scholarly journals Association of lipoprotein(a) with intrinsic and on-clopidogrel platelet reactivity

2021 ◽  
Author(s):  
Alexander Kille ◽  
Thomas Nührenberg ◽  
Kilian Franke ◽  
Christian M. Valina ◽  
Gregor Leibundgut ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Platelet Activation ◽  
Platelet Reactivity ◽  
Laboratory Data ◽  
Adenosine Diphosphate ◽  
Surface Proteins ◽  
Activation Markers ◽  
Platelet Surface ◽  
Lipoprotein A ◽  
Artery Disease

AbstractLipoprotein(a) [Lp(a)] is an independent, genetically determined, and causal risk factor for cardiovascular disease. Laboratory data have suggested an interaction of Lp(a) with platelet function, potentially caused by its interaction with platelet receptors. So far, the potential association of Lp(a) with platelet activation and reactivity has not been proven in larger clinical cohorts. This study analyzed intrinsic platelet reactivity before loading with clopidogrel 600 mg and on-treatment platelet reactivity tested 24 h following loading in patients undergoing elective coronary angiography. Platelet reactivity was tested by optical aggregometry following stimulation with collagen or adenosine diphosphate as well as by flow cytometry. Lp(a) levels were directly measured in all patients from fresh samples. The present analysis included 1912 patients. Lp(a) levels ranged between 0 and 332 mg/dl. There was a significant association of rising levels of Lp(a) with a higher prevalence of a history of ischemic heart disease (p < 0.001) and more extensive coronary artery disease (p = 0.001). Results for intrinsic (p = 0.80) and on-clopidogrel platelet reactivity (p = 0.81) did not differ between quartiles of Lp(a) levels. Flow cytometry analyses of expression of different platelet surface proteins (CD41, CD62P or PAC-1) confirmed these findings. Correlation analyses of levels of Lp(a) with any of the tested platelet activation markers did not show any correlation. The present data do not support the hypothesis of an interaction of Lp(a) with platelet reactivity.

Association of Lipoprotein(a) levels with intrinsic and on-clopidogrel platelet reactivity

2020 ◽  
Vol 41 (Supplement_2) ◽  
Author(s):  
A Kille ◽  
T Nuehrenberg ◽  
C.M Valina ◽  
F.J Neumann ◽  
W Hochholzer
Keyword(s):  
Flow Cytometry ◽  
Platelet Function ◽  
Platelet Reactivity ◽  
Laboratory Data ◽  
Secondary Analysis ◽  
Structural Similarity ◽  
Lipoprotein A ◽  
Causal Risk Factor ◽  
Premature Cardiovascular Disease ◽  
Potential Association

Abstract Background Lipoprotein(a) [Lp(a)] is an independent, genetic, and causal risk factor for premature cardiovascular disease (CVD). Laboratory data have suggested an interaction of Lp(a) with platelet function, potentially caused by its structural similarity to plasminogen. So far, the potential association of Lp(a) with platelet activation and reactivity has not been well established in larger clinical cohorts. Methods This secondary analysis of the EXCELSIOR study analyzed intrinsic platelet reactivity before loading with clopidogrel 600mg and on-treatment platelet reactivity tested 24 hours following loading in patients undergoing elective coronary angiography. Platelet reactivity was tested by optical aggregometry as final aggregation after 5 min following stimulation with 5μM ADP. Platelet reactivity was also assessed by flow cytometry (expression of CD62P and PAC1) following stimulation with ADP and TRAP. Levels of Lp(a) on admission of each patient were immediately measured from fresh samples in a central laboratory. Results The present analysis included 2046 patients. Levels of Lp(a) ranged between 0 and 332 mg/dl. Results for intrinsic (p=0.80) and on-clopidogrel platelet reactivity (p=0.81) did not differ between quartiles of Lp(a) levels (Figure). Flow cytometry analyses confirmed these findings. Conclusion The present data do not support the hypothesis of an interaction of Lp(a) with platelet function. This finding might be important to define the safety of evolving therapeutic options for lowering Lp(a). Funding Acknowledgement Type of funding source: None

scholarly journals In vivo effects of eltrombopag on platelet function in immune thrombocytopenia: no evidence of platelet activation

