Role of leukocyte CD11/CD18 complex in endotoxic and septic shock in rabbits

Efficacy of hemofiltration with PEPA membrane for IL-6 removal in a rat sepsis model

Recently, intensive care physicians have focused on continuous hemodiafiltration with a cytokine-adsorbing hemofilter in the treatment of sepsis. We aimed to establish extracorporeal circulation in a rat sepsis model to evaluate the cytokine removal properties of mini-modules using two types of membrane materials. Rats were divided into polyester polymer alloy (PEPA) and cellulose triacetate (CTA) groups as membrane materials of mini-modules. One hour after 0.1 mg/kg of lipopolysaccharide administration, continuous hemofiltration (CHF) was started in each group. Plasma interleukin-6 (IL-6), an important mediator of sepsis, was measured over time during hemofiltration. The peak IL-6 concentration in PEPA group was approximately 13,000 pg/mL, in comparison to approximately 31,000 pg/mL in CTA group. IL-6 clearance in PEPA group was much more than CTA group. Since IL-6 was not detected in the filtrate in PEPA group, it was considered that IL-6 was adsorbed to the membrane. In conclusion, our results suggest that CHF with PEPA hemofilter can be suitable for removing IL-6 from the blood stream efficiently.

Involvement of Gr-1 dull+ cells in the production of TNF-α and IL-17 and exacerbated systemic inflammatory response caused by lipopolysaccharide

Systemic inflammatory response syndrome (SIRS) is a life-threatening disease. Recent reports have demonstrated that the immunoregulatory cells that express Gr-1, a granulocyte surface antigen, play a critical role in various pathological conditions. In the present study, we have established a mouse model of SIRS and addressed the possible contribution of Gr-1+ cells in this model. C57BL/6 mice were injected intraperitoneally with anti-Gr-1 mAb or control IgG 1 day before administration of lipopolysaccharide (LPS). All of the mice that received anti-Gr-1 mAb and LPS died early as a result of hypothermia and severe emaciation, whereas mice treated with control IgG and LPS survived the observation period. In mice treated with anti-Gr-1 mAb and LPS, acute inflammatory changes with alveolar hemorrhage were observed in the lung and proximal convoluted tubule necrosis was observed in the kidney. Serum TNF-α and IL-17A levels were markedly increased in anti-Gr-1 mAb-pretreated mice compared with those in control IgG-treated mice at 1 and 3 h after LPS administration, respectively. Flow cytometric analysis revealed an increase in TNF-α and IL-17A expression in Gr-1 dull+ cells in the peripheral blood mononuclear cells. Neutralization of TNF-α by a specific mAb almost completely reversed the clinical course and inhibited the increased production of IL-17A. In addition, IL-17A KO mice were less susceptible to the lethality in this model. Thus, we established a mouse model of severe SIRS and suggested that Gr-1 dull+ cells may play a critical role in the development of this pathological condition.

Adrenergic nerves govern circadian leukocyte recruitment to tissues

The multistep sequence leading to leukocyte migration is thought to be locally regulated at the inflammatory site. Here, we show that broad systemic programs involving long-range signals from the sympathetic nervous system (SNS) delivered by adrenergic nerves regulate rhythmic recruitment of leukocytes in tissues. Constitutive leukocyte adhesion and migration in murine bone marrow (BM) and skeletal-muscle microvasculature fluctuated with circadian peak values at night. Migratory oscillations, altered by experimental jet lag, were implemented by perivascular SNS fibers acting on β-adrenoreceptors expressed on nonhematopoietic cells and leading to tissue-specific, differential circadian oscillations in the expression of endothelial cell adhesion molecules and chemokines. We showed that these rhythms have physiological consequences through alteration of hematopoietic cell recruitment and overall survival in models of septic shock, sickle cell vaso-occlusion, and BM transplantation. These data provide unique insights in the leukocyte adhesion cascade and the potential for time-based therapeutics for transplantation and inflammatory diseases.

