scholarly journals A Fifty Percent Reduction of Platelet Surface Glycoprotein Ib Does Not Affect Platelet Adhesion Under Flow Conditions

Blood ◽  
1998 ◽  
Vol 91 (7) ◽  
pp. 2353-2359 ◽  
Author(s):  
G. Henrita van Zanten ◽  
Harry F.G. Heijnen ◽  
Yaping Wu ◽  
Karin M. Schut-Hese ◽  
Pieter J. Slootweg ◽  
...  
Keyword(s):  
Platelet Adhesion ◽  
Umbilical Vein ◽  
Surface Expression ◽  
Surface Glycoprotein ◽  
Flow Conditions ◽  
Platelet Surface ◽  
Microscopic Studies ◽  
Umbilical Vein Endothelial Cells ◽  
Adhesive Proteins

Glycoprotein (GP) Ib is an adhesion receptor on the platelet surface that binds to von Willebrand Factor (vWF). vWF becomes attached to collagens and other adhesive proteins that become exposed when the vessel wall is damaged. Several investigators have shown that during cardiopulmonary bypass (CPB) surgery and also during platelet activation in vitro by thrombin or thrombin receptor activating peptide (TRAP) GPIb disappears from the platelet surface. Such a disappearance is presumed to lead to a decreased adhesive capacity. In the present study, we show that a 65% decrease in platelet surface expression of GPIb, due to stimulation of platelets in Orgaran anticoagulated whole blood with 15 μmol/L TRAP, had no effect on platelet adhesion to both collagen type III and the extracellular matrix (ECM) of human umbilical vein endothelial cells under flow conditions in a single-pass perfusion system. In contrast to adhesion, ristocetin-induced platelet agglutination was highly dependent on the presence of GPIb. Immunoelectron microscopic studies showed that GPIb almost immediately returned to the platelet surface once platelets had attached to collagen. In a subsequent series of experiments, we showed that when less than 50% of GPIb was blocked by an inhibitory monoclonal antibody against GPIb (6D1), platelet adhesion under flow conditions remained unaffected.

scholarly journals A Fifty Percent Reduction of Platelet Surface Glycoprotein Ib Does Not Affect Platelet Adhesion Under Flow Conditions

Blood ◽  
1998 ◽  
Vol 91 (7) ◽  
pp. 2353-2359 ◽  
Author(s):  
G. Henrita van Zanten ◽  
Harry F.G. Heijnen ◽  
Yaping Wu ◽  
Karin M. Schut-Hese ◽  
Pieter J. Slootweg ◽  
...  
Keyword(s):  
Platelet Adhesion ◽  
Umbilical Vein ◽  
Surface Expression ◽  
Surface Glycoprotein ◽  
Flow Conditions ◽  
Platelet Surface ◽  
Microscopic Studies ◽  
Umbilical Vein Endothelial Cells ◽  
Adhesive Proteins

AbstractGlycoprotein (GP) Ib is an adhesion receptor on the platelet surface that binds to von Willebrand Factor (vWF). vWF becomes attached to collagens and other adhesive proteins that become exposed when the vessel wall is damaged. Several investigators have shown that during cardiopulmonary bypass (CPB) surgery and also during platelet activation in vitro by thrombin or thrombin receptor activating peptide (TRAP) GPIb disappears from the platelet surface. Such a disappearance is presumed to lead to a decreased adhesive capacity. In the present study, we show that a 65% decrease in platelet surface expression of GPIb, due to stimulation of platelets in Orgaran anticoagulated whole blood with 15 μmol/L TRAP, had no effect on platelet adhesion to both collagen type III and the extracellular matrix (ECM) of human umbilical vein endothelial cells under flow conditions in a single-pass perfusion system. In contrast to adhesion, ristocetin-induced platelet agglutination was highly dependent on the presence of GPIb. Immunoelectron microscopic studies showed that GPIb almost immediately returned to the platelet surface once platelets had attached to collagen. In a subsequent series of experiments, we showed that when less than 50% of GPIb was blocked by an inhibitory monoclonal antibody against GPIb (6D1), platelet adhesion under flow conditions remained unaffected.

scholarly journals Oxidative Stress Induces HSP90 Upregulation on the Surface of Primary Human Endothelial Cells: Role of the Antioxidant 7,8-Dihydroxy-4-methylcoumarin in Preventing HSP90 Exposure to the Immune System

