, and coactivating substances that activate inflammatory and coagulant cascades, likely play a critical role in the lung allograft response to ischemia and reperfusion. The platelet response to the pulmonary allograft, however, has never been studied. Here we report significant platelet activation immediately after lung transplantation.

METHODS

We performed a prospective cohort study comparing markers of platelet activation in patients undergoing lung transplantation and patients undergoing nontransplant thoracotomy. Plasma levels of soluble P-selectin, soluble CD40 ligand, and platelet-leukocyte conjugates were measured before surgery, after skin closure, and at 6 postoperative hours.

RESULTS

Both soluble P-selectin and soluble CD40 ligand levels increased significantly after lung transplantation but not after thoracotomy. Additionally, platelet-monocyte conjugate fluorescence was significantly higher after lung transplantation than after thoracotomy alone.

CONCLUSION

These findings suggest that platelet activation is significantly increased after lung transplantation beyond that expected from the postoperative state. The increase in circulating platelet-monocyte conjugates suggests an important interaction between platelets and inflammatory cells. Further research should examine whether platelet activation affects early graft function after lung transplantation.

Factor H dysfunction in patients with atypical hemolytic uremic syndrome contributes to complement deposition on platelets and their activation

Atypical hemolytic uremic syndrome (aHUS) may be associated with mutations in the C-terminal of factor H (FH). FH binds to platelets via the C-terminal as previously shown using a construct consisting of short consensus repeats (SCRs) 15 to 20. A total of 4 FH mutations, in SCR15 (C870R) and SCR20 (V1168E, E1198K, and E1198Stop) in patients with aHUS, were studied regarding their ability to allow complement activation on platelet surfaces. Purified FH-E1198Stop mutant exhibited reduced binding to normal washed platelets compared with normal FH, detected by flow cytometry. Washed platelets taken from the 4 patients with aHUS during remission exhibited C3 and C9 deposition, as well as CD40-ligand (CD40L) expression indicating platelet activation. Combining patient serum/plasma with normal washed platelets led to C3 and C9 deposition, CD40L and CD62P expression, aggregate formation, and generation of tissue factor-expressing microparticles. Complement deposition and platelet activation were reduced when normal FH was preincubated with platelets and were minimal when using normal serum. The purified FH-E1198Stop mutant added to FH-deficient plasma (complemented with C3) allowed considerable C3 deposition on washed platelets, in comparison to normal FH. In summary, mutated FH enables complement activation on the surface of platelets and their activation, which may contribute to the development of thrombocytopenia in aHUS.

Cell-derived microparticles and exosomes in neuroinflammatory disorders

All blood cells and the vascular endothelium shed microparticles (MP) from their plasma membranes when suitably stimulated, and assay of MP in patient blood has found increasing application to the monitoring of disease states. In addition, mounting evidence suggests that MP are not mere epiphenomena but play significant roles in the pathophysiology of thromboses, inflammation, and cancers. This chapter endeavors to summarize the limited number of studies thus far done on MP in neurological disorders such as multiple sclerosis (MS), transient ischemic attacks, and the neurological manifestations of antiphospholipid syndrome (APS). In addition, the chapter offers some plausible hypotheses on possible roles of MP in the pathophsyiology of these disorders, chiefly, the hypothesis that MP are indeed important participants in some neuropathologies, especially those which are ischemic in nature, but probably also inflammatory ones. The chapter also goes over the history and general principles of MP studies (e.g., assay methods and pitfalls), comparison with alternative methods (e.g., soluble markers of disease states), subclasses of MP (such as exosomes), and other topics aimed at helping readers to consider MP studies in their own clinical fields. Tables include a listing of bioactive agents known to be carried on MP, many of which were heretofore considered strictly soluble, and some of which can be transferred from cell to cell via MP vectors, for example certain cytokine receptors.

Reperfusion injury following cerebral ischemia: pathophysiology, MR imaging, and potential therapies

Introduction

Restoration of blood flow following ischemic stroke can be achieved by means of thrombolysis or mechanical recanalization. However, for some patients, reperfusion may exacerbate the injury initially caused by ischemia, producing a so-called “cerebral reperfusion injury”. Multiple pathological processes are involved in this injury, including leukocyte infiltration, platelet and complement activation, postischemic hyperperfusion, and breakdown of the blood–brain barrier.

Methods/results and conclusions

Magnetic resonance imaging (MRI) can provide extensive information on this process of injury, and may have a role in the future in stratifying patients’ risk for reperfusion injury following recanalization. Moreover, different MRI modalities can be used to investigate the various mechanisms of reperfusion injury. Antileukocyte antibodies, brain cooling and conditioned blood reperfusion are potential therapeutic strategies for lessening or eliminating reperfusion injury, and interventionalists may play a role in the future in using some of these therapies in combination with thrombolysis or embolectomy. The present review summarizes the mechanisms of reperfusion injury and focuses on the way each of those mechanisms can be evaluated by different MRI modalities. The potential therapeutic strategies are also discussed.

