Posterolateral approach for open reduction and internal fixation of trimalleolar ankle fractures

ICAMs in Immunity, Intercellular Adhesion and Communication

Interactions among leukocytes and leukocytes with immune-associated auxiliary cells represent an essential feature of the immune response that requires the involvement of cell adhesion molecules (CAMs). In the immune system, CAMs include a wide range of members pertaining to different structural and functional families involved in cell development, activation, differentiation and migration. Among them, β2 integrins (LFA-1, Mac-1, p150,95 and αDβ2) are predominantly involved in homotypic and heterotypic leukocyte adhesion. β2 integrins bind to intercellular (I)CAMs, actin cytoskeleton-linked receptors belonging to immunoglobulin superfamily (IgSF)-CAMs expressed by leukocytes and vascular endothelial cells, enabling leukocyte activation and transendothelial migration. β2 integrins have long been viewed as the most important ICAMs partners, propagating intracellular signalling from β2 integrin-ICAM adhesion receptor interaction. In this review, we present previous evidence from pioneering studies and more recent findings supporting an important role for ICAMs in signal transduction. We also discuss the contribution of immune ICAMs (ICAM-1, -2, and -3) to reciprocal cell signalling and function in processes in which β2 integrins supposedly take the lead, paying particular attention to T cell activation, differentiation and migration.

Hemolymph exosomes inhibit Spiroplasma eriocheiris infection by promoting Tetraspanin-mediated hemocyte phagocytosis in crab

Exosomes released from infected cells are thought to play an important role in the dissemination of pathogens, as well as in host-derived immune molecules during infection. As an intracellular pathogen, Spiroplasma eriocheiris is harmful to multiple crustaceans. However, the immune mechanism of exosomes during Spiroplasma infection has not been investigated. Here, we found exosomes derived from S. eriocheiris-infected crabs could facilitate phagocytosis and apoptosis of hemocytes, resulting in increased crab survival and suppression of Spiroplasma intracellular replication. Proteomic analysis revealed the altered abundance of EsTetraspanin may confer resistance to S. eriocheiris, possibly by mediating hemocyte phagocytosis in Eriocheir sinensis. Specifically, knockdown of EsTetraspanin in E. sinensis increased susceptibility to S. eriocheiris infection and displayed compromised phagocytic ability, whereas overexpression of EsTetraspanin in Drosophila S2 cells inhibited S. eriocheiris infection. Further, it was confirmed that intramuscular injection of recombinant LEL domain of EsTetraspanin reduced the mortality of S. eriocheiris-infected crabs. Blockade with anti-EsTetraspanin serum could exacerbate S. eriocheiris invasion of hemocytes and impair hemocyte phagocytic activity. Taken together, our findings prove for the first time that exosomes modulate phagocytosis to resist pathogenic infection in invertebrates, which is proposed to be mediated by exosomal Tetraspanin, supporting the development of preventative strategies against Spiroplasma infection.

Lung single-cell RNA profiling reveals response of pulmonary capillary to sepsis-induced acute lung injury

Background

Sepsis-induced acute lung injury (ALI) poses a significant threat to human health. Endothelial cells, especially pulmonary capillaries, are the primary barriers against sepsis in the lungs. Therefore, investigating endothelial cell function is essential to understand the pathophysiological processes of sepsis-induced ALI.

Methods

We downloaded single-cell RNA-seq expression data from GEO with accession number GSE207651. The mice underwent cecal ligation and puncture (CLP) surgery, and lung tissue samples were collected at 0, 24, and 48 h. The cells were annotated using the CellMarker database and FindAllMarkers functions. GO enrichment analyses were performed using the Metascape software. Gene set enrichment Analysis (GSEA) and variation Analysis (GSVA) were performed to identify differential signaling pathways. Differential expression genes were collected with the "FindMarkers" function. The R package AUCell was used to score individual cells for pathway activities. The Cellchat package was used to explore intracellular communication.

Results

Granulocytes increased significantly as the duration of endotoxemia increased. However, the number of T cells, NK cells, and B cells declined. Pulmonary capillary cells were grouped into three sub-clusters. Capillary-3 cells were enriched in the sham group, but declined sharply in the CLP.24 group. Capillary-1 cells peaked in the CLP.24 group, while Capillary-2 cells were enriched in the CLP.48 group. Furthermore, we found that Cd74+ Capillary-3 cells mainly participated in immune interactions. Plat+ Capillary-1 and Clec1a+ Capillary-2 are involved in various physiological processes. Regarding cell-cell interactions, Plat+ Capillary-1 plays the most critical role in granulocyte adherence to capillaries during ALI. Cd74+ Capillary cells expressing high levels of major histocompatibility complex (MHC) and mainly interacted with Cd8a+ T cells in the sham group.

Conclusion

Plat+ capillaries are involved in the innate immune response through their interaction with neutrophils via ICAM-1 adhesion during endotoxemia, while Cd74+ capillaries epxressed high level of MHC proteins play a role in adaptive immune response through their interaction with T cells. However, it remains unclear whether the function of Cd74+ capillaries leans towards immunity or tolerance, and further studies are needed to confirm this.

Integrins and the Metastasis-like Dissemination of Acute Lymphoblastic Leukemia to the Central Nervous System

Acute lymphoblastic leukemia (ALL) disseminates with high prevalence to the central nervous system (CNS) in a process resembling aspects of the CNS surveillance of normal immune cells as well as aspects of brain metastasis from solid cancers. Importantly, inside the CNS, the ALL blasts are typically confined within the cerebrospinal fluid (CSF)-filled cavities of the subarachnoid space, which they use as a sanctuary protected from both chemotherapy and immune cells. At present, high cumulative doses of intrathecal chemotherapy are administered to patients, but this is associated with neurotoxicity and CNS relapse still occurs. Thus, it is imperative to identify markers and novel therapy targets specific to CNS ALL. Integrins represent a family of adhesion molecules involved in cell-cell and cell-matrix interactions, implicated in the adhesion and migration of metastatic cancer cells, normal immune cells, and leukemic blasts. The ability of integrins to also facilitate cell-adhesion mediated drug resistance, combined with recent discoveries of integrin-dependent routes of leukemic cells into the CNS, have sparked a renewed interest in integrins as markers and therapeutic targets in CNS leukemia. Here, we review the roles of integrins in CNS surveillance by normal lymphocytes, dissemination to the CNS by ALL cells, and brain metastasis from solid cancers. Furthermore, we discuss whether ALL dissemination to the CNS abides by known hallmarks of metastasis, and the potential roles of integrins in this context.

