The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Klaus Ley - One of the best experts on this subject based on the ideXlab platform.
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biomechanics of Leukocyte Rolling
Biorheology, 2011Co-Authors: Prithu Sundd, Maria K Pospieszalska, Luthur Siu Lun Cheung, Konstantinos Konstantopoulos, Klaus LeyAbstract:Leukocyte Rolling on endothelial cells and other P-selectin substrates is mediated by P-selectin binding to P-selectin glycoprotein ligand-1 expressed on the tips of Leukocyte microvilli. Leukocyte Rolling is a result of rapid, yet balanced formation and dissociation of selectin-ligand bonds in the presence of hydrodynamic shear forces. The hydrodynamic forces acting on the bonds may either increase (catch bonds) or decrease (slip bonds) their lifetimes. The force-dependent 'catch-slip' bond kinetics are explained using the 'two pathway model' for bond dissociation. Both the 'sliding-rebinding' and the 'allosteric' mechanisms attribute 'catch-slip' bond behavior to the force-induced conformational changes in the lectin-EGF domain hinge of selectins. Below a threshold shear stress, selectins cannot mediate Rolling. This 'shear-threshold' phenomenon is a consequence of shear-enhanced tethering and catch bond-enhanced Rolling. Quantitative dynamic footprinting microscopy has revealed that Leukocytes Rolling at venular shear stresses (>0.6 Pa) undergo cellular deformation (large footprint) and form long tethers. The hydrodynamic shear force and torque acting on the Rolling cell are thought to be synergistically balanced by the forces acting on tethers and stressed microvilli, however, their relative contribution remains to be determined. Thus, improvement beyond the current understanding requires in silico models that can predict both cellular and microvillus deformation and experiments that allow measurement of forces acting on individual microvilli and tethers.
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event tracking model of adhesion identifies load bearing bonds in Rolling Leukocytes
Microcirculation, 2009Co-Authors: Maria K Pospieszalska, Alexander Zarbock, John E Pickard, Klaus LeyAbstract:Objectives: P-selectin binding to P-selectin glycoprotein ligand-1 (PSGL)-1 mediates Leukocyte Rolling under conditions of inflammation and injury. The aims of this study were to develop an efficient, high temporal resolution model for direct simulation of Leukocyte Rolling and conduct a study of load-bearing bonds using the model.Materials and Methods: A stochastic π-calculus-driven event-tracking model of adhesion (ETMA) was developed and compared with experimental data. Multiple simulations for each case were conducted to obtain high-confidence numerical characteristics of Leukocyte Rolling.Results: Leukocyte Rolling and the underlying P-selectin—PSGL-1 bonds were studied under low wall shear rate (25–50 s−1) conditions from measured parameters of Leukocyte Rolling and bond properties. For the first time, the location, number, lifetime, history, and kinetics of load-bearing bonds and their influence on cell Rolling were identified and instantaneous cell displacements, translational and rotational veloc...
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dynamics of in silico Leukocyte Rolling activation and adhesion
BMC Systems Biology, 2007Co-Authors: Jonathan Tang, Klaus Ley, Anthony C HuntAbstract:Background We present a multilevel, agent based, in silico model that represents the dynamics of Rolling, activation, and adhesion of individual Leukocytes in vitro. Object-oriented software components were designed, verified, plugged together, and then operated in ways that represent the molecular and cellular mechanisms believed responsible for Leukocyte Rolling and adhesion. The result is an in silico analogue of an experimental in vitro system. The experimentally measured, phenotypic attributes of the analogue were compared and contrasted to those of Leukocytes in vitro from three different experimental conditions.
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dynamics of in silico Leukocyte Rolling activation and adhesion
BMC Systems Biology, 2007Co-Authors: Jonathan Tang, Klaus Ley, Anthony C HuntAbstract:We present a multilevel, agent based, in silico model that represents the dynamics of Rolling, activation, and adhesion of individual Leukocytes in vitro. Object-oriented software components were designed, verified, plugged together, and then operated in ways that represent the molecular and cellular mechanisms believed responsible for Leukocyte Rolling and adhesion. The result is an in silico analogue of an experimental in vitro system. The experimentally measured, phenotypic attributes of the analogue were compared and contrasted to those of Leukocytes in vitro from three different experimental conditions. The individual in silico dynamics of "Rolling" on simulated P-selectin, and separately on simulated VCAM-1, were an acceptable match to individual in vitro distance-time and velocity-time measurements. The analogues are also able to represent the transition from Rolling to adhesion on P-selectin and VCAM-1 in the presence of GRO-α chemokine. The individual in silico and in vitro behavioral similarities translated successfully to population level measures. These behavioral similarities were enabled in part by subdividing the functionality of the analogue's surface into 600 independent, "cell"-controlled, equally capable modules of comparable functionality. The overlap in phenotypic attributes of our analogue with those of Leukocytes in vitro confirm the considerable potential of our model for studying the key events that determine the behavioral outcome of individual Leukocytes during Rolling, activation, and adhesion. Our results provide an important foundation and framework for future in silico research into plausible causal links between well-documented, subcellular molecular level events and the variety of systemic phenotypic attributes that distinguish normal Leukocyte adhesion from abnormal disease-associated adhesion.