Blood ◽  
2012 ◽  
Vol 119 (17) ◽  
pp. 4066-4072 ◽  
Author(s):  
Bethan Psaila ◽  
James B. Bussel ◽  
Matthew D. Linden ◽  
Bracken Babula ◽  
Youfu Li ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Platelet Function ◽  
Whole Blood ◽  
Immune Thrombocytopenia ◽  
Ex Vivo ◽  
Platelet Reactivity ◽  
Adenosine Diphosphate ◽  
High Dose ◽  
Platelet Surface

Abstract The effects of eltrombopag, a thrombopoietin-receptor agonist, on platelet function in immune thrombocytopenia (ITP) are not fully characterized. This study used whole blood flow cytometry to examine platelet function in 20 patients receiving eltrombopag treatment at days 0, 7, and 28. Platelet surface expression of activated GPIIb/IIIa, P-selectin, and GPIb was measured with and without low and high adenosine diphosphate (ADP) and thrombin receptor activating peptide (TRAP) concentrations. Before eltrombopag treatment with no ex vivo agonist, platelet activation was higher in ITP patients than controls. Platelet GPIb and activated GPIIb/IIIa expression without added agonist was unchanged following eltrombopag treatment, whereas a slight increase in P-selectin was observed. Expression of P-selectin and activated GPIIb/IIIa in response to high-dose ADP was lower during eltrombopag treatment than at baseline. Eltrombopag led to a slight increase in platelet reactivity to TRAP only in responders to eltrombopag but not to levels above those in controls; whole blood experiments demonstrated that this increase was probably because of higher platelet counts rather than higher platelet reactivity. In conclusion, although thrombocytopenic ITP patients have higher baseline platelet activation than controls, eltrombopag did not cause platelet activation or hyper-reactivity, irrespective of whether the platelet count increased.

scholarly journals The Molecular Aspects of Disturbed Platelet Activation Through ADP/P2Y12 Pathway in Multiple Sclerosis

2021 ◽  
Vol 22 (12) ◽  
pp. 6572
Author(s):  
Angela Dziedzic ◽  
Elzbieta Miller ◽  
Joanna Saluk-Bijak ◽  
Marta Niwald ◽  
Michal Bijak
Keyword(s):  
Multiple Sclerosis ◽  
Platelet Activation ◽  
Platelet Reactivity ◽  
Adenosine Diphosphate ◽  
Receptor Expression ◽  
P2y12 Receptor ◽  
Platelet Surface ◽  
Molecular Abnormalities ◽  
Increased Risk ◽  
Ischemic Events

Epidemiological studies confirm a high risk of ischemic events in secondary-progressive multiple sclerosis (SP MS) patients, directly associated with an increased level of pro-thrombotic activity of platelets. Our work aimed to verify potential molecular abnormalities of the platelet P2Y12 receptor expression and functionality as a cause of an increased risk of thromboembolism observed in the course of MS. We have demonstrated an enhanced platelet reactivity in response to adenosine diphosphate (ADP) in SP MS relative to controls. We have also shown an increased mRNA expression for the P2RY12 gene in both platelets and megakaryocytes, as well as enhanced density of these receptors on the platelet surface. We postulate that one of the reasons for the elevated risk of ischemic events observed in MS may be a genetically or phenotypically reinforced expression of the platelet P2Y12 receptor. In order to analyze the effect of the PAR1 (protease activated receptor type 1) signaling pathway on the expression level of P2Y12, we also analyzed the correlation parameters between P2Y12 expression and the markers of platelet activation in MS induced by selective PAR1 agonist (thrombin receptor activating peptide-6, TRAP-6). Identifying the molecular base responsible for the enlarged pro-thrombotic activity of platelets in SP MS could contribute to the implementation of prevention and targeted treatment, reducing the development of cardiovascular disorders in the course of the disease.

scholarly journals No Association Between Platelet Function and Hemophilia B Phenotype

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 4994-4994 ◽  
Author(s):  
Roger E.G. Schutgens ◽  
Esther R. van Bladel ◽  
Kathelijn Fischer ◽  
Mark Roest ◽  
Rolf Urbanus
Keyword(s):  
Platelet Activation ◽  
Platelet Reactivity ◽  
Adenosine Diphosphate ◽  
Hemophilia B ◽  
Healthy Controls ◽  
Severe Hemophilia ◽  
Platelet Activity ◽  
Activation Markers ◽  
Receptor Associated Protein ◽  
The Individual