The Regulation of Neutrophil Migration in Patients with Sepsis: The Complexity of the Molecular Mechanisms and Their Modulation in Sepsis and the Heterogeneity of Sepsis Patients

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. Common causes include gram-negative and gram-positive bacteria as well as fungi. Neutrophils are among the first cells to arrive at an infection site where they function as important effector cells of the innate immune system and as regulators of the host immune response. The regulation of neutrophil migration is therefore important both for the infection-directed host response and for the development of organ dysfunctions in sepsis. Downregulation of CXCR4/CXCL12 stimulates neutrophil migration from the bone marrow. This is followed by transmigration/extravasation across the endothelial cell barrier at the infection site; this process is directed by adhesion molecules and various chemotactic gradients created by chemotactic cytokines, lipid mediators, bacterial peptides, and peptides from damaged cells. These mechanisms of neutrophil migration are modulated by sepsis, leading to reduced neutrophil migration and even reversed migration that contributes to distant organ failure. The sepsis-induced modulation seems to differ between neutrophil subsets. Furthermore, sepsis patients should be regarded as heterogeneous because neutrophil migration will possibly be further modulated by the infecting microorganisms, antimicrobial treatment, patient age/frailty/sex, other diseases (e.g., hematological malignancies and stem cell transplantation), and the metabolic status. The present review describes molecular mechanisms involved in the regulation of neutrophil migration; how these mechanisms are altered during sepsis; and how bacteria/fungi, antimicrobial treatment, and aging/frailty/comorbidity influence the regulation of neutrophil migration.

Phosphoproteomic mapping of CCR5 and ACKR2 signaling properties

ACKR2 is an atypical chemokine receptor which is structurally uncoupled from G proteins and is unable to activate signaling pathways used by conventional chemokine receptors to promote cell migration. Nonetheless, ACKR2 regulates inflammatory and immune responses by shaping chemokine gradients in tissues via scavenging inflammatory chemokines. To investigate the signaling pathways downstream to ACKR2, a quantitative SILAC-based phosphoproteomic analysis coupled with a systems biology approach with network analysis, was carried out on a HEK293 cell model expressing either ACKR2 or its conventional counterpart CCR5. The model was stimulated with the common agonist CCL3L1 for short (3 min) and long (30 min) durations. As expected, many of the identified proteins are known to participate in conventional signal transduction pathways and in the regulation of cytoskeleton dynamics. However, our analyses revealed unique phosphorylation and network signatures, suggesting roles for ACKR2 other than its scavenger activity. In conclusion, the mapping of phosphorylation events at a holistic level indicated that conventional and atypical chemokine receptors differ in signaling properties. This provides an unprecedented level of detail in chemokine receptor signaling and identifying potential targets for the regulation of ACKR2 and CCR5 function.

Ubiquitin-modified proteome analysis of Eriocheir sinensis hemocytes during Spiroplasma eriocheiris infection

Spiroplasma eriocheiris, the pathogen of Eriocheir sinensis tremor disease (TD), has bring a huge economic loss to China aquaculture. The hemocytes of crab as the first target cells of S. eriocheiris, but the interactive relationship between the E. sinensis and this pathogen not particularly clear. The present study is the first time to analysis the role of protein ubiquitination in the process of E. sinensis hemocytes response S. eriocheiris infection. By applying label-free quantitative liquid chromatography with tandem mass spectrometry proteomics, 950 lysine ubiquitination sites and 803 ubiquitination peptides on 458 proteins were identified, of which 48 ubiquitination sites on 40 proteins were quantified as significantly changed after the S. eriocheiris infection. Bioinformatics analysis of ubiquitination different proteins suggested many biological process and pathways were participated in the interaction between S. eriocheiris and host cell, such as ubiquitin system, endocytosis, prophenoloxidase system (proPO system), cell apoptosis, glycolysis. Our study can enhance our understanding of interaction between the crab and S. eriocheiris, and also provides basis to study the role of protein ubiquitination in other crustacean innate immune system.

Cell Polarity Regulators, Multifunctional Organizers of Lymphocyte Activation and Function

Cell polarity regulators are ubiquitous, evolutionary conserved multifunctional proteins. They contain a variety of protein–protein interaction domains endowing them the capacity to interact with cytoskeleton structures, membrane components and multiple regulatory proteins. In this way, they act in complexes and are pivotal for cell growth and differentiation, tissue formation, stability and turnover, cell migration, wound healing, and others. Hence some of these proteins are tumor suppressors.

These cellular processes rely on the establishment of cell polarity characterized by the asymmetric localization of proteins, RNAs, membrane domains, or organelles that together condition cell shape and function. Whether apparently stable, as in epithelia or neurons, or very dynamic, as in immune cells, cell polarity is an active process. It involves cytoskeleton reorganization and targeted intracellular traffic, and results in cellular events such as protein synthesis, secretion and assembly taking place at defined cell poles. Multiple polarity regulators orchestrate these processes.

Immune cells are particularly versatile in rapidly polarizing and assuming different shapes, so to swiftly adopt specialized behaviors and functions. Polarity regulators act in various ways in different immune cell types and at their distinct differentiation states. Here we review how cell polarity regulators control different processes and functions along T lymphocyte physiology, including cell migration through different tissues, immunological synapse formation and effector functions.

A methylation study of long-term depression risk

Recurrent and chronic major depressive disorder (MDD) accounts for a substantial part of the disease burden because this course is most prevalent and typically requires long-term treatment. We associated blood DNA methylation profiles from 581 MDD patients at baseline with MDD status 6 years later. A resampling approach showed a highly significant association between methylation profiles in blood at baseline and future disease status (P = 2.0 × 10^-16). Top MWAS results were enriched specific pathways, overlapped with genes found in GWAS of MDD disease status, autoimmune disease and inflammation, and co-localized with eQTLS and (genic enhancers of) of transcription sites in brain and blood. Many of these findings remained significant after correction for multiple testing. The major themes emerging were cellular responses to stress and signaling mechanisms linked to immune cell migration and inflammation. This suggests that an immune signature of treatment-resistant depression is already present at baseline. We also created a methylation risk score (MRS) to predict MDD status 6 years later. The AUC of our MRS was 0.724 and higher than risk scores created using a set of five putative MDD biomarkers, genome-wide SNP data, and 27 clinical, demographic and lifestyle variables. Although further studies are needed to examine the generalizability to different patient populations, these results suggest that methylation profiles in blood may present a promising avenue to support clinical decision making by providing empirical information about the likelihood MDD is chronic or will recur in the future.

Three-dimensional computed tomography mapping of posterior malleolar fractures

BACKGROUND

Posterior malleolar fractures have been reported to occur in < 40% of ankle fractures.

AIM

To reveal the recurrent patterns and characteristics of posterior malleolar fractures by creating fracture maps of the posterior malleolar fractures through the use of computed tomography mapping.

METHODS

A consecutive series of posterior malleolar fractures was used to create three-dimensional reconstruction images, which were oriented and superimposed to fit an ankle model template by both aligning specific biolandmarks and reducing reconstructed fracture fragments. Fracture lines were found and traced in order to generate an ankle fracture map.

RESULTS

This study involved 112 patients with a mean age of 49, comprising 32 pronation-external rotation grade IV fractures and 80 supination-external rotation grade IV fractures according to the Lauge-Hansen classification system. Three-dimensional maps showed that the posterior ankle fracture fragments in the supination-external rotation grade IV group were relatively smaller than those in the pronation-external rotation grade IV group after posterior malleolus fracture. In addition, the distribution analyses on posterior malleolus fracture lines indicated that the supination-external rotation grade IV group tended to have higher linear density but more concentrated and orderly distribution fractures compared to the pronation-external rotation grade IV group.