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analysis of Leukocyte Rolling in vivo and in vitro
Methods in Enzymology, 2006Co-Authors: Markus Sperandio, J E Pickard, Sunil Unnikrishnan, Scott T Acton, Klaus LeyAbstract:Leukocyte Rolling is an important step for the successful recruitment of Leukocytes from blood to tissues mediated by a specialized group of glycoproteins termed selectins. Because of the dynamic process of Leukocyte Rolling, binding of selectins to their respective counter-receptors (selectin ligands) needs to fulfill three major requirements: (1) rapid bond formation, (2) high tensile strength, and (3) fast dissociation rates. These criteria are perfectly met by selectins, which interact with specific carbohydrate determinants on selectin ligands. This chapter describes the theoretical background, technical requirements, and analytical tools needed to quantitatively assess Leukocyte Rolling in vivo and in vitro. For the in vivo setting, intravital microscopy allows the observation and recording of Leukocyte Rolling under different physiological and pathological conditions in almost every organ. Real-time and off-line analysis tools help to assess geometric, hemodynamic, and Rolling parameters. Under in vitro conditions, flow chamber assays such as parallel plate flow chamber systems have been the mainstay to study interactions between Leukocytes and adhesion molecules under flow. In this setting, adhesion molecules are immobilized on plastic, in a lipid monolayer, or presented on cultured endothelial cells on the chamber surface. Microflow chambers are available for studying Leukocyte adhesion in the context of whole blood and without blood cell isolation. The microscopic observation of Leukocyte Rolling in different in vivo and in vitro settings has significantly contributed to our understanding of the molecular mechanisms responsible for the stepwise extravasation of Leukocytes into inflamed tissues.
Anthony C Hunt - One of the best experts on this subject based on the ideXlab platform.
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identifying the rules of engagement enabling Leukocyte Rolling activation and adhesion
PLOS Computational Biology, 2010Co-Authors: Jonathan Tang, Anthony C HuntAbstract:The LFA-1 integrin plays a pivotal role in sustained Leukocyte adhesion to the endothelial surface, which is a precondition for Leukocyte recruitment into inflammation sites. Strong correlative evidence implicates LFA-1 clustering as being essential for sustained adhesion, and it may also facilitate rebinding events with its ligand ICAM-1. We cannot challenge those hypotheses directly because it is infeasible to measure either process during Leukocyte adhesion following Rolling. The alternative approach undertaken was to challenge the hypothesized mechanisms by experimenting on validated, working counterparts: simulations in which diffusible, LFA1 objects on the surfaces of quasi-autonomous Leukocytes interact with simulated, diffusible, ICAM1 objects on endothelial surfaces during simulated adhesion following Rolling. We used object-oriented, agent-based methods to build and execute multi-level, multi-attribute analogues of Leukocytes and endothelial surfaces. Validation was achieved across different experimental conditions, in vitro, ex vivo, and in vivo, at both the individual cell and population levels. Because those mechanisms exhibit all of the characteristics of biological mechanisms, they can stand as a concrete, working theory about detailed events occurring at the Leukocyte–surface interface during Leukocyte Rolling and adhesion experiments. We challenged mechanistic hypotheses by conducting experiments in which the consequences of multiple mechanistic events were tracked. We quantified rebinding events between individual components under different conditions, and the role of LFA1 clustering in sustaining Leukocyte–surface adhesion and in improving adhesion efficiency. Early during simulations ICAM1 rebinding (to LFA1) but not LFA1 rebinding (to ICAM1) was enhanced by clustering. Later, clustering caused both types of rebinding events to increase. We discovered that clustering was not necessary to achieve adhesion as long as LFA1 and ICAM1 object densities were above a critical level. Importantly, at low densities LFA1 clustering enabled improved efficiency: adhesion exhibited measurable, cell level positive cooperativity.
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in silico white blood cell a synthetic model of Leukocyte Rolling activation and adhesion during inflammation
Computer Applications in Industry and Engineering, 2009Co-Authors: Jonathan Tang, Anthony C HuntAbstract:We have constructed a synthetic in silico model for representing the dynamics of Leukocyte Rolling, activation, and adhesion on substrate-coated flow chambers. Software components were designed, instantiated, verified, plugged together, and then operated in ways that can map concretely to mechanisms believed responsible for Leukocyte Rolling, activation, and adhesion. Here, we show our model’s ability to represent data from in vitro flow chamber studies of Leukocyte Rolling, activation, and adhesion on P-Selectin, ICAM-1 and CXCL1 substratecoated surfaces.
