Platelet endothelial cell adhesion molecule-1 (PECAM-1) is a target glycoprotein in drug-induced thrombocytopenia

Drug-induced immune thrombocytopenia (DITP) is a serious complication of drug treatment. Previous studies demonstrated that most drug-dependent antibodies (DDAbs) react with the platelet membrane glycoprotein (GP) complexes IIb/IIIa and Ib/IX/V. We analyzed the sera from 5 patients who presented with DITP after intake of carbimazole. Notably, thrombocytopenia induced by carbimazole was relatively mild in comparison to patients with DITP induced by quinidine. The sera reacted with platelets in an immunoassay on addition of the drug. In immunoprecipitation experiments with biotin-labeled platelets and endothelial cells, reactivity with the platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31) could be demonstrated, whereas neither GPIIb/IIIa nor GPIb/IX was precipitated in the presence of the drug. These results could be confirmed by GP-specific immunoassay (MAIPA) using monoclonal antibodies (mabs) against PECAM-1. In addition, the binding of DDAbs could be abolished by preincubation with soluble recombinant PECAM-1. Carbimazole-dependent antibodies showed similar reactivity with platelets carrying the Leu(125) and Val(125) PECAM-1 isoforms, indicating that this polymorphic structure, which is located in the first extracellular domain, is not responsible for the epitope formation. Binding studies with biotin-labeled mutants of PECAM-1 and analysis of sera with mabs against different epitopes on PECAM-1 in MAIPA assay suggested that carbimazole-dependent antibodies prominently bound to the second immunoglobulin homology domain of the molecule. Analysis of 20 sera from patients with quinidine-induced thrombocytopenia by MAIPA assay revealed evidence that DDAbs against PECAM-1 are involved in addition to anti-GPIb/IX and anti-GPIIb/IIIa. We conclude that PECAM-1 is an important target GP in DITP. (Blood. 2000;96:1409-1414)     

替罗非班在非ST段抬高型急性冠脉综合征患者中的临床应用价值

目的 观察早期使用血小板膜糖蛋白（GP）Ⅱb/Ⅲa受体拮抗剂（替罗非班）对非ST段抬高型急性冠脉综合征（NSTE-ACS）患者疗效及安全性.方法 选取我院2010年1月～2012年12月诊断为NSTE-ACS的患者2000例,按是否使用替罗非班为标准分为替罗非班组（713例）和对照组（1287例）,分别比较两组的临床基线特征、两组患者在住院期间心血管事件发生率（全因死亡、顽固性心绞痛、再发心肌梗死）;心肌梗死1周后左室舒张末期内径及射血分数、梗死相关动脉无复流的发生率、PCI术后罪犯血管TIMI3级血流发生率、住院时间、血小板减少发生率、严重出血事件.结果 两组患者顽固性心绞痛发生率、再发心肌梗死发生率、心肌梗死1周后左室射血分数、术后TIMI3级血流发生率、梗死相关动脉无复流的发生率比较,差异均有统计学意义（P＜0.05）.住院时间、出血事件及血小板减少的发生率比较差异无统计学意义（P＞0.05）.结论 针对NSTE-ACS患者使用替罗非班可有效降低住院期间心血管事件的发生,改善TIMI血流,且不增加血小板减少及大出血的发生.     

Fibrinogen receptor antagonist-induced thrombocytopenia in chimpanzee and rhesus monkey associated with preexisting drug-dependent antibodies to platelet glycoprotein IIb/IIIa.

Most clinical trials with fibrinogen receptor antagonists (FRAs) have been associated with thrombocytopenia. This report describes the occurrence of thrombocytopenia in one chimpanzee and one rhesus monkey upon administration of potent FRAs. Chimpanzee A-264 experienced profound thrombocytopenia on two occasions immediately upon intravenous administration of two different potent FRAs, L-738, 167 and L-739,758. However, an equally efficacious antiaggregatory dose of another potent antagonist, L-734,217, caused no change in platelet count. These compounds did not affect platelet count in five other chimpanzees or numerous other nonhuman primates. Flow cytometric analysis showed drug-dependent antibodies (DDAbs) in the plasma of chimpanzee A-264 that bound to platelets of chimpanzees, humans, and all other primates tested only in the presence of the compounds that induced thrombocytopenia. Rhesus monkey 94-R021 experienced thrombocytopenia upon administration of a different antagonist, L-767,679, and several prodrugs that are converted into the active form, L-767,679, in the blood. More than 20 other FRAs, including those that induced thrombocytopenia in chimpanzee A-264, had no effect on platelet count in this monkey. Flow cytometric measurements again identified DDAbs that reacted with platelets of all primates tested and required the presence of L-767,679. Screening for DDAbs in the plasma of 1,032 human subjects with L-738, 167 and L-739,758 demonstrated that the incidence of these preexisting antibodies in this population was 0.8% +/- 0.6% and 1.1% +/- 0.6%, respectively.     

