PSGL-1 function in immunity and steady state homeostasis

Sialoadhesin ligand expression identifies a subset of CD4+Foxp3- T cells with a distinct activation and glycosylation profile

Sialoadhesin (Sn) is a sialic acid-binding Ig-like lectin expressed selectively on macrophage subsets. In a model of experimental autoimmune encephalomyelitis, Sn interacted with sialylated ligands expressed selectively on CD4(+)Foxp3(+) regulatory T cells (Tregs) and inhibited their proliferation. In this study, we examined the induction of Sn ligands (SnL) on all splenic CD4(+) T cells following in vitro activation. Most CD4(+) Tregs strongly upregulated SnL, whereas only a small subset of ~20% CD4(+)Foxp3(-) T cells (effector T cells [Teffs]) upregulated SnL. SnL(+) Teffs displayed higher levels of activation markers CD25 and CD69, exhibited increased proliferation, and produced higher amounts of IL-2 and IFN-γ than corresponding SnL(-) Teffs. Coculture of activated Teffs with Sn(+) macrophages or Sn(+) Chinese hamster ovary cells resulted in increased cell death, suggesting a regulatory role for Sn-SnL interactions. The key importance of α2,3-sialylation in SnL expression was demonstrated by increased binding of α2,3-linkage-specific Maackia amurensis lectin, increased expression of α2,3-sialyltransferase ST3GalVI, and loss of SnL following treatment with an α2,3-linkage-specific sialidase. The induction of SnL on activated CD4(+) T cells was dependent on N-glycan rather than O-glycan biosynthesis and independent of the mucin-like molecules CD43 and P-selectin glycoprotein ligand-1, previously implicated in Sn interactions. Induction of ligands on CD4(+)Foxp3(-) Teffs was also observed in vivo using the New Zealand Black × New Zealand White F1 murine model of spontaneous lupus and SnL levels on Teffs correlated strongly with the degree of proteinuria. Collectively, these data indicate that SnL is a novel marker of activated CD4(+) Teffs that are implicated in the pathogenesis of autoimmune diseases.

Multiple sclerosis and the blood-central nervous system barrier

The central nervous system (CNS) is isolated from the blood system by a physical barrier that contains efflux transporters and catabolic enzymes. This blood-CNS barrier (BCNSB) plays a pivotal role in the pathophysiology of multiple sclerosis (MS). It binds and anchors activated leukocytes to permit their movement across the BCNSB and into the CNS. Once there, these immune cells target particular self-epitopes and initiate a cascade of neuroinflammation, which leads to the breakdown of the BCNSB and the formation of perivascular plaques, one of the hallmarks of MS. Immunomodulatory drugs for MS are either biologics or small molecules, with only the latter having the capacity to cross the BCNSB and thus have a propensity to cause CNS side effects. However, BCNSB penetration is a desirable feature of MS drugs that have molecular targets within the CNS. These are nabiximols and dalfampridine, which target cannabinoid receptors and potassium channels, respectively. Vascular cell adhesion molecule-1, present on endothelial cells of the BCNSB, also serves as a drug discovery target since it interacts with α4-β1-integrin on leucocytes. The MS drug natalizumab, a humanized monoclonal antibody against α4-β1-integrin, blocks this interaction and thus reduces the movement of immune cells into the CNS. This paper further elaborates on the role of the BCNSB in the pathophysiology and pharmacotherapy of MS.

Single-nucleotide polymorphisms in GALNT8 are associated with the response to interferon therapy for chronic hepatitis C