CONCLUSION

Fracture maps revealed the fracture characteristics and recurrent patterns of posterior malleolar fractures, which might help to improve the understanding of ankle fracture as well as increase opportunities for follow-up research and aid clinical decision-making.

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.

L-selectin expression is regulated by CXCL8-induced reactive oxygen species produced during human neutrophil rolling

Neutrophils destroy invading microorganisms by phagocytosis by bringing them into contact with bactericidal substances, among which ROS are the most important. However, ROS also function as important physiological regulators of cellular signaling pathways. Here, we addressed the involvement of oxygen derivatives in the regulation of human neutrophil rolling, an essential component of the inflammatory response. Flow experiments using dihydroethidium-preloaded human neutrophils showed that these cells initiate an early production of intracellular ROS during the rolling phase of the adhesion cascade, a phenomenon that required cell rolling, and the interaction of the chemokine receptor CXCR2 with their ligand CXCL8. Flow cytometry experiments demonstrated that L-selectin shedding in neutrophils is triggered by ROS through an autocrine-paracrine mechanism. Preincubation of neutrophils with the NADPH oxidase complex inhibitor diphenyleniodonium chloride significantly increased the number of rolling neutrophils on endothelial cells. Interestingly, the same effect was observed when CXCL8 signaling was interfered using either a blocking monoclonal antibody or an inhibitor of its receptor. These findings indicate that, in response to CXCL8, neutrophils initiate ROS production during the rolling phase of the inflammatory response. This very early ROS production might participate in the modulation of the inflammatory response by inducing L-selectin shedding in neutrophils.

Molecular Mechanisms of T Cells Activation by Dendritic Cells in Autoimmune Diseases

The interaction between T cell and dendritic cells (DCs) that leads to T cell activation affects the progression of the immune response including autoimmune diseases. Antigen presentation on immune cell surface, formation of an immunological synapse (IS), and specific identification of complex by T cells including two activating signals are necessary steps that lead to T cell activation. The formation of stimulatory IS involves the inclusion of costimulatory molecules, such as ICAM-1/LFA-1 and CD28/B7-1, and so on. Some fusion proteins and monoclonal antibodies targeting costimulatory molecules have been developed and approved to treat autoimmune diseases, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), multiple sclerosis (MS), type I diabetes (T1D), inflammatory bowel disease (IBD), and psoriasis. These biological agents, including CTLA-4- and LFA-3-Ig, anti-CD3 monoclonal antibody, could prevent the successful engagement of DCs by T cell with significant efficacy and safety profile. In this article, we reviewed the molecular mechanisms of T cell activation during the interaction between T cells and DCs, and summarized some biological agents that target costimulatory molecules involved in the regulation of T cell activation.

Platelet adhesion on endothelium early after vein grafting mediates leukocyte recruitment and intimal hyperplasia in a murine model

Intimal hyperplasia (IH) is the substrate for accelerated atherosclerosis and limited patency of vein grafts. However, there is still no specific treatment targeting IH following graft surgery. In this study, we used a mouse model of vein grafting to investigate the potential for early intervention with platelet function for later development of graft IH. We transferred the inferior vena cava (IVC) from donor C57BL/6 mice to the carotid artery in recipients using a cuff technique. We found extensive endothelial injury and platelet adhesion one hour following grafting. Adhesion of leukocytes was distinct in areas of platelet adhesion. Platelet and leukocyte adhesion was strongly reduced in mice receiving a function-blocking antibody against the integrin αIIbβ3. This was followed by a reduction of IH one month following grafting. Depletion of platelets using antiserum also reduced IH at later time points. These findings indicate platelets as pivotal to leukocyte recruitment to the wall of vein grafts. In conclusion, the data also highlight early intervention of platelets and inflammation as potential treatment for later formation of IH and accelerated atherosclerosis following bypass surgery.

CD9 Regulates Major Histocompatibility Complex Class II Trafficking in Monocyte-Derived Dendritic Cells

Antigen presentation by dendritic cells (DCs) stimulates naive CD4⁺ T cells, triggering T cell activation and the adaptive arm of the immune response. Newly synthesized major histocompatibility complex class II (MHC-II) molecules accumulate at MHC-II-enriched endosomal compartments and are transported to the plasma membrane of DCs after binding to antigenic peptides to enable antigen presentation. In DCs, MHC-II molecules are included in tetraspanin-enriched microdomains (TEMs). However, the role of tetraspanin CD9 in these processes remains largely undefined. Here, we show that CD9 regulates the T cell-stimulatory capacity of granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent bone marrow-derived DCs (BMDCs), without affecting antigen presentation by fms-like tyrosine kinase 3 ligand (Flt3L)-dependent BMDCs. CD9 knockout (KO) GM-CSF-dependent BMDCs, which resemble monocyte-derived DCs (MoDCs), induce lower levels of T cell activation than wild-type DCs, and this effect is related to a reduction in MHC-II surface expression in CD9-deficient MoDCs. Importantly, MHC-II targeting to the plasma membrane is largely impaired in immature CD9 KO MoDCs, in which MHC-II remains arrested in acidic intracellular compartments enriched in LAMP-1 (lysosome-associated membrane protein 1), and MHC-II internalization is also blocked. Moreover, CD9 participates in MHC-II trafficking in mature MoDCs, regulating its endocytosis and recycling. Our results demonstrate that the tetraspanin CD9 specifically regulates antigenic presentation in MoDCs through the regulation of MHC-II intracellular trafficking.

Integrin α4β1 controls G9a activity that regulates epigenetic changes and nuclear properties required for lymphocyte migration

The mechanical properties of the cell nucleus change to allow cells to migrate, but how chromatin modifications contribute to nuclear deformability has not been defined. Here, we demonstrate that a major factor in this process involves epigenetic changes that underpin nuclear structure. We investigated the link between cell adhesion and epigenetic changes in T-cells, and demonstrate that T-cell adhesion to VCAM1 via α4β1 integrin drives histone H3 methylation (H3K9me2/3) through the methyltransferase G9a. In this process, active G9a is recruited to the nuclear envelope and interacts with lamin B1 during T-cell adhesion through α4β1 integrin. G9a activity not only reorganises the chromatin structure in T-cells, but also affects the stiffness and viscoelastic properties of the nucleus. Moreover, we further demonstrated that these epigenetic changes were linked to lymphocyte movement, as depletion or inhibition of G9a blocks T-cell migration in both 2D and 3D environments. Thus, our results identify a novel mechanism in T-cells by which α4β1 integrin signaling drives specific chromatin modifications, which alter the physical properties of the nucleus and thereby enable T-cell migration.

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.

Effect of Pseudopod Extensions on Neutrophil Hemodynamic Transport Near a Wall

During inflammation, circulating neutrophils roll on, and eventually tether to, the endothelial lining of blood vessels, allowing them to exit the bloodstream and enter the surrounding tissue to target pathogens. This process is mediated by the selectin family of adhesion proteins expressed by endothelial cells. Interestingly, only 10% of activated, migrating neutrophils transmigrate into the extravascular space; the other 90% detach from the wall and rejoin the blood flow. Neutrophils extrude pseudopods during the adhesion cascade; however, the transport behavior of this unique cell geometry has not been previously addressed. In this study, a three-dimensional computational model was applied to neutrophils with pseudopodial extensions to study the effect of cell shape on the hydrodynamic transport of neutrophils. The collision time, contact area, contact force, and collision frequency were analyzed as a function of pseudopod length. It was found that neutrophils experience more frequent collisions compared to prolate spheroids of equal volume and length. Longer pseudopods and lower shear rates increase the collision time integral contact area, a predictor of binding potential. Our results indicate that contact between the neutrophil and the vessel wall was found to be focused predominantly on the pseudopod tip.