早期应用替罗非班对急性ST段抬高型心肌梗死急诊介入治疗的有效性及安全性分析

目的评价在急性ST段抬高型心肌梗死经皮冠状动脉介入治疗（PCI）中早期应用血小板膜糖蛋白Ⅱb／Ⅲa受体拮抗剂替罗非班的有效性和安全性。方法将80例急性ST段抬高型心肌梗死患者随机分为替罗非班组（替罗非班＋直接PCI,40例）和对照组（直接PCI,40例）。比较两组患者梗死相关动脉PCI后即刻TIMI血流、术后90min心电图ST段回落百分比、术后7d左室射血分数、术后30d内主要不良心脏事件（心绞痛、心肌梗死、死亡）、出血和血小板减少的发生率。结果替罗非班组PCI后慢复流发生率及主要不良心脏事件的发生率均低于对照组（P〈0．05）,出血并发症的发生与对照组比较差异无统计学意义（P〉0．05）。结论早期应用替罗非班能改善急性ST段抬高型心肌梗死患者PCI后梗死相关血管的TIMI血流,减少PCI后主要不良心脏事件的发生率,临床应用安全有效。     

Heparin-induced thrombocytopenia and thrombosis: a prospective analysis of the incidence in patients with heart and cerebrovascular diseases

Heparin-induced thrombocytopenia and/or thrombosis (HITT) are serious complications of heparin treatment. The incidence, as previously reported, varies widely and, in consequence, is not precisely known. Moreover, most reports only concern clinically defined heparin-induced thrombocytopenia. Therefore we carried out a prospective study of the incidence of serologically confirmed HITT.
All patients admitted to the Departments of Cardiology and Neurology of our institution with an indication for treatment with therapeutic-dose intravenous unfractionated heparin were enrolled in the study. The patients were examined daily for the occurrence of thromboembolic complications. Regular platelet counts and tests for the presence of heparin-dependent antibodies were carried out using two different tests: a quantitative platelet factor 4/heparin (PF4/hep) Elisa, and a functional test, the heparin-induced platelet activation assay (HIPAA). HITT was defined as a rapidly occurring (within 5 d) decrease of the platelet count from normal values of >120 ×10⁹ l to <60 ×10⁹ l or to <100 ×10⁹ l if there was a rapid fall of >50% of starting value or >30% with concomitant acute thrombosis.
The observed incidence of HITT was 1/358 patients (0.3%, 95% confidence limits 0.01–1.5%). However, Elisa PF4/hep specific IgG antibodes were demonstrated in nine (2.5%) and IgM antibodies in seven (2.0%) of 358 patients. 30/358 patients (8.4%) had platelet activating antibodies in the HIPAA.
We conclude that the incidence of serologically confirmed HITT in this study is very low (0.3%) in patients with cardiac and neurologic diseases treated with intravenous unfractionated heparin. The frequency of heparin-dependent antibodies without concomitant occurrence of thrombocytopenia is much higher.     

Delayed-onset heparin-induced thrombocytopenia and thrombosis

BACKGROUND: Heparin-induced thrombocytopenia is a prothrombotic drug reaction caused by platelet-activating antibodies that recognize complexes of platelet factor 4 and heparin. OBJECTIVE: To describe a syndrome termed delayed-onset heparin-induced thrombocytopenia, in which thrombocytopenia and thrombotic events begin 5 or more days after withdrawal of heparin. DESIGN: Case series. SETTING: Secondary and tertiary care hospitals. PATIENTS: 12 patients who presented with serologically confirmed, delayed-onset heparin-induced thrombocytopenia, including 6 outpatients presenting after hospital discharge. MEASUREMENTS: The platelet serotonin-release assay was used to measure IgG-induced heparin-dependent and heparin-independent platelet activation; an enzyme immunoassay that detects IgG against platelet factor 4-heparin complexes was also used. RESULTS: Patients with delayed-onset heparin-induced thrombocytopenia presented with thrombocytopenia and associated thrombosis a mean of 9.2 days (range, 5 to 19 days) after stopping heparin therapy. Nine patients received additional heparin, with further decrease in platelet counts. Compared with controls, patients with delayed-onset heparin-induced thrombocytopenia had higher titers of IgG antibodies to platelet factor 4-heparin and greater IgG-induced heparin-dependent and heparin-independent platelet activation. CONCLUSIONS: Delayed-onset heparin-induced thrombocytopenia should be suspected when patients present with thrombocytopenia and thrombosis up to 3 weeks after exposure to heparin. This syndrome could be caused by high titers of platelet-activating IgG induced by heparin.     