New anti-hepatitis C virus (HCV) therapeutics developed recently are more effective and lead to improvements in sustained viral response. However, interferon (IFN) monotherapy is still used to a limited extent for fear of adverse effects. This study investigated host genetic factors affecting the IFN response in patients with chronic hepatitis C (CHC). Using a two-step design, a large-scale association screening including 1088 Japanese CHC patients treated with IFN was performed employing ~70 000 gene-based single-nucleotide polymorphisms (SNPs). Replication was tested in an independent Japanese cohort of 328 patients. Fine-mapping and functional analyses were also performed. Through two-step screening, it was found that rs2286580 in intron 6 of the gene encoding N-acetylgalactosaminyltransferase 8 (GALNT8) on chromosome 12 was significantly associated with a sustained viral response (combined P = 3.9×10(-6), odds ratio 1.52, 95 % confidence interval 1.29-1.82). The association was replicated in an additional cohort of 328 Japanese patients. In subgroup analysis, GALNT8 variants were associated with treatment outcome independently of HCV genotype. By contrast, the outcome of pegylated IFN and ribavirin combined therapy was not affected by the SNP. Fine-mapping analysis revealed that the association peak was at rs10849138 in intron 6 of GALNT8. Allele-specific transcription analysis demonstrated that GALNT8 expression was upregulated by an unfavourable allele of the variant. A luciferase reporter assay demonstrated that overexpression of GALNT8 attenuated IFN-α-induced gene transcription via the IFN-stimulated response element. These results suggest that GALNT8 variants contribute to the response to IFN therapy against CHC, providing a new insight into antiviral mechanisms of IFN.

The initial draining lymph node primes the bulk of the CD8 T cell response and influences memory T cell trafficking after a systemic viral infection

Lymphocytic choriomeningitis virus (LCMV) causes a systemic infection in mice with virus replication occurring in both peripheral tissues and secondary lymphoid organs. Because of the rapid systemic dissemination of the virus, the secondary lymphoid organs responsible for the induction of the LCMV-specific CD8 T cell response are poorly defined. We show that the mediastinal lymph node (MedLN) serves as the primary draining lymph node following LCMV infection. In addition, we demonstrate that the MedLN is responsible for priming the majority of the virus-specific CD8 T cell response. Following resolution of the acute infection, the draining MedLN exhibits characteristics of a reactive lymph node including an increased presence of germinal center B cells and increased cellularity for up to 60 days post-infection. Furthermore, the reactive MedLN harbors an increased frequency of CD62L(-) effector memory CD8 T cells as compared to the non-draining lymph nodes. The accumulation of LCMV-specific CD62L(-) memory CD8 T cells in the MedLN is independent of residual antigen and is not a unique feature of the MedLN as footpad infection with LCMV leads to a similar increase of virus-specific CD62L(-) effector memory CD8 T cells in the draining popliteal lymph node. Our results indicate that CD62L(-) effector memory CD8 T cells are granted preferential access into the draining lymph nodes for an extended time following resolution of an infection.

Neutrophil rolling at high shear: flattening, catch bond behavior, tethers and slings

Neutrophil recruitment to sites of inflammation involves neutrophil rolling along the inflamed endothelium in the presence of shear stress imposed by blood flow. Neutrophil rolling in post-capillary venules in vivo is primarily mediated by P-selectin on the endothelium binding to P-selectin glycoprotein ligand-1 (PSGL-1) constitutively expressed on neutrophils. Blood flow exerts a hydrodynamic drag on the rolling neutrophil which is partially or fully balanced by the adhesive forces generated in the P-selectin-PSGL-1 bonds. Rolling is the result of rapid formation and dissociation of P-selectin-PSGL-1 bonds at the center and rear of the rolling cell, respectively. Neutrophils roll stably on P-selectin in post-capillary venules in vivo and flow chambers in vitro at wall shear stresses greater than 6 dyn cm(-2). However, the mechanisms that enable neutrophils to roll at such high shear stress are not completely understood. In vitro and in vivo studies have led to the discovery of four potential mechanisms, viz. cell flattening, catch bond behavior, membrane tethers, and slings. Rolling neutrophils undergo flattening at high shear stress, which not only increases the size of the cell footprint but also reduces the hydrodynamic drag experienced by the rolling cell. P-selectin-PSGL-1 bonds behave as catch bonds at small detachment forces and thus become stronger with increasing force. Neutrophils rolling at high shear stress form membrane tethers which can be longer than the cell diameter and promote the survival of P-selectin-PSGL-1 bonds. Finally, neutrophils rolling at high shear stress form 'slings', which act as cell autonomous adhesive substrates and support step-wise peeling. Tethers and slings act together and contribute to the forces balancing the hydrodynamic drag. How the synergy between the four mechanisms leads to stable rolling at high shear stress is an area that needs further investigation.

