Platelet Surface Glycoprotein Research Articles

A novel (288delC) mutation in exon 2 of GPIIb associated with type I Glanzmann's thrombasthenia

This work reports the molecular genetic analysis of two patients who suffer mucocutaneous haemorrhages, prolonged bleeding time and failure of platelets to aggregate, either spontaneously or in response to agonists. The absence of platelet surface glycoprotein (GP)IIb–IIIa complexes confirmed the clinical diagnosis of Glanzmann's thrombasthenia (GT). Polymerase chain reaction single‐strand conformation polymorphism (PCR‐SSCP) analysis of exon 2 of GPIIb showed polymorphic bands caused by the homozygous deletion of a cytosine at position 288 relative to the translation start site, causing a shifting of the reading frame and appearance of a premature termination codon. The heterozygous relatives showed a reduced platelet content of GPIIb–IIIa, and a correlation was found between the levels of GPIIb mRNA and surface expression of GPIIb–IIIa complexes. Unlike other mRNAs carrying a nonsense mutation, (288Cdel)GPIIb does not force alternative splicing of GPIIb mRNA. As expected, co‐transfection of Chinese hamster ovary (CHO) cells with cDNAs encoding GPIIIa and (288delC)GPIIb failed to enhance the surface exposure of GPIIIa. It is concluded that the (288delC)GPIIb mutation is responsible for the thrombasthenic phenotype of the patients. In addition, it has also been determined that heterodimerization of GPIIb–IIIa requires the integrity of exons 2 and 3 of GPIIb.

A novel (288delC) mutation in exon 2 of GPIIb associated with type I Glanzmann's thrombasthenia.

This work reports the molecular genetic analysis of two patients who suffer mucocutaneous haemorrhages, prolonged bleeding time and failure of platelets to aggregate, either spontaneously or in response to agonists. The absence of platelet surface glycoprotein (GP)IIb-IIIa complexes confirmed the clinical diagnosis of Glanzmann's thrombasthenia (GT). Polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) analysis of exon 2 of GPIIb showed polymorphic bands caused by the homozygous deletion of a cytosine at position 288 relative to the translation start site. causing a shifting of the reading frame and appearance of a premature termination codon. The heterozygous relatives showed a reduced platelet content of GPIIb-IIIa, and a correlation was found between the levels of GPIIb mRNA and surface expression of GPIIb-IIIa complexes. Unlike other mRNAs carrying a nonsense mutation, (288Cdel)GPIIb does not force alternative splicing of GPIIb mRNA. As expected, co-transfection of Chinese hamster ovary (CHO) cells with cDNAs encoding GPIIIa and (288delC)GPIIb failed to enhance the surface exposure of GPIIIa. It is concluded that the (288delC)GPIIb mutation is responsible for the thrombasthenic phenotype of the patients. In addition, it has also been determined that heterodimerization of GPIIb-IIIa requires the integrity of exons 2 and 3 of GPIIb.

Aprotinin administration in the pericardial cavity does not prevent platelet activation

Objectives: Aprotinin is frequently administered systemically to patients undergoing cardiopulmonary bypass to inhibit activation of platelets and plasma protein systems and thus reduce postoperative blood loss. Two reports on local aprotinin administration, that is, into the pericardial cavity, also indicated improvement in postoperative blood loss, but the underlying mechanism was not investigated. We previously reported the disappearance of glycoprotein Ib from the platelet surface and the appearance of platelet-derived microparticles in the pericardial cavity of patients undergoing cardiopulmonary bypass as signs of platelet activation. Here, we investigated whether such local aprotinin administration reduced platelet activation. Methods: In a double-blind study, 6 patients received aprotinin (500,000 KIU) into the pericardial cavity during the operation and 7 patients received a placebo. Platelet surface glycoprotein Ib expression, concentration of microparticles, and concentration of complexes of platelets with leukocytes, erythrocytes, or each other, were measured by flow cytometry. Results: We confirmed the reduced glycoprotein Ib expression and the increased concentration of microparticles in the pericardial cavity, as previously reported, and found no increased concentration of platelet complexes. However, no differences between aprotinin and placebo treatments were observed in these platelet activation parameters in the pericardial cavity or the systemic circulation. Conclusion: We conclude that administration of aprotinin into the pericardial cavity during cardiopulmonary bypass and at concentrations similar to the systemic application does not reduce platelet activation in that compartment or the systemic circulation. (J Thorac Cardiovasc Surg 2000;120:552-7)

Inhibition of platelet activation by 5-aminosalicylic acid in inflammatory bowel disease.