Harmful and protective roles of neutrophils in sepsis

The current studies demonstrate protective and harmful effects of neutrophils (PMN) during experimental sepsis after cecal ligation and puncture (CLP). It is known that CLP induces signaling defects in blood PMN. When PMN were depleted 12 h after CLP, there were dramatic reductions in levels of bacteremia, evidence for reduced liver and renal dysfunction, sharp reductions in serum levels of cytokines (IL-1beta, IL-6, IL-10, TNF-alpha, and IL-2), and improved survival. In contrast, PMN depletion before CLP resulted in substantial increases in bacteremia and no evidence for attenuation of liver and renal failure dysfunction. These data suggest that at the onset of sepsis, PMN are important in regulating the levels of bacteremia, whereas after the onset of sepsis, as they lose innate immune functions, their presence is associated with higher levels of bacteremia and intensified organ dysfunction.

Can one use biologic modifiers to prevent multiple organ dysfunction syndrome after abdominal infections?

Postoperative or trauma-induced intra-abdominal infections can result in sepsis and multiple organ dysfunction syndrome (MODS). Enteric bacteria and endotoxin released from the gut into the peritoneal cavity in response to injury can directly stimulate the inflammatory cascade responsible for the development of systemic inflammation and subsequent MODS. Therapeutic strategies, such as biologic modifiers that are aimed at blocking or enhancing specific mediators of the inflammatory response, have been developed and tested in animal models with varying efficacy in preventing mortality. Specific therapies that have shown beneficial effects in animal models have not proved successful in prospective, randomized human studies, and it is as yet unclear whether cytokine-based therapies will ultimately have a role in preventing MODS. Testing novel therapies in appropriate animal models that closely simulate human intra-abdominal infection is crucial in developing drugs that will be beneficial in preventing sepsis-induced mortality in critically ill patients.

Peroxynitrite decomposition catalysts prevent myocardial dysfunction and inflammation in endotoxemic rats

OBJECTIVES

The aim of this study was to test whether peroxynitrite neutralizers would reduce peroxynitrite accumulation and improve myocardial contractile dysfunction and inflammation in endotoxin-treated rats.

BACKGROUND

Release of endogenous proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha in response to endotoxin is responsible for the production of large amounts of nitric oxide (NO), which may exert detrimental effects on the myocardium in animal models, isolated hearts, and isolated cardiac myocytes. Recent studies have indicated that many of the deleterious effects of NO are mediated by peroxynitrite, a powerful oxidant generated from a fast diffusion-limited reaction of NO and superoxide anion.

METHODS

We studied the effects of peroxynitrite neutralizers, such as mercaptoethylguanidine (MEG) sodium succinate (10 mg/kg) and 5,10,15,20-tetrakis(4-sulfonatophenyl)-porphyrinato iron (III) (FeTPPS) (30 mg/kg) on peroxynitrite accumulation, in vivo endothelial cell-leukocyte activation on the mesenteric venule, and myocardial contractile dysfunction and inflammation in a model of sepsis induced by injection of endotoxin (10 mg/kg) in rats.

RESULTS

Mercaptoethylguanidine sodium succinate and FeTPPS largely prevented the accumulation of peroxynitrite as measured by plasma rhodamine fluorescence and heart nitrotyrosine staining. Interestingly, MEG sodium succinate and FeTPPS improved endotoxin-induced myocardial contractile dysfunction, which was associated with reduced degradation of nuclear factor kappa B inhibitory protein I-kappa-B, plasma TNF-alpha levels, and microvascular endothelial cell-leukocyte activation.

CONCLUSIONS

These observations suggest that the beneficial effects of MEG and FeTPPS on endotoxin-induced myocardial contractile dysfunction could be related to the unique effects of these compounds on cardiovascular inflammation processes.