Golgi phosphoprotein 3 determines cell binding properties under dynamic flow by controlling Golgi localization of core 2 N-acetylglucosaminyltransferase 1

Core 2 N-acetylglucosaminyltransferase 1 (C2GnT1) is a key enzyme participating in the synthesis of core 2-associated sialyl Lewis x (C2-O-sLe(x)), a ligand involved in selectin-mediated leukocyte trafficking and cancer metastasis. To accomplish that, C2GnT1 needs to be localized to the Golgi and this step requires interaction of its cytoplasmic tail (CT) with a protein that has not been identified. Employing C2GnT1 CT as the bait to perform a yeast two-hybrid screen, we have identified Golgi phosphoprotein 3 (GOLPH3) as a principal candidate protein that interacts with C2GnT1 and demonstrated that C2GnT1 binds to GOLPH3 via the LLRRR(9) sequence in the CT. Confocal fluorescence microscopic analysis shows substantial Golgi co-localization of C2GnT1 and GOLPH3. Upon GOLPH3 knockdown, C2GnT1 is found mainly in the endoplasmic reticulum and decorated with complex-type N-glycans, indicating that the enzyme has been transported to the Golgi but is not retained. Also, we have found that a recombinant protein consisting of C2GnT1 CT(1-16)-Leu(17-32)-Gly(33-42)-GFP is localized to the Golgi although the same construct with mutated CT (AAAAA(9)) is not. The data demonstrate that the C2GnT1 CT is necessary and sufficient for Golgi localization of C2GnT1. Furthermore, GOLPH3 knockdown results in reduced synthesis of C2-O-sLe(x) associated with P-selectin glycoprotein ligand-1, reduced cell tethering to and rolling on immobilized P- or E-selectin, and compromised E-selectin-induced activation of spleen tyrosine kinase and cell adhesion to intercellular adhesion molecule-1 under dynamic flow. Our results reveal that GOLPH3 can regulate cell-cell interaction by controlling Golgi retention of C2GnT1.

Pharmacotherapeuetic Options for the Treatment of Multiple Sclerosis

Multiple sclerosis is the most common progressive and disabling neurological condition in young adults. Neuro-inflammation is an early and persistent change and forms the basis of most pharmacotherapy for this disease. Immunomodulatory drugs are mainly biologies (β-interferons, a four amino acid peptide, and a monoclonal antibody to a cell adhesion molecule on the blood-CNS barrier) that either attenuate the inflammatory response or block the movement of immune cells into the CNS. They reduce the rate of relapse, but have little or no effect on the progression of disability. The market landscape for MS drugs is in the midst of major change because the patent life of many of these medicines will soon expire, which will lead to the emergence of biosimilars. In addition, new small molecule immunomodulatory and palliative drugs have entered the market, with more in the pipeline; a number of monoclonal antibodies and other immunomodulatory drugs are also in clinical development.

Expression of functional P-selectin glycoprotein ligand 1 on hematopoietic progenitors is developmentally regulated

T cell development requires periodic importation of hematopoietic progenitors into the thymus. The receptor-ligand pair P-selectin and P-selectin glycoprotein ligand 1 (PSGL-1) are critically involved in this process. In this study, we examined the expression of functional PSGL-1 on bone marrow hematopoietic progenitors. We demonstrate that functional PSGL-1 is expressed at low levels on hematopoietic stem cells, but upregulated on the cell surface of progenitors that bear other homing molecules known to be important for thymic settling. We found that progenitors able to home to the thymus expressed high levels of PSGL-1 transcripts compared with hematopoietic stem cells. We further demonstrate that hematopoietic progenitors lacking fucosyltransferase 4 and 7 do not express functional PSGL-1, and do not home efficiently to the thymus. These studies provide insight into the developmentally regulated expression of a critical determinant involved in progenitor homing to the thymus.

