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PubMed2004

L-Selectin(hi) but not the L-selectin(lo) CD4+25+ T-regulatory cells are potent inhibitors of GVHD and BM graft rejection.

Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality after bone marrow transplantation (BMT). CD4(+)CD25(+) immune regulatory T cells (Tregs), long recognized for their critical role in induction and maintenance of self-tolerance and prevention of autoimmunity, are also important in the regulation of immune responses in allogeneic bone marrow (BM) and solid organ transplantation. Published data indicate that ex vivo activated and expanded donor Tregs result in significant inhibition of lethal GVHD. This study provides a direct comparison of LSel(hi) and LSel(lo) Tregs for GVHD inhibition and for the promotion of allogeneic BM engraftment. Imaging of green fluorescent protein-positive effectors in GVHD control mice and LSel(hi) and LSel(lo) Treg-treated mice vividly illustrate the multisystemic nature of GVHD and the profound inhibition of GVHD by LSel(hi) Tregs. Data indicate that LSel(hi) Tregs interfere with the activation and expansion of GVHD effector T cells in secondary lymphoid organs early after BMT. Either donor- or host-type LSel(hi), but not LSel(lo), Tregs potently increased donor BM engraftment in sublethally irradiated mice, an event occurring independently of transforming growth factor beta signaling of host T cells. These data indicate that Treg cellular therapy warrants clinical consideration for the inhibition of GVHD and the promotion of alloengraftment.

Animals↗
PubMed2005

P-selectin (CD62p) and P-selectin glycoprotein ligand-1 (PSGL-1) polymorphisms: minor phenotypic differences in the formation of platelet-leukocyte aggregates and response to clopidogrel.

INTRODUCTION: Formation of platelet-leukocyte aggregates (PLA) via the CD62p-ligand PSGL-1 represents an important mechanism by which leukocytes contribute to thrombotic and inflammatory events. Deficient variants (namely the Thr715Pro-SNP for CD62p and a VNTR-polymorphism for PSGL-1) might affect PLA formation and probably the response to clopidogrel (which is known to reduce PLA-formation). METHODS: CD62p-expression, PLA-formation and the up-regulation of CD11b before (V1) and 24 hours after (V2) a loading dose of clopidogrel 225 mg were investigated in ten wild-type controls, ten heterozygote carriers of the Thr715Pro-allele and five carriers of the rare PSGL-1 B-allele (2 A/B and 3 B/B). RESULTS: CD62p-expression before application of clopidogrel and under clopidogrel treatment in Pro715-haplotype samples did not differ from that in wild-type subjects. The response to clopidogrel was similar in all subjects. Pro715-carriers exhibited a significantly lower percentage of monocytes with platelets attached prior to clopidogrel treatment (ADP: median 22 (1st-3rd quartile 20-23), TRAP: 27 (25 - 38)) compared to the wild-type (ADP: 37 (31-44), TRAP: 55 (37-63)). These differences were not present under clopidogrel, and CD11b-expression was significantly reduced in both groups (controls: median 150 (quartile range 121 - 230) to 113 (121 - 230), Pro715-carriers: 147 (139 - 221) to 126 (109 - 170); all values refer to mean fluorescence intensity). Statistical analysis was not done in the case of PSGL-1 B-allele carriers, but PLA-formation before and under clopidogrel was always at the bottom end of the range seen in the control group and the Pro715-carriers or even below this range. CONCLUSION: Minor phenotypic differences in the CD62p-PSGL-1 axis could be demonstrated in this study. Carriers of these polymorphisms showed a full response to clopidogrel comparable to that in control subjects.

Blood Platelets↗
PubMed1994

[Selectin receptors. 2. Synthesis of HSO3-3'Le(a)--a sulfated ligand of the cell adhesion molecule, E-selectin].

HSO3-3'Gal beta 1-3(Fuc alpha 1-4)GlcNAc beta 1-O(CH2)3NH2 was synthesized by selective sulfation (Py.SO3/Py, O degree C) of a protected trisaccharide Lea derivative bearing unsubstituted hydroxyls at C2 and C3 of the galactose moiety, BdGal beta 1-3(Bn3Fuc alpha 1-4)6-BnGlcNAc beta 1-O(CH2)3NHCOCF3, followed by convenient deprotection. A monosaccharide derivative, HSO3-3Gal beta 1-O(CH2)3NH2, was also obtained in a similar way. Coupling of the aminopropyl glycosides with poly(4-nitrophenylacrylate) gave rise to polyacrylamide (PAA) conjugates; biotinylated probes of the Sug-PAA-biotin type were obtained as well.

