Function and evolutionary conservation of distinct epitopes on the leukocyte adhesion molecule-1 (TQ-1, Leu-8) that regulate leukocyte migration.

The leukocyte adhesion molecule-1 (LAM-1, TQ=1, Leu-8) in humans, like its murine homologue, MEL-14, is the principal receptor that mediates the binding of leukocytes to high endothelial venules (HEV) of peripheral lymph nodes. In this study, several regions of the protein which mediate receptor function were identified by using a large panel of murine mAb reactive with LAM-1. Individual mAb reacted with LAM-1+ cells with characteristic intensities of immunofluorescence staining, and each bound both lymphocytes and neutrophils. Lymphocyte attachment to HEV was significantly inhibited by the binding of five mAb. In contrast, only two of these mAb were able to completely block the binding of phosphomannan monoester core complex from the yeast Hansenula holstii cell wall (PPME), a phosphomannan monoester core polysaccharide that serves as a soluble model of the natural ligand of LAM-1. Interestingly, the binding of two anti-LAM-1 mAb to cells induced a significant increase in PPME binding, reminiscent of the increase in receptor affinity observed after leukocyte activation. Antibody cross-blocking studies indicated that many of the functionally important epitopes were spatially distinct, and domain mapping indicated that they recognized distinct domains of LAM-1. The expression and function of these epitopes were further assessed by using a variety of animal species to further characterize the functionally relevant epitopes defined in these studies. At least some anti-LAM-1 mAb reacted with leukocytes from monkey, cow, rabbit, sheep, dog, cat, pig, and goat, but not from chicken, rat, or mouse. The reactivity of anti-LAM-1 mAb in several animal species correlated with the ability of leukocytes to bind PPME, and mAb that inhibited lymphocyte binding to HEV in man could also inhibit this function in rhesus monkey and dog. Thus, several LAM-1 epitopes are structurally and functionally well conserved throughout recent mammalian evolution, emphasizing an important role for LAM-1 in the regulation of leukocyte traffic.     

The mouse lymph node homing receptor is identical with the lymphocyte cell surface marker Ly-22: role of the EGF domain in endothelial binding.

The lymph node homing receptor core polypeptide (mLHRc) is composed of a tandem collection of domains: a lectin domain, an epidermal growth factor (EGF) domain, and two repeats common in complement regulatory proteins. Here we demonstrate localization of mLHRc to chromosome 1, the portion syntenic with chromosome 1 in man. This locus is inseparable in mouse strains from the murine lymphocyte cell surface marker Ly-22. The data indicate that Ly-22 is an allelic determinant on the LHR resulting from a single amino acid interchange within the EGF domain. Cross-blocking experiments demonstrate that anti-Ly-22 and MEL-14 recognize independent epitopes and that Ly-22 is distinct from the carbohydrate binding region. Application of anti-Ly-22 in the in vitro binding assay shows inhibition of binding of lymphocytes to high endothelial venules (HEVs). The localization of the Ly-22 epitope in this novel chimeric protein suggests direct participation of the EGF domain in the adhesion of lymphocytes to HEV.     

A role for the epidermal growth factor-like domain of P-selectin in ligand recognition and cell adhesion

The selectin family of adhesion molecules mediates the initial interactions of leukocytes with endothelium. The extracellular region of each selectin contains an amino-terminal C-type lectin domain, followed by an EGF-like domain and multiple short consensus repeat units (SCR). Previous studies have indirectly suggested a role for each of the extracellular domains of the selectins in cell adhesion. In this study, a panel of chimeric selectins created by exchange of domains between L- and P-selectin was used to directly examine the role of the extracellular domains in cell adhesion. Exchange of only the lectin domains between L- and P-selectin conferred the adhesive and ligand recognition functions of the lectin domain of the parent molecule. However, chimeric selectins which contained both the lectin domain of L- selectin and the EGF-like domain of P-selectin exhibited dual ligand- binding specificity. These chimeric proteins supported adhesion both to myeloid cells and to high endothelial venules (HEV) of lymph nodes and mesenteric venules in vivo. Exchange of the SCR domains had no detectable effect on receptor function or specificity. Thus, the EGF- like domain of P-selectin may play a direct role in ligand recognition and leukocyte adhesion mediated by P-selectin, with the lectin plus EGF- like domains collectively forming a functional ligand recognition unit.     

