PubMed Health⌕ Search

Biomedical subjects

T Yednock

Publications and source records attributed to T Yednock.

18 recordsLinked to original sources
PubMed2000

The Src kinase p56(lck) up-regulates VLA-4 integrin affinity. Implications for rapid spontaneous and chemokine-triggered T cell adhesion to VCAM-1 and fibronectin.

In circulating lymphocytes, the VLA-4 integrin preexists in multiple affinity states that mediate spontaneous tethering, rolling, and arrest on its endothelial ligand, vascular cell adhesion molecule-1 (VCAM-1). The regulation and function of VLA-4 affinity in lymphocytes has never been elucidated. We show here that p56(lck), the major Src kinase in T cells, is a key regulator of high affinity VLA-4. This high affinity is essential for the rapid development of firm adhesion of resting T cells to VCAM-1 and to their extracellular matrix ligand, fibronectin. Lck-regulated VLA-4 function does not require intact TCR nor several key components of the TCR signaling pathway, including ZAP-70 and SLP-76. Furthermore, stimulation of p56(lck) by the phosphatase inhibitor, pervanadate, triggers firm VLA-4-dependent adhesion to VCAM-1. Although Lck is not required for chemokine receptor signaling to mitogen-activated protein kinase, the presence of Lck-regulated high affinity VLA-4 also facilitates firm adhesion triggered by the chemokine, SDF-1, at short-lived contacts. Surprisingly, bond formation rates, ability to tether cells to VLA-4 ligand, and VLA-4 tether bond stability under shear flow are not affected by VLA-4 affinity or Lck activity. Thus, the ability of high affinity VLA-4 to arrest cells on VCAM-1 under flow arises from instantaneous post-ligand strengthening rather than from increased kinetic stability of individual VLA-4 bonds. These results suggest that p56(lck) maintains high affinity VLA-4 on circulating lymphocytes, which determines their ability to strengthen VLA-4 adhesion and rapidly respond to proadhesive chemokine signals at endothelial sites.

Blotting, Western↗
PubMed2000

Peripherally administered antibodies against amyloid beta-peptide enter the central nervous system and reduce pathology in a mouse model of Alzheimer disease.

One hallmark of Alzheimer disease is the accumulation of amyloid beta-peptide in the brain and its deposition as plaques. Mice transgenic for an amyloid beta precursor protein (APP) mini-gene driven by a platelet-derived (PD) growth factor promoter (PDAPP mice), which overexpress one of the disease-linked mutant forms of the human amyloid precursor protein, show many of the pathological features of Alzheimer disease, including extensive deposition of extracellular amyloid plaques, astrocytosis and neuritic dystrophy. Active immunization of PDAPP mice with human amyloid beta-peptide reduces plaque burden and its associated pathologies. Several hypotheses have been proposed regarding the mechanism of this response. Here we report that peripheral administration of antibodies against amyloid beta-peptide, was sufficient to reduce amyloid burden. Despite their relatively modest serum levels, the passively administered antibodies were able to enter the central nervous system, decorate plaques and induce clearance of preexisting amyloid. When examined in an ex vivo assay with sections of PDAPP or Alzheimer disease brain tissue, antibodies against amyloid beta-peptide triggered microglial cells to clear plaques through Fc receptor-mediated phagocytosis and subsequent peptide degradation. These results indicate that antibodies can cross the blood-brain barrier to act directly in the central nervous system and should be considered as a therapeutic approach for the treatment of Alzheimer disease and other neurological disorders.

Alzheimer Disease↗
PubMed2000

Prevention and reduction of AD-type pathology in PDAPP mice immunized with A beta 1-42.

In AD certain brain structures contain a pathological density of A beta protein deposited into plaques. The effect of genetic mutations found in early onset AD patients was an overproduction of A beta 42, strongly suggesting that overproduction of A beta 42 is associated with AD. We hypothesized that an immunological response to A beta 42 might alter its turnover and metabolism. Young PDAPP transgenic mice were immunized with A beta 1-42, which essentially prevented amyloid deposition; astrocytosis was dramatically reduced and there was reduction in A beta-induced inflammatory response as well. A beta 1-42 immunization also appeared to arrest the progression of amyloidosis in older PDAPP mice. A beta immunization appears to increase clearance of amyloid plaques, and may therefore be a novel and effective approach for the treatment of AD.

Alzheimer Disease↗
PubMed2000

Alpha4beta1-integrin activation is necessary for high-efficiency T-cell subset interactions with VCAM-1 under flow.

