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Biomedical subjects

G Escolar

Publications and source records attributed to G Escolar.

At least 91 records · Page 5Linked to original sources
PubMed1996

Procoagulant effect of incompatible platelet transfusions in alloimmunized refractory patients.

The clinical effectiveness of platelet transfusion in refractory patients is still a subject of debate. We have evaluated the possible hemostatic effect of platelet transfusion in 16 alloimmunized thrombocytopenic patients whose platelet counts were less than 20,000/microliters. Platelet concentrates were always obtained by apheresis procedures from incompatible donors. The posttransfusion platelet recovery was greater than 15% only in 3 cases. In the first 6 patients, measurements of bleeding time performed immediately before transfusion were in all cases longer than 30 min and did not change significantly 10 and 60 min after platelet transfusions. In all patients, ex vivo perfusion experiments with Baumgartner's platelet adhesion model, using native nonanticoagulated blood, were performed immediately before and 10 and 60 min after transfusion. No difference in platelet deposition onto the subendothelial surface was observed after platelet transfusion. Unexpectedly, the deposition of fibrin on the subendothelial surface was statistically augmented in the posttransfusion studies. Quantification of thrombin-antithrombin complexes (TAT) in plasma showed statistically significant elevations (p < 0.01) in the posttransfusion samples (31.9 +/- 12.6 vs. baseline 5.8 +/- 1.7 ng/ml), not justified by TAT levels in the transfused material (2.3 +/- 0.17 ng/ml). Transfusion of incompatible platelets to refractory patients may activate coagulation mechanisms in the absence of an increase in peripheral platelet count.

Blood Group Incompatibility↗
PubMed1996

Existence of a platelet-adhesion defect in patients with cirrhosis independent of hematocrit: studies under flow conditions.

A defect in hemostasis has been repeatedly reported in patients with cirrhosis. However, the nature of this defect has not been fully characterized. We explored adhesive and cohesive functions of platelets from cirrhotic patients at different stages of disease development. The response of platelets to standard activating agents was tested by aggregometric procedures. The interaction of platelets with subendothelial components was explored in a perfusion system in which blood was exposed (shear rate, 800/s; 10 minutes) to denuded segments of rabbit aorta. Platelet interactions in these perfusions were analyzed morphometrically. Results were always compared with those obtained in similar studies using blood obtained from healthy subjects. Aggregation studies showed abnormal responses for single or several agonists. Abnormalities in aggregation were more evident in patients with severe disease (Child-Pugh class C), although they occasionally were abnormal for single agonists (ADP or U46619) in patients with less severe disease (Child-Pugh classes A or B). All the patient classes showed impaired platelet-subendothelial interactions (P < .01 vs. healthy subjects) that were not justified by the relative thrombocytopenia present in the more severely affected patients. Experimental increases in hematocrit in patients at stages B and C did not improve platelet-subendothelial interactions. Platelets from cirrhotic patients interact defectively with subendothelial components under flow conditions. The adhesion defect is more evident and consistent than the aggregation defects and may already be present in patients with mild liver failure. This adhesion defect may contribute to the defective hemostasis observed in cirrhotic patients.

Adult↗
PubMed1996

Antibodies to endothelial cells and to beta 2-glycoprotein I in the antiphospholipid syndrome: prevalence and isotype distribution.