The Membrane-Bound Aspartyl Protease BACE1: Molecular and Functional Properties in Alzheimer's Disease and Beyond

The β-site APP cleaving enzyme 1 (BACE1) is a transmembrane aspartyl protease involved in Alzheimer’s disease (AD) pathogenesis and in myelination. BACE1 initiates the generation of the pathogenic amyloid β-peptide, which makes BACE1 a major drug target for AD. BACE1 also cleaves and activates neuregulin 1, thereby contributing to postnatal myelination, in particular in the peripheral nervous system. Additional proteins are also cleaved by BACE1, but less is known about the physiological consequences of their cleavage. Recently, new phenotypes were described in BACE1-deficient mice. Although it remains unclear through which BACE1 substrates they are mediated, the phenotypes suggest a versatile role of this protease for diverse physiological processes. This review summarizes the enzymatic and cellular properties of BACE1 as well as its regulation by lipids, by transcriptional, and by translational mechanisms. The main focus will be on the recent progress in understanding BACE1 function and its implication for potential mechanism-based side effects upon therapeutic inhibition.

Naive, effector and memory CD8 T-cell trafficking: parallels and distinctions

Trafficking of CD8 T cells, in both the steady-state and during episodes of infection or inflammation, is a highly dynamic process and involves a variety of receptor-ligand interactions. A thorough, mechanistic understanding of how this process is regulated could potentially lead to disease prevention strategies, through either enhancing (for infectious diseases or tumors) or limiting (for autoimmunity) recruitment of antigen-specific CD8 T cells to areas of tissue inflammation. As CD8 T cells transition from naive to effector to memory cells, changes in gene expression will ultimately dictate anatomical localization of these cells in vivo. In this article, we discuss recent advances in understanding how antigenic stimulation influences expression of various trafficking receptors and ligands, and how this determines the tissue localization of CD8 T cells.

Role of O-glycosylation and expression of CD43 and CD45 on the surfaces of effector T cells in human T cell leukemia virus type 1 cell-to-cell infection

We used replication-dependent retroviral vectors to identify cell surface antigens involved in the cell-to-cell transmission of human T cell leukemia virus type 1 (HTLV-1). We generated monoclonal antibodies (MAbs) against Jurkat T cells and selected several IgM MAbs that strongly inhibited HTLV-1 but not human immune deficiency virus type 1 (HIV-1) cell-to-cell infection. These MAbs recognized the so-called Tn antigen (GalNAcα1-O-Ser/Thr) that arises on Jurkat cells from a mutation in the T-synthase-specific chaperone Cosmc and the consequent loss of O-glycan elongation. Anti-Tn MAbs precipitated two major O-glycan carrier proteins, CD43 and CD45, and caused a strong aggregation of Jurkat cells. The restoration of O-glycosylation in Jurkat cells by stably transducing the wild-type Cosmc gene resulted in a 3- to 4-fold increase in the level of surface expression of CD43 and enhanced HTLV-1 transmission 10-fold in comparison to that of parental cells. The short hairpin RNA (shRNA) knockdown of CD43 or CD45 expression in Jurkat-Cosmc, HBP-ALL, and CEM T cells decreased HTLV-1 infection severalfold. The knockdown of CD45 in Jurkat cells severely reduced both HTLV-1 and HIV-1 infections, but Cosmc coexpression partially rescued infection. HTLV-1 proteins, which assembled in small patches on Jurkat cells, formed large clusters on the surface of Jurkat-Cosmc cells. These data indicate that large aggregates of HTLV-1 assemblies are more infectious than multiple clustered virions. We suggest that heavily O-glycosylated CD43 and CD45 molecules render cells less adhesive, prevent inappropriate cell-cell contacts, and favor the assembly of HTLV-1 particles into large, highly infectious structures on the surface of T cells.

Glycoengineering of HCELL, the human bone marrow homing receptor: sweetly programming cell migration