Abstract Introduction In hemophilia, unravelling the mechanisms behind interindividual variability in phenotype remains a big challenge. Objectives To study platelet activation and platelet responsiveness in relation to hemostatic phenotypes in hemophilia B by 1) comparing hemophilia B patients to healthy controls and 2) relating these to the clinical phenotype of the individual patients with severe hemophilia B. Methods Platelet reactivity was determined in whole blood measuring expression of P-selectin and binding of fibrinogen with FACS analysis after stimulating or inhibiting platelets with concentration series of several (ant-)agonists, including adenosine diphosphate (ADP), convulxin (CVX) and thrombin receptor associated protein (TRAP)and iloprost. Concentration of soluble platelet activation markers (soluble P-selectin, β-Thromboglobulin and RANTES) were measured in platelet poor plasma by ELISA. Markers of platelet activation and responsiveness were compared between healthy controls (n=12), patients with mild/moderate (n=12) or severe hemophilia B (n=19). In severe hemophilia patients, annual FIX consumption/kg was calculated over the last 6 years. Data were analysed with linear regression using SPSS 20. Results Levels of basal platelet activation (both P-selectin and fibrinogen) were equal between controls, mild/moderate and severe hemophilia B (Figure 1). For basal P-selectin expression, the mean area under the curves for were 28.5 (95% CI 23.3-33.6), 33.0(95% CI 24.4-41.6) and 28.4(95% CI 23.9-32.9) respectively (p=0.4). After stimulation with ADP, CVX and TRAP (with and without iloprost), platelet responsiveness was similar in all groups. There was no relation between annual FIX consumption and any marker of platelet activity. For basal P-selectin expression, the beta coefficient was -0.212 (p=0.38)(Figure 2). Conclusion In hemophilia B, platelet activity and responsiveness was similar to healthy controls. In severe hemophilia patients, there was no relation between FIX consumption and platelet activity. Figure 1. Basal P-selectin activity between healthy controls and hemophilia patients Figure 1. Basal P-selectin activity between healthy controls and hemophilia patients Figure 2. Basal P-selectin activity according to FIX consumption in severe hemophilia B Figure 2. Basal P-selectin activity according to FIX consumption in severe hemophilia B Disclosures Schutgens: Pfizer: Research Funding.

Abstract 16292: Selective Platelet Protease-Activated-Receptor (PAR)1 and PAR4 Mediated Thrombin Desensitisation in the Elderly is Correlated With Inflammation and Chronic Thrombin Receptor Stimulation

Circulation ◽  
2020 ◽  
Vol 142 (Suppl_3) ◽  
Author(s):  
Sonali R Gnanenthiran ◽  
Gabrielle Pennings ◽  
Caroline Reddel ◽  
Heather Campbell ◽  
Justin Hamilton ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Platelet Activation ◽  
The Elderly ◽  
Elderly Subjects ◽  
Thrombin Receptor ◽  
Receptor Stimulation ◽  
Activation Markers ◽  
Tnf Α ◽  
D Dimer ◽  
Granule Release

Introduction: Platelet activation, by adenosine diphosphate (ADP) via P2Y 12 receptors and thrombin via PAR1 and PAR4, is a key therapeutic target in cardiovascular disease (CVD). The efficacy of antiplatelet agents diminishes in the elderly, but it is unknown whether these pathways change with aging. Hypothesis: Platelet activation pathways change with aging. Methods: Platelet activity was evaluated in young (20-30yrs), middle-aged (40-55yrs) and elderly (≥70yrs) healthy volunteers (n=174). Whole blood aggregometry and flow cytometry (P-selectin: α-granule release; CD63: dense granule release; PAC1 binding: activated GPIIb/IIIa) were performed under basal conditions and post ex vivo stimulation with ADP, thrombin, PAR1 agonist or PAR4 agonist. EC 50 and E max values were derived for each agonist. Receptor cleavage and quantification (P2Y 12 ; PAR1; PAR4; GPIbα) were assessed with flow cytometry. Thrombin generation (D-Dimer) and inflammation (interleukin [IL]-1β; tumour necrosis factor [TNF]-α) were assessed via ELISA. Results: The elderly had higher basal platelet activation markers (P-selectin, CD63, activated GPIIb/IIIa) than the young, with higher basal activity correlating with increasing IL-1β. P2Y 12 receptor density was higher in the elderly and associated with greater ADP-induced platelet aggregation and activation. Elderly subjects had less platelet activation in response to thrombin (higher EC 50 ), demonstrating hyporeactivity to selective stimulation of PAR1 or PAR4, more basal PAR1/PAR4 cleavage, and less inducible PAR1/PAR4 cleavage. This was associated with reduced thrombin binding receptor GPIbα and reduced secondary ADP contribution to thrombin-mediated activation. D-Dimer and TNF-α levels were elevated in the elderly, and inversely correlated with platelet thrombin sensitivity, implying a role of desensitization from chronic thrombin receptor stimulation. Conclusion: Aging is associated with increased basal platelet activation and hyperreactivity to ADP, but selective desensitization to thrombin. The latter appears mediated by chronic thrombin receptor stimulation and inflammation. Age-specific antiplatelet strategies may require selective targeting of these pathways to treat CVD in the elderly.