The aim of this study was to analyse the prevalence and isotype distribution of antibodies to endothelial cells (aEC) and to beta 2-glycoprotein I (a beta 2GPI) in the antiphospholipid syndrome (APS). Fifteen patients with an APS [nine associated with systemic lupus erythematosus (SLE) and six "primary'] and 15 with SLE without an APS were prospectively studied. The aEC were determined by an enzyme-linked immunosorbent assay (ELISA) using endothelial cells derived from human umbilical vein and the a beta 2GPI by ELISA using highly purified beta 2GPI. A positive titre of aEC was detected in 20 out of 30 patients (67%), but in none of the control group. Ten patients had both IgG and IgM isotypes, five had IgG only and five had only IgM. Thirteen patients with the APS (87%) were found to have a positive titre of aEC, while only seven with SLE but without a history of APS (47%) had aEC (P < 0.05). Nine patients with the APS (60%) had a positive titre of a beta 2GPI (four had both IgG and IgM isotypes, one had IgG only and four had only IgM), while none of the patients without an APS (0%) had these antibodies (P < 0.001). A significant association was also found between the presence of aPL and aEC (P < 0.05), as well as between aPL and a beta 2GPI (P < 0.001). Both aEC and a beta 2GPI can be found in the APS. This reinforces the theory that APS represents a complex autoimmune disorder in which several autoantibodies co-exist with aPL.

Adult↗
PubMed1996

Redistribution of membrane glycoproteins in platelets activated under flow conditions.

A reduction in the ability of GPIb to bind specific MoAbs or ligands (vWF) has been reported in platelets exposed to thrombin in suspension. We have analyzed modifications in the presence of glycoproteins (GPs) on platelets activated under flow conditions in a system which allows limited thrombin and fibrin generation. Normal blood anticoagulated with low molecular weight heparin (LMWH, Dalteparin 20 IU/ml) was recirculated for up to 10 min at 800 s-1 through annular chambers containing denuded arterial segments. Aliquots of blood were removed from the reservoir at 0, 1, 5 and 10 min and immediately mixed with paraformaldehyde. Membrane glycoproteins: GPIb (CD42b), GPIIb-IIIa (CD41a), GPIV (CD36); and activation dependent antigens: P-selectin (CD62P) and lysosomal glycoprortein (CD63), were detected in whole blood by dual color flow cytometry. Circulation of through the perfusion system resulted in platelet activated as demonstrated by the increased percentage of platelets positive for antigens CD62P and CD63. A gradual increase in the binding of MoAbs directed against GPIb, GPIIb-IIIa, and GPIV epitopes was noted during the entire perfusion period. Observed differences in mean fluorescence intensities at all the observation times were statistically significant (P < 0.001). Our results obtained on platelets in an experimental thrombosis system indicate that GPIb, GPIIb-IIIa and GPIV remain on the surface of activated platelets and actually increase their expression. Alterations detected at the level of GPIb in platelets activated by thrombin in suspension may not take place under in vivo situations.

Antibodies, Monoclonal↗
PubMed1996

Fate of the GPIb/IX receptor complex following activation of human platelets.

Many excellent workers have concluded that platelet glycoprotein Ib/IX complex, the receptor for von Willebrand factor (vWF) is down-regulated in its ability to bind vWF or monoclonal antibodies and virtually cleared from the exterior surface to internal membranes following exposure of the cells to thrombin in suspension. Studies carried out in our laboratory, however, have not supported the concept of down-regulation or clearance. Experiments employing aggregation-disaggregation-reaggregation, agglutination and flow cytometry have demonstrated that physiologic levels of calcium ions prevent or reverse the phenomenon of down-regulation. GPIb/IX receptors remain edge to edge on surface-activated platelets, whether or not the cells are also exposed to thrombin before or after spreading. Addition of two ligands, fibrinogen labeled gold to mark GPIIb/IIIa and vWF to identify GPIb/IX, to discoid platelets before surface activation demonstrates that GPIIb/IIIa is a mobile receptor that concentrates with its ligand in cell centers while vWF bound to GPIb/IX moves with the membrane as it expands to the lateral edges of spread cell margins. Immunogold studies of thrombin-activated platelets in suspension reveal no clearance of GPIb/IX receptors, bound or not to vWF, from exposed surfaces to internal membranes. The clearance to the OCS reported by others may be due to difficulties encountered in staining GPIb/IX lining OCS channels in resting discoid platelets.

Blood Platelets↗
PubMed1996

Platelet sensitivity to prostaglandin E1 inhibition is reduced in pre-eclampsia but not in nonproteinuric gestational hypertension.

