Identification of a carbohydrate-based endothelial ligand for a lymphocyte homing receptor

Expression of the alpha(1,3)fucosyltransferase Fuc-TVII in lymphoid aggregate high endothelial venules correlates with expression of L-selectin ligands

Lymphocyte homing to lymph nodes and Peyer's patches is mediated, in part, by adhesive interactions between L-selectin expressed by lymphocytes and L-selectin ligands displayed at the surface of the cuboidal endothelial cells lining the post-capillary venules within lymphoid aggregates. Candidate terminal oligosaccharide structures thought to be essential for effective L-selectin ligand activity include a sulfated derivative of the sialyl Lewis x tetrasaccharide. Cell type-specific synthesis of this oligosaccharide is presumed to require one or more alpha(1,3)fucosyltransferases, operating upon common 3'-sialylated and/or sulfated N-acetyllactosamine-type precursors. The identity of the alpha(1,3)fucosyltransferase(s) expressed in cells that bear L-selectin ligands has not been defined. We report here the molecular cloning and characterization of a murine alpha(1,3)fucosyltransferase locus whose expression pattern correlates with expression of high affinity ligands for L-selectin. In situ hybridization and immunohistochemical analyses demonstrate that this cDNA and its cognate alpha(1,3)fucosyltransferase are expressed in endothelial cells lining the high endothelial venules of peripheral lymph nodes, mesenteric lymph nodes, and Peyer's patches. These expression patterns correlate precisely with the expression pattern of L-selectin ligands identified with a chimeric L-selectin/IgM immunohistochemical probe and by the high endothelial venule-reactive monoclonal antibody MECA-79. Transcripts corresponding to this cDNA are also detected in isolated bone marrow cells, a source rich in the surface-localized ligands for E- and P-selectins. Sequence and functional analyses indicate that this murine enzyme corresponds to the human Fuc-TVII locus. These observations suggest that Fuc-TVII participates in the generation of alpha(1,3)fucosylated ligands for L-selectin and provide further evidence for a role for this enzyme in E- and P-selectin ligand expression in leukocytes.

Characterization of mouse ZP3-derived glycopeptide, gp55, that exhibits sperm receptor and acrosome reaction-inducing activity in vitro

During fertilization, free-swimming mouse sperm bind to mZP3 (approximately 83 000 Mr), one of three zona pellucida glycoproteins, and once bound undergo the acrosome reaction, a type of cellular exocytosis [Wassarman, P. M., & Litscher, E. S. (1995) Curr. Top. Dev. Biol. 30, 1-19]. Sperm recognize and bind to specific serine/threonine-linked oligosaccharides located at the mZP3 combining site for sperm. Here, we examined certain characteristics of gp55, a approximately 55 000 Mr glycopeptide derived from the carboxy-terminal half of mZP3 polypeptide to which sperm bind [Rosiere, T. K., & Wassarman, P. M. (1992) Dev. Biol. 154, 309-317]. gp55 is heterogeneous with respect to Mr (approximately 47 000-62 000 Mr) and has a relatively low pI (approximately 4.3-4.5) compared to the polypeptide portion of the glycopeptide (pI approximately 6.5). gp55 inhibits binding of sperm to eggs (i.e., exhibits sperm receptor activity) and induces sperm to undergo the acrosome reaction in vitro at about the same concentrations required for intact mZP3 (approximately 50-200 nM). Each of three different size-fractions of gp55, separated by SDS-PAGE, also exhibits bioactivity in vitro. Removal of asparagine-linked (N-linked) oligosaccharides from gp55, by extensive digestion with N-glycanase, reduces its Mr to approximately 21 000 and increases it pI to approximately 5.3, but does not significantly affect its ability to inhibit binding of sperm to eggs or to induce sperm to undergo the acrosome reaction. Similarly, digestion of gp55 with either endo-beta-galactosidase or neuraminidase alters its Mr and/or pI, but does not significantly affect either of its bioactivities. These observations are consistent with the proposal that neither N-linked oligosaccharides nor sialic acid is an essential element of the mZP3 combining site for sperm. They also indicate that a relatively small mZP3 glycopeptide is able to induce sperm to undergo the acrosome reaction (i.e., cellular exocytosis) in vitro.

Differential regulation of tissue-specific lymph node high endothelial venule cell adhesion molecules by tumour necrosis factor and transforming growth factor-beta 1

Lymphocytes migrate from blood into lymph nodes (LN) of rats specifically at segments of venules lined by high endothelium (HEV). We have previously shown that pretreatment of LN HEV cells with pro-inflammatory cytokines such as tumour necrosis factor-alpha (TNF-alpha) and interferon-gamma (IFN-gamma), augments their adhesiveness for thoracic duct lymphocytes (TDL). Here we report that a mouse monoclonal antibody, 3C10, recognized tissue-specific endothelial determinants on rat LN HEV cells and blocked their adhesiveness for TDL and EL-4J cells transfected with rat L-selectin. In contrast, 3C10 antibody did not inhibit lymphocyte attachment to Peyer's patch (PP) frozen sections or cultured PP HEV cells. The antibody immunoprecipitated from LN HEV cells two proteins with apparent molecular weights of 90,000 and 50,000. The expression of 3C10 antigen on LN HEV cells was increased by incubation with TNF-alpha or IFN-gamma. Furthermore, pretreatment of cytokine-stimulated LN HEV cells with 3C10 antibody blocked TDL binding in a dose-dependent manner. In contrast, 3C10 antigen expression on LN HEV cells was significantly decreased following incubation of cells with transforming growth factor-beta 1 (TGF-beta 1). In addition, TGF-beta 1 also abrogated the adhesiveness of LN HEV cells stimulated with TNF-alpha, IFN-gamma or both cytokines. Together, these data suggest that endothelial determinants recognized by the 3C10 antibody are tissue-specific ligands for lymphocyte adhesion and cytokines such as TNF-alpha and TGF-beta differentially regulate their expression and function.