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in silico white blood cell mechanisms underlying Leukocyte Rolling and adhesion during inflammation
Spring Simulation Multiconference, 2008Co-Authors: Jon Tang, Anthony C HuntAbstract:We have used the synthetic modeling method to construct a multilevel, agent oriented, in silico analogue of an in vitro experimental system for studying Leukocyte Rolling, activation, and adhesion during inflammatory conditions. We specify capabilities that the envisioned analogues must have to achieve long-term goals. Here, we report progress towards our goal of using variants of this model as experimental systems for exploring the potential role of hypothesized mechanisms that are thought to mediate Leukocyte Rolling, activation, and adhesion. We focus initially on diffusion and clustering events of the LFA-1 integrin receptor on the Leukocyte membrane during Rolling and adhesion.
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dynamics of in silico Leukocyte Rolling activation and adhesion
BMC Systems Biology, 2007Co-Authors: Jonathan Tang, Klaus Ley, Anthony C HuntAbstract:Background We present a multilevel, agent based, in silico model that represents the dynamics of Rolling, activation, and adhesion of individual Leukocytes in vitro. Object-oriented software components were designed, verified, plugged together, and then operated in ways that represent the molecular and cellular mechanisms believed responsible for Leukocyte Rolling and adhesion. The result is an in silico analogue of an experimental in vitro system. The experimentally measured, phenotypic attributes of the analogue were compared and contrasted to those of Leukocytes in vitro from three different experimental conditions.
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dynamics of in silico Leukocyte Rolling activation and adhesion
BMC Systems Biology, 2007Co-Authors: Jonathan Tang, Klaus Ley, Anthony C HuntAbstract:We present a multilevel, agent based, in silico model that represents the dynamics of Rolling, activation, and adhesion of individual Leukocytes in vitro. Object-oriented software components were designed, verified, plugged together, and then operated in ways that represent the molecular and cellular mechanisms believed responsible for Leukocyte Rolling and adhesion. The result is an in silico analogue of an experimental in vitro system. The experimentally measured, phenotypic attributes of the analogue were compared and contrasted to those of Leukocytes in vitro from three different experimental conditions. The individual in silico dynamics of "Rolling" on simulated P-selectin, and separately on simulated VCAM-1, were an acceptable match to individual in vitro distance-time and velocity-time measurements. The analogues are also able to represent the transition from Rolling to adhesion on P-selectin and VCAM-1 in the presence of GRO-α chemokine. The individual in silico and in vitro behavioral similarities translated successfully to population level measures. These behavioral similarities were enabled in part by subdividing the functionality of the analogue's surface into 600 independent, "cell"-controlled, equally capable modules of comparable functionality. The overlap in phenotypic attributes of our analogue with those of Leukocytes in vitro confirm the considerable potential of our model for studying the key events that determine the behavioral outcome of individual Leukocytes during Rolling, activation, and adhesion. Our results provide an important foundation and framework for future in silico research into plausible causal links between well-documented, subcellular molecular level events and the variety of systemic phenotypic attributes that distinguish normal Leukocyte adhesion from abnormal disease-associated adhesion.
Paul Kubes - One of the best experts on this subject based on the ideXlab platform.
