Soluble L-selectin at levels present in septic patients diminishes leukocyte-endothelial cell interactions in mice in vivo: a mechanism for decreased leukocyte delivery to remote sites in sepsis

Serum sSelectin-L is an early specific indicator of radiation injury

Objective

It's crucial to identify an easily detectable biomarker that is specific to radiation injury in order to effectively classify injured individuals in the early stage in large-scale nuclear accidents.

Methods

C57BL/6J mice were subjected to whole-body and partial-body γ irradiation, as well as whole-body X-ray irradiation to explore the response of serum sSelectin-L to radiation injury. Then, it was compared with its response to lipopolysaccharide-induced acute infection and doxorubicin-induced DNA damage to study the specificity of sSelectin-L response to radiation. Furthermore, it was further evaluated in serum samples from nasopharyngeal carcinoma patients before and after radiotherapy. Simulated rescue experiments using Amifostine or bone marrow transplantation were conducted in mice with acute radiation syndrome to determine the potential for establishing sSelectin-L as a prognostic marker. The levels of sSelectin-L were dynamically measured using the ELISA method.

Results

Selectin-L is mainly expressed in hematopoietic tissues and lymphatic tissues. Mouse sSelectin-L showed a dose-dependent decrease from 1 day after irradiation and exhibited a positive correlation with lymphocyte counts. Furthermore, the level of sSelectin-L reflected the degree of radiation injury in partial-body irradiation mice and in nasopharyngeal carcinoma patients. sSelectin-L was closely related to the total dose of γ or X ray. There was no significant change in the sSelectin-L levels in mice intraperitoneal injected with lipopolysaccharide or doxorubicin. The sSelectin-L was decreased slower and recovered faster than lymphocyte count in acute radiation syndrome mice treated with Amifostine or bone marrow transplantation.

Conclusions

Our study shows that sSelectin-L has the potential to be an early biomarker to classify injured individuals after radiation accidents, and to be a prognostic indicator of successful rescue of radiation victims.

Ethyl Pyruvate Reduces Systemic Leukocyte Activation via Caspase-1 and NF-κB After Blunt Chest Trauma and Haemorrhagic Shock

Background: Blunt chest (thoracic) trauma (TxT) and haemorrhagic shock with subsequent resuscitation (H/R) induce strong systemic and local inflammatory response, which is closely associated with apoptotic cell loss and subsequently impaired organ function. The underlying mechanisms are not completely understood, therefore, the treatment of patients suffering from TxT+H/R is challenging. In our recent studies, we have demonstrated local anti-inflammatory effects of ethyl pyruvate (EtP) in lung and liver after TxT+H/R. Here, the therapeutic potential of a reperfusion regime with EtP on the early post-traumatic systemic inflammatory response and apoptotic changes after TxT followed by H/R were investigated.

Methods: Female Lewis rats underwent TxT followed by haemorrhagic shock (60 min). Resuscitation was performed with own blood transfusion and either lactated Ringers solution (LR) or LR supplemented with EtP (50 mg/kg). Sham group underwent the surgical procedures. After 2 h blood as well as lung and liver tissues were obtained for analyses. Systemic activation of neutrophils (expression of CD11b and CD62L), leukocyte phagocytosis, apoptosis (caspase-3/7 activation), pyroptosis (caspase-1 activation) and NF-κB p65 activity were assessed. p < 0.05 was considered significant.

Results: TxT+H/R-induced systemic activation of neutrophils (increased CD11b and reduced CD62L expression) was significantly reduced by EtP. Trauma-induced delayed neutrophil apoptosis was further reduced by EtP reperfusion but remained unaltered in monocytes. Reperfusion with EtP significantly increased the phagocytizing capacity of granulocytes. Trauma-induced inflammasome activation, which was observed in monocytes and not in neutrophils, was significantly reduced by EtP in both cell entities. NF-κB p65 activation, which was increased in neutrophils and monocytes was significantly decreased in monocytes.

Conclusion: TxT+H/R-induced systemic activation of both neutrophils and monocytes concomitant with increased systemic inflammation was reduced by a reperfusion with EtP and was associated with a down-regulation of NF-κB p65 activation.

