Analysis of the mode of action of a novel immunosuppressant FTY720 in mice

Accelerated lymphocyte homing and apoptosis have been suggested to contribute to potent immunosuppressive effects of FTY720, however, its main mechanism of action remains to be fully elucidated. Here, we examined the mode of action of FTY720 in mice. FTY720, when given at a single dose of 1 mg/kg, markedly decreased the number of peripheral blood lymphocytes (PBL) but moderately increased the lymphocyte numbers in lymph nodes (LN) and Peyer's patches (PP) in normal mice, as previously observed in rats. However, the sharp decrease in PBL numbers was also observed in aly/aly mice lacking LN and PP, indicating that this phenomenon is not explained by accelerated lymphocyte homing to LN and PP. In addition, the finding that a single administration of FTY720 did not suppress proliferative responses of T cells suggested that the PBL reduction could occur without inhibiting lymphocyte functions. However, when administered at the same dose for 2 weeks, FTY720 induced severe systemic lymphopenia, as well as marked suppression of lymphocyte proliferative responses in normal mice. The same treatment also prolonged skin allograft survival in aly/aly mice. Our results suggest that FTY720 suppresses in vivo immune functions mainly by inducing systemic lymphopenia and also by inhibiting T cell functions.

Identification and characterization of ligands for L-selectin in the kidney. III. Characterization of L-selectin reactive heparan sulfate proteoglycans

L-Selectin, a leukocyte adhesion molecule, mediates leukocyte rolling on the endothelium and plays a critical role in leukocyte recruitment at inflammatory sites as well as in lymphocyte homing. We have previously shown that L-selectin reactive chondroitin sulfate and heparan sulfate proteoglycans (HSPGs) are both expressed in the distal tubules of the kidney and that versican is one of the chondroitin sulfate-type ligands. In the present study, we characterized the heparan sulfate-type ligand(s) in more detail. The molecular sizes of HSPGs were approximately 600 kDa with core protein sizes of 160 and 180 kDa. Western blotting analysis showed that L-selectin reactive HSPGs were neither agrin nor perlecan, major basement membrane HSPGs in the kidney. The binding to L-selectin was mediated by the lectin domain of L-selectin in a Ca2+-dependent manner and required heparan sulfate side chains, but not sialic acid. To our knowledge, this is the first biochemical characterization of the L-selectin reactive heparan sulfate proteoglycan(s) in the distal tubules of the kidney.

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

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

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

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

[Role of adhesion molecules in the pathogenesis of collagen diseases]

Adhesion molecules play important roles and involve in many aspects of cell-cell or cell-extracellular matrix interactions in collagen diseases. In the present article, we describe the role of adhesion molecules in the pathogenesis of collagen diseases. Adhesion molecules on endothelial cells participate in leukocyte recruitment in collagen diseases. Adhesion molecules on RA synoviocytes which interact with MNCs and destroy chondrocytes by pannus formation. In PSS, adhesion molecules on fibroblasts play important roles to form fibrosis by interacting with MNCs or collagen fibrils. We further mention on adhesion molecules in interaction between MNCs and muscle fibers in myositis, those in vasculitis in SLE and other diseases, and autoantibodies inducing adhesion molecules on endothelial cells in PSS and Wegener's granulomatosis.

HIV related knowledge and prevention among Thai female commercial sex workers in Japan

A survey of 87 Thai female commercial sex workers (TCSW) was conducted in Tokyo and surrounding areas to investigate their: 1) living conditions, 2) knowledge about HIV/AIDS and sources of information, and 3) working conditions and dealings with clients. Data were mainly collected by "snowballing" with semi-structured interviews. The results showed a majority of participants knew HIV could be contracted through sexual intercourse and that condom use could protect against HIV infection. However, some TCSW reported failing to use condoms despite having requested clients to do so. Reasons for client compliance with condom use were discussed. Although a majority of the participants underwent HIV testing at least once every 3 months, they did not learn much about HIV prevention through public information and education. The results suggest that workers and clients need more detailed information concerning HIV prevention as well as a greater accessibility.

