Neutrophils emigrate from venules by a transendothelial cell pathway in response to FMLP

Mechanisms of HIV-mediated blood-brain barrier compromise and leukocyte transmigration under the current antiretroviral era

HIV-associated neurological compromise is observed in more than half of all people with HIV (PWH), even under antiretroviral therapy (ART). The mechanism has been associated with the early transmigration of HIV-infected monocytes across the BBB in a CCL2 and HIV replication-dependent manner. However, the mechanisms of chronic brain damage are unknown. We demonstrate that all PWH under ART have elevated circulating ATP levels that correlate with the onset of cognitive impairment even in the absence of a circulating virus. Serum ATP levels found in PWH with the most severe neurocognitive impairment trigger the transcellular migration of HIV-infected leukocytes across the BBB in a JAM-A and LFA-1-dependent manner. We propose that targeting transcellular leukocyte transmigration could reduce or prevent the devastating consequences of HIV within the brains of PWH under ART.

Neutrophil breaching of the blood vessel pericyte layer during diapedesis requires mast cell-derived IL-17A

Neutrophil diapedesis is an immediate step following infections and injury and is driven by complex interactions between leukocytes and various components of the blood vessel wall. Here, we show that perivascular mast cells (MC) are key regulators of neutrophil behaviour within the sub-endothelial space of inflamed venules. Using confocal intravital microscopy, we observe directed abluminal neutrophil motility along pericyte processes towards perivascular MCs, a response that created neutrophil extravasation hotspots. Conversely, MC-deficiency and pharmacological or genetic blockade of IL-17A leads to impaired neutrophil sub-endothelial migration and breaching of the pericyte layer. Mechanistically, identifying MCs as a significant cellular source of IL-17A, we establish that MC-derived IL-17A regulates the enrichment of key effector molecules ICAM-1 and CXCL1 in nearby pericytes. Collectively, we identify a novel MC-IL-17A-pericyte axis as modulator of the final steps of neutrophil diapedesis, with potential translational implications for inflammatory disorders driven by increased neutrophil diapedesis.

Polymerization power: effectors of actin polymerization as regulators of T lymphocyte migration through complex environments

During their life span, T cells are tasked with patrolling the body for potential pathogens. To do so, T cells migrate through numerous distinct anatomical sites and tissue environments with different biophysical characteristics. To migrate through these different environments, T cells use various motility strategies that rely on actin network remodeling to generate shape changes and mechanical forces. In this review, we initially discuss the migratory journey of T cells and then cover the actin polymerization effectors at play in T cells, and finally, we focus on the function of these effectors of actin cytoskeleton remodeling in mediating T-cell migration through diverse tissue environments. Specifically, we will discuss the current state of the field pertaining to our understanding of the roles in T-cell migration played by members of the three main families of actin polymerization machinery: the Arp2/3 complex; formin proteins; and Ena/VASP proteins.

Neutrophils-From Bone Marrow to First-Line Defense of the Innate Immune System

Neutrophils (polymorphonuclear cells; PMNs) form a first line of defense against pathogens and are therefore an important component of the innate immune response. As a result of poorly controlled activation, however, PMNs can also mediate tissue damage in numerous diseases, often by increasing tissue inflammation and injury. According to current knowledge, PMNs are not only part of the pathogenesis of infectious and autoimmune diseases but also of conditions with disturbed tissue homeostasis such as trauma and shock. Scientific advances in the past two decades have changed the role of neutrophils from that of solely immune defense cells to cells that are responsible for the general integrity of the body, even in the absence of pathogens. To better understand PMN function in the human organism, our review outlines the role of PMNs within the innate immune system. This review provides an overview of the migration of PMNs from the vascular compartment to the target tissue as well as their chemotactic processes and illuminates crucial neutrophil immune properties at the site of the lesion. The review is focused on the formation of chemotactic gradients in interaction with the extracellular matrix (ECM) and the influence of the ECM on PMN function. In addition, our review summarizes current knowledge about the phenomenon of bidirectional and reverse PMN migration, neutrophil microtubules, and the microtubule organizing center in PMN migration. As a conclusive feature, we review and discuss new findings about neutrophil behavior in cancer environment and tumor tissue.

Heterologous Challenge with PRRSV-1 MLV in Pregnant Vaccinated Gilts: Potential Risk on Health and Immunity of Piglets

Simple Summary

Modified live virus (MLV) vaccines are considered as the key component to control the Porcine Reproductive and Respiratory Syndrome Virus (PRRSV). The majority of pig farms apply the ‘mass’ vaccination strategy in breeding female animals. However, this PRRS MLV vaccination protocol involves the risk of inoculation of sows in the last stage of gestation, resulting in possible infection of the fetus as the virus can efficiently cross the placenta during the last period of pregnancy. Thus, we evaluated the ability of the vaccine virus to act as a pathogenic strain, to be transmitted to fetuses and to affect the health status of neonatal piglets. The results indicated that the study gilts transmitted the vaccine virus to their offspring, as well as that the PRRSV-infected piglets showed a poor clinical performance. Consequently, the pig farms that apply PRRS MLV vaccination in a routine blanket vaccination strategy must avoid inoculating pregnant gilts the last week before their parturition.

Abstract

The objective of the present study was to evaluate the potential risks of the four commercial PRRS-1 MLV vaccines in pregnant vaccinated gilts at the last stage of gestation under field conditions. The study was conducted at four pig farms, including 25 gilts from each farm (25 × 4 = 100 gilts), which were equally allocated to five different study groups. A PRRS-1 MLV vaccination was applied on the 100th day of their pregnancy with the different commercial vaccines that are available in the Greek market. The results indicated virus congenital infection and viremia in piglets (20/200 = 10% PRRSV infected piglets), and detection of PRRSV-specific antibodies (181/200 = 90.5% piglets found with PRRSV antibodies). The subsequent phylogenetic analyses revealed high percentages of similarity between the PRRSV-1 strain detected in infected litters and the PRRSV-1 vaccine strain to which the study gilts had been previously exposed to. Health status analyses of trial piglets resulted in differences between litters from vaccinated sows and litters from non-vaccinated sows at 110th day of gestation as regards the number of weak-born piglets, mummies, and piglets with splay-leg and/or respiratory symptoms. The current study’s results indicate several potential dangers of the PRRS MLV vaccination in late gestation.

The endothelial diapedesis synapse regulates transcellular migration of human T lymphocytes in a CX3CL1- and SNAP23-dependent manner

Understanding how cytotoxic T lymphocytes (CTLs) efficiently leave the circulation to target cancer cells or contribute to inflammation is of high medical interest. Here, we demonstrate that human central memory CTLs cross the endothelium in a predominantly paracellular fashion, whereas effector and effector memory CTLs cross the endothelium preferably in a transcellular fashion. We find that effector CTLs show a round morphology upon adhesion and induce a synapse-like interaction with the endothelium where ICAM-1 is distributed at the periphery. Moreover, the interaction of ICAM-1:β2integrin and endothelial-derived CX3CL1:CX3CR1 enables transcellular migration. Mechanistically, we find that ICAM-1 clustering recruits the SNARE-family protein SNAP23, as well as syntaxin-3 and -4, for the local release of endothelial-derived chemokines like CXCL1/8/10. In line, silencing of endothelial SNAP23 drives CTLs across the endothelium in a paracellular fashion. In conclusion, our data suggest that CTLs trigger local chemokine release from the endothelium through ICAM-1-driven signals driving transcellular migration.

