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PubMed1981

Heparin-induced thrombocytopenia: effect of heparin platelet antibody on platelets.

The plasma of two patients with heparin-induced thrombocytopenia has been shown to cause platelet aggregation in the presence of heparin. The platelet aggregating factor was isolated in the IgG reaction of the patients' sera suggesting that it was an antibody. This heparin anti-platelet antibody (HAP-Ab) induced platelet aggregation and release but did not cause platelet lysis, although it fixed complement. Platelet aggregation was inhibited by EDTA and by inactivation of complement. There was a significant production of malondialdehyde (MDA) and thromboxane B2 (TXB2) implying a role of the prostaglandin synthesis pathway in HAP-Ab induced aggregation. ADP-release also appeared to be involved as apyrase blocked aggregation while hirudin, a thrombin inhibitor, had no effect. The thrombotic complications that have recently been reported in patients with heparin-induced thrombocytopenia may be explained by some effects of HAP-Ab on platelets, namely: the antibody mediated platelet factor 3 release, prostaglandin endoperoxides and thromboxane A2 (TXA2) production and platelet aggregation in vivo. These HAP-Ab mediated effects could be inhibited by anti-platelet drugs such as aspirin, indomethacin and dipyridamole and thus may have therapeutic implications.

Adenosine Diphosphate↗
PubMed1986

Different platelet specificities of heparin-dependent platelet aggregating factors in heparin-associated immune thrombocytopenia.

Delayed onset heparin-associated thrombocytopenia (HAT) is thought to be a result of formation of antiplatelet antibodies which cause platelet aggregation in the presence of heparin. Platelet aggregation in response to serum from patients with HAT has been studied in platelet-rich plasma (PRP) from a panel of normal blood donors. Heparin-dependent aggregation with any HAT serum occurred in PRP from only some donors. PRP from the non-responding donors did, however, aggregate in the presence of heparin with other HAT sera. The same patterns of aggregation or lack of response to HAT sera were seen in washed platelet suspensions. Heparin (0.06-2 U/ml) did not cause aggregation in the presence of normal serum with PRP from these donors. However, in PRP from four of the 17 individuals studied, heparin (0.25-1 U/ml) alone caused rapid platelet aggregation and some HAT sera heated at 56 degrees C caused platelet aggregation without added heparin. Sub-aggregating concentrations of adrenaline could replace heparin in promoting aggregation by heated HAT sera in PRP of the other donors. HAT IgG showed the same platelet specificities as the serum in causing either heparin- or adrenaline-dependent aggregation. Thus in HAT, antibodies are directed towards different platelet antigens which are expressed differently in different individuals. Platelet activation by heparin and adrenaline either exposes these antigens or causes aggregation of antibody-coated platelets.

Antibody Specificity↗
PubMed2004

Platelet degranulation and monocyte-platelet complex formation are increased in the acute and convalescent phases after ischaemic stroke or transient ischaemic attack.

Flow cytometric studies suggest that platelets are activated in ischaemic stroke or transient ischaemic attack (TIA). However, few studies have measured circulating leucocyte-platelet complexes in this patient population. Whole blood flow cytometry was used to quantify the expression of CD62P-, CD63-, and PAC1-binding, and the percentages of leucocyte-platelet complexes in acute (1-27 d, n = 79) and convalescent (79-725 d, n = 70) ischaemic cerebrovascular disease (CVD) patients compared with controls without CVD (n = 27). We performed a full blood count, and measured plasma levels of soluble P-selectin, soluble E-selectin, and von Willebrand factor antigen (VWF:Ag) as additional markers of platelet and/or endothelial cell activation. The median percentage CD62P expression and the median percentage monocyte-platelet complexes were higher in both acute and convalescent CVD patients than controls (P </= 0.02). The mean white cell count and mean VWF:Ag levels were significantly elevated in the acute and convalescent phases after ischaemic stroke or TIA (P </= 0.02). Otherwise, there was no significant increase in any other marker of platelet or endothelial activation in CVD patients. There was a positive correlation between the percentage expression of CD62P and the percentages of both neutrophil-platelet and monocyte-platelet complexes in the acute phase, and the percentages of all leucocyte-platelet complexes in the convalescent phase after ischaemic CVD. This study provides evidence for ongoing excessive platelet and/or endothelial activation in ischaemic CVD patients despite treatment with antithrombotic therapy.

