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

Sulfated glycoconjugates enhance CD36-dependent adhesion ofPlasmodium falciparum–infected erythrocytes to human microvascular endothelial cells

A novel adhesive pathway that enhances the adhesion ofPlasmodium falciparum-infected erythrocytes (IEs) to endothelial cells has been identified. The sulfated glycoconjugates heparin, fucoidan, dextran sulfate 5000, and dextran sulfate 500 000 caused a dramatic increase in adhesion of IEs to human dermal microvascular endothelial cells. The same sulfated glycoconjugates had little effect on IE adhesion to human umbilical vein endothelial cells, a CD36-negative cell line. The effect was abolished by a monoclonal antibody directed against CD36, suggesting that enhanced adhesion to endothelium is dependent on CD36. No effect was observed on adhesion to purified platelet CD36 cells immobilized on plastic. The same sulfated glycoconjugates enhanced adhesion of infected erythrocytes to COS cells transfected with CD36, and this was inhibited by the CD36 monoclonal antibody. These findings demonstrate a role for sulfated glycoconjugates in endothelial adherence that may be important in determining the location and magnitude of sequestration through endogenous carbohydrates. In addition, they highlight possible difficulties that may be encountered from the proposed use of sulfated glycoconjugates as antiadhesive agents in patients with severe malaria.

Sulfated glycoconjugates enhance CD36-dependent adhesion ofPlasmodium falciparum–infected erythrocytes to human microvascular endothelial cells

A novel adhesive pathway that enhances the adhesion ofPlasmodium falciparum-infected erythrocytes (IEs) to endothelial cells has been identified. The sulfated glycoconjugates heparin, fucoidan, dextran sulfate 5000, and dextran sulfate 500 000 caused a dramatic increase in adhesion of IEs to human dermal microvascular endothelial cells. The same sulfated glycoconjugates had little effect on IE adhesion to human umbilical vein endothelial cells, a CD36-negative cell line. The effect was abolished by a monoclonal antibody directed against CD36, suggesting that enhanced adhesion to endothelium is dependent on CD36. No effect was observed on adhesion to purified platelet CD36 cells immobilized on plastic. The same sulfated glycoconjugates enhanced adhesion of infected erythrocytes to COS cells transfected with CD36, and this was inhibited by the CD36 monoclonal antibody. These findings demonstrate a role for sulfated glycoconjugates in endothelial adherence that may be important in determining the location and magnitude of sequestration through endogenous carbohydrates. In addition, they highlight possible difficulties that may be encountered from the proposed use of sulfated glycoconjugates as antiadhesive agents in patients with severe malaria.

Cell adhesion receptors in lymphoma dissemination

Regulated lymphocyte trafficking is essential for the control and integration of systemic immune responses. This homing process disperses the immunologic repertoire, guides lymphocyte subsets to the specialized microenvironments that control their differentiation and survival, and targets immune effector cells to sites of antigenic insult. This review discusses data indicating that the adhesion receptors regulating the trafficking of normal lymphocytes are also expressed and functionally active in their malignant counterparts, the non-Hodgkin lymphomas. These “homing receptors” appear to mediate the highly tissue-specific dissemination of specific lymphoma subtypes, such as lymphomas of the mucosa-associated lymphoid tissues and lymphomas of the skin. Furthermore, as a result of their capability to enhance lymphoma dissemination and to transduce signals into the cell, promoting cell growth and survival, adhesion receptors may contribute to lymphoma aggressiveness. Taken together, the data offer a framework for understanding the dissemination routes of non-Hodgkin lymphomas and suggest that adhesion receptors, specifically those of the CD44 family, may present useful tools to predict prognosis in patients with lymphomas.

Epitope mapping of monoclonal antibodies specific for a macrophage lectin: a calcium-dependent epitope is in the carbohydrate recognition domain

Mouse macrophage galactose/N-acetylgalactosamine-specific calcium-type lectin (mMGL) has a calcium-dependent conformational epitope which is a ligand-induced binding site. A monoclonal antibody (mAb) specific for this epitope (LOM-11) stabilize lectin activity. We performed mapping for this conformational epitope using trypsin fragments that contain a carbohydrate recognition domain (CRD) and chimeric recombinant proteins between mMGL and a human counterpart of this molecule. Binding site for the mAb LOM-11 was mapped within the C-terminal 59 amino acids of CRD. Binding sites for all four mAbs that block carbohydrate ligand binding were also mapped in the C-terminal half of CRD. These results indicated that the calcium-dependent site potentially involved in protein-protein interaction, regulatory or for coordinated binding, is mapped within CRD in addition to the independent carbohydrate binding site, and that both of the distinct sites may have spatial proximity.

Constitutive expression of GlyCAM-1 core protein in the rat cochlea

Glycosylation-dependent cell adhesion molecule-1 (GlyCAM-1) is a mucin-like glycoprotein previously identified on high endothelial venules (HEV) of lymph nodes and also in lactating mammary glands. A specifically glycosilated form of GlyCAM-1 on HEV has been shown to be a ligand for a leukocyte L-selectin, which plays an important role in leukocyte rolling along the inflamed endothelium. Here we report that GlyCAM-1 is also expressed in the cochlea. Immunohistochemistry revealed the lateral wall of the cochlea, tectorial membrane, modiolus, organ of corti, and spiral modiolar vein (SMV) to be strongly stained with polyclonal anti-GlyCAM-1 antibody. Moreover, RT-PCR of the cochlear tissue by the use of specific oligonucleotide primers for rat GlyCAM-1 generated a 378 bp product which was then verified by nucleotide sequencing to represent GlyCAM-1. Electron microscopic investigation revealed the presence of GlyCAM-1 over the entire lumenal surface of the vessels, and the basolateral infoldings in stria vascularis. However, soluble L-selectin or mAb MECA-79 which recognizes a carbohydrate epitope on functional L-selectin ligands bound only to the spiral ligament, tectorial membrane and modiolus. These observations suggest that GlyCAM-1 expressed in the cochlear region is heterogenous in terms of its glycosylation.

Sulfotransferases of two specificities function in the reconstitution of high endothelial cell ligands for L-selectin

L-selectin, a lectin-like receptor, mediates rolling of lymphocytes on high endothelial venules (HEVs) in secondary lymphoid organs by interacting with HEV ligands. These ligands consist of a complex of sialomucins, candidates for which are glycosylation- dependent cell adhesion molecule 1 (GlyCAM-1), CD34, and podocalyxin. The ligands must be sialylated, fucosylated, and sulfated for optimal recognition by L-selectin. Our previous structural characterization of GlyCAM-1 has demonstrated two sulfation modifications, Gal-6-sulfate and GlcNAc-6-sulfate in the context of sialyl Lewis x. We now report the cloning of a Gal-6-sulfotransferase and a GlcNAc-6-sulfotransferase, which can modify GlyCAM-1 and CD34. The Gal-6-sulfotransferase shows a wide tissue distribution. In contrast, the GlcNAc-6-sulfotransferase is highly restricted to HEVs, as revealed by Northern analysis and in situ hybridization. Expression of either enzyme in Chinese hamster ovary cells, along with CD34 and fucosyltransferase VII, results in ligand activity, as detected by binding of an L-selectin/IgM chimera. When coexpressed, the two sulfotransferases synergize to produce strongly enhanced chimera binding.