Soluble adhesion molecules as markers for sepsis and the potential pathophysiological discrepancy in neonates, children and adults

Sepsis is a severe and life-threatening systemic inflammatory response to infection that affects all populations and age groups. The pathophysiology of sepsis is associated with aberrant interaction between leukocytes and the vascular endothelium. As inflammation progresses, the adhesion molecules that mediate these interactions become shed from cell surfaces and accumulate in the blood as soluble isoforms that are being explored as potential prognostic disease biomarkers. We critically review the studies that have tested the predictive value of soluble adhesion molecules in sepsis pathophysiology with emphasis on age, as well as the underlying mechanisms and potential roles for inflammatory shedding. Five soluble adhesion molecules are associated with sepsis, specifically, E-selectin, L-selectin and P-selectin, intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. While increased levels of these soluble adhesion molecules generally correlate well with the presence of sepsis, their degree of elevation is still poorly predictive of sepsis severity scores, outcome and mortality. Separate analyses of neonates, children and adults demonstrate significant age-dependent discrepancies in both basal and septic levels of circulating soluble adhesion molecules. Additionally, a range of both clinical and experimental studies suggests protective roles for adhesion molecule shedding that raise important questions about whether these should positively or negatively correlate with mortality. In conclusion, while predictive properties of soluble adhesion molecules have been researched intensively, their levels are still poorly predictive of sepsis outcome and mortality. We propose two novel directions for improving clinical utility of soluble adhesion molecules: the combined simultaneous analysis of levels of adhesion molecules and their sheddases; and taking age-related discrepancies into account. Further attention to these issues may provide better understanding of sepsis pathophysiology and increase the usefulness of soluble adhesion molecules as diagnostic and predictive biomarkers.

Regulation of L-selectin expression by trauma-relevant cytokines

The leukocyte adhesion molecule L-selectin is important for the rolling of neutrophil granulocytes (PMN), the first step of the cascade leading to adhesion, diapedesis, and subsequent organ dysfunction. The activation of leukocytes in the posttraumatic course is assumed to be induced by different pro-inflammatory cytokines. In the present study, we investigated the effects of stimulation with pro- and anti-inflammatory cytokines on the L-selectin surface expression on PMN. Twenty patients admitted to our institution for elective operations of the lower extremities were enrolled in a prospective clinical study. For the measurement of L-selectin expression, blood was taken before the operation (0 h), as well as 24 h and 48 h postoperatively. Without and after incubation with different pro- and anti-inflammatory cytokines (TNF-α, IL-1β, IL-6 and IL-10), the surface expression of L-selectin was detected using an anti-L-selectin-specific antibody and flow cytometry. L-selectin surface expression without any stimulation showed a non-significant increase 48 h after the operation (63.6±6.6 ng/ml at 0 h, 95.2±10.5 ng/ml at 48 h). Stimulation with TNF-α resulted in a significant decrease of L-selectin expression at 0 h (25.6±2.7 ng/ml; p<0.05) and 24 h (18.3±2.5 ng/ml; p<0.05), but not at 48 h (39.8±4.2 ng/ml). No significant differences were observed after stimulation with IL-1β, IL-6, and IL-10 in comparison to the non-stimulated group. The study results indicate that the primary pro-inflammatory cytokine TNF-α regulates the L-selectin surface expression on PMN after surgical trauma. Therefore, a regulation of neutrophil activation on this level might be crucial in the development of posttraumatic complications.

Matrix metalloproteinases as drug targets in infections caused by gram-negative bacteria and in septic shock

The mammalian immune system is optimized to cope effectively with the constant threat of pathogens. However, when the immune system overreacts, sepsis, severe sepsis, or septic shock can develop. Despite extensive research, these conditions remain the leading cause of death in intensive care units. The matrix metalloproteinases (MMPs) constitute a family of proteases that are expressed in developmental, physiological, and pathological processes and also in response to infections. Studies using MMP inhibitors and MMP knockout mice indicate that MMPs play essential roles in infection and in the host defense against infection. This review provides a brief introduction to some basic concepts of infections caused by gram-negative bacteria and reviews reports describing MMP expression and inhibition, as well as studies with MMP-deficient mice in models of infection caused by gram-negative bacteria and of septic shock. We discuss whether MMPs should be considered novel drug targets in infection and septic shock.