Acute Disease↗
PubMed1992

First autoclave-sterilized platelet-additive solution containing glucose with a physiological pH for the preparation of plasma-poor platelet concentrates.

The glucose-free platelet-additive solution (termed AR solution), developed by Adams and Rock [Transfusion 1988;28:217-220], was modified by adding glucose as an energy substrate for platelets and maltose to prevent platelet lysis and by replacing sodium gluconate with sodium phosphate for better pH maintenance. The new platelet-additive solution (termed Seto solution) contained 90 mM NaCl, 5 mM KCl, 3 mM MgCl2, 17 mM tri-sodium citrate, 4.9 mM NaH2PO4, 20.1 mM Na2HPO4, 23 mM sodium acetate, 28.8 mM maltose, and 23.5 mM glucose with a pH of 7.4. The solution was sterilized by autoclaving in plastic bags in nitrogen to prevent glucose caramelization at high pH. Plasma-poor platelet concentrates prepared by adding Seto solution to the pelleted platelet buttons were stored in a LE-2 polyolefin bag at 22 degrees C with constant agitation for 5 days. The platelets suspended in Seto solution maintained oxygen consumption at a rate of 1.1 nmol/min/10(9) platelets after 5-day storage, with glucose consumption and lactate production rates of 0.5 +/- 0.2 and 1.2 +/- 0.2 nmol/min/10(9) platelets, respectively. This resulted in a final mean pH of 7.0. Those suspended in AR solution ceased glycolysis within 3 days because residual plasma glucose had been consumed. This was associated with decreases in percent hypotonic shock response and aggregation induced by adenosine diphosphate and collagen. Lactate dehydrogenase discharge in AR solution was 5 and 8 times higher at day 3 and day 5, respectively, than that of Seto solution. Morphologically, there were no ballooned platelets after storage in Seto solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Platelets↗
PubMed2006

Platelet content and growth factor release in platelet-rich plasma: a comparison of four different systems.

BACKGROUND: Different systems for preparation of platelet-rich plasma are commercially available, but data for comparison of these systems have not been published so far. MATERIALS AND METHODS: We investigated the performance of Vivostat PRF Preparation Kit, PCCS Platelet Concentrate Collection System, Harvest SmartPReP 2 APC 60 Process, and Fibrinet Autologous Fibrin & Platelet System. The preparations provided by these systems are platelet concentrates with high numbers of platelets in a small volume of plasma and PDGF-AB is released continuously during the 5 days after preparation. RESULTS: Vivostat PRF Preparation Kit, PCCS Platelet Concentrate Collection System, Harvest SmartPReP 2 APC 60 Process are comparable in platelet yield and total amount of released PDGF-AB after 120 h while with Fibrinet the lowest platelet yield and PDGF-AB content of supernatant was achieved. The ability of growth factor release was equal in all four systems. CONCLUSION: In conclusion, all four systems for preparation of platelet-rich plasma investigated result in considerable growth factor release. In what extent the total content of PDGF-AB as a consequence of platelet yield has an impact on wound healing has to be further investigated.

Blood Platelets↗
PubMed1985

Measurement of platelet aggregation in diabetics using the new electronic platelet aggregometer.

Platelet function has been studied in diabetic subjects using a new electronic platelet aggregometer which enables platelet aggregation to be studied in whole blood. This may be a more physiological approach to the assessment of platelet behaviour as centrifugation is avoided and platelets are studied in the presence of other blood elements which may be important modulators of platelet function in vivo. Twenty insulin-dependent diabetic subjects were studied along with 20 age and sex-matched controls. Platelet aggregation to collagen (1 microgram/ml) and arachidonic acid (1 mM) was significantly increased in the diabetic group. In addition the sensitivity of diabetic platelets to the antiaggregatory effects of prostacyclin was significantly reduced. A significant inverse correlation was found between platelet sensitivity to prostacyclin and glycosylated haemoglobin concentration in the diabetic group. It is unlikely that the platelet abnormalities in this diabetic group are due to underlying vascular disease as none of the patients had evidence of diabetic complications. These findings may have important implications for the development of vascular disease in diabetics.

Adult↗
PubMed1987

Platelet-leukocyte interaction: activation of rabbit platelets by FMLP-stimulated neutrophils.