OBJECTIVE: The purpose of this study was to examine the relationship between alpha4beta1-integrin state of activation on CD4+ T-cell subsets and their adhesive interaction to VCAM-1 under flow. METHODS: Human CD4+ memory and naive T-cells were freshly isolated and effector-helper T-cell subsets. Th1 and Th2 cells, were differentiated in vitro from CD4+ naive T-cells. The expression of activation/ligand induced epitopes on beta1-integrins of each T-cell subset was assessed using mAb HUTS21 and mAb 15/7. T-cell subsets attachment and rolling on VCAM-1 was determined under defined flow conditions and the rates of attachment (ka), accumulation, and instantaneous rolling velocities were correlated to their beta1-integrin activation epitope expression. RESULTS: A subset of memory T-cells constitutively express activation/ligand induced epitopes on beta1-integrins recognized by mAb HUTS21 and 15/7, whereas expression levels on naive T-cells is low or not detectable. Consistent with an activated phenotype, memory T-cells exhibit significantly higher rates of attachment and accumulation on VCAM-1 under flow as compared to naive T-cells. Interestingly, the expression of activation/ligand induced epitopes on beta1-integrins on Th2 cells and the ability of these cells to interact with VCAM-1 are comparable to memory T-cells. In contrast, Th1 cells did not interact as efficiently with VCAM-1, which correlated with lower expression of activation/ligand induced epitopes on these cells. VCAM-1 interactions are inhibited completely by pretreatment of the T-cells with blocking mAb to alpha4-integrins or beta1-integrins, indicating that alpha4beta1 is the predominant T-cell integrin involved. CONCLUSIONS: Memory T-cells express constitutively active alpha4beta1-integrins, as compared to naive T-cells, which mediate high rates of initial attachment and sustained high-affinity adhesive interactions with VCAM-1 under flow conditions in vitro. Similarly, in vitro differentiated Th2 cells but not Th1 cells, which also express elevated levels of activated alpha4beta1-integrins, are capable of sustaining high-affinity adhesive interactions with VCAM-1. The differences observed in beta1-integrin activation on T-cell subsets may underlie selective recruitment patterns of T-cell subsets in vivo.

Cell Adhesion↗
PubMed1999

Immunization with amyloid-beta attenuates Alzheimer-disease-like pathology in the PDAPP mouse.

Amyloid-beta peptide (Abeta) seems to have a central role in the neuropathology of Alzheimer's disease (AD). Familial forms of the disease have been linked to mutations in the amyloid precursor protein (APP) and the presenilin genes. Disease-linked mutations in these genes result in increased production of the 42-amino-acid form of the peptide (Abeta42), which is the predominant form found in the amyloid plaques of Alzheimer's disease. The PDAPP transgenic mouse, which overexpresses mutant human APP (in which the amino acid at position 717 is phenylalanine instead of the normal valine), progressively develops many of the neuropathological hallmarks of Alzheimer's disease in an age- and brain-region-dependent manner. In the present study, transgenic animals were immunized with Abeta42, either before the onset of AD-type neuropathologies (at 6 weeks of age) or at an older age (11 months), when amyloid-beta deposition and several of the subsequent neuropathological changes were well established. We report that immunization of the young animals essentially prevented the development of beta-amyloid-plaque formation, neuritic dystrophy and astrogliosis. Treatment of the older animals also markedly reduced the extent and progression of these AD-like neuropathologies. Our results raise the possibility that immunization with amyloid-beta may be effective in preventing and treating Alzheimer's disease.

Alzheimer Disease↗
PubMed1999

The integrin alpha9beta1 mediates adhesion to activated endothelial cells and transendothelial neutrophil migration through interaction with vascular cell adhesion molecule-1.

The integrin alpha9beta1 has been shown to be widely expressed on smooth muscle and epithelial cells, and to mediate adhesion to the extracellular matrix proteins osteopontin and tenascin-C. We have found that the peptide sequence this integrin recognizes in tenascin-C is highly homologous to the sequence recognized by the closely related integrin alpha4beta1, in the inducible endothelial ligand, vascular cell adhesion mole-cule-1 (VCAM-1). We therefore sought to determine whether alpha9beta1 also recognizes VCAM-1, and whether any such interaction would be biologically significant. In this report, we demonstrate that alpha9beta1 mediates stable cell adhesion to recombinant VCAM-1 and to VCAM-1 induced on human umbilical vein endothelial cells by tumor necrosis factor-alpha. Furthermore, we show that alpha9beta1 is highly and selectively expressed on neutrophils and is critical for neutrophil migration on VCAM-1 and tenascin-C. Finally, alpha9beta1 and alpha4 integrins contribute to neutrophil chemotaxis across activated endothelial monolayers. These observations suggest a possible role for alpha9beta1/VCAM-1 interactions in extravasation of neutrophils at sites of acute inflammation.