Blood monocyte migration to acute lung inflammation involves both CD11/CD18 and very late activation antigen-4-dependent and independent pathways

In acute lung inflammation, blood neutrophils and monocytes migrate into the lung parenchyma and bronchoalveolar space. The infiltration of the inflamed lung by monocytes is poorly understood because of difficulties in quantifying these cells in the presence of resident macrophages. Radiolabeled monocytes were used to study monocyte migration into the inflamed rat lung. Monocytes and neutrophils were purified from blood, labeled with 51Cr and (111)In, respectively, and injected i.v. into rats given an intratracheal injection of LPS. The accumulation of 51Cr-labeled monocytes increased > 10-fold in the lung parenchyma and 170-fold in the bronchoalveolar lavage (BAL) 18 h after LPS. (111)In-labeled neutrophils increased > 30-fold in the lung tissue and 500-fold in the BAL. Treatment of rats with a blocking anti-CD18 mAb inhibited monocyte accumulation in the lung and BAL by about 30%, whereas blocking very late activation Ag-4 (VLA-4) had no effect. Combined blockade of VLA-4 and CD18 inhibited approximately 30% of the migration to the lung parenchyma, but decreased the BAL by 80%. Monocyte migration to cutaneous inflammation was completely abolished by the combined mAb treatment. Neutrophil accumulation in the lung and BAL was not decreased by blocking either CD18 or VLA-4 and was only partially reduced by blocking CD18 plus VLA-4. Thus, monocyte migration to the LPS inflamed lung is substantially CD11/CD18 and VLA-4 independent, but accumulation in BAL is mediated by CD18 and VLA-4. Monocytes as well as neutrophils may use a previously unrecognized endothelial adhesion and migration pathway in the lung.

Sulfatide protects rat skin flaps against ischemia-reperfusion injury

Monoclonal antibodies to adhesion molecules have been used in many trials to prevent ischemia-reperfusion injury. Sulfatide reacts strongly with P- and L-selectin, which play an important role in the initiation of neutrophil-endothelial interactions occurring in injured or inflamed tissues. The purpose of this study was to evaluate the effect of sulfatide on ischemia-reperfusion injury of the rat skin flap. Sulfatide was administered intravenously just before elevation of the right abdominal epigastric flap. The femoral artery and vein were clamped above and below the epigastric vessels for 10 or 11 h and then the clamp was released. Administration of sulfatide augmented significantly the flap area surviving in the 10-h ischemic model (7.18 +/- 0.47 cm2 versus control 5.15 +/- 0.39 cm2. P = 0.01). In the 11-h ischemic model the area was 4.59 +/- 0. 36 cm2 versus control 1.73 +/- 0.31 cm2 (P = 0.001). The ATP levels in the flap gradually increased after release of the clamp in the rat administered sulfatide, and the increase was significant at 48 h (P = 0.006). Histological examination 48 h after surgery showed greater leukocyte invasion into the control flap than into the flap of the rat administered sulfatide. Myeloperoxidase activity was significantly reduced 48 h after reperfusion in the 11-h ischemic model. This study indicates that sulfatide has a significant protective effect against ischemia and reperfusion in rat epigastric flaps.

Vascular and non-vascular ligands for L-selectin

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

A case of central carcinoma of the mandible arising from a recurrent odontogenic keratocyst: delineation of surgical margins and reconstruction with bilateral rectus abdominis myocutaneous free flaps

A case of central carcinoma of the mandible arising from a recurrent odontogenic keratocyst is reported. A 38-year-old man was admitted to the Tokai University Hospital due to postoperative infection of a recurrent odontogenic keratocyst of the left mandible. He had had a cystectomy for an odontogenic keratocyst 4 years ago. The lesion revealed bony destruction of the mandible with worm-eating shaped margins with extension to the facial skin. A biopsy specimen revealed squamous cell carcinoma. The mandible was resected with facial skin and the sublingual space was dissected to preserve the lingual nerve. The oral and the facial resections were reconstructed with a titanium plate and bilateral rectus abdominis myocutaneous free flaps. The plate was removed due to infection around the margins and readjustment of the flaps was conducted 5 months after the surgery. He has not had a local relapse, metastasis, or incisional hernia for 8 months following surgery. Good occlusion has been attained by the residual mandible, and he is able to eat without any problems.

