The complexities of leukocyte recruitment

STIM1/2 maintain signaling competence at ER-PM contact sites during neutrophil spreading

Neutrophils are highly motile leukocytes that migrate inside tissues to destroy invading pathogens. Ca2+ signals coordinate leukocytes migration, but whether Ca2+ fluxes mediated by Stim proteins at ER-PM contact sites regulate neutrophil actin-based motility is unclear. Here, we show that myeloid-specific Stim1/2 ablation decreases basal cytosolic Ca2+ levels and prevents adhesion-induced Ca2+ elevations in mouse neutrophils, reducing actin fiber formation and impairing spreading. Unexpectedly, more ER-PM contact sites were detected on the actin-poor adhesive membranes of Stim1/2-deficient neutrophils, which had reduced inositol-1,4,5-trisphosphate receptor (IP3R) immunoreactivity on confocal and immunogold micrographs despite preserved IP3R levels on western blots. Remarkably, Stim1/2-deficient neutrophils regained signaling and spreading competence in Ca2+-rich solutions and were recruited more effectively in mouse inflamed cremaster muscles in vivo. Our findings indicate that Stim1/2 preserve IP3R functionality in neutrophils, generating adhesion-dependent Ca2+ signals that control actin dynamics during neutrophil spreading. Stim proteins thus maintain IP3R signaling competence at adhesive membranes, enabling Ca2+-dependent actin remodeling during spreading in mouse neutrophils.

Shedding light on the molecular and regulatory mechanisms of TLR4 signaling in endothelial cells under physiological and inflamed conditions

Toll-like receptor 4 (TLR4) are part of the innate immune system. They are capable of recognizing pathogen-associated molecular patterns (PAMPS) of microbes, and damage-associated molecular patterns (DAMPs) of damaged tissues. Activation of TLR4 initiates downstream signaling pathways that trigger the secretion of cytokines, type I interferons, and other pro-inflammatory mediators that are necessary for an immediate immune response. However, the systemic release of pro-inflammatory proteins is a powerful driver of acute and chronic inflammatory responses. Over the past decades, immense progress has been made in clarifying the molecular and regulatory mechanisms of TLR4 signaling in inflammation. However, the most common strategies used to study TLR4 signaling rely on genetic manipulation of the TLR4 or the treatment with agonists such as lipopolysaccharide (LPS) derived from the outer membrane of Gram-negative bacteria, which are often associated with the generation of irreversible phenotypes in the target cells or unintended cytotoxicity and signaling crosstalk due to off-target or pleiotropic effects. Here, optogenetics offers an alternative strategy to control and monitor cellular signaling in an unprecedented spatiotemporally precise, dose-dependent, and non-invasive manner. This review provides an overview of the structure, function and signaling pathways of the TLR4 and its fundamental role in endothelial cells under physiological and inflammatory conditions, as well as the advances in TLR4 modulation strategies.

Immunological insights of selectins in human disease mechanism

Selectin enzymes are glycoproteins and are an important adhesion molecule in the mammalian immune system, especially in the inflammatory response and the healing process of tissues. Selectins play an important role in a variety of biological processes, including the rolling of leukocytes in endothelial cells, a process known as the adhesion cascade. It has recently been discovered and reported that the selectin mechanism plays a role in cancer and thrombosis disease. This process begins with non-covalent interactions-based selectin-ligand binding and the glycans play a role as a connector between cancer cells and the endothelium in this process. The selectin mechanism is critical for the immune system, but it is also involved in disease mechanisms, earning the selectins the nickname "Selectins-The Two Dr. Jekyll and Mr. Hyde Faces". As a result, the drug for selectins should have a multifaceted role and be a dynamic molecule that targets the disease mechanism specifically. This chapter explores the role of selectins in the disease mechanism at the mechanism level that provides the impact for identifying the selectin inhibitors. Overall, this chapter provides the molecular level insights on selectins, their ligands, involvement in normal and disease mechanisms.

Self-assisted wound healing using piezoelectric and triboelectric nanogenerators

The complex process of wound healing depends on the coordinated interaction between various immunological and biological systems, which can be aided by technology. This present review provides a broad overview of the medical applications of piezoelectric and triboelectric nanogenerators, focusing on their role in the development of wound healing technology. Based on the finding that the damaged epithelial layer of the wound generates an endogenous bioelectric field to regulate the wound healing process, development of technological device for providing an exogenous electric field has therefore been paid attention. Authors of this review focus on the design and application of piezoelectric and triboelectric materials to manufacture self-powered nanogenerators, and conclude with an outlook on the current challenges and future potential in meeting medical needs and commercialization.

Endothelin receptor antagonist improves donor lung function in an ex vivo perfusion system

BACKGROUND

A lung transplant is the last resort treatment for many patients with advanced lung disease. The majority of donated lungs come from donors following brain death (BD). The endothelin axis is upregulated in the blood and lung of the donor after BD resulting in systemic inflammation, lung damage and poor lung graft outcomes in the recipient. Tezosentan (endothelin receptor blocker) improves the pulmonary haemodynamic profile; however, it induces adverse effects on other organs at high doses. Application of ex vivo lung perfusion (EVLP) allows the development of organ-specific hormone resuscitation, to maximise and optimise the donor pool. Therefore, we investigate whether the combination of EVLP and tezosentan administration could improve the quality of donor lungs in a clinically relevant 6-h ovine model of brain stem death (BSD).

METHODS

After 6 h of BSD, lungs obtained from 12 sheep were divided into two groups, control and tezosentan-treated group, and cannulated for EVLP. The lungs were monitored for 6 h and lung perfusate and tissue samples were processed and analysed. Blood gas variables were measured in perfusate samples as well as total proteins and pro-inflammatory biomarkers, IL-6 and IL-8. Lung tissues were collected at the end of EVLP experiments for histology analysis and wet-dry weight ratio (a measure of oedema).

RESULTS

Our results showed a significant improvement in gas exchange [elevated partial pressure of oxygen (P = 0.02) and reduced partial pressure of carbon dioxide (P = 0.03)] in tezosentan-treated lungs compared to controls. However, the lungs hematoxylin-eosin staining histology results showed minimum lung injuries and there was no difference between both control and tezosentan-treated lungs. Similarly, IL-6 and IL-8 levels in lung perfusate showed no difference between control and tezosentan-treated lungs throughout the EVLP. Histological and tissue analysis showed a non-significant reduction in wet/dry weight ratio in tezosentan-treated lung tissues (P = 0.09) when compared to control.

CONCLUSIONS

These data indicate that administration of tezosentan could improve pulmonary gas exchange during EVLP.