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The oq-Integrin Supports Leukocyte Rolling and Adhesion in Chronically Inflamed PostcapillaryVenules In Vivo
2013Co-Authors: Brent Johnston, Thomas B. Issekutz, Paul KubesAbstract:A role for the 0~4-integrin (OL4 ~ 1 or 0t.4~7) , has been imphcated in the recruitment of peripheral blood mononuclear cells (PBMCs) to sites of inflammation. However, the adhesive interactions (i.e., tethering, Rolling, and adhesion) mediated by the ot4-integrin have not been characterized in vivo. The objective of this study was to establish a model wherein postcapillary venules were chronically inflamed, and then use intravital microscopy to identify the adhesive interactions mediated by the ot4-integrin in vivo. Between 4 and 20 d after immunization with Mycobacterium butyricum, animals developed a systemic vasculitis characterized by large increases in the numbers of Rolling and adhering Leukocytes within mesenteric venules. The selectins could only account for "50 % of the Leukocyte Rolling whereas the remaining cells rolled exclusively via the ot4-integrin. Anti-or 4 therapy also ehminated the increase in Leukocyte adhesion observed in this model, whereas selectin therapies and an anti-CD18 ([32-integrin) monoclonal antibody (mAb) did not reduce adhesion. A serum against polymorphonuclear Leukocytes (PMNs) was used to confirm that a significant proportion of Rolling cells, and most of the adhering cells were PBMCs. Sequential treatment with anti-PMN serum and the anti-cq mAb demonstrated that ot4-dependent Rolling was distinct from PMN Rolling populations. Initial leukocyt
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endothelin 1 causes p selectin dependent Leukocyte Rolling and adhesion within rat mesenteric microvessels
American Journal of Physiology-heart and Circulatory Physiology, 1999Co-Authors: Mariajesus Sanz, Brent Johnston, Andrew C Issekutz, Paul KubesAbstract:Endothelin-1 (ET-1) is a potent vasoconstrictor postulated to play a role in hypertension, ischemia-reperfusion, and atherosclerosis. In addition to these contributions, it has been also proposed to induce Leukocyte-endothelial cell interactions. The aim of the present study was to assess the mechanisms of action of ET-1 on Leukocyte recruitment in vivo. Intravital microscopy of the rat mesenteric postcapillary venules was used. Ten minutes after 1 nM ET-1 superfusion, a significant increase in Leukocyte Rolling (77.5 ± 22.6 vs. 20.5 ± 4.5 cells/min) and adhesion (15.5 ± 2.9 vs. 3.0 ± 0.8 cells/100 μm) but not emigration was observed. These effects were found not to be mediated by mast cell activation. No platelet-endothelial cell interactions were detected in this in vivo system and furthermore, flow cytometry analysis revealed no increase of P-selectin expression in rat platelets on ET-1 stimulation. Pretreatment of animals with an anti-rat P-selectin monoclonal antibody (mAb) dramatically reduced Leukocyte Rolling and adhesion by 100 and 94% respectively when compared with control mAb-treated animals. At this dose of ET-1, a very transient decrease in shear rate was detected, arteriolar diameter was significantly reduced but venular diameter remained unchanged. A similar mechanical reduction in blood flow did not induce Leukocyte recruitment. Thus this study demonstrates that ET-1 can directly cause significant Leukocyte Rolling and adhesion adding to its potential pathophysiological role in the development of disease states of the cardiovascular system.
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hydrogen peroxide induces Leukocyte Rolling modulation by endogenous antioxidant mechanisms including no
American Journal of Physiology-heart and Circulatory Physiology, 1996Co-Authors: Brent Johnston, Samina Kanwar, Paul KubesAbstract:In this study, intravital microscopy was used to examine the mechanisms that regulate H2O2-induced Leukocyte Rolling within rat mesenteric venules in vivo. H2O2 elicited Leukocyte Rolling within a narrow response window between 10 and 500 microM H2O2. Continuous superfusion with 100 microM H2O2 induced a large but transient increase in the flux of Rolling Leukocytes, whereas a short 5-min pulse elicited a sustained increase in Rolling flux. Both treatments caused increases in Leukocyte adhesion. H2O2-induced increases in Leukocyte flux and adhesion could be prevented with an anti-P-selectin antibody. Inhibition of endogenous catalase (aminotriazole), glutathione (diethyl maleate), or nitric oxide (NG-nitro-L-arginine methyl ester) shifted the effective concentration of H2O2; continuous superfusion with 10 microM H2O2 now elicited large and sustained increases in Leukocyte Rolling flux, whereas 100 microM H2O2 elicited less than optimal responses. Dual antioxidant inhibition further reduced the effective H2O2 concentration to 1 microM H2O2. A nitric oxide donor prevented the increased Rolling flux induced by 100 microM H2O2. These findings suggest that endogenous antioxidants are important regulators of H2O2-induced, P-selectin-dependent Leukocyte Rolling in vivo.
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The alpha 4-integrin supports Leukocyte Rolling and adhesion in chronically inflamed postcapillary venules in vivo.
Journal of Experimental Medicine, 1996Co-Authors: Brent Johnston, Thomas B. Issekutz, Paul KubesAbstract:A role for the alpha 4-integrin (alpha 4 beta 1 or alpha 4 beta 7), has been implicated in the recruitment of peripheral blood mononuclear cells (PBMCs) to sites of inflammation. However, the adhesive interactions (i.e., tethering, Rolling, and adhesion) mediated by the alpha 4-integrin have not been characterized in vivo. The objective of this study was to establish a model wherein postcapillary venules were chronically inflamed, and then use intravital microscopy to identify the adhesive interactions mediated by the alpha 4-integrin in vivo. Between 4 and 20 d after immunization with Mycobacterium butyricum, animals developed a systemic vasculitis characterized by large increases in the numbers of Rolling and adhering Leukocytes within mesenteric venules. The selectins could only account for approximately 50% of the Leukocyte Rolling whereas the remaining cells rolled exclusively via the alpha 4-integrin. Anti-alpha 4 therapy also eliminated the increase in Leukocyte adhesion observed in this model, whereas selectin therapies and an anti-CD18 (beta 2-integrin) monoclonal antibody (mAb) did not reduce adhesion. A serum against polymorphonuclear Leukocytes (PMNs) was used to confirm that a significant proportion of Rolling cells, and most of the adhering cells were PBMCs. Sequential treatment with anti-PMN serum and the anti-alpha 4 mAb demonstrated that alpha 4-dependent Rolling was distinct from PMN Rolling populations. Initial Leukocyte tethering via the alpha 4-integrin could not be demonstrated in this model, whereas L-selectin did support Leukocyte tethering. These data suggest that the alpha 4-integrin can mediate both Rolling and adhesion in the multistep recruitment of PMBCs in vivo, and these interactions occur independently of the selectins and beta 2-integrins.