Effects of the anti-ICAM-1 monoclonal antibody on dextran sodium sulphate-induced colitis in rats

Increased expression of intercellular adhesion molecule-1 (ICAM-1) in the colon of inflammatory bowel disease (IBD) has been reported. We evaluated the effects of monoclonal antibodies to ICAM-1 on acute colitis induced by dextran sodium sulphate (DSS) in rats. Colitis was induced by feeding rats 3% DSS for 7 days. Anti-ICAM-1 antibody or vehicle alone was injected intraperitoneally in rats daily from day 0 to day 6. On day 7 the rats were killed and colitis was evaluated histologically. Prophylactic treatment with anti-ICAM-1 significantly attenuated colonic damage, neutrophil infiltration and the shortening of the colon in DSS colitis. Our findings demonstrate that ICAM-1 plays an important role in this model of inflammatory bowel disease. Although this study does not directly address the effect of anti-ICAM-1 therapy in IBD, our findings encourage experiments using therapies that target ICAM-1 in rats with already developed disease.

Role of the leukocyte-adhesion molecule L-selectin in experimental autoimmune encephalomyelitis

L-selectin is an adhesion molecule expressed on T cells and monocytes. It mediates rolling--the initial step of transendothelial migration. In this study, we investigated the role of L-selectin in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis. EAE was induced in Lewis rats by active sensitization with myelin basic protein (MBP-EAE), or by adoptive transfer using MBP specific T cells (AT-EAE). Treatment with HRL3, a monoclonal antibody to L-selectin, and its F(ab')2 fragments efficiently suppressed MBP-EAE, and had a mild inhibitory effect on AT-EAE. Histological examination revealed a marked reduction of inflammatory infiltrates after treatment with HRL3. Administration of the control antibody HRL4 did not significantly alter the course of the disease. HRL3 caused T-cell depletion in the draining lymph nodes and spleen and a downregulation of L-selectin expression on T cells. We conclude that L-selectin-dependent mechanisms are involved in the pathogenesis of EAE. Modulation of L-selectin in vivo by antibodies or by competitive antagonists could be a novel therapeutic approach to autoimmune diseases of the central nervous system.

Cell-to-cell interaction is required to induce proteinuria in in situ immune complex glomerulonephritis

This experiment was performed to study the roles of intercellular adhesion molecule-1 (ICAM-1), lymphocyte function-associated antigen-1 (LFA-1), and another adhesion molecule, selectin, in the development of cationized antigen-induced in situ immune complex glomerulonephritis (CAICGN). CAICGN was induced in preimmunized rats by perfusing cationized human immunoglobulin G (CaIgG) through the left kidney. Albuminuria developed within 2 days of CaIgG perfusion and peaked around day 7. Marked polymorphonuclear leukocyte (PMN) infiltration was observed in the glomeruli 1 hour after CaIgG perfusion, but the infiltrate resolved by day 7. Immunofluorescent studies disclosed linear deposition of rat IgG and C3 along glomerular capillary walls 1 hour after CaIgG perfusion. Treatment with monoclonal antibodies (mAbs) to both ICAM-1 and LFA-1, as well as with a sulfatide, a ligand of L- and P-selectin, started within 2 days after CaIgG perfusion completely suppressed the development of proteinuria without affecting the glomerular deposition of immunoreactants. Although sulfatide attenuated the PMN response 1 hour after CaIgG perfusion, ICAM-1 and LFA-1 mAb treatment did not alter PMN infiltration. Treatment with ICAM-1 and LFA-1 mAbs started on day 5, or treatment with sulfatide started on day 4, after CaIgG perfusion did not affect albuminuria. These findings suggest that adhesion molecules play an important role in the development of proteinuria in CAICGN. The contribution of these molecules was evident for only a short interval after the induction of nephritis, when a significant infiltration of PMNs was observed.