Animals↗
PubMed1999

alpha9beta1 integrin is expressed on human neutrophils and contributes to neutrophil migration through human lung and synovial fibroblast barriers.

Accumulation of leukocytes in inflamed tissue involves their migration through vascular endothelium and then in the connective tissue. Recently we utilized a barrier of human synovial, dermal, and lung fibroblasts (HSF, HDF, and HLF) grown on polycarbonate filters as a model of human polymorphonuclear leukocyte (PMN) migration through connective tissue. The beta2 integrins (CD 11/ CD18) and alpha4, alpha5, and alpha6beta1 (VLA-4, -5, and -6) integrins each contributed to this PMN migration. Here we report that on human blood leukocytes, alpha9beta1 (VLA-9) is expressed only on PMNs and that it is up-regulated after PMN activation. Based on monoclonal antibody (mAb) blocking studies, alpha9beta1 integrin contributed to C5a-induced PMN migration through fibroblast (HLF and HSF) barriers. This role was apparent only when alternate mechanisms such as CD18, alpha4, alpha5, and alpha6beta1 integrins were blocked and then mAb to alpha9beta1 integrin inhibited the residual PMN migration (by 40-50%) through the HLF or HSF barrier, resulting in > or = 75% inhibition overall. In contrast, PMN migration across interleukin-1-activated endothelium (HUVEC) in response to a C5a gradient, which is partly (30-40%) via CD11/CD18-independent mechanisms, was not inhibited by adhesion blocking by mAbs to alpha4, alpha5, alpha6, and alpha9beta1 even in combination. These results indicate that alpha9beta1 integrin on PMN may have a special role, in conjunction with other beta1 integrins, in mediating PMN migration in the extravascular space, and may contribute to differential neutrophil function within tissues.

Animals↗
PubMed1998

Intracellular calcium requirements for beta1 integrin activation.

Human polymorphonuclear leukocytes (PMNs) express beta1 integrins that mediate adhesion to extracellular matrix proteins following stimulation with agonists that induce an increase in intracellular calcium. The purpose of these studies was to determine the contribution made by alterations in intracellular calcium ([Ca++]i) to inside-out activation of beta1 integrins using dimethyl sulfoxide (DMSO)-differentiated granulocytic HL60 cells as a model of human PMNs. Activation of beta1 integrins was determined by measuring the expression of an activation-dependent epitope on the beta1 subunit that is recognized by monoclonal antibody (mAb) 15/7. Exposure of granulocytic HL60 cells to calcium ionophore ionomycin (800 nM) alone did not increase the binding of mAb 15/7 to the cell surface, nor did it increase beta1 integrin-mediated adhesion of the cells to fibronectin. Similarly, exposure of the cells to the direct protein kinase C (PKC) activator, dioctanoylglycerol (di-C8) at 100 microM, neither increased binding of mAb 15/7 to these cells nor adhesion to fibronectin. Simultaneous addition of di-C8 and ionomycin, however, caused a significant increase in the expression of the 15/7 epitope and cell adhesion, suggesting synergy between elevating [Ca++]i and stimulating PKC in beta1 integrin activation. Chelation of [Ca++]i with Quin-2 and EGTA reduced both basal (unstimulated) expression of the 15/7 epitope and basal adhesion of granulocytic HL60 cells to fibronectin. In addition, chelation of [Ca++]i caused a significant decrease in 15/7 binding and adhesion stimulated by low (1 ng/ml) concentrations of phorbol myristate acetate (PMA). The inhibitory effect of [Ca++]i chelation on beta1 integrin activation was reversed by repleting [Ca++]i with ionomycin in a Ca++-containing buffer, or by the addition of higher concentrations of PMA (10 ng/ml). These data suggest a role for [Ca++]i in inside-out activation of beta1 integrins, probably through a synergistic effect with PKC activation.

Antibodies, Monoclonal↗
PubMed1996

Regulation of beta1-integrin function in cultured human vascular smooth muscle cells.