Granulocyte-macrophage colony-stimulating factor and other cytokines regulate surface expression of the leukocyte adhesion molecule-1 on human neutrophils, monocytes, and their precursors.

There is increasing evidence that cytokines such as granulocyte-macrophage (GM)-CSF can profoundly affect the adhesion, aggregation, and mobility of neutrophils both in vitro and in vivo. However, the mechanisms whereby these factors might alter the adhesive properties of neutrophils are incompletely understood. A new family of cellular adhesion molecules has recently been identified by cDNA cloning. The members of this family include human leukocyte adhesion molecule-1 (LAM-1), the human endothelial-leukocyte adhesion molecule, and the mouse leukocyte homing receptor for high endothelial venules, MEL-14. LAM-1 is the human homologue of murine MEL-14, and is believed to mediate binding of leukocytes to human high endothelial venules. LAM-1 can be identified by mAb TQ-1, Leu 8, or anti-LAM1.1. The expression and regulation of LAM-1 on granulocytes, monocytes, and their precursors was investigated using flow cytometry and the anti-LAM-1.1 mAb. Neutrophils, eosinophils, monocytes, marrow myeloid cells, granulocyte/macrophage colony-forming unit, and burst-forming unit for erythroid cells were LAM-1+ by flow microfluorimetry. The regulation of LAM-1 expression was tested by treating various cell populations with cytokines or other stimuli for 0-90 min. Exposure of neutrophils, monocytes, and marrow myeloid cells to GM-CSF induced rapid and complete loss of LAM-1 from the cell surface, but had no effect on LAM-1 expression by lymphocytes. The loss of LAM-1 was temporally correlated with up-regulation of CD11b (Mo1), an adhesion molecule involved in neutrophil aggregation. Several other factors known to activate neutrophils also caused down-regulation of LAM-1 and up-regulation of CD11b, including TNF, FMLP, and leukotriene B4. Interestingly, granulocyte-CSF and IFN-gamma had minimal effects on neutrophil LAM-1 expression. Similar results were observed on monocytes and myeloid precursor cells. Thus, exposure of neutrophils to GM-CSF results in a profound change in surface expression of adhesion molecules, with coordinated up-regulation of CD11b and down-regulation of LAM-1. These changes in adhesion proteins are likely to alter aggregation and mobility of both mature myeloid cells and their precursors in patients receiving certain types of cytokine therapy.     

Receptors involved in lymphocyte homing: relationship between a carbohydrate-binding receptor and the MEL-14 antigen

Blood-borne lymphocytes extravasate in large numbers within peripheral lymph nodes (PN) and other secondary lymphoid organs. It has been proposed that the initiation of extravasation is based upon a family of cell adhesion molecules (homing receptors) that mediate lymphocyte attachment to specialized high endothelial venules (HEV) within the lymphoid tissues. A putative homing receptor has been identified by the monoclonal antibody, MEL-14, which recognizes an 80-90-kD glycoprotein on the surface of mouse lymphocytes and blocks the attachment of lymphocytes to PN HEV. In a companion study we characterize a carbohydrate-binding receptor on the surface of mouse lymphocytes that also appears to be involved in the interaction of lymphocytes with PN HEV. This receptor selectively binds to fluorescent beads derivatized with PPME, a polysaccharide rich in mannose-6-phosphate. In this report we examine the relationship between this carbohydrate-binding receptor and the putative homing receptor identified by the MEL-14 antibody. We found that: MEL-14 completely and selectively blocks the activity of the carbohydrate-binding receptor on mouse lymphocytes; the ability of six lymphoma cell lines to bind PPME beads correlates with cell-surface expression of the MEL-14 antigen, as well as PN HEV-binding activity; selection of lymphoma cell line variants for PPME-bead binding by fluorescence-activated cell sorting (FACS) produces highly correlated (r = 0.974, P less than 0.001) and selective changes in MEL-14 antigen expression. These results show that the carbohydrate-binding receptor on lymphocytes and the MEL-14 antigen, which have been independently implicated as receptors involved in PN-specific HEV attachment, are very closely related, if not identical, molecules.     

