Browsing by Author "PEREIRA, J"

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    A STUDY ON THE ANTIGENIC NATURE OF CIRCULATING IMMUNE-COMPLEXES IN HEMOLYTIC-UREMIC SYNDROME - NO EVIDENCE OF PLATELET MEMBRANE GLYCOPROTEIN ANTIGENS
    (KARGER, 1994) OLAVARRIA, F; PEREIRA, J; MEZZANO, S; KUNICK, M; CASTILLO, A
    Circulating immune complexes (CIC) have been described in the hemolytic uremic syndrome (HUS) in children. They may represent an epiphenomenon or could be related to the platelet activation and endothelial damage observed in this disease. In an attempt to define this relationship, we investigated the CIC isolated in 17 patients with the classic form of HUS, by means of monoclonal antibodies against platelet surface glycoprotein Ib and IIb-IIIa complex. The negative results obtained do not support the possibility of platelet antigens being constituents of CIC and make an antibody-induced platelet activation in HUS very unlikely.
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    ACCUMULATION OF 5-HYDROXYTRYPTAMINE BY AGING PLATELETS - STUDIES IN A MODEL OF SUPPRESSED THROMBOPOIESIS IN DOGS
    (GEORG THIEME VERLAG KG, 1994) ARANDA, E; PIZARRO, M; PEREIRA, J; MEZZANO, D
    Thrombocytopenia was induced in healthy, male mongrel dogs by intramuscular injection of a single dose of estradiol valerate (1 mg/kg). A steady, almost linear decay of the blood platelet count starting about day 6 post-estradiol and attaining a mean value of 14 x 10(3) platelets/mu l one week later was observed. Thrombocytopenia is explained mainly by suppression of thrombocytopoiesis, as established by two independent ways: 1. Megakaryocytes in the bone marrow were markedly reduced. 2. Kinetic studies with In-111 labeled autologous platelets revealed a nearly linear decay of the radioactivity and mean survival times within the expected range. The progressive reduction in the platelet count is associated with an increase in the mean age of the platelets still circulating. Following estradiol injection, platelet 5-hydroxytryptamine (5-HT) increased from a basal value of 130 +/- 30 ng/10(8) platelets (platelet count of 351 +/- 53 x 10(3) platelets/mu l) to 343 +/- 100 ng/10(8) platelets eleven days latter, when the platelet count dropped to 32 +/- 18 x 10(3) platelets/mu l. No significant changes in the number or affinity of the 5-HT uptake receptors could be demonstrated in platelets exposed in vitro and in vivo to estradiol. Our results indicate that aging platelets accumulate 5-HT, probably by a sustained exposure to the monoamine in plasma, confirming previous observations based on models in which thrombopenia was induced by immune and mechanical means.
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    BLEEDING-TIME IN PREECLAMPSIA
    (MUNKSGAARD INT PUBL LTD, 1994) IVANKOVIC, M; PEREIRA, J; BIANCHI, M; GERMAIN, A; MEZZANO, D
    The association of preeclampsia with thrombocytopenia and prolonged bleeding time is reported. The analysis of bleeding time (Simplate II) and the platelet count (Automatic Coulter Counter) in 41 patients with different grades of preeclampsia is presented. Our results suggest that the decrease in the bleeding time observed in moderate preeclampsia and the increase observed in severe preeclampsia are not mainly dependent on the platelet count.
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    CYCLIC THROMBOCYTOPENIA OF APPARENT AUTOIMMUNE ETIOLOGY
    (1989) MENITOVE, JE; PEREIRA, J; HOFFMAN, R; ANDERSON, T; FRIED, W; ASTER, RH
    Serial studies were performed in two patients with cyclic thrombocytopenia to investigate the pathogenesis of this disorder. Mean life span of autologous platelets when platelet levels were declining was subnormal (2.4 and 0.8 days), and megakaryocytes were abundant in the bone marrow during thrombocytopenia. Megakaryocyte colony-stimulating activity could not be detected in the serum of either patient at any point of their cycles. In each patient, total platelet-associated IgG varied inversely with platelet levels. Surface platelet-associated IgG was measured only in patient 2 and was significantly elevated (> 1,280 IgG molecules per platelet) at all stages of the cycle, even durig thrombocytosis. However, the highest values were observed during thrombocytopenia. Platelet-bindable IgG in plasma declined to normal immediately before platelet levels began to rise. IgG eluted from the platelets of this patient reacted strongly with autologous and homologous platelets in contrast to a "mock eluate" prepared from platelets of a normal subject. The eluate from the patient''s platelets reacted strongly with immobilized autologous and homologous glycoprotein IIb/IIIa complex and weakly with GPIb but not with isolated GPIIIa alone. In each patient the decline in platelet levels was significantly delayed following administration of intravenous gamma globulin 0.4 g/kg body weight for five days. These findings suggest that platelet-reactive autoantibodies are of pathogenic significance in some patients with cyclic thrombocytopenia.
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    PLATELET AUTOANTIBODIES IN PATIENTS WITH CHRONIC LIVER-DISEASE
    (1995) PEREIRA, J; ACCATINO, L; ALFARO, J; BRAHM, J; HIDALGO, P; MEZZANO, D
    The thrombocytopenia in chronic liver disease (CLD) has been attributed mainly to hypersplenism, although other factors such as reduced mean life span with increased platelet turnover have also been demonstrated, Immunological abnormalities have been described in the pathogenesis and progression of CLD. In this sense, many studies have reported elevated levels of platelet associated IgG (PAIgG) in patients with CLD, and it has been suggested that PAIgG could represent true antiplatelet antibody. In this study we used a glycoprotein (GP)-specific immunoassay (MACE) to determine whether PAIgG or circulating antiplatelet antibodies, reacted against the GPIIb/IIIa or GPIb/IX complexes, in patients with CLD. Thirty-six patients with CLD of diverse etiology were studied (20 female, mean age 53 years, range 38-75 years). 23 out of 36 patients (64%) had anti-GP antibodies in MACE, Particularly, 12 had anti-GPIb, 4 anti-GPIIb/IIIa, and 7 had both types of autoantibodies, The existence of these anti-GP antibodies was not related with the blood platelet count or etiology of CLD,
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    TOTAL SIALIC-ACID IN HUMAN AND CANINE PLATELETS DOES NOT CHANGE WITH THE PLATELET AGE
    (WILEY-LISS, 1992) MEZZANO, D; ARANDA, E; GARCIA, ME; PEREIRA, J; QUIROGA, T; PEREZ, M
    Total platelet sialic acid (SA) was measured in three experimental conditions: (1) human and canine platelet density subpopulations obtained by centrifugation in arabinogalactan gradients, (2) circulating canine platelets during recovery from experimental immune and mechanical thrombocytopenias, and (3) platelets obtained from a patient with chronic immune thrombocytopenic purpura before and after splenectomy. The density of human and canine platelets is, in part, determined by their age. We found no significant differences in total SA between high-density (HD) and low-density (LD) platelets (9.32 +/- 2.0 vs. 9.55 +/- 1.3-mu-g/mg of platelet protein in dogs and 9.02 +/- 2.3 vs. 9.10 +/- 2.9 mu-g/mg in humans). In the human and canine thrombocytopenic models, the entrance of new platelets from the bone marrow is followed by their aging in the circulation. In these models, no significant changes in total SA content were detected in sequential measurements during the recovery of the thrombocytopenia. Accordingly, we conclude that total SA in human and canine platelets is unrelated to their age in circulation. These results do not support the notion that the loss of SA from membrane glycoproteins determines the recognition and removal of platelets from the circulation.