L-selectin shedding in sepsis limits leukocyte mediated microvascular injury at remote sites

BACKGROUND

Increased soluble L-selectin levels have been shown to attenuate local inflammation-mediated microvascular leakage, and failure to generate high levels has been associated with increased risk of acute respiratory distress syndrome in septic patients. We hypothesized that failure to shed L-selectin in systemic inflammation would result in increased local inflammation-induced leukocyte adherence and microvascular leakage.

METHODS

Using intraperitoneal lipopolysaccharide (LPS) or control bicarbonate buffered saline (BBS) and intrascrotal TNFalpha or BBS, mice were randomized to systemic inflammation (LPSip + BBSis), local inflammation (BBSip + TNFis), both (LPSip + TNFis), or control (BBSip+BBSis). Furthermore, mice received intraperitoneal L-selectin Sheddase inhibitor (Ro31-9790) or control vector. With intravital microscopy on cremaster muscle, we measured leukocyte-endothelial cell interactions and microvascular leakage (permeability index). Surface L-selectin was measured by flow cytometry (MCF).

RESULTS

Without Ro31-9790, systemic inflammation attenuated increases induced by local inflammation in leukocyte adherence and vascular leakage. Ro31-9790 significantly increased adherence and leakage in systemic and systemic + local inflammation. L-selectin was shed progressively by increasing degrees of inflammation. Ro31-9790 limited this shedding of L-selectin.

CONCLUSION

In systemic inflammation, L-selectin shedding is required to limit local inflammation-mediated leukocyte adherence and microvascular leakage. Failure to shed L-selectin may increase leukocyte-mediated end-organ injury in septic patients.

Sepsis and the heart

Sepsis is generally viewed as a disease aggravated by an inappropriate immune response encountered in the afflicted individual. As an important organ system frequently compromised by sepsis and always affected by septic shock, the cardiovascular system and its dysfunction during sepsis have been studied in clinical and basic research for more than 5 decades. Although a number of mediators and pathways have been shown to be associated with myocardial depression in sepsis, the precise cause remains unclear to date. There is currently no evidence supporting global ischemia as an underlying cause of myocardial dysfunction in sepsis; however, in septic patients with coexistent and possibly undiagnosed coronary artery disease, regional myocardial ischemia or infarction secondary to coronary artery disease may certainly occur. A circulating myocardial depressant factor in septic shock has long been proposed, and potential candidates for a myocardial depressant factor include cytokines, prostanoids, and nitric oxide, among others. Endothelial activation and induction of the coagulatory system also contribute to the pathophysiology in sepsis. Prompt and adequate antibiotic therapy accompanied by surgical removal of the infectious focus, if indicated and feasible, is the mainstay and also the only strictly causal line of therapy. In the presence of severe sepsis and septic shock, supportive treatment in addition to causal therapy is mandatory. The purpose of this review is to delineate some characteristics of septic myocardial dysfunction, to assess the most commonly cited and reported underlying mechanisms of cardiac dysfunction in sepsis, and to briefly outline current therapeutic strategies and possible future approaches.

Expression and regulation of the metalloproteinase ADAM-8 during human neutrophil pathophysiological activation and its catalytic activity on L-selectin shedding