Neutrophil transendothelial migration hotspots - mechanisms and implications

During inflammation, leukocytes circulating in the blood stream exit the vasculature in a process called leukocyte transendothelial migration (TEM). The current paradigm of this process comprises several well-established steps, including rolling, adhesion, crawling, diapedesis and sub-endothelial crawling. Nowadays, the role of the endothelium in transmigration is increasingly appreciated. It has been established that leukocyte exit sites on the endothelium and in the pericyte layer are in fact not random but instead may be specifically recognized by migrating leukocytes. Here, we review the concept of transmigration hotspots, specific sites in the endothelial and pericyte layer where most transmigration events take place. Chemokine cues, adhesion molecules and membrane protrusions as well as physical factors, such as endothelial junction stability, substrate stiffness, the presence of pericytes and basement membrane composition, may all contribute to local hotspot formation to facilitate leukocytes exiting the vasculature. In this Review, we discuss the biological relevance of such hotspots and put forward multiple mechanisms and factors that determine a functional TEM hotspot.

Regulatory mechanisms of neutrophil migration from the circulation to the airspace

The neutrophil, a short-lived effector leukocyte of the innate immune system best known for its proteases and other degradative cargo, has unique, reciprocal physiological interactions with the lung. During health, large numbers of ‘marginated’ neutrophils reside within the pulmonary vasculature, where they patrol the endothelial surface for pathogens and complete their life cycle. Upon respiratory infection, rapid and sustained recruitment of neutrophils through the endothelial barrier, across the extravascular pulmonary interstitium, and again through the respiratory epithelium into the airspace lumen, is required for pathogen killing. Overexuberant neutrophil trafficking to the lung, however, causes bystander tissue injury and underlies several acute and chronic lung diseases. Due in part to the unique architecture of the lung’s capillary network, the neutrophil follows a microanatomic passage into the distal airspace unlike that observed in other end-organs that it infiltrates. Several of the regulatory mechanisms underlying the stepwise recruitment of circulating neutrophils to the infected lung have been defined over the past few decades; however, fundamental questions remain. In this article, we provide an updated review and perspective on emerging roles for the neutrophil in lung biology, on the molecular mechanisms that control the trafficking of neutrophils to the lung, and on past and ongoing efforts to design therapeutics to intervene upon pulmonary neutrophilia in lung disease.

Oxidative Stress and Lipid Mediators Modulate Immune Cell Functions in Autoimmune Diseases

Autoimmune diseases, including psoriasis, systemic lupus erythematosus (SLE), and rheumatic arthritis (RA), are caused by a combination of environmental and genetic factors that lead to overactivation of immune cells and chronic inflammation. Since oxidative stress is a common feature of these diseases, which activates leukocytes to intensify inflammation, antioxidants could reduce the severity of these diseases. In addition to activating leukocytes, oxidative stress increases the production of lipid mediators, notably of endocannabinoids and eicosanoids, which are products of enzymatic lipid metabolism that act through specific receptors. Because the anti-inflammatory CB2 receptors are the predominant cannabinoid receptors in leukocytes, endocannabinoids are believed to act as anti-inflammatory factors that regulate compensatory mechanisms in autoimmune diseases. While administration of eicosanoids in vitro leads to the differentiation of lymphocytes into T helper 2 (Th2) cells, eicosanoids are also necessary for the different0iation of Th1 and Th17 cells. Therefore, their antagonists and/or the genetic deletion of their receptors abolish inflammation in animal models of psoriasis—RA and SLE. On the other hand, products of non-enzymatic lipid peroxidation, especially acrolein and 4-hydroxynonenal-protein adducts, mostly generated by an oxidative burst of granulocytes, may enhance inflammation and even acting as autoantigens and extracellular signaling molecules in the vicious circle of autoimmune diseases.

Hematopoietic stem and progenitor cells use podosomes to transcellularly cross the bone marrow endothelium

Bone marrow endothelium plays an important role in the homing of hematopoietic stem and progenitor cells upon transplantation, but surprisingly little is known on how the bone marrow endothelial cells regulate local permeability and hematopoietic stem and progenitor cells transmigration. We show that temporal loss of vascular endothelial-cadherin function promotes vascular permeability in BM, even upon low-dose irradiation. Loss of vascular endothelial-cadherin function also enhances homing of transplanted hematopoietic stem and progenitor cells to the bone marrow of irradiated mice although engraftment is not increased. Intriguingly, stabilizing junctional vascular endothelial-cadherin in vivo reduced bone marrow permeability, but did not prevent hematopoietic stem and progenitor cells migration into the bone marrow, suggesting that hematopoietic stem and progenitor cells use the transcellular migration route to enter the bone marrow. Indeed, using an in vitro migration assay, we show that human hematopoietic stem and progenitor cells predominantly cross bone marrow endothelium in a transcellular manner in homeostasis by inducing podosome-like structures. Taken together, vascular endothelial-cadherin is crucial for BM vascular homeostasis but dispensable for the homing of hematopoietic stem and progenitor cells. These findings are important in the development of potential therapeutic targets to improve hematopoietic stem and progenitor cell homing strategies.

Neutrophils Enable Local and Non-Invasive Liposome Delivery to Inflamed Skeletal Muscle and Ischemic Heart

Uncontrolled inflammation is a major pathological factor underlying a range of diseases including autoimmune conditions, cardiovascular disease, and cancer. Improving localized delivery of immunosuppressive drugs to inflamed tissue in a non-invasive manner offers significant promise to reduce severe side effects caused by systemic administration. Here, a neutrophil-mediated delivery system able to transport drug-loaded nanocarriers to inflamed tissue by exploiting the inherent ability of neutrophils to migrate to inflammatory tissue is reported. This hybrid system (neutrophils loaded with liposomes ex vivo) efficiently migrates in vitro following an inflammatory chemokine gradient. Furthermore, the triggered release of loaded liposomes and reuptake by target macrophages is studied. The migratory behavior of liposome-loaded neutrophils is confirmed in vivo by demonstrating the delivery of drug-loaded liposomes to an inflamed skeletal muscle in mice. A single low-dose injection of the hybrid system locally reduces inflammatory cytokine levels. Biodistribution of liposome-loaded neutrophils in a human-disease-relevant myocardial ischemia reperfusion injury mouse model after i.v. injection confirms the ability of injected neutrophils to carry loaded liposomes to inflammation sites. This strategy shows the potential of nanocarrier-loaded neutrophils as a universal platform to deliver anti-inflammatory drugs to promote tissue regeneration in inflammatory diseases.