Procedure-induced Inflammation and Endothelial Cell Activation in an Artificially Ventilated and Circulated Porcine Double-Lung Model

Systemic inflammation is induced during extracorporeal circulation, resulting in an increased bleeding tendency and endothelial cell activation. Lungs from seven piglets were perfused by autologous blood in an extracorporeal circuit, where the lungs and the left atrium were attached to polyvinyl chloride (PVC) tubings and the blood circulated by a roller pump. The trachea was intubated and attached to a ventilator. The lungs maintained good gas exchange, despite a slight increase in lactate levels. Plasma tPA increased slightly over time, suggesting endothelial cell activation. Activation of inflammatory systems was reflected in increased levels of plasma interleukin (IL)-6 and IL-10. A model for the study of lung endothelial activation during extracorporeal circulation has been shown to be reproducible. The lung tissue was shown to be capable of gas exchange and activation of endothelial cells and procedure-induced inflammation were noted.

Aprotinin attenuates the elevation of pulmonary vascular resistance after cardiopulmonary bypass

Pulmonary vascular resistance (PVR) is generally believed to be elevated after cardiopulmonary bypass (CPB) due to whole body inflammation. Aprotinin has an antiinflammatory action, and it was hypothesized that aprotinin would attenuate the PVR increase induced by CPB. Ten mongrel dogs were placed under moderately hypothermic CPB for 2 hr. The experimental animals were divided into a control group (n=5, group I) and an aprotinin group (n=5, group II). In group II, aprotinin was administered during pre-bypass (50,000 KIU/kg) and post-bypass (10,000 KIU/kg) periods. Additional aprotinin (50,000 KIU/kg) was mixed in CPB priming solution. PVRs at pre-bypass and post-bypass 0, 1, 2, 3 hr were calculated, and lung tissue was obtained after the experiment. Post-bypass PVRs were significantly higher than prebypass levels in all animals (n=10, p<0.001). PVR elevation in group II was less than in group I at 3 hr post-bypass (p=0.0047). Water content of the lung was lower in group II (74+/-9.4%) compared to that of group I (83+/-9.5%), but the difference did not reach significance (p=0.076). Pathological examination showed a near normal lung structure in group II, whereas various inflammatory reactions were observed in group I. We concluded that aprotinin may attenuate CPB-induced PVR elevation through its anti-inflammatory effect.

Levels of endothelial and platelet microparticles and their interactions with leukocytes negatively correlate with organ dysfunction and predict mortality in severe sepsis

OBJECTIVE

Mortality in sepsis is believed to be associated with exaggerated inflammatory responses, but recent evidence suggests that poor outcome is associated with reduced inflammation. To test this hypothesis, we measured several inflammatory markers to determine whether any of them or any combinations are associated with mortality or organ dysfunction.

DESIGN

Clinical study.

SETTING

School of medicine.

PATIENTS

Thirty-five patients with severe sepsis.

INTERVENTIONS

Markers of endothelial, platelet, and leukocyte activation were measured on days 1, 2, and 3 after enrollment. The markers were a) endothelial microparticles (EMPs) and their conjugates with monocytes (EMP/MONO); b) platelet microparticles (PMPs) and platelet activation marker CD62P; c) platelet-leukocyte conjugates (PLT/LEU) and leukocyte activation marker CD11b; and d) intracellular nitric oxide in leukocytes.

MEASUREMENTS AND MAIN RESULTS

The 28-day mortality rate was 51% (18 of 35). Significant differences between survivors and nonsurvivors on day 1 were found in PLT/LEU (p = .001), CD11b (p = 0.02), and EMP/MONO (p = .02) groups. Using logistic regression to assess if these markers predict mortality on day 1, we found that PLT/LEU had the best predictive value among the markers used (area under receiver operating characteristics curve = 0.82). All markers of cell activation and inflammation were significantly higher among survivors on days 2 and 3, except nitric oxide, which was lower. This marker showed significant negative correlation with the Sequential Organ Failure Assessment score throughout the study.

CONCLUSIONS

Our data support the hypothesis that early increased, not decreased, inflammatory response as measured by our markers is associated with improved survival rate. A high negative correlation was found between some of these markers and Sequential Organ Failure Assessment score.

Conditioned blood reperfusion markedly enhances neurologic recovery after prolonged cerebral ischemia

OBJECTIVES

To determine whether controlled reperfusion using conditioned leukodepleted blood can substantially limit cerebral reperfusion injury following prolonged ischemia.

METHODS

Eighteen pigs (25-35 kg) underwent 90 minutes of hypothermic circulatory arrest (19 degrees C) to produce brain ischemia. At the start of rewarming, 10 pigs received uncontrolled reperfusion with unmodified (normal) blood. The other 8 pigs underwent 10 minutes of controlled reperfusion by selectively perfusing both common carotid arteries with blood passed through a CoBRA filter. This filter conditions the blood by removing white blood cells, platelets, and attenuating complement. Two other pigs underwent cooling and rewarming only (controls) without ischemia. Neurologic assessment was done using neurologic deficit scoring (0 = normal, 500 = brain death), and jugular venous samples were obtained for biochemical analysis postreperfusion.