A disintegrin and metalloproteinase domain (ADAM) proteins are a family of transmembrane glycoproteins with heterogeneous expression profiles and proteolytic, cell-adhesion, -fusion, and -signaling properties. One of its members, ADAM-8, is expressed by several cell types including neurons, osteoclasts, and leukocytes and, although it has been implicated in osteoclastogenesis and neurodegenerative processes, little is known about its role in immune cells. In this study, we show that ADAM-8 is constitutively present both on the cell surface and in intracellular granules of human neutrophils. Upon in vitro neutrophil activation, ADAM-8 was mobilized from the granules to the plasma membrane, where it was released through a metalloproteinase-dependent shedding mechanism. Adhesion of resting neutrophils to human endothelial cells also led to up-regulation of ADAM-8 surface expression. Neutrophils isolated from the synovial fluid of patients with active rheumatoid arthritis expressed higher amounts of ADAM-8 than neutrophils isolated from peripheral blood and the concentration of soluble ADAM-8 in synovial fluid directly correlated with the degree of joint inflammation. Remarkably, the presence of ADAM-8 both on the cell surface and in suspension increased the ectodomain shedding of membrane-bound L-selectin in mammalian cells. All these data support a potential relevant role for ADAM-8 in the function of neutrophils during inflammatory response.

Binding of human serum amyloid P componentto L-selectin

Serum concentrations of soluble L-selectin by far exceed those of other soluble adhesion molecules, and serum soluble L-selectin concentrations are remarkably stable upon prolonged storage. We present evidence for Ca(2+)-dependent binding interactions between human serum amyloid P (SAP), a proteolysis-resistant pentraxin glycoprotein, and L-selectin, as shown by surface plasmon resonance measurements, protein band shift assays in a native PAGE system, and after SDS-PAGE and membrane transfer. Monoclonal antibodies to L-selectin strongly reduced binding of biotinylated SAP to L-selectin-IgG chimeras immobilized on microtiter plates. As binding was reduced by prior glycopeptidase F treatment of L-selectin but not of SAP, it appears to be based on SAP lectin domain interactions with N-linked L-selectin carbohydrates. In freshly prepared human lymphocytes, SAP incubation induced expression of a beta2 integrin neoepitope associated with high-affinity binding. This was partially blocked by pre-incubation with Fab fragments of two anti-L-selectin antibodies. In flow chamber experiments, SAP inhibited the adherence of human neutrophils to activated endothelium under shear stress. Thus, SAP binds to human L-selectin and affects L-selectin-dependent leukocyte-endothelial interactions.

Association between Adrenal Insufficiency and Ventilator Weaning

RATIONALE

Adrenal insufficiency is a common disorder in critically ill patients with mechanical ventilation and is usually associated with higher mortality and poor clinical outcome.

OBJECTIVES

To determine whether stress dose corticosteroid supplementation can improve ventilator weaning and clinical outcome in patients with adrenal insufficiency.

METHODS

A prospective, randomized, placebo controlled, double-blinded study was conducted in the intensive care unit of a tertiary teaching hospital. A total of 93 mechanically ventilated patients were enrolled in the ventilator weaning trial. Adrenal function was assessed in all patients. Patients with adrenal insufficiency were randomized to the treatment group (50 mg intravenous hydrocortisone every 6 h) and the placebo group.

MEASUREMENTS AND MAIN RESULTS

The successful ventilator weaning percentage was significantly higher in the adequate adrenal reserve group (88.4%) and in the stress dose hydrocortisone treatment group (91.4%) than in the placebo group (68.6%). The weaning period was shorter in the hydrocortisone treatment group than in the placebo group. No significant adverse effects were observed in the corticosteroid treatment group.

CONCLUSIONS

For patients with respiratory failure, early identification of adrenal insufficiency and appropriate supplementation with stress dose hydrocortisone increase the success of ventilator weaning and shortens the weaning period.

L-selectin: adhesion, signalling and its importance in pathologic posttraumatic endotoxemia and non-septic inflammation

The leucocyte expressed surface-bound L-selectin belongs to the selectin family of adhesion molecules. It exhibits adhesive as well as signalling functions. Mainly, it is of importance in lymphocyte homing and in the extravasation of leucocytes into the surrounding tissue during inflammation. Acting in the initial step of the cell adhesion cascade, L-selectin is responsible for the rolling of leucocytes on endothelial layers. Therefore, L-selectin is thought to be an adequate target for pharmacological interventions. Beneath the discussion of the molecules' general features like molecule structure and its regulation, the review focuses firstly on L-selectin in the context of posttraumatic inflammatory disorders, and secondly on the importance of L-selectin specific signalling events.