CALPAIN INHIBITORS IMPROVE MYOCARDIAL DYSFUNCTION AND INFLAMMATION INDUCED BY ENDOTOXIN IN RATS

Excessive activation of calpains has been implicated in the pathophysiology of inflammation, trauma, and ischemia reperfusion injury. Here, we investigated the effects of calpain inhibition on myocardial dysfunction and inflammation induced by endotoxin in rats. Rats were treated i.v. with endotoxin (10 mg/kg) or endotoxin plus calpain inhibitors and were then prepared after 4 h for myocardial contractility assessment, detection of endothelium leukocyte interactions, and plasma TNF-alpha, nitrite/nitrate, and endocan levels. Compared with vehicle-treated rats, hearts from endotoxin-treated rats had reduced systolic performance that was partially prevented by calpain inhibitors, i.e., acetyl-leucyl-leucyl-arginal (leupeptin), carbobenzoxy-valyl-phenylalanial (calpain inhibitor III), and N-acetyl-leucinyl-leucinyl-norleucinal (ALLN). Leupeptin and calpain inhibitor III reduced plasma TNF-alpha levels in endotoxin-treated rats. ALLN reduced plasma TNF-alpha and nitrite/nitrate levels in endotoxin-treated rats. Endotoxin treatment increased mesenteric venule leukocyte rolling (10 +/- 3 leukocytes/min vs. 44 +/- 10 leukocytes/min; P < 0.01) and adhesion (2 +/- 2 leukocytes/min vs. 15 +/- 3 leukocytes/min; P < 0.01), which was reduced by calpain inhibitors. Attenuation of leukocyte endothelium interactions observed in calpain inhibitor-treated rats with sepsis was associated with increases in plasma anti-adhesion molecule endocan. In conclusion, calpain inhibitors improved endotoxin-induced cardiac dysfunction, which may be attributed to the modulation of endothelium leukocyte interactions in the inflamed vasculature.

Protective effects of cyclosporin A from endotoxin-induced myocardial dysfunction and apoptosis in rats

Myocardial depression can be demonstrated following administration of endotoxin. Proposed mechanisms of endotoxin-induced myocardial dysfunction include the release of proinflammatory mediators, focal myocardial ischemia, and the presence of activated leukocytes within the myocardium. Recently, myocardial caspase activation and mitochondria-related apoptotic events (i.e., release of cytochrome c) were demonstrated in the failing septic heart. Here, we tested the hypothesis that immunosuppressors, cyclosporin A and tacrolimus (FK 506), would improve inflammation, heart nuclear apoptosis, and myocardial dysfunction in endotoxin-treated rats. Myocardial contractility was assessed using an isolated heart preparation. Heart leukocyte infiltration was assessed by measurement of heart myeloperoxidase activity. Leukocyte activation was studied using the intravital microscopy of the mesenteric venule. Apoptosis was detected as myocardial DNA fragmentation, downstream caspase activation, and mitochondrial cytochrome c release. Both cyclosporin A and FK 506 reduced heart leukocyte sequestration and venular adhesion in endotoxin-treated rats. Cyclosporin A, which blocks mitochondrial cytochrome c release, was able to reduce endotoxin-induced myocardial end-stage nuclear apoptosis and heart dysfunction, whereas tacrolimus had no such effects. These effects could be related to the unique properties of cyclosporin A to act on mitochondria.

Increased distribution and expression of CD64 on blood polymorphonuclear cells from patients with the systemic inflammatory response syndrome (SIRS)

Evidence is growing to suggest that the multiple organ damage of the systemic inflammatory response syndrome (SIRS) arises from the untoward activity of blood polymorphonuclear cells (PMNs), which upon activation acquire the IgG high affinity receptor, CD64. In the current study, flow cytometry was used to assess the prevalence of CD64-bearing PMNs and the intensity of expression of CD64 in whole blood samples from 32 SIRS patients, 11 healthy normal subjects and from eight non-SIRS patients in the intensive care unit (ICU). The percentage of PMNs expressing CD64 was higher in SIRS patients (mean 65%) than in non-SIRS patients (mean 42%; P < 0.02) and in healthy controls (mean 19%; P < 0.001) and was particularly evident in patients with SIRS and sepsis (mean 71%; P < 0.02) as opposed to SIRS alone (mean 55%). There were more CD64 molecules expressed on PMNs from patients with SIRS (median 1331 molecules/cell) in comparison with PMNs from healthy subjects (median 678 molecules/cell; P < 0.01). The highest intensity of CD64 expression was associated with PMNs from patients with both SIRS and sepsis. Functional studies revealed that the supranormal binding of PMNs from patients with SIRS to endothelial monolayers treated with TNFalpha was impeded by anti-CD64 antibodies (mean 24% inhibition; P < 0.01). Monitoring the distribution of CD64+ PMNs and their level of CD64 expression could be of assistance in the rapid discrimination of patients with SIRS from other ICU patients and in the identification of PMNs which are likely to participate in the pathological manifestations of the disease.

