Expression of beta 2-integrins and L-selectin on polymorphonuclear leukocytes in septic patients

Meprin and ADAM proteases as triggers of systemic inflammation in sepsis

Systemic inflammatory disorders (SIDs) comprise a broad range of diseases characterized by dysregulated excessive innate immune responses. Severe forms of SIDs can lead to organ failure and death, and their increasing incidence represents a major issue for the healthcare system. Protease-mediated ectodomain shedding of cytokines and their receptors represents a central mechanism in the regulation of inflammatory responses. The metalloprotease A disintegrin and metalloproteinase (ADAM) 17 is the best-characterized ectodomain sheddase capable of releasing TNF-α and soluble IL-6 receptor, which are decisive factors of systemic inflammation. Recently, meprin metalloproteases were also identified as IL-6 receptor sheddases and activators of the pro-inflammatory cytokines IL-1β and IL-18. In different mouse models of SID, particularly those mimicking a sepsis-like phenotype, ADAM17 and meprins have been found to promote disease progression. In this review, we summarize the role of ADAM10, ADAM17, and meprins in the onset and progression of sepsis and discuss their potential as therapeutic targets.

Aspartic Acid Isomerization Characterized by High Definition Mass Spectrometry Significantly Alters the Bioactivity of a Novel Toxin from Poecilotheria

Research in toxinology has created a pharmacological paradox. With an estimated 220,000 venomous animals worldwide, the study of peptidyl toxins provides a vast number of effector molecules. However, due to the complexity of the protein-protein interactions, there are fewer than ten venom-derived molecules on the market. Structural characterization and identification of post-translational modifications are essential to develop biological lead structures into pharmaceuticals. Utilizing advancements in mass spectrometry, we have created a high definition approach that fuses conventional high-resolution MS-MS with ion mobility spectrometry (HDMS^E) to elucidate these primary structure characteristics. We investigated venom from ten species of “tiger” spider (Genus: Poecilotheria) and discovered they contain isobaric conformers originating from non-enzymatic Asp isomerization. One conformer pair conserved in five of ten species examined, denominated PcaTX-1a and PcaTX-1b, was found to be a 36-residue peptide with a cysteine knot, an amidated C-terminus, and isoAsp33Asp substitution. Although the isomerization of Asp has been implicated in many pathologies, this is the first characterization of Asp isomerization in a toxin and demonstrates the isomerized product’s diminished physiological effects. This study establishes the value of a HDMS^E approach to toxin screening and characterization.

L-selectin: A Major Regulator of Leukocyte Adhesion, Migration and Signaling

L-selectin (CD62L) is a type-I transmembrane glycoprotein and cell adhesion molecule that is expressed on most circulating leukocytes. Since its identification in 1983, L-selectin has been extensively characterized as a tethering/rolling receptor. There is now mounting evidence in the literature to suggest that L-selectin plays a role in regulating monocyte protrusion during transendothelial migration (TEM). The N-terminal calcium-dependent (C-type) lectin domain of L-selectin interacts with numerous glycans, including sialyl Lewis X (sLe^x) for tethering/rolling and proteoglycans for TEM. Although the signals downstream of L-selectin-dependent adhesion are poorly understood, they will invariably involve the short 17 amino acid cytoplasmic tail. In this review we will detail the expression of L-selectin in different immune cell subsets, and its influence on cell behavior. We will list some of the diverse glycans known to support L-selectin-dependent adhesion, within luminal and abluminal regions of the vessel wall. We will describe how each domain within L-selectin contributes to adhesion, migration and signal transduction. A significant focus on the L-selectin cytoplasmic tail and its proposed contribution to signaling via the ezrin-radixin-moesin (ERM) family of proteins will be outlined. Finally, we will discuss how ectodomain shedding of L-selectin during monocyte TEM is essential for the establishment of front-back cell polarity, bestowing emigrated cells the capacity to chemotax toward sites of damage.