Human vascular adhesion protein 1 (VAP-1) is a unique sialoglycoprotein that mediates carbohydrate-dependent binding of lymphocytes to endothelial cells

The regulated interactions of leukocytes with vascular endothelial cells are crucial in controlling leukocyte traffic between blood and tissues. Vascular adhesion protein-1 (VAP-1) is a novel, human endothelial cell molecule that mediates tissue-selective lymphocyte binding. Two species (90 and 170 kD) of VAP-1 exist in lymphoid tissues. Glycosidase digestions revealed that the mature 170-kD form of VAP-1 expressed on the lumenal surfaces of vessels is a heavily sialylated glycoprotein. The sialic acids are indispensable for the function of VAP-1, since the desialylated form of VAP-1 no longer mediates lymphocyte binding. We also show that L-selectin is not required for binding of activated lymphocytes to VAP-1 under conditions of shear stress. The 90-kD form of VAP-1 was only seen in an organ culture model, and may represent a monomeric or proteolytic form of the larger species. These data indicate that L-selectin negative lymphocytes can bind to tonsillar venules via the VAP- 1-mediated pathway. Moreover, our findings extend the role of carbohydrate-mediated binding in lymphocyte-endothelial cell interactions beyond the known selectins. In conclusion, VAP-1 naturally exists as a 170-kD sialoglycoprotein that uses sialic acid residues to interact with its counter-receptors on lymphocytes under nonstatic conditions.

Immunoadhesins: principles and applications

The prototypic immunoadhesin is an antibody-like molecule that fuses the Fc region of an immunoglobulin and the ligand-binding region of a receptor or adhesion molecule. In this article, we review some important structural and functional principles of immunoadhesins. In addition, we highlight some unique advantages of immunoadhesins as experimental tools in biology, as well as some of their exciting potential applications in medicine.

Modulation of L-selectin ligand expression during an immune response accompanying tumorigenesis in transgenic mice

Immune surveillance depends on lymphocyte access to tissue. Lymphocytes emigrate from blood when adhesion receptors such as L-selectin and the alpha 4 beta 7 integrin on these cells bind to ligands expressed on venular endothelium. Among transgenic mouse lines expressing an oncoprotein (Tag) in islet beta cells, some recognize Tag as nonself. In these mice, Tag expression elicits both beta cell hyperplasia with subsequent progression to tumors and lymphocytic infiltration. Endothelial ligands for L-selectin and alpha 4 beta 7 were upregulated in infiltrated islets in these transgenic mice. These ligands were not expressed in tumors, which were devoid of lymphocytic infiltration. In contrast, the adhesion molecules PECAM-1, ICAM-1, and VCAM-1 were expressed on endothelium in both noninfiltrated tumors and infiltrated islets. Thus, upregulation of expression of endothelial ligands for L-selectin and alpha 4 beta 7 may contribute to autoimmune infiltration. Repression of expression of these same ligands may be involved in the failure of tumor immunity.

The selectins: insights into selectin-induced intracellular signaling in leukocytes

Characteristic features of the inflammatory and immune responses involve the recruitment of leukocytes to sites of tissue injury and the recirculation of lymphocytes through hematopoietic and lymphoid tissues. Recent studies indicate that the regulated cell surface expression of a family of protein adhesion molecules known as selectins and their counterreceptors on both leukocytes and endothelium play critical roles in both biologic processes. Initially, the function of these molecules was thought to be restricted to regulating cell-cell adhesive interactions. Selectin-dependent cell-cell binding has been shown to be essential in localizing leukocytes within tissues by promoting cell rolling along endothelium prior to the development of tight adhesion and subsequent cell migration. However, recent studies suggest that these molecules also play an active role in regulating additional leukocyte functions. This article will review the emerging evidence that indicates a broader and significant role of selectin molecules and their counterreceptors in the initiation of intracellular signaling pathways and regulation of other leukocyte functional responses including degranulation, cytokine expression, activation of the respiratory burst, and T lymphocyte activation.

PSGL-1 recognition of P-selectin is controlled by a tyrosine sulfation consensus at the PSGL-1 amino terminus

P-selectin binding to neutrophils requires a specific protein, P-selectin glycoprotein ligand 1 (PSGL-1), as well as sialyl-Lewis X (sLex) glycan determinants. We have found that a short segment near the amino terminus of PSGL-1 that contains a tyrosine sulfation consensus is essential for P-selectin adhesion and that addition of the amino-terminal segment to some but not all mucin-like molecules confers on those molecules the ability to bind P-selectin. PSGL-1 synthesized in the presence of sulfation inhibitors binds P-selectin weakly, and within the amino-terminal 20 residues, mutation of the tyrosines to phenylalanine abolishes binding. Rolling of HL-60 cells on P-selectin-coated coverslips is strongly attenuated by treatment of cells with an inhibitor of sulfation.

Synthetic mucin fragments: synthesis of O-sulfo and O-methyl derivatives of allyl O-(beta-D-galactopyranosyl)-(1-->3)-2-acetamido-2-deoxy-alpha-D- galactopyranoside as potential compounds for sulfotransferases

Allyl 2-acetamido-4,6-O-(4-methoxybenzylidene)-2-deoxy-alpha-D-galact opy ranoside (1) was condensed with either 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide (2) or 2,3,4-tri-O-benzoyl-6-O-bromoacetyl-alpha-D-galactopyranosyl bromide (14) in the presence of mercuric cyanide. Selective substitution with methyl, sulfo or both at desired positions, followed by the removal of protecting groups, afforded allyl O-(beta-D-galactopyranosyl)-(1-->3)-2-acetamido-2-deoxy-6-O-methyl-alpha -D- galactopyranoside (5), allyl O-(6-O-sulfo-beta-D-galactopyranosyl sodium salt)-(1-->3)-2-acetamido-2-deoxy-6- O-methyl-alpha-D-galactopyranoside (10), allyl O-(beta-D-galactopyranosyl)-(1-->3)-2-acetamido-2-deoxy-6-O-sulfo-alpha- D- galactopyranoside sodium salt (13), allyl O-(6-O-sulfo-beta-D-galactopyranosyl sodium salt)-(1-->3)-2-acetamido-2-deoxy- alpha-D-galactopyranoside (17) and allyl O-(3-O-sulfo-beta-D-galactopyranosyl sodium salt)-(1-->3)-2-acetamido-2-deoxy- alpha-D-galactopyranoside (22). The structures of compounds 5, 10, 13, 17 and 22 were established by 13C NMR and FAB mass spectroscopy.