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leukotriene c4 d4 induces p selectin and sialyl lewisx dependent alterations in Leukocyte kinetics in vivo
Circulation Research, 1995Co-Authors: Samina Kanwar, Brent Johnston, Paul KubesAbstract:The objective of this study was to assess the effect of leukotriene C4 (LTC4) on the flux of Rolling Leukocytes, Leukocyte Rolling velocity, and Leukocyte adhesion in postcapillary venules in vivo and to study the underlying molecular mechanisms involved. LTC4 (20 nmol/L) induced a rapid and significant increase in Leukocyte Rolling flux that was inhibitable by an anti-P-selectin antibody and soluble sialyl Lewis(x) (sLe(x)). LTC4 also induced a significant reduction in Leukocyte Rolling velocity, an event that was independent of P-selectin but entirely dependent on sLe(x). This LTC4-induced reduction in Leukocyte Rolling velocity was independent of any hemodynamic alterations. Another P-selectin effector, histamine, did not affect Leukocyte Rolling velocity even at > 5000 times the concentration of LTC4. Treatment with an anti-L-selectin antibody had no effect on the LTC4-induced increase in Leukocyte Rolling or reduction in Rolling velocity. Inhibition of LTC4 bioconversion to LTD4 by pretreatment with L-serine (100 mumol/L) prevented the LTC4-induced increase in Leukocyte Rolling flux and the LTC4-induced reduction in Leukocyte Rolling velocity. A subtle, yet significant, increase in Leukocyte adhesion was also observed with LTC4. Pretreatment with a platelet-activating factor receptor antagonist returned the LTC4-induced Leukocyte Rolling velocity to baseline levels. The addition of a very low concentration of platelet-activating factor (1 nmol/L) induced significant Leukocyte adhesion in the presence of LTC4 but not histamine.(ABSTRACT TRUNCATED AT 250 WORDS)
Henrik Thorlacius - One of the best experts on this subject based on the ideXlab platform.
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platelets regulate p selectin expression and Leukocyte Rolling in inflamed venules of the pancreas
European Journal of Pharmacology, 2012Co-Authors: Aree Abdulla, Darbaz Awla, Hannes Hartman, Hakan Weiber, Bengt Jeppsson, Sara Regner, Henrik ThorlaciusAbstract:Recent data suggest that platelets regulate inflammatory changes and tissue damage in acute pancreatitis although the role of platelets in Leukocyte-endothelium interactions in the pancreatic microcirculation is not known. The aim of this study was to define the impact of platelets on Leukocyte Rolling and adhesion in acute pancreatitis. Acute pancreatitis was induced in C57BL/6 mice by caerulein challenge. Mice were treated with an a anti-GP1b alpha (CD42b) antibody, which depletes platelets, or a control antibody before caerulein. Leukocyte Rolling and adhesion were determined by the use of intravital fluorescence microscopy 18 h after the last dose of caerulein. In separate experiments, Leukocyte-endothelium interactions were determined before and after administration of an anti-P-selectin, anti-PSGL-1 and a control antibody in mice with caerulein pancreatitis. Circulating platelet-neutrophil aggregates and pancreatic P-selectin mRNA were quantified 1 and 6 h respectively after caerulein challenge. Caerulein administration increased Leukocyte and platelet interactions in the pancreatic microvasculature, increased tissue damage and expression of P-selectin mRNA in the pancreas as well as platelet-neutrophil complexes in the circulation. Notably, platelet depletion markedly reduced caerulein-provoked Leukocyte Rolling and adhesion in postcapillary venules. Interestingly, depletion of platelets significantly decreased caerulein-induced gene expression of P-selectin in the pancreas. Moreover, immunoneutralization of P-selectin and PSGL-1 abolished Leukocyte Rolling in the pancreatic venules triggered by caerulein. Our novel findings demonstrate that platelets regulate Leukocyte Rolling in acute pancreatitis via induction of P-selectin, which was critical in supporting Leukocyte Rolling in inflamed venules of the pancreas. (C) 2012 Elsevier B.V. All rights reserved. (Less)