Avidity modulation and function of beta1-integrin receptors in cultured human vascular smooth muscle cells (SMCs) were investigated using monoclonal antibody (mAb) 8A2, which binds to the beta1 subunit of integrin heterodimers and induces a high avidity state. The adhesion of SMCs to extracellular matrix proteins, but not to poly-L-lysine, was enhanced by pretreatment with mAb 8A2. A qualitative alteration of beta1 integrin was assessed with mAb 15/7, which binds to an activation-dependent epitope on the beta1 subunit. Binding of mAb 15/7 was enhanced by mAb 8A2 in a dose-dependent manner. Arg-Gly-Asp peptide and soluble fibronectin also enhanced expression of the 15/7 epitope, suggesting that the 15/7 epitope is closely related to the ligand-occupied state of beta1 integrin. Platelet-derived growth factor (PDGF)-AA and -BB increased SMC adhesion to type I collagen but did not augment mAb 15/7 binding, suggesting that PDGFs increase binding avidity by a postreceptor mechanism. In addition, mAb 8A2 inhibited PDGF-BB-induced SMC migration through Matrigel-coated filters. These results suggest that avidity modulation of beta1 integrin may play an important role in the function of SMCs.

Antibodies, Monoclonal↗
PubMed1996

Evidence for a prolonged role of alpha 4 integrin throughout active experimental allergic encephalomyelitis.

The leukocyte integrin receptor, alpha 4 beta 1, and its endothelial cell ligand, vascular cell adhesion molecule 1, appear to be of critical importance in the leukocyte trafficking that accompanies CNS damage in experimental allergic encephalomyelitis (EAE). In this study, the persistence of the role for alpha 4 beta 1/VCAM-1 in EAE was established by observing antibody-mediated disease reversal up to 1 month following disease onset. Limited treatment with a monoclonal antibody against alpha 4 integrin, GG5/3, resulted in a significant decrease in both clinical and histopathologic signs. This was not observed in isotype control experiments. In the latter phase of progressive disease, widespread demyelination occurred in the animals that did not respond to 6 days of anti-alpha 4 treatment. These results demonstrate an essential role for alpha 4 beta 1 interactions throughout active EAE and illustrate the difference between reversible clinical deficits caused by edema and irreversible deficits associated with demyelination.

Animals↗
PubMed1996

Regulation and function of an activation-dependent epitope of the beta 1 integrins in vascular cells after balloon injury in baboon arteries and in vitro.

Migration and proliferation of endothelial cells (ECs) and smooth muscle cells (SMCs) contribute to the response to injury in damaged and atherosclerotic vessels. These events might be regulated by cellular interactions with extracellular matrix through the expression and activation of integrins. To study the functions of beta 1 integrins in the vessel wall, we used monoclonal antibody (MAb) 15/7, which recognizes an activation epitope of beta 1 integrin subunits, and MAb 8A2, which induces a high affinity form of beta 1 integrins recognized by MAb 15/7. Immunohistochemical analyses were done on samples of normal baboon saphenous arteries and from arteries subjected to balloon injury. EC and SMC expressed the activation epitope of beta 1 integrin in uninjured arteries. By contrast, in balloon-injured arteries 6 weeks after injury, regenerating EC did not express the activation epitope, and there was no decrease in the expression of total beta 1 integrin, whereas SMC migrating into the intima exhibited decreased expression of the total and activated beta 1 integrin. Flow cytometer analysis of cultured cells indicated that baboon EC and SMC weakly express the activation epitope of beta 1 integrin. Next, we determined by utilizing MAb 8A2 the effects of increased expression of activation epitope of beta 1 integrin on the functions of SMC and EC. The activation of beta 1 integrins on SMC induced by MAb 8A2 enhanced SMC adhesion and suppressed SMC migration in a Boyden chamber assay. SMC proliferation was inhibited by MAb 8A2 dose-dependently. Similarly, MAb 8A2-induced activation of beta 1 integrins on EC suppressed EC migration into a wound. However, MAb 8A2 did not affect the basic fibroblast growth factor-induced proliferation of EC, although it blocked the decrease in EC number caused by the removal of basic fibroblast growth factor. These results suggest that activation of beta 1 integrins in vascular cells is regulated in a cell-type dependent manner and plays an important role in modulating vascular cell functions.

Animals↗
PubMed1995

Stem cell factor modulates avidity of alpha 4 beta 1 and alpha 5 beta 1 integrins expressed on hematopoietic cell lines.