Megakaryocytes use in vivo podosome-like structures working collectively to penetrate the endothelial barrier of bone marrow sinusoids

BACKGROUND

Blood platelets are anucleate cell fragments that prevent bleeding and minimize blood vessel injury. They are formed from the cytoplasm of megakaryocytes located in the bone marrow. For successful platelet production, megakaryocyte fragments must pass through the sinusoid endothelial barrier by a cell biology process unique to these giant cells as compared with erythrocytes and leukocytes. Currently, the mechanisms by which megakaryocytes interact and progress through the endothelial cells are not understood, resulting in a significant gap in our knowledge of platelet production.

OBJECTIVE

The aim of this study was to investigate how megakaryocytes interact and progress through the endothelial cells of mouse bone marrow sinusoids.

METHODS

We used a combination of fluorescence, electron, and three-dimensional microscopy to characterize the cellular events between megakaryocytes and endothelial cells.

RESULTS

We identified protrusive, F-actin-based podosome-like structures, called in vivo-MK podosomes, which initiate the formation of pores through endothelial cells. These structures present a collective and spatial organization through their interconnection via a contractile network of actomyosin, essential to regulate the endothelial openings. This ensures proper passage of megakaryocyte-derived processes into the blood circulation to promote thrombopoiesis.

CONCLUSION

This study provides novel insight into the in vivo function of podosomes of megakaryocytes with critical importance to platelet production.

Formin-like 1 mediates effector T cell trafficking to inflammatory sites to enable T cell-mediated autoimmunity

Lymphocyte migration is essential for the function of the adaptive immune system, and regulation of T cell entry into tissues is an effective therapy in autoimmune diseases. Little is known about the specific role of cytoskeletal effectors that mediate mechanical forces and morphological changes essential for migration in complex environments. We developed a new Formin-like-1 (FMNL1) knock-out mouse model and determined that the cytoskeletal effector FMNL1 is selectively required for effector T cell trafficking to inflamed tissues, without affecting naïve T cell entry into secondary lymphoid organs. Here, we identify a FMNL1-dependent mechanism of actin polymerization at the back of the cell that enables migration of the rigid lymphocyte nucleus through restrictive barriers. Furthermore, FMNL1-deficiency impairs the ability of self-reactive effector T cells to induce autoimmune disease. Overall, our data suggest that FMNL1 may be a potential therapeutic target to specifically modulate T cell trafficking to inflammatory sites.

Distinguishing Specific CXCL12 Isoforms on Their Angiogenesis and Vascular Permeability Promoting Properties

Angiogenesis is associated with increased vessel sprouting and permeability. Important mediators of these angiogenic responses include local environment of signaling molecules and supporting extracellular matrix (ECM). However, dissecting the interplay of these instructive signals in vivo with multiple cells and extracellular molecules remains a central challenge. Here, microfluidic biomimicry is integrated with 3D ECM hydrogels that are well-characterized for molecular-binding and mechanical properties to reconstitute vessel-like analogues in vitro. This study focuses on three distinct isoforms of the pro-metastatic chemokine CXCL12. In collagen-only hydrogel, CXCL12-α is the most potent isoform in promoting sprouting and permeability, followed by CXCL12-β and CXCL12-γ. Strikingly, addition of hyaluronan (HA), a large and negatively charged glycosaminoglycan, with collagen matrices selectively increases vessel sprouting and permeability conferred by CXCL12-γ. This outcome is supported by the measured binding affinities to collagen/HA ECM, suggesting that negatively charged HA increases the binding of CXCL12-γ to augment its angiogenic potency. Moreover, it is shown that addition of HA to collagen matrices on its own decreases vessel sprouting and permeability, and these responses are nullified by blocking the HA receptor CD44. Collectively, these results demonstrate that differences in binding to extracellular HA help underlie CXCL12 isoform-specific responses toward directing angiogenesis.

Three-dimensional reconstruction of leukocyte internalisation in the luminal uterine epithelium following mating

Following mating, leukocytes are recruited to the uterine epithelium where they phagocytose spermatozoa and mediate maternal immune tolerance as well as a mild inflammatory response. In this ultrastructural study we utilised array tomography, a high-resolution volume scanning electron microscopy approach to 3D reconstruct the cellular relationships formed by leukocytes recruited to the luminal uterine epithelium 12 h post-mating in the rat. We report that following mating, neutrophils and macrophages are internalised by the luminal uterine epithelium, with multiple leukocytes internalised via contortion through a small tunnel in the apical membrane into a large membrane-bound vacuole within the cytoplasm of luminal uterine epithelial cells (UECs). Once internalised within the UECs, recruited leukocytes appear to phagocytose material within the membrane-bound vacuole and most ultimately undergo a specialised cell death, including vacuolisation and loss of membrane integrity. As these observations involve ultrastructurally normal leukocytic cells internalised within non-phagocytic epithelial cells, these observations are consistent with the formation of cell-in-cell structures via entosis, rather than phagocytic engulfment by UECs. Although cell-in-cell structures have been reported in normal and pathological conditions elsewhere, the data collected herein represents the first evidence of the formation of cell-in-cell structures within the uterine epithelium as a novel component of the maternal inflammatory response to mating.

Passing the Vascular Barrier: Endothelial Signaling Processes Controlling Extravasation

A central function of the vascular endothelium is to serve as a barrier between the blood and the surrounding tissue of the body. At the same time, solutes and cells have to pass the endothelium to leave or to enter the bloodstream to maintain homeostasis. Under pathological conditions, for example, inflammation, permeability for fluid and cells is largely increased in the affected area, thereby facilitating host defense. To appropriately function as a regulated permeability filter, the endothelium uses various mechanisms to allow solutes and cells to pass the endothelial layer. These include transcellular and paracellular pathways of which the latter requires remodeling of intercellular junctions for its regulation. This review provides an overview on endothelial barrier regulation and focuses on the endothelial signaling mechanisms controlling the opening and closing of paracellular pathways for solutes and cells such as leukocytes and metastasizing tumor cells.

VE-PTP stabilizes VE-cadherin junctions and the endothelial barrier via a phosphatase-independent mechanism

Juettner et al. describe a novel phosphatase-activity–independent mechanism by which the phosphatase VE-PTP restricts endothelial permeability. VE-PTP functions as a scaffold that binds and inhibits the RhoGEF GEF-H1, limiting RhoA-dependent tension across VE-cadherin junctions and decreasing VE-cadherin internalization to stabilize adherens junctions and reduce endothelial permeability.

Vascular endothelial (VE) protein tyrosine phosphatase (PTP) is an endothelial-specific phosphatase that stabilizes VE-cadherin junctions. Although studies have focused on the role of VE-PTP in dephosphorylating VE-cadherin in the activated endothelium, little is known of VE-PTP’s role in the quiescent endothelial monolayer. Here, we used the photoconvertible fluorescent protein VE-cadherin-Dendra2 to monitor VE-cadherin dynamics at adherens junctions (AJs) in confluent endothelial monolayers. We discovered that VE-PTP stabilizes VE-cadherin junctions by reducing the rate of VE-cadherin internalization independently of its phosphatase activity. VE-PTP serves as an adaptor protein that through binding and inhibiting the RhoGEF GEF-H1 modulates RhoA activity and tension across VE-cadherin junctions. Overexpression of the VE-PTP cytosolic domain mutant interacting with GEF-H1 in VE-PTP–depleted endothelial cells reduced GEF-H1 activity and restored VE-cadherin dynamics at AJs. Thus, VE-PTP stabilizes VE-cadherin junctions and restricts endothelial permeability by inhibiting GEF-H1, thereby limiting RhoA signaling at AJs and reducing the VE-cadherin internalization rate.