Sialomucin CD34 is the major L-selectin ligand in human tonsil high endothelial venules

Peripheral node addressin (PNAd) is a complex mixture of glycoproteins with L-selectin ligand activity that functions in lymphocyte homing. We have investigated the contribution of the sialomucin CD34 relative to other components of PNAd in lymphocyte tethering and rolling in in vitro laminar flow assays. PNAd was isolated with MECA-79 mAb-Sepharose from tonsillar stroma, and the CD34 component (PNAd,CD34+) and CD34-negative component (PNAd,CD34-) separated on CD34 mAb-Sepharose. Lymphocytes on the PNAd,CD34- fraction tether less efficiently, roll faster and are less resistant to shear detachment than on PNAd. The PNAd,CD34+ fraction constitutes about half the total functional activity. These studies show that CD34 is a major functional component of PNAd. Ligand activity in both the PNAd,CD34+ and PNAd,CD34- fractions is expressed on mucin-like domains, as shown with O-sialoglycoprotease. The CD34 component of PNAd has about four times higher tethering efficiency than total tonsillar CD34. CD34 from spleen shows no lymphocyte tethering. Although less efficient than the PNAd,CD34+ fraction from tonsil, CD34 from the KG1a hematopoietic cell line is functionally active as an L-selectin ligand despite lack of reactivity with MECA-79 mAb, which binds to a sulfation-dependent epitope. All four forms of CD34 are active in binding to E-selectin. KG1a CD34 but not spleen CD34 are active as L-selectin ligands, yet both lack MECA-79 reactivity and possess E-selectin ligand activity. This suggests that L-selectin ligands and E-selectin ligands differ in more respects than presence of the MECA-79 epitope.

Biosynthesis of GlyCAM-1, a mucin-like ligand for L-selectin

L-selectin, a member of the selectin family of leukocyte-endothelial adhesion proteins, mediates the initial attachment of lymphocytes to lymph node high endothelial venules during lymphocyte recirculation. One of the endothelial-associated ligands for L-selectin is GlyCAM-1, a mucin-like glycoprotein, which presents novel sulfated, sialylated and fucosylated O-glycans. In order to understand the generation of these glycans, we have examined the biosynthesis of GlyCAM-1 in lymph node organ culture. Using peptide-specific antibodies, lectins, and recombinant L-selectin, we detected the following species of GlyCAM-1: unglycosylated (< 28 kDa); modified with GalNAc only (28-33 kDa); modified with sialic acid, fucose, and sulfate but lacking L-selectin reactivity (40-50 kDa); and mature (L-selectin-reactive) ligand (50-60 kDa). Pulse-chase labeling at 15 degrees C suggested that GalNAc is added in a pre-Golgi compartment. Treatment with brefeldin A almost completely blocked sulfation, indicating that this modification occurs in the trans-Golgi network. Two distinct sialylation events occurred in the presence of brefeldin A, while fucosylation was partially blocked. We conclude that sialylation precedes both fucosylation and sulfation during biosynthesis. This ordering will help to identify the critical acceptor structures recognized by lymph node glycosyltransferases and sulfotransferases.

Peptides which bind to E-selectin and block neutrophil adhesion

E-selectin is an inducible cell adhesion molecule which mediates rolling of neutrophils on the endothelium, an early event in the development of an inflammatory response. Inhibition of selectin-mediated rolling is a possible means for controlling inflammation-induced diseases, and several classes of compounds have been tested for this use. We describe here the use of recombinant peptide library screening for identification and optimization of novel ligands which bind to E-selectin. Several of these peptides bind with Kd values in the low nanomolar range and block E-selectin-mediated adhesion of neutrophils in static and flow-cell assays. Administration of the peptide to mice undergoing an acute inflammatory response reduced the extent of neutrophil transmigration to the site of inflammation, demonstrating the utility of this compound as a potential therapeutic. The identification of a peptide ligand for E-selectin suggests that the complete natural ligand for this adhesion molecule may include protein as well as carbohydrate moieties.

Interleukin 1 beta up-regulates the expression of sulfoglucuronosyl paragloboside, a ligand for L-selectin, in brain microvascular endothelial cells

Treatment of cultured bovine brain microvascular endothelial cells (BMECs) with interleukin 1 beta (IL-1 beta), an inflammatory cytokine, was shown to induce the accumulation of sulfoglucuronosyl paragloboside (SGPG), a glycolipid bearing the HNK-1 epitope. This resulted in the attachment of a greater number of human lymphocytes to the treated than to the untreated BMEC monolayers. Attachment of human lymphocytes to the IL-1 beta-activated BMEC cells could be blocked either by incubation of the human lymphocytes with an anti-L-selectin antibody or by application of an anti-SGPG antibody to the BMECs. These results suggest that SGPG may act as an important ligand for L-selectin for the regulation of the attachment of activated lymphocytes and their subsequent invasion into the nervous system parenchyma in inflammatory disorders of the central and peripheral nervous systems.

L-selectin and alpha 4 beta 7 integrin homing receptor pathways mediate peripheral lymphocyte traffic to AKR mouse hyperplastic thymus

Before the development of thymic lymphoma, AKR mice undergo a striking lymphoid hyperplasia of the thymic medulla. We have previously shown that there is a marked increase in traffic of B and T lymphocytes from the periphery into the preneoplastic, hyperplastic thymuses of these mice, in contrast to the scant traffic of such cells to normal thymuses. The traffic of lymphocytes to lymph nodes and Peyer's patches is controlled in part by the interaction of lymphocyte adhesion molecules called homing receptors with their tissue-selective endothelial ligands known as vascular addressins. We have investigated the roles of homing receptors and vascular addressins in the traffic of lymphocytes to the AKR hyperplastic thymus. We demonstrate that development of hyperplasia is accompanied by an increase in the number of thymic medullary blood vessels with high endothelial venule morphology and expression of the peripheral node addressin (PNAd) and the mucosal addressin (MAdCAM-1). In vitro and in vivo functional assays show that the addressin/homing receptor pairs PNAd/L-selectin and MAdCAM-1/alpha 4 beta 7 are involved in lymphocyte traffic to the hyperplastic thymus. These results indicate that molecular adhesion mechanisms involved in tissue-selective migration of lymphocytes to peripheral lymph node and to mucosal lymphoid tissues play a role in the recruitment of B and T lymphocytes to the AKR thymus and thus in the pathogenesis of thymic hyperplasia.