L-selectin: mechanisms and physiological significance of ectodomain cleavage

L-selectin is a cell adhesion molecule consisting of a large, highly glycosylated, extracellular domain, a single spanning transmembrane domain and a small cytoplasmic tail. It is expressed on most leukocytes and is involved in their rolling on inflamed vascular endothelium prior to firm adhesion and transmigration. It is also required for the constitutive trafficking of lymphocytes through secondary lymphoid organs. Like most adhesion molecules, L-selectin function is regulated by a variety of mechanisms including gene transcription, post-translational modifications, association with the actin cytoskeleton, and topographic distribution. In addition, it is rapidly downregulated by proteolytic cleavage near the cell surface by ADAM-17 (TACE) and at least one other "sheddase". This process of "ectodomain shedding" results in the release of most of the extracellular portion of L-selectin from the cell surface while retaining the cytoplasmic, transmembrane, and eleven amino acids of the extracellular domain on the cell. This review will examine the mechanism(s) of L-selectin ectodomain shedding and discuss the physiological implications.

Statin Treatment After Onset of Sepsis in a Murine Model Improves Survival

Background— HMG-CoA-reductase inhibitors have been shown to exhibit pronounced immunomodulatory effects independent of lipid lowering. We have recently demonstrated that pretreatment with simvastatin profoundly improves survival in a cecal ligation and perforation (CLP) model of sepsis. Here, we studied whether treatment with simvastatin after onset of sepsis-induced hemodynamic alterations is beneficial and whether prolonged survival can also be achieved with other statins.

Methods and Results— Mice were rendered septic by CLP. At 6 hours after sepsis induction, when profound hemodynamic alterations were manifest, treatment with atorvastatin, fluvastatin, pravastatin, simvastatin, or placebo was initiated. Except for fluvastatin (27±2.3 hours), survival time was extended from 23±1.2 hours for placebo-treated mice to 37±3.6 hours for simvastatin-treated, to 40±4.2 hours for atorvastatin-treated, and to 39±3.9 hours for pravastatin-treated mice. This profound improvement is based on the preservation of cardiac function and hemodynamic status in statin-treated animals, both of which are severely impaired in untreated CLP mice. As underlying mechanisms, improved susceptibility to endothelial nitric oxide synthase stimulation and reduced endothelial adhesion of leukocytes could be demonstrated after statin treatment.

Conclusions— Well established in the treatment of lipid disorders and coronary artery disease, statins harbor the additional and novel potential of effective sepsis treatment. This benefit extends to several but not all statins tested.

HMG-CoA reductase inhibitor simvastatin profoundly improves survival in a murine model of sepsis

BACKGROUND

HMG-CoA reductase inhibitors, such as simvastatin, have been shown to exhibit pronounced immunomodulatory effects independent of lipid lowering but to date have not been used to treat severe inflammatory disease such as sepsis. We thus approached the question of whether treatment with simvastatin might improve cardiovascular function and survival in sepsis.

METHODS AND RESULTS

Mice treated with simvastatin and rendered septic by cecal ligation and perforation (CLP) show a mean survival time close to 4 times the value found in untreated mice. This dramatic improvement is based on a complete preservation of cardiac function and hemodynamic status, which are severely impaired in untreated CLP mice [eg, 20 hours after CLP, cardiac output declined from 1.24+/-0.09 to 0.87+/-0.11 mL x min(-1) x g(-1) in untreated mice (P<0.005; n=12), while remaining unaltered (1.21+/-0.08 mL x min(-1) x g(-1) at baseline and 1.15+/-0.1 mL x min(-1) x g(-1) 20 hours after CLP, P=NS, n=12) in CLP mice treated with simvastatin]. Untreated CLP mice remained refractory to beta-stimulation, whereas the responsiveness to dobutamine was restored by treatment with simvastatin. Susceptibility of coronary flow to endothelial nitric oxide synthase (eNOS) stimulation by bradykinin was close to 3 times as pronounced in untreated CLP mice as in untreated sham-operated mice, indicating a high level of eNOS activation secondary to sepsis. In addition, treatment with simvastatin reversed inflammatory alterations in CLP mice, namely, increased monocyte adhesion to endothelium.