Thrombocytopenia after treatment with platelet glycoprotein IIb/IIIa inhibitors

Abciximab, eptifibatide, and tirofiban are the three drugs approved by the US Food and Drug Administration designed to block platelet aggregation by binding glycoprotein IIb/IIIa. Results from large therapeutic trials demonstrate that all three agents induce thrombocytopenia in approximately 1% to 5% of cardiac patients. Thrombocytopenia is typically rapid in onset and antibody mediated. In vitro evidence suggests abciximab-induced thrombocytopenia is associated with antibodies directed to murine sequences within the chimeric anti-IIb/IIIa molecule. In addition, abciximab, eptifibatide, and tirofiban also function as mixed agonist-antagonists in vivo, inducing neoepitopes within the glycoprotein IIb/IIIa receptor that may react with pre-existing or induced antibodies. Screening for the development of these antibodies may reduce the incidence of thrombocytopenia associated with these agents, but it may limit their chronic usage.     

Antibodies against complement-regulatory proteins on platelets in immune thrombocytopenia

In immune thrombocytopenia (ITP), antibodies reacting with platelet membrane glycoproteins (GP) mediate premature platelet cleavage, resulting in thrombocytopenia and therefore a risk of bleeding. These antibodies may induce complement activation, thus mediating complement-induced platelet destruction. In this study, we investigated the possibility of an additional complement-related pathogenic mechanism, where antibodies against the complement-regulatory factors CD55 and CD59 may directly interfere with normal complement function. CD55 downregulates both the classic and the alternative activation pathways, while CD59 blocks the formation of the membrane attack complex; both proteins are present on platelets and may therefore be targets of autoantibodies.

Using the simultaneous analysis of specific platelet antibodies (SASPA) assay, we found that in some cases of immune-mediated thrombocytopenia, anti-CD55 and -CD59 antibodies are detectable in patients’ sera and/or on their autologous platelets in combination with antibodies against platelet-specific GP. Although antibodies against CD55 and CD59 seem to be a rare phenomenon, this finding may have clinical relevance due to the availability of highly effective therapeutics targeting the complement system.     

Fine specificity of drug-dependent antibodies reactive with a restricted domain of platelet GPIIIA

Drug-induced immune thrombocytopenia is caused by drug-dependent antibodies (DDAbs) that bind tightly to platelet glycoproteins only when drug is present. How drugs mediate this interaction is not yet resolved. Several studies indicate that sites recognized by DDAbs tend to cluster in specific structural domains, suggesting they may recognize a limited number of distinct epitopes. To address this issue, we characterized the binding sites for 16 quinine-dependent antibodies thought on the basis of preliminary studies to be possibly specific for a single epitope on glycoprotein IIIa (GPIIIa). Fourteen of the antibodies reacted with a 29-kDa GPIIIa fragment comprising only the GPIIIa hybrid and plextrin-semaphorin-integrin homology domains. However, studies with mutant GPIIIa and the blocking monoclonal antibody AP3 showed that the 14 DDAbs recognize at least 6 and possibly more distinct, but overlapping, structures involving GPIIIa residues 50 to 66. The findings suggest that even antibodies specific for restricted domains on a target glycoprotein may each have a slightly different fine specificity; ie, "unique" epitopes recognized by DDAbs may be rare or nonexistent. The observations are consistent with a recently proposed model in which drug reacts noncovalently with both target protein and antibody to promote binding of an otherwise nonreactive immunoglobulin.     

Heparin-induced thrombocytopenia

Hemorrhage is the most common and best-recognized complication of heparin treatment. However, a potentially more dangerous complication is the development of heparin-induced thrombocytopenia (HIT). All patients exposed to heparin, irrespective of the dose and route of administration, are at risk of developing HIT. It is due to the formation of antibodies against the heparin-platelet factor 4 complex, which cause secondary activation of platelets, coagulation and, finally, increased thrombin production. The main symptom is the sudden onset of thrombocytopenia involving a drop in the platelet count to less than 50% of the basal level, with or without the appearance of thrombotic complications some 5 to 14 days after the start of heparin therapy. Heparin-induced thrombocytopenia can be detected early in patients receiving heparin by monitoring the platelet count. Demonstration of heparin-dependent platelet activation using an antigen or functional assay confirms the clinical diagnosis. Once the diagnosis of HIT has been confirmed serologically or there is a high level of suspicion of HIT, heparin must be suspended and treatment with an alternative anticoagulant should be considered. This review contains a discussion of the diagnosis and treatment of this syndrome.     