Peripheral blood cell preparation influences the level of expression of leukocyte cell surface markers as assessed with quantitative multicolor flow cytometry

We have compared the influence of sample preparation upon the level of surface expression of T, B, and NK cell-related antigens as assessed by flow cytometry. Lysed whole blood (WBL), Ficoll-Paque separated peripheral blood lymphocyte (F-PBL), and frozen peripheral blood lymphocyte (Fr-PBL) were analyzed via single- and multicolor flow cytometry. The percentage of positive cells expressing the individual cell surface markers was not affected by the procedure for preparation of WBL, F-PBL, and Fr-PBL. In contrast, the fluorescence intensity level of individual cell surface markers varied depending on cell preparation. By using Quantum Simply Cellular (QSC) microbeads, the antibody binding capacity (ABC) of single-color stained cells was quantified and compared. The amount of monoclonal antibody (MAb) anti-CD3-FITC bound to Fr-PBL (mean ABC = 137,040) was significantly higher (P < 0.001) that the amounts bound to WBL (mean ABC = 112,410) and F-PBL (mean ABC = 107,738). In multicolor analysis, the fluorescence intensity of CD3-FITC and CD4-FITC was significantly higher on Fr-PBL than on WBL and F-PBL; CD8-PE and CD20-PerCP was significantly higher on WBL. Furthermore, the intensity of CD3 and CD4 was different on T-cell subsets. The intensity of CD3 staining in three-color analysis was lower than with single-color staining using the same fluorochrome. We conclude that particularly the method of cell preparation but also the selection of MAb combinations may influence the level of staining of certain lymphocyte antigens. This may be of relevance in the analysis of cellular activation and regulation of differentiation.

Characterization of a GlyCAM1-like gene (glycosylation-dependent cell adhesion molecule 1) which is highly and specifically expressed in the lactating bovine mammary gland

A bovine cDNA library, derived from the mammary gland of a lactating cow, was screened for identifying transcripts that specifically occur during lactation by means of differential hybridisation. Several of the clones isolated by this procedure shared 55 and 57% similarity with the mouse and rat glycosylation-dependent cell adhesion molecule 1 (GlyCAM1) cDNAs, respectively. Although the mouse and cattle proteins showed an overall similarity of only 41%, two specific regions of the proteins showed 83 and 81% similarity, respectively. The bovine protein also showed 55% similarity with a small protein isolated from the whey fraction of camel milk. Northern blot analysis showed that high-level expression of this gene was only observed in the mammary gland of lactating cows. The complete gene was isolated from a bovine genomic library and its organisation was determined. The gene was 2.5 kb in length and split into four exons. The size and organization of the gene as well as the position of the introns was identical to that of the mouse GlyCAM1 gene. In accordance with the tissue-specific expression of this gene in the mammary gland of lactating animals, potential mammary gland factor (MGF) binding sites were present in the promoter region of the gene. Based on the data presented in this study it is highly likely that this gene is the bovine homologue to the rat and mouse GlyCAM1 genes.

Interaction of acute leukemia cells with the bone marrow microenvironment: implications for control of minimal residual disease

There is increasing evidence for an interaction between acute leukemia cells and the microenvironment of the bone marrow. Blast cells from cases of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) bind to cellular and extracellular matrix components of the bone marrow stroma. In AML, adhesion to stroma is mediated by the combined action of beta 1 (principally VLA-4) and beta 2 integrins, while in precursor-B ALL VLA-4 and VLA-5 integrins play a major role. Adhesion molecules such as CD31, CD44, non-beta 1, beta 2 integrins, growth factor receptors such as c-kit, and other molecules are also likely to play a role. Binding of acute leukemia blasts to ligands on stroma has several pathophysiological consequences. Stromal contact is able to inhibit programmed cell death (apoptosis) in a proportion of cases of both AML and ALL. In ALL, diffusible molecules derived from stroma appear to contribute. Marrow stroma also plays a part in regulating leukemic cell proliferation. While this is partly due to stromal production of hemopoietic growth factors, in soluble or transmembrane form or bound to extracellular matrix, signalling mediated directly by binding of adhesion molecules on leukemic cells may also have a role. Contact of ALL blasts with marrow fibroblasts is followed by migration of leukemic cells, utilizing VLA-4 and VLA-5 integrins, potentially allowing homing of blasts to favourable microenvironmental sites, or controlling egress into the circulation. AML cells compete for stromal binding sites with natural killer cells and cytotoxic lymphocytes, which are known to inhibit their clonogenic growth. We speculate that these complex interactions between leukemic blasts, cellular and matrix components of stroma, and cytotoxic lymphocytes, play a critical role in determining the fate of small numbers of leukemic cells surviving after cytotoxic chemotherapy.

Selective modulation of the expression of L-selectin ligands by an immune response

BACKGROUND

The adhesion molecule L-selectin is expressed on the cell surface of lymphocytes and mediates their migration from the bloodstream into lymph nodes. L-selectin is able to recognize four glycoprotein ligands, three of which--Sgp50, Sgp90, and Sgp200--are sulphated, bind specifically to L-selectin and are synthesized by the high endothelial venules of the peripheral and mesenteric lymph nodes. One of these three sulphated L-selectin ligands, Sgp90, has been shown to be identical to the known surface marker CD34 and is expressed on the cell surface of endothelial cells. The cDNA encoding Sgp50 has been cloned, and its product, which has been designated GlyCAM-1, is secreted. The third ligand, Sgp200, is both secreted and cell-associated. We have investigated how the expression of these sulphated glycoproteins is regulated during an immune response.