CONCLUSIONS

Simvastatin, which is well established in the treatment of lipid disorders and coronary artery disease, might have the additional potential of being an effective agent in sepsis treatment.

Endocrine changes in critical illness

The homeostatic corrections that have emerged in the course of human evolution to cope with catastrophic events involve a complex multisystem endeavor, of which the endocrine contribution is an integral component. Although the repertoire of endocrine changes has been probed in some detail, discerning the vulnerabilities and failure of this system is far more challenging. The ensuing endocrine topics illustrate some of the current issues reflecting attempts to gain an improved insight and clinical outcome for critical illness.

Intra-abdominal sepsis attenuates local inflammation-mediated increases in microvascular permeability at remote sites in mice in vivo

BACKGROUND

Given that leukocyte delivery to remote sites is diminished in states of systemic inflammation, such as sepsis, and activated leukocytes may be responsible for endothelial injury leading to vascular leakage, we hypothesized that intra-abdominal sepsis would diminish microvascular leakage at remote sites by altering leukocyte-endothelial interactions.

METHODS

Using a murine intravital microscopy model, we examined leukocyte-endothelial interactions and vascular leakage at a peripheral site in the presence of local and/or systemic inflammation. Forty mice were randomized to 1 of 4 study groups: local infection (orchitis), systemic infection (intra-abdominal sepsis by cecal ligation and puncture), local and systemic infection, and control. Postcapillary venules of the cremaster muscle were examined by bright light and fluorescence intravital microscopy. Microvascular leakage was determined after intravenous administration of fluorescent albumin.

RESULTS

Systemic infection attenuated the increases in both leukocyte adherence and local infection-induced microvascular permeability. Neutrophil cell-surface expression of L-selectin, as determined by flow cytometry, diminished with both local and systemic infection, whereas expression of CD11b increased with systemic, but not local, infection.

CONCLUSIONS

These data suggest that systemic (intra-abdominal) sepsis diminishes local inflammation-mediated vascular leakage by attenuating leukocyte adherence.

The role of the endothelium in severe sepsis and multiple organ dysfunction syndrome

Severe sepsis, defined as sepsis with acute organ dysfunction, is associated with high morbidity and mortality rates. The development of novel therapies for sepsis is critically dependent on an understanding of the basic mechanisms of the disease. The pathophysiology of severe sepsis involves a highly complex, integrated response that includes the activation of a number of cell types, inflammatory mediators, and the hemostatic system. Central to this process is an alteration of endothelial cell function. The goals of this article are to (1) provide an overview of sepsis and its complications, (2) discuss the role of the endothelium in orchestrating the host response in sepsis, and (3) emphasize the potential value of the endothelium as a target for sepsis therapy.

Soluble E-selectin, soluble L-selectin and soluble ICAM-1 in bronchopulmonary dysplasia, and changes with dexamethasone

OBJECTIVE

To evaluate longitudinal change in arterial blood plasma levels of soluble adhesion molecules in infants of <30 weeks' gestation with respiratory distress syndrome (RDS) and to look for differences in these levels in neonates who subsequently developed bronchopulmonary dysplasia (BPD) compared with those neonates who did not, and also to investigate the effect of dexamethasone treatment on levels of soluble adhesion molecules in plasma.

METHODS

We measured plasma concentrations of soluble L-selectin (sL-selectin), soluble E-selectin (sE-selectin), and soluble intercellular adhesion molecule-1 on days 1, 3, 7, 14, 21, and 28 of life and before and 2 to 3 days after initiating a 6-day course of dexamethasone treatment. Infants with RDS were followed until discharge and were classified as non-BPD and either 1) BPD day 28 reflecting oxygen requirement on day 28 but not at 36 corrected weeks or 2) BPD 36 weeks reflecting oxygen requirement at 36 (corrected) weeks' gestation. The classification of presence or absence of BPD by oxygen requirement was supported by and was consistent with radiologic findings of BPD for all infants. The difference between BPD day 28 and BPD 36 weeks was supported by more extensive radiologic effects in the latter.