Hematological and immune changes in Piaractus mesopotamicus in the sepsis induced by Aeromonas hydrophila

The pathogenesis of sepsis involves complex systems and multiple interrelationships between the host and pathogen producing high mortality rates in various animal species. In this study, hematological disturbances, innate immunity and survival during the septic process in Piaractus mesopotamicus inoculated with Aeromonas hydrophila were studied. For this aim, fish blood samples were taken from control and infected groups 1, 3, 6, and 9 h post-inoculation (HPI). Leukogram showed reduction in the number of leukocytes and thrombocytes, followed by cessation of leukocyte chemotaxis 6 HPI and severe morphological changes in leukocytes and erythrocytes. At 3 HPI production of reactive oxygen species increased and at 6 HPI decreased. There was no change in serum lysozyme concentration and lytic activity of the complement system, despite the progressive increase in serum lytic activity and bacterial agglutination. Finally, the changes in clinical signs due to aeromonosis and increasing septicemia resulted in a reduction in survival to 57.14% after 36 HPI. It was possible concluded that these hematological and immune are crucial event in the worsening of sepsis in P. mesopotamicus, and these findings are utility for diagnosing and understanding the pathophysiology sepsis in pacu induced by A. hydrophila.

Extremely low frequency electromagnetic fields stimulation modulates autoimmunity and immune responses: a possible immuno-modulatory therapeutic effect in neurodegenerative diseases

Increasing evidence shows that extremely low frequency electromagnetic fields (ELF-EMFs) stimulation is able to exert a certain action on autoimmunity and immune cells. In the past, the efficacy of pulsed ELF-EMFs in alleviating the symptoms and the progression of multiple sclerosis has been supported through their action on neurotransmission and on the autoimmune mechanisms responsible for demyelination. Regarding the immune system, ELF-EMF exposure contributes to a general activation of macrophages, resulting in changes of autoimmunity and several immunological reactions, such as increased reactive oxygen species-formation, enhanced phagocytic activity and increased production of chemokines. Transcranial electromagnetic brain stimulation is a non-invasive novel technique used recently to treat different neurodegenerative disorders, in particular Alzheimer's disease. Despite its proven value, the mechanisms through which EMF brain-stimulation exerts its beneficial action on neuronal function remains unclear. Recent studies have shown that its beneficial effects may be due to a neuroprotective effect on oxidative cell damage. On the basis of in vitro and clinical studies on brain activity, modulation by ELF-EMFs could possibly counteract the aberrant pro-inflammatory responses present in neurodegenerative disorders reducing their severity and their onset. The objective of this review is to provide a systematic overview of the published literature on EMFs and outline the most promising effects of ELF-EMFs in developing treatments of neurodegenerative disorders. In this regard, we review data supporting the role of ELF-EMF in generating immune-modulatory responses, neuromodulation, and potential neuroprotective benefits. Nonetheless, we reckon that the underlying mechanisms of interaction between EMF and the immune system are still to be completely understood and need further studies at a molecular level.

Clinical translation of an ultrasmall inorganic optical-PET imaging nanoparticle probe

A first-in-human clinical trial of ultrasmall inorganic hybrid nanoparticles, "C dots" (Cornell dots), in patients with metastatic melanoma is described for the imaging of cancer. These renally excreted silica particles were labeled with (124)I for positron emission tomography (PET) imaging and modified with cRGDY peptides for molecular targeting. (124)I-cRGDY-PEG-C dot particles are inherently fluorescent, containing the dye, Cy5, so they may be used as hybrid PET-optical imaging agents for lesion detection, cancer staging, and treatment management in humans. However, the clinical translation of nanoparticle probes, including quantum dots, has not kept pace with the accelerated growth in minimally invasive surgical tools that rely on optical imaging agents. The safety, pharmacokinetics, clearance properties, and radiation dosimetry of (124)I-cRGDY-PEG-C dots were assessed by serial PET and computerized tomography after intravenous administration in patients. Metabolic profiles and laboratory tests of blood and urine specimens, obtained before and after particle injection, were monitored over a 2-week interval. Findings are consistent with a well-tolerated inorganic particle tracer exhibiting in vivo stability and distinct, reproducible pharmacokinetic signatures defined by renal excretion. No toxic or adverse events attributable to the particles were observed. Coupled with preferential uptake and localization of the probe at sites of disease, these first-in-human results suggest safe use of these particles in human cancer diagnostics.

First report of interruption of mast cell degranulation and endothelial cells activation by anti-inflammatory drugs controlling the acute response provoked by Pseudoplatystoma fasciatum fish venom

This is the first report describing in mice the envenoming that possible to occur in humans provoked by Pseudoplatystomafasciatum and evaluated the different class of mediators involved in the inflammatory injury, identifying important targets for drugs intervention. First we demonstrate that P. fasciatum venom induces an acute inflammatory response characterized by the recruitment of immune cells into peripheral tissues choreographed by chemoattractants including lipid mediators (LTB4 and PGE2), cytokines (IL-1β and TNF-α), and chemokines (KC and MCP-1). Intravital microscopy studies showed that only high dose (60 μg) of venom promoted hemodynamic changes inducing an abundant number of thrombi of varying sizes in venules leading to transient venular stasis with reduced blood flow. We found that serotonin, leukotrine and prostaglandin are involved in edematogenic and nociceptive responses, since a selective COX-2 inhibitor, a non-specific inhibitor for cytokines and COX-2, and a non-selective 5-HT receptor antagonist were able to reduce both symptoms. In conclusion, our data show that the main symptoms of acute inflammation as pain provoked by P. fasciatum fish venom could be well managed by available drugs as COX-2 inhibitors as well dexamethasone or non-selective 5-HT receptor antagonists.

Resolution of inflammation: mechanisms and opportunity for drug development

Inflammation is a beneficial host reaction to tissue damage and has the essential primary purpose of restoring tissue homeostasis. Inflammation plays a major role in containing and resolving infection and may also occur under sterile conditions. The cardinal signs of inflammation dolor, calor, tumor and rubor are intrinsically associated with events including vasodilatation, edema and leukocyte trafficking into the site of inflammation. If uncontrolled or unresolved, inflammation itself can lead to further tissue damage and give rise to chronic inflammatory diseases and autoimmunity with eventual loss of organ function. It is now evident that the resolution of inflammation is an active continuous process that occurs during an acute inflammatory episode. Successful resolution requires activation of endogenous programs with switch from production of pro-inflammatory towards pro-resolving molecules, such as specific lipid mediators and annexin A1, and the non-phlogistic elimination of granulocytes by apoptosis with subsequent removal by surrounding macrophages. These processes ensure rapid restoration of tissue homeostasis. Here, we review recent advances in the understanding of resolution of inflammation, highlighting the pharmacological strategies that may interfere with the molecular pathways which control leukocyte survival and clearance. Such strategies have proved beneficial in several pre-clinical models of inflammatory diseases, suggesting that pharmacological modulation of the resolution process may be useful for the treatment of chronic inflammatory diseases in humans.