Platelets play an important role in inflammation and are activated in inflammatory bowel disease. Micro-vascular thrombosis in the gut wall leading to intestinal micro-infarction may be a pathogenic feature of Crohn's disease. 5-Aminosalicylic acid is an effective treatment for patients with inflammatory bowel disease. To assess the effects of 5-aminosalicylic acid on platelet activation, when taken orally and in vitro by patients with inflammatory bowel disease. Spontaneous and thrombin-induced platelet activation were studied using fluorescent antibodies to the activated platelet surface glycoprotein P-selectin and flow cytometry. Baseline platelet activation in inflammatory bowel disease was significantly greater than that in controls (P=0.0003). Independent of diagnosis or disease activity, spontaneous ex-vivo platelet activation was 50% lower in patients with inflammatory bowel disease taking 5-aminosalicylic acid orally than in those not on such treatment (P < 0.05). In vitro, 5-aminosalicylic acid significantly reduced both spontaneous (P < 0. 03 for >/=1 microM 5-aminosalicylic acid) and thrombin-induced platelet activation (P < 0.02 for >/= 1 microM 5-aminosalicylic acid). 5-Aminosalicylic acid given either orally or in vitro inhibits platelet activation. If this effect reflects an in vivo action in the gut, it could contribute to the beneficial actions of 5-aminosalicylic acid in inflammatory bowel disease.

The use of electron microscopy in the investigation of the ultrastructural morphology of immune thrombocytopenic purpura platelets

Ultrastructural studies have proven useful for the accurate identification and classification of certain lymphoid and hematopoietic disorders; however, the value of electron microscopy in the diagnosis and clinical management of platelet pathology is less well defined. Electron microscopy has been used to evaluate inherited platelet disorders. In these disorders, certain platelet structural defects can be characteristic. Recently, we investigated the ultrastructural morphology and immunogold localization of IgG in platelets from patients with idiopathic thrombocytopenic purpura (ITP). The accelerated platelet destruction of ITP is mediated by antiplatelet autoantibodies directed against platelet surface glycoproteins and by the functional capacity of the reticuloendothelial system. The basic dysregulation that occurs in these patients remains unexplained. Traditionally, laboratory investigation of ITP has focused on the development of serologic assays to measure the autoantibodies. As an alternative investigative approach, determination of the immunomorphologic characteristics of platelet-associated IgG (PAIgG) in ITP platelets may prove useful in the diagnosis or clinical management of patients with ITP. Our results showed that the ultrastructural morphology of ITP platelets is similar to that observed for normal platelets. No structural abnormalities are observed in ITP platelets. Immunogold labeling of IgG within α-granules of ITP platelets is significantly higher than that of normal platelets. Additionally, in some ITP platelets, immunogold labeling is also observed on the platelet surface and within channels of the open-cannalicular system. In comparison, immunogold labeling of these structures in normal platelets, is rare, or absent. In conclusion, electron microscopic studies should contribute to furthering our understanding of this common autoimmune disorder, and may provide possible biological explanations for the increased levels of PAIgG in platelets from patients with ITP.