Simulation and Analysis of Tethering Behavior of Neutrophils with Pseudopods

P-selectin and P-selectin glycoprotein ligand-1 (PSGL-1) play important roles in mediating the inflammatory cascade. Selectin kinetics, together with neutrophil hydrodynamics, regulate the fundamental adhesion cascade of cell tethering and rolling on the endothelium. The current study uses the Multiscale Adhesive Dynamics computational model to simulate, for the first time, the tethering and rolling behavior of pseudopod-containing neutrophils as mediated by P-selectin/PSGL-1 bonds. This paper looks at the effect of including P-selectin/PSGL-1 adhesion kinetics. The parameters examined included the shear rate, adhesion on-rate, initial neutrophil position, and receptor number sensitivity. The outcomes analyzed included types of adhesive behavior observed, tether rolling distance and time, number of bonds formed during an adhesive event, contact area, and contact time. In contrast to the hydrodynamic model, P-selectin/PSGL-1 binding slows the neutrophil’s translation in the direction of flow and causes the neutrophil to swing around perpendicular to flow. Several behaviors were observed during the simulations, including tethering without firm adhesion, tethering with downstream firm adhesion, and firm adhesion upon first contact with the endothelium. These behaviors were qualitatively consistent with in vivo data of murine neutrophils with pseudopods. In the simulations, increasing shear rate, receptor count, and bond formation rate increased the incidence of firm adhesion upon first contact with the endothelium. Tethering was conserved across a range of physiological shear rates and was resistant to fluctuations in the number of surface PSGL-1 molecules. In simulations where bonding occurred, interaction with the side of the pseudopod, rather than the tip, afforded more surface area and greater contact time with the endothelial wall.

Complexity of the cell-cell interactions in the innate immune response after cerebral ischemia

In response to brain ischemia a cascade of signals leads to the activation of the brain innate immune system and to the recruitment of blood borne derived cells to the ischemic tissue. These processes have been increasingly shown to play a role on stroke pathogenesis. Here, we discuss the key features of resident microglia and different leukocyte subsets implicated in cerebral ischemia with special emphasis of neutrophils, monocytes and microglia. We focus on how leukocytes are recruited to injured brain through a complex interplay between endothelial cells, platelets and leukocytes and describe different strategies used to inhibit their recruitment. Finally, we discuss the possible existence of different leukocyte subsets in the ischemic tissue and the repercussion of different myeloid phenotypes on stroke outcome. The knowledge of the nature of these heterogeneous cell-cell interactions may open new lines of investigation on new therapies to promote protective immune responses and tissue repair after cerebral ischemia or to block harmful responses. This article is part of a Special Issue entitled SI: Cell Interactions In Stroke.

Prevention of neutrophil extravasation by α2-adrenoceptor-mediated endothelial stabilization

Adrenergic receptors are expressed on the surface of inflammation-mediating cells, but their potential role in the regulation of the inflammatory response is still poorly understood. The objectives of this work were to study the effects of α2-adrenergic agonists on the inflammatory response in vivo and to determine their mechanism of action. In two mouse models of inflammation, zymosan air pouch and thioglycolate-induced peritonitis models, the i.m. treatment with xylazine or UK14304, two α2-adrenergic agonists, reduced neutrophil migration by 60%. The α2-adrenergic antagonist RX821002 abrogated this effect. In flow cytometry experiments, the basal surface expression of L-selectin and CD11b was modified neither in murine nor in human neutrophils upon α2-agonist treatment. Similar experiments in HUVEC showed that UK14304 prevented the activation-dependent upregulation of ICAM-1. In contrast, UK14304 augmented electrical resistance and reduced macromolecular transport through a confluent HUVEC monolayer. In flow chamber experiments, under postcapillary venule-like flow conditions, the pretreatment of HUVECs, but not neutrophils, with α2-agonists decreased transendothelial migration, without affecting neutrophil rolling. Interestingly, α2-agonists prevented the TNF-α-mediated decrease in expression of the adherens junctional molecules, VE-cadherin, β-catenin, and plakoglobin, and reduced the ICAM-1-mediated phosphorylation of VE-cadherin by immunofluorescence and confocal analysis and Western blot analysis, respectively. These findings indicate that α2-adrenoceptors trigger signals that protect the integrity of endothelial adherens junctions during the inflammatory response, thus pointing at the vascular endothelium as a therapeutic target for the management of inflammatory processes in humans.

P-glycoprotein regulates trafficking of CD8(+) T cells to the brain parenchyma

The trafficking of cytotoxic CD8(+) T lymphocytes across the lining of the cerebral vasculature is key to the onset of the chronic neuro-inflammatory disorder multiple sclerosis. However, the mechanisms controlling their final transmigration across the brain endothelium remain unknown. Here, we describe that CD8(+) T lymphocyte trafficking into the brain is dependent on the activity of the brain endothelial adenosine triphosphate-binding cassette transporter P-glycoprotein. Silencing P-glycoprotein activity selectively reduced the trafficking of CD8(+) T cells across the brain endothelium in vitro as well as in vivo. In response to formation of the T cell-endothelial synapse, P-glycoprotein was found to regulate secretion of endothelial (C-C motif) ligand 2 (CCL2), a chemokine that mediates CD8(+) T cell migration in vitro. Notably, CCL2 levels were significantly enhanced in microvessels isolated from human multiple sclerosis lesions in comparison with non-neurological controls. Endothelial cell-specific elimination of CCL2 in mice subjected to experimental autoimmune encephalomyelitis also significantly diminished the accumulation of CD8(+) T cells compared to wild-type animals. Collectively, these results highlight a novel (patho)physiological role for P-glycoprotein in CD8(+) T cell trafficking into the central nervous system during neuro-inflammation and illustrate CCL2 secretion as a potential link in this mechanism.

HIV-1 induces cytoskeletal alterations and Rac1 activation during monocyte-blood-brain barrier interactions: modulatory role of CCR5

Background

Most HIV strains that enter the brain are macrophage-tropic and use the CCR5 receptor to bind and infect target cells. Because the cytoskeleton is a network of protein filaments involved in cellular movement and migration, we investigated whether CCR5 and the cytoskeleton are involved in endothelial-mononuclear phagocytes interactions, adhesion, and HIV-1 infection.