Interactions between hematopoietic cells and bone marrow (BM) stroma, composed of extracellular matrix and stromal cells, are crucial for hematopoiesis. Integrins facilitate these interactions by mediating adherence of hematopoiesis. Integrins facilitate these interactions by mediating adherence of hematopoietic cells to both the extracellular matrix and stromal cells. Marrow stromal cells secrete a variety of growth factors, including stem cell factor (SCF). Because treatment with SCF in vivo mobilizes primitive hematopoietic cells from the BM, we investigated the effect of the growth factor SCF of hematopoietic cell adhesion. These studies show that SCF modulates adhesive function in a dose- and time-dependent manner, but does not modulate expression of the integrins alpha 4 beta 1 and alpha 5 beta 1 in the SCF-responsive cell line MO7E. Treatment of MO7E cells with SCF (200 ng/mL) produced a transient increase in adherence to cytokine-activated human umbilical vein endothelial cells (HUVECs) or to vascular cell adhesion molecule 1 (VCAM-1)-transfected Chinese hamster ovary (CHO) cells with peak adhesion at 30 minutes and return to baseline by 60 to 90 minutes. This increase in adhesion was paralleled by increased binding of the beta 1 activation-dependent monoclonal antibody (MoAb) 15/7, as determined by flow cytometry. However, prolonged incubation of MO7E with SCF induced a marked decrease in integrin-mediated adherence, with maximal inhibition by 24 hours. No change in expression of integrins, as determined by flow cytometry, was observed with short- or long-term incubation with SCF. SCF-treated cells were still able to respond to phorbol esters and to the activating beta 1 MoAb 8A2 with increased adherence, but not to the level seen in control cells. This suggests that a subpopulation of expressed alpha 4 beta 1 and alpha 5 beta 1 integrins is disengaged by prolonged incubation with SCF.

Animals↗
PubMed1994

Pentoxifylline inhibits integrin-mediated adherence of interleukin-2- activated human peripheral blood lymphocytes to human umbilical vein endothelial cells, matrix components, and cultured tumor cells.

Peripheral blood lymphocytes (PBLs) cultured in the presence of recombinant human interleukin-2 (rhIL-2) develop a natural killer (NK) cell phenotype (CD16+, CD56+, CD3-) and are referred to as lymphokine-activated killer cells (LAK). In developing the LAK phenotype, enhanced adherence to matrix components and endothelial cells have been described. In this report we investigated the functional behavior of adhesion receptors in rhIL-2-activated PBLs by in vitro adhesion assay and by flow cytometry. Compared to PBLs, IL-2-activated PBLs had increased integrin-mediated adherence to: (1) fibronectin (FN), (2) human umbilical vein endothelial (HUVE) cells, and (3) cultured melanoma and pancreatic tumor cell lines. This increase in adherence was mediated by increased surface expression of members of the beta 1 and beta 2 integrin subfamilies, as determined by flow cytometric analysis. No induction of an activation-dependent beta 1 (CD29) epitope was detected. We also investigated the effects of the methylxanthine derivative pentoxifylline (PTX) on PBLs and rhIL-2-activated PBL adhesion. PBLs co-cultivated in the presence of rhIL-2 (1,000 U/mL) and PTX exhibited reduced adherence to FN, HUVE and cultured tumor cell lines. This inhibition by PTX was concentration- and time-dependent. The increased expression of integrins induced by rhIL-2 was only in part inhibited by PTX, suggesting that PTX induced a subpopulation of integrins that are expressed but functionally inactive.

Cell Adhesion↗
PubMed1993

Coordinate expression of beta 1 and beta 2 integrin "activation" epitopes during T cell responses in secondary lymphoid tissue.

