De novo expression of endothelial sialyl Lewis(a) and sialyl Lewis(x) during cardiac transplant rejection: superior capacity of a tetravalent sialyl Lewis(x) oligosaccharide in inhibiting L-selectin-dependent lymphocyte adhesion

The ascites N-glycome of epithelial ovarian cancer patients

Epithelial ovarian cancer (EOC) is worldwide the sixth most lethal form of cancer occurring in women. More than one third of ovarian patients have ascites at the time of diagnosis and almost all of them have it when recurrence occurs. Although its effect on tumor cell microenvironment remains poorly understood, its presence is correlated with bad diagnosis. In previous studies, we proposed a novel glycan-based biomarker for the diagnosis of EOC, which showed an improved sensitivity and specificity at any stage of the disease and an improved discrimination between malignant and benign ovarian tumors. In this work, we report for the first time the N-glycome profiles of ascitic fluid from primary serous EOC patients and compare them with the serum N-glycomes of the same patients as well as of healthy controls. N-Glycans were digested from equivalent amount of ascites and serum from 18 EOC patients and from serum of 20 age-matched controls and measured by MALDI-TOF-MS. Ascites N-glycome showed increased antennarity, branching, sialylation and Lewis^X motives compared to healthy serum. In addition, a correlation was established between ascites volume and degree of sialylation.

SIGNIFICANCE

Malignant ascitic fluid is the build-up of large volumes of fluid in the peritoneal cavity secondary to cancer. At least one-third of ovarian cancer patients develop ascites, a generally voluminous fluid containing cells of tumor origin, in the course of cancer and almost all when recurrence occurs. The proteome of ascites is known to be as complex as that of serum and contains high amount of proteins shed from inflammatory cells as well as from tumor cells. Although many attempts have been made to provide molecular insight into the proteomic and peptidomic content of malignant ascites, no data about the N-glycome of the ascitic fluid fraction from cancer patients has been reported to date. In this study, the N-glycosylation profile of ascites from 20 patients suffering from epithelial ovarian cancer (EOC) was analyzed by MALDI-TOF-mass spectrometry and compared to the pathologically modified N-glycan pattern obtained from serum of the same patients as well as to the pattern of serum from healthy individuals. Significant quantitative differences were observed in the ascites of EOC patients when compared to the serum of healthy subjects. The glycome of ascites shows typical features of inflammatory conditions, what was also found in the serum of patients suffering from EOC when compared to healthy serum. In addition, a correlation was established between ascites volume and degree of sialylation, showing that the high-volume ascites contains a higher amount of sialylated structures than the low-volume ascites.

Understanding high endothelial venules: Lessons for cancer immunology

High endothelial venules (HEVs) are blood vessels especially adapted for lymphocyte trafficking which are normally found in secondary lymphoid organs such as lymph nodes (LN) and Peyer's patches. It has long been known that HEVs develop in non-lymphoid organs during chronic inflammation driven by autoimmunity, infection or allografts. More recently, HEVs have been observed in solid, vascularized tumors and their presence correlated with reduced tumor size and improved patient outcome. It is proposed that newly formed HEV promote antitumor immunity by recruiting naive lymphocytes into the tumor, thus allowing the local generation of cancerous tissue-destroying lymphocytes. Understanding how HEVs develop and function are therefore important to unravel their role in human cancers. In LN, HEVs develop during embryonic and early post-natal life and are actively maintained by the LN microenvironment. Systemic blockade of lymphotoxin-β receptor leads to HEV de-differentiation, but the LN components that induce HEV differentiation have remained elusive. Recent elegant studies using gene-targeted mice have demonstrated clearly that triggering the lymphotoxin-β receptor in endothelial cells (EC) induces the differentiation of HEV and that CD11c⁺ dendritic cells play a crucial role in this process. It will be important to determine whether lymphotoxin-β receptor-dependent signaling in EC drives the development of HEV during tumorigenesis and which cells have HEV-inducer properties. This may reveal therapeutic approaches to promote HEV neogenesis and determine the impact of newly formed HEV on tumor immunity.

Essential domains of Anaplasma phagocytophilum invasins utilized to infect mammalian host cells

Anaplasma phagocytophilum causes granulocytic anaplasmosis, an emerging disease of humans and domestic animals. The obligate intracellular bacterium uses its invasins OmpA, Asp14, and AipA to infect myeloid and non-phagocytic cells. Identifying the domains of these proteins that mediate binding and entry, and determining the molecular basis of their interactions with host cell receptors would significantly advance understanding of A. phagocytophilum infection. Here, we identified the OmpA binding domain as residues 59 to 74. Polyclonal antibody generated against a peptide spanning OmpA residues 59 to 74 inhibited A. phagocytophilum infection of host cells and binding to its receptor, sialyl Lewis x (sLe^x-capped P-selectin glycoprotein ligand 1. Molecular docking analyses predicted that OmpA residues G61 and K64 interact with the two sLe^x sugars that are important for infection, α2,3-sialic acid and α1,3-fucose. Amino acid substitution analyses demonstrated that K64 was necessary, and G61 was contributory, for recombinant OmpA to bind to host cells and competitively inhibit A. phagocytophilum infection. Adherence of OmpA to RF/6A endothelial cells, which express little to no sLe^x but express the structurally similar glycan, 6-sulfo-sLe^x, required α2,3-sialic acid and α1,3-fucose and was antagonized by 6-sulfo-sLe^x antibody. Binding and uptake of OmpA-coated latex beads by myeloid cells was sensitive to sialidase, fucosidase, and sLe^x antibody. The Asp14 binding domain was also defined, as antibody specific for residues 113 to 124 inhibited infection. Because OmpA, Asp14, and AipA each contribute to the infection process, it was rationalized that the most effective blocking approach would target all three. An antibody cocktail targeting the OmpA, Asp14, and AipA binding domains neutralized A. phagocytophilum binding and infection of host cells. This study dissects OmpA-receptor interactions and demonstrates the effectiveness of binding domain-specific antibodies for blocking A. phagocytophilum infection.

Anaplasma phagocytophilum causes the potentially deadly bacterial disease granulocytic anaplasmosis. The pathogen replicates inside white blood cells and, like all other obligate intracellular organisms, must enter host cells to survive. Multiple A. phagocytophilum surface proteins called invasins cooperatively orchestrate the entry process. Identifying these proteins’ domains that are required for function, and determining the molecular basis of their interaction with host cell receptors would significantly advance understanding of A. phagocytophilum pathogenesis. In this study, the binding domains of two A. phagocytophilum surface proteins, OmpA and Asp14, were identified. The specific OmpA residues that interact with its host cell receptor were also defined. An antibody cocktail generated against the binding domains of OmpA, Asp14, and a third invasin, AipA, blocked the ability of A. phagocytophilum to infect host cells. The data presented within suggest that binding domains of OmpA, Asp14, and AipA could be exploited to develop a vaccine for granulocytic anaplasmosis.

Alpha-1,2-mannosidase and hence N-glycosylation are required for regulatory T cell migration and allograft tolerance in mice

Background

Specific immunological unresponsiveness to alloantigens can be induced in vivo by treating mice with a donor alloantigen in combination with a non-depleting anti-CD4 antibody. This tolerance induction protocol enriches for alloantigen reactive regulatory T cells (Treg). We previously demonstrated that alpha-1,2-mannosidase, an enzyme involved in the synthesis and processing of N-linked glycoproteins, is highly expressed in tolerant mice, in both graft infiltrating leukocytes and peripheral blood lymphocytes.