In Vivo Effects of Neostigmine and Physostigmine on Neutrophil Functions and Evaluation of Acetylcholinesterase and Butyrylcholinesterase as Inflammatory Markers during Experimental Sepsis in Rats

Introduction

Recent studies have shown that acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) may serve as important diagnostic and therapeutic targets in sepsis. Since polymorphonuclear neutrophils (PMNs) play a pivotal role in the early phase of sepsis, we evaluated the potential therapeutic effects of cholinesterase inhibitors on PMN functions during cecal ligation and puncture- (CLP-) induced sepsis and investigated the roles of AChE and BChE as inflammatory markers under standardized experimental conditions.

Methods

Sham surgery or CLP was performed in male Wistar rats (n = 60). Animals were randomized into four groups: physostigmine, 100 μg/kg; neostigmine, 75 μg/kg; 0.9% saline (control group); and sham group, each applied four times over 24 h. The levels of reactive oxygen species (ROS) production and CD11b/CD62l expression were quantified by flow cytometry at t = 0, 6, 15, 20, and 24 h. Blood gas analysis as well as AChE and BChE activity levels was measured by validated point-of-care measurements. Clinical scores and survival times were determined.

Results

CLP induced a significant increase in ROS production and CD11b upregulation by rat PMNs. Treatment with physostigmine or neostigmine significantly reduced ROS production and CD11b upregulation by PMNs 20 h after CLP induction. In physostigmine-treated animals, survival times were significantly improved compared to the control animals, but not in neostigmine-treated animals. While AChE activity significantly decreased in the control animals at t > 6 h, AChE activity did not change in the sham group. BChE activity decreased at t > 20 h in the control animals.

Conclusion

While AChE activity may serve as an acute inflammatory marker, BChE activity shows a delayed decrease. Administration of centrally acting physostigmine in CLP-induced sepsis in rats has protective effects on PMN functions and improves survival times, which may be of interest in clinical practice.

Structural insights into calmodulin-regulated L-selectin ectodomain shedding

The L-selectin glycoprotein receptor mediates the initial steps of leukocyte migration into secondary lymphoid organs and sites of inflammation. Following cell activation through the engagement of G-protein-coupled receptors or immunoreceptors, the extracellular domains of L-selectin are rapidly shed, a process negatively controlled via the binding of the ubiquitous eukaryotic calcium-binding protein calmodulin to the cytoplasmic tail of L-selectin. Here we present the solution structure of calcium-calmodulin bound to a peptide encompassing the cytoplasmic tail and part of the transmembrane domain of L-selectin. The structure and accompanying biophysical study highlight the importance of both calcium and the transmembrane segment of L-selectin in the interaction between these two proteins, suggesting that by binding this region, calmodulin regulates in an "inside-out" fashion the ectodomain shedding of the receptor. Our structure provides the first molecular insight into the emerging new role for calmodulin as a transmembrane signaling partner.

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.

Functional and phenotypic changes in polymorphonuclear neutrophils induced by catecholamines

PURPOSE

To elucidate differential functional and phenotypic changes in response to relevant catecholamines, the generation of oxidative free radicals by PMN, and changes in the expression of L-selectin and Mac-1 on the surface of PMN were examined in the presence of epinephrine, norepinephrine and dopamine in physiological and pharmacological concentrations.

MATERIALS AND METHODS

Human polymorphonuclear neutrophils were obtained from healthy donors and pretreated with 0.5 nM or 500 nM epinephrine; 1.18 nM or 1 180 nM norepinephrine; or 0.26 nM or 261 nM dopamine, followed by stimulation with FMLP. Stimulated neutrophils were incubated with antibodies against CD 11 b or CD 62 l and assessed by flow cytometry. Additional probes were assessed by flow cytometry for the generation of oxidative free radicals.

RESULTS

All catecholamines in high concentration inhibited the suppression of CD 62 l expression and CD 11 b upregulation following stimulation with FMLP. A high concentration of epinephrine suppresses generation of oxidative free radicals.