Microfluidic device for studying cell migration in single or co-existing chemical gradients and electric fields

Cell migration is involved in physiological processes such as wound healing, host defense, and cancer metastasis. The movement of various cell types can be directed by chemical gradients (i.e., chemotaxis). In addition to chemotaxis, many cell types can respond to direct current electric fields (dcEF) by migrating to either the cathode or the anode of the field (i.e., electrotaxis). In tissues, physiological chemical gradients and dcEF can potentially co-exist and the two guiding mechanisms may direct cell migration in a coordinated manner. Recently, microfluidic devices that can precisely configure chemical gradients or dcEF have been increasingly developed and used for chemotaxis and electrotaxis studies. However, a microfluidic device that can configure controlled co-existing chemical gradients and dcEF that would allow quantitative cell migration analysis in complex electrochemical guiding environments is not available. In this study, we developed a polydimethylsiloxane-based microfluidic device that can generate better controlled single or co-existing chemical gradients and dcEF. Using this device, we showed chemotactic migration of T cells toward a chemokine CCL19 gradient or electrotactic migration toward the cathode of an applied dcEF. Furthermore, T cells migrated more strongly toward the cathode of a dcEF in the presence of a competing CCL19 gradient, suggesting the higher electrotactic attraction. Taken together, the developed microfluidic device offers a new experimental tool for studying chemical and electrical guidance for cell migration, and our current results with T cells provide interesting new insights of immune cell migration in complex guiding environments.

Impaired function of Fanconi anemia type C-deficient macrophages

FA is a genetic disorder characterized by BM failure, developmental defects, and cancer predisposition. Previous studies suggest that FA patients exhibit alterations in immunologic function. However, it is unclear whether the defects are immune cell-autonomous or secondary to leukopenia from evolving BM failure. Given the central role that macrophages have in the innate immune response, inflammation resolution, and antigen presentation for acquired immunity, we examined whether macrophages from Fancc-/- mice exhibit impaired function. Peritoneal inflammation induced by LPS or sodium periodate resulted in reduced monocyte/macrophage recruitment in Fancc-/- mice compared with WT controls. Fancc-/- mice also had decreased inflammatory monocytes mobilized into the peripheral blood after LPS treatment compared with controls. Furthermore, Fancc-/- peritoneal macrophages displayed cell-autonomous defects in function, including impaired adhesion to FN or endothelial cells, reduced chemoattractant-mediated migration, and decreased phagocytosis. Moreover, dysregulated F-actin rearrangement was detected in Fancc-/- macrophages after adhesion to FN, which was consistent with an observed reduction in RhoA-GTP levels. Importantly, these data suggest that impaired cytoskeletal rearrangements in Fancc-/- macrophages may be the common mechanism responsible for cell-autonomous defects detected in vitro, as well as altered monocyte/macrophage trafficking in vivo.

Acute respiratory distress syndrome and multiple organ failure

PURPOSE OF REVIEW

Despite improvements in outcome due to lung protective ventilation strategies using low tidal volumes, the mortality rate from acute respiratory distress syndrome (ARDS) remains unacceptably high, ranging from 34 to 64%. The predominant cause of death in ARDS is not severe hypoxemia, which is one of the defining criteria of ARDS, but multiple organ failure (MOF).

RECENT FINDINGS

In view of the relationship between ARDS and MOF, two different but complementary pathophysiological perspectives will be developed in this article: ARDS as a consequence of MOF, and ARDS as the cause of MOF. This framework may be useful in guiding the development of novel therapeutic strategies that ultimately improve the outcome of ARDS and sepsis patients.

SUMMARY

ARDS is a severe lung disease characterized by a very complex pathophysiology, involving not only the respiratory system but also nonpulmonary distal organs. Elucidation of the pathophysiological mechanisms bi-directionally linking MOF to ARDS appears to be a promising area of research that hopefully will lead to improved outcomes for these devastating conditions.

Kaposi's sarcoma-associated herpesvirus infection of endothelial cells inhibits neutrophil recruitment through an interleukin-6-dependent mechanism: a new paradigm for viral immune evasion

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of Kaposi's sarcoma (KS), an endothelial cell (EC) neoplasm characterized by dysregulated angiogenesis and inflammation. KSHV infection of EC causes production of proinflammatory mediators, regarded as possible initiators of the substantial mononuclear leukocyte recruitment seen in KS. Conversely, KSHV immune evasion strategies exist, such as degradation of EC leukocyte adhesion receptors by viral proteins. Here, we report the effects of KSHV infection of primary EC on recruitment of flowing leukocytes. Infection did not initiate adhesion of any leukocyte subset per se. However, on cytokine-stimulated EC, KSHV specifically inhibited neutrophil, but not PBL or monocyte, transmigration, an observation consistent with the inflammatory cell profile found in KS lesions in vivo. This inhibition could be recapitulated on uninfected EC using supernatant from infected cultures. These supernatants contained elevated levels of human interleukin 6 (hIL-6), and both the KSHV- and the supernatant-induced inhibitions of neutrophil transmigration were abrogated in the presence of a hIL-6 neutralizing antibody. Furthermore, preconditioning of EC with hIL-6 mimicked the effect of KSHV. Using RNA interference (RNAi), we show that upregulation of suppressor of cytokine signaling 3 (SOCS3) was necessary for this effect of hIL-6. These studies reveal a novel paracrine mode of KSHV immune evasion, resulting in reduced recruitment of neutrophils, a cell type whose antiviral and antitumor roles are becoming increasingly appreciated. Moreover, the findings have implications for our understanding of the contribution of hIL-6 to the pathogenesis of other inflammatory disorders and tumors in which this cytokine is abundant.

Activated T lymphocytes migrate toward the cathode of DC electric fields in microfluidic devices

Immune cell migration is a fundamental process that enables immunosurveillance and immune responses. Understanding the mechanism of immune cell migration is not only of importance to the biology of cells, but also has high relevance to cell trafficking mediated physiological processes and diseases such as embryogenesis, wound healing, autoimmune diseases and cancers. In addition to the well-known chemical concentration gradient based guiding mechanism (i.e. chemotaxis), recent studies have shown that lymphocytes can respond to applied physiologically relevant direct current (DC) electric fields by migrating toward the cathode of the fields (i.e. electrotaxis) in both in vitro and in vivo settings. In the present study, we employed two microfluidic devices allowing controlled application of electric fields inside the microfluidic channel for quantitative studies of lymphocyte electrotaxis in vitro at the single cell level. The first device is fabricated by soft-lithography and the second device is made in glass with integrated on-chip electrodes. Using both devices, we for the first time showed that anti-CD3/CD28 antibodies activated human blood T cells migrate to the cathode of the applied DC electric field. This finding is consistent with previous electrotaxis studies on other lymphocyte subsets suggesting electrotaxis is a novel guiding mechanism for immune cell migration. Furthermore, the characteristics of electrotaxis and chemotaxis of activated T cells in PDMS microfluidic devices are compared.