OBJECTIVE: Platelet aggregometry was used to discriminate platelet sensitivity to prostaglandin E1 (PGE1) inhibition, to evaluate whether platelet behaviour in pre-eclamptic women was different in this respect than from that in nonproteinuric hypertensive women. METHODS: The amount of PGE1 required to inhibit in vitro platelet aggregation induced by arachidonic acid was determined in samples from 60 women: 20 nonpregnant controls, 20 women with normal pregnancies, 10 women with gestational hypertension and 10 with pre-eclampsia. RESULTS: The response to arachidonic acid was similar among the four groups. Amounts of PGE1 necessary to inhibit platelet aggregation were significantly higher in normal pregnant women compared with nonpregnant controls (P<0.001). Platelets from pre-eclamptic women required significantly higher concentrations of PGE1 to inhibit aggregation than the other groups studied (P<0.001). However, there was no significant difference between normal and nonproteinuric hypertensive pregnant women. CONCLUSIONS: Our findings support the notion that increased platelet reactivity during late pregnancy is exacerbated in pre-eclamptic women but not in nonproteinuric hypertensive women. This is in agreement with the hypothesis that pre-eclampsia and gestational hypertension are different conditions. Prospective studies are required to confirm if this simple test may be useful in the early identification of pregnant women at risk for pre-eclampsia.

Adult↗
PubMed1996

Hypercoagulable state in patients with antiphospholipid syndrome is related to high induced tissue factor expression on monocytes and to low free protein s.

Antiphospholipid antibodies (aPLs) are associated with thrombosis, but the mechanisms of this thrombotic tendency are unknown. We studied 56 patients 612 with systemic lupus erythematosus [SLE] and aPLs and previous thrombosis, 12 with SLE and aPLs but no thrombosis, 15 with SLE without aPLs or thrombosis, 11 with primary antiphospholipid syndrome with thrombosis, and 6 asymptomatic subjects with aPLs) to investigate the ability of aPLs to induce tissue factor (TF) expression on human normal monocytes. A double direct immunofluorescence technique (anti-CD14 and anti-TF) was used, and procoagulant activity in viable and disrupted cells was measured after plasma incubation for 6 hours at 37 degrees C with normal mononuclear cells. Hemostasis regulatory proteins, prothrombin fragment 1 + 2, and thrombin-antithrombin III complex levels were determined. Increased TF expression and procoagulant activity were observed using plasma samples from SLE patients with aPLs and thrombosis (P < .01) and from primary antiphospholipid syndrome patients (P < .01) but not from patients with SLE and aPLs but no thrombosis, patients with SLE without aPLs, or asymptomatic patients with aPLs. Purified aPL immunoglobulins from one primary antiphospholipid syndrome and two SLE patients added to normal plasma showed a significant increase in both TF expression and procoagulant activity (P < .05) compared with purified aPL from two SLE patients without thrombosis. The addition of nonspecific IgG from three SLE patients without aPLs and from three control subjects did not increase TF expression. Low free protein S was seen in eight patients. Increased TF expression and low free protein S correlated with thrombosis (P < .01) and with higher prothrombin fragment 1 + 2 and thrombin-antithrombin III values (P < .01). These observations may contribute to a further understanding of the thrombotic risk in aPL patients.

Antiphospholipid Syndrome↗
PubMed1996

Uptake of vWF-anti-vWF complexes by platelets in suspension.

Efforts to identify the translocation of glycoprotein (GP) Ib/IX receptors, either bound to von Willebrand factor (vWF) or not, from exposed surfaces to interior membranes of thrombin-activated platelets in suspension have been unsuccessful. To observe vWF uptake by platelets, we added an anti-vWF antibody and staphylococcal protein A-gold (to act as a marker for the antibody) to an incubation medium containing washed platelets and bovine plasma vWF or ristocetin-activated human vWF. Thin sections of platelets incubated for 10, 20, or 30 minutes with vWF but without antibody revealed no internalization and minimal changes in the original discoid form. Over the same 30-minute period with anti-vWF, however, GPIb/IX-vWF-anti-vWF complexes were cleared from cell exteriors to channels of the open canalicular system. Engorgement of the open canalicular system with vWF multimers resulted in changes in shape, internal transformation, and degranulation. Physical changes associated with anti-vWF-induced uptake of vWF are not seen in platelets that are involved in hemostatic plug formation or clot retraction.