scholarly journals Inhibition of collagen-induced platelet activation by 5'-p- fluorosulfonylbenzoyl adenosine: evidence for an adenosine diphosphate requirement and synergistic influence of prostaglandin endoperoxides

Blood ◽  
1986 ◽  
Vol 68 (2) ◽  
pp. 565-570 ◽  
Author(s):  
RW Colman ◽  
WR Figures ◽  
LM Scearce ◽  
AM Strimpler ◽  
FX Zhou ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Shape Change ◽  
Thromboxane A2 ◽  
Adenosine Diphosphate ◽  
Platelet Surface ◽  
Prostaglandin Endoperoxide ◽  
Fibrinogen Binding ◽  
Low Concentrations ◽  
Absolute Requirement

Abstract The relative roles of platelet autacoids such as adenosine diphosphate (ADP), prostaglandin endoperoxides, and thromboxane A2 (TXA2) in collagen-induced platelet activation are not fully understood. We reexamined this relationship using the ADP affinity analogue, 5'-p- fluorosulfonylbenzoyl adenosine (FSBA), which covalently modifies a receptor for ADP on the platelet surface, thereby inhibiting ADP- induced platelet activation. Collagen-induced shape change, aggregation, and fibrinogen binding were each fully inhibited under conditions in which FSBA is covalently incorporated and could not be overcome by raising the collagen used to supramaximal concentrations. In contrast, TXA2 synthesis stimulated by collagen under conditions that produced maximum aggregation was only minimally inhibited by FSBA. Since covalent incorporation of FSBA has been previously shown to specifically inhibit ADP-induced activation of platelets, the present study supports the contention that ADP is required for collagen-induced platelet activation. Under similar conditions, indomethacin, an inhibitor of cyclooxygenase, inhibited collagen-induced shape change, indicating that endoperoxides and/or TXA2 also play a role in this response. Shape change induced by low concentrations (10 nmol/L) of the stable prostaglandin endoperoxide, azo-PGH2, was also inhibited by FSBA. These observations indicate a role for ADP in responses elicited by low concentrations of endoperoxides. However, at higher concentrations of azo-PGH2 (100 nmol/L), inhibition by FSBA could be overcome. Thus, the effect of collagen apparently has an absolute requirement for ADP for aggregation and fibrinogen binding and for both ADP and prostaglandins for shape change. Aggregation and fibrinogen binding induced by prostaglandin endoperoxides also required ADP as a mediator, but ADP is not absolutely required at high endoperoxide concentration to induce shape change.

scholarly journals von Willebrand factor bound to glycoprotein Ib is cleared from the platelet surface after platelet activation by thrombin

Blood ◽  
1992 ◽  
Vol 79 (8) ◽  
pp. 2011-2021 ◽  
Author(s):  
P Hourdille ◽  
HR Gralnick ◽  
E Heilmann ◽  
A Derlon ◽  
AM Ferrer ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Platelet Activation ◽  
Von Willebrand Factor ◽  
Platelet Rich Plasma ◽  
Surface Expression ◽  
Von Willebrand Disease ◽  
Platelet Surface ◽  
Immunogold Staining ◽  
Von Willebrand ◽  
Willebrand Factor