Selective induction of endothelial L-selectin ligand in human lung inflammation

During inflammation, leukocyte emigration from the circulation can be directed by the endothelium, in part by the inducible endothelial adhesion ligand for L-selectin. In this study, endothelial L-selectin ligand expression was localized by immunohistochemistry in human lung in several different types of lung inflammation and in systemic inflammation. Endothelial L-selectin ligand was not seen in normal lung or in acute pneumonia involving neutrophil accumulation. However, the endothelial ligand was seen in most cases of chronic interstitial pneumonia with mononuclear cell accumulation (a mean of 5.9% of microvessels positive). Regarding granulomatous conditions, in sarcoidosis the endothelial ligand was not identified, but in tuberculous infection some expression was seen in a minority of cases (mean 3.3% of microvessels positive). In contrast, consistent, typically extensive ligand induction (mean 33.4% of microvessels positive) was present in bronchiectatic lung showing prominent lymphocytic accumulation and venules with thickened (high) endothelium, the latter being normally characteristic of lymphoid tissue in which L-selectin ligand is known to be constitutively expressed. Lung from subjects with systemic infection was negative for endothelial expression of the ligand. These studies show how in a defined extralymphoid tissue induction of endothelial L-selectin ligand depended not only on the presence or absence of an inflammatory state, but also on the nature of the inflammation.

Identification and characterization of ligands for L-selectin in the kidney. I. Versican, a large chondroitin sulfate proteoglycan, is a ligand for L-selectin

Ligands for a leukocyte adhesion molecule, L-selectin, are expressed not only in the specific vascular endothelium in lymph nodes and Peyer's patches but also in the extravascular tissues such as the brain white matter, choroid plexus and the kidney distal straight tubuli. However, the biological significance of these extravascular ligands is currently unknown. We now report the purification and characterization of a novel extravascular ligand for L-selectin in the kidney using a tubule-derived cell line, ACHN. Binding of L-selectin-IgG chimera (LEC-IgG) to the isolated ligand was specifically blocked with either (i) anti-L-selectin mAb, (ii) EDTA, (iii) fucoidan, (iv) chondroitin sulfate (CS) B or CS E, or (v) treatment with chondroitinases. Partial amino acid sequencing, Western blotting and immunoprecipitation analyses showed that a major ligand for L-selectin in ACHN cells is versican of 1600 kDa. Histochemical as well as biochemical analyses verified that a versican subspecies in the kidney was indeed reactive with L-selectin. Studies with cell lines including those derived from the kidney indicated that a certain glycoform and/or splice form of versican is reactive with L-selectin. Under pathological conditions such as those induced by unilateral ureteral obstruction, versican was shed from the distal straight tubuli and became localized in the adjacent vascular bundles around which a substantial leukocyte infiltration was concomitantly observed. Possible involvement of versican in leukocyte trafficking into the kidney under diseased conditions is discussed.

Identification and characterization of ligands for L-selectin in the kidney. II. Expression of chondroitin sulfate and heparan sulfate proteoglycans reactive with L-selectin

Ligands for the leukocyte adhesion molecule L-selectin are expressed not only in lymph node high endothelial venules (HEV) but also in the renal distal tubuli. Here we report that L-selectin-reactive molecules in the kidney are chondroitin sulfate and heparan sulfate proteoglycans of 500-1000 kDa, unlike those in HEV bearing sialyl Lewis X-like carbohydrates. Binding of L-selectin to these molecules was mediated by the lectin domain of L-selectin and required divalent cations. Binding was inhibited by chondroitinase and/or heparitinase but not sialidase. Thus, L-selectin can recognize chondroitin sulfate and heparan sulfate glycosaminoglycans structurally distinct from sialyl Lewis X-like carbohydrates.

Mechanisms that regulate the function of the selectins and their ligands

Selectins are a family of three cell adhesion molecules (L-, E-, and P-selectin) specialized in capturing leukocytes from the bloodstream to the blood vessel wall. This initial cell contact is followed by the selectin-mediated rolling of leukocytes on the endothelial cell surface. This represents the first step in a cascade of molecular interactions that lead to leukocyte extravasation, enabling the processes of lymphocyte recirculation and leukocyte migration into inflamed tissue. The central importance of the selectins in these processes has been well documented in vivo by the use of adhesion-blocking antibodies as well as by studies on selectin gene-deficient mice. This review focuses on the molecular mechanisms that regulate expression and function(s) of the selectins and their ligands. Cell-surface expression of the selectins is regulated by a variety of different mechanisms. The selectins bind to carbohydrate structures on glycoproteins, glycolipids, and proteoglycans. Glycoproteins are the most likely candidates for physiologically relevant ligands. Only a few glycoproteins are appropriately glycosylated to allow strong binding to the selectins. Recently, more knowledge about the structure and the regulated expression of some of the carbohydrates on these ligands necessary for selectin binding has been accumulated. For at least one of these ligands, the physiological function is now well established. A novel and exciting aspect is the signaling function of the selectins and their ligands. Especially in the last two years, convincing data have been published supporting the idea that selectins and glycoprotein ligands of the selectins participate in the activation of leukocyte integrins.

Vascular and non-vascular ligands for L-selectin

Ligands for L-selectin are expressed not only on vascular endothelial cells but also in the extravascular tissues. In this article, we summarize the current understanding of the "vascular" ligands for L-selectin. We also describe identification of "non-vascular" ligands for L-selectin and discuss their possible biological significance.

The Sialomucin CD164 (MGC-24v) Is an Adhesive Glycoprotein Expressed by Human Hematopoietic Progenitors and Bone Marrow Stromal Cells That Serves as a Potent Negative Regulator of Hematopoiesis

Mucin-like molecules represent an emerging family of cell surface glycoproteins expressed by cells of the hematopoietic system. We report the isolation of a cDNA clone that encodes a novel transmembrane isoform of the mucin-like glycoprotein MGC-24, expressed by both hematopoietic progenitor cells and elements of the bone marrow (BM) stroma. This molecule was clustered as CD164 at the recent workshop on human leukocyte differentiation antigens. CD164 was identified using a retroviral expression cloning strategy and two novel monoclonal antibody (MoAb) reagents, 103B2/9E10 and 105.A5. Both antibodies detected CD164/MGC-24v protein expression by BM stroma and subpopulations of the CD34+ cells, which include the majority of clonogenic myeloid (colony-forming unit–granulocyte-macrophage [CFU-GM]) and erythroid (blast-forming unit-erythroid [BFU-E]) progenitors and the hierarchically more primitive precursors (pre-CFU). Biochemical and functional characterization of CD164 showed that this protein represents a homodimeric molecule of approximately 160 kD. Functional studies demonstrate a role for CD164 in the adhesion of hematopoietic progenitor cells to BM stromal cells in vitro. Moreover, antibody ligation of CD164 on primitive hematopoietic progenitor cells characterized by the cell surface phenotype CD34BRIGHTCD38− results in the decreased recruitment of these cells into cell cycle, suggesting that CD164 represents a potent signaling molecule with the capacity to suppress hematopoietic cell proliferation.