The human peripheral lymph node vascular addressin is a ligand for LECAM-1, the peripheral lymph node homing receptor

The trafficking of lymphocytes from the blood and into lymphoid organs is controlled by tissue-selective lymphocyte interactions with specialized endothelial cells lining post capillary venules, in particular the high endothelial venules (HEV) found in lymphoid tissues and sites of chronic inflammation. Lymphocyte interactions with HEV are mediated in part by lymphocyte homing receptors and tissue-specific HEV determinants, the vascular addressins. A peripheral lymph node addressin (PNAd) has been detected immunohistologically in mouse and man by monoclonal antibody MECA-79, which inhibits lymphocyte homing to lymph nodes and lymphocyte binding to lymph node and tonsillar HEV. The human MECA-79 antigen, PNAd, is molecularly distinct from the 65-kD mucosal vascular addressin. The most abundant iodinated species by SDS-PAGE is 105 kD. When affinity isolated and immobilized on glass slides, MECA-79 immunoisolated material binds human and mouse lymphocytes avidly in a calcium dependent manner. Binding is blocked by mAb MECA-79, by antibodies against mouse or human LECAM-1 (the peripheral lymph node homing receptor, the MEL-14 antigen, LAM-1), and by treatment of PNAd with neuraminidase. Expression of LECAM-1 cDNA confers PNAd binding ability on a transfected B cell line. We conclude that LECAM-1 mediates lymphocyte binding to PNAd, an interaction that involves the lectin activity of LECAM-1 and carbohydrate determinants on the addressin.     

Further characterization of the interaction between L-selectin and its endothelial ligands.

L-Selectin is a lectin-like receptor on lymphocytes which mediates their attachment to high endothelial venules (HEV) within lymph nodes. Previous work has identified HEV-associated endothelial ligands for L-selectin as sialylated, fucosylated and sulphated glycoproteins of approximately 50 kDa and approximately 90 kDa (Sgp50 and Sgp90). The interaction of L-selectin with these ligands is carbohydrate directed, reflecting the involvement of its amino-terminal, calcium-type lectin domain. It has been reported, and we have confirmed, that anti-Ly22 blocks the adhesive function of L-selectin without reducing its binding to a carbohydrate- based ligand PPME (phosphomannan monoester core from Hansenula hostii). The epitope for this monoclonal antibody depends on the epidermal growth factor (EGF) domain of L-selectin. We demonstrate that anti-Ly22 inhibits the interaction of L-selectin with both of the Sgps, thus establishing that the interaction of L-selectin with HEV can be accounted for by the Sgps. Furthermore, the interaction of trypsin fragments of Sgp50 with L-selectin is inhibitable both by an antibody that maps to the lectin domain and by anti-Ly22. These findings raise the possibility that anti-Ly22 is affecting the function of the lectin domain of L-selectin rather than directly antagonizing the EGF domain. Toward a further characterization of L-selectin's carbohydrate specificity, we show that Sgp50 is partially inactivated by the linkage-specific Newcastle Disease virus sialidase (alpha 2,3 linkage). We additionally demonstrate that a sialyl Lewis x-related tetrasaccharide can interact with L-selectin, as has also been demonstrated for E-selectin and P-selectin.     