The Neutrophil’s Role During Health and Disease

Neutrophils have always been considered as uncomplicated front-line troopers of the innate immune system equipped with limited proinflammatory duties. Yet recently, the role of the neutrophil has been undergoing a rejuvenation of sorts. Neutrophils are now considered complex cells capable of a significant array of specialized functions, and as an effector of the innate immune response, they are able to regulate many processes such as acute injury and repair, cancer, autoimmunity, and chronic inflammatory processes. Furthermore, evidence exists to indicate that neutrophils also contribute to adaptive immunity by aiding the development of specific adaptive immune responses or guiding the subsequent adaptive immune response. With this revived interest in neutrophils and their many novel functions, it is prudent to review what is currently known about neutrophils and, even more importantly, understand what information is lacking. We discuss the essential features of the neutrophil, from its origins, lifespan, subsets, margination and sequestration of the neutrophil to the death of the neutrophil. We highlight neutrophil recruitment to both infected and injured tissues and outline differences in recruitment of neutrophils between different tissues. Finally, we examine how neutrophils use different mechanisms to either bolster protective immune responses or negatively cause pathological outcomes at different locations.

Neutrophil transendothelial migration: updates and new perspectives

Neutrophils represent the first line of cellular defense against invading microorganism by rapidly moving across the blood-endothelial cell (EC) barrier and exerting effector cell functions. The neutrophil recruitment cascade to inflamed tissues involves elements of neutrophil rolling, firm adhesion, and crawling onto the EC surface before extravasating by breaching the EC barrier. The interaction between neutrophils and ECs occurs via various adhesive modules and is a critical event determining the mode of neutrophil transmigration, either at the EC junction (paracellular) or directly through the EC body (transcellular). Once thought to be a homogenous entity, new evidence clearly points to the plasticity of neutrophil functions. This review will focus on recent advances in our understanding of the mechanism of the neutrophil transmigration process. It will discuss how neutrophil-EC interactions and the subsequent mode of diapedesis, junctional or nonjunctional, can be context dependent and how this plasticity may be exploited clinically.

Neoadjuvant Chemotherapy Based on Abraxane/Human Neutrophils Cytopharmaceuticals with Radiotherapy for Gastric Cancer

Gastric cancer remains one of the most lethal cancers with high incidence and mortality worldwide. The majority of gastric cancer patients are those who have first been diagnosed in advanced stage, in which the standard chemo-radiotherapy produces limited benefit along with severe general toxicity, thus the demand for improved therapeutic efficacy and decreased side effects drives the development of novel therapeutic strategies. Here, a neoadjuvant chemotherapy based on Abraxane/human neutrophils (NEs) cytopharmaceuticals with radiotherapy is presented for effective cancer treatment. Human NEs, the most abundant white blood cells in peripheral blood, are developed to carry Abraxane, the commercial albumin-bound paclitaxel nanoparticle, to form cytopharmaceuticals (Abraxane/NEs) which have been confirmed to maintain the intrinsic functions of human NEs. The modest radiation is applied not only to exert tumor disruption, but also to increase the release of inflammatory factors which guide the NEs homing to the tumoral sites. These amplified inflammatory factors at tumor sites excessively activate Abraxane/NEs to form neutrophil extracellular traps, along with a burst release of Abraxane to induce superior tumor suppression. This adjuvant chemo-radiotherapy based on cytopharmaceuticals may provide new opportunities for advanced cancer treatment, which reveals the huge clinical potential of human neutrophils as drug delivery vectors.

The Neutrophil Nucleus: An Important Influence on Neutrophil Migration and Function

Neutrophil nuclear morphology has historically been used in haematology for neutrophil identification and characterisation, but its exact role in neutrophil function has remained enigmatic. During maturation, segmentation of the neutrophil nucleus into its mature, multi-lobulated shape is accompanied by distinct changes in nuclear envelope composition, resulting in a unique nucleus that is believed to be imbued with extraordinary nuclear flexibility. As a rate-limiting factor for cell migration, nuclear morphology and biomechanics are particularly important in the context of neutrophil migration during immune responses. Being an extremely plastic and fast migrating cell type, it is to be expected that neutrophils have an especially deformable nucleus. However, many questions still surround the dynamic capacities of the neutrophil nucleus, and which nuclear and cytoskeletal elements determine these dynamics. The biomechanics of the neutrophil nucleus should also be considered for their influences on the production of neutrophil extracellular traps (NETs), given this process sees the release of chromatin "nets" from nucleoplasm to extracellular space. Although past studies have investigated neutrophil nuclear composition and shape, in a new era of more sophisticated biomechanical and genetic techniques, 3D migration studies, and higher resolution microscopy we now have the ability to further investigate and understand neutrophil nuclear plasticity at an unprecedented level. This review addresses what is currently understood about neutrophil nuclear structure and its role in migration and the release of NETs, whilst highlighting open questions surrounding neutrophil nuclear dynamics.

Migration through a small pore disrupts inactive chromatin organization in neutrophil-like cells

BACKGROUND

Mammalian cells are flexible and can rapidly change shape when they contract, adhere, or migrate. The nucleus must be stiff enough to withstand cytoskeletal forces, but flexible enough to remodel as the cell changes shape. This is particularly important for cells migrating through confined spaces, where the nuclear shape must change in order to fit through a constriction. This occurs many times in the life cycle of a neutrophil, which must protect its chromatin from damage and disruption associated with migration. Here we characterized the effects of constricted migration in neutrophil-like cells.

RESULTS

Total RNA sequencing identified that migration of neutrophil-like cells through 5- or 14-μm pores was associated with changes in the transcript levels of inflammation and chemotaxis-related genes when compared to unmigrated cells. Differentially expressed transcripts specific to migration with constriction were enriched for groups of genes associated with cytoskeletal remodeling. Hi-C was used to capture the genome organization in control and migrated cells. Limited switching was observed between the active (A) and inactive (B) compartments after migration. However, global depletion of short-range contacts was observed following migration with constriction compared to migration without constriction. Regions with disrupted contacts, TADs, and compartments were enriched for inactive chromatin.

CONCLUSION

Short-range genome organization is preferentially altered in inactive chromatin, possibly protecting transcriptionally active contacts from the disruptive effects of migration with constriction. This is consistent with current hypotheses implicating heterochromatin as the mechanoresponsive form of chromatin. Further investigation concerning the contribution of heterochromatin to stiffness, flexibility, and protection of nuclear function will be important for understanding cell migration in relation to human health and disease.