1 The effect of the chemotactic peptide, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP) was studied on cells in whole rabbit blood or on a mixture of purified rabbit platelets and neutrophils. 2 In blood, FMLP triggered cell aggregation (measured by electrical impedance) which was dependent upon the concentration of FMLP (9.9 +/- 0.7 and 5.2 +/- 1.2 ohms at 1 and 0.01 microM FMLP respectively). This aggregation was accompanied by a strong decrease in platelet counts (54.6 +/- 6.0 and 45.6 +/- 3.8% for 1 and 0.01 microM FMLP respectively) and by a smaller decrease in neutrophil counts (25.0 +/- 1.9 and 12.9 +/- 1.7% at 1 and 0.01 microM FMLP respectively). 3 When purified platelets and neutrophils were co-incubated, the addition of 0.1 microM induced a marked aggregation (50.0 +/- 1.6 vs. 19.5 +/- 1.6% of light transmission, n = 8, P less than 0.001), ATP secretion (8.4 +/- 1.0 vs. 0.1 +/- 0.1 nmol ml-1, n = 6, P less than 0.001) and a decrease in platelet counts. FMLP induced aggregation of purified neutrophils and release of lysozyme but lacked direct platelet-stimulating effects. The release of lactate dehydrogenase, a cytoplasmic marker and lysozyme were unchanged under the interaction conditions. 4 Platelet activation was reduced by about 30% with 100 microM aspirin or indomethacin and by about 70% with 100 microM BW 755C. Two Paf-acether antagonists, BN 52021 (100 microM) and WEB 2086 (1 microM) suppressed platelet activation by 70-80%. 5 The supernatant of FMLP-stimulated neutrophils induced platelet activation only when bovine serum albumin was present. Rabbit neutrophils stimulated in the presence of serum albumin by 1 microM FMLP formed 2 nM Paf-acether of which half was released to the extracellular medium. 6 Our results indicate that the stimulation of neutrophils by FMLP induces platelet activation in whole blood and on isolated cells and that both arachidonic acid-metabolites and Paf-acether participate in platelet activation.

Acetylglucosaminidase↗
PubMed1982

Function ex vivo of 111In-labelled human platelets. Simultaneous aggregation of labelled and unlabelled platelets induced by collagen.

The function of 111In-labelled platelets has been assessed by collagen-induced aggregation of platelets in samples of whole blood. The blood samples were drawn after injection of autologous 111In-labelled platelets in 19 subjects undergoing platelet kinetic studies. It was thus possible to measure the aggregability of labelled and unmanipulated platelets simultaneously. 111In-labelled platelets aggregated to the same extent as unmanipulated platelets when tested from 10 min to 24 h after injection of the labelled platelets. The results confirm the assumption that minimal damage is inflicted on the platelets during the isolation and labelling procedures, and support the concept that platelets manipulated in vitro may recover in vivo within a few minutes after reinjection.

Blood Platelet Disorders↗
PubMed1987

Type IIB von Willebrand factor with normal sialic acid content induces platelet aggregation in the absence of ristocetin. Role of platelet activation, fibrinogen, and two distinct membrane receptors.

Three preparations of purified von Willebrand factor (vWF), obtained from unrelated patients affected by type IIB von Willebrand disease, were found to have normal sialic acid content (between 129 and 170 nmol/mg of vWF, as compared with 158 +/- 17 nmol/mg in four normal preparations) and to induce platelet aggregation in the presence of physiologic levels of divalent cations and without addition of ristocetin. A monoclonal antibody that blocks the vWF binding domain of the platelet glycoprotein (GP)Ib caused complete inhibition of IIB vWF-induced aggregation. In contrast, a monoclonal antibody that blocks the receptor for adhesive proteins on the platelet GPIIb/IIIa complex failed to inhibit the initial response of platelets to high concentrations of IIB vWF. Moreover, IIB vWF caused agglutination of formalin-fixed platelets that was blocked only by the anti-GPIb antibody, suggesting that the binding of vWF to GPIb, even in the absence of ristocetin, results in platelet-platelet interaction that is followed by exposure of the GPIIb/IIIa receptors for adhesive proteins. Endogenous ADP, normally active platelet metabolism and fibrinogen binding to GPIIb/IIIa were necessary for maximal and irreversible platelet aggregation. In the absence of fibrinogen, however, aggregation was mediated by vWF binding to GPIIb/IIIa. A 52/48-kD tryptic fragment containing the GPIb binding domain of normal vWF completely blocked the aggregation induced by all three IIB vWF preparations. The present study defines in detail the mechanisms involved in IIB vWF-induced platelet aggregation. Moreover, it establishes that the GPIb binding domain of normal and IIB vWF are closely related and that desialylation is not required for the direct interaction of IIB vWF with GPIb.