Results

Using a cytoskeleton phospho-antibody microarray, we showed that after co-culture with human brain microvascular endothelial cells (HBMEC), HIV-1 infected monocytes increased expression and activation of cytoskeleton-associated proteins, including Rac1/cdc42 and cortactin, compared to non-infected monocytes co-cultured with HBMEC. Analysis of brain tissues from HIV-1-infected patients validated these findings, and showed transcriptional upregulation of Rac1 and cortactin, as well as increased activation of Rac1 in brain tissues of HIV-1-infected humans, compared to seronegative individuals and subjects with HIV-1-encephalitis. Confocal imaging showed that brain cells expressing phosphorylated Rac1 were mostly macrophages and blood vessels. CCR5 antagonists TAK-799 and maraviroc prevented HIV-induced upregulation and phosphorylation of cytoskeleton-associated proteins, prevented HIV-1 infection of macrophages, and diminished viral-induced adhesion of monocytes to HBMEC. Ingenuity pathway analysis suggests that during monocyte-endothelial interactions, HIV-1 alters protein expression and phosphorylation associated with integrin signaling, cellular morphology and cell movement, cellular assembly and organization, and post-translational modifications in monocytes. CCR5 antagonists prevented these HIV-1-induced alterations.

Conclusions

HIV-1 activates cytoskeletal proteins during monocyte-endothelial interactions and increase transcription and activation of Rac1 in brain tissues. In addition to preventing macrophage infection, CCR5 antagonists could diminish viral-induced alteration and phosphorylation of cytoskeletal proteins, monocyte adhesion to the brain endothelium and viral entry into the central nervous system.

Miro-1 links mitochondria and microtubule Dynein motors to control lymphocyte migration and polarity

The recruitment of leukocytes to sites of inflammation is crucial for a functional immune response. In the present work, we explored the role of mitochondria in lymphocyte adhesion, polarity, and migration. We show that during adhesion to the activated endothelium under physiological flow conditions, lymphocyte mitochondria redistribute to the adhesion zone together with the microtubule-organizing center (MTOC) in an integrin-dependent manner. Mitochondrial redistribution and efficient lymphocyte adhesion to the endothelium require the function of Miro-1, an adaptor molecule that couples mitochondria to microtubules. Our data demonstrate that Miro-1 associates with the dynein complex. Moreover, mitochondria accumulate around the MTOC in response to the chemokine CXCL12/SDF-1α; this redistribution is regulated by Miro-1. CXCL12-dependent cell polarization and migration are reduced in Miro-1-silenced cells, due to impaired myosin II activation at the cell uropod and diminished actin polymerization. These data point to a key role of Miro-1 in the control of lymphocyte adhesion and migration through the regulation of mitochondrial redistribution.

Jak3 enables chemokine-dependent actin cytoskeleton reorganization by regulating cofilin and Rac/Rhoa GTPases activation

We have previously shown that Jak3 is involved in the signaling pathways of CCR7, CCR9 and CXCR4 in murine T lymphocytes and that Jak3^−/− lymphocytes display an intrinsic defect in homing to peripheral lymph nodes. However, the molecular mechanism underlying the defective migration observed in Jak3^−/− lymphocytes remains elusive. Here, it is demonstrated for the first time, that Jak3 is required for the actin cytoskeleton reorganization in T lymphocytes responding to chemokines. It was found that Jak3 regulates actin polymerization by controlling cofilin inactivation in response to CCL21 and CXCL12. Interestingly, cofilin inactivation was not precluded in PTX- treated cells despite their impaired actin polymerization. Additionally, Jak3 was required for small GTPases Rac1 and RhoA activation, which are indispensable for acquisition of the migratory cell phenotype and the generation of a functional leading edge and uropod, respectively. This defect correlates with data obtained by time-lapse video-microscopy showing an incompetent uropod formation and impaired motility in Jak3-pharmacologically inhibited T lymphocytes. Our data support a new model in which Jak3 and heterotrimeric G proteins can use independent, but complementary, signaling pathways to regulate actin cytoskeleton dynamics during cell migration in response to chemokines.

High-resolution imaging of intravascular atherogenic inflammation in live mice

RATIONALE

The inflammatory processes that initiate and propagate atherosclerosis remain poorly understood, largely because defining the intravascular behavior of immune cells has been technically challenging. Respiratory and pulsatile movements have hampered in vivo visualization of leukocyte accumulation in athero-prone arteries at resolutions achieved in other tissues.

OBJECTIVE

To establish and to validate a method that allows high-resolution imaging of inflammatory leukocytes and platelets within the carotid artery of atherosusceptible mice in vivo.

METHODS AND RESULTS

We have devised a procedure to stabilize the mouse carotid artery mechanically without altering blood dynamics, which dramatically enhances temporal and spatial resolutions using high-speed intravital microscopy in multiple channels of fluorescence. By applying this methodology at different stages of disease progression in atherosusceptible mice, we first validated our approach by assessing the recruitment kinetics of various leukocyte subsets and platelets in athero-prone segments of the carotid artery. The high temporal and spatial resolution allowed the dissection of both the dynamic polarization of and the formation of subcellular domains within adhered leukocytes. We further demonstrate that the secondary capture of activated platelets on the plaque is predominantly mediated by neutrophils. Finally, we couple this procedure with triggered 2-photon microscopy to visualize the 3-dimensional movement of leukocytes in intimate contact with the arterial lumen.

CONCLUSIONS

The improved imaging of diseased arteries at subcellular resolution presented here should help resolve many outstanding questions in atherosclerosis and other arterial disorders.

Angiostatin inhibits activation and migration of neutrophils

There is a critical need to identify molecules that modulate the biology of neutrophils because activated neutrophils, though necessary for host defense, cause exuberant tissue damage through production of reactive oxygen species and increased lifespan. Angiostatin, an endogenous anti-angiogenic cleavage product of plasminogen, binds to integrin αvβ3, ATP synthase and angiomotin and its expression is increased in inflammatory conditions. We test the hypothesis that angiostatin inhibits neutrophil activation, induces apoptosis and blocks recruitment in vivo and in vitro. The data show immuno-reactivity for plasminogen/angiostatin in resting neutrophils. Angiostatin conjugated to FITC revealed that angiostatin was endocytozed by activated mouse and human neutrophils in a lipid raft-dependent fashion. Co-immunoprecipitation of human neutrophil lysates, confocal microscopy of isolated mouse and human neutrophils and functional blocking experiments showed that angiostatin complexes with flotillin-1 along with integrin αvβ3 and ATP synthase. Angiostatin inhibited fMLP-induced neutrophil polarization, as well as caused inhibition of hsp-27 phosphorylation and stabilization of microtubules. Angiostatin treatment, before or after LPS-induced neutrophil activation, inhibited phosphorylation of p38 and p44/42 MAPKs, abolished reactive oxygen species production and released the neutrophils from suppressed apoptosis, as indicated by expression of activated caspase-3 and morphological evidence of apoptosis. Finally, intravital microscopy and myeloperoxidase assay showed inhibition of neutrophil recruitment in post-capillary venules of TNFα-treated cremaster muscle in mouse. These in vitro and in vivo data demonstrate angiostatin as a broad deactivator and silencer of neutrophils and an inhibitor of their migration. These data potentially open new avenues for the development of anti-inflammatory drugs.