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Leukocyte Rolling is exclusively mediated by p selectinin colonic venules
British Journal of Pharmacology, 2002Co-Authors: M X Wan, Amjid Ali Riaz, Rene Schramm, Yusheng Wang, Dietmar Vestweber, Michael D Menger, Henrik ThorlaciusAbstract:1. The objective of the present study was to examine the role of the endothelial selectins (i.e. P- and E-selectin) in Leukocyte-endothelium interactions in colonic venules by use of intravital microscopy. 2. Balb/c mice were exposed to dextran sodium sulphate (DSS) in the drinking water for 5 days or treated intraperitoneally (i.p.) with tumour necrosis factor-alpha (TNF-alpha) for 3 h. 3. In DSS-treated mice, mRNA of both P- and E-selectin were expressed and Leukocyte Rolling and adhesion was increased to 27+/-3 cells min(-1) and 36+/-8 cells mm(-1), respectively. An anti-P-selectin antibody abolished DSS-induced Leukocyte Rolling, whereas an antibody against E-selectin had no effect. Established Leukocyte adhesion was insensitive to inhibition of the selectins. 4. DSS markedly increased production of TNF-alpha in the colon. TNF-alpha increased Leukocyte Rolling to 22+/-3 cells min(-1) and adhesion to 45+/-4 cells mm(-1). Only inhibition of P-selectin significantly reduced (>94%) Leukocyte Rolling provoked by TNF-alpha. Leukocyte adhesion was not changed by late anti-P-selectin antibody treatment. In contrast, pretreatment with the anti-P-selectin antibody not only abolished Leukocyte Rolling but also completely inhibited firm adhesion in response to TNF-alpha. 5. This study demonstrates that P-selectin plays an important role in Leukocyte Rolling in colonic venules, both in experimental colitis and when stimulated with TNF-alpha. Moreover, P-selectin-dependent Leukocyte Rolling was found to be a precondition for TNF-alpha-induced firm adhesion. Thus, these findings suggest that P-selectin may be a key target to reduce pathological recruitment of inflammatory cells in the colon.
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Leukocyte recruitment in hepatic injury selectin mediated Leukocyte Rolling is a prerequisite for cd18 dependent firm adhesion
Journal of Hepatology, 2002Co-Authors: Daniel Klintman, Rene Schramm, Michael D Menger, Henrik ThorlaciusAbstract:Abstract Background/Aims : This study was designed to examine the role of selectins and CD18 in Leukocyte recruitment in hepatic injury induced by tumor necrosis factor- α (TNF- α ) and galactosamine (Gal) in vivo. Methods : Intravital fluorescence microscopy of the hepatic microcirculation was used to quantify Leukocyte–endothelium interactions provoked by 24 h of systemic TNF- α /Gal challenge in rats. Hepatic injury was evaluated with liver enzymes. Results : When administered after 24 h of TNF- α /Gal challenge, fucoidan, a selectin-function inhibitor, reduced Leukocyte Rolling by 69%, whereas firm adhesion was unaltered. In contrast, passive immunization against CD18 decreased Leukocyte adhesion by 60%, whereas Rolling remained unchanged. Notably, when administered prior to TNF- α /Gal, fucoidan attenuated both Leukocyte Rolling and adhesion, by 57 and 69%, respectively. Pretreatment with an anti-CD18 antibody decreased TNF- α /Gal-induced Rolling and firm adhesion by 25 and 90%, respectively. Moreover, pretreatment with fucoidan and the anti-CD18 antibody both protected against TNF- α /Gal-induced increases in liver enzymes. For example, the pretreatments reduced alanine aminotransferase by 59 and 87%, respectively. Conclusions : Our data suggest that TNF- α /Gal-induced Leukocyte Rolling is selectin-mediated and a precondition for CD18-dependent firm adhesion in hepatic venules. Thus, reducing Leukocyte recruitment by inhibition of selectins or CD18 may be useful to control TNF- α -induced liver injury.