CONCLUSIONS

The effect of catecholamines on the expression of CD 62 l explains the increased expression of L-selection on PMN observed after trauma. The suppression of CD 11 b reduces leukocyte adherence and consecutive abnormalities in microvascular flow. Epinephrine inhibits the generation of oxidative free radicals by PMN with potentially detrimental effects with respect to bacterial clearance.

POLYMORPHONUCLEAR LEUKOCYTE DYSFUNCTION SYNDROME IN PATIENTS WITH INCREASING SEPSIS SEVERITY

Production of oxygen radicals is required for both microbicidal and tissue-toxic effector functions of granulocytes. Inasmuch as an ambivalent role of polymorphonuclear leukocytes (PMNs) may become apparent during sepsis, we studied levels of hydrogen peroxide (H2O2) production by PMNs depending upon the nature of different particulate and soluble stimuli in patients with increasing sepsis severity. Patients with sepsis (n = 15), severe sepsis (n = 12), or septic shock (n = 33) were prospectively enrolled in the study. Healthy volunteers of comparable age and sex served as controls (n = 50). Unopsonized and opsonized zymosan particles were used to assess adhesion, phagocytosis, and the associated H2O2 production. Zymosan particles are rich in beta-glucans and lectin structures that are known to trigger H2O2 production via two major non-toll-like receptor pathogen recognition receptors, comprising the lectin-binding site in the alpha-chain (CD11b) of the complement receptor type 3 and the more recently identified nonclassical C-type lectin, dectin-1. To determine H2O2 production upon cell activation by soluble stimuli, PMNs were activated by the chemotactic tripeptide (N-formyl-methionyl-leucyl-phenylalanine [fMLP]) alone or after priming of cells by preincubation with tumor necrosis factor alpha. To get insight into the changes of fMLP receptor classical intracellular signaling pathways, PMNs were also incubated with the calcium ionophore A23187 and the phorbol ester phorbol myristate acetate, bypassing receptor-dependent signal transduction to directly activate calcium/calmodulin kinase- and protein kinase C-dependent pathways, respectively. As compared with healthy volunteers, levels of H2O2 production by PMNs from septic patients varied depending upon the nature of the activating signal: reduced (zymosan), unchanged (phorbol myristate acetate, opsonized zymosan), and enhanced (spontaneous, fMLP, fMLP + tumor necrosis factor alpha, A23187), with the changes most pronounced in patients with septic shock. Specifically, phagocytosis of zymosan and the associated H2O2 production were significantly decreased whereas spontaneous and stimulated H2O2 production elicited by soluble stimuli strongly increased. Thus, these findings suggest the development of a PMN dysfunction syndrome in patients with increasing sepsis severity. Moreover, as binding of zymosan particles to the PMNs' surface remained unchanged despite increasingly suppressed phagocytosis and associated H2O2 production, observed effects are likely to reflect defects in signaling by the lectin-binding site of CD11b and/or the beta-glucan receptor dectin-1, respectively.

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.

I-domain of lymphocyte function-associated antigen-1 mediates rolling of polystyrene particles on ICAM-1 under flow

In their active state, beta(2)-integrins, such as LFA-1, mediate the firm arrest of leukocytes by binding intercellular adhesion molecules (ICAMs) expressed on endothelium. Although the primary function of LFA-1 is assumed to be the ability to mediate firm adhesion, recent work has shown that LFA-1 can contribute to cell tethering and rolling under hydrodynamic flow, a role previously largely attributed to the selectins. The inserted (I) domain of LFA-1 has recently been crystallized in the wild-type (wt) and locked-open conformations and has been shown to, respectively, support rolling and firm adhesion under flow when expressed in alpha(L)beta(2) heterodimers or as isolated domains on cells. Here, we report results from cell-free adhesion assays where wt I-domain-coated polystyrene particles were allowed to interact with ICAM-1-coated surfaces in shear flow. We show that wt I-domain can independently mediate the capture of particles from flow and support their rolling on ICAM-1 surfaces in a manner similar to how carbohydrate-selectin interactions mediate rolling. Adhesion is specific and blocked by appropriate antibodies. We also show that the rolling velocity of I-domain-coated particles depends on the wall shear stress in flow chamber, I-domain site density on microsphere surfaces, and ICAM-1 site density on substrate surfaces. Furthermore, we show that rolling is less sensitive to wall shear stress and ICAM-1 substrate density at high density of I-domain on the microsphere surface. Computer simulations using adhesive dynamics can recreate bead rolling dynamics and show that the mechanochemical properties of ICAM-1-I-domain interactions are similar to those of carbohydrate-selectin interactions. Understanding the biophysics of adhesion mediated by the I-domain of LFA-1 can elucidate the complex roles this integrin plays in leukocyte adhesion in inflammation.