Principal Findings

In this study we have identified that alpha-1,2-mannosidase expression increases in CD25⁺CD4⁺ Treg when they encounter alloantigen in vivo. When alpha-1,2-mannosidase enzyme activity was blocked, Treg retained their capacity to suppress T cell proliferation in vitro but were unable to bind to physiologically relevant ligands in vitro. Further in vivo analysis demonstrated that blocking alpha-1,2-mannosidase in Treg resulted in the migration of significantly lower numbers to the peripheral lymph nodes in skin grafted mice following adoptive transfer, where they were less able to inhibit the proliferation of naïve T cells responding to donor alloantigen and hence unable prevent allograft rejection in vivo.

Significance

Taken together, our results suggest that activation of alloantigen reactive Treg results in increased alpha-1,2-mannosidase expression and altered N-glycosylation of cell surface proteins. In our experimental system, altered N-glycosylation is not essential for intrinsic Treg suppressive capacity, but is essential in vivo as it facilitates Treg migration to sites where they can regulate immune priming. Migration of Treg is central to their role in regulating in vivo immune responses and may require specific changes in N-glycosylation upon antigen encounter.

Endothelial L-selectin ligand expression in nasal polyps

BACKGROUND

L-selectins on leukocytes and their counter-receptors on endothelial cells have been shown to be involved in leukocyte recruitment in chronic rhinosinusitis without nasal polyps (NP).

OBJECTIVES

The purpose of this study was to evaluate the expression level of functionally active endothelial L-selectin ligands in NP obtained from patients with NP of different etiology [simple NP, antro-choanal polyps (ACP) and cystic fibrosis (CF) NP] and inferior turbinate specimens of healthy controls and to compare these levels to the presence of various leukocyte subsets.

METHODS

Nasal polyp specimens and healthy nasal mucosa specimens were obtained from patients undergoing surgery and were immunohistochemically stained with monoclonal antibodies detecting CD34, sialyl Lewis x (sLe(x)) of sulfated extended core 1 lactosamines and various leukocyte subsets.

RESULTS

All NP are characterized by a decrease in the number of CD34+ vessels. The number of eosinophils and the percentage of vessels expressing endothelial sulfated sLe(x) epitopes is upregulated in all groups of simple NP. Tissue eosinophilia is increased in those patients with increased disease severity (acetyl salicylic acid intolerance), but the percentage of endothelial sulfated sLe(x) epitopes is not. Results on CF NP are similar to those observed for simple NP. Antro-choanal polyps, on the contrary, are characterized by low numbers of tissue eosinophils and relatively few vessels expressing endothelial sulfated sLe(x) epitopes.

CONCLUSIONS

Our results suggest that functionally active L-selectin ligands might play a role in guiding leukocyte traffic into NP in patients with simple NP and CF NP but not ACP.

Mucosal eosinophils and l-selectin ligands are associated with invasive and noninvasive sinus surgery outcomes

BACKGROUND

Chronic rhinosinusitis (CRS) is characterized by persistent inflammation of the nasal and paranasal mucosa with numerous emigrated leukocytes. L-Selectin on leukocytes and its endothelial glycosylated ligands initiate leukocyte infiltration into inflamed tissues. Endoscopic sinus surgery (ESS) is the major approach for restoring sinus physiology after failure of conservative therapy; however, the effect of enlarging the maxillary sinus ostium is still unknown. Here, we compared two histological markers of local inflammation, the number of mucosal eosinophils, and the expression of endothelial L-selectin ligands, with clinical outcomes after enlarging or saving the maxillary sinus ostium.

METHODS

Twenty-three patients with CRS underwent uncinectomy on one side and additional middle meatal antrostomy on the other side. Maxillary sinus mucosa biopsy specimens from these patients and nine healthy subjects were taken for immunohistochemical evaluations of the number of mucosal eosinophils and endothelial L-Selectin ligands. Also, symptoms and mucociliary clearance were measured.

RESULTS

The postoperative reduction of the endothelial L-Selectin ligands was independent of the operation technique. There was a correlation between postoperative number of mucosal eosinophils and symptom score, which was also independent of the surgical technique. The postoperative decrease of mucosal eosinophils, as well as the correlation of the intraoperative eosinophils with the postoperative symptom score, was found only on antrostomy side.

CONCLUSION

ESS decreases the expression of endothelial L-Selectin ligands, which might lead to decreased eosinophil traffic into maxillary sinus mucosa, putatively more when enlarging the maxillary sinus ostium. Both intra- and postoperative low number of eosinophils seem to be indicators of good subjective recovery.

Conjugation of oligosaccharides by reductive amination to amine modified chondroitin oligomer and γ-cyclodextrin

Carbohydrates present on cell surfaces participate in numerous biological recognition phenomena including cell-cell interactions, cancer metastasis and pathogen invasion. Therefore, synthetic carbohydrates have a potential to act as pharmaceutical substances for treatment of various pathological phenomena by inhibiting specifically the interaction between cell surface carbohydrates and their protein receptors (lectins). However, the inherently low affinity of carbohydrate-protein interactions has often been an obstacle for successful generation of carbohydrate based pharmaceuticals. Multivalent glycoconjugates, i.e. structures carrying several copies of the active carbohydrate sequence in a carrier molecule, have been constructed to overcome this problem. Here we present two novel types of multivalent carbohydrate conjugates based on chondroitin oligomer and cyclodextrin carriers. These carriers were modified to express primary amino groups, and oligosaccharides were then bound to carrier molecules by reductive amination. Multivalent conjugates were produced using the human milk type oligosaccharides LNDFH I (Lewis-b hexasaccharide), LNnT, and GlcNAcbeta1-3Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc.

Differential gene expression of GDP-L-fucose-synthesizing enzymes, GDP-fucose transporter and fucosyltransferase VII

L-fucose is a fundamental monosaccharide component of many mammalian glycoproteins and glycolipids. Fucosylation requires GDP-L-fucose as a donor of fucose and a specific fucosyltransferase (Fuc-T) to catalyze the transfer of L-fucose to various lactosamine acceptor molecules. The biosynthesis of GDP-L-fucose consists of two pathways. The constitutively active de novo pathway involves conversion of cellular GDP-D-mannose to GDP-L-fucose by GDP-D-mannose-4,6-dehydratase (GMD) and GDP-4-keto-6-deoxy-D-mannose-3,5-epimerase-4-reductase (FX). In the alternative biosynthetic pathway, in the salvage metabolism, L-fucokinase (Fuk) synthesizes L-fucose-1-phosphate from free fucose. L-fucose-1-phosphate is further catalyzed to GDP-L-fucose by GDP-L-fucose pyrophosphorylase (Fpgt). GDP-L-fucose, synthesized in the cytosol, is translocated to the Golgi for fucosylation by a specific GDP-fucose transporter (FUCT1). Glycans that contain alpha(1,3)-fucosylated modifications, e.g. sialyl Lewis X-type glycans, have an important role in inflammation and in tumorigenesis. We studied the mRNA expression levels of GDP-L-fucose-synthesizing enzymes, GDP-fucose transporter and fucosyltransferase VII by quantitative real-time PCR in mouse endothelial cells, macrophages and lymphoid tumor cells. Moreover, the expression of the same transcripts was detected in acute inflammation using rat kidney allograft as model system. Our results indicate the simultaneous upregulation of the GDP-L-fucose synthesizing enzymes of the de novo pathway, GDP-fucose transporter and fucosyltransferase VII in inflammation and in tumorigenesis.