Antibody binding to a conformation-dependent epitope induces L-selectin association with the detergent-resistant cytoskeleton

L-Selectin mediates leukocyte rolling on endothelium and immobilized leukocytes. Its regulation has been the subject of much study, and the conformation of the molecule may play an important role in its function. Here we report that a conformational change in L-selectin, induced by an anti-lectin domain mAb (LAM1-116) and recognized by another mAb directed to a conserved epitope on L-selectin (EL-246), predisposed L-selectin to cytoskeletal association. This effect was due to direct binding of the mAb, not to overt signaling events, and was specific to LAM1-116. Nineteen other anti-L-selectin mAbs directed against the lectin, epidermal growth factor, or short consensus repeat domains lacked this activity. The induced conformational change occurred at 37 degrees C, at 4 degrees C, in the presence of sodium azide and tyrosine kinase inhibitors herbimycin A and genistein, and with soluble detergent-extracted L-selectin. In the presence of LAM1-116, EL-246 induced cytoskeletal association of L-selectin in the absence of Ab cross-linking as visualized by L-selectin staining after low dose detergent treatment of the cells. We propose that the conformational change described herein regulates L-selectin-mediated events by exposing a high avidity binding site that, when engaged, triggers association of L-selectin with the cytoskeleton, which may lead to stronger tethers with physiological ligands.     

Leukocyte adhesion molecule-1 (LAM-1, L-selectin) interacts with an inducible endothelial cell ligand to support leukocyte adhesion.

The human lymphocyte homing receptor, LAM-1, mediates the adhesion of lymphocytes to specialized high endothelial venules (HEV) of peripheral lymph nodes. We now report that LAM-1 is also a major mediator of leukocyte attachment to activated human endothelium. In a novel adhesion assay, LAM-1 was shown to mediate approximately 50% of the adhesion of both lymphocytes and neutrophils to TNF-activated human umbilical vein endothelial cells at 4 degrees C. The contribution of LAM-1 to leukocyte adhesion was only detectable when the assays were carried out under rotating (nonstatic) conditions, suggesting that LAM-1 is involved in the initial attachment of leukocytes to endothelium. In this assay at 37 degrees C, essentially all lymphocyte attachment to endothelium was mediated by LAM-1, VLA-4/VCAM-1, and the CD11/CD18 complex, whereas neutrophil attachment was mediated by LAM-1, endothelial-leukocyte adhesion molecule-1, and CD11/CD18. Thus, multiple receptors are necessary to promote optimal leukocyte adhesion to endothelium. LAM-1 also appeared to be involved in optimal neutrophil transendothelial migration using a videomicroscopic in vitro transmigration model system. LAM-1-dependent leukocyte adhesion required the induction and surface expression of a neuraminidase-sensitive molecule that was expressed for at least 24 h on activated endothelium. Expression of the LAM-1 ligand by endothelium was optimally induced by LPS and the proinflammatory cytokines TNF-alpha and IL-1 beta, whereas IFN-gamma and IL-4 induced lower levels of expression. The LAM-1 ligand on HEV and cytokine treated endothelium may be similar carbohydrate-containing molecules, because phosphomannan monoester core complex from yeast Hansenula hostii cell wall blocked binding of lymphocytes to both cell types, and identical epitopes on LAM-1-mediated lymphocyte attachment to HEV and activated endothelium. Thus, LAM-1 and its inducible endothelial ligand constitute a new pair of adhesion molecules that may regulate initial leukocyte/endothelial interactions at sites of inflammation.     

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

Lymphocyte attachment to high endothelial venules within lymph nodes is mediated by the peripheral lymph node homing receptor (pnHR), originally defined on mouse lymphocytes by the MEL-14 mAb. The pnHR is a calcium-dependent lectin-like receptor, a member of the LEC-CAM family of adhesion proteins. Here, using a soluble recombinant form of the homing receptor, we have identified an endothelial ligand for the pnHR as an approximately 50-kD sulfated, fucosylated, and sialylated glycoprotein, which we designate Sgp50 (sulfated glycoprotein of 50 kD). Recombinant receptor binding to this lymph node-specific glycoprotein requires calcium and is inhibitable by specific carbohydrates and by MEL-14 mAb. Sialylation of the component is required for binding. Additionally, the glycoprotein is precipitated by MECA-79, an adhesion-blocking mAb reactive with lymph node HEV. A related glycoprotein of approximately 90 kD (designated as Sgp90) is also identified.     