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
Elisabetta Profumo ◽  
Brigitta Buttari ◽  
Lavinia Tinaburri ◽  
Daniela D’Arcangelo ◽  
Maurizio Sorice ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Endothelial Cells ◽  
Umbilical Vein ◽  
Protein A ◽  
Heat Shock Protein 90 ◽  
Surface Expression ◽  
Enzyme Linked Immunosorbent Assay ◽  
Protein Levels ◽  
Umbilical Vein Endothelial Cells

We have previously demonstrated that human heat shock protein 90 (HSP90), an intracellular self protein, is the target of cellular and humoral autoimmune responses in patients with carotid atherosclerosis. In this study, we evaluated in vitro whether oxidative stress, a feature of atherosclerotic plaque, alters HSP90 expression in endothelial cells, thus inducing surface localization of this molecule and whether the antioxidant compound 7,8-dihydroxy-4-methylcoumarin (7,8-DHMC) is able to prevent oxidative stress-induced alterations of HSP90 localization. By the use of flow cytometry, immunofluorescence, enzyme-linked immunosorbent assay, and semiquantitative reverse-transcription polymerase chain reaction, we demonstrated that exposure of human umbilical vein endothelial cells (HUVEC) to the prooxidant compound H2O2 upregulated HSP90 surface expression and reduced its secretion without altering HSP90 gene expression and intracytoplasmic protein levels. Pretreatment of HUVEC with 7,8-DHMC prevented H2O2-induced alterations of HSP90 cellular distribution and secretion. Our results suggest that the strong oxidative conditions of atherosclerotic plaques promote the upregulation of HSP90 surface expression on endothelial cells, thus rendering the protein a possible target of autoimmune reactions. The antioxidant 7,8-DHMC, by preventing oxidative-stress-triggered HSP90 surface upregulation, may be useful to counteract possible autoreactive reactions to HSP90.

Downregulation of the platelet surface glycoprotein Ib-IX complex in whole blood stimulated by thrombin, adenosine diphosphate, or an in vivo wound [see comments]

Blood ◽  
1991 ◽  
Vol 77 (4) ◽  
pp. 770-779 ◽  
Author(s):  
AD Michelson ◽  
PA Ellis ◽  
MR Barnard ◽  
GB Matic ◽  
AF Viles ◽  
...  
Keyword(s):  
Whole Blood ◽  
Actin Polymerization ◽  
Flow Cytometric Analysis ◽  
Adenosine Diphosphate ◽  
Surface Expression ◽  
Surface Glycoprotein ◽  
Platelet Surface ◽  
Granule Secretion

Abstract In washed platelet systems, thrombin has been demonstrated to downregulate the platelet surface expression of glycoprotein (GP) Ib and GPIX. In the present study, we addressed the question as to whether, in the more physiologic milieu of whole blood, downregulation of platelet surface GPIb and GPIX can be induced by thrombin, adenosine diphosphate (ADP), and/or by an in vivo wound. Thrombin-induced downregulation of GPIb and GPIX on the surface of individual platelets in whole blood was demonstrated by the use of flow cytometry, a panel of monoclonal antibodies (MoAbs) and, to inhibit fibrin polymerization, the peptide glycyl-L-prolyl-L-arginyl-L-proline. Platelets were identified in whole blood by a GPIV-specific MoAb and exclusion of monocytes by light scattering properties. Flow cytometric analysis of whole blood emerging from a standardized bleeding-time wound established that downregulation of platelet surface GPIb and GPIX can occur in vivo. A GPIb-IX complex-specific antibody indicated that the GPIb and GPIX remaining on the surface of platelets activated in vivo or in vitro were fully complexed. Simultaneous analysis of individual platelets by two fluorophores demonstrated that thrombin-induced platelet surface exposure of GMP-140 (degranulation) was nearly complete at the time that downregulation of platelet surface GPIb-IX was initiated. However, degranulation was not a prerequisite because ADP downregulated platelet surface GPIb-IX without exposing GMP-140 on the platelet surface. Inhibitory effects of cytochalasins demonstrated that the activation-induced downregulation of both GPIX and GPIb are dependent on actin polymerization. In summary, downregulation of the platelet surface GPIb-IX complex occurs in whole blood stimulated by thrombin, ADP, or an in vivo wound, and is independent of alpha granule secretion.