Cloning and expression of rat fucosyltransferase VII at sites of inflammation

The sialyl Lewis x (NeuAcalpha2-3Galbeta1-4(Fucalpha1-3)GlcNAc) determinants serve as ligands in the selectin-mediated adhesion of leukocytes to activated endothelium. The final step in the sialyl Lewis x synthesis is catalyzed by alpha1-3-fucosyltransferase, which transfers fucose to sialylated type 2 chain. We report the cloning of rat alpha1-3-fucosyltransferase gene (rFUT) isolated from rat lymph node and kidney allograft. The rFUT is expressed as two splice variants, but only the long one showed enzymatic activity towards sialylated lactosamine. Also flow cytometry analysis with the sLex mAbs indicated that the cloned rFuc-T was a functional enzyme and a member of the Fuc-TVII family. The rFuc-TVII mRNA expression level was strongly enhanced during acute inflammatory reaction induced by kidney allograft rejection, which could be detected by in situ hybridization and quantitative real-time PCR.

Abnormalities caused by carbohydrate alterations in Ibeta6-N-acetylglucosaminyltransferase-deficient mice

Ibeta6-N-acetylglucosaminyltransferase (IGnT) catalyzes the branching of poly-N-acetyllactosamine carbohydrate chains. In both humans and mice, three spliced forms of IGnT have been identified, and a common exon is present in all of them. We generated mice deficient in the common exon to understand the physiological function of poly-N-acetyllactosamine branching. IGnT activity was abolished in the stomach, kidney, bone marrow, and cerebellum of the deficient mice, while a low level of the activity persisted in the small intestine. Immunohistochemical analysis confirmed the loss of I antigen from the lung, stomach, and kidney. The deficient mice had reduced spontaneous locomotive activity. The number of peripheral blood lymphocytes was also reduced and renal function decreased in the deficient mice. Furthermore, in aged mice, vacuolization occurred in the kidney, and epidermoid cysts were frequently formed. However, cataracts did not develop earlier in the deficient mice. Decreased levels of lysosomal proteins, LAMP-2 and synaptotagmin VII, were found in the kidney of the deficient mice and correlated with renal abnormalities.

Glycans in cancer and inflammation--potential for therapeutics and diagnostics

Changes in glycosylation are often a hallmark of disease states. For example, cancer cells frequently display glycans at different levels or with fundamentally different structures than those observed on normal cells. This phenomenon was first described in the early 1970s, but the molecular details underlying such transformations were poorly understood. In the past decade advances in genomics, proteomics and mass spectrometry have enabled the association of specific glycan structures with disease states. In some cases, the functional significance of disease-associated changes in glycosylation has been revealed. This review highlights changes in glycosylation associated with cancer and chronic inflammation and new therapeutic and diagnostic strategies that are based on the underlying glycobiology.

Endothelial L-selectin ligands in sinus mucosa during chronic maxillary rhinosinusitis

RATIONALE

Chronic rhinosinusitis is characterized by persistent inflammation of the nasal and paranasal mucosa with numerous emigrated leukocytes. L-selectin on leukocytes and its endothelial glycosylated ligands initiate organ-specific leukocyte infiltration into inflamed tissues.

OBJECTIVES

The purpose of this study was to evaluate the endothelial expression of functionally active endothelial L-selectin ligands, sulfated sialyl Lewis x, in maxillary sinus mucosa from patients with chronic rhinosinusitis and from normal control subjects.

METHODS

Maxillary sinus mucosa specimens (116) were obtained surgically and immunohistochemically stained with monoclonal antibodies detecting sialyl Lewis x or sulfated extended core 1 lactosamines. The severity of the inflammation was determined by intraoperative endoscopic findings, computed tomography scans, and histopathologic assessment of the specimens.

MEASUREMENTS AND MAIN RESULTS

The percentage of vessels expressing endothelial sulfated sialyl Lewis x epitopes increased during chronic rhinosinusitis compared with uninflamed control tissue, especially in patients with additional allergic rhinitis, and decreased in specimens from aspirin-intolerant patients with preoperative oral corticosteroid treatment. In addition, the expression level of endothelial sulfated sialyl Lewis x epitopes and the number of mucosal eosinophils correlated with the severity of the inflammation, and decreased in specimens taken 9 months postoperatively compared with intraoperative samples, especially in patients with intranasal corticosteroid treatment.

CONCLUSIONS

Our results suggest that functionally active L-selectin ligands might guide leukocyte traffic into maxillary sinus mucosa preferentially in patients with severe findings of chronic maxillary rhinosinusitis, thus leading to aggravation of the inflammation.

A HEV-restricted sulfotransferase is expressed in rheumatoid arthritis synovium and is induced by lymphotoxin-alpha/beta and TNF-alpha in cultured endothelial cells

BACKGROUND

The recruitment of lymphocytes to secondary lymphoid organs relies on interactions of circulating cells with high endothelial venules (HEV). HEV are exclusive to these organs under physiological conditions, but they can develop in chronically-inflamed tissues. The interaction of L-selectin on lymphocytes with sulfated glycoprotein ligands on HEV results in lymphocyte rolling, which represents the initial step in lymphocyte homing. HEV expression of GlcNAc6ST-2 (also known as HEC-GlcNAc6ST, GST-3, LSST or CHST4), an HEV-restricted sulfotransferase, is essential for the elaboration of L-selectin functional ligands as well as a critical epitope recognized by MECA-79 mAb.

RESULTS

We examined the expression of GlcNAc6ST-2 in relationship to the MECA-79 epitope in rheumatoid arthritis (RA) synovial vessels. Expression of GlcNAc6ST-2 was specific to RA synovial tissues as compared to osteoarthritis synovial tissues and localized to endothelial cells of HEV-like vessels and small flat-walled vessels. Double MECA-79 and GlcNAc6ST-2 staining showed colocalization of the MECA-79 epitope and GlcNAc6ST-2. We further found that both TNF-alpha and lymphotoxin-alphabeta induced GlcNAc6ST-2 mRNA and protein in cultured human umbilical vein endothelial cells.

CONCLUSION

These observations demonstrate that GlcNAc6ST-2 is induced in RA vessels and provide potential cytokine pathways for its induction. GlcNAc6ST-2 is a novel marker of activated vessels within RA ectopic lymphoid aggregates. This enzyme represents a potential therapeutic target for RA.

Co-expression of two mammalian glycosyltransferases in the yeast cell wall allows synthesis of sLex

Interactions between selectins and their oligosaccharide-decorated counter-receptors play an important role in the initiation of leukocyte extravasation in inflammation. L-selectin ligands are O-glycosylated with sulphated sialyl Lewis X epitopes (sulpho-sLex). Synthetic sLex oligosaccharides have been shown to inhibit adhesion of lymphocytes to endothelium at sites of inflammation. Thus, they could be used to prevent undesirable inflammatory reactions such as rejection of organ transplants. In vitro synthesis of sLex glycans is dependent on the availability of recombinant glycosyltransferases. Here we expressed the catalytic domain of human alpha-1,3-fucosyltransferase VII in the yeasts Saccharomyces cerevisiae and Pichia pastoris. To promote proper folding and secretion competence of this catalytic domain in yeast, it was fused to the Hsp150 delta carrier, which is an N-terminal fragment of a secretory glycoprotein of S. cerevisiae. In both yeasts, the catalytic domain acquired an active conformation and the fusion protein was externalised, but remained mostly attached to the cell wall in a non-covalent fashion. Incubation of intact S. cerevisiae or P. pastoris cells with GDP-[14C]fucose and sialyl-alpha-2,3-N-acetyllactosamine resulted in synthesis of radioactive sLex, which diffused to the medium. Finally, we constructed an S. cerevisiae strain co-expressing the catalytic domains of alpha-2,3-sialyltransferase and alpha-1,3-fucosyltransferase VII, which were targeted to the cell wall. When these cells were provided with N-acetyllactosamine, CMP-sialic acid and GDP-[14C]fucose, radioactive sLex was produced to the medium. These data imply that yeast cells can provide a self-perpetuating source of fucosyltransferase activity immobilized in the cell wall, useful for the in vitro synthesis of sLex.