Laboratory tests for identification or exclusion of heparin induced thrombocytopenia: HIT or miss?

Heparin induced thrombocytopenia (HIT) is a potentially fatal condition that arises subsequent to formation of antibodies against complexes containing heparin, usually platelet‐factor 4‐heparin (“anti‐PF4‐heparin”). Assessment for HIT involves both clinical evaluation and, if indicated, laboratory testing for confirmation or exclusion, typically using an initial immunological assay (“screening”), and only if positive, a secondary functional assay for confirmation. Many different immunological and functional assays have been developed. The most common contemporary immunological assays comprise enzyme‐linked immunosorbent assay [ELISA], chemiluminescence, lateral flow, and particle gel techniques. The most common functional assays measure platelet aggregation or platelet activation events (e.g., serotonin release assay; heparin‐induced platelet activation (HIPA); flow cytometry). All assays have some sensitivity and specificity to HIT antibodies, but differ in terms of relative sensitivity and specificity for pathological HIT, as well as false negative and false positive error rate. This brief article overviews the different available laboratory methods, as well as providing a suggested approach to diagnosis or exclusion of HIT.     

Modulation of platelet caspases and life-span by anti-platelet antibodies in mice

Anti-platelet antibodies are known to contribute to some types of thrombocytopenia. In this work we investigated anti-platelet antibodies with opposite influence upon activation and kinetics of platelet caspases. A rabbit anti-platelet antibody induced a profound thrombocytopenia, which was associated with an increase of microparticles in plasma and an activation of platelet caspases, as detected by the binding of a carboxyfluorescein-labeled fluoromethyl ketone probe (FAM-VAD-fmk). Furthermore, microparticles and thrombocytopenia were prevented by the injection of a caspase inhibitor ZVAD-fmk. In contrast, an anti-CD18 mAb (M18.2) induced a thrombocytosis, due to an increased platelet life-span and which was evident in wild-type (+/+), but not in CD18-/- or CD87-/-, mice indicating a requirement of these two surface molecules. Activation of caspases was decreased in platelets from mice injected with the M 18.2 mAb, as evidenced by a decreased binding of the VAD probe, detected by flow cytometry, or an increase in the level of pro-caspase-3, seen on Western blots. These observations indicate firstly, that anti-platelet antibodies can either promote or inhibit activation of platelet caspases, and secondly, that the activation of caspases regulates platelet life-span.     

Acute thrombocytopenia after treatment with tirofiban or eptifibatide is associated with antibodies specific for ligand-occupied GPIIb/IIIa

Acute thrombocytopenia is a recognized complication of treatment with GPIIb/IIIa inhibitors whose cause is not yet known. We studied 9 patients who developed severe thrombocytopenia (platelets less than 25 x 10(9)/L) within several hours of treatment with the GPIIb/IIIa inhibitors tirofiban (4 patients) and eptifibatide (5 patients). In each patient, acute-phase serum contained a high titer (range, 1:80-1:20 000) IgG antibody that reacted with the glycoprotein IIb/IIIa complex only in the presence of the drug used in treatment. Four patients had been previously treated with the same drug, but 5 had no known prior exposure. Pretreatment serum samples from 2 of the latter patients contained drug-dependent antibodies similar to those identified after treatment. No tirofiban- or eptifibatide-dependent antibodies were found in any of 100 randomly selected healthy blood donors, and only 2 of 23 patients receiving tirofiban or eptifibatide who did not experience significant thrombocytopenia had extremely weak (titer, 1:2) tirofiban-dependent antibodies. In preliminary studies, evidence was obtained that the 9 antibodies recognize multiple target epitopes on GPIIb/IIIa complexed with the inhibitor to which the patient was sensitive, indicating that they cannot all be specific for the drug-binding site. The findings indicate that acute thrombocytopenia after the administration of tirofiban or eptifibatide can be caused by drug-dependent antibodies that are "naturally occurring" or are induced by prior exposure to drug. These antibodies may be human analogs of mouse monoclonal antibodies that recognize ligand-induced binding sites (LIBS) induced in the GPIIb/IIIa heterodimer when it reacts with a ligand-mimetic drug.     