scholarly journals The Antithrombotic Function of Sphingosine-1-Phosphate on Human Adipose-Stem-Cell-Recellularized Tissue Engineered Vascular Graft In Vitro

2019 ◽  
Vol 20 (20) ◽  
pp. 5218
Author(s):  
Chih-Hsun Lin ◽  
Jen-Her Lu ◽  
Kai Hsia ◽  
Hsinyu Lee ◽  
Chao-Ling Yao ◽  
...  
Keyword(s):  
Platelet Adhesion ◽  
Umbilical Vein ◽  
Sodium Dodecyl ◽  
Antithrombotic Effect ◽  
Human Ascs ◽  
Sphingosine 1 Phosphate ◽  
Nuclear Component ◽  
Umbilical Vein Endothelial Cells ◽  
Umbilical Arteries

Adipose stem cells (ASCs) show potential in the recellularization of tissue engineerined vascular grafts (TEVGs). However, whether sphingosine-1-phosphate (S1P) could further enhance the adhesion, proliferation, and antithrombosis of ASCs on decellularized vascular scaffolds is unknown. This study investigated the effect of S1P on the recellularization of TEVGs with ASCs. Human ASCs were derived from lipoaspirate. Scaffolds were derived from human umbilical arteries (HUAs) with treatment of 0.1% sodium dodecyl sulfate (SDS) for 48 h (decellularized HUAs; DHUAs). The adhesion, proliferation, and antithrombotic functions (kinetic clotting time and platelet adhesion) of ASCs on DHUAs with S1P or without S1P were evaluated. The histology and DNA examination revealed a preserved structure and the elimination of the nuclear component more than 95% in HUAs after decellularizaiton. Human ASCs (hASCs) showed CD29(+), CD73(+), CD90(+), CD105(+), CD31(–), CD34(–), CD44(–), HLA-DR(–), and CD146(–) while S1P-treated ASCs showed marker shifting to CD31(+). In contrast to human umbilical vein endothelial cells (HUVECs), S1P didn’t significantly increase proliferation of ASCs on DHUAs. However, the kinetic clotting test revealed prolonged blood clotting in S1P-treated ASC-recellularized DHUAs. S1P also decreased platelet adhesion on ASC-recellularized DHUAs. In addition, S1P treatment increased the syndecan-1 expression of ASCs. TEVG reconstituted with S1P and ASC-recellularized DHUAs showed an antithrombotic effect in vitro. The preliminary results showed that ASCs could adhere to DHUAs and S1P could increase the antithrombotic effect on ASC-recellularized DHUAs. The antithrombotic effect is related to ASCs exhibiting an endothelial-cell-like function and preventing of syndecan-1 shedding. A future animal study is warranted to prove this novel method.

scholarly journals Deacylated lipopolysaccharide inhibits neutrophil adherence to endothelium induced by lipopolysaccharide in vitro.

1987 ◽  
Vol 165 (5) ◽  
pp. 1393-1402 ◽  
Author(s):  
T H Pohlman ◽  
R S Munford ◽  
J M Harlan
Keyword(s):  
Fatty Acids ◽  
Umbilical Vein ◽  
Surface Expression ◽  
Specific Cell ◽  
Dependent Manner ◽  
Toxic Activity ◽  
Neutrophil Adherence ◽  
Umbilical Vein Endothelial Cells

Selective deacylation of the nonhydroxylated fatty acids from S. typhimurium LPS by an acyloxyacyl hydrolase isolated from leukocytes reduces toxic activity of LPS in vivo. We examined the effect of deacylated LPS on neutrophil adherence to human umbilical vein endothelial cells (HUVE). Pretreatment of HUVE with LPS (13 ng/ml for 4 h) produced a marked increase in the adherence of subsequently added neutrophils. In contrast, there was no increase in the adherence of neutrophils to HUVE pretreated with deacylated LPS (up to 260 ng/ml for 4 h). Neutrophil adherence to HUVE pretreated with LPS decreased as the degree of LPS deacylation increased. Deacylated LPS was not only itself inactive, but it inhibited neutrophil-endothelial interactions induced by LPS. Neutrophil adherence to HUVE pretreated with LPS was inhibited by deacylated LPS in a dose-dependent manner. Complete inhibition of adherence was observed at a 20:1 ratio (wt/wt) of deacylated LPS to LPS. Significantly, inhibition of neutrophil adherence to HUVE pretreated with LPS was observed even when deacylated LPS was added to HUVE up to 60 min after LPS. Deacylated LPS, however, did not inhibit neutrophil adherence induced by pretreatment of HUVE with IL-1 or TNF-alpha. We conclude that enzymatic deacylation of the nonhydroxylated fatty acids of LPS abolishes the ability of LPS to induce surface expression of a neutrophil adherence promoting activity in HUVE. Furthermore, deacylated LPS inhibits neutrophil adherence to HUVE induced by LPS, perhaps by preventing the interaction of LPS with a specific cell-surface or intracellular target.