Role of L-Selectin in the Vascular Homing of Peripheral Blood-Derived Endothelial Progenitor Cells

Ex vivo expanded endothelial progenitor cells (EPCs) represent a new potential approach for the revascularization of ischemic sites. However, local accumulation of infused EPCs in these sites is poor, and the mechanisms responsible for their homing are largely unknown. We observed the expression of L-selectin, an adhesion receptor that regulates lymphocyte homing and leukocyte rolling and migration, on ex vivo expanded blood-derived human EPCs. When EPCs were subcloned in SV40-T large Ag-transfected isolates, the copresence of L-selectin and endothelial lineage markers was confirmed. We therefore demonstrated that the expression of L-selectin by EPCs was functional because it mediates interaction with a murine endothelial cell line (H.end) expressing L-selectin ligands by way of transfection with alpha(1,3/4)-fucosyltransferase. Indeed, adhesion of EPCs after incubation at 4 degrees C on a rotating platform was enhanced on alpha(1,3/4)-fucosyltransferase-transfected H.end cells compared with control vector-transfected cells, and treatment with anti-L-selectin Abs prevented this event. We then studied the role of L-selectin in EPC homing in vivo. H.end cells were implanted s.c. in SCID mice to form endothelioma tumors, and EPCs were subsequently i.v. injected. L-selectin+ EPCs localized into alpha(1,3/4)-fucosyltransferase-transfected endothelial tumors to a greater extent than in control tumors, and they were able to directly contribute to tumor vascularization by forming L-selectin+ EPC-containing vessels. In conclusion, our results showed that a mechanism typical of leukocyte adhesion is involved in the vascular homing of EPCs within sites of selectin ligand expression. This observation may provide knowledge about the substrate to design strategies to improve EPC localization in damaged tissues.

Human milk oligosaccharides reduce platelet-neutrophil complex formation leading to a decrease in neutrophil beta 2 integrin expression

Human milk is thought by many authorities to be preferable to formula as a source of nutrients for infants. Some of the benefits may stem from its high concentration of unbound oligosaccharides (5-10 g/L). These sugars have structural similarities to selectin ligands, known to mediate important cell-cell interactions in the immune system. Platelet-neutrophil complexes (PNC) exist in healthy individuals but have been implicated in disease states. Formation of these complexes requires selectins and as such, could be influenced by human milk oligosaccharides (HMO). Here, we investigate this possibility by examining the effect of HMO on the formation of PNC and activation of associated neutrophils. We collected blood from 10 healthy volunteers, activated platelets with adenosine 5'-diphosphate, and added HMO, oligosaccharide standards, or phosphate-buffered saline as a control. We determined the influence of HMO on PNC formation and adjacent neutrophil activation with fluorescein-activated cell sorter analysis after labeling with antibodies for the platelet marker CD42a and the neutrophil activation marker CD11b. Within physiologically achievable concentrations (6.25-125 microg/mL), an acidic HMO fraction reduced PNC formation up to 20%, which was similar to the effect seen with high concentrations of sialyl-Lewis x. Associated neutrophils showed a dose-dependent decrease in beta 2 integrin expression, up to 30%, at high but physiological concentrations. The neutral HMO fraction had no effect. These results support the hypothesis that acidic HMO serve as anti-inflammatory components of human milk and thus, contribute to the lower incidence of inflammatory diseases such as necrotizing enterocolitis in breast-fed versus formula-fed infants.

Detection of a sulfotransferase (HEC-GlcNAc6ST) in high endothelial venules of lymph nodes and in high endothelial venule-like vessels within ectopic lymphoid aggregates: relationship to the MECA-79 epitope

The interaction of L-selectin on lymphocytes with sulfated ligands on high endothelial venules (HEVs) of lymph nodes results in lymphocyte rolling and is essential for lymphocyte homing. The MECA-79 monoclonal antibody reports HEV-expressed ligands for L-selectin by recognizing a critical sulfation-dependent determinant on these ligands. HEC-GlcNAc6ST, a HEV-localized sulfotransferase, is essential for the elaboration of functional ligands within lymph nodes, as well as the generation of the MECA-79 epitope. Here, we use an antibody against murine HEC-GlcNAc6ST to study its expression in relationship to the MECA-79 epitope. In lymph nodes, the enzyme is expressed in the Golgi apparatus of high endothelial cells, in close correspondence with luminal staining by MECA-79. In lymph node HEVs of HEC-GlcNAc6ST-null mice, luminal staining by MECA-79 is almost abolished, whereas abluminal staining persists although reduced in intensity. HEV-like vessels in several examples of inflammation-associated lymphoid neogenesis, including nonobese diabetic mice, also exhibit concomitant expression of the sulfotransferase and luminal MECA-79 reactivity. The correlation extends to ectopic lymphoid aggregates within the pancreas of RIP-BLC mice, in which CXCL13 is expressed in islets. Analysis of the progeny of RIP-BLC by HEC-GlcNAc6ST-null mice establishes that the enzyme is responsible for the MECA-79 defined luminal ligands.

?1-Acid glycoprotein fucosylation as a marker of carcinoma progression and prognosis

BACKGROUND

Serum alpha1-acid glycoprotein (AGP), an acute-phase protein secreted by the liver, carries alpha(1,3)-fucosylated structures on its 5 highly branched, N-linked sugar chains.

METHODS

Serum AGP levels in patients with various types of malignancies (n=214 patients) were measured using an enzyme-linked immunosorbent assay with anti-AGP antibody. To investigate glycoforms that differed in their degree of branching and extent of fucosylation, serum AGP samples were analyzed by crossed affinoimmunoelectrophoresis (CAIE) with concanavalin A, and Aleuria aurantia lectin (AAL), and anti-AGP antibody.

RESULTS

A significant difference (P <0.001) in serum AGP levels was observed in preoperative patients compared with levels in the healthy control group, but the levels in individual patients did not reflect their clinical status. Conversely, it was found not only that the patterns of AGP glycoforms differed widely in the patient group compared with the healthy control group, but they also changed depending on each patient's clinical status. Furthermore, AGP glycoforms seemed to be appropriate markers of disease progression and prognosis according to follow-up studies of 45 patients during prolonged preoperative and postoperative periods.

CONCLUSIONS

Patients with advanced malignancies who had AGP glycoforms that contained highly fucosylated triantennary and tetraantennary sugar chains for long periods after surgery were likely to have a poor prognosis. However, patients who had AGP glycoforms without such changes were expected to have a good prognosis.

Core 2 Branching β1,6-N-Acetylglucosaminyltransferase and High Endothelial Venule-restricted Sulfotransferase Collaboratively Control Lymphocyte Homing

L-selectin mediates lymphocyte homing by facilitating lymphocyte adhesion to carbohydrate ligands expressed on high endothelial venules (HEV) of the secondary lymphoid organs. Previous studies demonstrated that L-selectin ligand sulfotransferase (LSST) forms 6-sulfo sialyl Lewis x (sLe(x)) on both core 2 branch and MECA-79-positive extended core 1 O-glycans, but the chemical nature and roles of HEV ligands elaborated by LSST and core 2 beta1,6-N-acetylglucosaminyltransferase-1 (Core2GlcNAcT) have been undefined. In the present study, we have generated mutant mice with deficient LSST and show that inactivation of LSST gene alone leads to only partial impairment of lymphocyte homing to peripheral lymph nodes and moderate reduction in lymphocyte counts in the peripheral lymph nodes, despite the fact that L-selectin ligands that contain 6-sulfo sLe(x) are reduced at HEV. By contrast, LSST/Core2GlcNAcT double null mice exhibited a markedly reduced lymphocyte homing and reduced lymphocyte counts as a result of significantly decreased 6-sulfo sLe(x) on HEV L-selectin counterreceptors, relative to LSST- or Core2GlcNAcT-single null mice. Moreover, induction of LSST and Core2GlcNAcT transcripts was observed in HEV-like structure formed in the salivary gland of the non-obese diabetic mouse, which displays chronic inflammation. These results indicate that LSST and Core2GlcNAcT cooperatively synthesize HEV-specific L-selectin ligands required for lymphocyte homing and suggest that LSST and Core2GlcNAcT play a critical role in lymphocyte trafficking during chronic inflammation.