Report of a patient with heparin-induced thrombocytopenia type II associated with IgA antibodies only.

Heparin-induced thrombocytopenia type II (HIT II) is usually mediated by immunoglobulin G (IgG) antibodies that lead to platelet activation via the FcgammaIIA-receptor. Here we describe a patient who developed HIT II after aortocoronary bypass surgery. His serum contained an antibody that was detectable by the heparin-induced platelet activation assay (HIPA) and by the ID-HPF4 particle agglutination assay. The flow cytometric analysis showed that the antibody was of the IgA class.     

Tirofiban-associated acute thrombocytopenia

Randomized clinical trials of glycoprotein IIb/IIIa inhibition during percutaneous coronary intervention have shown significant clinical efficacy and safety in reducing the morbidity and mortality. In Turkey, only tirofiban is available. Tirofiban is a safe and effective agent in combination with heparin and aspirin in the setting of an acute coronary syndrome. In previous studies involving tirofiban, the incidence of bleeding complications was more frequent than heparin alone but major bleeding complications were seen in 5.3% of patients receiving tirofiban and not significantly different from the heparin-only treated patients.The incidence of thrombocytopenia, defined as an absolute platelet count of < 90,000/mm3, was 0.4% in the PRISM, 1.9% in PRISM-PLUS and 1.1% in RESTORE trials. We reported a case of acute profound thrombocytopenia 48 hours after the administration of tirofiban in the treatment of a patient with an acute coronary syndrome and tirofiban discontinuation was sufficient in the management of this condition.     

Glycoprotein IIb/IIIa complex is the target in mirtazapine-induced immune thrombocytopenia

Mirtazapine (MW 265.36), a tetracyclic antidepressant of the piperazine-azapine group which augments central noradrenergic and serotonergic activity, is currently used as an oral antidepressant. We report a case of severe thrombocytopenia in a 66-year-old patient occurring after mirtazapine administration, suggesting an immune mechanism. This report documents the first case of mirtazapine-induced immune thrombocytopenia. The patient's serum was screened for drug-induced anti-platelet antibody with the chromium(51) (Cr(51)) platelet lysis technique. The drug-dependent antibody was characterized using flow cytometry, the monoclonal antibody immobilization of platelet antigens assay (MAIPA assay), and immunoprecipitation. By the Cr(51) platelet lysis technique, we obtained an equivocal result for the detection of mirtazapine-induced antibody. However, the patient's serum tested positive for mirtazapine-induced antibody by flow cytometry. The results showed that the binding ratio of 5.7 (mean fluorescence intensity) in the presence of the patient's serum and mirtazapine in a final concentration of 1.0 mmol/L was strongly positive. The antibody was found to bind the glycoprotein (GP) IIb/IIIa complex by MAIPA assay by using five different monoclonal antibodies against GP complexes Ib/IX, GPIIb/IIIa, or GPIa/IIa. Immunoprecipitation studies showed that the GPIIb/IIIa complex was precipitated by antibody in the presence, but not in the absence, of mirtazapine. These findings provide evidence that immune thrombocytopenia can be caused by sensitivity to the antidepressant mirtazapine. This is the first well-documented case of mirtazapine-induced immune thrombocytopenia.     

冠脉内注射替罗非班治疗急性冠脉综合征 介入术后无复流的有效性和安全性

目的 评价冠脉内注射国产盐酸替罗非班对急性冠脉综合征（ACS）介入术后无复流患者TIMI血流的影响及安全性。方法 ACS患者行支架植入术后判定无复流者46例,随机分为替罗非班组(冠脉内注射盐酸替罗非班10 μg/kg)26例,硝酸甘油组(冠脉内注射硝酸甘油200 μg)20例。观察给药后30 min TIMI血流分级及校正的TIMI计帧数（CTFC）,2 d后安全性的终点及30 d主要不良心血管事件(MACE)发生率。结果 替罗非班组介入术后无复流患者TIMI Ⅲ级血流获得率显著高于硝酸甘油组(65% vs 30%,P<0.05);校正的TIMI计帧数显示替罗非班组血流快于硝酸甘油组［(72±19) vs (93±22),P<0.01］,两组患者30 d的MACE发生率替罗非班组低于硝酸甘油组(4% vs 20%),但差异未达到显著水平。替罗非班组出血不良反应较硝酸甘油组略高（12% vs 10%）,但差别无统计学意义,两组均未见血小板减少。结论 冠脉内注射国产盐酸替罗非班治疗ACS介入术后无复流患者是有效和安全的。     