Rapid cytoskeleton remodelling in dendritic cells following invasion by Toxoplasma gondii coincides with the onset of a hypermigratory phenotype

Host cell manipulation is an important feature of the obligate intracellular parasite Toxoplasma gondii. Recent reports have shown that the tachyzoite stages subvert dendritic cells (DC) as a conduit for dissemination (Trojan horse) during acute infection. To examine the cellular basis of these processes, we performed a detailed analysis of the early events following tachyzoite invasion of human monocyte-derived DC. We demonstrate that within minutes after tachyzoite penetration, profound morphological changes take place in DC that coincide with a migratory activation. Active parasite invasion of DC led to cytoskeletal actin redistribution with loss of adhesive podosome structures and redistribution of integrins (CD18 and CD11c), that concurred with the onset of DC hypermotility in vitro. Inhibition of parasite rhoptry secretion and invasion, but not inhibition of parasite or host cell protein synthesis, abrogated the onset of morphological changes and hypermotility in DC dose-dependently. Also, infected DC, but not by-stander DC, exhibited upregulation of C-C chemokine receptor 7 (CCR7). Yet, the onset of parasite-induced DC hypermotility preceded chemotactic migratory responsesin vitro. Collectively, present data reveal that invasion of DC by T. gondii initiates a series of regulated events, including rapid cytoskeleton rearrangements, hypermotility and chemotaxis, that promote the migratory activation of DC.

Lymphatic endothelium forms integrin-engaging 3D structures during DC transit across inflamed lymphatic vessels

Dendritic cell (DC) transmigration across the lymphatic endothelium is critical for the initiation and sustenance of immune responses. Under noninflammatory conditions, DC transit across the lymphatic endothelial cell (LEC) has been shown to be integrin independent. In contrast, there is increasing evidence for the participation of integrins and their ligands in DC transit across lymphatic endothelium under inflammation. In this sense, we describe the formation of ICAM-1 (CD54)-enriched three-dimensional structures on LEC/DC contacts, as these DCs adhere to inflamed skin lymphatic vessels and transmigrate into them. In vitro imaging revealed that under inflammation ICAM-1 accumulated on microvilli projections surrounding 60% of adhered DCs. In contrast, these structures were scarcely formed in noninflammatory conditions. Furthermore, ICAM-1-enriched microvilli were important in promoting DC transendothelial migration and DC crawling over the LEC surface. Microvilli formation was dependent on the presence of β-integrins on the DC side and on integrin conformational affinity to ligand. Finally, we observed that LEC microvilli structures appeared in close vicinity of CCL21 depots and that their assembly was partially inhibited by CCL21-neutralizing antibodies. Therefore, under inflammatory conditions, integrin ligands form three-dimensional membrane projections around DCs. These structures offer docking sites for DC transit from the tissue toward the lymphatic vessel lumen.

The tetraspanin CD37 orchestrates the α(4)β(1) integrin-Akt signaling axis and supports long-lived plasma cell survival

Signaling by the serine and threonine kinase Akt (also known as protein kinase B), a pathway that is common to all eukaryotic cells, is central to cell survival, proliferation, and gene induction. We sought to elucidate the mechanisms underlying regulation of the kinase activity of Akt in the immune system. We found that the four-transmembrane protein CD37 was essential for B cell survival and long-lived protective immunity. CD37-deficient (Cd37(-/-)) mice had reduced numbers of immunoglobulin G (IgG)-secreting plasma cells in lymphoid organs compared to those in wild-type mice, which we attributed to increased apoptosis of plasma cells in the germinal centers of the spleen, areas in which B cells proliferate and are selected. CD37 was required for the survival of IgG-secreting plasma cells in response to binding of vascular cell adhesion molecule 1 to the α(4)β(1) integrin. Impaired α(4)β(1) integrin-dependent Akt signaling in Cd37(-/-) IgG-secreting plasma cells was the underlying cause responsible for impaired cell survival. CD37 was required for the mobility and clustering of α(4)β(1) integrins in the plasma membrane, thus regulating the membrane distribution of α(4)β(1) integrin necessary for activation of the Akt survival pathway in the immune system.

Cholesteryl butyrate solid lipid nanoparticles inhibit the adhesion and migration of colon cancer cells

BACKGROUND AND PURPOSE Cholesteryl butyrate solid lipid nanoparticles (cholbut SLN) provide a delivery system for the anti-cancer drug butyrate. These SLN inhibit the adhesion of polymorphonuclear cells to the endothelium and may act as anti-inflammatory agents. As cancer cell adhesion to endothelium is crucial for metastasis dissemination, here we have evaluated the effect of cholbut SLN on adhesion and migration of cancer cells. EXPERIMENTAL APPROACH Cholbut SLN was incubated with a number of cancer cell lines or human umbilical vein endothelial cells (HUVEC) and adhesion was quantified by a computerized micro-imaging system. Migration was detected by the scratch 'wound-healing' assay and the Boyden chamber invasion assay. Expression of ERK and p38 MAPK was analysed by Western blot. Expression of the mRNA for E-cadherin and claudin-1 was measured by RT-PCR. KEY RESULTS Cholbut SLN inhibited HUVEC adhesiveness to cancer cell lines derived from human colon-rectum, breast, prostate cancers and melanoma. The effect was concentration and time-dependent and exerted on both cancer cells and HUVEC. Moreover, these SLN inhibited migration of cancer cells and substantially down-modulated ERK and p38 phosphorylation. The anti-adhesive effect was additive to that induced by the triggering of B7h, which is another stimulus inhibiting both ERK and p38 phosphorylation, and cell adhesiveness. Furthermore, cholbut SLN induced E-cadherin and inhibited claudin-1 expression in HUVEC. CONCLUSION AND IMPLICATIONS These results suggest that cholbut SLN could act as an anti-metastastic agent and they add a new mechanism to the anti-tumour activity of this multifaceted preparation of butyrate.

Endothelial membrane reorganization during leukocyte extravasation

Leukocyte trafficking from the bloodstream to inflamed tissues across the endothelial barrier is an essential response in innate immunity. Leukocyte adhesion, locomotion, and diapedesis induce signaling in endothelial cells and this is accompanied by a profound reorganization of the endothelial cell surfaces that is only starting to be unveiled. Here we review the current knowledge on the leukocyte-mediated alterations of endothelial membrane dynamics and their role in promoting leukocyte extravasation. The formation of protein- and lipid-mediated cell adhesion nanodomains at the endothelial apical surface, the extension of micrometric apical membrane docking structures, which are derived from microvilli and embrace adhered leukocytes, as well as the vesicle-trafficking pathways that are required for efficient leukocyte diapedesis, are discussed. The coordination between these different endothelial membrane-remodeling events probably provides the road map for transmigrating leukocytes to find exit points in the vessel wall, in a context of severe mechanical and inflammatory stress. A better understanding of how vascular endothelial cells respond to immune cell adhesion should enable new therapeutic strategies to be developed that can abrogate uncontrolled leukocyte extravasation in inflammatory diseases.

Transcriptomic analysis of the stress response to weaning at housing in bovine leukocytes using RNA-seq technology

Background

Weaning of beef calves is a necessary husbandry practice and involves separating the calf from its mother, resulting in numerous stressful events including dietary change, social reorganisation and the cessation of the maternal-offspring bond and is often accompanied by housing. While much recent research has focused on the physiological response of the bovine immune system to stress in recent years, little is known about the molecular mechanisms modulating the immune response. Therefore, the objective of this study was to provide new insights into the molecular mechanisms underlying the physiological response to weaning at housing in beef calves using Illumina RNA-seq.