Angiopoietin-1 protects against the development of cardiac allograft arteriosclerosis

BACKGROUND

Angiopoietin (Ang)-1 is an angiogenic growth factor that counteracts the permeability and proinflammatory effects of vascular endothelial growth factor and other proinflammatory cytokines. Recently, we demonstrated that vascular endothelial growth factor enhances cardiac allograft arteriosclerosis. Here, we studied the roles of Ang1, its natural antagonist Ang2, and their receptor Tie2 in rat cardiac allograft arteriosclerosis.

METHODS AND RESULTS

Heterotopic cardiac allografts and syngrafts were transplanted from Dark Agouti (DA) to Wistar-Furth rats and from DA to DA rats, respectively. Immunohistochemistry disclosed that only a few mesenchymal cells expressed Ang1 in normal hearts and syngrafts, whereas no immunoreactivity was found in cardiac allografts undergoing chronic rejection. Ang2 and Tie2 immunoreactivity was induced mainly in capillaries and postcapillary venules in chronic allografts when compared with syngeneic controls, but no immunoreactivity was found in arterial endothelium. Intracoronary perfusion of cardiac allografts with a clinical-grade adenoviral vector encoding human Ang1 (Ad.Ang1) protected against the development of allograft arteriosclerosis. Ad.Ang1 perfusion reduced Ang2 expression in microcirculation, the numbers of graft-infiltrating leukocytes, and the level of immunoactivation and interstitial fibrosis, as well as both the incidence and intensity of intimal lesions. Ad.Ang1 perfusion also increased CD34+ stem cell counts in peripheral blood.

CONCLUSIONS

Our findings suggest that the antiinflammatory properties of Ang1 may offer an entirely new therapeutic approach to prevent cardiac allograft arteriosclerosis.

Glycosylation might provide endothelial zip codes for organ-specific leukocyte traffic into inflammatory sites

Inflammatory diseases are characterized by the leukocyte infiltration into tissues. L-selectin on lymphocytes and its endothelial glycosylated ligands are instrumental in the initiation of lymphocyte extravasation. Immunohistochemical stainings with monoclonal antibodies against functionally active glycan-decorated L-selectin ligands, ie, sialyl-Lewis x (sLex, 2F3, and HECA-452) or sulfated extended core 1 lactosamine (MECA-79), were performed on more than 400 specimen representatives for thyroiditis, myocarditis, psoriasis, vasculitis, ulcerative colitis, and their corresponding noninflamed tissues. The endothelial expression of sLex or sulfo sLex glycans in postcapillary venules was either absent or low in control tissues. The de novo induction of endothelial expression of sLex or sulfo sLex glycans was detected in all inflamed tissues. Furthermore, each organ carried its own modification of sLex or sulfo sLex glycans, ie, zip code. Our results suggest that these zip code glycans may provide means for organ selective leukocyte traffic that could be used in selective leukocyte traffic inhibition.

A peptide mimic of selectin ligands abolishes in vivo inflammation but has no effect on the rat heart allograft survival1

Acute heart allograft rejection is characterized by leukocyte infiltration and myocyte damage, key elements in the histological grading of rejection. The induction of selectins and their ligands on the graft postcapillary venular endothelium increases leukocyte tethering to, rolling on, and extravasation through the endothelium into graft parenchyma. We have characterized peptide mimicking selectin ligands by screening phage peptide libraries using anti-Lewis A antibodies and E-selectin as target molecules. The effect of this selectin- binding peptide, IELLQAR, on the prevention of inflammation and tissue damage and on the prolongation of graft survival in inbred DA (RT1a) rat heart allografts transplanted to WF (RT1v) recipients was tested. Bovine serum albumin (0.1%, solvent), VTSIAQA (control peptide), or IELLQAR were either continuously infused into the peritoneum via osmotic mini pumps or injected twice daily IV. Treatment with bovine serum albumin and VTSIAQA did not alter the number of graft infiltrating leukocytes or the histological grade of acute rejection, all scored as grade 4. On the contrary, the selectin binding peptide, IELLQAR, dose-dependently reduced inflammation and at the highest dose (6.0 mg/kg per day) eliminated the majority of graft infiltrating leukocytes, reduced the histological grade from 4 to 1B, but had no effect on graft survival. These data indicate that the intensity of inflammation related to the allograft rejection does not correlate to the graft survival.

P-selectin-dependent macrophage migration into the tubulointerstitium in unilateral ureteral obstruction

BACKGROUND

Interstitial infiltration of macrophages (Mø) is one of the main causal factors for the tubulointerstitial injury. However, precise mechanisms of Mø infiltration into tubulointerstitium have not been fully explored. The purposes of this study were to assess the role of selectins in the acute infiltration of Mø in rats with unilateral ureteral obstruction (UUO) and to evaluate the role of vasa recta, that is, whether they facilitate massive influx of Mø into the interstitium by functioning as specialized vessels.

METHODS

To evaluate the role of selectins in Mø infiltration into tubulointerstitium, the expression of selectins and L-selectin ligands was examined by immunohistochemistry and immunoelectron microscopy. The functional role of P-selectin in vasa recta was studied by Stamper-Woodruff assay, in vivo p-Mø migration assay and in vivo blocking experiments with the monoclonal antibody (mAb) ARP2-4.

RESULTS

Selective expression of P-selectin was detected in vasa recta as early as one hour after UUO, and the expression increased thereafter for 96 hours. In contrast, endothelial expression of L-selectin ligands and E-selectin were not detectable. In the Stamper-Woodruff assay on kidney sections of rats with UUO, the adhesion of isolated rat peritoneal Mø (p-Mø) to vasa recta was significantly inhibited by the mAb ARP2-4 (P-selectin blocker; P < 0.01), but not by mAb ARE-5 (E-selectin blocker) or rLECIg (rat L-selectin chimeric protein). In the in vivo transfer experiments with fluorescein-labeled p-Mø into rats 48 hours after UUO, labeled p-Mø had accumulated around vasa recta at three minutes and had infiltrated predominantly into the outer medulla at 180 minutes. The number of labeled p-Mø was reduced when the rats were pretreated with ARP2-4 (P < 0.01). Finally, ARP2-4 (10 mg/kg), injected 15 minutes before UUO, reduced the number of infiltrated Mø (P < 0.01).

CONCLUSION

The results suggest that vasa recta, which express P-selectin, contribute to massive infiltration of Mø into the interstitium by functioning as specialized post-capillary venules.