Animals↗
PubMed1996

Antibodies to CD36 (GPIV) inhibit platelet adhesion to subendothelial surfaces under flow conditions.

The membrane glycoprotein CD36 (glycoprotein [GP] IV) has previously been shown to accelerate the initial interaction of platelets with purified type I collagen in both static and flow systems. In the present study, the role of CD36 on platelet interaction with physiologically relevant collagenous surfaces was addressed. Using arterial subendothelium (SE) and endothelial cell extracellular matrix (ECM), studies were performed under flow conditions with annular and parallel-plate perfusion chambers, respectively, at a shear rate of 800 s-1 for 2, 5, and 10 minutes. Perfusates consisted of citrated normal blood samples incubated with Fab fragments of a monospecific polyclonal anti-CD36 antibody or with each of three new anti-CD36 monoclonal antibodies (MoAbs) that inhibit platelet adhesion to purified type I collagen in a static system (131.4, 131.5, and 131.7). Perfusions over SE were also carried out using citrated blood samples from a Naka-negative donor, whose platelets lack CD36. Morphometric evaluation of the perfused samples showed that polyclonal anti-CD36 Fab and the three monoclonal anti-CD36 antibodies inhibited platelet adhesion to the two substrates by 40% after 2 minutes of perfusion and by 30% after 5 minutes (P < .005 on SE and P < .01 on ECM), but at 10 minutes, significant inhibition was seen only on SE with polyclonal anti-CD36 Fab. Similar inhibitions were seen with Naka-negative platelets on SE. These studies demonstrate that CD36 plays a role in the early stages of platelet adhesion to physiologically relevant subendothelial surfaces.

Antibodies, Monoclonal↗
PubMed1996

Prelabeled glycoprotein Ib/IX receptors are not cleared from exposed surfaces of thrombin-activated platelets.

The present investigation has re-examined the hypothesis proposing that glycoprotein (GP)Ib/IX receptors for von Willebrand factor are rapidly cleared from exposed surfaces to internal membrane systems after activation of platelets by thrombin in suspension. Platelets were prelabeled with either a polyclonal antibody to GPIb alpha, antiglycocalicin (A-Gl), or a cocktail of two monoclonal antibodies, AP1 and 6D1, exposed to 0.1 or 0.2 U/ml thrombin for 5 or 10 minutes, fixed and stained with Staphylococcus protein A coupled to gold to detect A-Gl or goat anti-mouse IgG bound to gold particles to locate AP1 and 6D1 before or after preparation of frozen thin sections or embedding for plastic thin sections. The frequency and distribution of protein-A-gold markers for GPIb/IX on thrombin-activated platelets viewed in thin plastic sections did not differ from the density on resting platelets stained with A-Gl. Cryosections of A-Gl-prelabeled platelets labeled again on cryosections revealed GPIb present on linings of the open canalicular system of resting and activated platelets, but the density of gold in interior channels and frequency of gold particles on exterior surfaces were not altered by thrombin stimulation. Platelets prelabeled with the cocktail of 6D1 and AP1 and studied in cryosections also failed to reveal uptake of GPIb/IX receptors into the open canalicular system after activation by thrombin. The findings do not support the concept that thrombin causes clearance of GPIb/IX receptors from exterior surfaces to interior membranes of activated platelets.

Antibodies↗
PubMed1995

Retention of glycoprotein Ib/IX receptors on external surfaces of thrombin-activated platelets in suspension.