ω-3 Fatty acids suppress monocyte adhesion to human endothelial cells: role of endothelial PAF generation

2002 ◽  
Vol 283 (2) ◽  
pp. H811-H818 ◽  
Author(s):  
Konstantin Mayer ◽  
Martina Merfels ◽  
Marion Muhly-Reinholz ◽  
Stephanie Gokorsch ◽  
Simone Rosseau ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Endothelial Cells ◽  
Adhesion Molecule ◽  
Inflammatory Diseases ◽  
Umbilical Vein ◽  
Platelet Activating Factor ◽  
Surface Expression ◽  
Intercellular Adhesion Molecule ◽  
Umbilical Vein Endothelial Cells

Monocyte-endothelium interaction is a fundamental process in many acute and chronic inflammatory diseases. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are fish oil-derived alternative (ω-3) precursor fatty acids implicated in the suppression of inflammatory events. We investigated their influence on rolling and adhesion of monocytes to human umbilical vein endothelial cells (HUVEC) under laminar flow conditions in vitro. Exposure of HUVEC to tumor necrosis factor (TNF-α) strongly increased 1) surface expression of intercellular adhesion molecule (ICAM-1), vascular cell adhesion molecule (VCAM-1), and E-selectin, 2) platelet-activating factor (PAF) synthesis as assessed by thrombin challenge, and 3) rate of rolling and adhesion of monocytes. Preincubation of HUVEC with EPA or DHA markedly suppressed PAF synthesis, monocyte rolling, and adherence, whereas expression of endothelial adhesion molecules was unchanged. Also, PAF receptor antagonists markedly suppressed the adhesion rate of monocytes, and EPA or DHA revealed no additional inhibitory capacity. In contrast, arachidonic acid partially reversed the effect of the antagonist. We conclude that ω-3 fatty acids suppress rolling and adherence of monocytes on activated endothelial cells in vitro by affecting endothelial PAF generation.

Small-molecule cyclic αVβ3 antagonists inhibit sickle red cell adhesion to vascular endothelium and vasoocclusion

2007 ◽  
Vol 293 (2) ◽  
pp. H1038-H1045 ◽  
Author(s):  
Eileen M. Finnegan ◽  
Gilda A. Barabino ◽  
Xiao-du Liu ◽  
Hee-Yoon Chang ◽  
Alfred Jonczyk ◽  
...  
Keyword(s):  
Small Molecule ◽  
Vascular Endothelium ◽  
Cyclic Peptides ◽  
Therapeutic Strategy ◽  
Umbilical Vein ◽  
Platelet Activating Factor ◽  
Αvβ3 Integrin ◽  
Flow Conditions ◽  
Umbilical Vein Endothelial Cells ◽  
Adhesive Proteins

Abnormal adhesion of sickle red blood cells (SS RBCs) to vascular endothelium may play an important role in vasoocclusion in sickle cell disease. Accruing evidence shows that endothelial αVβ3-integrin has an important role in SS RBC adhesion because of its ability to bind several adhesive proteins implicated in this interaction. In the present studies, we tested therapeutic efficacy of small-molecule cyclic pentapeptides for their ability to block αVβ3-mediated SS RBC adhesion by using two well-established assay systems, i.e., cultured human umbilical vein endothelial cells (HUVEC) and artificially perfused mesocecum vasculature of the rat under flow conditions. We tested the efficacy of two RGD-containing cyclic pentapeptides, i.e., cRGDFV (EMD 66203) and cRGDF-ACHA (α-amino cyclohexyl carboxylic acid) (EMD 270179), based on their known ability to bind αVβ3. An inactive peptide, EMD 135981 (cRβ-ADFV) was used as control. Cyclization and the introduction of d-Phe (F) results in a marked increase in the ability of cyclic peptides to selectively bind αVβ3 receptors. In the mesocecum vasculature, both EMD 66203 and EMD 270179 ameliorated platelet-activating factor-induced enhanced SS RBC adhesion, postcapillary blockage, and significantly improved hemodynamic behavior. Infusion of a fluorescent derivative of EMD 66203 resulted in colocalization of the antagonist with vascular endothelium. Also, pretreatment of HUVEC with either αVβ3 antagonist resulted in a significant decrease in SS RBC adhesion. Because of their metabolic stability, the use of these cyclic αVβ3 antagonists may constitute a novel therapeutic strategy to block SS RBC adhesion and associated vasoocclusion under flow conditions.