A third measure-metastable state in the dynamics of spontaneous shape change in healthy human's white cells

Human polymorphonuclear leucocytes, PMN, are highly motile cells with average 12-15 µm diameters and prominent, loboid nuclei. They are produced in the bone marrow, are essential for host defense, and are the most populous of white blood cell types. PMN also participate in acute and chronic inflammatory processes, in the regulation of the immune response, in angiogenesis, and interact with tumors. To accommodate these varied functions, their behavior is adaptive, but still definable in terms of a set of behavioral states. PMN morphodynamics have generally involved a non-equilibrium stationary, spheroid Idling state that transitions to an activated, ellipsoid translocating state in response to chemical signals. These two behavioral shape-states, spheroid and ellipsoid, are generally recognized as making up the vocabulary of a healthy PMN. A third, "random" state has occasionally been reported as associated with disease states. I have observed this third, Treadmilling state, in PMN from healthy subjects, the cells demonstrating metastable dynamical behaviors known to anticipate phase transitions in mathematical, physical, and biological systems. For this study, human PMN were microscopically imaged and analyzed as single living cells. I used a microscope with a novel high aperture, cardioid annular condenser with better than 100 nanometer resolution of simultaneous, mixed dark field and intrinsic fluorescent images to record shape changes in 189 living PMNs. Relative radial roundness, R(t), served as a computable order parameter. Comparison of R(t) series of 10 cells in the Idling and 10 in the Treadmilling state reveals the robustness of the "random" appearing Treadmilling state, and the emergence of behaviors observed in the neighborhood of global state transitions, including increased correlation length and variance (divergence), sudden jumps, mixed phases, bimodality, power spectral scaling and temporal slowing. Wavelet transformation of an R(t) series of an Idling to Treadmilling state change, demonstrated behaviors concomitant with the observed transition.

Microfluidic gradient platforms for controlling cellular behavior

Concentration gradients play an important role in controlling biological and pathological processes, such as metastasis, embryogenesis, axon guidance, and wound healing. Microfluidic devices fabricated by photo- and soft lithography techniques can manipulate the fluidic flow and diffusion profile to create biomolecular gradients in a temporal and spatial manner. Furthermore, microfluidic devices enable the control of cell-extracellular microenvironment interactions, including cell-cell, cell-matrix, and cell-soluble factor interaction. In this paper, we review the development of microfluidic-based gradient devices and highlight their biological applications.

Innate immunity of the liver microcirculation

The liver is a complex organ with a unique microcirculation and both synthetic and immune functions. Innate immune responses have been studied in response to single inflammatory mediators and several clinically relevant models of infection and injury. While standard histological techniques have been used in many models, the liver microcirculation is also amenable to in vivo examination using epifluorescent, confocal and transillumination intravital microscopy. These techniques have begun to clarify not only the molecular mechanisms but also the specific cell populations involved in the liver inflammation. In this review, we discuss the cells and mediators involved in hepatic innate immunity in simple and complex models of injury and infection, and present the view that the liver microcirculation utilizes non-classical pathways for leukocyte recruitment.

Microcirculatory effects of local and remote ischemic preconditioning in supraceliac aortic clamping

INTRODUCTION

Supraceliac aortic clamping in major vascular procedures promotes splanchnic ischemia and reperfusion (I/R) injury that may induce endothelial dysfunction, widespread inflammation, multiorgan dysfunction, and death. We tested the hypothesis that local or remote ischemic preconditioning (IPC) may be protective against injury after supraceliac aortic clamping through the modulation of mesenteric leukocyte-endothelial interactions, as evaluated with intravital microscopy and expression of adhesion molecules.

METHODS

Fifty-six male Wistar rats (weight, 190 to 250 g), were divided into four groups of 14 rats each: control-sham surgery without aortic occlusion; I/R through supraceliac aortic occlusion for 20 minutes, followed by 120 minutes of reperfusion; local IPC through supraceliac aortic occlusion for two cycles of 5 minutes of ischemia and 5 minutes of reperfusion, followed by the same protocol of the IR group; remote IPC through infrarenal aortic occlusion for two cycles of 10 minutes of ischemia and 10 minutes of reperfusion, followed by the same protocol of the IR group. Seven animals per group were used to evaluate in vivo leukocyte-endothelial interactions in postcapillary venules with intravital microscopy and another seven animals per group were used to collect mesentery samples for immunohistochemistry demonstration of adhesion molecules expression.

RESULTS

Supraceliac aortic occlusion increased the number of rolling leukocytes with slower velocities and increased the number of adherent leukocytes to the venular surface and leukocyte migration to the interstitium. The expression of P-selectin, E-selectin, and intercellular adhesion molecule-1 was also increased significantly after I/R. Local or remote IPC reduced the leukocyte recruitment in vivo and normalized the expression of adhesion molecules.

CONCLUSIONS

Local or remote IPC reduces endothelial dysfunction on mesenteric microcirculation caused by I/R injury after supraceliac aortic clamping.

A role for the endothelial glycosaminoglycan hyaluronan in neutrophil recruitment by endothelial cells cultured for prolonged periods

Glycosaminoglycans (GAGs) presented on the surface of endothelial cells (ECs) are believed to influence leukocyte recruitment during inflammation, but their roles remain uncertain. Here we report an in vitro model of prolonged culture of human EC in which the contributions of heparan sulphate (HS) and hyaluronan (HA) to the process of neutrophil recruitment could be studied. Previously, we reported that increasing EC culture duration (up to 20 days) enhanced neutrophil recruitment in response to low dose (1 U/ml) but not high dose (100 U/ml) of tumour necrosis factor-α (TNF). Here we found that HS and HA were present at much higher levels on the surface of day 20 cultures than day 3 cultures. Neutrophil recruitment on both day 3 and day 20 ECs was mediated through CXCR chemokine receptors and interleukin-8 (IL-8). In addition, mRNA levels for TNF receptors, signalling pathway constituents, adhesion receptors, and chemokines involved in neutrophil recruitment were similar for day 3 and day 20 ECs. To test whether the enhanced neutrophil recruitment on day 20 EC was mediated by GAGs, they were removed enzymatically. Removal of HA (but not HS) inhibited neutrophil recruitment, as did antibody blockade of CD44, a counter-receptor for HA on neutrophils. Supernatants from hyaluronidase-treated day 20 ECs were more potent in activating neutrophils than supernatants from untreated EC. Thus, HA has a role in neutrophil recruitment that is revealed in long-term cultures where it increases potency of response to sub-optimal levels of TNF. This effect appears to occur through a dual mechanism involving chemokine presentation and interaction with CD44.

Molecular mechanisms of endothelial hyperpermeability: implications in inflammation

Endothelial hyperpermeability is a significant problem in vascular inflammation associated with trauma, ischaemia-reperfusion injury, sepsis, adult respiratory distress syndrome, diabetes, thrombosis and cancer. An important mechanism underlying this process is increased paracellular leakage of plasma fluid and protein. Inflammatory stimuli such as histamine, thrombin, vascular endothelial growth factor and activated neutrophils can cause dissociation of cell-cell junctions between endothelial cells as well as cytoskeleton contraction, leading to a widened intercellular space that facilitates transendothelial flux. Such structural changes initiate with agonist-receptor binding, followed by activation of intracellular signalling molecules including calcium, protein kinase C, tyrosine kinases, myosin light chain kinase, and small Rho-GTPases; these kinases and GTPases then phosphorylate or alter the conformation of different subcellular components that control cell-cell adhesion, resulting in paracellular hypermeability. Targeting key signalling molecules that mediate endothelial-junction-cytoskeleton dissociation demonstrates a therapeutic potential to improve vascular barrier function during inflammatory injury.