Carbohydrate Sequence↗
PubMed1998

Contribution of E-selectin to cellular infiltration during endotoxin-induced uveitis.

PURPOSE: The selectin family is a group of early-reactive adhesion molecules that plays a role in the rolling phase of leukocytes in cellular infiltration. It has been reported that P-selectin is expressed on vascular endothelium in the iris-ciliary body 15 minutes after lipopolysaccharide (LPS) treatment in endotoxin-induced uveitis (EIU) and may contribute to the initial phase of ocular inflammation. The objective of the present study was to identify the expression pattern of E-selectin, another member of the selectin family, and to investigate the role of E-selectin during the course of EIU. METHODS: Endotoxin-induced uveitis was induced in male Lewis rats by a footpad injection of 200 microg LPS. The time-dependent expressions of E-selectin in EIU in the iris- ciliary body and the retina were studied by immunohistochemistry using wholemounts and paraffin-embedded sections and by monitoring the level of E-selectin mRNA expression. A monoclonal antibody to E-selectin and a control antibody were each injected intravenously to evaluate the effects of E-selectin inhibition on ocular inflammation at the time of maximum uveitis. In the anterior uvea, the effect was evaluated by the number of infiltrated cells and by the protein concentration in the aqueous humor 24 hours after LPS treatment; in the retina, the myeloperoxidase (MPO) activity was measured 48 hours after LPS treatment. The effect of the combined injection of anti-P-selectin and anti-E-selectin antibodies was also studied. It was then determined whether the delayed inhibition of E-selectin (6, 12, or 24 hours after LPS injection) could contribute to the early resolution of the uveitis. RESULTS: E-selectin immunoreactivity was observed on the vessel walls of the iris and retina 7 hours after LPS treatment in wholemounts and paraffin-embedded sections and remained positive for 24 hours after LPS treatment. The expression of E-selectin messenger RNA gene peaked at 6 hours and again at 18 hours after LPS treatment in the iris- ciliary body and retina. The expression returned to the basal level 24 hours after LPS treatment in the iris- ciliary body and 48 hours after LPS treatment in the retina. The selective inhibition of E-selectin significantly blocked the cellular infiltration into the aqueous humor (P < 0.005) but had a milder effect on the protein concentration in the aqueous humor (P=0.0536). The inhibition of E-selectin and P-selectin almost abrogated cellular infiltration (P < 0.001). Myeloperoxidase activity in the retina 48 hours after LPS treatment was again significantly decreased by the inhibition of E-selectin alone and by the inhibition of E-selectin and P-selectin (P < 0.0001). A single injection of anti-E-selectin antibody 6, 12, or 24 hours after LPS injection effectively blocked cellular infiltration in the aqueous humor 24 and 48 hours after LPS treatment. CONCLUSIONS: In EIU, E-selectin may be expressed on the vascular endothelium and remain after the period of expression of P-selectin and until approximately the time of maximum uveitis. The present results suggest that, in contrast to the role of P-selectin as an initiator of cellular infiltration, E-selectin may contribute to continuing cellular infiltration into the inflammatory site during inflammation, and its inhibition may contribute to the early resolution of the uveitis.

Animals↗
PubMed1995

Neutrophils use both shared and distinct mechanisms to adhere to selectins under static and flow conditions.

Both P-selectin glycoprotein ligand-1 (PSGL-1) and L-selectin are localized on the microvilli of neutrophils and have been implicated in the attachment of neutrophils to P-selectin or E-selectin. We directly compared the attachment and rolling of neutrophils on P-selectin and E-selectin under flow, with emphasis on the functions of PSGL-1 and L-selectin. Flowing neutrophils attached more avidly and rolled at lower velocities on P-selectin than on E-selectin at matched densities. Studies with purified molecules indicated that P-selectin and E-selectin bound to a related site on PSGL-1 that overlapped the epitope for the anti-PSGL-1 mAb PL1. E-selectin bound with lower affinity than P-selectin to this site and also bound to an additional site(s) on PSGL-1.PL1 abolished adhesion of neutrophils to P-selectin under shear or static conditions, whereas DREG-56, a mAb to L-selectin, had no effect on adhesion to P-selectin. PL1 inhibited attachment of neutrophils to E-selectin under flow but not static conditions. DREG-56 also inhibited attachment of flowing neutrophils to E-selectin, and a combination of DREG-56 and PL1 nearly eliminated attachment to E-selectin under flow. These data suggest that PSGL-1 functions cooperatively with L-selectin to mediate optimal attachment of flowing neutrophils to E-selectin but not to P-selectin. Neutrophils attach more efficiently and with greater strength to P-selectin, perhaps because of the higher affinity of P-selectin for the PL1-defined site on PSGL-1.