RESULTS

Here we demonstrated that, during a primary immune response, the expression and secretion of both GlyCAM-1 and Sgp200 are reduced, recovering to normal levels 7-10 days after antigen stimulation. In contrast, the expression of cell-associated CD34 and Sgp200 is relatively unaffected. These results may account for the modest decreases in the binding of an L-selectin-IgG fusion protein to high endothelial venules of inflamed peripheral lymph nodes that have been observed after antigen exposure. In vivo experiments show that, following the decrease in the levels of secreted GlyCAM-1 and Sgp200, migration of lymphocytes from the blood stream into lymph nodes remains L-selectin-dependent, but more lymphocytes home to antigen-primed than unprimed peripheral lymph nodes.

CONCLUSIONS

We suggest that the secreted forms of the L-selectin ligands GlyCAM-1 and Sgp200 act as modulators of cell adhesion, and that cell-associated CD34 and Sgp200 are the ligands that mediate the initial loose binding of lymphocytes to high endothelial venules.

Structure of the O-glycans in GlyCAM-1, an endothelial-derived ligand for L-selectin

L-selectin, the leukocyte selectin, mediates the carbohydrate-dependent attachment of circulating leukocytes to endothelium, preceding emigration into tissues. It functions in inflammatory leukocyte trafficking and in lymphocyte homing to lymph nodes. From previous work, the binding of L-selectin to endothelial-associated glycoprotein ligands, GlyCAM-1 and CD34, requires oligosaccharide sialylation, sulfation, and probably fucosylation. We have recently identified a major capping group in GlyCAM-1 as 6' sulfated sialyl Lewis x, a novel structure which potentially satisfies all of these requirements. In the present study, we define the complete structure of beta-eliminated chains of GlyCAM-1 using metabolic radiolabeling, plant lectin binding, and glycosidase digestions in conjunction with high pH anion-exchange chromatography. The majority of the O-glycans in GlyCAM-1 contain the T-antigen, i.e. Gal beta 1-->3GalNAc, which is incorporated into the core-2 structure, i.e. Gal beta 1-->3[GlcNAc beta 1-->6]GalNAc or larger core structures with additional GlcNAc residues. The structures of two O-glycans, based on core-2, were determined to be: [sequence: see text] The implications of these structures and more complex O-glycans for binding by L-selectin are discussed.

Leukocyte trafficking mediated by selectin-carbohydrate interactions

The selectins have attracted intense interest because of their carbohydrate-recognition properties and their pivotal roles in leukocyte trafficking. Future studies will center on the mechanisms for regulating the expression of the selectins and their ligands, the molecular details of selectin binding to glycoprotein ligands and small carbohydrates, and the biophysical principles that selectins employ to mediate attachment and rolling of leukocytes under flow.

Prevention of in vitro neutrophil-endothelial attachment through shedding of L-selectin by nonsteroidal antiinflammatory drugs

The activation of the endothelial cells by extravascular stimuli is the key event in the extravasation of circulating leukocytes to target tissues. L-selectin, a member of the selectin family, is constitutively expressed by white cells, and is the molecule involved in the initial binding of leukocytes to activated endothelium. After activation, leukocytes rapidly release L-selectin from the cell surface, suggesting that the functional activity of this molecule is controlled in large part by its appearance and disappearance from cell surface. We have studied in a neutrophil-activated endothelial cell binding assay, the effect of different antiinflammatory drugs (steroidal and nonsteroidal) in the L-selectin-mediated interaction of neutrophils with activated endothelial cells. Some nonsteroidal antiinflammatory drugs (NSAIDs), such as indomethacin, diclofenac, ketoprofen, and aspirin, but not steroids, strongly inhibited the neutrophil-endothelial cell attachment. Furthermore, we also investigated the underlying mechanism of this functional effect. The expression of L-selectin on the neutrophil surface rapidly decreased in the presence of different NSAIDs, in a dose- and time-dependent manner, whereas no changes in the expression of other adhesion molecules such as CD11a, CD11b, CD31, or ICAM-3 (CD50) were observed. Interestingly, studies in vivo on healthy volunteers treated with physiological doses of indomethacin showed a significant decrease of L-selectin neutrophil expression. Only diclofenac induced an upregulation of CD11b expression, suggesting an activating effect on neutrophils. No enzyme release was observed upon treatment of neutrophils with different NSAIDs, indicating a lack of degranulatory activity of NSAIDs, with the exception of diclofenac. The downregulation of L-selectin expression was due to the rapid cleavage and shedding of the membrane L-selectin, as determined by both immunoprecipitation from 125I-labeled neutrophils, and quantitative estimation in cell-free supernatants. These results suggest that NSAIDs exert a specific action on adhesion receptor expression in neutrophils, which might account, at least in part, for the antiinflammatory activities of NSAIDs.

Rolling of lymphocytes and neutrophils on peripheral node addressin and subsequent arrest on ICAM-1 in shear flow

We studied leukocyte interactions in shear flow with peripheral lymph node addressin (PNAd), a mixture of glycoproteins expressed on high endothelial venules (HEV) that is required for lymphocyte homing and has been shown to contain a ligand for L-selectin. T lymphocytes and neutrophils tether and roll on plastic-immobilized PNAd and E-selectin at 1.8 dyn/cm2 wall shear stress, but fail to interact with immobilized ICAM-1, a ligand for LFA-1 and Mac-1, at the same flow rate. Cells roll faster on PNAd than on P-selectin or E-selectin. L-selectin mAb inhibit T lymphocyte and neutrophil tethering to PNAd, but do not inhibit T lymphocyte tethering to purified E-selectin. If allowed to interact with ICAM-1 under static conditions, phorbol ester-treated T lymphocytes, but not resting T lymphocytes, are able to form stationary adhesions that withstand the detachment force generated by 36 dyn/cm2 wall shear stress. In contrast, a wall shear stress of 7.3 dyn/cm2 detaches 50% of resting T lymphocytes bound to PNAd. Incubating T lymphocytes on PNAd and ICAM-1 does not result in adhesion strengthening, suggesting that adhesion through PNAd by L-selectin does not stimulate lymphocyte LFA-1 avidity for ICAM-1. Chemoattractant stimulation of neutrophils or phorbol ester stimulation of lymphoblasts rolling on coimmobilized PNAd and ICAM-1 results in rapid arrest and firm sticking, extending the model of sequential selectin-mediated rolling and subsequent integrin-mediated firm arrest to lymphocytes and ligands expressed on HEV.