Integrin dimerization and ligand organization: key components in integrin clustering for cell adhesion

Cell adhesion requires both integrin occupancy and integrin clustering. In this work, we investigate a mechanism based on organizing ligand into islands and integrin dimerization for the initiation of integrin clustering. To study integrin clustering and integrin occupancy we develop a two-dimensional Monte Carlo lattice description of the cell-substrate interface to simulate the diffusion and reaction of integrins. We demonstrate that integrin dimerization can drive integrins into clusters of sizes greater than two. Ligand organization or integrin dimerization alone is unable to increase the number of bound integrins, but when both are present they cooperate to increase both binding and clustering of integrins. In addition, when integrin dimerization and ligand organization are both present large integrin clusters, which may act as nucleation sites for the formation of adhesion complexes, are observed. These results describe a potential mechanism for the clustering of integrin receptors and avidity modulation in cellular adhesion and have implications for the designs of surfaces to control cell responses to external ligands and to manipulate cell adhesion for tissue-engineering applications.

Interplay between rolling and firm adhesion elucidated with a cell-free system engineered with two distinct receptor-ligand pairs

The firm arrest of leukocytes to the endothelium during inflammation is known to be mediated by endothelial intercellular adhesion molecules (ICAMs) binding to activated integrins displayed on leukocyte surface. Selectin-ligand interactions, which mediate rolling, are believed to be important for facilitating firm adhesion, either by activating integrins or by facilitating the transition to firm adhesion by making it easier for integrins to bind. Although leukocytes employ two distinct adhesion molecules that mediate different states of adhesion, the fundamental biophysical mechanisms by which two pairs of adhesion molecules facilitate cell adhesion is not well understood. In this work, we attempt to understand the interaction between two molecular systems using a cell-free system in which polystyrene microspheres functionalized with the selectin ligand, sialyl Lewis(X) (sLe(X)), and an antibody against ICAM-1, aICAM-1, are perfused over P-selectin/ICAM-1 coated surfaces in a parallel plate flow chamber. Separately, sLe(X)/P-selectin interactions support rolling and aICAM-1/ICAM-1 interactions mediate firm adhesion. Our results show that sLe(X)/aICAM-1 microspheres will firmly adhere to P-selectin/ICAM-1 coated surfaces, and that the extent of firm adhesion of microspheres is dependent on wall shear stress within the flow chamber, sLe(X)/aICAM-1 microsphere site density, and P-selectin/ICAM-1 surface density ratio. We show that P-selectin's interaction with sLe(X) mechanistically facilitates firm adhesion mediated by antibody binding to ICAM-1: the extent of firm adhesion for the same concentration of aICAM-1/ICAM-1 interaction is greater when sLe(X)/P-selectin interactions are present. aICAM-1/ICAM-1 interactions also stabilize rolling by increasing pause times and decreasing average rolling velocities. Although aICAM-1 is a surrogate for beta(2)-integrin, the kinetics of association between aICAM-1 and ICAM-1 is within a factor of 1.5 of activated integrin binding ICAM-1, suggesting the findings from this model system may be insightful to the mechanism of leukocyte firm adhesion. In particular, these experimental results show how two molecule systems can interact to produce an effect not achievable by either system alone, a fundamental mechanism that may pervade leukocyte adhesion biology.