O-glycans on human high endothelial CD34 putatively participating in L-selectin recognition

Leukocyte traffic into lymph nodes and sites of inflammation is guided by L-selectin. Experiments performed in vitro and with gene-deleted mice suggest that CD34 recognizes L-selectin if decorated by 6-sulfo sialyl Lewis x (sLex) saccharides and the MECA-79 epitope. However, very little is known about glycosylation of human L-selectin ligands. We report here on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) profiles of N- and O-linked oligosaccharide fractions from human tonsillar endothelial CD34. All detected O-glycans were sialylated; some were also monosulfated or monosulfated and monofucosylated. If a given CD34-glycan may carry all requirements for L-selectin recognition, that is, both 6-sulfo-sLex and MECA-79 epitopes, only one O-glycan fraction, O-9, SA(2)Hex(3)HexNAc(3)- Fuc(1)(SO(3))(1), meets the criteria. A candidate structure is SAalpha2-3Galbeta1-4(Fucalpha1-3)(6-sulfo)GlcNAcbeta1-3Galbeta1-3(SAalpha2-3Galbeta1-4GlcNAcbeta1-6)GalNAc. However, if sulfo sLex glycans are supplemented with separate sulfated, nonfucosylated O-glycans, saccharides in O-6, O-8, or O-9, putatively carrying MECA-79 epitopes, could form multiglycan binding epitopes for L-selectin.

L-selectin in health and disease

This article reviews recent advances in the knowledge of the role of L-selectin, an adhesion molecule that is expressed on the surface of circulating leucocytes, in animal and human physiology and pathophysiology. After a brief discussion on nomenclature and structure, it progresses through the evidence for expression and regulation of L-selectin, cell collection and purification, physiological function and roles. The special role of knock out mice and monoclonal antibodies in determining a role for L-selectin in inflammatory states is described before proceeding to discuss the importance of L-selectin ligands and shed L-selectin. A second section describes a role for L-selectin in pathophysiological states in animals and man, with special reference to trauma, systemic inflammatory syndromes and sepsis. The review concludes with a summary of the potential role of anti-inflammatory medication and L-selectin blockers in the management of inflammation.

Functional analysis of promoter activity of murine beta-1,6-N-acetylglucosaminyltransferase

In the mouse, beta-1,6-N-acetylglucosaminyltransferase (IGnT) forms branches in poly-N-acetyllactosamines, which are good scaffolds for oncodevelopmental cell-surface antigens and recognition markers. There are two isoforms of IGnT, IGnT A and B, which are produced by alternative splicing of the IGnT gene; the unique portion is encoded by exon 1 and common portion is encoded by exons 2 and 3. Thus, the expression of each isoform is controlled by a different promoter. Here, we identified the regulatory regions of the mouse IGnT A and B genes. The promoter regions for IGnT A and B did not contain putative TATA or CAAT boxes, but each contained GT boxes. The upstream regulatory region of each gene was examined by transient luciferase reporter gene transfection experiments and gel mobility shift assay. Promoter activity for each gene was detected in F9 embryonal carcinoma cells, which express IGnT A and B, but not in N2a cells, which do not express the gene. Deletion analysis demonstrated that the regions 308 bp upstream from the transcriptional initiation site of IGnT A and 430 bp upstream from the transcriptional initiation site of IGnT B showed minimal promoter activity. Mutation of the single GT box in IGnT A and two GT boxes in IGnT B caused marked reduction of the promoter activity. These findings provided strong evidence that the GT boxes play crucial roles in transcriptional regulation of the genes.

Biosynthesis and function of beta 1,6 branched mucin-type glycans

The contribution of carbohydrate structure to biomolecular, cellular, and organismal function is well-established, but has not yet received the attention it deserves, perhaps due to the complexity of the structures involved and to a lack of simple experimental methods for relating structure and function. In particular, beta1,6 GlcNAc branching plays a key functional role in processes ranging from inflammation and immune system function to tumor cell metastasis. For instance, synthesis of the core 2 beta1,6 branched structure in the mucin glycan chain by C2GnT enables the expression of functional structures at the termini of polylactosamine chains, such as blood group antigens and sialyl Lewis x. Also, IGnT can create multiple branches on the polylactosamine chain, which may serve as a mechanism for amplifying the functional potency of cell surface glycoproteins and glycolipids. The family of enzymes which creates beta1,6 branched structure in mucin glycans is proving to be quite complex, since multiple isoforms appear to exist for these enzymes, and some of the enzymes are adept at forming more than one type of beta1,6 branched structure, as in the case of C2GnT-M. Furthermore, the enzymes do not appear to be restricted to acting on mucin-type acceptor structures, but are able to act on glycolipid structures as well. Much remains to be learned regarding the specific biological niche filled by each of these enzymes and how their activities complement one another, as well as the manner in which the activities of these enzymes are regulated in the cell.

The acceptor and site specificity of alpha 3-fucosyltransferase V. High reactivity of the proximal and low of the distal galbeta 1-4GlcNAc unit in i-type polylactosamines

We report here on in vitro acceptor and site specificity of recombinant alpha3-fucosyltransferase V (Fuc-TV) with 40 oligosaccharide acceptors. Galbeta1-4GlcNAc (LN) and GalNAcbeta1-4GlcNAc (LDN) reacted rapidly; Galbeta1-3GlcNAc (LNB) reacted moderately, and GlcNAcbeta1-4GlcNAc (N, N'-diacetyl-chitobiose) reacted slowly yet distinctly. In neutral and terminally alpha3-sialylated polylactosamines of i-type, the reducing end LN unit reacted rapidly and the distal (sialyl)LN group very slowly; the midchain LNs revealed intermediate reactivities. The data suggest that a distal LN neighbor enhances but a proximal LN neighbor reduces the reactivity of the midchain LNs. This implies that Fuc-TV may bind preferably the tetrasaccharide sequence Galbeta1-4GlcNAcbeta1-3Galbeta1-4GlcNAc for transfer at the underlined monosaccharide. Terminal alpha3-sialylation of i-type polylactosamines almost doubled the reactivities of the LN units at all positions of the chains. We conclude that, in comparison with human Fuc-TIV and Fuc-TIX, Fuc-TV reacted with a highly distinct site specificity with i-type polylactosamines. The Fuc-TV reactivity of free LNB resembled that of LNBbeta1-3'R of a polylactosamine, contrasting strongly with the dissimilarity of the reactivities of the analogous pair of LN and LNbeta1-3'R. This observation supports the notion that LN and LNB may be functionally bound at distinct sites on Fuc-TV surface. Our data show that Fuc-TV worked well with a very wide range of LN-glycans, showing weak reactivity only with distal (sialyl)LN units of i-type polylactosamines, biantennary N-glycans, and I branches of polylactosamines.

Inhibition of selectin-mediated cell adhesion and prevention of acute inflammation by nonanticoagulant sulfated saccharides. Studies with carboxyl-reduced and sulfated heparin and with trestatin a sulfate

Selectins play a major role in the inflammatory reaction by initiating neutrophil attachment to activated vascular endothelium. Some heparin preparations can interact with L- and P-selectin; however, the determinants required for inhibiting selectin-mediated cell adhesion have not yet been characterized. We now report that carboxyl-reduced and sulfated heparin (prepared by chemical modifications of porcine intestinal mucosal heparin leading to the replacement of carboxylates by O-sulfate groups) and trestatin A sulfate (obtained by sulfation of trestatin A, a non-uronic pseudo-nonasaccharide extracted from Streptomyces dimorphogenes) exhibit strong anti-P-selectin and anti-L-selectin activity while lacking antithrombin-mediated anticoagulant activity. In vitro experiments revealed that both compounds inhibited P-selectin- and L-selectin-mediated cell adhesion under laminar flow conditions. Moreover, carboxyl-reduced and sulfated heparin and trestatin A sulfate were also active in vivo, as assessed by experiments showing 1) that microinfusion of trestatin A sulfate reduced by 96% leukocyte rolling along rat mesenteric postcapillary venules and 2) that both compounds inhibited (by 58-81%) neutrophil migration into thioglycollate-inflamed peritoneum of BALB/c mice. These results indicate that nonanticoagulant sulfated saccharides targeted at P-selectin and L-selectin may have therapeutic potential in inflammatory disorders.