Abstract We recently reported that after activation of human platelets by thrombin, glycoprotein (GP) Ib-IX complexes are translocated to the surface-connected canalicular system (SCCS) (Blood 76:1503, 1990). As GPIb is a major receptor for von Willebrand factor (vWF) in platelet adhesion, we have now examined the consequences of thrombin activation on the organization of vWF bound to GPIb on the platelet surface. Studies were performed using monoclonal or polyclonal antibodies in either immunogold staining and electron microscopy (Au-EM) or in flow cytometry. When unstirred platelet-rich plasma was incubated with ristocetin, bound vWF was located by Au-EM as discrete masses regularly distributed over the cell surface. Platelets from a patient with Glanzmann's thrombasthenia, lacking GPIIb-IIIa complexes, gave a similar pattern, confirming that this represented binding to GPIb. That ristocetin was not precipitating vWF before their binding to the platelets was shown by the detection of similar masses on the surface of platelets of a patient with type IIB von Willebrand disease. Experiments were continued using washed normal platelets incubated in Tyrode-EDTA, the purpose of the EDTA being to limit the surface expression of endogenous vWF after platelet stimulation. Under these conditions, platelets were treated with ristocetin for 5 minutes at 37 degrees C in the presence of increasing amounts of purified vWF. This was followed by incubation with thrombin (0.5 U/mL) for periods of up to 10 minutes. Flow cytometry showed a time-dependent loss in the surface expression of vWF bound to GPIb and these changes were confirmed by Au-EM. In particular, immunogold staining performed on ultrathin sections showed that the bulk of the vWF was being cleared to internal membrane systems. Surface clearance of vWF during thrombin- induced platelet activation is a potential mechanism for regulating platelet adhesivity.

scholarly journals Factor XIIIa binding to activated platelets is mediated through activation of glycoprotein IIb-IIIa

Blood ◽  
1994 ◽  
Vol 83 (4) ◽  
pp. 1006-1016 ◽  
Author(s):  
AD Cox ◽  
DV Devine
Keyword(s):  
Monoclonal Antibody ◽  
Flow Cytometry ◽  
Platelet Activation ◽  
Factor Xiiia ◽  
Cross Linking ◽  
Platelet Surface ◽  
Activated Platelets ◽  
Fibrinogen Binding ◽  
A Chain ◽  
Functional Receptor

Abstract Stabilization of a clot is dependent on fibrin cross-linking mediated by the transglutaminase, factor XIIIa (FXIIIa). In addition to fibrin stabilization, FXIIIa acts on a number of platelet-reactive proteins, including fibronectin and vitronectin, as well as the platelet proteins, glycoprotein (GP) IIb-IIIa, myosin, and actin. However, conditions inducing the platelet-activation dependent binding of FXIIIa have not been characterized nor have the sites mediating FXIIIa binding been identified. The generation of FXIIIa and consequent detection of FXIIIa on the platelet surface were compared with other thrombin- induced activation events; the rate at which FXIIIa bound to activated platelets was much slower than platelet degranulation or fibrin(ogen) binding. Whereas platelets could be rapidly induced to express a functional receptor for FXIIIa, the rate of FXIIIa binding to platelets is limited by the rate of conversion of FXIII to FXIIIa. Immunoprecipitation of radiolabeled platelets using polyclonal anti- FXIII A-chain antibody identified two proteins corresponding to GPIIb and GPIIIa. Preincubation of intact platelets with 7E3, a monoclonal antibody that blocks the fibrinogen binding site, or GRGDSP peptide inhibited FXIIIa binding by about 95% when measured by flow cytometry; FXIIIa binding to purified GPIIb-IIIa was also inhibited by 7E3. The binding of FXIIIa to purified GPIIb-IIIa was enhanced by the addition of fibrinogen, but not by that of fibronectin or thrombospondin, suggesting that FXIIIa also binds to fibrinogen associated with the complex. These observations suggest that activated platelets bearing FXIIIa may enhance stabilization of platelet-rich thrombi through surface-localized cross-linking events.

scholarly journals Erythrocytes metabolically enhance collagen-induced platelet responsiveness via increased thromboxane production, adenosine diphosphate release, and recruitment