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inhibition of selectin function and Leukocyte Rolling protects against dextran sodium sulfate induced murine colitis
Scandinavian Journal of Gastroenterology, 2001Co-Authors: Xiao Wei Zhang, Qing Liu, Henrik ThorlaciusAbstract:Background: The selectin family of adhesion molecules (P-, E- and L-selectin) plays an important role in inflammatory reactions by mediating interactions between Leukocytes and activated endothelial cells. However, a recent study using gene-targeted mice has suggested that adhesion molecules (P- and E-selectin and ICAM-1) may not be relevant targets in intestinal inflammation. The objective of the present study was to re-evaluate the potential role of selectins in experimental colitis in wild-type mice using the polysaccharide fucoidan, which inhibits the function of P- and L-selectin. Methods: For this purpose, Balb/c mice were exposed to 5% dextran sodium sulfate (DSS) in the drinking water for 5 days with and without daily administration of fucoidan (25 mg/kg, i.v.). In separate experiments, the effect of fucoidan on Leukocyte-endothelium interactions was examined by use of intravital microscopy. Results: It was found that pretreatment with fucoidan (25 mg/kg/day) reduced mucosal damage and crypt destruction in the colon of DSS-treated mice. Moreover, this fucoidan treatment markedly reduced the colonic MPO activity in mice exposed to DSS. In vivo microscopy revealed that the dose of fucoidan used in the present study abolished TNF-alpha -induced venular Leukocyte Rolling and extravascular recruitment. Conclusions: These results suggest that selectins mediate Leukocyte infiltration and tissue damage in experimental colitis. Moreover, our data support: the concept that functional interference with adhesion molecules of the selectin family may have a beneficial effect in the treatment of inflammatory bowel disease. (Less)
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characteristics of histamine induced Leukocyte Rolling in the undisturbed microcirculation of the rat mesentery
British Journal of Pharmacology, 1998Co-Authors: Kohji Yamaki, Lennart Lindbom, Per Hedqvist, Henrik Thorlacius, Johan RaudAbstract:The main objective of this study was to analyse the role and mode of action of the mast cell mediator histamine in Leukocyte-endothelium interactions in small venules in vivo. For this purpose, we used a histological approach (combined with intravital microscopy) that allows studies of rapid mediator-induced venular Leukocyte accumulation, reflecting Leukocyte Rolling, in the undisturbed microcirculation of the rat mesentery where Rolling is normally absent. We first examined the relative importance of histamine and 5-hydroxytryptamine (5-HT) in acute mast cell-dependent Leukocyte recruitment. The mast cell secretagogue compound 48/80 (i.p. for 15 min) induced a marked venular accumulation of polymorphonuclear Leukocytes (PMNL) which was almost abolished by combined histamine1 (H1)- and histamine2 (H2)-receptor blockade. In contrast, the 5-HT-receptor antagonist methysergide was inactive in this regard. Moreover, exogenous 5-HT was less active than exogenous histamine in evoking venular PMNL accumulation (histamine response dose-dependent; 5-HT response bell shaped). Prostaglandin D2 did not cause PMNL accumulation. The venular PMNL response to exogenous histamine peaked between 15 min and 1 h, was still significantly elevated at 2 h, and then returned to prechallenge values after 3 h. At all time points, the histamine-induced PMNL accumulation was nearly abolished by i.v. treatment with the polysaccharide fucoidin (which blocks Rolling but not firm adhesion per se), suggesting that the PMNL response to histamine was due to Rolling rather than firm adhesion over the entire 3 h period. At no time point did histamine trigger accumulation of mononuclear Leukocytes (MNL). To examine the role of histamine-receptors in the histamine-induced PMNL accumulation (i.e. Rolling), the animals were pretreated with diphenhydramine (H1-receptor antagonist), cimetidine, or ranitidine (H2-receptor antagonists). Diphenhydramine alone inhibited the venular PMNL response to histamine by 52%, while both H2-receptor antagonists were completely inactive. However, the combination of cimetidine and diphenhydramine reduced the histamine-induced PMNL Rolling by 82%. Furthermore, in contrast to an H3-receptor agonist, challenge with either the H1-receptor agonist 2-thiazolylethylamine or two different H2-receptor agonists (impromidine, dimaprit) was sufficient to provoke significant venular PMNL accumulation. Treatment with the nitric oxide-synthase inhibitor L-NAME did not affect the histamine-induced PMNL Rolling. On the other hand, 3 h pretreatment with dexamethasone reduced the PMNL response to histamine by 73%, and flow cytometric analysis showed that the dexamethasone treatment almost completely inhibited binding of soluble P-selectin to rat isolated PMNLs. We conclude that initial Leukocyte recruitment after mast cell activation in the rat mesentery is critically dependent on histamine release. The cellular response to histamine was specifically due to PMNL Rolling, involved activation of both H1- and H2-receptors, and lasted for 2–3 h. Moreover, the histamine-induced PMNL Rolling was not dependent on nitric oxide synthesis, but was sensitive to glucocorticoid treatment, possibly via inhibition of expression or function of leukocytic P-selectin ligand(s). British Journal of Pharmacology (1998) 123, 390–399; doi:10.1038/sj.bjp.0701614
Jonathan Tang - One of the best experts on this subject based on the ideXlab platform.