RESULTS

There were no statistical differences in hemodynamics between groups. At 6 hours postanesthesia, all animals receiving normal blood were substantially neurologically impaired. At 24 hours, they all had abnormal positioning and all but 1 were unable to sit or stand (neurologic score 124 +/- 19). In contrast, nonischemic controls and pigs receiving conditioned blood reperfusion showed only minor neurologic deficits at 6 hours, and at 24 hours all were considered normal (neurologic scores 0 and 6 +/- 5; P <.005 vs uncontrolled reperfusion). Compared with pigs receiving normal blood reperfusion, oxygen free radical formation (conjugated dienes 1.70 +/- 0.03 vs 1.60 +/- 0.02 Abs 240 nm; P <.05 vs uncontrolled reperfusion), and endothelin-1 release (2.12 +/- 0.09 vs 1.84 +/- 0.06 pg/mL; P <.05 vs uncontrolled reperfusion) were also significantly lower in animals receiving conditioned blood.

CONCLUSIONS

Following prolonged cerebral ischemia, reperfusion injury is avoided by delivering conditioned blood, which is devoid of white cells, platelets, and membrane attack complex. These results suggest that this modality is clinically useful in situations where the brain is subjected to prolonged ischemia.

Pharmacological inhibition of plasma coagulation and platelet activation during experimental long-term perfusion

OBJECTIVE

During extracorporeal circulation, initial contact between blood and the artificial surface of the circuit induces an overall activation of the hemostatic system. The objective of this study was to investigate the combined effect of epoprostenol (PGI (2) ), nitric oxide (NO) and nafamostat mesilate (FUT-175, a serine protease inhibitor), on plasma coagulation and platelet activation during experimental long-term perfusion.

DESIGN

Two identical extracorporeal life support (ECLS) circuits were primed with fresh, heparinized human blood, and circulated for 24 h. FUT was given with a bolus dose of 85 mg/l blood at the initiation of the experiment and thereafter as a continuous infusion of 14 mg/l/h. PGI (2), at a rate of 2.4 microg/l/h, was also administered to the experimental circuit, and 120 ppm NO gas was added to the oxygenator sweep gas. The other circuit was used as a control.

RESULTS

Higher platelet count and platelet membrane expression of GPIb were found in the experimental circuits as compared with control circuits. The levels of thrombin/antithrombin III complex (TAT) and prothrombin fragment 1 + 2 (F1 + 2) increased significantly over time in the control circuits but remained low in the experimental circuits. Plasma levels of plasminogen activator inhibitor 1 (PAI-1) decreased rapidly in both circuits but were higher in the control circuits at each time point studied.

CONCLUSION

The activation of platelets and of the coagulation system encountered during extracorporeal perfusion is consistently inhibited by a combination of PGI (2), NO and FUT-175. The combination of these drugs appears to be more effective than each drug separately.

Severe meningococcal disease is characterized by early neutrophil but not platelet activation and increased formation and consumption of platelet-neutrophil complexes

Approximately 25% of polymorphonuclear leukocytes (PMNL) circulate in heterotypic complexes with one or more activated platelets. These platelet-neutrophil complexes (PNC) require platelet CD62P expression for their formation and represent activated subpopulations of both cell types. In this study, we have investigated the presence, time course, and mechanisms of PNC formation in 32 cases of severe pediatric meningococcal disease (MD) requiring intensive care. There were marked early increases in PMNL CD11b/CD18 expression and activation, and reduced CD62L expression compared with intensive care unit control cases. Minimal platelet expression of the active form of alphaIIbbeta3 (GpIIb/IIIa) was seen. PNC were reduced on presentation and fell to very low levels after 24 h. Immunostaining of skin biopsies demonstrated that PNC appear outside the circulation in MD. In vitro studies of anticoagulated whole blood inoculated with Neisseria meningitidis supported these clinical findings with marked increases in PMNL CD11b/CD18 expression and activation but no detectable changes in platelet-activated alphaIIbbeta3 or CD62P expression. In vitro PMNL activation with N. meningitidis (or other agonists) potentiated the formation of PNC in response to platelet activation with adenine diphosphate. Therefore, in severe MD, PMNL activation is likely to promote PNC formation, and we suggest that the reduced levels of PNC seen in established MD reflect rapid loss of PNC from the circulation rather than reduced formation.

Deterioration of gas exchange in patients with severe thrombotic thrombocytopenic purpura with respiratory failure during therapeutic plasma exchange

Therapeutic plasma exchange (TPE) is a procedure performed on patients suffering from various disorders, including thrombotic thrombocytopenic purpura (TTP). As we noted a frequent transient deterioration in respiratory function when the procedure was performed on intensive care unit (ICU) patients, we studied retrospectively the incidence of respiratory deterioration during and shortly after TPE and looked for a probable correlation with a change in the white blood cell (WBC) counts. Over a period of 10 months six patients with TTP, five of whom had parenchymal lung disease due to different medical reasons, underwent TPE. The oxygen saturation was measured continuously before, during, and after TPE; additionally, the WBC and differential counts were measured pre- and post-TPE. The ratio of the oxygen saturation by pulse oxymetry (SpO2) to the fraction of inspired oxygen (FiO2) was calculated before, during and after TPE. In these five patients with lung disorders, there was a consistent trend of a decreasing SpO2/FiO2 quotient during and within 2 h post TPE compared to the pre-TPE value. The decrease in SpO2/FiO2 range was 0.20-0.89 with an average of 0.56. In the same 5 patients there was an increase in the WBC count in the range of 2.3-19.7 x 10(9)/L with an average increase of 9.3 x 10(9)/L. The percent neutrophils of the total WBC counts also increased following most of the sessions, this increase was in the range of 1-15 % with an average of 7%. The effect of TPE on the SpO2/FiO2 ratio and the correlation to the WBC count and to a possible neutrophil activation has not been previously reported. We postulate that TPE can accentuate respiratory deterioration in patients with TTP who already have acute lung injury. This may be due to the priming and activation of the leukocytes that could lead to the release of cytokines and inflammatory mediators during the procedure. Thus, it is important to be aware of the possible deterioration in respiratory function and gas exchange while administering TPE to patients with pre-existing parenchymal lung injury.