© 1998 by The American Society of Hematology.

The Sialomucin CD164 (MGC-24v) Is an Adhesive Glycoprotein Expressed by Human Hematopoietic Progenitors and Bone Marrow Stromal Cells That Serves as a Potent Negative Regulator of Hematopoiesis

Mucin-like molecules represent an emerging family of cell surface glycoproteins expressed by cells of the hematopoietic system. We report the isolation of a cDNA clone that encodes a novel transmembrane isoform of the mucin-like glycoprotein MGC-24, expressed by both hematopoietic progenitor cells and elements of the bone marrow (BM) stroma. This molecule was clustered as CD164 at the recent workshop on human leukocyte differentiation antigens. CD164 was identified using a retroviral expression cloning strategy and two novel monoclonal antibody (MoAb) reagents, 103B2/9E10 and 105.A5. Both antibodies detected CD164/MGC-24v protein expression by BM stroma and subpopulations of the CD34+ cells, which include the majority of clonogenic myeloid (colony-forming unit–granulocyte-macrophage [CFU-GM]) and erythroid (blast-forming unit-erythroid [BFU-E]) progenitors and the hierarchically more primitive precursors (pre-CFU). Biochemical and functional characterization of CD164 showed that this protein represents a homodimeric molecule of approximately 160 kD. Functional studies demonstrate a role for CD164 in the adhesion of hematopoietic progenitor cells to BM stromal cells in vitro. Moreover, antibody ligation of CD164 on primitive hematopoietic progenitor cells characterized by the cell surface phenotype CD34BRIGHTCD38− results in the decreased recruitment of these cells into cell cycle, suggesting that CD164 represents a potent signaling molecule with the capacity to suppress hematopoietic cell proliferation.

© 1998 by The American Society of Hematology.

Regulation of fucosyltransferase-VII expression in peripheral lymph node high endothelial venules

Binding of L-selectin to the highly glycosylated peripheral lymph node addressins (PNAd) plays a central role in the normal recirculation of lymphocytes between the bloodstream and the lymph node. This interaction requires correct fucosylation of the PNAd, mediated by the recently identified fucosyltransferase-VII (Fuc-TVII). Here we show that during ontogeny Fuc-TVII is absent at the day of birth, barely detectable on day 1, and clearly present from day 2 onwards. PNAd expression as detected by the MECA-79 antibody precedes the expression of Fuc-TVII. Furthermore, we demonstrate that in adult mice antigenic stimulation of peripheral lymph nodes leads to a temporary disappearance of Fuc-TVII at days 2 and 3 after stimulation, followed by a complete reappearance by day 4, while expression of MECA-79 is never completely absent during this period. Finally, occlusion of afferent lymphatics to peripheral lymph nodes resulted in a decreased expression of Fuc-TVII in the high endothelial venules by day 5, and complete disappearance within 8 days. We conclude that the activity of Fuc-TVII in cells of high endothelial venules is directly affected by afferent lymph and activation processes that occur in the lymph node after antigenic stimulation. The expression of Fuc-TVII is therefore yet another level at which the function of high endothelial venules, and thus lymphocyte trafficking, can be regulated.

Synthesis of Gal-beta-(1-->4)-GlcNac-beta-(1-->6)-[Gal-beta-(1-->3]-GalNAc-alpha- OBn oligosaccharides bearing O-methyl or O-sulfo groups at C-3 of the Gal residue: specific acceptors for Gal: 3-O-sulfotransferases

Our recent studies have revealed the existence of two distinct Gal: 3-O-sulfotransferases capable of acting on the C-3 position of galactose in a Core 2 branched structure, e.g., Galbeta1-->4GlcNAcbeta1-->6(Galbeta1-->3)GalNacalph a1-->OBenzyl as acceptor to give 3-O-sulfoGalbeta1-->4GlcNAcbeta1-->3(Galbeta1-->3)G alNAcalpha1-->OB 20 and Galbeta1-->4GlcNAcbeta1-->6(3-O-sulfoGalbeta1-->3)G alNAcalpha1-->OB 23. We herein report the synthesis of these two compounds and also that of other modified analogs that are highly specific acceptors for the two sulfotransferases. Appropriately protected 1-thio-glycosides 7, 8, and 10 were employed as glycosyl donors for the synthesis of our target compounds.

Molecular cloning and characterization of an N-acetylglucosamine-6-O-sulfotransferase

We isolated a cDNA clone encoding mouse N-acetylglucosamine-6-O-sulfotransferase based on sequence homology to the previously cloned mouse chondroitin 6-sulfotransferase. The cDNA clone contained an open reading frame that predicts a type II transmembrane protein composed of 483 amino acid residues. The expressed enzyme transferred sulfate to the 6 position of nonreducing GlcNAc in GlcNAcbeta1-3Galbeta1-4GlcNAc. Galbeta1-4GlcNAcbeta1-3Galbeta1-4GlcNAc and various glycosaminoglycans did not serve as acceptors. Expression of the cDNA in COS-7 cells resulted in production of a cell-surface antigen, the epitope of which was NeuAcalpha2-3Galbeta1-4(SO4-6)GlcNAc; double transfection with fucosyltransferase IV yielded Galbeta1-4(Fucalpha1-3)(SO4-6)GlcNAc antigen. The sulfotransferase mRNA was strongly expressed in the cerebrum, cerebellum, eye, pancreas, and lung of adult mice. In situ hybridization revealed that the mRNA was localized in high endothelial venules of mesenteric lymph nodes. The sulfotransferase was concluded to be involved in biosynthesis of glycoconjugates bearing the 6-sulfo N-acetyllactosamine structure such as 6-sulfo sialyl Lewis X. The products of the sulfotransferase probably include glycoconjugates with intercellular recognition signals; one candidate of such a glycoconjugate is an L-selectin ligand.