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identifying the rules of engagement enabling Leukocyte Rolling activation and adhesion
PLOS Computational Biology, 2010Co-Authors: Jonathan Tang, Anthony C HuntAbstract:The LFA-1 integrin plays a pivotal role in sustained Leukocyte adhesion to the endothelial surface, which is a precondition for Leukocyte recruitment into inflammation sites. Strong correlative evidence implicates LFA-1 clustering as being essential for sustained adhesion, and it may also facilitate rebinding events with its ligand ICAM-1. We cannot challenge those hypotheses directly because it is infeasible to measure either process during Leukocyte adhesion following Rolling. The alternative approach undertaken was to challenge the hypothesized mechanisms by experimenting on validated, working counterparts: simulations in which diffusible, LFA1 objects on the surfaces of quasi-autonomous Leukocytes interact with simulated, diffusible, ICAM1 objects on endothelial surfaces during simulated adhesion following Rolling. We used object-oriented, agent-based methods to build and execute multi-level, multi-attribute analogues of Leukocytes and endothelial surfaces. Validation was achieved across different experimental conditions, in vitro, ex vivo, and in vivo, at both the individual cell and population levels. Because those mechanisms exhibit all of the characteristics of biological mechanisms, they can stand as a concrete, working theory about detailed events occurring at the Leukocyte–surface interface during Leukocyte Rolling and adhesion experiments. We challenged mechanistic hypotheses by conducting experiments in which the consequences of multiple mechanistic events were tracked. We quantified rebinding events between individual components under different conditions, and the role of LFA1 clustering in sustaining Leukocyte–surface adhesion and in improving adhesion efficiency. Early during simulations ICAM1 rebinding (to LFA1) but not LFA1 rebinding (to ICAM1) was enhanced by clustering. Later, clustering caused both types of rebinding events to increase. We discovered that clustering was not necessary to achieve adhesion as long as LFA1 and ICAM1 object densities were above a critical level. Importantly, at low densities LFA1 clustering enabled improved efficiency: adhesion exhibited measurable, cell level positive cooperativity.
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in silico white blood cell a synthetic model of Leukocyte Rolling activation and adhesion during inflammation
Computer Applications in Industry and Engineering, 2009Co-Authors: Jonathan Tang, Anthony C HuntAbstract:We have constructed a synthetic in silico model for representing the dynamics of Leukocyte Rolling, activation, and adhesion on substrate-coated flow chambers. Software components were designed, instantiated, verified, plugged together, and then operated in ways that can map concretely to mechanisms believed responsible for Leukocyte Rolling, activation, and adhesion. Here, we show our model’s ability to represent data from in vitro flow chamber studies of Leukocyte Rolling, activation, and adhesion on P-Selectin, ICAM-1 and CXCL1 substratecoated surfaces.
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dynamics of in silico Leukocyte Rolling activation and adhesion
BMC Systems Biology, 2007Co-Authors: Jonathan Tang, Klaus Ley, Anthony C HuntAbstract:Background We present a multilevel, agent based, in silico model that represents the dynamics of Rolling, activation, and adhesion of individual Leukocytes in vitro. Object-oriented software components were designed, verified, plugged together, and then operated in ways that represent the molecular and cellular mechanisms believed responsible for Leukocyte Rolling and adhesion. The result is an in silico analogue of an experimental in vitro system. The experimentally measured, phenotypic attributes of the analogue were compared and contrasted to those of Leukocytes in vitro from three different experimental conditions.
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dynamics of in silico Leukocyte Rolling activation and adhesion
BMC Systems Biology, 2007Co-Authors: Jonathan Tang, Klaus Ley, Anthony C HuntAbstract:We present a multilevel, agent based, in silico model that represents the dynamics of Rolling, activation, and adhesion of individual Leukocytes in vitro. Object-oriented software components were designed, verified, plugged together, and then operated in ways that represent the molecular and cellular mechanisms believed responsible for Leukocyte Rolling and adhesion. The result is an in silico analogue of an experimental in vitro system. The experimentally measured, phenotypic attributes of the analogue were compared and contrasted to those of Leukocytes in vitro from three different experimental conditions. The individual in silico dynamics of "Rolling" on simulated P-selectin, and separately on simulated VCAM-1, were an acceptable match to individual in vitro distance-time and velocity-time measurements. The analogues are also able to represent the transition from Rolling to adhesion on P-selectin and VCAM-1 in the presence of GRO-α chemokine. The individual in silico and in vitro behavioral similarities translated successfully to population level measures. These behavioral similarities were enabled in part by subdividing the functionality of the analogue's surface into 600 independent, "cell"-controlled, equally capable modules of comparable functionality. The overlap in phenotypic attributes of our analogue with those of Leukocytes in vitro confirm the considerable potential of our model for studying the key events that determine the behavioral outcome of individual Leukocytes during Rolling, activation, and adhesion. Our results provide an important foundation and framework for future in silico research into plausible causal links between well-documented, subcellular molecular level events and the variety of systemic phenotypic attributes that distinguish normal Leukocyte adhesion from abnormal disease-associated adhesion.