Thrombin and leukocyte recruitment in endotoxemia

Because thrombin has been implicated in sepsis, it has been proposed that antithrombin III (AT III) is beneficial due to its anticoagulatory and antiadhesive effects. Using intravital microscopy, we visualized leukocyte-endothelium interactions in postcapillary venules of the feline mesentery exposed to lipopolysaccharide (LPS). At a concentration of AT III that blocks leukocyte adhesion in postischemic mesentery, we found no role for thrombin in LPS-induced rolling, adhesion and emigration, or microvascular dysfunction. Furthermore, AT III did not attenuate leukocyte-endothelial interactions after tumor necrosis factor-alpha superfusion of the mesentery. In contrast, fucoidan, a selectin inhibitor, prevented almost all LPS-induced rolling and reduced adhesion, emigration, and microvascular dysfunction. In a model of endotoxemia, leukocyte recruitment into mesentery or lungs was unaffected by AT III. Finally, in a human cell system that mimics the flow conditions in vivo, human neutrophils rolled, adhered, and emigrated similar to the feline postcapillary microvessels, and AT III had no effect on leukocyte recruitment induced by LPS. If AT III has beneficial effects in endotoxemia, it is not due to a direct effect upon leukocyte rolling, adhesion, or emigration in postcapillary venules in vivo.

Immunotargeting of glucose oxidase to endothelium in vivo causes oxidative vascular injury in the lungs

Vascular immunotargeting is a novel approach for site-selective drug delivery to endothelium. To validate the strategy, we conjugated glucose oxidase (GOX) via streptavidin with antibodies to the endothelial cell surface antigen platelet endothelial cell adhesion molecule (PECAM). Previous work documented that 1) anti-PECAM-streptavidin carrier accumulates in the lungs after intravenous injection in animals and 2) anti-PECAM-GOX binds to, enters, and kills endothelium via intracellular H(2)O(2) generation in cell culture. In the present work, we studied the targeting and effect of anti-PECAM-GOX in animals. Anti-PECAM-GOX, but not IgG-GOX, accumulated in the isolated rat lungs, produced H(2)O(2,) and caused endothelial injury manifested by a fourfold elevation of angiotensin-converting enzyme activity in the perfusate. In intact mice, anti-PECAM-GOX accumulated in the lungs (27 +/- 9 vs. 2.4 +/- 0.3% injected dose/g for IgG-GOX) and caused severe lung injury and 95% lethality within hours after intravenous injection. Endothelial disruption and blebbing, elevated lung wet-to-dry ratio, and interstitial and alveolar edema indicated that anti-PECAM-GOX damaged pulmonary endothelium. The vascular injury in the lungs was associated with positive immunostaining for iPF(2alpha)-III isoprostane, a marker for oxidative stress. In contrast, IgG-GOX caused a minor lung injury and little (5%) lethality. Anti-PECAM conjugated with inert proteins induced no death or lung injury. None of the conjugates caused major injury to other internal organs. These results indicate that an immunotargeting strategy can deliver an active enzyme to selected target cells in intact animals. Anti-PECAM-GOX provides a novel model of oxidative injury to the pulmonary endothelium in vivo.

Inhaled nitric oxide modulates leukocyte kinetics in the mesenteric venules of endotoxemic rats

OBJECTIVE

to determine whether inhaled nitric oxide (NO) would alter leukocyte kinetics in the septic microvasculature.

DESIGN

Randomized, controlled trial.

SETTING

Experimental laboratory.

SUBJECTS

Male Sprague Dawley rats.

INTERVENTIONS

Rats were treated with either saline or endotoxin (10 mg/kg, iv) and then allowed to breathe either air or air plus NO (10 ppm).

MEASUREMENTS AND MAIN RESULTS

After a 4-hr period, rolling, firm adhesion, and emigration of leukocytes and endothelial dysfunction were monitored in mesenteric venules by using intravital videomicroscopy. Compared with controls, endotoxemic rats exhibited a profound influx in mesenteric venule rolling leukocytes (55+/-17 vs. 70+/-19 leukocytes/min; p < .05), associated with a reduction of leukocyte rolling velocity (83+/-14 vs. 34+/-3 microm/sec; p < .05). In endotoxemic rats, venular endothelium leukocyte firm adhesion (1.15+/-0.32 vs. 4.08+/-0.96 leukocytes/ 100 microm; p < .05) and emigration (0.84+/-0.47 vs. 4.23+/-1.2 leukocytes/100 microm; p < .05) increased compared with controls. Inhaled NO had no effect on leukocyte kinetics in control rats. Inhaled NO significantly attenuated endotoxin-induced venular endothelium leukocyte adhesion (4.08+/-0.96 vs. 1.86+/-0.76 leukocytes/100 microm; p < .05) and emigration (4.23+/-1.2 vs. 1.68+/-0.72 leukocytes/100 microm; p < .05). Compared with control rats, macromolecular (FITC-dextran) vascular leakage, expressed as the perivenular/intravenular fluorescence intensity ratio, increased in endotoxemic rats (0.56+/-0.02 vs. 0.81+/-0.05; p < .01). Endotoxin-induced macromolecular vascular leakage increases were partially prevented by inhaled NO (0.66+/-0.01 vs. 0.56+/-0.02; p < .05).