Chapter 15. A microfluidics-based method for chemoattractant gradients

Leukocyte trafficking in tissues mediates cellular immune responses and can be directed by chemotactic factors such as chemokines. Understanding chemotactic responses of leukocytes to chemoattractant gradients is of great interest and importance to both basic science and clinical research. Conventional methods for studying leukocyte migration and chemotaxis generally lack the ability to maintain and manipulate gradient profiles. In contrast, microfluidic devices can generate well-defined stable chemical gradients and can precisely modify gradient conditions in space and time. Previously, microfluidic gradient-generating devices have been used to investigate various aspects of leukocyte migration in different chemoattractant fields with the focus on human blood neutrophils. Recently, chemotaxis of human blood T cells in chemokine gradients was successfully demonstrated in a microfluidic device. In this chapter, the detailed method of analyzing the migration of human blood neutrophils and T cells in chemoattractant gradients with microfluidic devices is described.

Neutrophil adhesion and activation under flow

Neutrophil recruitment into inflamed tissue in response to injury or infection is tightly regulated. Reduced neutrophil recruitment can result in a reduced ability to fight invading microorganisms. During inflammation, neutrophils roll along the endothelial wall of postcapillary venules and integrate inflammatory signals. Neutrophil activation by selectins and chemokines regulates integrin adhesiveness. Binding of activated integrins to their counter-receptors on endothelial cells induces neutrophil arrest and firm adhesion. Adherent neutrophils can be further activated to undergo cytoskeletal rearrangement, crawling, transmigration, superoxide production, and respiratory burst. Signaling through G-protein-coupled receptors, selectin ligands, Fc receptors and outside-in signaling through integrins are all involved in neutrophil activation, but their interplay in the multistep process of recruitment is only beginning to emerge. This review provides an overview of signaling in rolling and adherent neutrophils.

Modeling the role of homologous receptor desensitization in cell gradient sensing

G-protein-coupled chemoattractant receptors signal transiently upon ligand binding to effect cell orientation and motility but then are rapidly desensitized. The importance of desensitization has been unclear, because mutated nondesensitizable receptors mediate efficient chemotaxis. We hypothesized that homologous receptor desensitization is required for cellular navigation in fields of competing attractants. Modeling of receptor-mediated orientation shows that desensitization allows integration of attractant signals. Cells expressing normal receptors are predicted to 1) orient preferentially to distant gradients; 2) seek an intermediate position between balanced agonist sources; 3) and can be repositioned between chemoattractant-defined microenvironmental domains by modest changes in receptor number. In contrast, in the absence of desensitization, orientation is dominated by local agonist sources, precluding continued navigation. Furthermore, cell orientation in competing ligand gradients depends on the relative kinetic rates of receptor desensitization and recycling. We propose that homologous receptor desensitization is critical for cellular navigation in complex chemoattractant fields.

Lymphocyte electrotaxis in vitro and in vivo

Electric fields are generated in vivo in a variety of physiologic and pathologic settings, including penetrating injury to epithelial barriers. An applied electric field with strength within the physiologic range can induce directional cell migration (i.e., electrotaxis) of epithelial cells, endothelial cells, fibroblasts, and neutrophils suggesting a potential role in cell positioning during wound healing. In the present study, we investigated the ability of lymphocytes to respond to applied direct current (DC) electric fields. Using a modified Transwell assay and a simple microfluidic device, we show that human PBLs migrate toward the cathode in physiologically relevant DC electric fields. Additionally, electrical stimulation activates intracellular kinase signaling pathways shared with chemotactic stimuli. Finally, video microscopic tracing of GFP-tagged immunocytes in the skin of mouse ears reveals that motile cutaneous T cells actively migrate toward the cathode of an applied DC electric field. Lymphocyte positioning within tissues can thus be manipulated by externally applied electric fields, and may be influenced by endogenous electrical potential gradients as well.

PI3K accelerates, but is not required for, neutrophil chemotaxis to fMLP

PI3K activity, resulting in the accumulation of PIP(3) along the leading edge of a chemotaxing cell, has been proposed to be an indispensable signaling event that is required for cells to undergo chemotaxis to endogenous and exogenous chemoattractants. Some studies have suggested that this might be the case for chemoattractants such as IL8, whereas chemotaxis to other stimuli, such as the bacterial peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP), might occur normally in the absence of PI3K activity. Herein, we systematically analyze the role of PI3K in mediating chemotaxis to fMLP, both in vitro and in vivo. Using short- and long-term in vitro assays, as well as an in vivo chemotaxis assay, we investigated the importance of PI3K in response to the prototypic chemoattractant fMLP. Exposure of neutrophils to fMLP induced an immediate polarization, which resulted in directional migration towards fMLP within 2-3 minutes. PI3K-inhibited cells also polarized and migrated in a directional fashion towards fMLP; however, this process was delayed by approximately 15 minutes, demonstrating that PI3K accelerates the initial response to fMLP, but an alternative pathway replaces PI3K over time. By contrast, p38-MAPK-inhibited cells, or cells lacking MK2, were unable to polarize in response to fMLP. Long-term chemotaxis assays using a pan-PI3K inhibitor, a PI3Kdelta-specific inhibitor or PI3Kgamma-knockout neutrophils, demonstrated no role for PI3K in mediating chemotaxis to fMLP, regardless of the steepness of the fMLP gradient. Similar results were observed in vivo, with PI3Kgamma(-/-) cells displaying a delayed, but otherwise normal, chemotactic response to gradients of fMLP. Together, these data demonstrate that, although PI3K can enhance early responses to the bacterial chemoattractant fMLP, it is not required for migration towards this chemoattractant.

Effects of endothelial basement membrane on neutrophil adhesion and migration

The influence of the sub-endothelial basement membrane (BM) on the adhesion and migration of leukocytes is not well-defined. We therefore investigated the behaviour of human neutrophils on purified BM proteins and on BM deposited by short- or long-term cultures of endothelial cells (EC). The adhesion, but not migration velocities, of neutrophils activated with interleukin-8 was dependent on the coating concentrations of purified collagen, laminin or fibronectin. In contrast, adhesion was similar on matrices deposited by 3-day or 20-day cultures of EC, but neutrophils migrated more slowly on the distinct BM that formed over 20 days. In addition, while adhesion on all surfaces was greatly reduced when neutrophils were treated with antibody against beta(2)-integrins, antibody against beta(1)-integrins only inhibited adhesion to the 20-day BM. Thus, the native BM has distinct effects on integrin usage and migration by neutrophils, which are not reproduced by purified proteins or matrix deposited early during endothelial culture.

Stromal cell-derived factor-1/CXCL12 stimulates chemorepulsion of NOD/LtJ T-cell adhesion to islet microvascular endothelium

OBJECTIVE

Diabetogenic T-cell recruitment into pancreatic islets facilitates beta-cell destruction during autoimmune diabetes, yet specific mechanisms governing this process are poorly understood. The chemokine stromal cell-derived factor-1 (SDF-1) controls T-cell recruitment, and genetic polymorphisms of SDF-1 are associated with early development of type 1 diabetes.