Platelet and leukocyte activation and design consequences for thoracic artificial lungs

Blood contact with the prosthetic surfaces of artificial lungs causes extensive activation of molecular and cellular mediators of coagulation and inflammation that can lead to patient morbidity and mortality. To determine the effects of artificial lung fiber bundle shear stress and surface area on blood activation, porcine blood was recirculated for 4 hours through circuits containing mock artificial lungs with bundle shear stresses of 11.6, 7.3, and 3.9 dynes/cm2 and surface areas of 5.2, 3.5, and 1.7 cm2/ml of circuit volume. Blood from these circuits was assayed for platelet and leukocyte counts, soluble P-selectin concentrations, and lactoferrin concentrations to determine the level of platelet and leukocyte adherence to the circuit, platelet activation, and leukocyte activation, respectively. Neither platelet nor leukocyte counts were significantly affected by shear stress or surface area. P-selectin and lactoferrin concentrations were significantly greater at a fiber bundle shear stress of 11.6 dynes/ cm2. P-selectin and lactoferrin concentrations were significantly greater at a fiber bundle surface area of 5.2 cm2/ml of circuit volume. Artificial lungs, therefore, should be designed with average bundle shear stresses < 11.6 dynes/cm2 and with surface areas < 5.2 cm2/ml of circuit volume. Current thoracic artificial lungs meet both these requirements.

Reactive hemophagocytic syndrome associated with thrombotic thrombocytopenic purpura during therapeutic plasma exchange

Hemophagocytic lymphohistiocytosis (HLH) is characterized by fever, cytopenia, splenomegaly, and lymphohistiocytic proliferation with hemophagocytosis. Sporadic, familial, and reactive HLH varieties exist. The latter, also termed the reactive hemophagocytic syndrome (RHS), has been associated with a variety of infectious and noninfectious etiologies. Activation of monocytes in RHS is due to stimulation by high levels of activating cytokines. RHS has not been associated previously with thrombotic thrombocytopenic purpura (TTP). TTP is a multisystem disorder characterized by consumptive thrombocytopenia, microangiopathic hemolytic anemia, neurologic symptoms, renal impairment, and fever. We report on a 33 year old male patient with a classic picture of TTP who initially responded to therapeutic plasma exchange but then became refractory to treatment and developed RHS. It is likely that a specific pathophysiology involving the activation of neutrophils during TPE is present for the development of cytokine-induced hemophagocytosis during TTP treatment. The consequent development of RHS possibly caused early TTP relapse.

The effects of platelet apheresis in total hip replacement surgery on platelet activation

BACKGROUND

Autologous platelet rich plasma (PRP) harvest with autotransfusion devices has been used for 10 years in cardiac surgery and recently in orthopedics as a blood saving method. The quality of the harvested platelets has not been adequately examined, in part because of methodological difficulties in studying platelet function during surgery.

METHODS

Twenty patients undergoing primary total hip replacement (THR) were studied. Ten patients underwent an immediate preoperative platelet apheresis to obtain concentrated platelet rich plasma (c-PRP). The other 10 patients not undergoing apheresis were allocated to a control group. Platelet activation was evaluated as the population expressing P-selectin on the surface of platelets in the c-PRP and in blood samples collected pre-, per- and postoperatively. The method used was flow cytometry.

RESULTS AND CONCLUSIONS

A minor population of activated platelets was found to be circulating in the patients' blood, with a highly significant difference between patients (P = 0.005), and with a range of 1-23% in peroperative activation. PRP harvest did not significantly alter platelet activity. The platelet apheresis procedure did not inhibit platelet function in the c-PRP, as judged by a high proportion of platelets that could be activated in ADP stimulation experiments (mean value +/- SD 86% +/- 7.5%).