CONCLUSION

These observations suggest that inhaled NO reduces leukocyte adhesion and the degree of vascular permeability dysfunction in mesenteric venule of endotoxemic rats.

LPS pretreatment ameliorates peritonitis-induced myocardial inflammation and dysfunction: role of myocytes

Peritonitis induced by cecal ligation and puncture (CLP) produces a systemic inflammatory response that can be largely mitigated by pretreatment of the animals with lipopolysaccharide (LPS tolerance). Although cells of myeloid origin and endothelial cells have been shown to contribute to the development of LPS tolerance, little is known regarding the potential role of parenchymal cells in this phenomenon. The major aim of the present study was to assess whether cardiac parenchymal cells (myocytes) contribute to the development of LPS tolerance. Six hours after induction of CLP rats were neutropenic and acidotic, the myocardium contained a leukocyte infiltrate [myeloperoxidase (MPO) activity was increased], and myocardial contractile function was impaired (left ventricular developed pressure was decreased). In animals that were pretreated with LPS these manifestations of sepsis were largely reversed. Further studies focused on the responses of cardiac myocytes to CLP and whether myocytes contributed to the development of LPS tolerance. Myocytes were isolated from rat hearts 6 h after induction of CLP. These myocytes 1) exhibited an impaired ability to shorten in response to pacing, 2) contained the nuclear transcription factor NF-kappaB in their nuclei, 3) increased their surface levels of intercellular adhesion molecule-1 (ICAM-1), and 4) were hyperadhesive for neutrophils. All of these events did not occur in myocytes obtained from animals that were pretreated with LPS before induction of CLP. These findings indicate that LPS tolerance can be induced in myocytes with respect to polymorphonuclear leukocyte adhesion, presumably by an inability of CLP to mobilize NF-kappaB to the myocyte nuclei and, thereby, preventing an increase in surface levels of ICAM-1.

Neutrophil and endothelial cell interactions in sepsis. The role of adhesion molecules

Although adhesion molecules present on circulating neutrophils and endothelial cells are essential for normal host defense, generalized activation of these molecules has been implicated in the inflammatory tissue injury occurring during sepsis and septic shock. A review of both preclinical and clinical studies suggests, however, that although these molecules mediate tissue injury related to a variety of microbial and host inflammatory mediators, their predominant role during sepsis with infection is a protective one.

The Role of Leukocyte Emigration and IL-8 on the Development of Lipopolysaccharide-Induced Lung Injury in Rabbits

Leukocyte emigration and alveolar macrophage-derived cytokines may contribute to lung microvascular injury associated with adult respiratory distress syndrome. We have used mAbs against cell adhesion molecules on leukocytes (anti-CD18 and anti-CD49d) or against IL-8 to investigate these contributions. Intratracheal (i.t.) instillation of LPS (50 μg/kg) caused a significant increase in bronchoalveolar lavage polymorphonuclear leukocytes (PMNs) without an increase in mononuclear cells (MNCs) or an increase in lung permeability. Injection of LPS (10 μ/kg) i.v. at 24 h after i.t. LPS caused significant increases in bronchoalveolar lavage PMNs, MNCs, IL-8, and monocyte chemotactic protein-1, as well as increases in lung permeability. Rabbits that were administered i.t. LPS followed by i.v. LPS and treated with anti-CD18 mAb had a significantly lower lung permeability index and emigration of fewer PMNs but no change in MNC emigration compared with saline treatment. Anti-IL-8 mAb treatment resulted in a significantly lower lung permeability index with no change in PMN emigration compared with no treatment. These results suggest that PMN emigration is necessary but not sufficient for the development of LPS-induced lung injury, and that IL-8 plays a significant role in PMN-dependent lung injury, independent of PMN emigration.