Evaluation of Platelet Function by Flow Cytometry

Platelet function in whole blood can be comprehensively evaluated by flow cytometry. Flow cytometry can be used to measure platelet reactivity, circulating activated platelets, platelet–platelet aggregates, leukocyte–platelet aggregates, procoagulant platelet-derived microparticles, and calcium flux. Clinical applications of whole blood flow cytometric assays of platelet function in disease states (e.g., acute coronary syndromes, angioplasty, and stroke) may include identification of patients who would benefit from additional antiplatelet therapy and prediction of ischemic events. Circulating monocyte–platelet aggregates appear to be a more sensitive marker of in vivo platelet activation than circulating P-selectin-positive platelets. Flow cytometry can also be used in the following clinical settings: monitoring of GPIIb–IIIa antagonist therapy, diagnosis of inherited deficiencies of platelet surface glycoproteins, diagnosis of storage pool disease, diagnosis of heparin-induced thrombocytopenia, and measurement of the rate of thrombopoiesis.

Influence of Feiliuping no. 2 on platelet surface glycoprotein expression in mid-late stage lung cancer patientson platelet surface glycoprotein expression in mid-late stage lung cancer patients

Influence of Feiliuping no. 2 on platelet surface glycoprotein expression in mid-late stage lung cancer patientson platelet surface glycoprotein expression in mid-late stage lung cancer patients

Therapeutic heparin concentrations augment platelet reactivity: Implications for the pharmacologic assessment of the glycoprotein IIb/IIIa antagonist abciximab

Background This study evaluated the effect of heparin on the platelet reactivity and the pharmacodynamic profile of abciximab. Methods and Results Ex vivo studies were performed on patients undergoing elective percutaneous coronary intervention (n = 26) who were at moderate to high risk of ischemic complications. Patients received a 12,000-U bolus of heparin followed by a 0.25-mg/kg bolus of abciximab. Before abciximab treatment, platelet aggregation responses to a variety of stimuli were assessed immediately before and 10 minutes after the heparin bolus. Heparin increased platelet aggregation to 2 and 5 μmol/L adenosine diphosphate (ADP) and 5 μg/ml collagen by 36%, 25%, and 46%, respectively ( P ≤ .001), but did not influence platelet reactivity to thrombin receptor-activating peptide or 20 μmol/L ADP and had no appreciable effect on platelet surface glycoprotein (GP) IIb/IIIa receptor numbers. To assess the impact of heparin on the pharmacodynamic profile of abciximab, GP IIb/IIIa receptor blockade and platelet aggregation inhibition estimates obtained after abciximab administration were calculated relative to the basal levels observed both before and after the heparin bolus. At 2 and 24 hours after the abciximab bolus, GP IIb/IIIa receptor blockade measurements normalized to either the preheparin or postheparin baseline determinations were equivalent. For all ADP concentrations tested, the 2-hour post-abciximab bolus platelet aggregation inhibition estimates based on the preheparin and postheparin baseline values were comparable. However, for 2 and 5 μmol/L ADP, the 24-hour post-abciximab platelet aggregation inhibition measurements based on preheparin baseline values were significantly lower than postheparin baseline determinations (both P ≤ .003). In vitro studies revealed that therapeutic heparin doses induced a concentration-dependent reduction in the extent of platelet inhibition produced by amounts of abciximab that elicit partial inhibition of platelet aggregation. However, at abciximab concentrations that achieved platelet aggregation blockade of >80%, the levels of inhibition of platelet aggregation in the presence and absence of heparin were equivalent. Conclusions The cumulative ex vivo and in vitro data indicate that for certain stimuli, heparin alters the platelet inhibitory profile of abciximab at concentrations of the agent that yield partial suppression of platelet function.

Idiopathic Thrombocytopenic Purpura

Idiopathic Thrombocytopenic Purpura

Characterization of platelet glycoproteins and platelet/endothelial cell antibodies in patients with thrombotic thrombocytopenic purpura