The successful clinical implementation of adoptive cell therapeutics, including bone marrow transplantation and other stem cell-based treatments, depends critically on the ability to deliver cells to sites where they are needed. E-selectin, an endothelial C-type lectin, binds sialofucosylated carbohydrate determinants on its pertinent ligands. This molecule is expressed in a constitutive manner on bone marrow and dermal microvascular endothelium, and inducibly on post-capillary venules at all sites of tissue injury. Engagement of E-selectin with relevant ligand(s) expressed on circulating cells mediates initial "tethering/rolling" endothelial adhesive interactions prerequisite for extravasation of blood-borne cells at any target tissue. Most mammalian cells express high levels of a transmembrane glycoprotein known as CD44. A specialized glycoform of CD44 called "Hematopoietic Cell E-/L-selectin Ligand" (HCELL) is a potent E-selectin ligand expressed on human cells. Under native conditions, HCELL expression is restricted to human hematopoietic stem/progenitor cells. We have developed a technology called "Glycosyltransferase-Programmed Stereosubstitution" (GPS) for custom-modifying CD44 glycans to create HCELL on the surface of living cells. GPS-based glycoengineering of HCELL endows cell migration to endothelial beds expressing E-selectin. Enforced HCELL expression targets human mesenchymal stem cell homing to marrow, licensing transendothelial migration without chemokine signaling via a VLA-4/VCAM-1-dependent "Step 2-bypass pathway." This review presents an historical framework of the homing receptor concept, and will describe the discovery of HCELL, its function as the bone marrow homing receptor, and how enforced expression of this molecule via chemical engineering of CD44 glycans could enable stem cell-based regenerative medicine and other adoptive cell therapeutics.

The role of sugars in dendritic cell trafficking

Dendritic cells (DCs) are crucial components of the immune response, strategically positioned as immune sentinels. Complex trafficking and accurate positioning of DCs are indispensable for both immunity and tolerance. This is particularly evident for their therapeutic application where an unmet clinical need exists for DCs with improved migratory capacity upon adoptive transfer into patients. One critical step that directs the trafficking of DCs throughout the body is their egress from the vasculature, starting with their adhesive interactions with vascular endothelium under shear flow. Both tethering and rolling rely on interactions mediated by specific glycans attached to glycoproteins and glycolipids present on the DC surface. In DCs, surface glycosylation, including the expression of selectin ligands, changes significantly depending on the local microenvironment and the functional state of the cells. These changes have been documented and have potential implications in important cell functions such as migration. In this article, we review the glycobiological aspects in the context of DC interaction with endothelium, and offer insights on how it can be applied to modulate DC applicability in therapy.

Metabolic oligosaccharide engineering: implications for selectin-mediated adhesion and leukocyte extravasation

Metabolic oligosaccharide engineering is an emerging technology wherein non-natural monosaccharide analogs are exogenously supplied to living cells and are biosynthetically incorporated into cell surface glycans. A recently reported application of this methodology employs fluorinated analogs of ManNAc, GlcNAc, and GalNAc to modulate selectin-mediated adhesion associated with leukocyte extravasation and cancer cell metastasis. This monograph outlines possible mechanisms underlying the altered adhesion observed in analog-treated cells; these range from the most straightforward explanation (e.g., structural changes to the selectin ligands ablate interaction with their receptors) to the alternative mechanism where the analogs inhibit or otherwise perturb ligand production to more indirect mechanisms (e.g., changes to the biophysical properties of the selectin binding partner, the nanoenviroment of the binding partners, or the entire cell surface).

Glycosylation of mouse and human immune cells: insights emerging from N-glycomics analyses

N-glycans are key players mediating cell–cell communication in the immune system, interacting with glycan-binding proteins. In the present article, we discuss key themes that are emerging from the structural analysis of complex-type N-linked glycans from human and murine immune cell lines, employing high-sensitivity MALDI (matrix-assisted laser desorption ionization)–TOF (time-of-flight) MS technology. Particular focus is given to terminal epitopes, the abundance of multiply branched N-glycans and how glycosylation can affect human health in diseases such as congenital neutropenia and glycogen storage disease.

Biomechanics of leukocyte rolling

Leukocyte rolling on endothelial cells and other P-selectin substrates is mediated by P-selectin binding to P-selectin glycoprotein ligand-1 expressed on the tips of leukocyte microvilli. Leukocyte rolling is a result of rapid, yet balanced formation and dissociation of selectin-ligand bonds in the presence of hydrodynamic shear forces. The hydrodynamic forces acting on the bonds may either increase (catch bonds) or decrease (slip bonds) their lifetimes. The force-dependent 'catch-slip' bond kinetics are explained using the 'two pathway model' for bond dissociation. Both the 'sliding-rebinding' and the 'allosteric' mechanisms attribute 'catch-slip' bond behavior to the force-induced conformational changes in the lectin-EGF domain hinge of selectins. Below a threshold shear stress, selectins cannot mediate rolling. This 'shear-threshold' phenomenon is a consequence of shear-enhanced tethering and catch bond-enhanced rolling. Quantitative dynamic footprinting microscopy has revealed that leukocytes rolling at venular shear stresses (>0.6 Pa) undergo cellular deformation (large footprint) and form long tethers. The hydrodynamic shear force and torque acting on the rolling cell are thought to be synergistically balanced by the forces acting on tethers and stressed microvilli, however, their relative contribution remains to be determined. Thus, improvement beyond the current understanding requires in silico models that can predict both cellular and microvillus deformation and experiments that allow measurement of forces acting on individual microvilli and tethers.