Apyrase↗
PubMed2004

Fibrin-incorporated vitronectin is involved in platelet adhesion and thrombus formation through homotypic interactions with platelet-associated vitronectin.

When a blood clot is formed, vitronectin (VN) is incorporated. Here we studied the consequence of VN incorporation for platelet interactions under flow. Perfusion of whole blood over a fibrin network, formed from purified fibrinogen, resulted in approximately 20% surface coverage with blood platelets. Incorporation of purified multimeric VN into the fibrin network resulted in a 2-fold increase in surface coverage with platelets and in enhancement of platelet aggregate formation. A human monoclonal antibody (huMab VN18), directed against the multimeric form of VN, inhibited platelet adhesion to the combined fibrin/VN matrix to the level of adhesion on fibrin alone. This inhibition was also shown when whole blood was perfused over a plasma-derived clot. Surprisingly, the inhibitory action of the antibody was not directed toward VN incorporated into the fibrin network but toward VN released from the platelets. We conclude that VN-potentiated platelet-clot interaction requires VN in the clot and multimeric VN bound to the platelet surface. Our results provide evidence that homotypic VN interactions contribute to platelet adhesion and aggregation to a blood clot. This report demonstrates for the first time that self-assembly of VN may provide a physiologically relevant contribution to platelet aggregation on a blood clot.

Antibodies, Monoclonal↗
PubMed2005

Platelet-derived soluble factors induce human extravillous trophoblast migration and differentiation: platelets are a possible regulator of trophoblast infiltration into maternal spiral arteries.

In early pregnancy, human extravillous trophoblasts (EVTs) invade and remodel maternal arteries. We have previously demonstrated that CCR1 is expressed on perivascular/endovascular trophoblasts and that CCR1 ligands promote EVT migration. In this study, we examined the physiologic roles of platelet-derived chemoattractants on EVT invasion. By immunohistochemistry, maternal platelets were localized among endovascular trophoblasts within the lumen of spiral arteries. Extracellular matrices (ECMs) were also detected among endovascular trophoblasts and platelets, suggesting that the platelets in these arteries were activated by ECMs. In vitro, platelets attached to EVTs isolated from human villous explant cultures and expressed P-selectin on the cell surface. Platelets significantly enhanced migration of EVTs without affecting proliferation of EVTs or secretion of MMP-2 or MMP-9. The invasion-enhancing effect of platelet-derived culture medium on EVTs was neutralized by anti-CCR1 antibody. Heat treatment completely abrogated the invasion-promoting effects of platelet-derived culture medium, but charcoal stripping did not. Platelets also induced endovascular trophoblast-like morphologic changes and integrin alpha1 expression in EVTs during 48-hour culture. These findings suggest that maternal platelets activated in the spiral arteries can regulate trophoblastic vascular infiltration and differentiation by releasing various soluble factors.

Arteries↗
PubMed2001

Platelet glycoprotein V binds to collagen and participates in platelet adhesion and aggregation.

Glycoprotein V (GPV) is a subunit of the platelet GPIb-V-IX receptor for von Willebrand factor and thrombin. GPV is cleaved from the platelet surface during activation by thrombin, but its role in hemostasis is still unknown. It is reported that GPV knockout mice had a decreased tendency to form arterial occluding thrombi in an intravital thrombosis model and abnormal platelet interaction with the subendothelium. In vitro, GPV-deficient platelets exhibited defective adhesion to a collagen type I-coated surface under flow or static conditions. Aggregation studies demonstrated a decreased response of the GPV-deficient platelets to collagen, reflected by an increased lag phase and reduced amplitude of aggregation. Responses to adenosine diphosphate, arachidonic acid, and the thromboxane analog U46619 were normal but were enhanced to low thrombin concentrations. The defect of GPV null platelets made them more sensitive to inhibition by the anti-GPVI monoclonal antibody (mAb) JAQ1, and this was also the case in aspirin- or apyrase-treated platelets. Moreover, an mAb (V.3) against the extracellular domain of human GPV selectively inhibited collagen-induced aggregation in human or rat platelets. V.3 injected in rats as a bolus decreased the ex vivo collagen aggregation response without affecting the platelet count. Finally, surface plasmon resonance studies demonstrated binding of recombinant soluble GPV on a collagen-coupled matrix. In conclusion, GPV binds to collagen and appears to be required for normal platelet responses to this agonist. (Blood. 2001;98:1038-1046)

Animals↗
PubMed2001

Effects of platelet clumping on platelet concentrations measured by use of impedance or buffy coat analysis in dogs.