Platelets and sera from 12 patients with thrombotic thrombocytopenic purpura (TTP) and 12 healthy normal control subjects were examined. As determined by quantitative flow cytometry, prior to plasma exchange therapy platelet surface glycoprotein (GP) Ib levels were similar in TTP patients and normal controls (mean 20 188 and 20 226 molecules/platelet, respectively). Platelets from patients with TTP did, however, have significantly reduced levels of GPIIb/IIIa prior to plasmapheresis (mean 36 348 v 52 505 molecules/platelet in controls; P = 0.0004) and of GPIV (mean 13 321 v 26 212 molecules/platelet in controls; P = 0.0002). An increase in activated platelets, as determined by CD62 expression, was observed in 82% of patients. Increased platelet-associated immunoglobulins and/or complement was also seen in approximately 60% of the patients. In general, with return of platelet counts to normal levels following seven plasmaphereses, the above abnormalities were reversed, although often not to normal levels. Western blot analysis indicated the presence of antibodies reactive to platelet GPIV (88 kD) in 70% of pretreatment sera from patients with TTP; a similar band was observed in 80% of patient sera against microvascular endothelial cells. Immunofluorescence microscopic examination indicated the presence of antibody in pretreatment sera from patients with TTP to microvascular (73%) and large vessel (36%) endothelial cells. As measured by an indirect flow cytometric assay, pretreatment sera from 55% of patients with TTP were reactive with large vessel endothelial cells and 100% reacted with microvascular endothelial cells; reactivity was significantly greater against the microvascular endothelial cells (P = 0.0048) and was reduced following plasma exchange therapy. These results indicate abnormalities in platelet glycoprotein expression in TTP and suggest that anti-platelet and anti-endothelial cell antibodies play a role in the thrombocytopenia and vasculitis characteristic of this disorder.

Laboratory markers of platelet activation and their clinical significance.

Whole blood flow cytometry is a powerful new laboratory technique for assessment of platelet activation and function. Flow cytometry can be used to measure platelet hyperreactivity, circulating activated platelets, leukocyte-platelet aggregates, and procoagulant platelet-derived microparticles in a number of clinical settings, including acute coronary syndromes, angioplasty, cardiopulmonary bypass, acute cerebrovascular ischemia, peripheral vascular disease, diabetes mellitus, preeclampsia, and Alzheimer's disease. Clinical applications of whole blood flow cytometric assays of platelet function in these diseases may include identification of patients who would benefit from additional antiplatelet therapy and prediction of ischemic events. Circulating monocyte-platelet aggregates appear to be a more sensitive marker of in vivo platelet activation than circulating P-selectin-positive platelets. Flow cytometry can also be used in the following clinical settings: monitoring of glycoprotein IIb-IIIa antagonist therapy, diagnosis of inherited deficiencies of platelet surface glycoproteins, diagnosis of storage pool disease, diagnosis of heparin-induced thrombocytopenia, and measurement of the rate of thrombopoiesis.

T-antigen (Gal β3 GaINAc α-) containing glycoproteins of human reace

Desialation of cell surface glycoconjugates due to bacterial or viral infection can expose epitopes like T-antigenic structure which can also occur during oncological transformations. Human platelet plasma membrane glycoproteins were isolated by jacalin affinity chromatography. Potential T-antigen containing glycoproteins which were not reported before could be identified on the Western blot using peanut agglutinin-horse radish peroxidase (PNA-HRP) after neuraminidase treatment. Alpha-galactosyl epitopes recognized by anti-gal were found to be absent in human platelet plasma membrane glycoproteins. Under the experimental conditions employed, the Gp IIbα was identified most rich in T-antigenic structures. Probable role of exposed T-antigenic structures and α-galactosyl epitopes in pathological conditions is discussed. The identity of major glycoprotein bands was confirmed by differential lectin-binding studies with Concanavalin A on the Western blot. The higher binding affinity of jacalin for T-antigenic structures when compared to PNA enabled the isolation and detection of the antigen containing platelet surface glycoproteins which were not reported before.