P-selectin glycoprotein ligand-1 mediates rolling of human neutrophils on P-selectin

Neutrophils roll on P-selectin expressed by activated platelets or endothelial cells under the shear stresses in the microcirculation. P-selectin glycoprotein ligand-1 (PSGL-1) is a high affinity ligand for P-selectin on myeloid cells. However, it has not been demonstrated that PSGL-1 contributes to the rolling of neutrophils on P-selectin. We developed two IgG mAbs, PL1 and PL2, that appear to recognize protein-dependent epitopes on human PSGL-1. The mAbs bound to PSGL-1 on all leukocytes as well as on heterologous cells transfected with PSGL-1 cDNA. PL1, but not PL2, blocked binding of 125-I-PSGL-1 to immobilized P-selectin, binding of fluid-phase P-selectin to myeloid and lymphoid leukocytes, adhesion of neutrophils to immobilized P-selectin under static conditions, and rolling of neutrophils on P-selectin-expressing CHO cells under a range of shear stresses. PSGL-1 was localized to microvilli on neutrophils, a topography that may facilitate its adhesive function. These data indicate that (a) PSGL-1 accounts for the high affinity binding sites for P-selectin on leukocytes, and (b) PSGL-1 must interact with P-selectin in order for neutrophils to roll on P-selectin at physiological shear stresses.

Characterization of a bovine mammary gland PP3 cDNA reveals homology with mouse and rat adhesion molecule GlyCAM-1

A full length PP3 (Proteose-Peptone component 3) cDNA of 679 bp was isolated from a bovine mammary gland cDNA library. The cDNA encodes a signal peptide of 18 amino acids followed by the mature PP3 sequence of 135 amino acids. This polypeptide showed homology with mouse and rat GlyCAM-1 (Glycosylation dependent Cell Adhesion Molecule 1) a protein which has been shown to act as a ligand for lymphocytes. The similarity was most profound between the signal peptides and three short regions of the mature polypeptides. Additionally structural conservation was predicted by computer analysis in the shape of a C-terminal amphipathic helix. PP3 was found to be expressed in mammary gland but not in peripheral lymph nodes, Peyer's pathes, lung, spleen, heart, and muscle.

Sulfation-dependent recognition of high endothelial venules (HEV)-ligands by L-selectin and MECA 79, and adhesion-blocking monoclonal antibody

L-selectin is a lectin-like receptor that mediates the attachment of lymphocytes to high endothelial venules (HEV) of lymph nodes during the process of lymphocyte recirculation. Two sulfated, mucin-like glycoproteins known as Sgp50/GlyCAM-1 and Sgp90/CD34 have previously been identified as HEV-associated ligands for L-selectin. These proteins were originally detected with an L-selectin/Ig chimera called LEC-IgG. GlyCAM-1 and CD34 are also recognized by an antiperipheral node addressin (PNAd) mAb called MECA 79, which blocks L-selectin-dependent adhesion and selectively stains lymph node HEV. The present study compares the requirements for the binding of MECA 79 and LEC-IgG to HEV-ligands. Whereas desialylation of GlyCAM-1 and CD34 drastically reduced binding to LEC-IgG, this treatment enhanced the binding of GlyCAM-1 to MECA 79. In contrast, the binding of both MECA 79 and LEC-IgG to GlyCAM-1 and CD34 was greatly decreased when the sulfation of these ligands was reduced with chlorate, a metabolic inhibitor of sulfation. Because MECA 79 stains HEV-like vessels at various sites of inflammation, recognition by L-selectin of ligands outside of secondary lymphoid organs may depend on sulfation. In addition to their reactivity with GlyCAM-1 and CD34, both MECA 79 and LEC-IgG recognize an independent molecule of approximately 200 kD in a sulfate-dependent manner. Thus, this molecule, which we designate Sgp200, is an additional ligand for L-selectin.

Distinct cell surface ligands mediate T lymphocyte attachment and rolling on P and E selectin under physiological flow

Memory T lymphocytes extravasate at sites of inflammation, but the mechanisms employed by these cells to initiate contact and tethering with endothelium are incompletely understood. An important part of leukocyte extravasation is the initiation of rolling adhesions on endothelial selectins; such events have been studied in monocytes and neutrophils but not lymphocytes. In this study, the potential of T lymphocytes to adhere and roll on endothelial selectins in vitro was investigated. We demonstrate that T cells can form tethers and rolling adhesions on P selectin and E selectin under physiologic flow conditions. Tethering and rolling on P selectin was independent of cell-surface cutaneous lymphocyte antigen (CLA) expression, which correlated strictly with the capacity of T cells to form rolling adhesions under flow on E selectin. T cell tethering to P selectin was abolished by selective removal of cell surface sialomucins by a P. haemolytica O-glycoprotease, while cutaneous lymphocyte antigen expression was unaffected. A sialomucin molecule identical or closely related to P selectin glycoprotein ligand-1 (PSGL-1), the major P selectin ligand on neutrophils and HL-60 cells, appears to be a major T cell ligand for P selectin. P selectin glycoprotein ligand-1 does not appear to support T cell rolling on E selectin. In turn, E selectin ligands do not appear to be associated with sialomucins. These data demonstrate the presence of structurally distinct ligands for P or E selectins on T cells, provide evidence that both ligands can be coexpressed on a single T cell, and mediate tethering and rolling on the respective selectins in a mutually exclusive fashion.

The selectins and their ligands

The selectins are a family of carbohydrate-binding proteins, or lectins, that have stimulated tremendous interest because of their involvement in a wide array of interactions between leukocytes and endothelial cells. Highlights of recent progress include an extension of the list of instances of selectin participation in inflammatory diseases, further definition of selectin carbohydrate specificities, and identification of their carbohydrate-based ligands.