OBJECTIVE: To determine whether platelet clumps are homogeneously distributed in blood samples, and whether platelet concentrations (PC) obtained by use of impedance and buffy coat analysis can be considered minimum values when platelet clumps are present. DESIGN: Prospective study. SAMPLE POPULATION: 50 blood samples obtained from 30 dogs. PROCEDURE: 10 blood samples containing platelet clumps were used and 10 smears were made from each sample; amount of platelet clumping was graded for all 100 smears. Blood from each of 20 healthy dogs was divided between 2 EDTA tubes before and after platelet clumping was induced by adenosine diphosphate (ADP). The PC for each ADP-treated and untreated sample were measured, using impedance and quantitative buffy coat analyzers. RESULTS: Platelet clumps were evident in all 100 blood smears, but the amount of clumping varied considerably within some samples. Using the impedance analyzer, the PC of ADP-treated samples were significantly lower and never higher than the PC of untreated samples. Using the buffy coat analyzer, some ADP-treated samples had increased PC; however, significant differences were not detected between treated and untreated samples. CONCLUSIONS AND CLINICAL RELEVANCE: Platelet clumping was not homogeneous within blood samples. When platelet clumps were identified by direct examination of blood smears, the PC detected by use of the impedance analyzer could be considered minimum values. In contrast, the PC detected by use of the buffy coat analyzer were sometimes increased. Useful information can be obtained by measuring PC in blood with platelet clumps; values obtained by use of impedance can be considered minimums, and values obtained by use of buffy coat analysis may be either minimum values or reasonable estimates of PC.

Adenosine Diphosphate↗
PubMed1999

Measurement of GPV released by activated platelets using a sensitive immunocapture ELISA--its use to follow platelet storage in transfusion.

Thrombin, the most potent platelet agonist, plays a central role in haemostasis and in the occurrence of thrombotic events. This agonist activates platelets by cleaving the PAR G-protein coupled receptors and by binding to glycoprotein (GP) Ib and also cleaves GPV at the platelet surface to liberate the soluble 69 kDa fragment GPVf1. Monoclonal antibodies (MoAbs) to GPV were developed as tools to study the mechanism of platelet GPV cleavage and measure release of GPV in pathological situations. Specificity of the MoAbs for GPV was confirmed by flow cytometry and immunoprecipitation of proteins from human platelets and Dami megakaryocytic cells. A sensitive immunocapture sandwich ELISA for soluble GPV was developed using two MoAbs recognizing different epitopes of GPV and purified platelet or recombinant GPV as reference protein. This ELISA was employed to determine the mean plasma concentration of GPV in 100 normal individuals (17.3 ng/ml), to demonstrate the dose-dependent release of GPVf1 from washed platelets stimulated with thrombin and to follow the progressive release of GPVf1 during storage of therapeutic platelet concentrates. The present report describes a sensitive GPV ELISA of direct application to survey the processing and storage of platelet concentrates for transfusion and of potential value to monitor platelet activation in thrombotic states.

Animals↗
PubMed2000

Cloning of the human platelet F11 receptor: a cell adhesion molecule member of the immunoglobulin superfamily involved in platelet aggregation.

This study demonstrates that the human platelet F11 receptor (F11R) functions as an adhesion molecule, and this finding is confirmed by the structure of the protein as revealed by molecular cloning. The F11R is a 32-/35-kd protein duplex that serves as the binding site through which a stimulatory monoclonal antibody causes platelet aggregation and granule secretion. A physiological role for the F11R protein was demonstrated by its phosphorylation after the stimulation of platelets by thrombin and collagen. A pathophysiological role for the F11R was revealed by demonstrating the presence of F11R-antibodies in patients with thrombocytopenia. Adhesion of platelets through the F11R resulted in events characteristic of the action of cell adhesion molecules (CAMs). To determine the structure of this protein, we cloned the F11R cDNA from human platelets. The predicted amino acid sequence demonstrated that it is an integral membrane protein and an immunoglobulin superfamily member containing 2 extracellular C2-type domains. The structure of the F11R as a member of a CAM family of proteins and its activity in mediating adhesion confirm each another. We conclude that the F11R is a platelet-membrane protein involved in 2 distinct processes initiated on the platelet surface. The first is antibody-induced platelet aggregation and secretion that are dependent on both the FcgammaRII and the GPIIb/IIIa integrin and that may be involved in pathophysiological processes associated with certain thrombocytopenias. The second is an F11R-mediated platelet adhesion that is not dependent on either the FcgammaRII or the fibrinogen receptor and that appears to play a role in physiological processes associated with platelet adhesion and aggregation. (Blood. 2000;95:2600-2609)

Amino Acid Sequence↗
PubMed2000

Occurrence of amphoterin (HMG1) as an endogenous protein of human platelets that is exported to the cell surface upon platelet activation.