L-Selectin-Specific Autoantibodies in Murine Lupus: Possible Involvement in Abnormal Homing and Polarization of CD4+ T Cell Subsets

One notable functional abnormality in murine and human systemic lupus erythematosus (SLE) is the defect in the production of IL-2 in association with the deficit in naive CD4+ T cells. The mechanism is unknown, but one idea is that naturally occurring autoantibodies with specificities to the naive CD4+ T cell subpopulation are related to this event. We selected hybridoma monoclonal autoantibodies from SLE-prone (New Zealand Black (NZB) × New Zealand White (NZW))F1 mice that reacted with restricted populations of CD4+ T cells. One of these, H32, was specific for L-selectin, as determined by 1) distribution of Ag H32 on lymphoid cells similar to Mel-14, an epitope of L-selectin; 2) shedding of 80-kDa molecules with epitope H32 from the surface of lymph node cells coincidentally with Mel-14, when stimulated with phorbol ester; 3) cross-inhibitory activities on Ag binding between H32 and Mel-14; and 4) reactivity of H32 with recombinant mouse L-selectin. Pretreatment of 51Cr-labeled lymphocytes from BALB/c mice with H32 significantly inhibited their homing to lymph nodes in vivo. The BALB/c splenic H32+ CD4+ T cell subset produced few cytokines except IL-2, thus corresponding to naive ThP-type cells. This subset was markedly selectively depleted in aged (NZB × NZW)F1 mice. There was an age-associated increase in frequencies and titers of anti-L-selectin autoantibodies in sera from (NZB × NZW)F1 mice. Thus, abnormalities of naive CD4+ T cell subset, including IL-2 production in subjects with SLE, are at least partly attributed to the generation of autoantibodies to L-selectin.

Coordinated binding of sugar, calcium, and antibody to macrophage C-type lectin

Mouse macrophage galactose/N-acetylgalactosamine-specific C-type lectin (MMGL) is a type II transmembrane glycoprotein belonging to the C-type lectin family. Our development of monoclonal antibodies led us to discover that a calcium-dependent conformational change is detected by an antibody (termed mAb LOM-11) and that the antibody's binding to the respective site locks the lectin in an active conformation. These findings correspond to the divalent cation-mediated regulatory mechanisms in a family of cell adhesion molecule integrins that have gained much attention. We now provide direct evidence that mAb LOM-11 increases the affinity of the lectin for calcium ions as a mechanism for the conformational lock using a soluble recombinant form of MMGL (rML) produced in bacteria. Furthermore, we discovered by using an enzyme-linked immunosorbent assay that specific monosaccharides induced a binding site for mAb LOM-11 on the immobilized rML under low calcium environments. We also demonstrated that cell surface MMGL on a transfectant cell line underwent a conformational change upon addition of calcium or ligands, as detected by the binding of mAb LOM-11. These properties are reminiscent of ligand-induced binding sites defined for integrins. The present results suggest a possibility that the mAb LOM-11 binding site on the lectin may be a site at which protein-protein interaction helps to fine tune the specificity of the C-type lectins by means of coordinated recognition mechanisms.

Identification of an N-acetylglucosamine-6-0-sulfotransferase activity specific to lymphoid tissue: an enzyme with a possible role in lymphocyte homing

BACKGROUND

The leukocyte adhesion molecule L-selection participates in the initial attachment of blood-borne lymphocytes to high endothelial venules (HEVs) during lymphocyte homing to secondary lymphoid organs, and contributes to leukocyte adhesion and extravasation in HEV-like vessels at sites of chronic inflammation. The L-selection ligands on lymph mode HEVs are mucin-like glycoproteins adorned with the unusual sulfated carbohydrate epitope, 6-sulfo sialyl Lewis x. Sulfation of this epitope on the N-acetylglucosamine (GlcNAc) residue confers high-avidity L-selection binding, and is thought to be restricted in the vasculature to sites of sustained lymphocyte recruitment. The GlcNAc-6-0 sulfotransferase that installs the sulfate ester may be a key modulator of lymphocyte recruitment to secondary lymphoid organs and sites of chronic inflammation and is therefore a potential target for anti-inflammatory therapy.

RESULTS

A GlcNAc-6-0-sulfotransferase activity was identified within porcine lymph nodes and characterized using a rapid, sensitive, and quantitative assay. We synthesized two unnatural oligosaccharide substrates, GlcNAc beta 1-->6Gal alpha-R and Gal beta 1-->4GlcNAc beta 1-->6Gal alpha-R, that incorporate structural motifs from the native L-selection ligands into an unnatural C-glycosyl hydrocarbon scaffold. The sulfotransferase incorporated greater than tenfold more sulfate into the disaccharide than the trisaccharide, indicating a requirement for a terminal GlcNAc. Activity across tissues was highly restricted to the HEVs within peripheral lymph node.

CONCLUSIONS

The restricted expression of the GlcNAc-6-0-sulfotransferase activity to lymph node HEVs strongly suggestions a role in the biosynthesis of L-selection ligands. In addition, similar sulfated epitopes are known to be expressed on HEV-like vessels of chronically inflamed tissues; indicating that this sulfotransferase may also contribute to inflammatory lymphocyte recruitment. We identified a concise disaccharide motif, GlcNAc beta 1-->6Gal alpha-R, that preserved both recognition and specificity determinants for the GlcNAc-6-0-sulfotransferase. The absence of activity on the trisaccharide Gal beta 1-->6Gal alpha-R indicates a requirement for a substrate with a terminal GlcNAc residue, suggesting that sulfation precedes further biosynthetic assembly of L-selection ligands.

Identification of podocalyxin-like protein as a high endothelial venule ligand for L-selectin: parallels to CD34

The leukocyte adhesion molecule, L-selectin, mediates the recruitment of lymphocytes to secondary lymphoid organs via interactions with specific ligands presented on high endothelial venules (HEV). Although the HEV-derived ligands for L-selectin are still incompletely defined, they share a common sialomucin-like structure which is thought to present clustered oligosaccharides to the lectin domain of L-selectin. Podocalyxin-like protein (PCLP) is a transmembrane sialomucin that is similar in structure to the well-characterized L-selectin ligand CD34. PCLP has been shown previously to be expressed on the foot processes of podocytes in the kidney glomerulus as well as on vascular endothelium at some sites. We have determined that PCLP is present on HEV, where it binds to both recombinant L-selectin and the HEV-specific monoclonal antibody MECA-79. Furthermore, purified HEV-derived PCLP is able to support the tethering and rolling of lymphocytes under physiological flow conditions in vitro. These results suggest a novel function for PCLP as an adhesion molecule and allow the definition of conserved structural features in PCLP and CD34, which may be important for L-selectin ligand function.