Nasal-associated lymphoid tissue: phenotypic and functional evidence for the primary role of peripheral node addressin in naive lymphocyte adhesion to high endothelial venules in a mucosal site.

Nasal-associated lymphoid tissue (NALT), a mucosal inductive site for the upper respiratory tract, is important for the development of mucosal immunity locally and distally to intranasally introduced Ag. To more fully understand the induction of nasal mucosal immunity, we investigated the addressins that allow for lymphocyte trafficking to this tissue. To investigate the addressins responsible for naive lymphocyte binding, immunofluorescent and immunoperoxidase staining of frozen NALT sections were performed using anti-mucosal addressin cell adhesion molecule-1 (MAdCAM-1), anti-peripheral node addressin (PNAd), and anti-VCAM-1 mAbs. All NALT high endothelial venules (HEV) expressed PNAd, either associated with MAdCAM-1 or alone, whereas NALT follicular dendritic cells expressed both MAdCAM-1 and VCAM-1. These expression profiles were distinct from those of the gut mucosal inductive site, Peyer's patches (PP). The functionality of NALT HEV was determined using a Stamper-Woodruff ex vivo assay. The anti-L-selectin MEL-14 mAb blocked >90% of naive lymphocyte binding to NALT HEV, whereas the anti-MAdCAM-1 mAb, which blocks almost all naive lymphocyte binding to PP, minimally blocked binding to NALT HEV. NALT lymphocytes exhibited a unique L-selectin expression profile, differing from both PP and peripheral lymph nodes. Finally, NALT HEV were found in increased amounts in the B cell zones, unlike PP HEV. These results suggest that NALT is distinct from the intestinal PP, that initial naive lymphocyte binding to NALT HEV involves predominantly L-selectin and PNAd rather than alpha4beta7-MAdCAM-1 interactions, and that MAdCAM-1 and VCAM-1 expressed by NALT follicular dendritic cells may play an important role in lymphocyte recruitment and retention.     

FMC46, a cell protrusion-associated leukocyte adhesion molecule-1 epitope on human lymphocytes and thymocytes.

In this report, we describe a 76-kDa glycoprotein recognized by mAb FMC46 that, by virtue of its concentration on cell protrusions involved in motility, may be important in lymphoid cell locomotion. FMC46 detects an epitope of the leukocyte adhesion molecule-1 (LAM-1), a member of the selecting family (LAM-1, Endothelial Leukocyte Adhesion Molecular-1 (ELAM-1), and Granule Membrane Protein-140 (GMP-140), that is expressed on LAM-1-transfected cell lines, is a glycosylation epitope based on its loss after culture in tunicamycin, and is closely related to the LAM-1.2 epitope. FMC46 is expressed at high density on the majority of CD45RA+ and CD45RO+ peripheral blood T cells (60 to 70%) and on a subset of thymocytes that includes the multinegative CD3- CD4- CD8- progenitor cells (100% FMC46hi) and the CD45R0- presumptive thymic generative lineage (70% FMC46hi). It appears at reduced density and frequency on CD45RA- thymocytes (50% FMC46lo), comprised mainly of death-committed thymocytes. Among thymic subsets defined by expression of CD4 and/or CD8, FMC46 is expressed at high density predominantly on a subset of single-positive cells and not on double-positive cells. These results suggest a fundamental role for LAM-1 in thymic development, with a high density preferentially expressed on cells involved in thymic generative processes and a low density on cells progressing to intrathymic death. A major subset of peripheral blood B cells and thymic B cells also express FMC46. Immunohistochemistry on frozen sections indicated strong staining in splenic follicles and around blood vessels, staining of the thymic medulla and subcapsular areas, and staining of the mantle zone of germinal centers of the lymph node. FMC46+ lymphocytes accumulated along high endothelial venules in the lymph node. On locomoting multinegative thymocytes, FMC46 is concentrated on the leading tip of extended processes, on pseudopods, and on ruffles, unlike the distribution of either CD44 or TQ1 (LAM 1.2), suggesting a role in locomotion. On dividing multinegative thymocytes, FMC46 was found almost exclusively along the cleavage furrow, implicating it in detachment processes. We conclude that the properties of the LAM-1 molecule recognized by FMC46 are consistent with a role in detachment phases of motility and of cell interactions.     