Serine protease autotransporters from Shigella flexneri and pathogenic Escherichia coli target a broad range of leukocyte glycoproteins

The serine protease autotransporters of Enterobacteriaceae (SPATEs) are secreted by pathogenic Gram-negative bacteria through the autotransporter pathway. We previously classified SPATE proteins into two classes: cytotoxic (class 1) and noncytotoxic (class 2). Here, we show that Pic, a class 2 SPATE protein produced by Shigella flexneri 2a, uropathogenic and enteroaggregative Escherichia coli strains, targets a broad range of human leukocyte adhesion proteins. Substrate specificity was restricted to glycoproteins rich in O-linked glycans, including CD43, CD44, CD45, CD93, CD162 (PSGL-1; P-selectin glycoprotein ligand 1), and the surface-attached chemokine fractalkine, all implicated in leukocyte trafficking, migration, and inflammation. N-terminal sequencing of proteolytic products revealed Pic (protease involved in colonization) cleavage sites to occur before Thr or Ser residues. The purified carbohydrate sLewis-X implied in inflammation and malignancy inhibited cleavage of PSGL-1 by Pic. Exposure of human leukocytes to purified Pic resulted in polymorphonuclear cell activation, but impaired chemotaxis and transmigration; Pic-treated T cells underwent programmed cell death. We also show that the Pic-related protease Tsh/Hbp, implicated in extraintestinal infections, exhibited a spectrum of substrates similar to those cleaved by Pic. In the guinea pig keratoconjunctivitis model, a Shigella pic mutant induced greater inflammation than its parent strain. We suggest that the class-2 SPATEs represent unique immune-modulating bacterial virulence factors.

The interplay between surfaces and soluble factors define the immunologic and angiogenic properties of myeloid dendritic cells

BACKGROUND

Dendritic cells (DCs) are antigen presenting cells capable of inducing specific immune responses against microbial infections, transplant antigens, or tumors. Interestingly, microenvironment conditions such as those present in tumor settings might induce a DC phenotype that is poorly immunogenic and with the capability of promoting angiogenesis. We hypothesize that this plasticity may be caused not only by the action of specific cytokines or growth factors but also by the properties of the surfaces with which they interact, such as extracellular matrix (ECM) components.

RESULTS

Herewith we studied the effect of different surfaces and soluble factors on the biology of DCs. To accomplish this, we cultured murine myeloid(m) DCs on surfaces coated with fibronectin, collagen I, gelatin, and Matrigel using poly-D-lysine and polystyrene as non-biological surfaces. Further, we cultured these cells in the presence of regular DC medium (RPMI 10% FBS) or commercially available endothelial medium (EGM-2). We determined that mDCs could be kept in culture up to 3 weeks in these conditions, but only in the presence of GM-CSF. We were able to determine that long-term DC cultures produce an array of angiogenic factors, and that some of these cultures still retain the capability to induce T cell responses.

CONCLUSIONS

Altogether these data indicate that in order to design DC-based vaccines or treatments focused on changing the phenotype of DCs associated with diseases such as cancer or atherosclerosis, it becomes necessary to fully investigate the microenvironment in which these cells are present or will be delivered.