The present study has evaluated the hypothesis stating that glycoprotein (GP) Ib/IX, the receptor for von Willebrand factor (vWF), is downregulated and cleared from exposed surfaces to channels of the open canalicular system (OCS) on platelets activated by thrombin in suspension. Cryosections of resting and thrombin-activated platelets fixed at intervals of 1 to 30 minutes after stimulation by thrombin and stained with antiglycocalicin antibody and protein A gold showed no decrease in the density of GPIb/IX receptors on the platelet surface or increase on linings of the OCS at any interval after stimulation by thrombin. Thin sections of platelets exposed to thrombin in suspension followed by settling onto a plastic chamber for intervals of 1 to 30 minutes revealed retention of GPIb/IX receptors on exposed surfaces detected by vWF, anti-vWF, and protein A gold throughout the 30-minute period of study. Results of this investigation indicate that GPIb/IX receptors remain on the surface of platelets activated by thrombin in suspension, are not cleared to the OCS, and retain the ability to bind vWF for at least 30 minutes.

Blood Platelets↗
PubMed1995

[Hemorrhagic incidents during prolonged ambulatory treatment with acenocoumarol].

BACKGROUND: To analyze hemorrhagic complications in a series of outpatients treated with acenocoumarol in an anticoagulant specialized unit by a prospective observational clinical study. PATIENTS AND METHODS: 1,200 outpatients (682 women/518 men, mean age 54.6 +/- 15.8 yrs.) treated with acenocoumarol for at least 6 weeks, with a total follow-up of 2,795 patients-yr. Prevalence and incidence of bleeding was analyzed. The episodes that were potentially life-threatening, or forced to blood transfusion or hospital patient admittance were considered as major bleedings, and the remainder episodes were minor. RESULTS: There were 379 minor bleedings in 258 patients (incidence 13.56/100 patients-yr.), 45 major bleedings (1.61/100 patients-yr.) and 2 lethal bleedings (0.07/100 patients-yr.). Minor bleedings correlated with more advanced age (57.3 +/- 11.8 vs. 53.9 +/- 16.7 yrs., p = 0.002), with the first two months in treatment in the 511 patients who start the treatment during the study (31.09 vs. 13.04/100 patients-yr., p < 0.001), and with a worse achievement of the desired anticoagulation (72.4% vs. 81.6%; p = 0.002). Major bleeding was associated with local causes in 48.9%, and with an excessive anticoagulation in 35.6%. CONCLUSIONS: Bleeding is relatively frequent during acenocoumarol therapy, mainly in patients with worse control, but only in a few of these episodes is severe, and is usually associated with local lesions.

Acenocoumarol↗
PubMed1995

Reticulated platelets in uremic patients: effect of hemodialysis and continuous ambulatory peritoneal dialysis.

Platelet RNA content can be detected by flow cytometry using thiazole orange staining to identify platelets recently released into the circulation. We studied platelet RNA content and platelet function in uremic patients under different treatment regimens. Four groups were studied: (I) 15 end-stage renal disease (ESRD) patients (10M/5F) on maintenance hemodialysis (HD); (II) 11 ESRD patients (6M/5F) on continuous ambulatory peritoneal dialysis (CAPD); (III) 8 patients with chronic renal failure managed conservatively (5M/3F); and (IV) 34 controls (20M/14F). A double color labeling technique using a phycoerythrin-tagged antibody against glycoprotein Ib (CD42b) and RNA labeling by thiazole orange was performed and read by flow cytometry. Aggregation studies were made in platelet-rich plasma using ADP, epinephrine, collagen, arachidonic acid, and ristocetin. In group I, samples were also obtained after HD. Platelet counts did not differ among the groups. Aggregation studies showed a lower response to ADP and ristocetin in the HD patients, but not in the CAPD or in the chronic renal failure patients. The percentage of platelets with high RNA content in group I was significantly lower than in controls (3.72 +/- 1.72% vs. 9.05 +/- 3.53%, P < 0.01), but was also lower than in the remaining groups (I vs. II P < 0.01, and I vs. III P < 0.01). No differences were seen in platelet RNA content among groups II (8.67 +/- 2.73%), III (9.14 +/- 3.04%) and IV. In group I, the percentage of reticulated platelets decreased further after HD (2.14 +/- 1.09%, P < 0.01). Aggregation studies showed a significantly lower response to ADP and ristocetin in group I (P < 0.05), but not in groups II or III in comparison with controls. Aggregation response to ADP and ristocetin decreased after HD (P < 0.05). In conclusion, HD may decrease the percentage of RNA-rich platelets through elimination of the younger and more active platelets and worsen the thrombopathy present in uremic patients.