Leukocyte activation and flow behavior in rat skeletal muscle in sepsis

In animal models of endotoxemia, sepsis is associated with the accumulation of leukocytes and altered microvascular perfusion. In order to test the hypothesis that bacterial sepsis upregulates leukocyte-endothelial adhesion, we used intravital microscopy to examine the flow behavior of leukocytes in the postcapillary venules (PCV) of rats made septic by cecal ligation and perforation (CLP). Animals were randomized to CLP or sham study groups and studied 6 h, 24 h, or 48 h later. In postcapillary venules of the extensor digitorum longus muscle, we found that: (1) over the course of the study, leukocyte adhesion and extravasation increased in both experimental groups (analysis of variance [ANOVA], significant time effect: adhesion, p < 0.001; extravasation, p < 0.05); (2) leukocyte adhesion was decreased by CLP treatment (ANOVA, sepsis effect, p = 0.05), particularly after 24 to 48 h of sepsis (ANOVA, sepsis x time interaction, p < 0.05); and (3) the reduction in leukocyte adhesion in CLP animals was associated with a decrease in leukocyte extravasation (ANOVA, sepsis effect, p < 0.01). After correction for the reduction in systemic leukocyte count associated with CLP, the effect of sepsis on leukocyte adhesion and extravasation no longer reached statistical significance. These findings suggest that chronic (6 to 48 h) bacterial sepsis does not upregulate leukocyte adhesion in a manner similar to that seen in models of acute endotoxemia. These data suggest that the increased microcirculatory flow heterogeneity seen in this and other models of bacterial sepsis may not be explained by leukocyte entrapment in postcapillary venules.

CD11/CD18 leukocyte integrins: new signaling receptors for bacterial endotoxin

Exaggerated responses by phagocytes to bacterial endotoxin [lipopolysaccharide (LPS)] may result in the sepsis syndrome. While a number of LPS-binding proteins have been identified on immune cells, only CD14 has been definitively shown to be involved in signal transduction in response to LPS. The beta2 leukocyte integrins are a family of transmembrane receptors whose expression is restricted to leukocytes. Among their many functions, the beta2 integrins are phagocytic receptors that bind a variety of bacterial products, including LPS. We hypothesize that this binding results in signal transduction. Chinese hamster ovary (CHO) fibroblast cell lines expressing the CD11a/CD18 or CD11b/CD18 antigen were engineered by gene transfection. The cell lines were stimulated with LPS. LPS-induced nuclear translocation of nuclear factor kappa B (NF-kappaB) was analyzed by electrophoretic mobility shift assay. Heterologous expression of CD11a/CD18 and CD11b/CD18 in otherwise LPS-nonresponsive fibroblasts imparted the ability to respond to LPS. Responses to LPS were observed at levels of LPS of 100 ng/ml, as were responses to whole Gram-negative bacteria. The CD11/CD18 leukocyte integrins mediate cellular responses to the LPS component of Gram-negative bacteria. CD11/CD18-mediated responses of cells to LPS are likely to affect the phagocytosis, intracellular trafficking, and killing of invading bacteria as well as to help mediate cytokine responses during endotoxemia. The development of novel therapies to prevent the end-organ damage frequently observed during sepsis will require an understanding of these complex cellular events.

Host defense against systemic infection with Streptococcus pneumoniae is impaired in E-, P-, and E-/P-selectin-deficient mice

Endothelial selectins mediate rolling of leukocytes on endothelium, a crucial step for leukocyte firm adhesion and emigration into sites of tissue injury and infection. To characterize the role of the endothelial selectins during bacterial sepsis in vivo, Streptococcus pneumoniae (1-10 x 10(6) colony-forming units) was inoculated intraperitoneally into wild-type mice and mice with E-, P-, or E-/P-selectin deficiencies. Mice were followed 10 d for morbidity, survival, clearance of bacteremia, and leukocyte migration to the peritoneal cavity and organs 48 h after infection. All selectin-deficient mice showed a more pronounced morbidity, a significantly higher mortality associated with persistent bacteremia, and a higher bacterial load when compared with wild-type mice. These differences were most remarkable in the E-selectin-deficient mice, which showed the highest rate of mortality and bacteremia (P </= 0.0001). No significant differences were observed among the groups in the inflammatory response present in the peritoneal cavity, brain, liver, spleen, or kidney at 48 h after inoculation. Extensive hepatic and splenic necrosis and thrombosis were noted in E- and P-selectin-deficient mice. Although the absence of endothelial selectins did not substantially impair leukocyte emigration to sites of infection 48 h after pneumococcal sepsis, it resulted in increased mortality and a higher bacterial load in the bloodstream of selectin-deficient mice. These results demonstrate a definitive phenotypic abnormality in E-selectin-deficient mice, and suggest that E- and P-selectin are important in the host defense against S. pneumoniae infection.