Inflammation After Cardiopulmonary Bypass: Therapy for the Postpump Syndrome

Cardiopulmonary bypass (CPB) is used in most, but not all, complex heart operations. CPB is associated with a systemic inflammatory response in adults and children. Many materials-dependent (exposure of blood to non- physiologic surfaces and conditions) and materials-in dependent (surgical trauma, ischemia-perfusion to the organs, changes in body temperature, and release of endotoxin) factors during CPB have been implicated in the etiology of this complex response. The mechanisms involved may include complement activation, release of cytokines, leukocyte activation with expression of ad hesion molecules, and production of various vasoactive and immunoactive substances. Postpump inflamma tion may lead to postoperative complications and may result in respiratory failure, renal dysfunction, bleeding disorders, neurologic dysfunction, altered liver func tion, and ultimately multiple organ failure. Significant efforts are being made to decrease the generation and effects of postpump inflammation. Interventions to this end have included avoiding CPB when possible, im proving the biocompatibility of the involved mechani cal devices, and administering medications that main tain cellular integrity. This article provides an overview of the etiology, pathophysiology, and treatment of postpump inflammation. Perhaps with additional in sight into this syndrome, CPB can be made a safer and more efficacious modality of cardiorespiratory support. Copyright© 2001 by W.B. Saunders Company.

Effects of combining three different antiplatelet agents on platelets and leukocytes in whole blood in vitro

1. Antiplatelet drugs have been demonstrated to reduce the incidence of recurrent events in patients with symptomatic vascular disease. However, there is no experimental data indicating the effects of these agents when given together on platelets and leukocytes. We investigated the ability of aspirin (an inhibitor of cyclo-oxygenase), dipyridamole (an inhibitor of phospodiesterases and adenosine uptake) and AR-C69931 (a direct acting P(2T) antagonist with effects similar to those of clopidogrel which can be used in vitro) when used alone or in combination to inhibit platelet and leukocyte function. 2. Measurements of platelet and leukocyte function were performed in blood taken from normal volunteers, and the inhibitory effects of aspirin (100 micromol l(-1)), dipyridamole (10 micromol l(-1)) and AR-C66931 (100 nmol l(-1)) were determined. Platelet aggregation was induced by stirring blood with and without adenosine diphosphate (ADP) or platelet activating factor (PAF) and measured by platelet counting. Platelet P-selectin expression, platelet-leukocyte conjugate formation, and leukocyte activation were determined by flow cytometry. 3. Dipyridamole, AR-C69931, dipyridamole and AR-C69931, dipyridamole and aspirin, AR-C69931 and aspirin, and all three agents together inhibited platelet aggregation induced by stirring, ADP and PAF (P<0.01). However, it was only the combination of all three agents inhibited P-selectin expression (P<0.01). Similarly, it was the combination of all three antiplatelet agents that most consistently inhibited platelet-monocyte and platelet-neutrophil conjugate formation and monocyte and neutrophil activation. 4. Since both platelets and leukocytes are thought to contribute to arterial thrombosis and atherosclerosis, it is possible that combinations of different antiplatelet agents with different mechanisms of action may afford better protection than individual or pairs of agents used on their own.

Activation of circulating platelets and platelet response to activating agents in children with cyanotic congenital heart disease: their relevance to palliative systemic-pulmonary shunt

Abnormal platelet function has been hypothesised to play a role in the haemostatic abnormalities in cyanotic congenital heart disease (CCHD) patients. Using whole blood flow cytometry we found that platelets from cyanotic patients were hyperreactive and we related such hyperreactivity directly to young age, unoperated state, high haematocrit, reduced saturation with oxygen and low platelet count. Circulating platelets from CCHD children showed significantly enhanced P-selectin expression (P<0.004) and remained more reactive to 0.2 IU/ml thrombin, 1-8 microM TRAP and 2-4 microM ADP (P<0.04), especially in younger (0-3-year-olds) patients. Such a platelet 'priming' largely concerned CCHD children who were not subjected to modified Blalock-Taussig shunts in the past (non-MBTS). Only non-MBTS cyanotic children, but not MBTS-operated patients, showed significantly higher platelet reactivity compared to controls in response to ADP or 1 microM TRAP with respect to P-selectin expression (p<0.05) and in response to all examined agonists with respect to GPIb expression (P<0.045). The enhanced P-selection expression in MBTS-operated CCHD children and reduced GPIb expression in non-MBTS patients, especially in younger patients, were positively associated with the occurrence of the polymorphic variant Pl(A2) of platelet membrane glycoprotein IIIa gene. Altered blood morphology parameters (elevated RBC, Hb, Hct and MCHC, for all P<0.0005) in CCHD children correlated with the enhanced degranulation of circulating blood platelets and their hyperreactivity in response to some agonists (P<0.05). Overall, our data encourage the reasoning that circulating platelets are remarkably hyperreactive in non-MBTS cyanotic children, which are at higher risk to often encounter platelets activation in circulation. It seems unlikely that the apparently unchanged platelet reactivity in MBTS-operated children is due to the advantageous effects of the shunt, since these patients showed neither altered haematological parameters nor improved oxygen carrying capacity. Otherwise, it may rather result from more frequent episodes of platelet degranulation and preactivation in the past, and/or post-operative enhanced platelet consumption.