Low-dose chymotrypsin treatment inhibits neutrophil migration into sites of inflammation in vivo: effects on Mac-1 and MEL-14 adhesion protein expression and function

Antibody blocking studies in the mouse suggest that the MEL-14 antigen is involved in neutrophil-endothelial cell interactions and may be important in neutrophil extravasation to sites of inflammation in vivo. We recently showed that chemotactic factor activation causes a rapid (within minutes) shedding of a large fragment of the MEL-14 antigen from the surface of neutrophils. We report here that chymotrypsin, at low doses (0.1 units/1 x 10(6) cells), but not trypsin, elastase, or collagenase, causes an activation-independent rapid loss (greater than 90%) of the MEL-14 antigen from the surface of murine neutrophils. Under the same treatment conditions chymotrypsin has no effect on the expression of four other neutrophil surface antigens, including the Mac-1 adhesion protein. Chymotrypsin treatment has no effect on neutrophil adhesion to plastic, migration to C5a, regulation of the Mac-1 antigen, but causes a greater than 95% reduction in neutrophil binding to high endothelial venules (HEV) in peripheral lymph nodes measured in the ex vivo frozen section HEV binding assay. The level of inhibition of neutrophil adhesion to HEV was comparable to that seen with the MEL-14 antibody. This experimental system allows us for the first time to specifically examine the consequences of removing the MEL-14 antigen from the surface of neutrophils on function in vivo. We show that treatment with chymotrypsin blocks greater than 85% of the ability of neutrophils injected back into the animal to home to the inflamed peritoneum. In similar in vivo experiments the MEL-14 antibody blocks neutrophil homing by 60-70%. These results further support the importance of the MEL-14 antigen in neutrophil extravasation in vivo and indicate that chymotrypsin could be useful in examining the molecular mechanisms involved in extravasation of leukocytes into a variety of diverse tissue sites of inflammation.     

Spatial configuration of hepatitis E virus antigenic domain

Hepatitis E virus (HEV) is a human pathogen that causes acute hepatitis. When an HEV capsid protein containing a 52-amino-acid deletion at the C terminus and a 111-amino-acid deletion at the N terminus is expressed in insect cells, the recombinant HEV capsid protein can self-assemble into a T=1 virus-like particle (VLP) that retains the antigenicity of the native HEV virion. In this study, we used cryoelectron microscopy and image reconstruction to show that anti-HEV monoclonal antibodies bind to the protruding domain of the capsid protein at the lateral side of the spikes. Molecular docking of the HEV VLP crystal structure revealed that Fab224 covered three surface loops of the recombinant truncated second open reading frame (ORF2) protein (PORF2) at the top part of the spike. We also determined the structure of a chimeric HEV VLP and located the inserted B-cell tag, an epitope of 11 amino acids coupled to the C-terminal end of the recombinant ORF2 protein. The binding site of Fab224 appeared to be distinct from the location of the inserted B-cell tag, suggesting that the chimeric VLP could elicit immunity against both HEV and an inserted foreign epitope. Therefore, the T=1 HEV VLP is a novel delivery system for displaying foreign epitopes at the VLP surface in order to induce antibodies against both HEV and the inserted epitope.     