scholarly journals Effect of interleukin-5 exposure during in vitro eosinophilopiesis on MAC-1 adhesion molecule expression and function on cultured human eosinophils

Blood ◽  
1996 ◽  
Vol 88 (9) ◽  
pp. 3575-3582 ◽  
Author(s):  
KJ Hamann ◽  
SP Neeley ◽  
TL Dowling ◽  
JA Grant ◽  
AR Leff
Keyword(s):  
Endothelial Cells ◽  
Umbilical Vein ◽  
Surface Expression ◽  
Human Umbilical Cord Blood ◽  
Human Umbilical Cord ◽  
Cd11b Expression ◽  
Interleukin 5 ◽  
Umbilical Vein Endothelial Cells ◽  
Cells Cultured

We examined the selective effects of interleukin (IL-5) in regulating the maturational expression of surface adhesion molecules on human eosinophils and adhesion to endothelial cells during eosinophiiopolesis in vitro. Expression of the beta 2 integrins (CD11/CD18) and the beta 1 integrin, VLA-4 (CD49d/ CD29), was assessed during development in culture with IL-3, IL-5, and granulocyte-macrophage colony stimulating factor in cultures of human umbilical cord blood-derived eosinophil (CDE) precursor cells. Expression of both CD11b and CD18 subunits of Mac-1 was lower on CDE which were continuously (= chronically) exposed to IL-5 than on CDE which were cultured without IL-5 for the final week of culture. CD11b expression on cells grown without IL-5 was 71.3 +/- 5.92 (mean specific fluorescence value [MSF] as measured by flow cytometry) versus 52.5 +/- 4.48 MSF for Mac-1 alpha (CD11b) on CDE grown in the continued presence of 2 x 10 – 11 mol/L IL-5 (P < .01). Although expression of VLA-4 decreased as CDE matured, expression of CD29 and CD49d were similar regardless of cytokine exposure for the final week of culture. For eosinophils cultured without IL-5, acute stimulation with 10 – 8 mol/L IL-5 increased CD11b surface expression and increased the number of cells adhering to unstimulated human umbilical vein endothelial cells (HUVEC) from 4,570 +/- 780 cells (9.14 +/- 1.56% adhesion) to 8,385 +/- 515 cells (16.8 +/- 1.03% adhesion) (P < .01). Basal adhesion to unstimulated HUVEC of CDE cultured continuously with IL-5 was comparable (8.62 +/- 1.12% adhesion; P = NS), but neither CD11b expression (50.3 +/- 11.8 MSF; P = NS v control) nor adhesion to HUVEC (6.77 +/- 1.35%; P = NS) was enhanced in these eosinophils after acute stimulation with IL-5. Blockade of adhesion to IL-1-stimulated HUVEC caused by the anti-CD49d monoclonal antibody (MoAb), HP2/1, was comparable for cells cultured with IL-5 and without IL-5. However, the anti-CD18 MoAb, R15.7, caused 47.6 +/- 5.08% inhibition of adhesion of eosinophils cultured without IL-5 and only 25.8 +/- 5.20% for cells cultured continuously with IL-5 (P < .01), and failed to block significantly the adhesion of only the latter cells to IL-4-stimulated HUVEC. Our data show that continuous, chronic exposure to low concentrations of IL-5 causes decreased expression of Mac-1 and refractoriness to acute stimulation with IL-5 of adhesion to HUVEC. These data further demonstrate that CDE maturing in the continued presence of IL-5 adhere to HUVEC predominantly through VLA-4 ligation.

scholarly journals Downregulation of the platelet surface glycoprotein Ib-IX complex in whole blood stimulated by thrombin, adenosine diphosphate, or an in vivo wound [see comments]