Results

The leukocyte transcriptome was significantly altered for at least 7 days following either housing or weaning at housing. Analysis of differentially expressed genes revealed that four main pathways, cytokine signalling, transmembrane transport, haemostasis and G-protein-coupled receptor (GPRC) signalling were differentially regulated between control and weaned calves and underwent significant transcriptomic alterations in response to weaning stress on day 1, 2 and 7. Of particular note, chemokines, cytokines and integrins were consistently found to be up-regulated on each day following weaning. Evidence for alternative splicing of genes was also detected, indicating a number of genes involved in the innate and adaptive immune response may be alternatively transcribed, including those responsible for toll receptor cascades and T cell receptor signalling.

Conclusions

This study represents the first application of RNA-Seq technology for genomic studies in bovine leukocytes in response to weaning stress. Weaning stress induces the activation of a number of cytokine, chemokine and integrin transcripts and may alter the immune system whereby the ability of a number of cells of the innate and adaptive immune system to locate and destroy pathogens is transcriptionally enhanced. Stress alters the homeostasis of the transcriptomic environment of leukocytes for at least 7 days following weaning, indicating long term effects of stress exposure in the bovine. The identification of gene signature networks that are stress activated provides a mechanistic framework to characterise the multifaceted nature of weaning stress adaptation in beef calves. Thus, capturing subtle transcriptomic changes provides insight into the molecular mechanisms that underlie the physiological response to weaning stress.

A neuronal transmembrane protein LRFN4 complexes with 14-3-3s and NCK1 to induce morphological change in monocytic cells via Rac1-mediated actin cytoskeleton reorganization

We previously reported that leucine-rich repeat and fibronectin type III domain-containing 4 (LRFN4) functioned in migration and morphological change (i.e. cell elongation) of monocytic cells. Here, we examined a molecular mechanism regulating LRFN4-mediated cell elongation. We found that 14-3-3 and NCK proteins complexed with LRFN4, and they were involved in LRFN4-mediated cell elongation. We also identified the regions of LRFN4 interacting with NCK1 and 14-3-3s. Finally, we demonstrated that a Rac1 small GTPase was involved in LRFN4-mediated cell elongation. These results indicated that LRFN4 complexed with 14-3-3s and NCK1 to mediate elongation in monocytic cells via Rac-1-mediated actin cytoskeleton reorganization.

Regulation of eosinophil trafficking by SWAP-70 and its role in allergic airway inflammation

Eosinophils are the predominant inflammatory cells recruited to allergic airways. In this article, we show that human and murine eosinophils express SWAP-70, an intracellular RAC-binding signaling protein, and examine its role in mediating eosinophil trafficking and pulmonary recruitment in a murine model of allergic airway inflammation. Compared with wild-type eosinophils, SWAP-70-deficient (Swap-70(-/-)) eosinophils revealed altered adhesive interactions within inflamed postcapillary venules under conditions of blood flow by intravital microscopy, exhibiting enhanced slow rolling but decreased firm adhesion. In static adhesion assays, Swap-70(-/-) eosinophils adhered poorly to VCAM-1 and ICAM-1 and exhibited inefficient leading edge and uropod formation. Adherent Swap-70(-/-) eosinophils failed to translocate RAC1 to leading edges and displayed aberrant cell surface localization/distribution of α4 and Mac-1. Chemokine-induced migration of Swap-70(-/-) eosinophils was significantly decreased, correlating with reduced intracellular calcium levels, defective actin polymerization/depolymerization, and altered cytoskeletal rearrangement. In vivo, recruitment of eosinophils to the lungs of allergen-challenged Swap-70(-/-) mice, compared with wild-type mice, was significantly reduced, along with considerable attenuation of airway inflammation, indicated by diminished IL-5, IL-13, and TNF-α levels; reduced mucus secretion; and improved airway function. These findings suggest that regulation of eosinophil trafficking and migration by SWAP-70 is important for the development of eosinophilic inflammation after allergen exposure.

A neuronal transmembrane protein LRFN4 induces monocyte/macrophage migration via actin cytoskeleton reorganization

Leucine-rich repeat and fibronectin type III domain-containing (LRFN) family proteins are thought to be neuronal-specific proteins that play essential roles in neurite outgrowth and synapse formation. Here, we focused on expression and function of LRFN4, the fourth member of the LRFN family, in non-neural tissues. We found that LRFN4 was expressed in a wide variety of cancer and leukemia cell lines. We also found that expression of LRFN4 in the monocytic cell line THP-1 and in primary monocytes was upregulated following macrophage differentiation. Furthermore, we demonstrated that LRFN4 signaling regulated both the transendothelial migration of THP-1 cells and the elongation of THP-1 cells via actin cytoskeleton reorganization. Our data indicate that LRFN4 signaling plays an important role in the migration of monocytes/macrophages.

Conformational switching in ezrin regulates morphological and cytoskeletal changes required for B cell chemotaxis

B cell chemotaxis occurs in response to specific chemokine gradients and is critical for homeostasis and immune response. The molecular regulation of B cell membrane-actin interactions during migration is poorly understood. In this study, we report a role for ezrin, a member of the membrane-cytoskeleton cross-linking ezrin-radixin-moesin proteins, in the regulation of the earliest steps of B cell polarization and chemotaxis. We visualized chemokine-induced changes in murine B cell morphology using scanning electron microscopy and spatiotemporal dynamics of ezrin in B cells using epifluorescence and total internal reflection microscopy. Upon chemokine stimulation, ezrin is transiently dephosphorylated to assume an inactive conformation and localizes to the lamellipodia. B cells expressing a phosphomimetic conformationally active mutant of ezrin or those in which ezrin dephosphorylation was pharmacologically inhibited displayed impaired microvillar dynamics, morphological polarization, and chemotaxis. Our data suggest a 2-fold involvement of ezrin in B cell migration, whereby it first undergoes chemokine-induced dephosphorylation to facilitate membrane flexibility, followed by relocalization to the actin-rich lamellipodia for dynamic forward protrusion of the cells.

Dendritic cells adhere to and transmigrate across lymphatic endothelium in response to IFN-α

Migration of DC into lymphatic vessels ferries antigenic cargo and pro-inflammatory stimuli into the draining LN. Given that tissues under the influence of viral infections produce type I IFN, it is conceivable that these cytokines enhance DC migration in order to facilitate an antiviral immune response. Cultured lymphatic endothelium monolayers pretreated with TNF-α were used to model this phenomenon under inflammatory conditions. DC differentiated in the presence of either IFN-α2b or IFN-α5 showed enhanced adhesion to cultured lymphatic endothelial cells. These pro-adhesive effects were mediated by DC, not the lymphatic endothelium, and correlated with increased DC transmigration across lymphatic endothelial cell monolayers. Transmigration was guided by chemokines acting on DC, and blocking experiments with mAb indicated a role for LFA-1. Furthermore, incubation of DC with IFN-α led to the appearance of active conformation epitopes on the CD11a integrin chains expressed by DC. Differentiation of mouse DC in the presence of IFN-α also increased DC migration from inflammed footpads toward popliteal LN. Collectively, these results indicate a role for type I IFN in directing DC toward LN under inflammatory conditions.