Down-regulation of homing receptors after T cell activation

The specific pattern of lymphocyte localization and recirculation is important for the induction and expression of normal immune responses. In order to home to lymph nodes (LN), lymphocytes must first recognize and bind to specific high endothelial venules (HEV) in the LN. Binding to LN HEV is mediated by specific lymphocyte receptors, termed homing receptors, which are recognized by the mAb MEL-14. We examined the changes that occur in homing receptor expression after activation of murine T lymphocytes in vitro. Cells activated in MLC or by Con A undergo a 75% loss in their ability to recognize HEV, as demonstrated by a decrease in binding to HEV in vitro. Large, activated cells isolated from a primary MLC by elutriator centrifugation were completely unable to recognize HEV, whereas the small cells in the same culture continued to bind well. Flow cytometric analysis with MEL-14 showed that the activated fraction had lost expression of gp90MEL-14, the homing receptor Ag, whereas the inactivated cells remained MEL-14+. Concomitant with the loss of homing receptor expression, most of the activated cells became strongly peanut agglutinin (PNA)-positive, demonstrating a marked change in surface glycosylation. Thus, these MLC consist of two major populations of T cells--small, inactivated lymphocytes that are MEL-14+PNAlo and large, activated blast cells that are MEL-14-PNAhi. Purified MEL-14+ T cells activated by Con A gave rise to MEL-14- progeny, showing that gp90MEL-14 is lost from gp90MEL-14-positive precursors, rather than from the selective growth of MEL-14- cells. Furthermore, the loss of Ag expression on at least some activated cells is reversible in resting culture, with almost half of the cells reverting to MEL-14+ after the cessation of stimulation. These experiments show that activation of T cells results in down-regulation of surface homing receptors, resulting in their inability to recognize and bind to the endothelial surface of HEV. This suggests that the activation of T cells in vivo would result in a dramatic and physiologically significant change in their migration and localization properties which would be important during a normal immune response.     

Neutrophils, monocytes, and lymphocytes bind to cytokine-activated kidney glomerular endothelial cells through L-selectin (LAM-1) in vitro.

The role of L-selectin (LAM-1) as a regulator of leukocyte adhesion to kidney microvascular glomerular endothelial cells was assessed in vitro by using L-selectin-directed mAb and an L-selectin cDNA-transfected cell line. The initial attachment of neutrophils, monocytes, and lymphocytes to TNF-activated bovine glomerular endothelial cells was significantly inhibited by the anti-LAM1-3 mAb. Under static conditions, anti-LAM1-3 mAb inhibited neutrophil adhesion by 15 +/- 5%, whereas the anti-LAM1-10 mAb, directed against a functionally silent epitope of L-selectin, was without effect. The binding of a CD18 mAb inhibited adhesion by 47 +/- 6%. In contrast, when the assays were carried out under nonstatic conditions or at 4 degrees C, the anti-LAM1-3 mAb generated significantly greater inhibition (approximately 60%). CD18-dependent adhesion was minimal (approximately 10%) under these conditions. TNF-activated glomerular endothelial cells also supported adhesion of a mouse pre-B cell line transfected with L-selectin cDNA, but not wild-type cells. This process was also inhibited by the anti-LAM1-3 mAb. Leukocyte adhesion to unstimulated endothelial cells was independent of L-selectin, but, after TNF stimulation, L-selectin-mediated adhesion was observed at 4 h, with maximal induction persisting for 24 to 48 h. Leukocyte adhesion was not observed if glomerular endothelial cells were exposed to TNF in the presence of RNA or protein synthesis inhibitors. Leukocyte attachment to TNF-activated glomerular endothelial cells was also partially inhibited by treatment of the cells with mannose-6-phosphate or phosphomannan monoester, a soluble complex carbohydrate, or by prior treatment of glomerular endothelial cells with neuraminidase, suggesting that the glomerular endothelial cell ligand shares functional characteristics with those expressed by lymph node and large vessel endothelial cells. These data suggest that TNF activation induced the biosynthesis and surface expression of a ligand(s) for L-selectin on glomerular endothelial cells, which supports neutrophil, monocyte, and lymphocyte attachment under nonstatic conditions.     

Lectin domain peptides from selectins interact with both cell surface ligands and Ca2+ ions.