RESEARCH DESIGN AND METHODS

Here, we examined the role of SDF-1 regulation of diabetogenic T-cell adhesion to islet microvascular endothelium. Islet microvascular endothelial cell monolayers were activated with tumor necrosis factor-alpha (TNF-alpha), subsequently coated with varying concentrations of SDF-1 (1-100 ng/ml), and assayed for T-cell/endothelial cell interactions under physiological flow conditions.

RESULTS

TNF-alpha significantly increased NOD/LtJ T-cell adhesion, which was completely blocked by SDF-1 in a dose-dependent manner, revealing a novel chemorepulsive effect. Conversely, SDF-1 enhanced C57BL/6J T-cell adhesion to TNF-alpha-activated islet endothelium, demonstrating that SDF-1 augments normal T-cell adhesion. SDF-1 chemorepulsion of NOD/LtJ T-cell adhesion was completely reversed by blocking G(i)alpha-protein-coupled receptor activity with pertussis toxin. CXCR4 protein expression was significantly decreased in NOD/LtJ T-cells, and inhibition of CXCR4 activity significantly reversed SDF-1 chemorepulsive effects. Interestingly, SDF-1 treatment significantly abolished T-cell resistance to shear-mediated detachment without altering adhesion molecule expression, thus demonstrating decreased integrin affinity and avidity.

CONCLUSIONS

In this study, we have identified a previously unknown novel function of SDF-1 in negatively regulating NOD/LtJ diabetogenic T-cell adhesion, which may be important in regulating diabetogenic T-cell recruitment into islets.

Hepatic leukocyte recruitment in response to time-limited expression of TNF-alpha and IL-1beta

The development of chronic liver diseases is mediated by sustained hepatic inflammation. Our objective was to characterize the molecular mechanisms responsible for the hepatic inflammatory response to time-limited TNF-alpha and IL-1beta expression. C57Bl/6 mice were injected with 2 x 10(7) plaque forming units intraperitoneally of an adenoviral vector containing TNF-alpha or IL-1beta (AdTNF-alpha or AdIL-1beta). A nonreplicating adenoviral vector served as control. Four days later, under ketamine and xylazine anesthesia, the liver microvasculature was examined by intravital microscopy. In the postsinusoidal venules, leukocyte rolling increased significantly in response to both AdTNF-alpha and AdIL-1beta, compared with controls. This response was significantly reduced following injection of an anti-alpha4-integrin monoclonal antibody (MAb). Postsinusoidal rolling was further reduced to baseline following injection of an anti-P-selectin or anti-L-selectin MAb. Sinusoidal adhesion was greater in mice treated with AdIL-1beta than with AdTNF-alpha. Blocking alpha4-integrin, P-selectin, or L-selectin had no significant effect on sinusoidal or postsinusoidal adhesion. In separate experiments, we administered AdTNF-alpha or AdIL-1beta to mice deficient in ICAM-1. In ICAM-1-/- mice, postsinusoidal leukocyte rolling significantly increased following expression of IL-1beta but not TNF-alpha. AdIL-1beta- but not AdTNF-alpha-mediated sinusoidal adhesion was ICAM-1 dependent. AdTNF-alpha-induced sinusoidal adhesion was significantly reduced following 4 days of anti-MIP-2 MAb and anti-KC MAb. Prolonged expression of the cytokines TNF-alpha and IL-1beta increases hepatic leukocyte-endothelial cell interactions. Interestingly, the mechanisms through which these cytokines bring about adhesion within the sinusoids differ; AdIL-1beta sinusoidal adhesion uses an ICAM-1-dependent mechanism whereas AdTNF-alpha-mediated adhesion is ICAM-1 independent but CXC chemokine dependent.

The Duffy antigen receptor for chemokines in acute renal failure: A facilitator of renal chemokine presentation

OBJECTIVE

Acute renal failure remains a major challenge in critical care medicine. Both neutrophils and chemokines have been proposed as key components in the development of acute renal failure. Although the Duffy antigen receptor for chemokines (DARC) is present in several tissues and a highly specific ligand for various chemokines, its exact role in vivo remains unclear.

DESIGN

Prospective, controlled experimental study.

SETTING

University-based research laboratory.

SUBJECTS

C57BL/6 wild-type and DARC gene-deficient mice (DARC-/-).

INTERVENTIONS

To unravel the functional relevance of DARC in vivo, we compared wild-type and DARC-/- using neutrophil-dependent models of acute renal failure, induced by either local (renal ischemia-reperfusion) or systemic (endotoxemia, lipopolysaccharide) injury.

MEASUREMENTS AND MAIN RESULTS

Plasma creatinine and blood urea nitrogen concentrations served as indicators of renal function or dysfunction. Enzyme-linked immunosorbent assays were used to measure tissue and plasma chemokine concentrations. We also performed immunostaining to localize chemokine expression and flow cytometry to evaluate neutrophil recruitment into the kidney. Following renal injury, wild-type mice developed moderate renal ischemia-reperfusion(lipopolysaccharide, 300% increase in plasma creatinine concentrations) to severe acute renal failure (renal ischemia-reperfusion, 40% mortality) as well as extensive renal neutrophil recruitment. DARC-/- mice exhibited no renal dysfunction (renal ischemia-reperfusion) or only very mild renal dysfunction (lipopolysaccharide, 20% increase in serum creatinine concentrations). DARC-/- mice showed no postischemic neutrophil infiltration. Although DARC-/- and wild-type mice exhibited similar global renal neutrophil-recruitment during endotoxemia, DARC-/- mice showed significantly impaired neutrophil extravasation. Total renal concentrations of the chemokine macrophage inflammatory protein 2, which has been shown to bind to DARC and to be crucial in postischemic acute renal failure, were either identical (lipopolysaccharide) or only moderately different (renal ischemia-reperfusion) between wild-type and DARC-/- mice. Immunostaining revealed an absence of macrophage inflammatory protein-2 in renal endothelial cells of DARC-/- mice.

CONCLUSIONS

We suggest that DARC predominantly exerts its effects by controlling spatial chemokine distribution, which in turn regulates neutrophil recruitment and subsequent acute renal failure.

Roles of phosphatidylinositol 3-kinase and NF-kappaB in human cytomegalovirus-mediated monocyte diapedesis and adhesion: strategy for viral persistence

Infected peripheral blood monocytes are proposed to play a key role in the hematogenous dissemination of human cytomegalovirus (HCMV) to tissues, a critical step in the establishment of HCMV persistence and the development of HCMV-associated diseases. We recently provided evidence for a unique strategy involved in viral dissemination: HCMV infection of primary human monocytes promotes their transendothelial migration and differentiation into proinflammatory macrophages permissive for the replication of the original input virus. To decipher the mechanism of hematogenous spread, we focused on the viral dysregulation of early cellular processes involved in transendothelial migration. Here, we present evidence that both phosphatidylinositol 3-kinase [PI(3)K] and NF-kappaB activities were crucial for the HCMV induction of monocyte motility and firm adhesion to endothelial cells. We found that the beta(1) integrins, the beta(2) integrins, intracellular adhesion molecule 1 (ICAM-1), and ICAM-3 were upregulated following HCMV infection and that they played a key role in the firm adhesion of infected monocytes to the endothelium. The viral regulation of adhesion molecule expression is complex, with PI(3)K and NF-kappaB affecting the expression of each adhesion molecule at different stages of the expression cascade. Our data demonstrate key roles for PI(3)K and NF-kappaB signaling in the HCMV-induced cellular changes in monocytes and identify the biological rationale for the activation of these pathways in infected monocytes, which together suggest a mechanism for how HCMV promotes viral spread to and persistence within host organs.