L-selectin in health and disease

This article reviews recent advances in the knowledge of the role of L-selectin, an adhesion molecule that is expressed on the surface of circulating leucocytes, in animal and human physiology and pathophysiology. After a brief discussion on nomenclature and structure, it progresses through the evidence for expression and regulation of L-selectin, cell collection and purification, physiological function and roles. The special role of knock out mice and monoclonal antibodies in determining a role for L-selectin in inflammatory states is described before proceeding to discuss the importance of L-selectin ligands and shed L-selectin. A second section describes a role for L-selectin in pathophysiological states in animals and man, with special reference to trauma, systemic inflammatory syndromes and sepsis. The review concludes with a summary of the potential role of anti-inflammatory medication and L-selectin blockers in the management of inflammation.

L-selectin in trauma patients: a marker for organ dysfunction and outcome?

BACKGROUND

Systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS) are important factors affecting morbidity and mortality after trauma. Adhesion molecules, e.g. L-selectin (CD62 L), play crucial roles in both conditions.

PATIENTS AND METHODS

In 51 multiple trauma patients, CD62 L surface expression on granulocytes, monocytes, lymphocytes, as well as sCD62 L plasma concentrations were determined during the first 6 days after trauma, starting at the site of accident. Clinical parameters were severity of injury scores (ISS, APACHE II), requirement of red blood cell transfusion, acute lung or liver failure, development of MODS or SIRS, early (< or = 6 d) or late (> 6 d), and outcome.

RESULTS

CD62 L expression was reversibly elevated on granulocytes, T cells and monocytes in comparison with initial values. sCD62 L plasma concentrations did not show temporal variations but were depressed throughout observation period, in comparison with healthy controls. Lung failure within the first 6 days was associated with increased CD62 L expression on monocytes and B cells on admission and increased sCD62 L concentrations after 12 and 24 h. Patients with more severe injuries (APACHE II > 20 points) had higher sCD62 L concentrations after 24 h. Non-survivors had decreased sCD62 L (on admission) and T-cell CD62 L expression (after 4 h). Patients with early MODS or SIRS showed increased monocyte CD62 L expression after 6 days.

CONCLUSIONS

In multiple trauma patients, severe organ dysfunction is associated with altered CD62 L expression on leukocytes and circulating sCD62 L plasma concentrations. However, the obvious complexity of the pattern currently restricts use of CD62 L quantitation for clinical purposes.

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.

Vulnerable caregivers of patients with Alzheimer's disease have a deficit in circulating CD62L- T lymphocytes

OBJECTIVE

The cell adhesion molecule, L-selectin (CD62L), serves a crucial role in the migration of naive T lymphocytes and is typically shed on cell activation. The objective of this study was to determine the effects of chronic stress on L-selectin expression on peripheral lymphocytes in elderly spousal caregivers of patients with Alzheimer's disease.

METHODS

Twenty caregivers (mean age, 73.5 years) had their lymphocytes and catecholamine levels sampled at rest and in response to an acute psychological stressor. Ten of the caregivers were classified as susceptible or "vulnerable" based on the large amount of care required by the patient relative to the amount of respite the caregiver received during the previous 6 months.

RESULTS

At rest, vulnerable caregivers had 60% fewer L-selectin negative CD8+ T cells (CD8+CD62L-) (p=.01) but no difference in CD8+CD62L+ cells. Vulnerable caregivers also showed significantly fewer CD4+CD62L- T lymphocytes (p=.04) but no difference in CD4+CD62L+ lymphocytes. Resting plasma epinephrine levels were 44% higher in vulnerable caregivers as compared with nonvulnerable caregivers (p=.01). The acute stressor increased circulating levels of CD8+CD62L- and CD8+CD62L+ lymphocytes and catecholamines similarly in both groups.

CONCLUSIONS

The findings suggest that caregivers who are more vulnerable to the chronic stress of caregiving show a decrement in circulating CD62L- T lymphocytes, possibly by adrenomedullary activation. The data also suggest the identity of lymphocyte subsets that may underlie prior observations of immunologic decrements associated with the chronic stress of caregiving.