Selectins are receptors that mediate leukocyte adhesion to platelets or endothelial cells through Ca(2+)-dependent interactions with cell surface oligosaccharides. We found that peptides corresponding to residues 23-30, 54-63, and 70-79 of the N-terminal lectin domain of P-selectin inhibited leukocyte adhesion to P-selectin. Peptides corresponding to the homologous 23-30 and 54-63 regions of E-selectin and L-selectin also prevented cell binding to P-selectin. Immobilized albumin conjugates of the three P-selectin peptides supported adhesion of myeloid cells and certain other cells expressing fucosylated oligosaccharides. Ca2+ was required for optimal cell adhesion to the conjugates containing the 23-30 and 54-63 sequences. Furthermore, Ca2+ interacted with the 23-30 and 54-63 peptides of all three selectins, as detected by changes in intrinsic fluorescence emission intensity. These data suggest that residues contained within the 23-30 and 54-63 regions of the selectins represent contact sites for carbohydrate structures on target cells. Furthermore, binding of Ca2+ to these sequences may directly enhance their ability to interact with cell surface ligands.     

Leukocyte-endothelial cell recognition: evidence of a common molecular mechanism shared by neutrophils, lymphocytes, and other leukocytes

The interaction of leukocytes with endothelial cells is intrinsic to the process of leukocyte extravasation, whether during the entry of blood polymorphonuclear leukocytes and monocytes into sites of acute and chronic inflammation, or during the homing of lymphocytes to lymphoid organs. A lymphocyte surface glycoprotein, defined by monoclonal antibody MEL-14, has been described that appears to mediate lymphocyte recognition of postcapillary venules in peripheral lymph nodes, and to control the migration of lymphocytes from the blood into these lymphoid organs. We now report that the antigenic determinant recognized by MEL-14 is present at high levels on other leukocytes as well, including neutrophils, monocytes, and eosinophils; and we demonstrate involvement of the MEL-14 antigen in neutrophil-endothelial cell interactions. MEL-14 immunoprecipitates a neutrophil surface protein of Mr approximately 100,000, similar in m.w. to the 80,000 to 90,000 dalton lymphocyte surface MEL-14 antigen, and it blocks the interaction of neutrophils with endothelial cells in an in vitro model of adhesion to postcapillary venules in lymph node frozen sections. Neutrophil binding to lymph node venules is also inhibited by PPME, a mannose-6-phosphate-rich yeast polysaccharide that is thought to mimic the endothelial cell ligand for the MEL-14-defined lymphocyte receptor. Interestingly, neither MEL-14 nor PPME exhibit a major effect on neutrophil binding to postcapillary venules in Peyer's patches, suggesting that as for lymphocytes, the neutrophil MEL-14 antigen is involved in recognition of tissue-specific endothelial determinants. Finally, we show that MEL-14 inhibits the capacity of neutrophils to migrate from the blood into sites of acute inflammation in the skin. These observations lead us to propose that receptors for tissue-specific endothelial determinants are utilized by neutrophils and lymphocytes and probably other leukocytes during the physiologic process of leukocyte extravasation in vivo.     

Structural and functional studies of the endothelial activation antigen endothelial leucocyte adhesion molecule-1 using a panel of monoclonal antibodies.

We have produced a panel of mAb to the endothelial activation Ag endothelial leucocyte adhesion molecule-1 (ELAM-1), using both a conventional immunization protocol and one involving immunosuppression. By constructing ELAM-1 mutants we have demonstrated that seven of these antibodies recognize epitopes within the lectin domain of ELAM-1 and that one binds within the complement regulatory protein domains. These studies also suggest that the EGF-like domain is important in maintaining the conformation of the neighbouring lectin domain. In functional studies, U937 cells bound to Cos cells expressing either ELAM-1 or ELAM-1 with the complement regulatory protein domains deleted. No adhesion was observed to Cos cells expressing ELAM-1 mutants lacking either the lectin or EGF-like domains. The fact that antibodies directed against the lectin domain can inhibit adhesion suggest that this domain is directly involved in cell binding.