Adhesion shapes T cells for prompt and sustained T-cell receptor signalling

During T-cell migration, cell polarity is orchestrated by chemokine receptors and adhesion molecules and involves the functional redistribution of molecules and organelles towards specific cell compartments. In contrast, it is generally believed that the cell polarity established when T cells meet antigen-presenting cells (APCs) is controlled by the triggered T-cell receptor (TCR). Here, we show that, during activation of human T lymphocytes by APCs, chemokines and LFA-1 establish cell polarity independently of TCR triggering. Chemokine-induced LFA-1 activation results in fast recruitment of MTOC and mitochondria towards the potential APC, a process required to amplify TCR Ca(2+) signalling at the upcoming immunological synapse, to promote nuclear translocation of transcriptional factor NFATc2 and boost CD25 expression. Our data show that the initial adhesive signals delivered by chemokines and LFA-1 shape and prepare T cells for antigen recognition.

Tumor-infiltrating lymphocytes and hepatocellular carcinoma: molecular biology

Tumor-infiltrating lymphocytes (TIL) are one of the representative components of host antitumor immune responses. Both the quality and quantity of TIL determine the effect of the antitumor immune reaction. Previous studies have indicated that patients with cancers showing massive infiltration of CD8(+) T cells generally have a better clinical outcome. Conversely, patients with marked infiltration of immunosuppressive cells such as regulatory T cells tend to have a worse prognosis for several types of cancer. The density and distribution of TIL are also strongly affected by the trafficking route. Tumor-associated blood vessels in various cancers are structurally and functionally abnormal, and such abnormal vessels reportedly become an obstacle for infiltration of immune effector cells into tumors. Recently, understanding of the molecular mechanisms of lymphocyte trafficking has progressed rapidly. This review focuses on the mechanisms of lymphocyte trafficking to tumor cells and also discusses the importance of blood vessel for TIL trafficking, especially in relation to hepatocarcinogenesis.

B7h triggering inhibits umbilical vascular endothelial cell adhesiveness to tumor cell lines and polymorphonuclear cells

Vascular endothelial cells (ECs) are key players in leukocyte recruitment into tissues and metastatic dissemination of tumor cells. ECs express B7h, which is the ligand of the ICOS T cell costimulatory molecule. The aim of this work was to assess the effect of B7h triggering by a soluble form of ICOS (ICOS-Fc) on the adhesion of colon carcinoma cell lines to HUVECs. We found that B7h triggering inhibited HUVEC adhesiveness to HT29 and DLD1 cells (by 50 and 35%, respectively) but not to HCT116 cells. The effect was dependent on the ICOS-Fc dose and was detectable as early as 30 min after treatment and was still present after 24 h. It was inhibited by soluble anti-ICOS reagents (mAb and B7h-Fc) and silencing of B7h on HUVECs, and it was not displayed by an F119S mutated form of ICOS-Fc that does not bind B7h. HUVEC treatment with ICOS-Fc did not modulate expression of adhesion molecules and cytokines, but it substantially downmodulated ERK phosphorylation induced by E-selectin triggering or osteopontin, which may influence HUVEC adhesiveness. Moreover, HUVEC treatment with ICOS-Fc also inhibited adhesion of polymorphonuclear cells and several tumor cell lines from different origins. Therefore, the B7h-ICOS interaction may modulate spreading of cancer metastases and recruitment of polymorphonuclear cells in inflammatory sites, which opens a view on the use of ICOS-Fc as an immunomodulatory drug.

Polarization and migration of hematopoietic stem and progenitor cells rely on the RhoA/ROCK I pathway and an active reorganization of the microtubule network

Understanding the physiological migration of hematopoietic progenitors is important, not only for basic stem cell research, but also in view of their therapeutic relevance. Here, we investigated the role of the Rho kinase pathway in the morphology and migration of hematopoietic progenitors using an ex vivo co-culture consisting of human primary CD34(+) progenitors and mesenchymal stromal cells. The addition of the Rho kinase inhibitor Y-27632 led to the abolishment of the uropod and microvillar-like structures of hematopoietic progenitors, concomitant with a redistribution of proteins found therein (prominin-1 and ezrin). Y-27632-treated cells displayed a deficiency in migration. Time-lapse video microscopy revealed impairment of the rear pole retraction. Interestingly, the knockdown of ROCK I, but not ROCK II, using RNA interference (RNAi) was sufficient to cause the referred morphological and migrational changes. Unexpectedly, the addition of nocodazole to either Y-27632- or ROCK I RNAi-treated cells could restore their polarized morphology and migration suggesting an active role for the microtubule network in tail retraction. Finally, we could demonstrate using RNAi that RhoA, the upstream regulator of ROCK, is involved in these processes. Collectively, our data provide new insights regarding the role of RhoA/ROCK I and the microtubules in the migration of stem cells.

Differential expression of biofunctional GM1 and GM3 gangliosides within the plastic-adherent multipotent mesenchymal stromal cell population

BACKGROUND AIMS

It is unclear whether the plastic-adherent multipotent mesenchymal stromal cells (MSC) isolated from human bone marrow (BM) represent a uniform cell population or are heterogeneous in terms of cell-surface constituents and hence functionality.

METHODS

We investigated the expression profile of certain biofunctional lipids by plastic-adherent MSC, focusing particularly on two membrane microdomain (lipid raft)-associated monosialogangliosides, GM1 and GM3, using indirect confocal laser scanning fluorescence microscopy and flow cytometry.

RESULTS

Phenotypically, we observed a differential expression where certain MSC subsets exhibited GM1, GM3 or both at the plasma membrane. Furthermore, disialoganglioside GD2 detection increased the complexity of the expression patterns, giving rise to seven identifiable cell phenotypes. Variation of standard culture conditions, such as the number of cell passage and period in culture, as well as donors, did not influence the heterologous ganglioside expression profile. In contrast, the binding of various lectins appeared homogeneous throughout the MSC population, indicating that the general glycosylation pattern remained common. Morphologically, the expression of a given ganglioside-based phenotype was not related to a cell with particular size or shape. Interestingly, a segregation of GM1 and GM3 clusters was observed, GM3 being mostly excluded from the highly curved plasma membrane protrusions.

CONCLUSIONS

These data highlight the phenotypic heterogeneity of plastic-adherent MSC in terms of certain lipid constituents of the plasma membrane, and the presence and/or absence of distinct ganglioside-based membrane microdomains suggest their potential functional diversity.

Breaching multiple barriers: leukocyte motility through venular walls and the interstitium

The shuttling of leukocytes between the bloodstream and interstitial tissues involves different locomotion strategies that are governed by locally presented soluble and cell-bound signals. Recent studies have furthered our understanding of the rapidly advancing field of leukocyte migration, particularly regarding cellular and subcellular events at the level of the venular wall. Furthermore, emerging cellular models are now addressing the transition from an adherent mode to a non-adherent state, incorporating mechanisms that support an efficient migratory profile of leukocytes in the interstitial tissue beyond the venular wall.