Collagen Receptor Signaling in Platelets and Megakaryocytes

IntroductionThe extracellular matrix protein, collagen, plays a primary role in hemostasis. Collagen fibers provide an important site for adhesion of platelets to the exposed subendothelium, trapping them at the site of vascular damage and enabling the formation of a monolayer of cells over the damaged area. Collagen fibers also stimulate platelet activation, leading to inside-out regulation of the integrin glycoprotein (GP) IIb-IIIa (also known as αIIbβ3), secretion from dense and α granules, generation of thromboxanes, and expression of procoagulant activity, all of which support the hemostatic process. The role of collagen in supporting platelet adhesion to the subendothelium is mediated through indirect and direct interactions. The indirect interaction is mediated through von Willebrand factor (vWF), which binds to the GP Ib-IX-V complex on the platelet surface.1-3 The interaction with vWF is critical for platelet adhesion at medium to high rates of flow because of the fast rate of association between vWF and GP Ib-IX. The importance of this interaction is demonstrated by the severe bleeding problems experienced by individuals with functional impairment of vWF (von Willebrand disease) or GP Ib-IX (Bernard-Soulier syndrome). At low rates of flow, collagen fibers are able to support adhesion in the absence of vWF through a direct interaction with a number of platelet surface glycoproteins i.e. collagen receptors,4,5 this also serves to support vWF-dependent adhesion at higher rates of flow by preventing dissociation. Crosslinking of platelet surface glycoproteins by collagen also generates intracellular signals, leading to platelet activation.The number of proteins on the platelet surface proposed to be collagen receptors is approaching double figures, but it is generally accepted that the integrin GP Ia-IIa (also known as α2β1) and glycoprotein VI (GP VI) are among the most important of these, playing critical roles in adhesion and activation, respectively6 (Fig. 1). This is illustrated by the mild bleeding problems of patients with a low level of expression or the presence of autoantibodies to GP Ia-IIa and the spontaneous, severe bleeding episodes that are occasionally seen in patients whose platelets are deficient in GP VI.6 There is evidence, however, that other collagen receptors have supporting roles in adhesion and activation. For example, GP VI supports platelet adhesion to collagen7 and GP IV, also known as CD36, may also play a similar role.8 The role of the recently cloned collagen receptor p65 in adhesion is not known. Evidence that the interaction of collagen with receptors, such as GPIV and p65, is of less importance than for interactions with GP Ia-IIa, and GP VI is provided by the absence of individuals with bleeding problems caused by deficiencies in these proteins. This is illustrated most clearly for GP IV, which is absent in 3% to 5 % of the Japanese population, and yet such individuals display no major vascular problems.Due to the large number of glycoproteins that bind collagen on the platelet surface, it has been difficult to gain a full understanding of the role of individual collagen receptors in adhesion and activation responses. This is complicated further by the interactions between vWF and GP Ib-IX-V, vWF or fibrinogen to activated GP IIb-IIIa especially as both glycoprotein receptors generate intracellular signals. The relative importance of individual collagen receptors in adhesion also varies with the rate of flow and between collagen types. A full discussion of platelet adhesion to collagen is beyond the scope of this article, and the reader is referred to a number of excellent recent reviews for further information.4-6,9,10 The present chapter focuses on the signaling events generated by the activation (or more correctly crosslinking) of platelet surface glycoproteins by collagen and the implications that this has for platelet activation under normal and diseased conditions.

Ethylenediaminetetraacetic Acid-Dependent Pseudothrombocytopenia in a Cardiac Surgical Patient

Ethylenediaminetetraacetic Acid-Dependent Pseudothrombocytopenia in a Cardiac Surgical Patient

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

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.

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

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.

Relationship between haemoglobin, ristocetin-induced platelet aggregation and platelet surface glycoproteins GPIb and BPIIb/IIIa in haemodialysis patients under therapy with recombinant human erythropoietin

Relationship between haemoglobin, ristocetin-induced platelet aggregation and platelet surface glycoproteins GPIb and BPIIb/IIIa in haemodialysis patients under therapy with recombinant human erythropoietin