Two time-resolved fluorometric high-throughput assays for quantitation of GDP-L-fucose

Two rapid and simple procedures for the quantitative analysis of GDP-l-fucose (GDP-Fuc) are described. The methods are based on time-resolved fluorescence and microplate assay technology. The first assay relies on measuring the enzyme activity of alpha1, 3-fucosyltransferase. In this assay, transfer of fucose from GDP-Fuc converts sialyllactosamine to sialyl Lewis x tetrasaccharide, which is detected and quantified by relevant antibodies on a microplate. The formation of the reaction product is directly dependent on the presence of GDP-Fuc in the concentration range of 10-10,000 nM. In the second method GDP-Fuc inhibits the binding of fucose-specific Aleuria aurantia lectin to fucosylated glycan on a microwell. The lectin-based assay is less sensitive than the enzyme assay, but it is cheaper and faster. We used these assays in monitoring the amount of GDP-Fuc in crude lysates of transgenic yeast, which expresses the enzymes producing GDP-Fuc. The newly developed assays are versatile and applicable to measure also other nucleotide sugars or glycosyltransferase activities in a high-throughput manner.

Endothelial sulfated sialyl Lewis x glycans, putative L-selectin ligands, are preferentially expressed in bronchial asthma but not in other chronic inflammatory lung diseases

Lymphocyte infiltrate is a hallmark of inflammatory responses. We have previously shown that de novo-induced endothelial sialyl Lewis x (sLex) expression guides lymphocytes in an L-selectin-dependent manner to sites of acute organ transplant rejections. In this research, we have analyzed five groups of chronic lung inflammations to determine the presence of properly glycosylated, i.e., sulfated, sLex-decorated, L-selectin ligands. Two anti-sLex (2F3 and HECA-452) and one anti-6- and/or 6'-sulfated and/or 6,6'-bisulfated (MECA-79) monoclonal antibodies (mAbs) were used. The control lung specimens did not express L-selectin ligands on endothelium. In contrast, the endothelial staining intensity and the number of positive peribronchial venules and capillaries with mAbs 2F3, HECA-452, and MECA-79 were significantly greater in bronchial biopsies from patients with asthma compared with normal specimens (P<0.003). However, no significant increase of peribronchial endothelial reactivity with these antibodies was observed in adult respiratory distress syndrome, chronic bronchitis, fibrosing alveolitis, and granulomatous inflammation compared with controls. These data suggest that sulfated sLex glycans, acting putatively as ligands for L-selectin, could be instrumental in lymphocyte extravasation into human peribronchial lung tissue during asthma, but not so important in several other inflammatory lung diseases.

Endothelial L-selectin ligands are likely to recruit lymphocytes into rejecting human heart transplants

L-selectin-dependent lymphocyte extravasation is a hallmark of acute heart allograft rejection in rats. On screening over 600 endomyocardial biopsies (EMBs), taken at different time points after heart transplantation in man, we identified 91 samples with histological signs of acute rejection. Rejection and nonrejection EMBs were analyzed for the presence of properly glycosylated, ie, sulfated sialyl Lewis-x (sLex) decorated L-selectin ligands. Two anti-sLex (2F3 and HECA-452) and one anti-6- or 6'-sulfated and/or 6, 6'-bisulfation (MECA-79) monoclonal antibodies were used. Nonrejecting heart endothelium did not express, or expressed only weakly, sulfated and or sLex decorations of L-selectin ligands. On the contrary, these epitopes were readily detectable on endothelium of capillaries and venules at the onset and during acute rejection episodes. The more intense the sulfated sLex expression was, the more severe the rejection episode was in histological grading. The endothelial expression of L-selectin ligands decreased to background levels as the rejection resolved. Our data demonstrate a complete correlation between the level of expression of the sulfated sLex-decorated ligands on the one hand and the histological severity of acute heart allograft rejection on the other hand. These data suggest that functionally active endothelial L-selectin ligands are instrumental in lymphocyte extravasation into the human heart allografts at the onset and during acute rejection episodes.

High endothelial cells synthesize and degrade sLex. Putative implications for L-selectin-dependent recognition

L-selectin guides lymphocytes into peripheral lymphoid tissues by recognizing glycoprotein ligands decorated with 6-sulfated sialyl Lewis x (sulfo sLex). Here we have used a rat peripheral lymph node high endothelial cell line (Ax) to study in detail the synthesis, expression and degradation of sLex epitope. We show here that Ax cells possess active alpha(1,3)fucosyltransferase Fuc-TVII, the enzyme responsible for the final fucosylation of sialyl-N-acetyllactosamine during sLex synthesis, and express sLex on the cell surface. Furthermore, these cells degrade sLex, primarily by desialylating it to neutral Lex epitopes by alpha(2,3)sialidase(s).

In vivo ligand specificity of E-selectin binding to multivalent sialyl Lewisx N-linked oligosaccharides

The in vivo specificity for E-selectin binding to a panel of N-linked oligosaccharides containing a clustered array of one to four sialyl Lewisx (SLex; NeuAcalpha2-3Gal[Fucalpha1-3]beta1-4GlcNAc) determinants was studied in mice. Following intraperitoneal dosing with lipopolysaccharide, radioiodinated tyrosinamide N-linked oligosaccharides were dosed i.v. and analyzed for their pharmacokinetics and biodistribution. Specific targeting was determined from the degree of SLex oligosaccharide targeting relative to a sialyl oligosaccharide control. Oligosaccharides targeted the kidney with the greatest selectivity after a 4-h induction period following lipopolysaccharide dosing. Unique pharmacokinetic profiles were identified for SLex biantennary and triantennary oligosaccharides but not for monovalent and tetraantennary SLex oligosaccharides or sialyl oligosaccharide controls. Biodistribution studies established that both SLex biantennary and triantennary oligosaccharides distributed to the kidney with 2-3-fold selectivity over sialyl oligosaccharide controls, whereas monovalent and tetraantennary SLex oligosaccharides failed to mediate specific kidney targeting. Simultaneous dosing of SLex biantennary or triantennary oligosaccharide with a mouse anti-E-selectin monoclonal antibody blocked kidney targeting, whereas co-administration with anti-P-selectin monoclonal antibody did not significantly block kidney targeting. The results suggest that SLex biantennary and triantennary are N-linked oligosaccharide ligands for E-selectin and implicate E-selectin as a bivalent receptor in the murine kidney endothelium.

A novel, high endothelial venule-specific sulfotransferase expresses 6-sulfo sialyl Lewis(x), an L-selectin ligand displayed by CD34

L-selectin mediates lymphocyte homing by facilitating lymphocyte adhesion to unique carbohydrate ligands, sulfated sialyl Lewis(x), which are expressed on high endothelial venules (HEV) in secondary lymphoid organs. The nature of the sulfotransferase(s) that contribute to sulfation of such L-selectin counterreceptors has been uncertain. We herein describe a novel L-selectin ligand sulfotransferase, termed LSST, that directs the synthesis of the 6-sulfo sialyl Lewis(x) on L-selectin counterreceptors CD34, GlyCAM-1, and MAdCAM-1. LSST is predominantly expressed in HEV and exhibits striking catalytic preference for core 2-branched mucin-type O-glycans as found in natural L-selectin counterreceptors. LSST enhances L-selectin-mediated adhesion under shear compared to nonsulfated controls. LSST therefore corresponds to an HEV-specific sulfotransferase that contributes to the biosynthesis of L-selectin ligands required for lymphocyte homing.