RESULTS

The arterial plasma level of sL-selectin in infants who had RDS and did not develop BPD was significantly decreased compared with term healthy infants, as was the level of sE-selectin. Compared with infants who had RDS and did not develop BPD, sL-selectin levels were even further decreased in infants who had RDS and did develop BPD both at birth and throughout the first 4 weeks of life (day 1 through day 28). Infants with BPD also showed increasing levels of sE-selectin during this period of time, whereas infants without BPD did not. Levels of soluble intercellular adhesion molecule-1 in infants without BPD were not different from infants with BPD initially but increased in infants with BPD compared with infants without BPD, significant on day 28 in both groups. Dexamethasone treatment increased concentration of sL-selectin and decreased concentration of sE-selectin.

CONCLUSIONS

Low sL-selectin may be an early indicator of enhanced risk for BPD. Low levels of sL-selectin and increasing levels of sE-selectin may be risk factors for BPD. The effects of dexamethasone treatment include significant modulation of adhesion molecules.

Regional and systemic cytokine responses to acute inflammation of the vermiform appendix

OBJECTIVE

To measure local (peritoneal fluid) and systemic (plasma) cytokine profiles in patients with infection-inflammation of the vermiform appendix, a relatively mild, localized inflammatory process.

SUMMARY BACKGROUND DATA

The systemic host response to invading microorganisms, often termed the systemic inflammatory response syndrome (SIRS), includes changes in heart rate, respiratory rate, body temperature, and circulating white blood cell numbers. Although these changes can be induced experimentally by administering proinflammatory cytokines, the mediators that appear in the bloodstream during early, localized infection in humans have not been defined.

METHODS

The authors studied 56 patients with pathologically proven appendicitis. Blood was obtained before the induction of anesthesia, when 82% of the patients met the criteria for SIRS. Peritoneal fluid (PF) was obtained by intraoperative lavage. Cytokines were measured by immunoassay. To assess the net impact of the mediators within plasma, the authors studied the ability of patient plasma to augment or suppress bacterial lipopolysaccharide (LPS) stimulation of monocytes in vitro.

RESULTS

Of the proinflammatory cytokines, tumor necrosis factor-alpha was present in PF but not in plasma, interleukin (IL)-1beta and interferon-gamma were found in low concentrations in both PF and plasma, and IL-12 (p70) was detectable in plasma but not PF. In contrast, IL-6 and IL-1 receptor antagonist (IL-1ra) were the most abundant cytokines in the PF and plasma, and the concentrations of IL-4 and IL-10 were also elevated in both compartments. Patients with more severe appendicitis had higher plasma levels of IL-6 and IL-10 and lower plasma levels of IL-12 and interferon-gamma than did those with uncomplicated disease. Patient plasma inhibited LPS-induced stimulation of a monocyte cell line, and this inhibition was accentuated by complicated disease.

CONCLUSIONS

As judged from the pattern of soluble cytokines in plasma and the effect of the plasma on monocyte activation by LPS, mild, localized infection can induce a systemic response that is predominantly anti-inflammatory.

Recent developments in the treatment of sepsis

Despite advances in supportive care, septic shock remains a major cause of morbidity and mortality. With the identification of the systemic inflammatory response as a major component in the pathogenesis of the septic shock syndrome, much of the recent work has focused on modulating this response. This includes antiendotoxin therapies in patients with Gram-negative sepsis, and therapies to modulate the pro-inflammatory mediators produced in response to infection, such as TNF-alpha, platelet-activating factor and complement. High-flow haemofiltration has the potential advantage of clearing both endotoxin and pro-inflammatory mediators. Antithrombotic strategies have been investigated and have yielded the first major success in the treatment of sepsis with activated protein C. Nitric oxide produces the cardiovascular features of sepsis and investigators have looked at both reducing its production and mopping up the excess. Attempts to reduce apoptosis have been a new focus in the treatment of sepsis. There have also been recent developments in supportive care suggesting a role for vasopressin and replacement corticosteroid therapy.