Animals↗
PubMed1999

Production of soluble P-selectin by platelets and endothelial cells.

The distribution of a soluble form of a cell adhesion molecule, P-selectin, in human platelets and cultivated endothelial cells has been studied by enzyme-linked immunosorbent assay (ELISA). The concentration of soluble P-selectin in the blood plasma of healthy donors and patients with abnormal platelet count has also been determined. P-selectin was measured in the Triton X-100 lysate of platelets and endothelial cells (total P-selectin), in the 100,000g supernatant obtained after sedimentation of the membrane fraction from the homogenate of sonicated platelets and endothelial cells (intracellular soluble P-selectin), in the supernatant of activated and nonactivated platelets, and in the culture medium of endothelial cells. A soluble form of P-selectin which did not coprecipitate with the membrane fraction was detected in platelets and accounted for approximately 10% of the total P-selectin. Platelet activation by thrombin, ADP, or a thromboxane A2 analog resulted in the secretion of 30-50% of the intracellular soluble P-selectin. Measurements of P-selectin in endothelial cell culture revealed that endothelium from aorta contained about twofold more P-selectin than endothelium from umbilical vein. Intracellular soluble P-selectin was identified in both types of endothelial cells. In endothelial cells from the umbilical vein this form made up approximately 10% of the total P-selectin. Soluble P-selectin was also detected in the medium of cultivated endothelial cells, where its content correlated with the total cellular P-selectin. Concentration of P-selectin in blood plasma strongly correlated with the platelet count in the blood of healthy donors and patients with thrombocytosis and thrombocytopenia. These data indicate that platelets serve as one of the main source of plasma P-selectin. However, the presence of P-selectin in the plasma of patients with severe thrombocytopenia suggests that endothelium can also be involved in plasma P-selectin production. Thus, in vitro experiments as well as measurements of plasma P-selectin have shown that both platelets and endothelial cells can produce a soluble form of the protein. Platelet-derived soluble P-selectin and plasma P-selectin were shown to react with antibodies against the cytoplasmic domain of P-selectin. These data prove that at least part of soluble P-selectin is produced by synthesis employing special mRNA which lacks the sequence encoding the transmembrane domain, but not by the proteolytic shedding of the extracellular portion of membrane P-selectin.

Antibodies↗
PubMed1999

A direct comparison of selectin-mediated transient, adhesive events using high temporal resolution.

Leukocyte capture and rolling on the vascular endothelium is mediated principally by the selectin family of cell adhesion receptors. In a parallel plate flow chamber, neutrophil rolling on purified selectins or a selectin-ligand substrate was resolved by high speed videomicroscopy as a series of ratchet-like steps with a characteristic time constant (Kaplanski, G., C. Farnarier, O. Tissot, A. Pierres, A.-M. Benoliel, M. C. Alessi, S. Kaplanski, and P. Bongrand. 1993. Biophys. J. 64:1922-1933; Alon, R., D. A. Hammer, and T. A. Springer. 1995. Nature (Lond.). 374:539-542). Under shear, neutrophil arrests due to bond formation events were as brief as 4 ms. Pause time distributions for neutrophils tethering on P-, E-, L-selectin, or peripheral node addressin (PNAd) were compared at estimated single bond forces ranging from 37 to 250 pN. Distributions of selectin mediated pause times were fit to a first order exponential, resulting in a molecular dissociation constant (k(off)) for the respective selectin as a function of force. At estimated single bond forces of 125 pN and below, all three selectin dissociation constants fit the Bell and Hookean spring models of force-driven bond breakage equivalently. Unstressed k(off) values based on the Bell model were 2.4, 2.6, 2.8, 3.8 s(-1) for P-selectin, E-selectin, L-selectin, and PNAd, respectively. Bond separation distances (reactive compliance) were 0.39, 0.18, 1.11, 0.59 A for P-selectin, E-selectin, L-selectin, and PNAd, respectively. Dissociation constants for L-selectin and P-selectin at single bond forces above 125 pN were considerably lower than either Bell or Hookean spring model predictions, suggesting the existence of two regimes of reactive compliance. Additionally, interactions between L-selectin and its leukocyte ligand(s) were more labile in the presence of flow than the L-selectin endothelial ligand, PNAd, suggesting that L-selectin ligands may have different molecular and mechanical properties. Both types of L-selectin bonds had a higher reactive compliance than P-selectin or E-selectin bonds.