Selectins--glycoprotein targets for therapeutic intervention in inflammation

Inflammation can be a beneficial response in the host for the control of infection and injury. However, occasionally, the inflammatory response can result in acute systemic collapse or, more frequently, a chronic reaction such as that observed in autoimmune disease, Crohn's disease and asthma. Injury to tissues or organs results in leukocyte adhesion to the endothelial cell surface, followed by diapedesis. Investigation of the initial leukocyte-endothelium adhesion processes has clearly shown the involvement of an inducible set of molecules, called selectins, on the endothelial and leukocyte cell surfaces. These molecules are of interest as the interactions with their respective ligands appear to involve carbohydrates. The exact nature of these interactions is still being elucidated. Therapeutic intervention using carbohydrate small-molecule mimetics may be beneficial in the modification of the inflammatory process.

Myelin localization of a central nervous system ligand for L-selectin

L-selectin is a lectin-like receptor involved in lymphocyte attachment to lymph node high endothelial venules (HEV). Previously, we showed that L-selectin also participates in the in vitro attachment of lymphocytes to central nervous system (CNS) white matter. Use of an L-selectin chimera demonstrated ligand sites within CNS white matter but not the peripheral nervous system (PNS). Now employing higher resolution mapping, including EM cytochemistry, we localize the ligands to the actual myelin sheaths of CNS neurons. In the shiverer mouse, which lacks compact myelin, ligands are greatly diminished. Comparison of the myelin-associated ligand with the previously characterized HEV-ligands demonstrates a number of differences.

Selectin ligands

The selectins initiate many critical interactions among blood cells. The volume of information and diversity of opinions on the nature of the biologically relevant ligands for selectins is remarkable. This review analyzes the matter and suggests the hypothesis that at least some of the specificity may involve recognition of "clustered saccharide patches."

A liquid-phase binding analysis for L-selectin. A strong dependency on highly clustered sulfate groups

L-selectin, together with E- and P-selectins, forms a newer group of cell adhesion molecules which are believed to interact with carbohydrate ligands [Lasky, L. A., Singer, M. S., Yednoch, T. A., Dowbenko, D., Fennie, C., Rodriguez, H., Nguyen, T., Stachel, S. & Rosen, S. D. (1989) Cell 56, 1045-1055]. Using radiolabeled fucoidan as a reference ligand, we have developed a new liquid-phase microcentrifugation assay where fine differences in binding affinity can be compared accurately. We found that glucan sulfates strongly inhibited the binding of fucoidan by murine L-selectin-IgG chimera. The efficacy of inhibition is extremely dependent on the size (up to 12 kDa) and the sulfate density (up to two sulfate groups/glucose molecule) of the glucan sulfates. The nature of the inter-glucose linkages is also important. These data suggest that the binding by L-selectin prefers certain clustering and proper spatial arrangement of the anionic groups.

Purification and characterization of N-acetylglucosamine-6-sulfate sulfatase from bovine kidney: evidence for the presence of a novel endosulfatase activity

N-Acetylglucosamine-6-sulfate sulfatase (NG6SS) is an enzyme that catalyzes the hydrolysis of sulfate esters from the C-6 hydroxyl of N-acetylglucosamine. We report our purification and characterization of the enzyme and the discovery that it can remove sulfate from internally sulfated GlcNAc on glycopeptides and glycoproteins. The enzyme was purified from bovine kidney over 200,000-fold using a combination of ion-exchange and size-exclusion chromatography. NG6SS is soluble and occurs as a single subunit with apparent solution molecular weight of 60.2 kDa on gel filtration chromatography and approximately 52.5 and 57.8 kDa on reducing and nonreducing SDS/PAGE, respectively. The enzyme is highly basic and exhibits a broad pH range with an optimum at pH 6.5 and a temperature optimum of 37 degrees C. Among the mono- and disaccharide sulfates tested, only GlcNAc-6-SO4 is an effective substrate with a Km of 4.7 mM, and either free sulfate or phosphate inhibits the activity. Unexpectedly, we found that the enzyme displays endosulfatase activity and quantitatively releases 35SO4 from 35SO4-labeled glycopeptides and intact glycoproteins isolated from human Molt-3 cells, which we have previously shown to synthesize glycoproteins containing GlcNAc-6-SO4 residues within the sequence Gal beta 1-4[SO-3-6]-GlcNAc beta 1-R of complex-type N-linked oligosaccharides. The N-terminal sequence of the bovine NG6SS was homologous to a human-liver-derived N-acetylglucosamine-6-sulfatase. The endosulfatase activity of bovine kidney NG6SS may be important in its potential role in the degradation of sulfated glycans and may make this enzyme a valuable reagent to study the biological functions of sulfated glycoproteins.

Monospecific and common glycoprotein ligands for E- and P-selectin on myeloid cells

E- and P-selectin are inducible cell adhesion molecules on endothelial cells, which function as Ca(2+)-dependent lectins and mediate the binding of neutrophils and monocytes. We have recently identified a 150-kD glycoprotein ligand for E-selectin on mouse myeloid cells, using a recombinant antibody-like form of mouse E-selectin. Here, we report that this ligand does not bind to an analogous P-selectin fusion protein. Instead, the chimeric P-selectin-IgG protein recognizes a 160-kD glycoprotein on the mouse neutrophil progenitor 32D cl 3, on mature mouse neutrophils and on human HL60 cells. The binding is Ca(2+)-dependent and requires the presence of sialic acid on the ligand. This P-selectin-ligand is not recognized by E-selectin. Removal of N-linked carbohydrate side chains from the 150-kD and the 160-kD monospecific selectin ligands abolishes the binding of both ligands to the respective selectin. Treatment of HL60 cells with Peptide: N-glycosidase F inhibited cell binding to P- and E-selectin. In addition, glycoproteins of 230 and 130 kD were found on mature mouse neutrophils, which bound both to E- and P-selectin in a Ca(2+)-dependent fashion. The signals detected for these ligands were 15-20-fold weaker than those for the monospecific ligands. Both proteins were heavily sialylated and selectin-binding was blocked by removal of sialic acid, but not by removal of N-linked carbohydrates. Our data reveal that E- and P-selectin recognize two categories of glycoprotein ligands: one type requires N-linked carbohydrates for binding and is monospecific for each of the two selectins and the other type binds independent of N-linked carbohydrates and is common for both endothelial selectins.