Adult↗
PubMed1995

Platelet concentrates promote procoagulant activity: evidence from experimental studies using a perfusion technique.

BACKGROUND: Evaluation of the hemostatic effectiveness of platelet transfusions is difficult. Perfusion methods have been employed to test the quality and function of platelet concentrates, allowing differentiation between platelet-platelet and platelet-surface interactions. STUDY DESIGN AND METHODS: A study was performed to investigate platelet adhesive and cohesive properties as well as the formation of fibrin when aliquots of platelet concentrates were added to thrombocytopenic blood. Blood previously anticoagulated with low-molecular-weight heparin (20 U/mL) underwent platelet and white cell reduction by filtration. Perfusates were prepared by adding to filtered blood platelets obtained from standard concentrates (stored for 1, 3, and 5 days). The final platelet count in these perfusates was standardized at 80,000 per microL. After perfusions, platelet-subendothelium interaction and fibrin formation were analyzed morphometrically. Results were always compared with those obtained in unfiltered blood (> 150,000 platelets/microL). RESULTS: A slight impairment in the ability of stored platelets to interact with the subendothelium was noticed during the storage period. However, the presence of fibrin was significantly greater than that observed in studies with unfiltered blood (Day 1 = 23.48 +/- 9.43%*; Day 3 = 26.99 +/- 6.74%*; Day 5 = 17.95 +/- 9.06% vs. unfiltered blood = 12.60 +/- 3.08%; *p < 0.05). The lower platelet counts (80,000/microL) in the perfusates containing platelets from concentrates could account for the reduced platelet-subendothelium interactions, but they cannot explain the increments in fibrin formation. CONCLUSION: While the preparation and storage of platelets have a detrimental effect on platelet adhesiveness, such procedures can positively influence the platelet procoagulant activity necessary to platelet hemostasis.

Animals↗
PubMed1995

Uraemic medium causes endothelial cell dysfunction characterized by an alteration of the properties of its subendothelial matrix.

Uraemic patients suffer from haemorrhagic disorders and accelerated atherosclerosis. To evaluate the possible role of the vessel wall in these haemostatic alterations associated with uraemia, we investigated the effect of a uraemic milieu on human endothelial cell (EC) cultures and the reactivity of the extracellular matrices (ECM) generated by these cells towards platelets. EC cultures were exposed to a pool of sera (20% in the culture medium) obtained either from uraemic patients or from normal donors, and the following parameters were evaluated: (1) EC viability (trypan blue exclusion test); (2) von Willebrand factor (vWF) levels in supernatants and associated with ECM; (3) the reactivity of EC and EC-derived ECM towards platelets, measured 'ex vivo' under flow conditions (5 min, wall shear rate 800 s-1); and (4) ultrastructure of the ECM. The viability of EC cultured in the presence of uraemic sera was similar to controls. Platelet interaction with ECM generated by EC exposed to uraemic sera was significantly reduced (P < 0.05). This decrease was mainly related to a reduction in platelet adhesion (9.8 +/- 1.9% vs 16.7 +/- 1.8% in controls, P < 0.02). VWF levels in supernatants and associated with ECM were similar to controls. Ultrastructural analysis of the ECM generated by EC exposed to uraemic sera revealed a deficient matrix. An increased removal of EC was observed in experiments in which EC cultured in the presence of uraemic sera were perfused with citrated blood. These results indicate that a uraemic milieu induces quantitative and qualitative changes in the vascular subendothelium, characterized by a less intrincate network of fibrils, as well as a decreased attachment of EC and reduced thrombogenicity to the ECM. These changes may represent another mechanism which contributes to the haemostatic dysfunction observed in uraemic patients.