Biophysical Phenomena↗
PubMed1995

Differential colon cancer cell adhesion to E-, P-, and L-selectin: role of mucin-type glycoproteins.

E-, P-, and L-selectin support the adhesion of leukocytes to the vessel wall through the recognition of specific carbohydrate ligands, which often contain sialylated, fucosylated lactosamines such as sialyl Lewis x [sLex; Neu5Ac alpha 2-3Gal beta 1-4(Fuc alpha 1-3)GlcNAc-]. E-selectin expressed by activated endothelium has been shown to support the adhesion of sLex-bearing colon cancer cells. In the present study, we examine the interactions of multiple colon cancer cell lines with all three selectins. Three colon cancer cell lines (LS 180, T84, and COLO 205) bound to recombinant purified E-, P-, and L-selectin. The colon cancer line COLO 320 bound to P- and L-selectin but not E-selectin; conversely, HT-29 cells bound E-selectin but not P- and L-selectin. Caco-2 showed little or no interaction with any of the three selectins. Treatment of the cells with O-sialoglycoprotease from Pasteurella haemolytica, an enzyme that selectively cleaves mucin-type O-linked glycoproteins, reduced binding to purified P- and L-selectin in all cases. In addition, recombinant soluble P- and L-selectin bound to affinity-purified mucins from all adherent tumor cell lines. Of the four tumor cell lines that interacted with E-selectin, O-glycoprotease treatment substantially diminished adhesion of LS 180 and T84, had little effect on COLO 205, and failed to inhibit the binding of HT-29. As predicted by these data, E-selectin showed substantial binding only to mucins purified from LS 180 and T84. These findings suggest that L- and P-selectin interact primarily with mucin-type ligands on colon cancers, whereas E-selectin can recognize both mucin and nonmucin ligands. Binding of the colon cancer lines to purified selectins correlates with their adhesion to activated endothelial cells (E-selectin-dependent), platelets (P-selectin-dependent), and neutrophils (L-selectin-dependent). These differential tumor cell-selectin interactions may influence metastatic spread and may also contribute to the observed variability in host response to tumor progression.

Animals↗
PubMed2000

TNF-alpha, IL-4, and IFN-gamma regulate differential expression of P- and E-selectin expression by porcine aortic endothelial cells.

P- and E-selectin are surface glycoproteins that mediate leukocyte rolling on the surface of endothelium in inflammation. We have cloned porcine P-selectin cDNA and generated a mAb, 12C5, with which to examine P-selectin expression by porcine aortic endothelial cells (PAEC) in comparison with that of E-selectin. Basal expression by PAEC of P-selectin was greater than that of E-selectin, whereas E-selectin expression was more prominently enhanced than that of P-selectin by stimulation with TNF-alpha or IL-1alpha. Both human or porcine IL-4 led to an increase in P-selectin expression, with kinetics that were delayed compared with those seen following stimulation with TNF-alpha or IL-1alpha, but IL-4 did not stimulate expression of E-selectin. When cells were stimulated with TNF-alpha in the presence of IL-4, we observed enhanced P-selectin expression with a parallel reduction in E-selectin expression. Finally, the increase in P-selectin expression due to human IL-4 was reduced in the presence of porcine but not human IFN-gamma. These observations show that E-selectin and P-selectin expression are differentially regulated in PAEC, and that IL-4 leads to a shift in the relative surface density of the two molecules toward P-selectin. The ability of porcine IFN-gamma to inhibit IL-4-induced P-selectin expression suggests that the balance between Th1 and Th2 cytokine production may determine the relative densities of the two selectins in chronic immune-mediated inflammation. Because the increased expression of P-selectin induced by human IL-4 was not inhibited by human IFN-gamma, this balance may be shifted toward P-selectin expression in porcine xenografts infiltrated by human lymphocytes.

Amino Acid Sequence↗
PubMed2004

[Selectins in the pathogenesis and diagnosis of early atherosclerotic changes in children and adolescents with risk factors (obesity, hypertension and diabetes)].