The Role of Two Distinct Endothelial Molecules, Vascular Adhesion Protein-1 and Peripheral Lymph Node Addressin, in the Binding of Lymphocyte Subsets to Human Lymph Nodes

Lymphocyte binding to high endothelial venules (HEV) in noninflamed peripheral lymph nodes (PLN) relies heavily on two endothelial adhesion molecules called vascular adhesion protein-1 (VAP-1) defined by mAb 1B2 and the peripheral lymph node addressins (PNAd) defined by mAb MECA-79. Data from several different groups indicate that these two molecules share several characteristics in expression, biochemical structure, and function, raising the possibility that VAP-1 may be identical to the 170- and 90-kDa species of PNAd glycoproteins. In this study, we show that many PLN HEV coexpress these two molecules. In parallel SDS-PAGE analyses, the m.w. of the 90- and 170-kDa forms of these molecules are indistinguishable. Nevertheless, we show by different metabolic labelings, by reciprocal cross-precipitations, and by immunofluorescence stainings of newly established VAP-1 transfectants that the 90- and 170-kDa species of PNAd and VAP-1 are distinct molecules. In functional terms, VAP-1 is strikingly selective in mediating PLN HEV adhesion of CD8-positive, but not of CD4-positive T cells. In contrast, PNAd contributes to the adhesion of both CD4-positive and CD8-positive cells to these vessels. Together, these data show that initial adhesion of CD8-positive lymphocytes to PLN HEV requires a PNAd- and a VAP-1-dependent step that are both essential and may occur simultaneously or sequentially.

L-Selectin ligands that are O-glycoprotease resistant and distinct from MECA-79 antigen are sufficient for tethering and rolling of lymphocytes on human high endothelial venules

During the process of lymphocyte recirculation, lymphocytes bind via L-selectin to sulfated sialyl-Lewisx (sLex)-containing carbohydrate ligands expressed on the surface of high endothelial venules (HEV). We have examined the expression of sLex on HEV using a panel of mAbs specific for sLex and sLex-related structures, and have examined the function of different sLex-bearing structures using an in vitro assay of lymphocyte rolling on HEV. We report that three sLex mAbs, 2F3, 2H5, and CSLEX-1, previously noted to bind with high affinity to glycolipid-linked sLex, vary in their ability to stain HEV in different lymphoid tissues and bind differentially to O-linked versus N-linked sLex on glycoproteins. Treatment of tissue sections with neuraminidase abolished staining with all three mAbs but slightly increased staining with MECA-79, a mAb to a sulfation-dependent HEV-associated carbohydrate determinant. Treatment of tissue sections with O-sialoglycoprotease under conditions that removed the vast majority of MECA-79 staining, only partially reduced staining with the 2F3 and 2H5 mAbs. Using a novel rolling assay in which cells bind under flow to HEV of frozen tissue sections, we demonstrate that a pool of O-sialoglycoprotease-resistant molecules is present on HEV that is sufficient for attachment and rolling of lymphocytes via L-selectin. This interaction is not inhibited by the mAb MECA-79. Furthermore, MECA-79 mAb blocks binding to untreated sections by only 30%, whereas the sLex mAb 2H5 blocks binding by approximately 60% and a combination of MECA-79 and 2H5 mAb blocks binding by 75%. We conclude that a pool of O-glycoprotease-resistant sLex-like L-selectin ligands exist on human HEV that is distinct from the mucin-associated moieties recognized by MECA-79 mAb. We postulate that these ligands may participate in lymphocyte binding to HEV.

Complexity and differential expression of carbohydrate epitopes associated with L-selectin recognition of high endothelial venules

Carbohydrate ligands for lymphocyte L-selectin are expressed on high endothelial venules (HEVs) in peripheral lymph nodes and sites of chronic inflammation and mediate the recruitment of lymphocytes from the blood into these tissues. In the mouse, these ligands, collectively termed the peripheral lymph node addressin (PNAd), have been shown to contain fucose, sialic acid, and sulfate and to include several HEV glycoproteins including GlyCAM-1, CD34, and MAdCAM-1. Monoclonal antibody (MAb) MECA-79, which binds a sulfate-dependent epitope, recognizes PNAd in both mouse and man. In humans, only CD34 has been identified among the glycoprotein species that react with MECA-79. Although P-selectin is highly expressed in tonsil HEVs, it was not found to react with MECA-79 or to support L-selectin-mediated lymphocyte rolling. To further characterize human PNAd, MAbs were developed against purified PNAd immunoisolated from human tonsil. MAbs JG-1, JG-5, JG-9, and JG-10, like MECA-79, bind HEVs in human tonsil and react similarly in Western blots, and JG-9 and JG-10 also block lymphocyte rolling on purified PNAd. In addition, by competitive ELISA on purified tonsil PNAd, all MAbs were found to react with overlapping epitopes. However, JG-1, JG-5, JG-9, and JG-10 do not recognize mouse PNAd, and unlike MECA-79, they recognize determinants that are sensitive to neuraminidase. Strikingly, the epitope recognized by JG-1, although abundant in tonsil and peripheral lymph node, is absent from appendix HEVs or HEVs in some samples of chronically inflamed skin, even though these HEVs are MECA-79 reactive. Moreover, although JG-5 and JG-9 react well with tonsil, peripheral lymph node, and inflamed skin HEVs, they react only with occasional endothelial cells in appendix tissues. These findings point to significant diversity in the carbohydrate determinants expressed by HEVs and recognized by L-selectin and demonstrate their differential representation in different sites in vivo. These antibodies should be useful in probing the precise structure of human L-selectin ligands.

Molecular cloning of a new secreted sulfated mucin-like protein with a C-type lectin domain that is expressed in lymphoblastic cells

We have previously demonstrated hyposialylation of the two major CD45 and leukosialin (CD43) molecules at the surface of latently human immunodeficiency virus type 1-infected CEM T cells (CEMLAI/NP), (Lefebvre, J. C., Giordanengo, V., Doglio, A., Cagnon, L., Breittmayer, J. P., Peyron, J. F., and Lesimple, J. (1994) Virology 199, 265-274; Lefebvre, J. C., Giordanengo, V., Limouse, M., Doglio, A., Cucchiarini, M., Monpoux, F., Mariani, R., and Peyron, J. F. (1994) J. Exp. Med. 180, 1609-1617). Searching to clarify mechanism(s) of hyposialylation, we observed two sulfated secreted glycoproteins (molecular mass approximately 47 and approximately 40 kDa) (P47 and P40), which were differentially sulfated and/or differentially secreted in the culture supernatants of CEMLAI/NP cells when compared with parental CEM cells. A hybridoma clone (7H1) resulting from the fusion between CEMLAI/NP and human embryonic fibroblasts MRC5 cells produced very large amounts of P47 that was purified using Jacalin lectin (specific for O-glycans) and microsequenced. Cloning of P47 was achieved using a CEMLAI/NP cDNA library screened with a degenerate oligonucleotide probe based on its NH2-terminal amino acid sequence. A single open reading frame encoding a protein of 323 amino acids was deduced from the longest isolated recombinant (1.4 kilobase). P47 is a secreted sulfated protein. It carries an NH2-terminal RGD (Arg-Gly-Asp) triplet, a striking alpha-helical leucine zipper composed of six heptads, and a C-terminal C-type lectin domain. The NH2-terminal portion is rich in glutamic acids with a predicted pI of 3.9. In addition, a hinge region with numerous condensed potential sites for O-glycan side chains, which are also the most likely sulfation sites, is located between the RGD and leucine zipper domains. Transcripts were detected in lymphoid tissues (notably bone marrow) and abundantly in T and B lymphoblastoid but very faintly in monocytoid cell lines.

