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Isolation and characterization of an antifactor V antibody causing activated protein C resistance from a patient with severe thrombotic manifestations
No full textBlood. 2002 Jun 1;99(11):3985-92.
Isolation and characterization of an antifactor V antibody causing activated
protein C resistance from a patient with severe thrombotic manifestations.
Kalafatis M, Simioni P, Tormene D, Beck DO, Luni S, Girolami A.
Department of Chemistry, Cleveland State University, The Cleveland Clinic
Foundation, Cleveland, OH 44115, USA. [email protected]
A 44-year-old woman with a history of severe thrombotic manifestations presented
with a markedly reduced activated protein C-sensitivity ratio (APC-SR). DNA
sequencing of and around the regions encoding the APC cleavage sites in the
factor Va molecule excluded the presence of the factor VLeiden mutation and of
other known genetic mutations. No antiphospholipid antibodies were present in the
patient's plasma and both prothrombin time and activated partial thromboplastin
time were normal. The total immunoglobulin fraction was isolated from the
patient's plasma and found to induce severe APC resistance when added to normal
plasma and to factor V-deficient plasma supplemented with increasing
concentrations of factor V. Immunoblotting and immunoprecipitation experiments
with the total immunoglobulin fraction purified from the patient's plasma
demonstrated that the antibody recognizes factor V, is polyclonal, and has
conformational epitopes on the entire factor V molecule (heavy and light chains,
and B region). Thus, the immunoglobulin fraction interferes with the
anticoagulant pathway involving factor V. The inhibitor was isolated by
sequential affinity chromatography on protein G-Sepharose and factor V-Sepharose.
The isolated immunoglobulin fraction inhibited factor Va inactivation by APC
because of impaired cleavage at Arg306 and Arg506 of the heavy chain of the
cofactor. The isolated immunoglobulin fraction was also found to inhibit the
cofactor effect of factor V for the inactivation of factor VIII by the
APC/protein S complex. Our data provide for the first time the demonstration of
an antifactor V antibody not related to the presence of antiphospholipid
antibodies, which is responsible for thrombotic rather than hemorrhagic symptoms.
PMID: 12010798 [PubMed - indexed for MEDLINE
Phenotype and genotype expression in pseudohomozygous R2 factor V
No full textCoagulation Phenotype and FV genotype expression in pseudohomozygous R2 factor
An antifibrinolytic mechanism describing the prothrombotic effect associated with factor VLeiden.
No full textPlatelet-derived factor V/Va Leiden cofactor activities are sustained on the surface of activated platelets despite the presence of activated protein C
No full textWe investigated the role of the thrombin-activated platelet in modulating the rate and extent of activated protein C (APC)-catalyzed inactivation of platelet-derived factor Va and factor VaLeiden. Platelet-derived factor Va and factor VaLeiden were inactivated by APC at near identical rates; however, complete inactivation of the cofactors was never achieved. Greater residual cofactor activity remained when using thrombin-activated platelets compared with that observed with synthetic phospholipid vesicles and platelet-derived microparticles, suggesting that thrombin-activated platelets protect the cofactors from APC-catalyzed inactivation. This apparent protection was not due to (1) an insufficient number of membrane binding sites for APC or factor Va; (2) the destruction of these sites; or (3) the presence of a platelet-associated APC inhibitor. Results from a plasma-based clotting assay (with or without APC) with platelets or PCPS vesicles added to induce clot formation indicated that, even in the presence of high concentrations of APC, platelets offered protection of the cofactor by delaying cleavage at Arg506. This resulted in incomplete proteolysis of the heavy chain, suggesting that platelets can also protect plasma-derived factor Va from APC-catalyzed inactivation. However, additional experiments indicated that the plasma-derived cofactor, bound to thrombin-activated platelets, was completely inactivated by APC, suggesting that the plasma and platelet-derived cofactor pools represent different substrates for APC. Collectively, these results indicate that platelets sustain procoagulant events by providing a membrane surface that delays cofactor inactivation and by releasing a cofactor molecule that displays an APC resistant phenotype. Thus, at sites of arterial injury, the factor VLeiden mutation may not as readily predict arterial thrombosis, because the normal and variant platelet-derived cofactors are equally resistant to APC at the activated platelet surface
Isolation and characterization o fan anti-factor VIII antibody from a patient with acquired hemophilia
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Increased tissue factor-initiated prothrombin activation as a result of the Arg506-->Gln mutation in factor V Leiden.
Full text linkThe effect of the Arg506 --> Gln mutation in factor VLEIDEN on thrombin generation was evaluated in a reconstituted system using the purified components of the tissue factor (TF) pathway to thrombin and the components of the protein C pathway. Recombinant full-length tissue factor pathway inhibitor (RTFPI) was included in the system because of a previously observed synergistic inhibitory effect of TFPI and the protein C pathway on TF-initiated thrombin generation. Thrombin generation initiated by 1.25 pM factor VIIa.TF in the absence of the protein C pathway components occurs following an initiation phase, after which prothrombin is quantitatively converted to 1.4 microM thrombin. The factor VLEIDEN mutation did not influence thrombin generation in the reconstituted model in the absence of the protein C pathway. In the presence of 2.5 nM TFPI, 65 nM protein C, and 10 nM recombinant soluble thrombomodulin (Tm), thrombin generation catalyzed by normal factor V was abolished after the initial formation of 25 nM thrombin. In contrast, persistent thrombin generation was observed in the presence of factor VLEIDEN in the same system, although the rate of thrombin generation was slower compared with the reaction without protein C and Tm. The rate of thrombin generation with factor VLEIDEN increased with time and ultimately resulted in quantitative prothrombin activation. When the TFPI concentration was reduced to 1.25 nM, thrombin generation is still curtailed in the presence of normal factor V. In contrast, under similar conditions using factor VLEIDEN, the protein C pathway totally failed to down-regulate thrombin generation. The dramatic effect of a 50% reduction in TFPI concentration on the inhibitory potential of the protein C pathway on thrombin generation catalyzed by factor VLEIDEN suggests that the observed synergy between TFPI and the protein C pathway is directly governed by the TFPI concentration and by cleavage of the factor Va heavy chain at Arg506. This cleavage appears to have a dramatic regulatory effect in the presence of low concentrations of TFPI. Markedly increased thrombin generation in the presence of both 1.25 nM TFPI and factor VLEIDEN was also observed when antithrombin-III was added to the system to complete the natural set of coagulation inhibitors. Protein S (300 nM) had a minimal effect in the model on the inhibition of thrombin generation by protein C, Tm, and TFPI, with either normal factor V or factor VLEIDEN. Protein S also failed to significantly potentiate the action of the protein C pathway in the presence of antithrombin-III in reactions employing normal factor V or factor VLEIDEN. The absence of an effect of protein S in the model, which employs saturating concentrations of phospholipid, suggests that the reported interactions of protein S with coagulation factors are not decisive in the reaction. Altogether the data predict that TFPI levels in the lower range of normal values are a risk factor for thrombosis when combined with the Arg506 --> Gln mutation in factor VLEIDEN
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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