UNLABELLED: Selectins are the group of adhesion molecules, which main role is the tethering of leukocytes to the endothelium. They induce relatively weak and transient adhesion allowing the cells to roll along the vascular wall. That mean, that selectins play part in the earliest stages of the atherosclerotic process. The aim of the study was to evaluate levels of E-selectin, L-selectin and P-selectin in children and adolescents with traditional atherosclerosis risk factors (obesity, hypertension and diabetes), correlation with lipid parameters, blood pressure values and BMI as well as the attempt to answer the question whether selectins, and which of them can be useful in predicting cardiovascular risk in these young patients. MATERIAL AND METHODS: We studied 66 children aged 14.8+/-2.6 years. They were divided into 4 subgroups according to the diagnosis: children with obesity--OP (n=12), children with obesity with hypertension--OP and NT (n=14), children with hypertension--NT (n=12), children with diabetes--C (n=28). Control group consisted of 15 healthy, slim children and adolescents, aged 15.4+/-2.2 yrs. Levels of E-selectin, P-selectin and L-selectin were evaluated by immunoenzymatic methods with use of R&D Systems ELISA kits. RESULTS: In the study group we found significantly higher level of E-selectin--86+/-28 ng/mL compared to control group: 64+/-20 ng/mL (p<0.05). Similarly in all subgroups levels of E-selectin were significantly higher: in obese children E-selectin level was 95+/-31 ng/mL (p<0.05), in obese and hypertensive group--88+/-12 ng/mL (p<0.05), in hypertensive group--79+/-19 (p<0.05), and in diabetic children--83+/-25 ng/mL (p<0.05). L-selectin level in the study group was 1552+/-290 ng/mL and did not differ from control group--1652+/-281 ng/mL (ns). P-selectin level in the study group was 652+/-419 ng/mL and was similar to the level of P-selectin in the control group--669+/-295 ng/mL (ns). Correlation analysis showed significant relationship between E-selectin and BMI (r=0.23, p<0.05) and diastolic blood pressure (r=0.24, p<0.05). CONCLUSIONS: 1. Young patients with atherosclerosis risk factors have elevated level of E-selectin. 2. E-selectin level correlates with BMI and diastolic blood pressure. 3. Elevated level of E-selectin may confirm endothelial dysfunction in young patients with atherosclerosis risk factors and can serve as a marker of early atherosclerosis phases.

Adolescent↗
PubMed2002

A functional role for circulating mouse L-selectin in regulating leukocyte/endothelial cell interactions in vivo.

L-selectin mediates the initial capture and subsequent rolling of leukocytes along inflamed vascular endothelium and mediates lymphocyte migration to peripheral lymphoid tissues. Leukocyte activation induces rapid endoproteolytic cleavage of L-selectin from the cell surface, generating soluble L-selectin (sL-selectin). Because human sL-selectin retains ligand-binding activity in vitro, mouse sL-selectin and its in vivo relevance were characterized. Comparable with humans, sL-selectin was present in adult C57BL/6 mouse sera at approximately 1.7 micro g/ml. Similar levels of sL-selectin were present in sera from multiple mouse strains, despite their pronounced differences in cell surface L-selectin expression levels. Adhesion molecule-deficient mice prone to spontaneous chronic inflammation and mice suffering from leukemia/lymphoma had 2.5- and 20-fold increased serum sL-selectin levels, respectively. By contrast, serum sL-selectin levels were reduced by 70% in Rag-deficient mice lacking mature lymphocytes. The majority of serum sL-selectin had a molecular mass of 65-75 kDa, consistent with its lymphocyte origin. Slow turnover may explain the relatively high levels of sL-selectin in vivo. The t(1/2) of sL-selectin, assessed by transferring sera from wild-type mice into L-selectin-deficient mice and monitoring serum sL-selectin levels by ELISA, was >20 h, and it remained detectable for longer than 1 wk. Short-term in vivo lymphocyte migration assays demonstrated that near physiologic levels ( approximately 0.9 micro g/ml) of sL-selectin decreased lymphocyte migration to peripheral lymph nodes by >30%, with dose-dependent inhibition occurring with increasing sL-selectin concentrations. These results suggest that sL-selectin influences lymphocyte migration in vivo and that the increased sL-selectin levels present in certain pathologic conditions may adversely affect leukocyte migration.

Adoptive Transfer↗
PubMed1995

The cytoplasmic domain of L-selectin interacts with cytoskeletal proteins via alpha-actinin: receptor positioning in microvilli does not require interaction with alpha-actinin.