Imaging receptor microdomains on leukocyte subsets in live mice

We present a simple method to identify the recruitment of leukocyte subsets and determine concurrent surface-receptor clustering in live mice. We show that CD45+ F4/80- Gr-1+ neutrophils are robustly recruited in surgery-activated cremasteric venules, whereas adherent CD45+ B220+ B lymphocytes were dominant in bone marrow venules. Most adherent Gr-1+ leukocytes are not firmly stationary but actively migrate on TNF-alpha-activated cremasteric venular endothelium and exhibit marked polarization of surface PSGL-1, but not LFA-1, to the trailing edge.

Complete reversal of acid-induced acute lung injury by blocking of platelet-neutrophil aggregation

Acute lung injury (ALI) causes high mortality, but its molecular mechanisms are poorly understood. Acid aspiration is a frequent cause of ALI, leading to neutrophil sequestration, increased permeability, and deterioration of gas exchange. We investigated the role of platelet-neutrophil interactions in a murine model of acid-induced ALI. Acid aspiration induced P-selectin-dependent platelet-neutrophil interactions in blood and in lung capillaries. Reducing circulating platelets or blocking P-selectin halted the development of ALI. Bone marrow chimeras showed that platelet, not endothelial, P-selectin was responsible for the injury. The interaction of platelets with neutrophils and endothelia was associated with TXA(2) formation, with detrimental effects on permeability and tissue function. Activated platelets induced endothelial expression of ICAM-1 and increased neutrophil adhesion. Inhibition of platelet-neutrophil aggregation improved gas exchange, reduced neutrophil recruitment and permeability, and prolonged survival. The key findings were confirmed in a sepsis-induced model of ALI. These findings may translate into improved clinical treatments for ALI.

Recombinant integrin CD11b A-domain blocks polymorphonuclear cells recruitment and protects against skeletal muscle inflammatory injury in the rat

The beta2 integrin CD11b/CD18 (CR3) is a major adhesion receptor of neutrophils, normally utilized to fend off infections. This receptor contributes, however, to multiple forms of non-infectious inflammatory injury when dysregulated as shown in gene knock-outs and through the use of blocking monoclonal antibodies. The major ligand recognition site of CR3 has been mapped to the A-domain in the CD11b subunit (CD11bA). The recombinant form of this domain exhibits a ligand binding profile similar to that of the holoreceptor. To assess the potential anti-inflammatory activity of CD11bA as a competitive antagonist of CR3 in vivo, we assessed its effects on a developed animal model of traumatic skeletal muscle injury in the rat. Recombinant soluble rat CD11bA-domain fused to glutathione-S-transferase (GST) was administered intravenously in a single dose at 1 mg/kg to nine groups of Wistar rats, five in each group, 30 min before inducing traumatic skeletal muscle injury. Control animals received either a function-blocking anti-CD11b/CD18 monoclonal antibody (1 mg/kg), non-functional mutant forms of the CD11bA (D140GS/AGA, T209/A, D242/A), recombinant GST or buffer alone. In control animals, the wounded muscle showed oedema, erythrocyte extravasation and myonecrosis both within and outside the immediate wounded area (5-10 mm zone) and influx of neutrophils was detected 30 min post-wound, followed by a second wave 3 hr later. Wild-type CD11bA- or anti-CD11b monoclonal antibody (mAb)-treated rats showed a comparable and significant decrease in the number of infiltrating PMN (78 + 4%, n = 70 and 86 +/- 2%, n = 50, respectively) and preservation of the muscular fibres outside the immediate zone of necrosis (75 + 4%, n = 70, 84 +/- 1%, n = 50, respectively), compared to controls. These data demonstrate that CD11bA can be an effective tissue-preserving agent in acute inflammatory muscular injury.

Reevaluation of P-selectin and alpha 4 integrin as targets for the treatment of experimental autoimmune encephalomyelitis

There has been a great deal of interest in adhesion molecules as targets for the treatment of multiple sclerosis and other inflammatory diseases. In this study, we systematically evaluate alpha(4) integrin and P-selectin as targets for therapy in murine models of multiple sclerosis-for the first time directly measuring the ability of their blockade to inhibit recruitment and relate this to clinical efficacy. Experimental autoimmune encephalomyelitis was induced in C57BL/6 or SJL/J mice and intravital microscopy was used to quantify leukocyte interactions within the CNS microvasculature. In both strains, pretreatment with blocking Abs to either alpha(4) integrin or P-selectin reduced firm adhesion to a similar extent, but did not block it completely. The combination of the Abs was more effective than either Ab alone, although the degree of improvement was more evident in SJL/J mice. Similarly, dual blockade was much more effective at preventing the subsequent accumulation of fluorescently labeled leukocytes in the tissue in both strains. Despite evidence of blockade of leukocyte recruitment mechanisms, no clinical benefit was observed with anti-adhesion molecule treatments or genetic deletion of P-selectin in the C57BL/6 model, or in a pertussis toxin-modified model in SJL/J mice. In contrast, Abs to alpha(4) integrin resulted in a significant delay in the onset of clinical signs of disease in the standard SJL/J model. Despite evidence of a similar ability to block firm adhesion, Abs to P-selectin had no effect. Importantly, combined blockade of both adhesion molecules resulted in significantly better clinical outcome than anti-alpha(4) integrin alone.

A microfluidic multi-injector for gradient generation

This paper describes a microfluidic multi-injector (MMI) that can generate temporal and spatial concentration gradients of soluble molecules. Compared to conventional glass micropipette-based methods that generate a single gradient, the MMI exploits microfluidic integration and actuation of multiple pulsatile injectors to generate arbitrary overlapping gradients that have not previously been possible. The MMI device is fabricated in poly(dimethylsiloxane) (PDMS) using multi-layer soft lithography and consists of fluidic channels and control channels with pneumatically actuated on-chip barrier valves. Repetitive actuation of on-chip valves control pulsatile release of solution that establishes microscopic chemical gradients around the orifice. The volume of solution released per actuation cycle ranged from 30 picolitres to several hundred picolitres and increased linearly with the duration of valve opening. The shape of the measured gradient profile agreed closely with the simulated diffusion profile from a point source. Steady state gradient profiles could be attained within 10 minutes, or less with an optimized pulse sequence. Overlapping gradients from 2 injectors were generated and characterized to highlight the advantages of MMI over conventional micropipette assays. The MMI platform should be useful for a wide range of basic and applied studies on chemotaxis and axon guidance.