Blood Platelets↗
PubMed1995

Redistribution of GPIb/IX and GPIIb/IIIa during spreading of discoid platelets.

The purpose of the present study was to prelabel mobile receptors on discoid platelets with specific ligands identifiable in the electron microscope and follow their redistribution during spreading. Platelets were incubated in suspension with cytochalasin E (CE) to preserve discoid form, chilled and mounted on cold formvar grids or glass slide fragments to inhibit receptor movement, covered with cold bovine or ristocetin-activated human plasmas as sources of vWF to bind GPIb/IX, fibrinogen-coated gold particles (Fgn/Au) to couple GPIIb/IIIa, or both probes simultaneously, washed to remove CE and rewarmed to 37 degrees C for intervals up to 30 min to stimulate spreading. After brief fixation grids and glass fragments were incubated with anti-vWF antibody and, subsequently, staphylococcal protein A coupled to 5 nm and 10 nm gold particles to detect vWF multimers. Virtually all of the CE-treated chilled platelets retained their discoid shape. Half of the discs (53.3%) bound Fgn/Au, and all bound vWF. Receptors for both ligands were randomly dispersed on discoid cells from edge to edge. During rewarming discoid platelets expanded into spread forms. Fgn/Au-GPIIb/IIIa complexes moved into caps over cell centres and into residual channels of the open canalicular system (OCS). vWF bound to GPIb/IX moved with the cell membrane as the surface expanded during spreading. Discoid platelets prelabelled with both ligands demonstrated similar findings. During rewarming Fgn/Au-GPIIb/IIIa complexes moved to cell centres and into OCS channels. vWF multimers bound to GPIb/IX moved apart from each other toward peripheral margins of the spread cells. Thus, surface activation resulting in conversion of discoid platelets to spread forms does not cause clearance of GPIb/IX receptors to cell centres and channels of the OCS in the manner that GPIIb/IIIa receptors coupled to Fgn/Au are simultaneously translocated and concentrated in OCS channels.

Blood Platelets↗
PubMed1995

Induction of GPIb/IX-vWF receptor-ligand translocation on surface-activated platelets.

Multimers of von Willebrand factor (vWF) readily bind to glycoprotein (GP) Ib/IX receptors on spread human platelets and cover the cell from edge to edge. Addition of anti-vWF antibody to spread platelets covered with vWF caused the multimers to move from peripheral margins into caps over platelet centers. Despite almost complete centralization of receptor-ligand complexes, a significant number of GPIb/IX receptors capable of binding multimers remained available on the peripheral zone. Fixation followed by a second incubation with vWF, anti-vWF, and staph protein A coupled to 5-nm gold particles (PAG5) revealed multimers extending from the centrally concentrated cap of vWF to cell margins. If spread platelets with central caps of vWF were exposed a second time to multimers and anti-vWF antibody before fixation and stained with PAG5 after, the residual GPIb/IX receptors and second wave of vWF formed a ring around the cap, leaving a clear margin. If after fixation and staining with PAG5 the grids with caps and rings of vWF were washed, exposed a third time to vWF, refixed, and then incubated with anti-vWF and PAG10, the clear margin was covered with multimers of vWF forming a second ring around the first circle of receptor-ligand complexes. Thin sections of spread platelets with central caps of GPIb/IX-vWF complexes revealed only rare examples of uptake by the open canalicular system. The interaction of GPIb/IX with vWF multimers observed in the present study suggests a mechanism by which platelets under high shear forces may adhere and attach firmly to a denuded vascular surface.

Antibodies↗