Conditioned blood reperfusion during angioplasty (CoBRA) treatment of acute myocardial infarction

Acute myocardial infarct (MI) results in ischemia distal to lesions which puts heart muscle at risk for reperfusion injury (RI). Neutrophils, platelets and complement are putative mediators of RI. Recent advances in filtration technology provide integrated neutrophil and platelet removal together with complement-attenuating properties in a single blood-conditioning device. The present study characterizes the properties of a blood-conditioning filter and describes its clinical effect when used in conjunction with active hemoperfusion for acute MI. The filter reduces leukocytes by 99.9998 +/- 0.0002% (p<0.0001) and platelets by 99.9934 +/- 0.0069% (p<0.0001). Human plasma, derived from heparinized blood that was 'conditioned' by filtration, was studied using the Langendorff isolated rabbit heart preparation. The deposition of membrane attack complex and the resultant functional myocardial impairments [reflected in hemodynamic and biochemical measurements, including developed pressure, coronary blood flow, lymph-derived myocardial creatine kinase (CK)] are significantly attenuated by blood conditioning. Integration of the blood-conditioning filter into an active hemoperfusion system during primary percutaneous transluminal coronary angioplasty (PTCA) for acute MI (n=8) did not delay the procedure or cause any complications. Reperfusion of occluded coronary arteries with 300 cm3 of conditioned blood led to significant improvement in echocardiographic global wall motion scores (in standard deviations) following treatment (-1.64 +/- 0.18 to -1.45 +/- 0.15, p=0.02). Initial reperfusion of totally occluded coronary arteries with conditioned blood leads to acutely improved ventricular function. Collectively, these data provide a strong indication for continued investigation of conditioned blood reperfusion in angioplasty following acute MI for the long-term effect upon recovery of salvagable myocardium.

Aprotinin administration in the pericardial cavity does not prevent platelet activation

OBJECTIVES

Aprotinin is frequently administered systemically to patients undergoing cardiopulmonary bypass to inhibit activation of platelets and plasma protein systems and thus reduce postoperative blood loss. Two reports on local aprotinin administration, that is, into the pericardial cavity, also indicated improvement in postoperative blood loss, but the underlying mechanism was not investigated. We previously reported the disappearance of glycoprotein Ib from the platelet surface and the appearance of platelet-derived microparticles in the pericardial cavity of patients undergoing cardiopulmonary bypass as signs of platelet activation. Here, we investigated whether such local aprotinin administration reduced platelet activation.

METHODS

In a double-blind study, 6 patients received aprotinin (500,000 KIU) into the pericardial cavity during the operation and 7 patients received a placebo. Platelet surface glycoprotein Ib expression, concentration of microparticles, and concentration of complexes of platelets with leukocytes, erythrocytes, or each other, were measured by flow cytometry.

RESULTS

We confirmed the reduced glycoprotein Ib expression and the increased concentration of microparticles in the pericardial cavity, as previously reported, and found no increased concentration of platelet complexes. However, no differences between aprotinin and placebo treatments were observed in these platelet activation parameters in the pericardial cavity or the systemic circulation.

CONCLUSION

We conclude that administration of aprotinin into the pericardial cavity during cardiopulmonary bypass and at concentrations similar to the systemic application does not reduce platelet activation in that compartment or the systemic circulation.

Heparin, platelet aggregation, neutrophils, and cardiopulmonary bypass

Cardiopulmonary bypass (CPB) is associated with both neutrophil activation and failure of platelets to form large stable aggregates. We aimed to determine the effects of heparin and of neutrophil activation on platelet aggregation in whole blood. Fourteen patients undergoing routine aortocoronary bypass grafting and NSAID-free for over 7 days were studied before and after heparinisation, and at end-CPB. Whole blood, anticoagulated with rHirudin, was stirred for 3 minutes, and macroaggregation in response to collagen (0.6 microg. mL(-1)) or the neutrophil stimulant fMLP (10(-7)M) was determined by whole blood impedance aggregometry. Microaggregation was measured by counting unaggregated single platelets (corrected for haemodilution). The blood of volunteers was studied in vitro.

PATIENTS

Before CPB, heparin effectively abolished platelet macroaggregation induced by collagen (20.5 to 1.4 Ohms) or fMLP (3.9 to 0 Ohms (p<0.0001). CPB had no additional effect. Heparinisation also reduced the platelet count from 127 (110-170) to 95 (64-117). The inhibition of macroaggregation could not be reversed by ex vivo heparinase.

VOLUNTEERS

In vitro, the same heparin concentration, as measured in vivo (4 micromL(-1)), inhibited collagen-induced macroaggregation (20.3 to 14.7 Omega), but this effect was less than that observed ex vivo and was reversed by heparinase. In vitro heparin promoted fMLP macroaggregation (2.9 to 8.6 Omega). The inhibition of macroaggregation resulted from heparinisation, per se, rather than CPB and was insensitive to heparinase. There was less inhibition by in vitro heparin, which was reversible by heparinase, indicating a direct effect of heparin in vitro. The disparate findings are suggestive of an indirect action by heparin in vivo on macroaggregation, although heparin had a small direct stimulatory action on microaggregation.

Selective blockade of membrane attack complex formation during simulated extracorporeal circulation inhibits platelet but not leukocyte activation

OBJECTIVE

Complement activation is induced by cardiopulmonary bypass, and previous work found that late complement components (C5a, C5b-9) contribute to neutrophil and platelet activation during bypass. In the present study, we blocked C5b-9 formation during extracorporeal recirculation of whole blood to assess whether the membrane attack complex was responsible for both platelet and leukocyte activation.