A functional role for circulating mouse L-selectin in regulating leukocyte/endothelial cell interactions in vivo

L-selectin mediates the initial capture and subsequent rolling of leukocytes along inflamed vascular endothelium and mediates lymphocyte migration to peripheral lymphoid tissues. Leukocyte activation induces rapid endoproteolytic cleavage of L-selectin from the cell surface, generating soluble L-selectin (sL-selectin). Because human sL-selectin retains ligand-binding activity in vitro, mouse sL-selectin and its in vivo relevance were characterized. Comparable with humans, sL-selectin was present in adult C57BL/6 mouse sera at approximately 1.7 micro g/ml. Similar levels of sL-selectin were present in sera from multiple mouse strains, despite their pronounced differences in cell surface L-selectin expression levels. Adhesion molecule-deficient mice prone to spontaneous chronic inflammation and mice suffering from leukemia/lymphoma had 2.5- and 20-fold increased serum sL-selectin levels, respectively. By contrast, serum sL-selectin levels were reduced by 70% in Rag-deficient mice lacking mature lymphocytes. The majority of serum sL-selectin had a molecular mass of 65-75 kDa, consistent with its lymphocyte origin. Slow turnover may explain the relatively high levels of sL-selectin in vivo. The t(1/2) of sL-selectin, assessed by transferring sera from wild-type mice into L-selectin-deficient mice and monitoring serum sL-selectin levels by ELISA, was >20 h, and it remained detectable for longer than 1 wk. Short-term in vivo lymphocyte migration assays demonstrated that near physiologic levels ( approximately 0.9 micro g/ml) of sL-selectin decreased lymphocyte migration to peripheral lymph nodes by >30%, with dose-dependent inhibition occurring with increasing sL-selectin concentrations. These results suggest that sL-selectin influences lymphocyte migration in vivo and that the increased sL-selectin levels present in certain pathologic conditions may adversely affect leukocyte migration.

Soluble L-selectin attenuates tumor necrosis factor-alpha-mediated leukocyte adherence and vascular permeability: a protective role for elevated soluble L-selectin in sepsis

OBJECTIVE

We have previously demonstrated that leukocyte delivery to remote sites is decreased in sepsis and that increased concentrations of soluble L-selectin are, in part, responsible for this finding. Given that leukocytes have been implicated in the pathogenesis of vascular leakage, we hypothesized that the elevated soluble L-selectin concentrations in sepsis may translate into decreased inflammation-mediated leukocyte-endothelial cell interactions and vascular leakage at these sites.

DESIGN

Prospective, controlled animal study.

SETTING

Surgical research laboratory in a university hospital.

SUBJECTS

Swiss white male mice weighing 25-35 g.

INTERVENTIONS

Mice were randomized to one of three study groups: intracremaster tumor necrosis factor-alpha with subsequent intravenous bicarbonate buffered solution; intracremaster tumor necrosis factor-alpha with intravenous soluble L-selectin (10 microg/mL); and intracremaster bicarbonate buffered solution with intravenous bicarbonate buffered solution. The cremaster muscle was prepared for both light and fluorescence intravital microscopy 2 hrs after intracremaster injection, and fluorescein isothiocyanate-labeled albumin was injected intravenously. Leukocyte-endothelial interactions (rolling flux, rolling velocity, and adherence) were counted off-line. Postcapillary venule leakage was determined by the permeability index (perivenular/intravenular fluorescence) after intravenous injection of fluorescent albumin.

MEASUREMENTS AND MAIN RESULTS

Soluble L-selectin significantly attenuated tumor necrosis factor-alpha-mediated increases in leukocyte adherence and vascular leakage. Leukocyte rolling velocity was restored to baseline with soluble L-selectin; however, rolling flux was not altered. Blood pressure, shear rate, and leukocyte counts did not differ between groups.

CONCLUSIONS

Soluble L-selectin decreases local inflammation-mediated leukocyte adherence and vascular leakage in vivo. The increased concentrations of soluble L-selectin in sepsis may represent a protective mechanism by which the host attempts to diminish the deleterious systemic effects of activated leukocytes during sepsis.