The monoclonal antibodies (mAb) 15/7 and 24 recognize unique activation-dependent, conformational epitopes on beta 1 and beta 2-integrins, respectively. The expression of both of these epitopes closely correlates with the ligand binding ability of their respective integrins, and thus serves as indicators of functional integrin "activation". Here, we have used six-parameter flow cytometry to examine the expression of these epitopes and conventional beta 1- and beta 2-integrin epitopes during human T cell activation in secondary lymphoid tissues in vivo, focusing particularly on the virgin to memory/effector cell transition. Fresh tonsil lymphocytes were stained with mAb against conventional or activation-dependent integrin epitopes, followed by staining with mAb against CD3, CD45RA, and CD45RO, thus allowing the determination of integrin epitope expression on virgin (CD3+) T cells (CD45RA+/RO-to+/-), memory/effector (CD45RA-/RO++) T cells, and T cells undergoing the virgin to memory/effector transition: transition region-1 (T1; CD45RA+to++/RO+); -2 (T2; CD45RA++/RO++); and -3 (T3; CD45RA+/RO++). Conventional beta 1- and beta 2-integrin epitopes progressively increase during the virgin to T3 stages of the transition in tonsil, in keeping with the generally higher levels of these adhesion molecules on memory/effector vs. virgin T cells. Expression of both the beta 1 (15/7)- and beta 2 (24)-integrin activation epitopes first appears on transitional T cells, and is maintained on a relatively constant number of cells (averaging 25-30%) throughout the T1-T3 stages. These epitopes are also noted on a subset of activated memory/effector T cells. Importantly, on both transitional and activated memory/effector T cell subsets, the expression patterns of the 15/7 and 24 epitopes vs. a variety of T cell activation antigens are identical, and the expression of these epitopes relative to each other is linearly correlated, findings strongly supporting the coordinate activation of beta 1 and beta 2 integrins during T cell activation in vivo. These results provide the first evidence of integrin activation during an in vivo immunologic response, and demonstrate the usefulness of mAb recognizing conformational epitopes and multiparameter flow cytometry in delineating the dynamic interplay of adhesion molecules during complex physiologic processes.

Adolescent↗
PubMed1993

VLA-4-dependent adhesion activities of U937 cells and guinea pig bronchoalveolar lavage leukocytes.

VLA-4-dependent binding to fibronectin (FN) and to a human vascular cell adhesion molecule (hVCAM-1)-transfected murine cell line was measured using U937 cells and guinea pig (GP) bronchoalveolar lavage (BAL) cells. A species cross-reactive, blocking monoclonal antibody directed against human VLA-4 (TY 21.6) inhibited U937/FN binding by 71 +/- 7%. The presence of TY21.6 inhibited the stimulated binding of U937 cells to hVCAM-1 by 84%. However, TY 21.6 was unable to inhibit the BAL/FN binding. With the addition of TY 21.6, the binding of PMA-stimulated BAL cells to hVCAM-1 was inhibited by 57 +/- 5%. In summary, human and guinea-pig leukocytes express binding activity to both FN and hVCAM-1. A specific VLA-4 blocking monoclonal antibody, TY 21.6, inhibited U937 and BAL cell binding to hVCAM-1, but only inhibited FN binding with U937 cells.

Animals↗
PubMed1983

Reversible disruption of cultured endothelial monolayers by sulphated fucans.

We have examined the effects of a variety of polysaccharides and glycoconjugates on the organization and morphology of cultured A14CL-1 endothelial monolayers. The sulphated fucose-containing polysaccharides, fucoidin and sea-urchin egg jelly fucan, induce a dramatic disruption of the organization of the monolayers, characterized by the retraction of adjacent borders of cells exposing areas of the subendothelial matrix. This effect, which occurs at a fucoidin concentration of 10 micrograms/ml, is rapidly reversible after the fucoidin-containing medium is removed. Within 1 h after replacement with fresh medium many cell contacts are re-established; within 20 h the fucoidin-treated monolayers closely resemble the untreated controls. The effect of the sulphated fucose-containing polysaccharides is specific. Of a wide variety of sulphated polysaccharides and glycoconjugates tested, only fucoidin and the egg jelly fucan produce a detectable alteration in the morphology of cultured endothelial monolayers. The endothelial monolayer has specific binding sites for fucoidin. The binding of fucoidin is saturable and a maximum of 4.5 X 10(5) molecules of fucoidin are bound per cell with an apparent affinity of 2.3 X 10(-7) M. A significant proportion (26%) of the total monolayer-associated fucoidin is apparently internalized by the endothelial cells after incubation with fucoidin for 1 h at 37 degrees C. The morphological response to fucoidin is probably not due to its internalization, since the effect is observed at 7 degrees C where little uptake (3.5%) occurs. Fucoidin appears to bind at two distinct sites on endothelial monolayers. One site is inhibitable by heparin, while the other site seems to be specific for fucoidin. The observation that fucoidin still induces the retraction of the endothelial cells in the presence of a 100-fold excess of heparin, suggests that binding at the fucoidin-specific site is responsible for the morphological effect of fucoidin. In addition, fucoidin has no detectable effect on monolayers of 3T3 and BHK fibroblast-like cells at 1 mg/ml, 100-fold higher than the concentration required to produce an effect on endothelial cells. Among the possible interpretations of these results is that sulphated fucose-containing glycoconjugates may play a role in the adhesive interactions of endothelial cells.

Animals↗