METHODS

In a simulated extracorporeal model that activates complement (C3a and sC5b-9), platelets (CD62P expression, leukocyte-platelet conjugate formation), and leukocytes (increased CD11b expression and neutrophil elastase), we examined an anti-human C8 monoclonal antibody that inhibits C5b-9 generation for its effects on cellular activation.

RESULTS

Anti-C8 significantly inhibited sC5b-9 formation but did not block C3a generation. Anti-C8 also significantly inhibited the increase in platelet CD62P and monocyte-platelet conjugate formation seen with control circulation. Moreover, compared with control circulation, in which the number of circulating platelets fell by 45%, addition of anti-C8 completely preserved platelet counts. In contrast to blockade of both C5a and sC5b-9 during simulated extracorporeal circulation, neutrophil activation was not inhibited by anti-C8. However, circulating neutrophil and monocyte counts were preserved by addition of anti-C8 to the extracorporeal circuit.

CONCLUSIONS

The membrane attack complex, C5b-9, is the major complement determinant of platelet activation during extracorporeal circulation, whereas C5b-9 blockade has little effect on neutrophil activation. These data also suggest a role for platelet activation or C5b-9 (or both) in the loss of monocytes and neutrophils to the extracorporeal circuit.

Rapid in vitro biocompatibility assay of endovascular stents by flow cytometry using platelet activation and platelet-leukocyte aggregation

Clinical studies suggest that stent design and surface texture are responsible for differences in biocompatibility of metallic endovascular stents. A simple in vitro experimental setup was established to test stent-induced degree of platelet and leukocyte activation and platelet-leukocyte aggregation by flow cytometry. Heparin-coated tantalum stents and gold-coated and uncoated stainless steel stents were tested. Stents were implanted into silicone tubes and exposed to blood from healthy volunteers. Platelet and leukocyte activation and percentage of leukocyte-platelet aggregates were determined in a whole-blood assay by subsequent staining for activation-associated antigens (CD41a, CD42b, CD62p, and fibrinogen binding) and leukocyte antigens (CD14 and CD45) and flow cytometric analysis. Blood taken directly after venous puncture or exposed to the silicone tube alone was used as negative controls. Positive control was in vitro stimulation with thrombin receptor activating peptide (TRAP-6). Low degree of platelet activation and significant increase in monocyte- and neutrophil-platelet aggregation were observed in blood exposed to stents (P < 0.05). In addition, leukocyte activation was induced as measured by increased CD45 and CD14 expression. Heparin coated stents continuously induced less platelet activation and leukocyte-platelet aggregation than uncoated stainless steel stents of the same length and shorter stents of the same structure. Stent surface coating and texture plays a role in platelet and leukocyte activation and leukocyte-platelet aggregation. Using this simple in vitro assay and whole blood and flow cytometry, it seems possible to differentiate stents by their potency to activate platelets and/or leukocytes. This assay could be applied for improving the biocompatibility of coronary stents.

Platelet hyporeactivity in young infants during cardiopulmonary bypass

Platelet dysfunction is one of the most important factors contributing to a postoperative hemorrhagic diathesis in children with congenital heart disease undergoing operations requiring cardiopulmonary bypass (CPB). However, very little is known about the influence of CPB on platelets in neonates and young infants. We studied 16 patients--8 young infants (<2 mo old) and 8 children (>12 mo old)--with congenital heart disease undergoing CPB. Surface density of an important platelet adhesive receptor, glycoprotein Ib, and degree of platelet activation, indicated by p-selectin positivity, were measured by whole blood flow cytometry in samples obtained at seven time points during the operations. We found that the percentage of p-selectin-positive platelets increased significantly in children, but not in young infants, during CPB. The young infant group exhibited a significantly smaller reduction of glycoprotein Ib than the child group during CPB (21.0% +/- 12.0% vs 32.7% +/- 18.1%; P < 0.05). Lack of CPB-induced increase of p-selectin and a smaller decrease of glycoprotein Ib in young infants in the current study suggest reduced platelet reactivity in young infants and neonates during CPB. The clinical significance of the reduced platelet reactivity in young infants and neonates remains to be determined.

IMPLICATIONS

Platelets of young infants are less reactive than those of children during cardiopulmonary bypass, as determined by the cardiopulmonary bypass-induced alterations in platelet membrane adhesive receptors.

Chimeric 7E3 Fab (ReoPro) decreases detectable CD11b on neutrophils from patients undergoing coronary angioplasty

OBJECTIVES

The purpose of this study was to monitor the effects of chimeric 7E3 Fab (ReoPro) on leukocyte and platelet activation and interaction during coronary angioplasty.

BACKGROUND

Increased expression of CD11b on monocytes and neutrophils promotes their adhesion to endothelial cells, extracellular matrix and smooth muscle cells. Thrombin-activated platelets adhere via P-selectin to monocytes and neutrophils. These cell interactions may affect the outcome of coronary angioplasty.

METHODS

During coronary angioplasty, venous blood was obtained for flow cytometric detection of leukocyte CD11b; platelet CD41a, CD61a and CD62P; the percentage of leukocytes with adherent platelets and the intensity of bound platelet fluorescence.