[Viewing sepsis and autoimmune disease in relation with infection and NETs-formation]

Neutrophil has been widely recognized as body's first line of defence against pathogens. NETosis was first reported in 2004 as a programmed cell death of neutrophil and distinguished from apoptosis and necrosis. This phenomenon has been already observed in both basic and clinical research. NETosis is induced by various stimulants such as PMA, IL-8, DAMPs/PAMPs, bacteria, and antigen-antibody complex including self-antibody such as ANCA. It is known that there are two types of NETosis following bacterial infections. Although both of them have the ability to capture and kill bacteria, they also damage the host tissues. The inhibition of the NETs-related enzymes prevents the NETs formation at that time. The production of O₂^- from respiratory burst of neutrophils triggers NETs formation. In the first type of NETosis, neutrophils are completely collapsed, while in the second type, they maintain the morphology and the ability of phagocytosis. However, bacteria can escape from NETs by degrading NETs with their secreting nucleases. Thus the animal models of infection, using these bacteria, oftentimes suffer from severe infectious diseases. Human CGD (Chronic Granulomatosis Disease) patients who do not have Nox2 are immunocompromised, and highly susceptible to infection due to the defect of NETs formation. On the other hand, SLE patients are unable to break down the NETs as their serum inhibits the DNase1 activity, which results in autoantibody generation against NETs as well as self-DNA. It is getting clear that there is a relationship between inflammatory diseases, including infectious diseases, Sepsis and autoimmune diseases, and NETs. Therefore, it is important to re-evaluate the inflammatory disorders from NETs' perspective, and to incorporate the emerging concepts for better understanding the mechanisms involved.

Sensing of Vascular Permeability in Inflamed Vessel of Live Animal

Increase in vascular permeability is a conclusive response in the progress of inflammation. Under controlled conditions, leukocytes are known to migrate across the vascular barriers to the sites of inflammation without severe vascular rupture. However, when inflammatory state becomes excessive, the leakage of blood components may occur and can be lethal. Basically, vascular permeability can be analyzed based on the intensity of blood outflow. To evaluate the amount and rate of leakage in live mice, we performed cremaster muscle exteriorization to visualize blood flow and neutrophil migration. Using two-photon intravital microscopy of the exteriorized cremaster muscle venules, we found that vascular barrier function is transiently and locally disrupted in the early stage of inflammatory condition induced by N-formylmethionyl-leucyl-phenylalanine (fMLP). Measurement of the concentration of intravenously (i.v.) injected Texas Red dextran inside and outside the vessels resulted in clear visualization of real-time increases in transient and local vascular permeability increase in real-time manner. We successfully demonstrated repeated leakage from a target site on a blood vessel in association with increasing severity of inflammation. Therefore, compared to other methods, two-photon intravital microscopy more accurately visualizes and quantifies vascular permeability even in a small part of blood vessels in live animals in real time.

PKD regulates actin polymerization, neutrophil deformability, and transendothelial migration in response to fMLP and trauma

Neutrophils are important mediators of the innate immune defense and of the host response to a physical trauma. Because aberrant infiltration of injured sites by neutrophils was shown to cause adverse effects after trauma, we investigated how neutrophil infiltration could be modulated at the cellular level. Our data indicate that protein kinase D (PKD) is a vital regulator of neutrophil transmigration. PKD phosphorylates the Cofilin-phosphatase Slingshot-2L (SSH-2L). SSH-2L in turn dynamically regulates Cofilin activity and actin polymerization in response to a chemotactic stimulus for neutrophils, for example, fMLP. Here, we show that inhibition of PKD by two specific small molecule inhibitors results in broad, unrestricted activation of Cofilin and strongly increases the F-actin content of neutrophils even under basal conditions. This phenotype correlates with a significantly impaired neutrophil deformability as determined by optical stretcher analysis. Consequently, inhibition of PKD impaired chemotaxis as shown by reduced extravasation of neutrophils. Consequently, we demonstrate that transendothelial passage of both, neutrophil-like NB4 cells and primary PMNs recovered from a hemorrhagic shock trauma model was significantly reduced. Thus, inhibition of PKD may represent a promising modulator of the neutrophil response to trauma.

The role of kindlin in neutrophil recruitment to inflammatory sites

PURPOSE OF REVIEW

Since the discovery of the lack of kindlin-3 expression as the reason for the immunopathology leukocyte adhesion deficiency III syndrome, the role of kindlin-3 in inflammatory processes was investigated in a numerous studies. This review gives an overview about recent findings regarding the role of kindlin-3 in neutrophil activation and recruitment.

RECENT FINDINGS

Kindlin-3, together with talin-1, contributes essentially to the activation of β2-integrins in neutrophils. During inside-out signaling, kindlin-3 binds to the β-cytoplasmic integrin tail and is indispensable for the integrin conformational shift into the high-affinity ligand binding conformation, but not for the intermediate (extended) conformation. During outside-in signaling (as a consequence of integrin ligand binding) kindlin-3 interacts with distinct signaling molecules and is required for cell-autonomous functions like migration and spreading.

SUMMARY

Leukocyte adhesion deficiency III syndrome, which is caused by absence of kindlin-3, is a rarely occurring disease. However, the investigation of the clinical symptoms as well as the underlying molecular mechanisms gave rise to a huge amount of new insights into the processes of integrin activation in neutrophils and the consequences of defects in these processes.

Transendothelial migration: unifying principles from the endothelial perspective

Transendothelial migration (TEM) of polymorphonuclear leukocytes (PMN) involves a carefully orchestrated dialog of adhesion and signaling events between leukocyte and endothelial cell. This article focuses on the contribution of endothelial cells to transmigration. The initiation of TEM itself generally requires interaction of PECAM on the leukocyte with PECAM at the endothelial cell border. This is responsible for the transient elevation of cytosolic-free calcium ions in endothelium that is required for TEM and for recruitment of membrane from the lateral border recycling compartment (LBRC). TEM requires LBRC to move to the site at which TEM will take place and for VE-cadherin to move away. Targeting of the LBRC to this site likely precedes movement of VE-cadherin and may play a role in clearing VE-cadherin from the site of TEM. The process of TEM can be dissected into steps mediated by distinct pairs of PMN/endothelial interacting molecules. CD99 regulates a step at or close to the end of TEM. CD99 signals through soluble adenylyl cyclase to activate PKA to trigger ongoing targeted recycling of the LBRC. Paracellular transmigration predominates (≥90% of events) in the cremaster muscle circulation, but transcellular migration may be more important at sites such as the blood-brain barrier. Both processes involve many of the same molecules and recruitment of the LBRC.

Intravital Imaging of Myeloid Cells: Inflammatory Migration and Resident Patrolling

Myeloid cell recruitment to sites of infection and injury started out as a simple model that has been referred to as the universal concept of leukocyte recruitment. However, as we gain more insight into the different mechanisms, it is becoming clear that each organ and perhaps even each cell has its own unique mechanism of recruitment. Moreover, as the ability to visualize specific cell types in specific organs becomes more accessible, it is also becoming clear that there are resident populations of leukocytes, some within the tissues and others attached to the vasculature of tissues, the latter poised to affect the local environment. In this review, we will first highlight the imaging approaches that have allowed us to gain spectacular insight into locale and function of specific cell types, and then we will discuss what we have learned from this approach as far as myeloid cells are concerned. We will also highlight some of the gaps in our knowledge, which exist almost certainly because of the challenges of being able to visualize certain compartments of the body.