Platelet and neutrophil alloantigen genotyping in clinical practice

Immune responses to platelet and neutrophil alloantigens are involved in the pathogenesis of several clinical syndromes including: neonatal alloimmune thrombocytopenia (NATP), post-transfusion purpura (PTP), refractory responses to platelet transfusion, neonatal alloimmune neutropenia (NAN), transfusion-related acute lung injury (TRALI), and chronic benign autoimmune neutropenia of infancy. Initially, platelet alloantigens were only characterized serologically. Subsequently, they were localized to specific platelet surface glycoprotein structures and ultimately defined to the level of nucleic acid polymorphisms on platelet glycoprotein genes. These advances allowed the tools of molecular biology to be applied to typing for platelet alloantigens. The advantages of such typing methods include: 1) patient platelets are no longer required for the typing assays, and therefore, platelet types can be established on extremely thrombocytopenic samples (by using peripheral blood white blood cells [WBC]); 2) The genotyping methods eliminate the requirement for rare serologic reagents. A number of different genotyping methods have been developed. These include: restriction fragment length polymorphism (RFLP), sequence specific primers (SSP), and Dot-Blot hybridization. Clinical applications of this methodology include: determining the platelet genotype of fetuses at risk for NATP, in the diagnosis of PTP, and identifying causes of refractory responses to platelet transfusions. Analogous to platelet alloantigens, a limited number of neutrophil alloantigens can now be determined by molecular biologic methods. The new methods obviate the need to isolate fresh neutrophils for serologic typing and do not require rare serologic reagents. To date, molecular polymorphisms associated with alloantigens on the neutrophil Fc gamma RIIIb surface glycoprotein have been elucidated. These include the allo-antigens NA1, NA2, and SH.

A Heparin-coated Circuit Maintains Platelet Aggregability in Response to Shear Stress in an In Vitro Model of Cardiopulmonary Bypass

Alterations in platelet aggregability may play a role in the pathogenesis of qualitative platelet defects associated with cardiopulmonary bypass (CPB). We circulated fresh heparinized whole blood through tubing sets coated with heparin (C group, n = 10) and through non-coated sets (N group, n = 10) as a simulated CPB circuit. Shear stress (108 dyne/cm2)-induced platelet aggregation (hSIPA), plasma von Willebrand factor (vWF) activity and platelet glycoprotein (GP) Ib expression were measured, before, during, and after this in vitro set up of circulation. In the two groups, the extent of hSIPA significantly decreased during circulation and was partially restored after circulation. Decreases in the extent of hSIPA were significantly less with use of heparin-coated circuits. There was an equivalent reduction in plasma vWF activity, in the two groups. Expression of platelet surface GP Ib decreased significantly during circulation and recovered after circulation. Reduction of surface GP Ib expression during circulation was significantly less in the C group than that in the N group. Decrease in surface GP Ib expression correlated (r = 0.88 in either group) with the magnitude of hSIPA, in the two groups. The progressive removal of surface GP Ib was mainly attributed to redistribution of GP Ib from the membrane skeleton into the cytoskeleton. Our observations suggest that use of heparin-coated circuits partly blocks the reduction of hSIPA, as a result of a lesser degree of redistribution of GP Ib.

Anti-platelet antibodies in patients with systemic lupus erythematosus and the primary antiphospholipid antibody syndrome: their relationship with the observed thrombocytopenia.

The role of antiphospholipid antibodies in the pathogenesis of the thrombocytopenia observed during primary antiphospholipid antibody syndrome (APAS) and systemic lupus erythematosus (SLE) remains controversial. We have used the MAIPA test to examine the frequency and specificity of anti-platelet antibodies directed against the major platelet membrane glycoproteins (GP IIb-IIIa, GP Ib-IX, GP Ia-IIa and GP IV) in patients where SLE and APAS were associated or not with thrombocytopenia. Results were compared with a series of 26 ITP patients, 46% of whom were shown to possess anti-platelet antibodies directed against one or more of the platelet surface glycoproteins. When APAS was associated with thrombocytopenia, 7/10 patients possessed antibodies against GP IIb-IIIa and/or GP Ib-IX. For SLE patients with thrombocytopenia, 6/10 patients were shown to have antiplatelet antibodies against GP IIb-IIIa, GP Ib-IX or GP IV. In contrast, for APAS (n=11) and SLE patients (n=11) without thrombocytopenia, only one patient had an antibody directed against GP IIb-IIIa and one patient had an antibody to GP IV. Our results suggest that antibodies directed against major platelet membrane glycoproteins may play a role in the thrombocytopenia that is seen during SLE and APAS.