Neutrophil sequestration and pulmonary dysfunction in a canine model of open heart surgery with cardiopulmonary bypass. Evidence for a CD18-dependent mechanism

BACKGROUND

Previous studies documented an inflammatory reaction to cardiopulmonary bypass with neutrophil (PMN) sequestration in the lungs, contributing to microvascular injury and postoperative pulmonary dysfunction. This study explored the hypothesis that the beta 2 integrin CD18, a leukocyte adhesion molecule, mediates this response.

METHODS AND RESULTS

Fifteen adult, mixed-breed dogs underwent 90 minutes of cardiopulmonary bypass with 3 hours of subsequent recovery. Seven additional dogs were treated before cardiopulmonary bypass with a 1-mg/kg IV bolus of R15.7 IgG, a monoclonal antibody to CD18. Both groups were compared with 5 sham bypass control dogs. Bypassed dogs demonstrated an increased number of PMNs sequestered in the lungs 3 hours after bypass compared with sham bypass control dogs (1466 +/- 75 versus 516 +/- 43 PMN/mm2 alveolar surface area, mean +/- SEM, P < .001). Also, when PMNs from bypass dogs were compared with those from sham dogs, they produced more H2O2 (305 +/- 45 versus 144 +/- 48 amol H2O2 per phagocyte per 20 minutes, P < .05). Bypass dogs had significantly decreased arterial oxygenation 3 hours after the procedure compared with shams (457 +/- 20 versus 246 +/- 49 mm Hg, P < .05), and they had a significantly increased lung wet-to-dry weight ratio (5.38 +/- 0.14 versus 4.54 +/- 0.15, P = .003), demonstrating a significant increase in lung water. R15.7 markedly attenuated pulmonary PMN accumulation in bypass dogs (412 +/- 73 PMN/mm2, P < .001) and significantly inhibited PMN production of H2O2 (146 +/- 18 amol H2O2 per phagocyte per 20 minutes, P < .05) Bypass dogs pretreated with R15.7 also had improved oxygenation (445 +/- 28 mm Hg, P < .05) and tended to have less lung water accumulation after bypass (4.99 +/- 0.20).

CONCLUSIONS

Pulmonary dysfunction after cardiopulmonary bypass is caused, at least in part, by a neutrophil-mediated, CD18-dependent mechanism.

Differential effects of monoclonal antibody blockade of adhesion molecules on in vivo susceptibility to soft tissue infection

Leukocyte adherence to endothelial cells has been implicated in the pathogenesis of microvascular injury as well as in host defense against various infectious microorganisms. Administration of monoclonal antibodies directed against the beta chain of the leukocyte integrins inhibits leukocyte-endothelial-cell adherence and has been reported to modulate ischemia-reperfusion and inflammatory injury. However, such inhibition of adhesion molecule function adversely affects resistance to infection. The following studies were carried out to determine whether monoclonal antibodies to other adhesion molecules, including L-selectin (CD62L), and CD11a (the alpha chain of LFA-1), also increase susceptibility to infection. New Zealand White rabbits were shaved and given subcutaneous injections on their dorsa with 10(9) CFU of Staphylococcus aureus ATCC 25923 at two sites and with 10(8) CFU at two sites. A second set of rabbits were given subcutaneous injections with 10(8) CFU of P. aeruginosa ATCC 27853 at two sites and with 10(7) CFUs at two sites. The animals were monitored for 1 week. There were three blinded experimental groups: controls given saline and two groups given blocking monoclonal antibodies to either L-selectin (Dreg-200) or CD11a (R7.1). In contrast to monoclonal antibodies to CD18, none of the monoclonal antibodies significantly increased the risk of abscess formation by S. aureus, although inhibition of CD11a increased the rate of abscess formation by P. aeruginosa.