Toll-like receptor 4 signaling leads to neutrophil migration impairment in polymicrobial sepsis*

OBJECTIVE

We have documented an impaired neutrophil migration toward the infectious focus in severe sepsis. This phenomenon appears to be mediated by nitric oxide, the release of which is stimulated by circulating inflammatory cytokines released by immune cells after stimulation by bacteria and/or their products. Toll-like receptor 4 (TLR4) is the major recognition receptor for lipopolysaccharide, a component of Gram-negative bacterial cell walls. In the present study, we investigated whether TLR4 is involved in the failure of neutrophil migration in mice subjected to polymicrobial or Gram-negative sepsis.

DESIGN

Controlled animal study.

SETTING

University research laboratory.

SUBJECTS

Male C3H/HeJ (TLR4-deficient) and C3H/HePas (TLR4-normal) mice.

INTERVENTIONS

Mice were subjected to sublethal or lethal polymicrobial sepsis, both induced by cecal ligation and puncture or intraperitoneal polymicrobial inoculation, and subjected to sublethal Gram-negative sepsis induced by intraperitoneal Salmonella typhimurium inoculation (GNI). Survival was monitored for 5 days. In separate experiments, mice were killed 6 hrs after sepsis induction, and intraperitoneal neutrophil migration, bacteremia, lung neutrophil sequestration, and levels of cytokines, chemokines, and nitrate were evaluated.

MEASUREMENTS AND RESULTS

TLR4-deficient (C3H/HeJ) mice presented incapacity to promote neutrophil recruitment to the infectious site after sublethal GNI, resulting in high mortality. However, TLR4 signaling is not essential to display neutrophil migration in sublethal polymicrobial sepsis induced by both cecal ligation and puncture and polymicrobial inoculation models, but surprisingly, it is crucial to establish the impairment of neutrophil migration in lethal polymicrobial sepsis, since TLR4-deficient mice that underwent lethal cecal ligation and puncture or polymicrobial inoculation did not present failure of neutrophil migration to infectious focus. As a consequence, these animals presented low bacteremia and a high survival rate and did not display systemic inflammation, determined by high levels of circulating cytokines and lung neutrophil sequestration and chemokine production.

CONCLUSION

These results highlight the harmful role of TLR4 signaling in polymicrobial severe sepsis.

Timing of Neutrophil Activation and Expression of Proinflammatory Markers Do Not Support a Role for Neutrophils in Cervical Ripening in the Mouse1

The mechanisms that facilitate remodeling of the cervix in preparation for and during parturition remain poorly understood. In the current study, we have evaluated the timing of inflammatory cell migration in cervix through comparisons between wild-type mice and steroid 5alpha-reductase type 1 null mice (Srd5a1-/-), which fail to undergo cervical ripening due to insufficient local progesterone metabolism. The timing of migration and distribution of macrophages, monocytes, and neutrophils were examined using cervices from wild-type and Srd5a1-/- mice before Day 15 (d15) and during cervical ripening (late d18), and postpartum (d19). Neutrophil numbers were quantitated by cell counts and activity was estimated by measurement of myeloperoxidase activity. The mRNA and/or protein expression of neutrophil chemoattractants, CXCL2 and CXCL1, and other proinflammatory and adhesion molecules, including IL1A, IL1B, TNF, CCL11, CCL5, CCL3, ITGAM, and ICAM1, were measured in cervices collected before, during, and after birth. The effect of neutrophil depletion on parturition was tested. Tissue macrophages, myeloperoxidase activity, and expression of proinflammatory molecules are not increased within the cervix until after birth. Neutrophil numbers do not change after birth and neutrophil depletion before term has no effect on timing or success of parturition. These results suggest that cervical ripening does not require neutrophils. Moreover, neutrophil activation and a general inflammatory response are not initiated within the cervix until shortly after parturition. The timing of inflammatory cell migration and activation in pregnant cervix suggest a role for these cells in postpartum remodeling of the cervix rather than in the initiation of cervical ripening at parturition.

TNF-alpha-secreting monocytes are recruited into the brain of cholestatic mice

Signaling occurs between the liver and brain in cholestatic liver disease, giving rise to sickness behaviors such as fatigue. However, the signaling pathways involved are poorly defined. Circulating inflammatory mediator levels are increased in cholestasis, leading to speculation that they may be capable of activating circulating immune cells that subsequently could gain access to the brain. Indeed, we have identified that at day 10 after bile duct resection-induced cholestasis, there is activation of circulating monocytes that express tumor necrosis factor alpha (TNF-alpha) in conjunction with increased expression of adhesion molecules by cerebral endothelium. Moreover, using intravital microscopy, we have identified markedly enhanced leukocytes rolling along cerebral endothelial cells, mediated by P-selectin, in bile duct-resected (BDR) but not control mice. In addition, we have identified increased infiltration of monocytes (but not lymphocytes) into the brains of BDR mice and found that these infiltrating monocytes produce TNF-alpha. Furthermore, infiltration of TNF-alpha-secreting monocytes into the brains of cholestatic mice is associated with a broad activation of resident brain macrophages to produce TNF-alpha. In conclusion, cholestasis is associated with an activation of cerebral endothelium that recruits TNF-alpha-producing monocytes into the brain. We hypothesize that enhanced TNF-alpha release within the brain may contribute to the development of cholestasis-associated sickness behaviors, including fatigue.

Lipopolysaccharide signaling in endothelial cells

Sepsis is the systemic immune response to severe bacterial infection. The innate immune recognition of bacterial and viral products is mediated by a family of transmembrane receptors known as Toll-like receptors (TLRs). In endothelial cells, exposure to lipopolysaccharide (LPS), a major cell wall constituent of Gram-negative bacteria, results in endothelial activation through a receptor complex consisting of TLR4, CD14 and MD2. Recruitment of the adaptor protein myeloid differentiation factor (MyD88) initiates an MyD88-dependent pathway that culminates in the early activation of nuclear factor-kappaB (NF-kappaB) and the mitogen-activated protein kinases. In parallel, a MyD88-independent pathway results in a late-phase activation of NF-kappaB. The outcome is the production of various proinflammatory mediators and ultimately cellular injury, leading to the various vascular sequelae of sepsis. This review will focus on the signaling pathways initiated by LPS binding to the TLR4 receptor in endothelial cells and the coordinated regulation of this pathway.

Function-blocking antibodies to human vascular adhesion protein-1: a potential anti-inflammatory therapy

Human vascular adhesion protein-1 (VAP-1) is a homodimeric 170-kDa sialoglycoprotein that is expressed on the surface of endothelial cells and functions as a semicarbazide-sensitive amine oxidase and as an adhesion molecule. Blockade of VAP-1 has been shown to reduce leukocyte adhesion and transmigration in in vivo and in vitro models, suggesting that VAP-1 is a potential target for anti-inflammatory therapy. In this study we have constructed mouse-human chimeric antibodies by genetic engineering in order to circumvent the potential problems involved in using murine antibodies in man. Our chimeric anti-VAP-1 antibodies, which were designed to lack Fc-dependent effector functions, bound specifically to cell surface-expressed recombinant human VAP-1 and recognized VAP-1 in different cell types in tonsil. Furthermore, the chimeric antibodies prevented leukocyte adhesion and transmigration in vitro and in vivo. Hence, these chimeric antibodies have the potential to be used as a new anti-inflammatory therapy.