The leukocyte adhesion molecule L-selectin mediates binding to lymph node high endothelial venules (HEV) and contributes to leukocyte rolling on endothelium at sites of inflammation. Previously, it was shown that truncation of the L-selectin cytoplasmic tail by 11 amino acids abolished binding to lymph node HEV and leukocyte rolling in vivo, but the molecular basis for that observation was not determined. This study examined potential interactions between L-selectin and cytoskeletal proteins. We found that the cytoplasmic domain of L-selectin interacts directly with the cytoplasmic actin-binding protein alpha-actinin and forms a complex with vinculin and possibly talin. Solid phase binding assays using the full-length L-selectin cytoplasmic domain bound to microtiter wells demonstrated direct, specific, and saturable binding of purified alpha-actinin to L-selectin (Kd = 550 nM), but no direct binding of purified talin or vinculin. Interestingly, talin potentiated binding of alpha-actinin to the L-selectin cytoplasmic domain peptide despite the fact that direct binding of talin to L-selectin could not be measured. Vinculin binding to the L-selectin cytoplasmic domain peptide was detectable only in the presence of alpha-actinin. L-selectin coprecipitated with a complex of cytoskeletal proteins including alpha-actinin and vinculin from cells transfected with L-selectin, consistent with the possibility that alpha-actinin binds directly to L-selectin and that vinculin associates by binding to alpha-actinin in vivo to link actin filaments to the L-selectin cytoplasmic domain. In contrast, a deletion mutant of L-selectin lacking the COOH-terminal 11 amino acids of the cytoplasmic domain failed to coprecipitate with alpha-actinin or vinculin. Surprisingly, this mutant L-selectin localized normally to the microvillar projections on the cell surface. These data suggest that the COOH-terminal 11 amino acids of the L-selectin cytoplasmic domain are required for mediating interactions with the actin cytoskeleton via a complex of alpha-actinin and vinculin, but that this portion of the cytoplasmic domain is not necessary for proper localization of L-selectin on the cell surface. Correct L-selectin receptor positioning is therefore insufficient for leukocyte adhesion mediated by L-selectin, suggesting that this adhesion may also require direct interactions with the cytoskeleton.

Actinin↗
PubMed1998

Differential interactions of heparin and heparan sulfate glycosaminoglycans with the selectins. Implications for the use of unfractionated and low molecular weight heparins as therapeutic agents.

The selectins are calcium-dependent C-type lectins that bind certain sialylated, fucosylated, sulfated glycoprotein ligands. L-selectin also recognizes endothelial proteoglycans in a calcium-dependent manner, via heparan sulfate (HS) glycosaminoglycan chains enriched in unsubstituted glucosamine units. We now show that these HS chains can also bind P-selectin, but not E-selectin. However, while L-selectin binding requires micromolar levels of free calcium, P-selectin recognition is largely divalent cation-independent. Despite this, HS chains bound to P-selectin are eluted by ethylenediamine tetraacetic acid (EDTA), but only at high concentrations. Porcine intestinal mucosal (mast cell-derived) heparin (PIM-heparin) shows similar properties, with no binding to E-selectin, calcium-dependent binding of a subfraction to L-selectin and to P-selectin, and calcium-independent binding of a larger fraction to P-selectin, the latter being disrupted by high EDTA concentrations. Analysis of defined heparin fragment pools shows a size dependence for interaction, with tetradecasaccharides showing easily detectable binding to L- and P-selectin affinity columns. L-selectin binding fragments include more heavily sulfated and epimerized regions and, as with the endothelial HS chains, they are enriched in free amino groups. The P-selectin binding component includes this fraction as well as some less highly modified regions. Thus, endothelium-derived HS chains and mast cell-derived heparins could play a role in modulating the biology of selectins in vivo. Notably, P- and L-selectin binding to sialyl-Lewisx and to HL-60 cells (which are known to carry the native ligand PSGL-1) is inhibited by unfractionated pharmaceutical heparin preparations at concentrations 12-50-fold lower than those recommended for effective anticoagulation in vivo. In contrast, two low molecular weight heparins currently considered as clinical replacements for unfractionated heparin are much poorer inhibitors. Thus, patients undergoing heparin therapy for other reasons may be experiencing clinically significant inhibition of L- and P-selectin function, and the current switchover to low-molecular weight heparins may come at some loss of this effect. Low-dose unfractionated heparin should be investigated as a treatment option for acute and chronic diseases in which P- and L-selectin play pathological roles.

Animals↗