RESULTS

Leukocyte CD11b expression increased after angioplasty in control patients (neutrophils 171+/-25 to 255+/-31 mean fluorescence intensity [MFI, mean+/-SEM], n=25, p < 0.0001; monocytes 200+/-40 to 248+/-36 MFI, n=17, p < 0.05) and decreased in the patients selected to receive chimeric 7E3 Fab (neutrophils 146+/-30 to 82+/-22 MFI, n=25, p < 0.0001; monocytes 256+/- 53 to 160+/-38 MFI, n= 17, p < 0.05). Neutrophil CD11b decreased after in vitro incubation of whole blood with chimeric 7E3 Fab (n=5, p=0.01), but fMLP-induced increases in CD11b were not prevented. The CD11b expression was unchanged and increased with fMLP stimulation after in vitro incubation of isolated neutrophils with chimeric 7E3 Fab. Direct-labeled chimeric 7E3 Fab was not detected bound to neutrophils in whole blood or isolated cells using flow cytometric techniques. Adhesion of isolated neutrophils to protein-coated glass was not prevented by in vitro incubation with chimeric 7E3 Fab. Platelet activation increased after angioplasty in control patients (CD62P 8.9+/-0.8 to 12.3+/-1.2 MFI, n=25, p < 0.05; CD41a 382+/-25 to 454+/-26 MFI, n=25, p < 0.05, CD61a 436+/-52 to 529+/-58 MFI, n=11, p < 0.05); it did not increase in the patients selected to receive chimeric 7E3 Fab (CD62P 13.2+/-1.0 to 9.0+/-0.9 MFI, n=25, p < 0.05; CD61a 398+/-32 to 410+/-38 MFI, n=7, p=NS). Leukocytes with adherent platelets tended to increase in the control group of patients and decrease after the procedure in patients selected to receive chimeric 7E3 Fab; individual and procedure-related variability were marked.

CONCLUSIONS

Despite standard aspirin and heparin therapy, leukocyte and platelet activation with platelet adherence to leukocytes occurs after coronary angioplasty. Although chimeric 7E3 Fab does not bind to leukocytes directly, it influences CD11b expression in whole blood. Modulation of platelet and leukocyte activation and interaction by chimeric 7E3 Fab may contribute to an improved outcome after coronary angioplasty.

Platelet-leukocyte aggregates during hemodialysis: effect of membrane type

Hemodialysis is associated with the formation of platelet-leukocyte aggregates. Whether this phenomenon is hemodialysis (HD) membrane dependent is unclear. To evaluate this process, we examined respectively platelet activation (anti-CD41, anti-CD62, and antifibrinogen monoclonal antibodies [MoAb] binding), leukocyte activation (CD11b expression), and the appearance of platelet specific antigens on leukocytes as an index of platelet-leukocyte aggregation during HD using 3 different membrane materials, Cuprophan, Hemophan, and polysulfone. Flow cytometric techniques and specific MoAb were used. All parameters were assayed 5 min after initiation of HD to avoid the confounding variable of leukopenia and resultant cell subpopulation analysis. Platelet activation (anti-CD62 and antifibrinogen binding) occurred only with Cuprophan. All 3 membranes induced equivalent increases in CD11b expression on neutrophils and similarly increased the binding of anti-CD41 to neutrophils, reflecting an increment in the formation of platelet neutrophil aggregates. However, only Cuprophan induced an increase in anti-CD62 binding to neutrophils, suggesting that the aggregated platelets linked to neutrophils were activated. Increased anti-CD41 binding by monocytes was similarly observed with all 3 membranes. However, only polysulfone induced an increase in CD11b expression and fibrinogen binding to monocytes. We conclude that while the formation of platelet leukocyte aggregates appears to be a universal phenomenon in HD occurring with a variety of membrane types, subtypes of this phenomenon consisting of activated platelets and fibrinogen binding may be membrane dependent. This phenomenon may serve as a new biocompatibility parameter and may shed light on some of the biologic consequences of hemodialysis.

Effects of cardiopulmonary bypass on leukocyte and endothelial adhesion molecules

During the inflammatory response, triggered by cardiopulmonary bypass, interaction between activated leukocytes, platelets, and endothelial cells is mediated through the expression of three main groups of adhesion molecules: the selectins, the integrins, and the immunoglobulin superfamily. The selectins, which mediate the initial rolling of the leukocyte on the endothelium, are divided in three subgroups: L-selectin is expressed on all three leukocyte types, P-selectin is expressed on platelets and endothelial cells, and E-selectin is only expressed on endothelial cells. Integrins can be found on most cell types, consist of an alpha and a beta subunit and mediate firm adhesion of the leukocyte and migration into the tissues. They are classified into subgroups according to the type of their beta subunit. Immunoglobulins such as ICAM-1 and VCAM-1 are expressed mainly on endothelium and act as ligands for certain integrins. This review article summarizes the existing, and rapidly expanding, literature concerning the effects of cardiopulmonary bypass on the expression of leukocyte and endothelial adhesion molecules. Deeper understanding of the, behavior and the role of adhesion molecules during cardiopulmonary bypass may facilitate effective intervention in the inflammatory response process and suppression of its adverse effects.