Laboratory testing for VITT antibodies

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a highly prothrombotic disorder that like heparin-induced thrombocytopenia (HIT) is caused by platelet-activating antibodies that recognize platelet factor 4 (PF4). However, unlike HIT—where heparin at low concentrations (0.1-0.5 U/mL) typically enhances antibody-induced platelet activation, platelet activation by VITT sera is usually inhibited by heparin. Further, conventional platelet activation assays for HIT, such as the serotonin-release assay (SRA) and heparin-induced platelet activation (HIPA) test, often yield negative or atypical results when testing VITT sera. Nevertheless, VITT (like HIT) is a “clinical-pathological” disorder whereby laboratory detectability of platelet-activating anti-PF4 antibodies is crucial for diagnosis. VITT antibodies follow 2 fundamental principles of HIT laboratory testing: (1) high probability of a positive PF4-dependent enzyme-immunoassay (EIA), and (2) high probability of a positive platelet activation assay. However, optimal detection of VITT in platelet activation assays requires the addition of PF4, for example, PF4-enhanced SRA (PF4-SRA) and PF4-enhanced HIPA (PIPA). A novel whole blood assay, called the PF4-induced flow cytometry-based platelet activation (PIFPA) assay, exhibits high sensitivity and specificity for VITT. HIT and VITT sera/plasmas differ in their reactivity in rapid HIT immunoassays (90-97% sensitivity for HIT, <25% sensitivity for VITT), consistent with distinct antigen sites on PF4 recognized by HIT and VITT antibodies.     

Platelet function after a high dose bolus of tirofiban immediately after coronary angioplasty

In the TARGET trial, the lower incidence of cardiac events at one month with abciximab compared with tirofiban was attributed to a lack of efficacy in the first hour because of suboptimal dosage. The object of this study was to confirm that high dose tirofibal is associated with over 90% platelet inhibition during the first hour and to analyse the effect of this new dosage on platelet activation. Thirty-three patients treated with clopidogrel and aspirin for an acute coronary syndrome without ST elevation were given before angioplasty a bolus of 25 microg/Kg of tirofiban injected in 3 minutes, followed by an infusion of 0.15 microg/kg/min. Blood samples were taken before the treatment (TO) and at the 45th minute (T1) to measure platelet aggregation induced by ADP, the expression of P-selection, the quantification of circulating monocyte-platelet aggregates and the phospholyration of VASP protein. The results showed that all patients had over 90% (100%) inhibition of platelet aggregation at T1. The expression of P-selection was significantly reduced (T0: 0.195 +/- 0.057 MFI; T1: 0.186 +/- 0.055 MFI, p = 0.03). There was no significant difference in the number of monocyte-platelet aggregates or in the phosphorylation of VASP. In conclusion, a bolus of 25 microg/Kg/3 min of tirofiban provides over 90% inhibition of platelet aggregation in the first hour. The initial platelet proactivator effect at this dosage was shown to have disappeared with an inhibition of platelet activation.     

Antibodies to platelet glycoproteins in haemophiliacs infected with HIV

Summary The techniques of Western blotting and the monoclonal antibody specific immobilization of platelet antigen (MAIPA) assay were used to detect antibodies to platelet glycoproteins in 43 samples of serum from 23 anti-HIV positive haemophiliacs (8 with severe thrombocytopenia, 6 with moderate thrombocytopenia, and 9 with a normal platelet count), six anti-HIV negative haemophiliacs and ten controls. Antibodies were present in the majority of anti-HIV positive patients' sera even before the onset of thrombocytopenia. Thrombocytopenia was associated with an increase in the incidence of antibodies to GPIIIa and GPIb, whereas the antigen most frequently recognized in patients without thrombocytopenia was GPIIb. Anti-GPIIb and/or GPIIIa reactivity was also seen in three out of the six anti-HIV negative patients. There was no correlation between the absolute platelet count and the detection of antibodies in either assay. Effective therapy for thrombocytopenia with zidovudine, interferon or splenectomy did not influence the presence of antibody. Eight of nine patients with AIDS were negative in the MAIPA assay, consistent with their depressed immune status. It is concluded that the production of antibodies to platelet membrane glycoprotein in anti-HIV positive haemophiliacs is influenced by factors other than HIV. The presence of such antibodies is independent of the platelet count and is therefore unlikely to play a causative role in HIV-related thrombocytopenia.