Novel Insights into the Mechanisms of Gut Homing and Antiadhesion Therapies in Inflammatory Bowel Diseases

Therapeutic compounds interfering with T cell trafficking are a new column of inflammatory bowel disease (IBD) treatment. Currently, the anti-α4β7 integrin antibody vedolizumab is successfully used in the clinic and further drugs are likely to follow. Despite these clinical advances, the precise mechanistic background of their action is only gradually elucidated and still a matter of intensive research. Only recently, advances made with the help of new in vivo models and human studies have contributed to shape our concept of T cell trafficking in IBD by deciphering some important and so far unanswered questions. At the same time, basic and clinical data have generated new issues to be addressed on the way toward a clear perception of trafficking mechanisms and toward elucidation of the action of compounds interfering with this process. In this review, we will give a comprehensive outline of all components of T cell trafficking in regard to IBD before discussing the current knowledge concerning targeted interference with integrins in this complex network. Moreover, we will summarize remaining ambiguity and give an outlook on potential future targets.

Involvement of CX3CL1 in the Migration of Osteoclast Precursors Across Osteoblast Layer Stimulated by Interleukin-1ß

The trigger for bone remodeling is bone resorption by osteoclasts. Osteoclast differentiation only occurs on the old bone, which needs to be repaired under physiological conditions. However, uncontrolled bone resorption is often observed in pro-inflammatory bone diseases, such as rheumatoid arthritis. Mature osteoclasts are multinuclear cells that differentiate from monocyte/macrophage lineage cells by cell fusion. Although Osteoclast precursors should migrate across osteoblast layer to reach bone matrix before maturation, the underlying mechanisms have not yet been elucidated in detail. We herein found that osteoclast precursors utilize two routes to migrate across osteoblast layer by confocal- and electro-microscopic observations. The osteoclast supporting activity of osteoblasts inversely correlated with osteoblast density and was positively related to the number of osteoclast precursors under the osteoblast layer. Osteoclast differentiation was induced by IL-1ß, but not by PGE₂ in high-density osteoblasts. Osteoblasts and osteoclast precursors expressed CX3CL1 and CX3CR1, respectively, and the expression of CX3CL1 increased in response to interleukin-1ß. An anti-CX3CL1-neutralizing antibody inhibited the migration of osteoclast precursors and osteoclast differentiation. These results strongly suggest the involvement of CX3CL1 in the migration of osteoclast precursors and osteoclastogenesis, and will contribute to the development of new therapies for bone diseases. J. Cell. Physiol. 232: 1739-1745, 2017. © 2016 Wiley Periodicals, Inc.

The evidence for and against different modes of tumour cell extravasation in the lung: diapedesis, capillary destruction, necroptosis, and endothelialization

The development of lung metastasis is a significant negative prognostic factor for cancer patients. The extravasation phase of lung metastasis involves interactions of tumour cells with the pulmonary endothelium. These interactions may have broad biological and medical significance, with potential clinical implications ranging from the discovery of lung metastasis biomarkers to the identification of targets for intervention in preventing lung metastases. Because of the potential significance, the mechanisms of tumour cell extravasation require cautious, systematic studies. Here, we discuss the literature pertaining to the proposed mechanisms of extravasation and critically compare a recently proposed mechanism (tumour cell-induced endothelial necroptosis) with the already described extravasation mechanisms in the lung. We also provide novel data that may help to explain the underlying physiological basis for endothelialization as a mechanism of tumour cell extravasation in the lung. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

How leukocytes trigger opening and sealing of gaps in the endothelial barrier

The entry of leukocytes into tissues requires well-coordinated interactions between the immune cells and endothelial cells which form the inner lining of blood vessels. The molecular basis for recognition, capture, and adhesion of leukocytes to the endothelial apical surface is well studied. This review will focus on recent advances in our understanding of events following the firm interaction of leukocytes with the inner surface of the blood vessel wall. We will discuss how leukocytes initiate the transmigration (diapedesis) process, trigger the opening of gaps in the endothelial barrier, and eventually move through this boundary.

Leukocyte transendothelial migration: A local affair

Inflammation is part of the complex biological response of body tissues to harmful stimuli, such as pathogens. It serves as a protective response that involves leukocytes, blood vessels and molecular mediators with the purpose to eliminate the initial cause of cell injury and to initiate tissue repair. Inflammation is tightly regulated by the body and is associated with transient crossing of leukocytes through the blood vessel wall, a process called transendothelial migration (TEM) or diapedesis. TEM is a close collaboration between leukocytes on one hand and the endothelium on the other. Limiting vascular leakage during TEM but also when the leukocyte has crossed the endothelium is essential for maintaining vascular homeostasis. Although many details have been uncovered during the recent years, the molecular mechanisms from the vascular part that drive TEM still shows significant gaps in our understanding. This review will focus on the local signals that are induced in the endothelium that regulate leukocyte TEM and simultaneous preservation of endothelial barrier function.

Migration in Confined 3D Environments Is Determined by a Combination of Adhesiveness, Nuclear Volume, Contractility, and Cell Stiffness

In cancer metastasis and other physiological processes, cells migrate through the three-dimensional (3D) extracellular matrix of connective tissue and must overcome the steric hindrance posed by pores that are smaller than the cells. It is currently assumed that low cell stiffness promotes cell migration through confined spaces, but other factors such as adhesion and traction forces may be equally important. To study 3D migration under confinement in a stiff (1.77 MPa) environment, we use soft lithography to fabricate polydimethylsiloxane (PDMS) devices consisting of linear channel segments with 20 μm length, 3.7 μm height, and a decreasing width from 11.2 to 1.7 μm. To study 3D migration in a soft (550 Pa) environment, we use self-assembled collagen networks with an average pore size of 3 μm. We then measure the ability of four different cancer cell lines to migrate through these 3D matrices, and correlate the results with cell physical properties including contractility, adhesiveness, cell stiffness, and nuclear volume. Furthermore, we alter cell adhesion by coating the channel walls with different amounts of adhesion proteins, and we increase cell stiffness by overexpression of the nuclear envelope protein lamin A. Although all cell lines are able to migrate through the smallest 1.7 μm channels, we find significant differences in the migration velocity. Cell migration is impeded in cell lines with larger nuclei, lower adhesiveness, and to a lesser degree also in cells with lower contractility and higher stiffness. Our data show that the ability to overcome the steric hindrance of the matrix cannot be attributed to a single cell property but instead arises from a combination of adhesiveness, nuclear volume, contractility, and cell stiffness.