Inhibition of leukocyte rolling with polysaccharide fucoidin prevents pleocytosis in experimental meningitis in the rabbit

Inflammatory recruitment of leukocytes into the cerebrospinal fluid (CSF) during bacterial meningitis has been shown to contribute significantly to the neurological damage commonly associated with this serious disease. In this study we tested whether or not inhibition of leukocyte rolling, a precondition for firm leukocyte adhesion to vascular endothelium in vivo, may reduce CSF leukocyte recruitment and associated inflammatory changes in rabbits with experimental meningitis. As documented by intravital microscopy of small venules in the rabbit mesentery and tenuissimus muscle, leukocyte rolling was rapidly and profoundly reduced by intravenous treatment with the polysaccharide fucoidin, a homopolymer of sulfated L-fucose known to block the function of the leukocytic "rolling receptor" L-selectin. Moreover, fucoidin treatment dramatically reduced the accumulation of both leukocytes and plasma protein in the CSF of rabbits challenged intrathecally with pneumococcal antigen. These main findings thus illustrate that inhibition of leukocyte rolling, an early and obligatory step in the process of leukocyte extravasation, may be an effective therapeutic approach to attenuate leukocyte-dependent central nervous system damage in bacterial meningitis.

The role of sialic acid in the localization of lymphocytes in the spleen

The role of carbohydrate structures in the interaction of lymphocytes and endothelial cells is well established. Here the influence of sialic acid in the entrance and localization of lymphocytes in the lymphoid white pulp area of the spleen was studied by injecting sialidase in vivo. A role for sialic acid molecules on stromal elements of the spleen was determined. Although the identity of the cells that bear sialidase sensitive receptors could not be established, a role for marginal zone macrophages could be ruled out by macrophage depletion studies.

Selectins

The selectins are three related receptors that initiate rolling of leukocytes on activated platelets or endothelium through Ca(2+)-dependent recognition of cell surface carbohydrates. Cell adhesion may be enhanced by a limited number of membrane glycoproteins that present high affinity carbohydrate ligands to specific selectins. The synthesis and surface display of the selectins is normally tightly controlled, but inappropriate expression may contribute to inflammatory disorders. Recent in vivo studies confirm the importance of the selectins in both physiological and pathological leukocyte recruitment.

Potential adhesion mechanisms for localisation of haemopoietic progenitors to bone marrow stroma

Haemopoiesis occurs in intimate physical association with the stromal elements of the bone marrow. Current evidence supports the hypothesis that the restriction of primitive haemopoietic progenitor cells (HPC) to the bone marrow involves developmentally regulated adhesive interactions between HPC and the stromal cell microenvironment. This review examines the expression and function of cell adhesion molecules (CAM) on human HPC and marrow stromal cells. These data demonstrate that a broad range of CAMs representing at least three adhesion molecule superfamilies (integrins, selectins, immunoglobulin gene superfamily) participate in these adhesive interactions. We discuss the potential contribution of these various adhesion molecules to homing of HPC to the bone marrow, their retention within the extravascular haemopoietic compartment and their egress into the peripheral circulation. It is likely that each process is mediated not by a single binding event but requires the coordinated participation of multiple receptor-ligand pairs.

L-selectin-mediated lymphocyte rolling on MAdCAM-1

The L-selectin, a cell surface C-type lectin, directs lymphocyte traffic to lymph nodes, and contributes to lymphocyte homing to Peyer's patches and to leukocyte interactions with inflamed venules. Here we report that the mucosal vascular addressin MAdCAM-1, a mucosal endothelial adhesion molecule with immunoglobulin- and mucin-like domains, is a facultative ligand for L-selectin. MAdCAM-1 isolated from mesenteric lymph nodes, but not from cultured endothelioma cells, bears N-glycanase-resistant sialic acid-containing carbohydrate which supports adhesion of L-selectin-transfected lymphoid cells under shear. Interacting lymphoid cells display a 'rolling' behaviour similar to the selectin-dependent rolling of neutrophils observed in inflamed venules. MAdCAM-1 is also a ligand for the lymphocyte integrin homing receptor for Peyer's patches, alpha 4 beta 7 (ref. 7), and may be uniquely adapted to support both selectin-mediated lymphocyte rolling and integrin-mediated adhesion and arrest in vivo.

Interferon-alpha induces the expression of the L-selectin homing receptor in human B lymphoid cells

The L-selectin homing receptor expressed by lymphocytes mediates the initial attachment of these cells to high endothelial venules within peripheral lymph nodes. This adhesive interaction is required for the migration of B and T lymphocytes from the blood into peripheral lymph nodes. There is currently little information regarding the nature of the factors involved in the regulation of the synthesis and expression of L-selectin by lymphocytes. In this report, the immunomodulatory cytokine interferon-alpha (IFN-alpha) was shown to markedly upregulate the surface density of L-selectin in the established human B lymphoid Daudi cell line and in a subpopulation of tissue-derived human B lymphoid cells. Other cytokines such as IFN-gamma, tumor necrosis factor-alpha, interleukin (IL)-1 beta, IL-2, IL-4, IL-6, and low molecular weight B cell growth factor did not affect L-selectin surface expression in the model Daudi B cell line. Upregulation of L-selectin surface density in IFN-alpha-treated Daudi B cells correlated directly with an increase in L-selectin mRNA steady state levels and enhanced L-selectin-dependent binding to a carbohydrate-based ligand, phosphomonoester core polysaccharide. Regulation of L-selectin mRNA by IFN-alpha had characteristics similar to that of classical IFN-stimulated genes including rapid kinetics of induction, protein-synthesis-independent induction, and sensitivity to tyrosine-kinase inhibitors. IFN-alpha did not upregulate L-selectin mRNA levels or surface expression in an IFN-resistant Daudi subclone which exhibits a defect in the signal transduction pathway required for the transcriptional induction of IFN-stimulated genes. These data demonstrate a fundamental role for IFN-alpha in regulating L-selectin synthesis and expression in human B lymphoid cells and suggest a mechanism whereby this cytokine regulates the regional trafficking of B cells to peripheral lymph nodes.