Circulating activated platelets reconstitute lymphocyte homing and immunity in L-selectin-deficient mice

Peripheral lymph nodes (PLN) are critical for immunologic memory formation in response to antigens that penetrate the skin. Blood-borne lymphocytes first encounter such antigens after they home to PLN through a multi-step adhesion process that is normally initiated by L-selectin (CD62L) in high endothelial venules (HEV). Since naive T cells can not enter PLN normally in L-selectin-deficient mice, a delayed type hypersensitivity response to cutaneously applied antigen cannot be mounted. In this study, we report that the administration of activated platelets into the systemic circulation of L-selectin knockout mice restores lymphocyte trafficking to PLN, and reconstitutes T cell-mediated immunity in response to a cutaneous antigen. These effects required platelet-expressed P-selectin that allows activated platelets to transiently form a bridge between lymphocytes and HEV, thereby enabling lymphocytes to undergo subsequent beta2 integrin-dependent firm adhesion. These profound effects of platelet-mediated cell-cell interactions on lymphocyte trafficking and formation of immunologic memory may impact on a variety of autoimmune and inflammatory conditions.

Affinity and kinetic analysis of L-selectin (CD62L) binding to glycosylation-dependent cell-adhesion molecule-1

The selectin family of cell adhesion molecules mediates the tethering and rolling of leukocytes on blood vessel endothelium. It has been postulated that the molecular basis of this highly dynamic adhesion is the low affinity and rapid kinetics of selectin interactions. However, affinity and kinetic analyses of monomeric selectins binding their natural ligands have not previously been reported. Leukocyte selectin (L-selectin, CD62L) binds preferentially to O-linked carbohydrates present on a small number of mucin-like glycoproteins, such as glycosylation-dependent cell adhesion molecule-1 (GlyCAM-1), expressed in high endothelial venules. GlyCAM-1 is a soluble secreted protein which, following binding to CD62L, stimulates beta2-integrin-mediated adhesion of lymphocytes. Using surface plasmon resonance, we show that a soluble monomeric form of CD62L binds to purified immobilized GlyCAM-1 with a dissociation constant (Kd) of 108 microM. CD62L dissociates from GlyCAM-1 with a very fast dissociation rate constant (>/=10 s-1) which agrees well with the reported dissociation rate constant of CD62L-mediated leukocyte tethers. The calculated association rate constant is >/=10(5) M-1 s-1. At concentrations just above its mean serum level (approximately 1.5 microg/ml or approximately 30 nM), GlyCAM-1 binds multivalently to immobilized CD62L. It follows that soluble GlyCAM-1 may cross-link CD62L when it binds to cells, suggesting a mechanism for signal transduction.

Adhesion molecules in haemopoiesis

In the adult mammal, haemopoiesis is restricted to the extravascular compartment of the bone marrow (BM) where primitive haemopoietic stem cells (HSC) and their clonogenic progeny develop in intimate contiguity with a heterogeneous population of stromal cells that comprise the haemopoietic micro-environment (HM). Although the importance of cellular interactions between primitive haemopoietic progenitor cells (HPC) and marrow stromal cells is well established, precise definition of the nature of many of these interactions at the molecular level is lacking and remains an objective of fundamental importance to understanding of haemopoietic regulation. Current data suggest that a wide variety of cell surface molecules representing several adhesion molecule superfamilies, including integrins, selectins, sialomucins and the immunoglobulin gene superfamily, are involved in supporting cell-cell and cell-extracellular matrix (ECM) interactions. These diverse CAM-ligand interactions, rather than simply serving to initiate and maintain contact between HPC and stromal cells and ECM components, also have an additional, more direct role in controlling the growth and development of primitive haemopoietic cells.

L-Selectin--a signalling receptor for lipopolysaccharide

The activation of leukocytes by bacterial cell-wall lipopolysaccharide contributes to the pathogenesis of septic shock. We propose that in neutrophils, and possibly other leukocytes, L-selectin can act as a low-affinity lipopolysaccharide receptor. Inhibitors of L-selectin may therefore be of therapeutic value in treating this life-threatening condition.

An ELISA for selectins based on binding to a physiological ligand

Members of the selectin family of adhesion receptors, consisting of L-, P- and E-selectin, mediate the initial interaction between leukocytes and endothelium during leukocyte trafficking from the blood into tissue sites. These receptors have attracted great attention in recent years due to their participation in a number of acute and chronic inflammatory diseases. We describe here a new ELISA that measures the binding between selectin-IgG chimeras and a physiological ligand for L-selectin and can be used to screen selectin inhibitors. The ligand used is a mucin-like glycoprotein known as GlyCAM-1, which is derived from high endothelial venules in secondary lymphoid organs. We demonstrate binding of all three selectins to GlyCAM-1 and demonstrate that the binding interactions satisfy a number of important criteria. The advantage of this ELISA over previous assays is that a macromolecular physiological ligand is employed, rather than a fortuitous or simplified carbohydrate ligand. Thus, the protein-carbohydrate interactions, as well as other interactions contributing to ligand recognition, can be investigated. The assay is suitable for high-throughout screening of compounds and may find use in the identification of selectin antagonists with anti-inflammatory potential.

A Hematopoietic Cell L-Selectin Ligand Exhibits Sulfate-Independent Binding Activity

L-selectin is a leukocyte cell-surface glycoprotein that mediates adhesive interactions between circulating cells and vascular endothelium. All endothelial ligands of L-selectin characterized to date are glycoproteins that require sulfation for activity and share reactivity with MECA 79, a monoclonal antibody that recognizes a sulfate-dependent epitope involved in L-selectin attachment. We have recently identified by functional assay a glycoprotein L-selectin ligand expressed on the human hematopoietic cell line KG1a. We report here that this ligand is not recognized by MECA 79 and that it retains binding activity after metabolic inhibition of sulfation by chlorate. A native membrane L-selectin ligand exhibiting sulfate-independent function has not been described previously. Identification of this novel ligand on a nonendothelial cell type suggests that structural determinants conferring L-selectin binding may vary in a cell- and tissue-specific manner.