N-acetylgalactosamine glycans function in cancer cell adhesion to endothelial cells: A role for truncated O-glycans in metastatic mechanisms

Failure in O-glycan chain extension exposing Tn antigen (GalNAc-O-Ser/Thr) is clinically associated with cancer metastasis. This study provides evidence of a functional role for aberrant GalNAc-glycans in cancer cell capture from blood flow and/or adhesion to endothelium. Adhesion of breast cancer cells to human umbilical vein endothelial cell monolayers was modelled under sweeping flow. Adhesion of metastatic, GalNAc glycan-rich, MCF7 and ZR 75 1 cells to endothelium increased over timepoints up to 1.5 hour, after which it plateaued. Adhesion was significantly inhibited (p < 0.001) when cell surface GalNAc-glycans were masked, an effect not seen in GalNAc glycan-poor, non-metastatic BT 474 cells. Masking irrelevant galactose- and mannose-glycans had no inhibitory effect. Imaging of cells post-adhesion over a 24 hour time course using confocal and scanning electron microscopy revealed that up to 6 hours post-adhesion, motile, rounded cancer cells featuring lamellipodia-like processes crawled on an intact endothelial monolayer. From 6-12 hours post-adhesion, cancer cells became stationary, adopted a smooth, circular flattened morphology, and endothelial cells retracted from around them leaving cleared zones in which the cancer cells proceeded to form colonies through cell division.

Adhesion Molecules: Master Controllers of the Circulatory System

This manuscript will review our current understanding of cellular adhesion molecules (CAMs) relevant to the circulatory system, their physiological role in control of vascular homeostasis, innate and adaptive immune responses, and their importance in pathophysiological (disease) processes such as acute lung injury, atherosclerosis, and pulmonary hypertension. This is a complex and rapidly changing area of research that is incompletely understood. By design, we will begin with a brief overview of the structure and classification of the major groups of adhesion molecules and their physiological functions including cellular adhesion and signaling. The role of specific CAMs in the process of platelet aggregation and hemostasis and leukocyte adhesion and transendothelial migration will be reviewed as examples of the complex and cooperative interplay between CAMs during physiological and pathophysiological processes. The role of the endothelial glycocalyx and the glycobiology of this complex system related to inflammatory states such as sepsis will be reviewed. We will then focus on the role of adhesion molecules in the pathogenesis of specific disease processes involving the lungs and cardiovascular system. The potential of targeting adhesion molecules in the treatment of immune and inflammatory diseases will be highlighted in the relevant sections throughout the manuscript.

Leukocytes Crossing the Endothelium: A Matter of Communication

Leukocytes cross the endothelial vessel wall in a process called transendothelial migration (TEM). The purpose of leukocyte TEM is to clear the causing agents of inflammation in underlying tissues, for example, bacteria and viruses. During TEM, endothelial cells initiate signals that attract and guide leukocytes to sites of tissue damage. Leukocytes react by attaching to these sites and signal their readiness to move back to endothelial cells. Endothelial cells in turn respond by facilitating the passage of leukocytes while retaining overall integrity. In this review, we present recent findings in the field and we have endeavored to synthesize a coherent picture of the intricate interplay between endothelial cells and leukocytes during TEM.

Crossing the Vascular Wall: Common and Unique Mechanisms Exploited by Different Leukocyte Subsets during Extravasation

Leukocyte extravasation is one of the essential and first steps during the initiation of inflammation. Therefore, a better understanding of the key molecules that regulate this process may help to develop novel therapeutics for treatment of inflammation-based diseases such as atherosclerosis or rheumatoid arthritis. The endothelial adhesion molecules ICAM-1 and VCAM-1 are known as the central mediators of leukocyte adhesion to and transmigration across the endothelium. Engagement of these molecules by their leukocyte integrin receptors initiates the activation of several signaling pathways within both leukocytes and endothelium. Several of such events have been described to occur during transendothelial migration of all leukocyte subsets, whereas other mechanisms are known only for a single leukocyte subset. Here, we summarize current knowledge on regulatory mechanisms of leukocyte extravasation from a leukocyte and endothelial point of view, respectively. Specifically, we will focus on highlighting common and unique mechanisms that specific leukocyte subsets exploit to succeed in crossing endothelial monolayers.

How leukocytes cross the vascular endothelium

Immune responses depend on the ability of leukocytes to move from the circulation into tissue. This is enabled by mechanisms that guide leukocytes to the right exit sites and allow them to cross the barrier of the blood vessel wall. This process is regulated by a concerted action between endothelial cells and leukocytes, whereby endothelial cells activate leukocytes and direct them to extravasation sites, and leukocytes in turn instruct endothelial cells to open a path for transmigration. This Review focuses on recently described mechanisms that control and open exit routes for leukocytes through the endothelial barrier.

Mechanism of Diapedesis: Importance of the Transcellular Route

The neutrophil transmigration across the blood endothelial cell barrier represents the prerequisite step of innate inflammation. Neutrophil recruitment to inflamed tissues occurs in a well-defined stepwise manner, which includes elements of neutrophil rolling, firm adhesion, and crawling onto the endothelial cell surface before transmigrating across the endothelial barrier. This latter step known as diapedesis can occur at the endothelial cell junction (paracellular) or directly through the endothelial cell body (transcellular). The extravasation cascade is controlled by series of engagement of various adhesive modules, which result in activation of bidirectional signals to neutrophils and endothelial cells for adequate cellular response. This review will focus on recent advances in our understanding of mechanism of leukocyte crawling and diapedesis, with an emphasis on leukocyte-endothelial interactions and the signaling pathways they transduce to determine the mode of diapedesis, junctional or nonjunctional. I will also discuss emerging evidence highlighting key differences in the two modes of diapedesis and why it is clinically important to understand specificity in the regulation of diapedesis.

Glial influences on BBB functions and molecular players in immune cell trafficking

The blood-brain barrier (BBB) constitutes an elaborate structure formed by specialized capillary endothelial cells, which together with pericytes and perivascular glial cells regulates the exchanges between the central nervous system (CNS) and the periphery. Intricate interactions between the different cellular constituents of the BBB are crucial in establishing a functional BBB and maintaining the delicate homeostasis of the CNS microenvironment. In this review, we discuss the role of astrocytes and microglia in inducing and maintaining barrier properties under physiological conditions as well as their involvement during neuroinflammatory pathologies. This article is part of a Special Issue entitled: Neuro Inflammation edited by Helga E. de Vries and Markus Schwaninger.

Tumors: wounds that do not heal-redux

Similarities between tumors and the inflammatory response associated with wound healing have been recognized for more than 150 years and continue to intrigue. Some years ago, based on our then recent discovery of vascular permeability factor (VPF)/VEGF, I suggested that tumors behaved as wounds that do not heal. More particularly, I proposed that tumors co-opted the wound-healing response to induce the stroma they required for maintenance and growth. Work over the past few decades has supported this hypothesis and has put it on a firmer molecular basis. In outline, VPF/VEGF initiates a sequence of events in both tumors and wounds that includes the following: increased vascular permeability; extravasation of plasma, fibrinogen and other plasma proteins; activation of the clotting system outside the vascular system; deposition of an extravascular fibrin gel that serves as a provisional stroma and a favorable matrix for cell migration; induction of angiogenesis and arterio-venogenesis; subsequent degradation of fibrin and its replacement by "granulation tissue" (highly vascular connective tissue); and, finally, vascular resorption and collagen synthesis, resulting in the formation of dense fibrous connective tissue (called "scar tissue" in wounds and "desmoplasia" in cancer). A similar sequence of events also takes place in a variety of important inflammatory diseases that involve cellular immunity.