The β-secretase enzyme BACE1 as a therapeutic target for Alzheimer's disease

Amyloid plaques are defining histopathologic lesions in the brains of Alzheimer's disease (AD) patients and are composed of the amyloid-beta peptide, which is widely considered to play a critical role in the pathogenesis of AD. The β-secretase, or β-site amyloid precursor protein cleaving enzyme 1 (BACE1; also called Asp2, memapsin 2), is the enzyme that initiates the generation of amyloid beta. Consequently, BACE1 is an attractive drug target for lowering cerebral levels of amyloid beta for the treatment or prevention of AD. Much has been learned about BACE1 since its discovery over 10 years ago. In the present article, we review BACE1 properties and characteristics, cell biology, in vivo validation, substrates, therapeutic potential, and inhibitor drug development. Studies relating to the physiological functions of BACE1 and the promise of BACE1 inhibition for AD will also be discussed. We conclude that therapeutic inhibition of BACE1 should be efficacious for AD, although careful titration of the drug dose may be necessary to limit mechanism-based side effects.

Endogenous PMN sialidase activity exposes activation epitope on CD11b/CD18 which enhances its binding interaction with ICAM-1

Diapedesis is a dynamic, highly regulated process by which leukocytes are recruited to inflammatory sites. We reported previously that removal of sialyl residues from PMNs enables these cells to become more adherent to EC monolayers and that sialidase activity within intracellular compartments of resting PMNs translocates to the plasma membrane following activation. We did not identify which surface adhesion molecules were targeted by endogenous sialidase. Upon activation, β2 integrin (CD11b/CD18) on the PMN surface undergoes conformational change, which allows it to bind more tightly to the ICAM-1 and ICAM-2 on the EC surface. Removal of sialyl residues from CD18 and CD11b, by exogenous neuraminidase or mobilization of PMN sialidase, unmasked activation epitopes, as detected by flow cytometry and enhanced binding to ICAM-1. One sialidase isoform, Neu1, colocalized with CD18 on confocal microscopy. Using an autoperfused microflow chamber, desialylation of immobilized ICAM-1 enhanced leukocyte arrest in vivo. Further, treatment with a sialidase inhibitor in vivo reversed endotoxin-induced binding of leukocytes to ICAM-1, thereby suggesting a role for leukocyte sialidase in the cellular arrest. These data suggest that PMN sialidase could be a physiologic source of the enzymatic activity that removes sialyl residues on β2 integrin and ICAM-1, resulting in their enhanced interaction. Thus, PMN sialidase may be an important regulator of the recruitment of these cells to inflamed sites.

P-selectin glycoprotein ligand-1 modulates immune inflammatory responses in the enteric lamina propria

P-selectin glycoprotein ligand-1 (PSGL-1), a leukocyte adhesion receptor that interacts with selectins, induces a tolerogenic programme in bone marrow-derived dendritic cells (DCs), which in turn promotes the generation of T regulatory (Treg) lymphocytes. In the present study, we have used a mouse model of dextran sulphate sodium (DSS)-induced colitis and studied the characteristics of the inflammatory cell infiltrate in the lamina propria (LP), mesenteric lymph nodes (mLNs) and Peyer's patches (PPs) to assess the possible role of PSGL-1 in the modulation of the enteric immune response. We have found that untreated PSGL-1-deficient mice showed an altered proportion of innate and adaptive immune cells in mLNs and PPs as well as an activated phenotype of macrophages and DCs in the colonic LP that mainly produced pro-inflammatory cytokines. Administration of an anti-PSGL-1 antibody also reduced the total numbers of macrophages, DCs and B cells in the colonic LP, and induced a lower expression of MHC-II by DCs and macrophages. After DSS treatment, PSGL-1(-/-) mice developed colitis earlier and with higher severity than wild-type (WT) mice. Accordingly, the colonic LP of these animals showed an enhanced number of Th1 and Th17 lymphocytes, with enhanced synthesis of IL-1α, IL-6 and IL-22, and increased activation of LP macrophages. Together, our data indicate that PSGL-1 has a relevant homeostatic role in the gut-associated lymphoid tissue under steady-state conditions, and that this adhesion receptor is able to down-regulate the inflammatory phenomenon in DSS-induced colitis.