Expression of L-Selectin Ligands by Transformed Endothelial Cells Enhances T Cell-Mediated Rejection

Recent immunohistochemical studies have suggested that L-selectin ligands may be implicated in the infiltration of tumors and rejected transplants by lymphocytes. In the present study, polyoma-middle T Ag-transformed endothelial cells (H.end), which typically form in vivo immunogenic vascular tumors resembling Kaposi’s sarcoma, were engineered to express L-selectin ligands by stable transfection with a cDNA encoding α(1,3/4)-fucosyltransferase (H.endft). The ability of these cells to form tumors in the s.c. tissues of normal and immunocompromised mice was then compared with that of H.end cells transfected with the hygromycin-resistance vector only (H.endhygro). H.endhygro cells rapidly formed local and metastatic tumors in normal syngeneic mice, leading to death within 2–3 mo postinjection. By contrast, tumors derived from H.endft cells displayed a slower rate of growth, an absence of metastasis, and marked lymphocyte infiltration. Animals bearing these tumors survived for a significantly longer duration than animals injected with H.endhygro cells. Alternatively, H.endft and H.endhygro cells formed tumors with comparable aggressiveness in immunocompromised mice, resulting in animal death within 3 wk of injection. H.endft but not H.endhygro cells supported L-selectin-dependent adhesion and cytolytic T cell activity in vitro. Taken together, our observations indicate that the in situ expression of fucosyltransferase may significantly influence the cellular immune response in endothelioma tumors. These results may be relevant in understanding the development of vascular opportunistic tumors such as Kaposi’s sarcoma.

Leukocyte adhesion--a fundamental process in leukocyte physiology

Leukocyte adhesion is of pivotal functional importance. The adhesion involves several different adhesion molecules, the most important of which are the leukocyte beta 2-integrins (CD11/CD18), the intercellular adhesion molecules, and the selectins. We and others have extensively studied the specificity and binding sites in the integrins and the intercellular adhesion molecules for their receptors and ligands. The integrins have to become activated to exert their functions but the possible mechanisms of activation remain poorly understood. Importantly, a few novel intercellular adhesion molecules have been recently described, which seem to function only in specific tissues. Furthermore, it is becoming increasingly apparent that changes in integrins and intercellular adhesion molecules are associated with a number of acute and chronic diseases.

Regulation of I-branched poly-N-acetyllactosamine synthesis. Concerted actions by I-extension enzyme, I-branching enzyme, and beta1,4-galactosyltransferase I

I-branched poly-N-acetyllactosamine is a unique carbohydrate composed of N-acetyllactosamine branches attached to linear poly-N-acetyllactosamine, which is synthesized by I-branching beta1, 6-N-acetylglucosaminyltransferase. I-branched poly-N-acetyllactosamine can carry bivalent functional oligosaccharides such as sialyl Lewisx, which provide much better carbohydrate ligands than monovalent functional oligosaccharides. In the present study, we first demonstrate that I-branching beta1, 6-N-acetylglucosaminyltransferase cloned from human PA-1 embryonic carcinoma cells transfers beta1,6-linked GlcNAc preferentially to galactosyl residues of N-acetyllactosamine close to nonreducing terminals. We then demonstrate that among various beta1, 4-galactosyltransferases (beta4Gal-Ts), beta4Gal-TI is most efficient in adding a galactose to linear and branched poly-N-acetyllactosamines. When a beta1,6-GlcNAc branched poly-N-acetyllactosamine was incubated with a mixture of beta4Gal-TI and i-extension beta1,3-N-acetylglucosaminyltransferase, the major product was the oligosaccharide with one N-acetyllactosamine extension on the linear Galbeta1-->4GlcNAcbeta1-->3 side chain. Only a minor product contained galactosylated I-branch without N-acetyllactosamine extension. This finding was explained by the fact that beta4Gal-TI adds a galactose poorly to beta1,6-GlcNAc attached to linear poly-N-acetyllactosamines, while beta1, 3-N-acetylglucosaminyltransferase and beta4Gal-TI efficiently add N-acetyllactosamine to linear poly-N-acetyllactosamines. Together, these results strongly suggest that galactosylation of I-branch is a rate-limiting step in I-branched poly-N-acetyllactosamine synthesis, allowing poly-N-acetyllactosamine extension mostly along the linear poly-N-acetyllactosamine side chain. These findings are entirely consistent with previous findings that poly-N-acetyllactosamines in human erythrocytes, PA-1 embryonic carcinoma cells, and rabbit erythrocytes contain multiple, short I-branches.

Enzymatic synthesis of alpha3'sialylated and multiply alpha3fucosylated biantennary polylactosamines. A bivalent [sialyl diLex]-saccharide inhibited lymphocyte-endothelium adhesion organ-selectively

Multifucosylated sialo-polylactosamines are known to be high affinity ligands for E-selectin. PSGL-1, the physiological ligand of P-selectin, is decorated in HL-60 cells by a sialylated and triply fucosylated polylactosamine that is believed to be of functional importance. Mimicking some of these saccharide structures, we have synthesized enzymatically a bivalent [sialyl diLex]-glycan, Neu5Acalpha2-3'Lexbeta1-3'Lexbeta1-3'(Neu5Acalpha2-3'Lexbeta1-3Lexbe ta1-6')LN [where Neu5Ac is N-acetylneuraminic acid, Lex is the trisaccharide Galbeta1-4(Fucalpha1-3)GlcNAc and LN is the disaccharide Galbeta1-4GlcNAc]. Several structurally related, novel polylactosamine glycans were also constructed. The inhibitory effects of these glycans on two L-selectin-dependent, lymphocyte-to-endothelium adhesion processes of rats were analysed in ex-vivo Stamper-Woodruff binding assays. The IC50 value of the bivalent [sialyl diLex]-glycan at lymph node high endothelium was 50 nm, but at the capillaries of rejecting cardiac allografts it was only 5 nm. At both adhesion sites, the inhibition was completely dependent on the presence of fucose units on the sialylated LN units of the inhibitor saccharide. These data show that the bivalent [sialyl diLex]-glycan is a high affinity ligand for L-selectin, and may reduce extravasation of lymphocytes at sites of inflammation in vivo without severely endangering the normal recirculation of lymphocytes via lymph nodes.

Inhibition of L-selectin-mediated leukocyte rolling by synthetic glycoprotein mimics

Synthetic carbohydrate and glycoprotein mimics displaying sulfated saccharide residues have been assayed for their L-selectin inhibitory properties under static and flow conditions. Polymers displaying the L-selectin recognition epitopes 3',6-disulfo Lewis x(Glc) (3-O-SO3-Galbeta1alpha4(Fucalpha1alpha3)-6-O-SO3-Glcbeta+ ++-OR) and 3',6'-disulfo Lewis x(Glc) (3, 6-di-O-SO3-Galbeta1alpha4(Fucalpha1alpha3)Glcbeta-OR) both inhibit L-selectin binding to heparin under static, cell-free binding conditions with similar efficacies. Under conditions of shear flow, however, only the polymer displaying 3',6-disulfo Lewis x(Glc) inhibits the rolling of L-selectin-transfected cells on the glycoprotein ligand GlyCAM-1. Although it has been shown to more effective than sialyl Lewis x at blocking the L-selectin-GlyCAM-1 interaction in static binding studies, the corresponding monomer had no effect in the dynamic assay. These data indicate that multivalent ligands are far more effective inhibitors of L-selectin-mediated rolling than their monovalent counterparts and that the inhibitory activities are dependent on the specific sulfation pattern of the recognition epitope. Importantly, our results indicate the L-selectin specificity for one ligand over another found in static, cell-free binding assays is not necessarily retained under the conditions of shear flow. The results suggest that monovalent or polyvalent carbohydrate or glycoprotein mimetics that inhibit selectin binding in static assays may not block the more physiologically relevant process of selectin-mediated rolling.

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.