TLR2 and TLR9 contribute to alcohol-mediated liver injury through induction of CXCL1 and neutrophil infiltration

Although previous studies reported the involvement of the TLR4-TRIF pathway in alcohol-induced liver injury, the role of TLR2 and TLR9 signaling in alcohol-mediated neutrophil infiltration and liver injury has not been elucidated. Since alcohol binge drinking is recognized to induce more severe form of alcohol liver disease, we used a chronic-binge ethanol-feeding model as a mouse model for early stage of alcoholic hepatitis. Whereas a chronic-binge ethanol feeding induced alcohol-mediated liver injury in wild-type mice, TLR2- and TLR9-deficient mice showed reduced liver injury. Induction of neutrophil-recruiting chemokines, including Cxcl1, Cxcl2, and Cxcl5, and hepatic neutrophil infiltration were increased in wild-type mice, but not in TLR2- and TLR9-deficient mice. In vivo depletion of Kupffer cells (KCs) by liposomal clodronate reduced liver injury and the expression of Il1b, but not Cxcl1, Cxcl2, and Cxcl5, suggesting that KCs are partly associated with liver injury, but not neutrophil recruitment, in a chronic-binge ethanol-feeding model. Notably, hepatocytes and hepatic stellate cells (HSCs) produce high amounts of CXCL1 in ethanol-treated mice. The treatment with TLR2 and TLR9 ligands synergistically upregulated CXCL1 expression in hepatocytes. Moreover, the inhibitors for CXCR2, a receptor for CXCL1, and MyD88 suppressed neutrophil infiltration and liver injury induced by chronic-binge ethanol treatment. Consistent with the above findings, hepatic CXCL1 expression was highly upregulated in patients with alcoholic hepatitis. In a chronic-binge ethanol-feeding model, the TLR2 and TLR9-dependent MyD88-dependent pathway mediates CXCL1 production in hepatocytes and HSCs; the CXCL1 then promotes neutrophil infiltration into the liver via CXCR2, resulting in the development of alcohol-mediated liver injury.

Leukocyte transcellular diapedesis: Rap1b is in control

The neutrophil transmigration across the blood endothelial cell barrier represents the prerequisite step of innate inflammation. It is well known that neutrophils cross the endothelial barrier by transmigrating at the endothelial cell junction ('paracellular'). However, in vivo and in vitro evidence have clearly demonstrated occurrence of an alternate mode of migration directly through the endothelial cell body ('transcellular'). Despite our knowledge on mechanisms of transendothelial migration, it remains unclear which factors determine distinct modes of migration. We recently found that the Ras-like Rap1b GTPase limits neutrophil transcellular migration. Rap1b restrains transcellular migration by suppressing Akt-driven invasive protrusions while leaving the paracellular route unaffected. Furthermore, Rap1b limits neutrophil tissue infiltration in mice and prevents hyper susceptibility to endotoxin shock. These findings uncover a novel role for Rap1b in neutrophil migration and inflammation. Importantly, they offer emerging evidences that paracellular and transcellular migration of neutrophils are regulated by separate mechanisms. Here, we discuss the mechanisms of neutrophil transmigration and their clinical importance for vascular integrity and innate inflammation.

Intercellular adhesion molecule-1 expression in the hippocampal CA1 region of hyperlipidemic rats with chronic cerebral ischemia

Chronic cerebral ischemia is a pathological process in many cerebrovascular diseases and it is induced by long-term hyperlipidemia, hypertension and diabetes mellitus. After being fed a high-fat diet for 4 weeks, rats were subjected to permanent occlusion of bilateral common carotid arteries to establish rat models of chronic cerebral ischemia with hyperlipidemia. Intercellular adhesion molecule-1 expression in rat hippocampal CA1 region was determined to better understand the mechanism underlying the effects of hyperlipidemia on chronic cerebral ischemia. Water maze test results showed that the cognitive function of rats with hyperlipidemia or chronic cerebral ischemia, particularly in rats with hyperlipidemia combined with chronic cerebral ischemia, gradually decreased between 1 and 4 months after occlusion of the bilateral common carotid arteries. This correlated with pathological changes in the hippocampal CA1 region as detected by hematoxylin-eosin staining. Immunohistochemical staining showed that intercellular adhesion molecule-1 expression in the hippocampal CA1 region was noticeably increased in rats with hyperlipidemia or chronic cerebral ischemia, in particular in rats with hyperlipidemia combined with chronic cerebral ischemia. These findings suggest that hyperlipidemia aggravates chronic cerebral ischemia-induced neurological damage and cognitive impairment in the rat hippocampal CA1 region, which may be mediated, at least in part, by up-regulated expression of intercellular adhesion molecule-1.

Neutrophil migration under normal and sepsis conditions

Neutrophil migration is critical for pathogen clearance and host survival during severe sepsis. Interaction of neutrophil adhesion receptors with ligands on endothelial cells results in firm adhesion of the circulating neutrophils, followed by neutrophil activation and directed migration to sites of infection through the basement membrane and interstitial extracellular matrix. Proteolytic enzymes and reactive oxygen species are produced and released by neutrophils in response to a variety of inflammatory stimuli. Although these mediators are important for host defense, they also promote tissue damage. Excessive neutrophil migration during the early stages of sepsis may lead to an exaggerated inflammatory response with associated tissue damage and subsequent organ dysfunction. On the other hand, dysregulation of migration and insufficient migratory response that occurs during the latter stages of severe sepsis contributes to neutrophils' inability to contain and control infection and impaired wound healing. This review discusses the major steps and associated molecules involved in the balance of neutrophil trafficking, the precise regulation of which during sepsis spells life or death for the host.

Simple microfluidic device for studying chemotaxis in response to dual gradients

Chemotaxis is a fundamental biological process where complex chemotactic gradients are integrated and prioritized to guide cell migration toward specific locations. To understand the mechanisms of gradient dependent cell migration, it is important to develop in vitro models that recapitulate key attributes of the chemotactic cues present in vivo. Current in vitro tools for studying cell migration are not amenable to easily study the response of neutrophils to dual gradients. Many of these systems require external pumps and complex setups to establish and maintain the gradients. Here we report a simple yet innovative microfluidic device for studying cell migration in the presence of dual chemotactic gradients through a 3-dimensional substrate. The device is tested and validated by studying the migration of the neutrophil-like cell line PLB-985 to gradients of fMLP. Furthermore, the device is expanded and used with heparinised whole blood, whereupon neutrophils were observed to migrate from whole blood towards gradients of fMLP eliminating the need for any neutrophil purification or capture steps.