Characterization of a 180 kDa molecule apparently reactive with recombinant L-selectin

In the present study we identified a 180 kDa molecule (p180) in rat lymph nodes (LN) apparently reactive with silkworm derived recombinant L-selectin (LEC-IgG) in a Ca(2+)-dependent manner. Analysis of amino acid sequence revealed that p180 has a strong homology to the macrophage mannose receptor (MMR), which was corroborated by the observation that p180 reacted with polyclonal anti-alveolar MMR antibody and mannosyl-BSA-agarose. In agreement with this notion, the binding of p180 to the silkworm LEC-IgG was inhibited by alpha-methyl-D-mannoside. However, in sharp contrast to its reactivity against the silkworm LEC-IgG, p180 failed to bind LEC-IgG produced by COS-7 cells, suggesting that p180 reacted with the silkworm LEC-IgG through the recognition of oligomannose-type oligosaccharides expressed on the silkworm products and that the lectin activity of L-selectin was not involved in the interaction. These results, together with the immunohistochemical studies showing that p180 was absent from the majority of high endothelial venules (HEV) but present in medullary macrophages, led us to conclude that p180 obtained from LN lysates by the use of the silkworm LEC-IgG is not a physiological ligand for L-selectin, warning against the use of recombinant proteins expressed in the baculovirus/ silkworm expression system for the detection of carbohydrate ligands.

Zona pellucida glycoprotein mZP3 bioactivity is not dependent on the extent of glycosylation of its polypeptide or on sulfation and sialylation of its oligosaccharides

During fertilization in mice, free-swimming sperm bind to mZP3, one of three egg zona pellucida glycoproteins. Sperm recognize and bind to specific serine/threonine-linked (O-linked) oligosaccharides located at the mZP3 combining site for sperm. Shortly after binding to mZP3, sperm undergo the acrosome reaction, a form of cellular exocytosis. Here, we examined the influence of extent of glycosylation, sulfation, and sialylation of mZP3 (M(r) approximately 65,000-100,000) on its bioactivity; i.e. its ability to inhibit binding of sperm to eggs and to induce the acrosome reaction in vitro. Low (av. M(r) approximately 70,000), medium (av. M(r) approximately 82,000), and high (av. M(r) approximately 94,000) M(r) fractions of mZP3 were purified and shown to vary in extent of asparagine-linked (N-linked) glycosylation. All three size-fractions exhibited bioactivity, suggesting that the ability of mZP3 to inhibit binding of sperm to eggs is not related to the extent of glycosylation of its polypeptide (M(r) approximately 44,000). Digestion of mZP3 by neuraminidase decreased its average M(r) from approximately 83,000 to approximately 77,000 and increased its average pI from approximately 4.7 to approximately 6.0, but did not significantly affect mZP3 bioactivity. Terminal sialic acid largely accounts for the glycoprotein's acidic nature, but is not an essential element of the mZP3 combining site for sperm. Experiments with stably transfected embryonal carcinoma (EC) cells that secrete bioactive EC-mZP3 revealed that, of the sulfate present, approximately 70–75% was located on N-linked and approximately 25–30% on O-linked oligosaccharides. EC-mZP3 devoid of sulfate inhibited binding of sperm to eggs and induced the acrosome reaction to the same extent as sulfated EC-mZP3. These results suggest that sulfation of EC-mZP3 oligosaccharides is not essential for bioactivity. Overall, these findings contrast with those reported for certain other glycoproteins involved in cellular adhesion that require sulfate and/or sialic acid for bioactivity.

Genetic defect in T lymphocyte-specific homing into peripheral lymph nodes

Lymphocytes circulating in the bloodstream home into lymph nodes (LN). T cells predominate in peripheral LN (PLN) and B cells in spleen or mucosal tissue, e.g. Peyer's patches (PP). DDD/1 mice are unique in marked paucity of LN cells, especially T cells. T cell frequency in PLN was 20-40% in this strain, compared to 60-80% in others. Immunohistochemistry confirmed the low density of T cells in the subcortical area but normal colonization of B cells in cortical area in PLN of DDD/1. In contrast, the T cell content of peripheral blood and spleen was higher in DDD/1 but that in PP was not significantly different compared to other strains. It was thus concluded that this abnormality in DDD/1 results from a homing defect of T cells into PLN but not from lymphopenia. Genetical analysis showed that the defect in T cell-specific homing was regulated by a single autosomal recessive gene, tentatively designated plt (paucity of lymph node T cells). Reciprocal bone marrow transplantation indicated that the plt phenotype may arise from some defect in PLN stroma but not in lymphocytes. An in vivo homing assay using fluorescence-labeled lymphocytes demonstrated that the homing defect was specific for T cells but not for B cells. A Stamper-Woodruff assay revealed that the binding between lymphocytes and PLN high endothelial venules was normal and that L-selectin and its ligand, peripheral node vascular addressin (PNAd), were expressed and functioned normally in DDD/1. These results taken together indicate that the T cell-specific homing into PLN is disturbed at a post-adhesion stage in DDD/1. The product of the plt locus may play a pivotal role at this stage.

Lectin-carbohydrate interaction in the immune system

The immune system consists of various types of cells and molecules that specifically interact with each other to initiate the host defense mechanism. Recent studies have shown that carbohydrates and lectins (carbohydrate-binding proteins) play an essential role in mediating such interactions. Both lectins and carbohydrates are widely distributed in the mammalian tissues as well as in microorganisms. Carbohydrates, due to their chemical nature, can potentially form structures that are more variable than proteins and nucleic acids. Lectins can exist in either soluble or cell-associated form, and although overall structures vary, invariably possess carbohydrate-recognition domains (CRD) with various specificities. The interaction between lectins and carbohydrates have been shown to be involved in such activities as opsonization of microorganisms, phagocytosis, cell adhesion and migration, cell activation and differentiation, and apoptosis. The number of lectins identified in the immune system is increasing at a rapid pace. The development in this area has opened a new aspect in studying the immune system, and at the same time, provided new therapeutic routes for the treatment and prevention of disease.

Analysis of neurocan structures interacting with the neural cell adhesion molecule N-CAM

Neurocan is a brain-specific chondroitin sulfate proteoglycan, which has been shown to bind to the neural cell adhesion molecule N-CAM and to inhibit its homophilic interaction. To study in more detail the structures of neurocan responsible for this interaction, various recombinant neurocan fragments were generated. The ability of these fragments to interact with N-CAM was investigated in several different in vitro assay systems, enzyme-linked immunosorbent assay-type binding assays, Covasphere-aggregation assays, and assays based on an optical biosensor (BIAcoreTM) system. The analysis of the homophilic N-CAM interaction in the BIAcore system revealed a KD of 64 nM. This homophilic interaction could be reduced by preincubation of soluble N-CAM with neurocan. Direct binding of N-CAM to immobilized neurocan core protein and recombinant neurocan fragments could also be demonstrated, and KD values between 25 and 100 nM were obtained. In addition, direct binding of N-CAM to chondroitin sulfate could be demonstrated. Binding of N-CAM to the immobilized neurocan core protein could be inhibited with all recombinant fragments containing chondroitin sulfate or major parts of the mucin-like central region of neurocan. For the inhibition of homophilic N-CAM interactions, however, a combination of globular and extended structures was required.