β1 integrin is critical for the maintenance of antigen-specific CD4 T cells in the bone marrow but not long-term immunological memory

The long-term maintenance of memory CD4 T cells promotes protective immunity against future pathogen reinfection. As a site rich in survival cytokines, the bone marrow is proposed to be a critical niche for the survival of memory CD4 T cells. We demonstrate that endogenous, polyclonal Ag-specific CD4 T cells rapidly enter and are recovered long-term from the bone marrow following i.v. infection with Listeria monocytogenes. β(1) integrin-deficient CD4 T cells also populate the bone marrow early following an infection, but their numbers in this site rapidly decline. This decline was not caused by increased death of T cells lacking β(1) integrin but rather by reduced retention in the bone marrow after the primary immune response. The loss of memory CD4 T cells from the bone marrow does not lead to a loss of the predominant source of memory CD4 T cells in the spleen or the ability to mount a memory response. Thus, β(1) integrin-dependent maintenance of memory CD4 T cells in the bone marrow is not required for long-term CD4 T cell memory.

Contribution of neutrophils to acute lung injury

Treatment of acute lung injury (ALI) and its most severe form, acute respiratory distress syndrome (ARDS), remain unsolved problems of intensive care medicine. ALI/ARDS are characterized by lung edema due to increased permeability of the alveolar-capillary barrier and subsequent impairment of arterial oxygenation. Lung edema, endothelial and epithelial injury are accompanied by an influx of neutrophils into the interstitium and broncheoalveolar space. Hence, activation and recruitment of neutrophils are regarded to play a key role in progression of ALI/ARDS. Neutrophils are the first cells to be recruited to the site of inflammation and have a potent antimicrobial armour that includes oxidants, proteinases and cationic peptides. Under pathological circumstances, however, unregulated release of these microbicidal compounds into the extracellular space paradoxically can damage host tissues. This review focuses on the mechanisms of neutrophil recruitment into the lung and on the contribution of neutrophils to tissue damage in ALI.

Humoral immunotherapy of multiple myeloma: perspectives and perplexities

IMPORTANCE OF THE FIELD

Multiple myeloma (MM) is a hematological malignancy still remaining incurable despite the various therapies available, mainly because of the high fraction of refractory/relapsing cases. Therefore, the development of novel therapeutic approaches is urgently needed to overcome conventional treatment resistance.

AREAS COVERED IN THIS REVIEW

In the era of targeted therapies, treatments combining a high specificity for neoplastic cells and the capability to interfere with environmental signals should be regarded as the weapons of choice. Monoclonal antibody (mAb)-based humoral immunotherapy could satisfy both these requirements when applied to MM. Indeed, many of the molecules expressed on MM cells, such as CD38, CD40, CD49d, CD138 and CD162 are involved in the adhesive dynamics regulating the crosstalk between MM and the BM-microenvironment.

WHAT THE READER WILL GAIN

In this study we review those MM-associated molecules that have shown promising antitumor effects as targets of specific mAbs in preclinical settings, thus deserving to be considered for clinical investigation.

TAKE HOME MESSAGE

mAbs directed against MM-associated adhesion markers should be taken into account in clinical practice, since they could possibly represent the best available combination of tumor cytotoxicity, environmental signal deprivation and immune system redirection.

Human L-selectin preferentially binds synthetic glycosulfopeptides modeled after endoglycan and containing tyrosine sulfate residues and sialyl Lewis x in core 2 O-glycans

Endoglycan is a mucin-like glycoprotein expressed by endothelial cells and some leukocytes and is recognized by L-selectin, a C-type lectin important in leukocyte trafficking and extravasation during inflammation. Here, we show that recombinant L-selectin and human T lymphocytes expressing L-selectin bind to synthetic glycosulfopeptides (GSPs). These synthetic glycosulfopeptides contain 37 amino acid residues modeled after the N-terminus of human endoglycan and contain one or two tyrosine sulfates (TyrSO(3)) along with a nearby core-2-based Thr-linked O-glycan with sialyl Lewis x (C2-SLe(x)). TyrSO(3) at position Y118 was more critical for binding than at Y97. C2-SLe(x) at T124 was required for L-selectin recognition. Interestingly, under similar conditions, neither L-selectin nor T lymphocytes showed appreciable binding to the sulfated carbohydrate epitope 6-sulfo-SLe(x). P-selectin also bound to endoglycan-based GSPs but with lower affinity than toward GSPs modeled after PSGL-1, the physiological ligand for P- and L-selectin that is expressed on leukocytes. These results demonstrate that TyrSO(3) residues in association with a C2-SLe(x) moiety within endoglycan and PSGL-1 are preferentially recognized by L-selectin.