Amphoterin (HMG1) is a 30-kD heparin-binding protein which is functionally associated with the outgrowth of cytoplasmic processes in developing neurones. Amphoterin has been shown to mediate adhesive and proteolytic interactions at the leading edge of motile cells. Recently it was shown that inhibition of amphoterin interactions with its cell surface receptor (RAGE) suppresses tumour growth and metastasis. In this work we have identified amphoterin polypeptide and its mRNA in human platelets. Amphoterin had a cytoplasmic localisation in resting platelets according to subcellular fractionation studies and immunogold electronmicroscopy. After platelet activation, part of amphoterin was associated with the external surface of plasma membrane. Externalisation of amphoterin during platelet activation was also detected in immunofluorescence studies. Amphoterin was detectable in human serum (0.2 ng/ml) but not in plasma. Resting platelets treated with PGI2 and forskolin bound to immobilised recombinant amphoterin independently of divalent cations. The binding induced a spicular morphology in platelets, and was effectively inhibited by heparin. Amphoterin-binding protein components on the platelet surface were not identified, but amphoterin bound to phosphatidylserine and sulfatide in lipid binding assays. Our results suggest that amphoterin is an endogenous protein in human platelets, which is exported to the cell surface during platelet activation. Interaction of amphoterin with the platelet surface may be mediated by sulfoglycolipids and phospholipids.

Blood Platelets↗
PubMed2001

Platelet activation and platelet-erythrocyte aggregates in end-stage renal disease patients on hemodialysis.

Activated platelets may engage in dynamic interplay with other blood cells. We examined the evidence for platelet activation and the formation of platelet-erythrocyte aggregates in chronic hemodialysis patients. Circulating activated platelets (P-selectin/CD63-positive platelets) were higher than normal controls (p < 0.001) and further increased during hemodialysis sessions, the increase being higher when patients were dialyzed with cellulosic than with synthetic membranes. We found direct evidence of uremic platelet-erythrocyte adherence in vitro and increased levels of circulating platelet-erythrocyte aggregates in dialysis patients, which represents a new observation in uremia. Platelet-erythrocyte aggregates were subject to further increase during hemodialysis, and again higher levels were found with cellulosic than synthetic membranes. This phenomenon was reproduced in vitro by both ADP and PAF, but not by either complement factor C3a or by heparin concentrations corresponding to those used for clinical hemodialysis. We conclude that platelet-erythrocyte aggregates occur in hemodialysis patients probably owing to a primary platelet activation mechanism.

Adenosine Diphosphate↗
PubMed2002

Transfer of tissue factor from platelets to monocytes: role of platelet-derived microvesicles and CD62P.

Tissue factor (TF) is the most important initiator of intravascular coagulation. Platelets contribute to TF exposure on monocytes, but the mechanism is not completely understood. Here we examined the possibility that platelets may release TF that can be transferred to monocytes by platelet-derived microvesicles. When human citrated platelet-rich plasma was incubated with collagen there was an increase in the plasma levels of TF and CD62P. Incubation of plasma obtained from collagen-stimulated PRP with a sediment of red and white blood cells resulted in an increase in the number of monocytes that express TF, CD62P and the platelet-specific antigen CD42a on their surface. This transfer of platelet-derived antigens to monocytes was reduced when CD62P was blocked by a specific antibody or when platelet-derived microvesicles were removed from the plasma either by high speed centrifugation (17,500 x g for 30 min) or by filtration (pore size 0.2 microm). The data indicate that platelet-derived microvesicles that are released from collagen-stimulated platelets may carry TF, CD62P and CD42a and may transfer these antigens to the surface of monocytes. The interaction of platelet-derived microvesicles with monocytes and the transfer of TF to monocytes strongly depend on CD62P.

Blood Platelets↗