Publications (10) View all
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Article: Heparin-induced thrombocytopenia.
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ABSTRACT: Heparin-induced thrombocytopenia (HIT) is caused by platelet-activating immunoglobulin (Ig) G antibodies that recognize multimolecular complexes of platelet factor 4 (PF4) bound to heparin or other polyanions. Most laboratory assays for HIT have a high sensitivity for anti-PF4/heparin antibodies and a negative test generally excludes HIT (high negative predictive value), especially in a setting of a low pretest probability. The magnitude of a positive test result correlates with greater likelihood of HIT. Therefore, a combined diagnostic approach that considers the clinical picture and the magnitude of a positive test result is recommended for accurate diagnosis of HIT.Methods in molecular biology (Clifton, N.J.) 01/2013; 992:301-18. -
Article: Heparin-induced thrombocytopenia: in vitro studies on the interaction of dabigatran, rivaroxaban, and low-sulfated heparin, with platelet factor 4 and anti-PF4/heparin antibodies.
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ABSTRACT: Heparin is a widely used anticoagulant. Because of its negative charge, it forms complexes with positively charged platelet factor 4 (PF4). This can induce anti-PF4/heparin IgG Abs. Resulting immune complexes activate platelets, leading to the prothrombotic adverse drug reaction heparin-induced thrombocytopenia (HIT). HIT requires treatment with alternative anticoagulants. Approved for HIT are 2 direct thrombin inhibitors (DTI; lepirudin, argatroban) and danaparoid. They are niche products with limitations. We assessed the effects of the DTI dabigatran, the direct factor Xa-inhibitor rivaroxaban, and of 2-O, 3-O desulfated heparin (ODSH; a partially desulfated heparin with minimal anticoagulant effects) on PF4/heparin complexes and the interaction of anti-PF4/heparin Abs with platelets. Neither dabigatran nor rivaroxaban had any effect on the interaction of PF4 or anti-PF4/heparin Abs with platelets. In contrast, ODSH inhibited PF4 binding to gel-filtered platelets, displaced PF4 from a PF4-transfected cell line, displaced PF4/heparin complexes from platelet surfaces, and inhibited anti-PF4/heparin Ab binding to PF4/heparin complexes and subsequent platelet activation. Dabigatran and rivaroxaban seem to be options for alternative anticoagulation in patients with a history of HIT. ODSH prevents formation of immunogenic PF4/heparin complexes, and, when given together with heparin, may have the potential to reduce the risk for HIT during treatment with heparin.Blood 11/2011; 119(5):1248-55. · 9.90 Impact Factor -
Article: Development of a method for magnetic labeling of platelets.
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ABSTRACT: Platelets play a dominant role in the pathogenesis of bleeding disorders and cardiovascular pathology (e.g., myocardial infarction). Nonradioactive labeling of platelets may offer several clinical applications, ranging from survival studies of transfused platelet concentrates to studies on the pathogenesis of stroke. We used ferucarbotran superparamagnetic nanoparticles (NPs) for cell labeling. Platelets incorporated these NPs by endocytosis (without linkers or binding agents). Flow cytometry using FITC-conjugated magnetic NPs showed ex vivo labeling of about 98% of platelets; NPs were predominantly located inside the platelet granules as confirmed by fluorescence microscopy and transmission electron microscopy. Iron concentrations of 2 pg per platelet were reached as determined by atomic absorption spectroscopy. This will enable sensitive ex vivo determination of transfused labeled platelets, allowing survival studies. In vitro, labeled platelets gave a clear signal by 7 Tesla magnetic resonance tomography. Magnetic labeling of platelets may offer a new tool for diagnosis and research in transfusion medicine and cardiovascular medicine. FROM THE CLINICAL EDITOR: In this study a platelet labeling method is discussed and described for in vivo and ex vivo applications, using a binder or linker free fluorescent superparamagnetic iron nanoparticle system. Magnetic labeling of platelets may offer a new tool for diagnosis and research in transfusion medicine and cardiovascular medicine.Nanomedicine: nanotechnology, biology, and medicine 10/2011; 8(5):537-44. · 5.44 Impact Factor -
Article: Epitope mapping of antibodies directed against the human neutrophil alloantigen 3a.
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ABSTRACT: Severe transfusion-related acute lung injury is often caused by antibodies directed against the human neutrophil alloantigen (HNA)-3a. HNA-3a results from an amino acid exchange (Arg154Gln) in the first extracellular loop of the choline transporter-like protein 2 (CTL2). The characteristics of the binding domain(s) of HNA-3a antibodies are unknown. For epitope mapping, a library of 23 different HNA-3a (R(154)) and three HNA-3b (Q(154)) peptides covering different parts of the first extracellular loop of CTL2 (aa(55-231)) was synthesized in Escherichia coli and tested by Western blot with two HNA-3a alloantibody-containing plasma samples and by enzyme immunoassay (EIA) with different HNA-3a- (n = 21) and HNA-3b- (n = 1) positive plasma samples. Despite promising Western blot results using highly reactive plasma samples, we found widely varying reactivities of different HNA-3a plasmas in the EIA, with only 11 of 21 HNA-3a antibodies binding to any of the tested HNA-3a peptides and with no peptide recognized by more than nine of the 21 antibodies. The HNA-3b plasma did not react with R(154) peptides in the EIA nor with R(154) or Q(154) peptides in Western blot experiments. Plasma reactivity profiles with the peptides did not correlate with those observed using granulocyte agglutination and granulocyte immunofluorescence tests. Binding of HNA-3a alloantibodies depends on the conformation of the intact CTL2 protein and their binding sites may differ substantially. Peptide-based assays for detection of HNA-3a antibodies bear the risk to be insensitive and require systematic validation with a large panel of antibodies.Transfusion 03/2011; 51(10):2160-7. · 3.22 Impact Factor -
Article: Platelet factor 4 binds to bacteria, [corrected] inducing antibodies cross-reacting with the major antigen in heparin-induced thrombocytopenia.
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ABSTRACT: A clinically important adverse drug reaction, heparin-induced thrombocytopenia (HIT), is induced by antibodies specific for complexes of the chemokine platelet factor 4 (PF4) and the polyanion heparin. Even heparin-naive patients can generate anti-PF4/heparin IgG as early as day 4 of heparin treatment, suggesting preimmunization by antigens mimicking PF4/heparin complexes. These antibodies probably result from bacterial infections, as (1) PF4 bound charge-dependently to various bacteria, (2) human heparin-induced anti-PF4/heparin antibodies cross-reacted with PF4-coated Staphylococcus aureus and Escherichia coli, and (3) mice developed anti-PF4/heparin antibodies during polymicrobial sepsis without heparin application. Thus, after binding to bacteria, the endogenous protein PF4 induces antibodies with specificity for PF4/polyanion complexes. These can target a large variety of PF4-coated bacteria and enhance bacterial phagocytosis in vitro. The same antigenic epitopes are expressed when pharmacologic heparin binds to platelets augmenting formation of PF4 complexes. Boosting of preformed B cells by PF4/heparin complexes could explain the early occurrence of IgG antibodies in HIT. We also found a continuous, rather than dichotomous, distribution of anti-PF4/heparin IgM and IgG serum concentrations in a cross-sectional population study (n = 4029), indicating frequent preimmunization to modified PF4. PF4 may have a role in bacterial defense, and HIT is probably a misdirected antibacterial host defense mechanism.Blood 10/2010; 117(4):1370-8. · 9.90 Impact Factor