Neutrophil CD18 expression and blockade after traumatic shock and endotoxin challenge

OBJECTIVE

The expression of the leukocyte CD18 adhesion complex on polymorphonuclear leukocytes (PMNs) was measured, and the physiologic effects of blockade of the complex were studied after trauma and sepsis.

SUMMARY BACKGROUND DATA

Margination of PMNs occurs early during inflammation and depends, in part, on expression of the CD18 adhesion complex. Blockade of this adherence complex can reduce PMN-mediated damage. This study tests the hypothesis that PMN activation after resuscitated trauma produces an occult endothelial injury that increases the vulnerability to a delayed inflammatory stimulus.

METHODS

Anesthetized (fentanyl) mongrel pigs were sham injured or fluid resuscitated from soft tissue injury +35% hemorrhage. Systemic blood was collected at 24-hour intervals from awake animals. The CD18 density on circulating PMNs was determined with flow cytometry using mean channel fluorescence (MCF). The CD18 receptors were blocked with monoclonal antibodies either immediately before trauma or immediately before an endotoxin (lipopolysaccharide [LPS]) challenge that was administered to all groups 3 days after the shock episode. Bronchoscopy was performed before trauma, pre-LPS, and post-LPS, and protein content was measured in bronchoalveolar lavage (BAL).

RESULTS

Mean channel fluorescence was reduced on PMNs for 48 hours in animals with trauma versus animals with sham injuries. Anti-CD18 therapy produced higher circulating PMN counts compared with nontreated sham or shock groups. The incremental rise of BAL protein after shock was prevented with anti-CD18; the increment after LPS was attenuated. Anti-CD18 was administered before trauma and reduced the fluids necessary to maintain cardiac filling pressures after LPS.

CONCLUSIONS

These data suggest that PMNs are activated after resuscitation from traumatic shock and that these cells produce an endothelial injury that may increase the vulnerability to a septic challenge. The broad implication is that temporarily blocking PMN adhesiveness at the time of trauma might salvage some host tissue and reduce the incidence of septic complications in the post-trauma period.

Role of neutrophil-endothelial cell adhesion in inflammatory disorders

Polymorphonuclear leukocytes are armed with an impressive arsenal of bactericidal agents that allow these cells to play a vital role in host defense against invading pathogens. However, these same agents can produce extensive cellular damage in host tissues when leukocytes are activated during inflammatory conditions. Recognition of this fact, when coupled with the observation that leukocyte adhesion to post-capillary venules is a critical first step in the inflammatory process, has led to the development of the concept that inhibition of neutrophil-endothelial cell adhesion (NECA) may represent a novel therapeutic strategy for the prevention of leukocyte-dependent injury in inflammatory conditions. Indeed, pharmacological or immunologic inhibition of NECA reduces cellular injury, dysfunction, and necrosis induced by ischemia/reperfusion, circulatory shock and resuscitation, organ transplantation, cardiopulmonary bypass, frostbite, and thermal trauma. NECA also appears to play an important role in the pathobiology of airway inflammation and asthma, pulmonary oxygen toxicity, arthritis, bacterial meningitis, and cerebral malaria. The aim of this review is to summarize the evidence implicating NECA in the pathogenesis of these inflammatory conditions.

Endothelial-leukocyte adhesion molecules in human disease

An effective host response to infection or tissue damage requires focal accumulation of leukocytes. Leukocyte adhesion to the vessel wall, a key step in this process, depends on the ordered expression of specific endothelial cell surface molecules. The endothelial molecules that support adhesion include selectins that recognize leukocyte cell surface glycoconjugates as well as members of the immunoglobulin superfamily that interact with leukocyte integrins. Although inflammation can occur with minimal damage to the vessel wall and surrounding tissues, control mechanisms sometimes appear to fail, and the inflammatory response itself becomes a significant clinical problem. In this review, we discuss endothelial-leukocyte adhesion molecules with particular emphasis on their expression and function in human disease. Pathophysiological processes presented include atherosclerosis, ischemia-reperfusion injury, acute lung injury, rheumatoid arthritis, and graft rejection. A more detailed description of the discovery and characterization of the key molecules appears in the antecedent article entitled "Endothelial-Leukocyte Adhesion Molecules".