Cytokine and adhesion molecule requirements for lung injury induced by anti-glomerular basement membrane antibody

Acute hemorrhagic lung injury occurs in humans with anti-GBM antibody (Goodpasture's syndrome), however, the mechanism of this injury is still largely unknown. To date, treatment has been confined to steroids and plasmaphoresis. Infusion of anti-GBM antibody into rats caused lung injury with intra-alveolar hemorrhage and intrapulmonary accumulation of neutrophils. Lung injury was dependent on the presence of neutrophils and complement and required both TNF alpha and IL-1. Experiments employing blocking antibodies to adhesion molecules demonstrated requirements for the beta 1 integrin VLA-4, beta 2 integrins LFA-1 and Mac-1, and L-selection. The endothelial cell adhesion molecules, E-selectin and ICAM-1, were also required for the full development of lung injury. Inhibition of TNF alpha or IL-1 or adhesion molecules reduced both lung injury and tissue neutrophil accumulation. Thus, this study underscores cytokine and adhesion molecule requirements for neutrophil mediated injury in lung and kidney caused by anti-GBM, suggesting potential targets for the treatment of Goodpasture's syndrome in humans.

Engraftment of human myelodysplastic syndrome derived cell line in transgenic severe combined immunodeficient (TG-SCID) mice expressing human GM-CSF and IL-3

A transgenic SCID (TG-SCID) mouse expressing the human cytokines interleukin-3 (IL-3) and granulocyte-macrophage colony-stimulating factor (GM-CSF) has been generated with the aim of making a model system allowing the in vivo proliferation of human hematopoietic cells. Using TG-SCID mice expressing high levels (30-35 ng/ml in the serum) of human GM-CSF and IL-3, we attempted to engraft a human myeloid leukemia cell line, F-36P, derived from a myelodysplastic syndrome (MDS) patient. When F-36P cells were transferred intravenously into sublethally irradiated TG-SCID mice, extensive proliferation of F-36P cells was found 4-6 wk later. Successful engraftment, however, required the preadministration of a monoclonal antibody to mouse interleukin-2 receptor (IL-2R) beta chain, neutralizing NK activity. Surprisingly, all the transplanted TG-SCID mice engrafted with F-36P cells developed hind leg paralysis approximately 6 wk after transfer. Histological analysis demonstrated extensive invasion and formation of osteolytic lesions by the F-36P cells in the vertebrae. These data indicate that transgenic SCID mice expressing human IL-3 and GM-CSF provide a useful system for the study of human leukemia. In addition, NK cells appear to play an important role in rejection of human cells.

Transplantation tolerance by a combined therapy with sulfatide, anti-LFA-1/ICAM-1 monoclonal antibodies and FK506 in rat cardiac transplantation

Selectins promote a rolling phenomenon of leukocytes along activated endothelial surfaces, which is the first step in the events that ultimately lead to leukocyte transmigration at acute inflammatory sites. Our previous study revealed that sulfatide, which is one of the selectin inhibitors, prolonged graft survival in rat cardiac allografts. In the present study, to obtain a longer graft acceptance, we examined a combination treatment of sulfatide, monoclonal antibodies (mAbs) against LFA-1/ICAM-1, and FK506 in a Fischer 344 (F344, RT1lvl) to Lewis (LEW, RT1l) rat heart transplantation. FK506 alone (n = 6) and FK506/sulfatide-treated LEW rats (n = 6) rejected F344 heart grafts with an MST of 49 and 55.2 days, respectively. Otherwise, four out of six heart grafts treated with sulfatide, mAbs against LFA-1/ICAM-1, and FK506 (n = 6) survived for over 100 days after transplantation. The proliferative response of alloreactive T cells obtained from tolerant rats against both F344 alloantigen and third-party alloantigen on day 104 postgrafting was significantly suppressed as compared to that from naive LEW rats. On light microscopic examination, specimens of tolerant rat on day 104 postgrafting showed an almost normal appearance. Our results suggested that blocking both each step of leukocyte entry and recognition of alloantigens by a combination treatment of sulfatide, mAbs against LFA-1/ICAM-1, and FK506 could lead to tolerance.