Blood ◽  
1991 ◽  
Vol 78 (1) ◽  
pp. 154-162 ◽  
Author(s):  
J Valles ◽  
MT Santos ◽  
J Aznar ◽  
AJ Marcus ◽  
V Martinez-Sales ◽  
...  
Keyword(s):  
Platelet Activation ◽  
Therapeutic Potential ◽  
Platelet Reactivity ◽  
Adenosine Diphosphate ◽  
Stimulus Response ◽  
Absolute Requirement ◽  
Thromboxane Production ◽  
And Function ◽  
Aspirin Ingestion

Abstract Erythrocytes promoted platelet reactivity in a plasma medium, as demonstrated in an in vitro system that independently evaluated the biochemistry of platelet activation and recruitment. The prothrombotic erythrocyte effects were metabolically regulated, as evidenced by lack of activity of ATP-depleted or glutaraldehyde-fixed erythrocytes. They occurred in the absence of cell lysis as verified by lactate dehydrogenase assays, and had an absolute requirement for platelet activation. The presence of erythrocytes induced a twofold increase in platelet thromboxane B2 (TXB2) synthesis upon collagen stimulation, indicating that erythrocytes modulated platelet eicosanoid formation. Cell-free releasates from stimulated platelet-erythrocyte suspensions, which exhibited increased recruiting capacity, contained 6.9-fold more ADP and 4.9-fold more ATP than releasates from stimulated platelets alone. Following aspirin ingestion, TXB2 formation was blocked, but erythrocyte promotion of platelet reactivity persisted at those doses of collagen that reinduced platelet activation. Moreover, when platelet mixtures consisted of as little as 10% obtained before aspirin plus 90% obtained post-aspirin ingestion, significant erythrocyte enhancement of platelet reactivity occurred, even at low agonist concentrations. These erythrocyte effects would decrease the therapeutic potential of inhibition of platelet cyclooxygenase by aspirin. The erythrocyte- induced modulation of platelet biochemistry and function emphasizes the importance of cell-cell interactions in stimulus-response coupling.

DETECTION OF ACTIVATED PLATELETS IN WHOLE BLOOD BY FLOW CYTOMETRY

1987 ◽  
Author(s):  
S J Shattil ◽  
J A Hoxie ◽  
M Cunningham ◽  
C S Abrahms ◽  
J O’Brien ◽  
...  
Keyword(s):  
Flow Cytometry ◽  
Monoclonal Antibodies ◽  
Platelet Activation ◽  
Whole Blood ◽  
Thrombus Formation ◽  
Membrane Surface ◽  
White Blood Cells ◽  
Color Flow ◽  
Platelet Surface ◽  
Activated Platelets

Platelets may become activated in a number of clinical disorders and participate in thrombus formation. We have developed a direct test for activated platelets in whole blood that utilizes dual-color flow cytometry and requires no washing steps. Platelets were distinguished from erythrocytes and white blood cells in the flow cytometer by labeling the platelets with biotin-AP1, an antibody specific for membrane glycoprotein lb, and analyzing the cells for phycoerythrin-streptavidin fluorescence. Membrane surface changes resulting from platelet activation were detected with three different FITC-labeled monoclonal antibodies: 1) PAC1, an antibody specific for the fibrinogen receptor on activated platelets; 2) 9F9, which binds to the D-domain of fibrinogen and detects platelet-bound fibrinogen; and 3) S12, which binds to an alpha-granule membrane protein that associates with the platelet surface during secretion. Unstimulated platelets demonstrated no PAC1, 9F9, or S12-specific fluorescence, indicating that they did not bind these antibodies. Upon stimulation with agonists, however, the platelets demonstrated a dose-dependent increase in FITC-fluorescence. The binding of 9F9 to activated platelets required fibrinogen. Low concentrations of ADP and epinephrine, which induce fibrinogen receptors but little secretion, stimulated near-maximal PAC1 or 9F9 binding but little S12 binding. On the other hand, a concentration of phorbol myristate acetate that evokes full platelet aggregation and secretion induced maximal binding of all three antibodies. When blood samples containing activated and non-activated platelets were mixed, as few as 0.8% activated platelets could be detected by this technique. There was a direct correlation between ADP-induced FITC-PAC1 binding and binding determined in a conventional 125I-PAC1 binding assay (r = 0.99; p < 0.001). These studies demonstrate that activated platelets can be reliably detected in whole blood using activation-dependent monoclonal antibodies and flow cytometry. This method may be useful to assess the degree of platelet activation and the efficacy platelet inhibitor therapy in thrombotic disorders.

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