P-selectin glycoprotein ligand 1 is a ligand for L-selectin on neutrophils, monocytes, and CD34+ hematopoietic progenitor cells

Selectins play a critical role in initiating leukocyte binding to vascular endothelium. In addition, in vitro experiments have shown that neutrophils use L-selectin to roll on adherent neutrophils, suggesting that they express a nonvascular L-selectin ligand. Using a L-selectin/IgM heavy chain (mu) chimeric protein as an immunocytological probe, we show here that L-selectin can bind to neutrophils, monocytes, CD34+ hematopoietic progenitors, and HL-60 and KG-1 myeloid cells. The interaction between L-selectin and leukocytes was protease sensitive and calcium dependent, and abolished by cell treatment with neuraminidase, chlorate, or O-sialoglycoprotein endopeptidase. These results revealed common features between leukocyte L-selectin ligand and the mucin-like P-selectin glycoprotein ligand 1 (PSGL-1), which mediates neutrophil rolling on P- and E-selectin. The possibility that PSGL-1 could be a ligand for L-selectin was further supported by the ability of P-selectin/mu chimera to inhibit L-selectin/mu binding to leukocytes and by the complete inhibition of both selectin interactions with myeloid cells treated with mocarhagin, a cobra venom metalloproteinase that cleaves the amino terminus of PSGL-1 at Tyr-51. Finally, the abrogation of L- and P-selectin binding to myeloid cells treated with a polyclonal antibody, raised against a peptide corresponding to the amino acid residues 42-56 of PSGL-1, indicated that L- and P-selectin interact with a domain located at the amino-terminal end of PSGL-1. The ability of the anti-PSGL-1 mAb PL-1 to inhibit L- and P-selectin binding to KG-1 cells further supported that possibility. Thus, apart from being involved in neutrophil rolling on P- and E-selectin, PSGL-1 also plays a critical role in mediating neutrophil attachment to adherent neutrophils. Interaction between L-selectin and PSGL-1 may be of major importance for increasing leukocyte recruitment at inflammatory sites.

Purification and quantification of L-selectin-reactive GlyCAM-1 from mouse serum

GlyCAM-1 is an endothelial-derived mucin found in the conditioned medium of organ-cultured lymph nodes and in serum. It is a ligand for L-selectin, but also interacts with P and E-selectin. It may play a role in the modulation of leukocyte trafficking into secondary lymphoid tissues as well as chronic inflammatory sites. Here we report the development of an ELISA that quantifies GlyCAM-1 in complex biological fluids such as serum. The ELISA response is linear over a concentration range of 13-800 ng/ml. The level of GlyCAM-1 in mouse serum was found to be 1.3-1.6 micrograms/ml. Using mouse serum as starting material, we report a rapid and efficient purification scheme for the isolation of biologically active GlyCAM-1. This material may now be used to address the biological functions of GlyCAM-1 and to further define its structural features.

Peripheral lymphoid tissue-like adhesion molecule expression in nodular infiltrates in inflammatory myopathies

Non-granulomatous nodular accumulations of inflammatory cells in inflammatory myopathies were studied to characterize adhesion mechanisms used for leukocyte recruitment. The nodules had a B-cell-rich center surrounded by a helper T-cell-rich peripheral zone, resembling lymph nodes. The T-cell-rich zones harbored high-walled venules resembling high endothelial venules (HEV), whose endothelia frequently expressed ICAM-1, VCAM-1, and less constantly E-selectin. This endothelial adhesion molecule profile differs from that found in polymyositis, inclusion body myositis, or dermatomyositis, but resembles that in lymphoid tissues. Also, the peripheral lymph node addressin, a vascular addressin specific for peripheral lymphoid tissue HEV, was present on many HEV. This adhesion system is probably responsible for the excessive lymphocyte recruitment. The similar cellular organization and lymphocyte recirculation mechanisms of the nodular infiltrates in muscle and of lymph nodes suggest that the former may also produce antibodies.

Platelet-mediated lymphocyte delivery to high endothelial venules

Circulating lymphocytes gain access to lymph nodes owing to their ability to initiate rolling along specialized high endothelial venules (HEVs). One mechanism of rolling involves L-selectin binding to peripheral node addressin (PNAd) on HEVs. Activated platelets are shown to bind to circulating lymphocytes and to mediate rolling in HEVs, in vivo, through another molecule, P-selectin, which also interacts with PNAd. In vitro, activated platelets enhanced tethering of lymphocytes to PNAd and sustained lymphocyte rolling, even in the absence of functional L-selectin. Thus, a platelet pathway operating through P-selectin provides a second mechanism for lymphocyte delivery to HEVs.

Ligand-specificity of the selectins

The selectins are carbohydrate-binding cell adhesion molecules acting in the vascular system. They mediate the docking of leukocytes to the blood vessel wall and the rolling of these cells along the endothelial cell surface. These adhesion phenomena initiate the entry of leukocytes into sites of inflammation as well as the migration of recirculating lymphocytes into secondary lymphoid tissues. Blocking selectin function with antibodies or oligosaccharides has proven to be beneficial in various animal models of inflammation and models of ischemia/reperfusion damage. This has raised much interest in the identification of the physiological ligands of the selectins. Several glycoprotein ligands have been identified, some of which can even be selectively isolated from cellular detergent extracts using a selectin as an affinity probe. Four of these "high affinity" ligands have been cloned. The structural requirements of their interaction with the selectins is discussed.

Calcium-dependent oligonucleotide antagonists specific for L-selectin

The selectins are calcium-dependent C-type lectins that recognize complex anionic carbohydrate ligands, initiating many cell-cell interactions in the vascular system. Selectin blockade shows therapeutic promise in a variety of inflammatory and postischemic pathologies. However, the available oligosaccharide ligand mimetics have low affinities and show cross-reaction among the three selectins, precluding efficient and specific blockade. The SELEX (systematic evolution of ligands by exponential enrichment) process uses combinatorial chemistry and in vitro selection to yield high affinity oligonucleotides with unexpected binding specificities. Nuclease-stabilized randomized oligonucleotides subjected to SELEX against recombinant L-selectin yielded calcium-dependent antagonists with approximately 10(5) higher affinity than the conventional oligosaccharide ligand sialyl LewisX. Most of the isolated ligands shared a common consensus sequence. Unlike sialyl LewisX, these antagonists show little binding to E- or P-selectin. Moreover, they show calcium-dependent binding to native L-selectin on peripheral blood lymphocytes and block L-selectin-dependent interactions with the natural ligands on high endothelial venules.