FK506 (tacrolimus) inhibits extravasation of lymphoid cells by abrogating VLA-4/VCAM-1 mediated transendothelial migration

Extravasation is a critical process for the physiological lymphocyte traffic as well as the hematogenous spread of malignant hemopoietic cells. Here we report that abrogation of calcineurin activity leads to in vitro transendothelial migration and in vivo infiltration of human lymphoma Nalm-6 cells, which are associated with the abrogation of the VLA-4/VCAM-1 mediated pathway. Rapamycin, which can antagonize FK506 but not CsA to inhibit calcineurin, abrogates FK-506 mediated but not CsA mediated inhibition of in vitro transendothelial migration. FK506 may exert its potent immunosuppressive action partly by inhibiting VLA-4/VCAM-1 mediated transendothelial migration or insinuation of lymphoid cells to tissues.

Cytokine and adhesion molecule requirements for neutrophil recruitment during glycogen-induced peritonitis

OBJECTIVE

Requirements for cytokines and adhesion molecules for peritoneal neutrophil recruitment during glycogen-induced peritonitis in rats were systematically defined.

SUBJECTS

Male Long Evans rats (275-300 g).

METHODS

Four hours after intraperitoneal injection of 25 mg oyster glycogen, neutrophilic exudates were harvested. Effects of blocking reagents (injected intravenously) to rat E-, L- and P-selectins, beta1 (VLA-4) and beta2 integrins (LFA-1 and Mac-1), ICAM-1, and the cytokines TNFalpha, IL- and IL-8 were assessed.

RESULTS

Administration of synthetic sialyl Lewis(x) oligosaccharide reduced neutrophil recruitment to the peritoneum by 26%. Antibody to E-selectin reduced neutrophil accumulation by 71%, while anti-L-selectin reduced neutrophil accumulation by 59%, and anti-P-selectin was without an effect. Similar patterns of inhibition were found when selectin-Ig chimeras were employed. Antibodies to LFA-1 (CD11a), Mac-1 (CD11b) or CD18 reduced neutrophil accumulation by 62 percent, 59 percent and 86%, respectively, while anti-VLA-4 was without effect. Anti-ICAM-1 reduced cell influx by 65%. IL-1 receptor antagonist and antibodies to IL-1 and human IL-8 reduced neutrophil accumulation by 43alpha, 40% and 62 percent, respectively. Unexpectedly, blockade of TNFalpha had no effect.

CONCLUSIONS

These studies identify requirements for selectins, beta2 integrins, IL-1 and a rat chemokine(s) similar to human IL-8 for neutrophil recruitment during glycogen-induced peritonitis. The lack of participation of VLA-4, P-selectin and TNFalpha suggests organ-specific cytokine and adhesion molecule requirements for neutrophil recruitment.

Japan's egalitarian health care system: a brief historical analysis

Japan is one of several East Asian countries that share an ethical system of mutual support. A review of Japan's health care system reveals a strong egalitarian ethos often considered unique by outside observers.