Blood ◽  
1991 ◽  
Vol 77 (4) ◽  
pp. 770-779 ◽  
Author(s):  
AD Michelson ◽  
PA Ellis ◽  
MR Barnard ◽  
GB Matic ◽  
AF Viles ◽  
...  
Keyword(s):  
Whole Blood ◽  
Actin Polymerization ◽  
Flow Cytometric Analysis ◽  
Adenosine Diphosphate ◽  
Surface Expression ◽  
Surface Glycoprotein ◽  
Platelet Surface ◽  
Granule Secretion

In washed platelet systems, thrombin has been demonstrated to downregulate the platelet surface expression of glycoprotein (GP) Ib and GPIX. In the present study, we addressed the question as to whether, in the more physiologic milieu of whole blood, downregulation of platelet surface GPIb and GPIX can be induced by thrombin, adenosine diphosphate (ADP), and/or by an in vivo wound. Thrombin-induced downregulation of GPIb and GPIX on the surface of individual platelets in whole blood was demonstrated by the use of flow cytometry, a panel of monoclonal antibodies (MoAbs) and, to inhibit fibrin polymerization, the peptide glycyl-L-prolyl-L-arginyl-L-proline. Platelets were identified in whole blood by a GPIV-specific MoAb and exclusion of monocytes by light scattering properties. Flow cytometric analysis of whole blood emerging from a standardized bleeding-time wound established that downregulation of platelet surface GPIb and GPIX can occur in vivo. A GPIb-IX complex-specific antibody indicated that the GPIb and GPIX remaining on the surface of platelets activated in vivo or in vitro were fully complexed. Simultaneous analysis of individual platelets by two fluorophores demonstrated that thrombin-induced platelet surface exposure of GMP-140 (degranulation) was nearly complete at the time that downregulation of platelet surface GPIb-IX was initiated. However, degranulation was not a prerequisite because ADP downregulated platelet surface GPIb-IX without exposing GMP-140 on the platelet surface. Inhibitory effects of cytochalasins demonstrated that the activation-induced downregulation of both GPIX and GPIb are dependent on actin polymerization. In summary, downregulation of the platelet surface GPIb-IX complex occurs in whole blood stimulated by thrombin, ADP, or an in vivo wound, and is independent of alpha granule secretion.

Ultrastructural observations on the in vitro cytoadherence of Plasmodium falciparum infected red blood cells

1990 ◽  
Vol 48 (3) ◽  
pp. 914-915
Author(s):  
D.J.P. Ferguson ◽  
A.R. Berendt ◽  
J. Tansey ◽  
K. Marsh ◽  
C.I. Newbold
Keyword(s):  
Plasmodium Falciparum ◽  
Red Blood Cells ◽  
Blood Cells ◽  
Umbilical Vein ◽  
Cell Types ◽  
Amelanotic Melanoma ◽  
Cytoplasmic Process ◽  
Umbilical Vein Endothelial Cells

In human malaria, the most serious clinical manifestation is cerebral malaria (CM) due to infection with Plasmodium falciparum. The pathology of CM is thought to relate to the fact that red blood cells containing mature forms of the parasite (PRBC) cytoadhere or sequester to post capillary venules of various tissues including the brain. This in vivo phenomenon has been studied in vitro by examining the cytoadherence of PRBCs to various cell types and purified proteins. To date, three Ijiost receptor molecules have been identified; CD36, ICAM-1 and thrombospondin. The specific changes in the PRBC membrane which mediate cytoadherence are less well understood, but they include the sub-membranous deposition of electron-dense material resulting in surface deformations called knobs. Knobs were thought to be essential for cytoadherence, lput recent work has shown that certain knob-negative (K-) lines can cytoadhere. In the present study, we have used electron microscopy to re-examine the interactions between K+ PRBCs and both C32 amelanotic melanoma cells and human umbilical vein endothelial cells (HUVEC).We confirm previous data demonstrating that C32 cells possess numerous microvilli which adhere to the PRBC, mainly via the knobs (Fig. 1). In contrast, the HUVEC were relatively smooth and the PRBCs appeared partially flattened onto the cell surface (Fig. 2). Furthermore, many of the PRBCs exhibited an invagination of the limiting membrane in the attachment zone, often containing a cytoplasmic process from the endothelial cell (Fig. 2).

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