In vitro and in vivo selectin-blocking activities of sulfated lipids and sulfated sialyl compounds

There is accumulating evidence that sulfated lipids, sulfated oligosaccharides and other sulfated compounds are reactive with selectins in a manner that interferes with selectin interactions with their natural ligands. In the report we describe the ability of sulfated lipids (sulfatides and gangliosides) and multimeric forms of sulfated sialic acid to block binding of P- and E-selectin-Ig to neutrophils. The in vivo ability of these compounds to block lung injury in rats following i.v. infusion of purified cobra venom factor (CVF), which induces injury that is L- and P-selectin dependent, was also determined as well as effects on recruitment of neutrophils, as measured by lung myeloperoxidase. There was a significant correlation between the ability of sulfated lipids and sialyl compounds to interfere in vitro with P-selectin-Ig binding to neutrophils and to protect against P-selectin-dependent acute lung injury induced by CVF. The biological effects of these sulfated compounds were also associated with diminished accumulation of neutrophils. The protective effects of these compounds may be linked to their ability to interfere with P-selectin binding to counter-receptors on neutrophils.

Intracellular Signal-transducing elements involved in transendothelial migration of lymphoma cells

To investigate the molecular mechanisms underlying transendothelial migration of tumor cells, an essential process for their hematogenous dissemination, we developed an in vitro model system that allows the separate monitoring of cell adhesion and transmigration processes. This system uses a human pre-B lymphoma cell line, Nalm-6, and a cultured mouse endothelial cell line, KOP2.16. Nalm-6 cells rapidly adhered to KOP2.16 and subsequently transmigrated underneath them. Using this model, we examined the effects on transendothelial migration, of various reagents which specifically interfere with the function of intracellular signal transduction molecules. Treatment of Nalm-6 cells with wortmannin (WMN), herbimycin A, pertussis toxin, or C3 exoenzyme of Clostridium botulinum, which specifically inhibit P13 kinase and/or myosin light chain kinase, herbimycin-sensitive tyrosine kinases, heterotrimeric G proteins, and the small G proteins, and the small G proteins rho/rac, respectively, reduced transmigration in a dose-dependent manner, Pretreatment of KOP2.16 endothelial cells with WMN also reduced transmigration in a dose-dependent manner. Binding of Nalm-6 binding to KOp2.16 was not affected, even when Nalm-6 or KOP2.16 cells were pretreated with these inhibitors, indicating that the reduction of transmigration was not due to a reduction of Nalm-6 to KOP2.16. These results also indicate that the signal transduction pathway(s) involved in transmigration can be dissociated from that of adhesion. Our results support the notion that endothelial cells are not a passive barrier in lymphoma extravasation, but that they assist lymphoma cell extravasation.

A functional epitope on P-selectin that supports binding of P-selectin to P-selectin glycoprotein ligand-1 but not to sialyl Lewis X oligosaccharides

P-selectin mediates the adhesion of leukocytes to activated platelets and endothelial cells. To characterize the functional domains of P-selectin for ligand recognition, we established nine hybridoma cell lines secreting anti-rat P-selectin mAb. Among them, the mAb C215 bound both rat and human P-selectins, and inhibited binding of rat and human P-selectins to P-selectin glycoprotein ligand-1 (PSGL-1) from HL-60 cells. In contrast, mAb C215 failed to inhibit the binding of rat and human P-selectin-IgG to sialyl Lewis X (sLe(x)) oligosaccharides. Epitope mapping of mAb C215 using synthetic decapeptides revealed that mAb C215 binds specifically to an eight-residue epitope that spans amino acids 76-83 of rat P-selectin, a region completely conserved by human P-selectin. Synthetic peptides containing the mAb C215 epitope inhibited binding of P-selectin to PSGL-1, but not to sLe(x) oligosaccharides, suggesting that the C215 epitope on P-selectin may directly interact with a particular site on the PSGL-1 core protein essential for interaction with P-selectin, such as sulfated tyrosine residues. Our results suggest the presence of two ligand recognition sites on P-selectin necessary for binding to PSGL-1--one recognizes sLe(x), while the other recognises the PSGL-1 core protein.