The trans-sialidase from Trypanosoma cruzi induces thrombocytopenia during acute Chagas' disease by reducing the platelet sialic acid contents

Strong thrombocytopenia is observed during acute infection with Trypanosoma cruzi, the parasitic protozoan agent of American trypanosomiasis or Chagas' disease. The parasite sheds trans-sialidase, an enzyme able to mobilize the sialyl residues on cell surfaces, which is distributed in blood and is a virulence factor. Since the sialic acid content on the platelet surface is crucial for determining the half-life of platelets in blood, we examined the possible involvement of the parasite-derived enzyme in thrombocytopenia induction. We found that a single intravenous injection of trans-sialidase into naïve mice reduced the platelet count by 50%, a transient effect that lasted as long as the enzyme remained in the blood. CD43(−/−) mice were affected to a similar extent. When green fluorescent protein-expressing platelets were treated in vitro with trans-sialidase, their sialic acid content was reduced together with their life span, as determined after transfusion into naïve animals. No apparent deleterious effect on the bone marrow was observed. A central role for Kupffer cells in the clearance of trans-sialidase-altered platelets was revealed after phagocyte depletion by administration of clodronate-containing liposomes and splenectomy. Consistent with this, parasite strains known to exhibit more trans-sialidase activity induced heavier thrombocytopenia. Finally, the passive transfer of a trans-sialidase-neutralizing monoclonal antibody to infected animals prevented the clearance of transfused platelets. Results reported here strongly support the hypothesis that the trans-sialidase is the virulence factor that, after depleting the sialic acid content of platelets, induces the accelerated clearance of the platelets that leads to the thrombocytopenia observed during acute Chagas' disease

Predacion de semillas de Amaranthus quitensis H.B.K. en un cultivo de soja: influencia del sistema de siembra Predation of Amaranthus quitensis H.B.K. seeds in soybean crops: influence of the tillage system

El objetivo fue evaluar las pérdidas del banco superficial de semillas de Amaranthus quitensis H.B.K. (yuyo colorado) debidas a la predación por insectos en un cultivo de soja y en el barbecho posterior, en dos sistemas de laboreo. Los experimentos se realizaron durante las campañas 94/95 y 95/96. Para calcular la tasa de predación se emplearon bandejas cubiertas con tejido para evitar el ingreso de roedores y con tela de tul en los tratamientos testigos; en cada una se sembraron 100 semillas de la maleza y cada 15 días se registró el número de semillas remanentes. Para determinar los insectos presentes y su abundancia se emplearon trampas "pitfall". Entre los insectos capturados se encontró el carábido Notiobia cupripennis, su mayor abundancia se registró en marzo (4,5 y 5,8 insectos/trampa en convencional y 2,7 y 3,3 insectos/trampa en siembra directa), coincidiendo con las tasas de predación más altas (5,6% y 8% en convencional y 2,7% y 3,8% en siembra directa); tanto en abundancia como en predación se observaron diferencias significativas entre ambos sistemas. A partir de este mes, las diferencias no fueron significativas, el número de insectos y la tasa de predación disminuyeron. En ambos años existió una correlación positiva entre estas variables.<br>The objective was to evaluate the losses of the superficial bank of Amaranthus quitensis seeds, due to insect predation, in a soybean crop and in the subsequent fallow, in two tillage systems. Experiments were conducted during 1994/95 and 1995/96. To estimate predation rates, trays covered with wire meshes to prevent rodent predation, and with fine sheer net (tulle) in the control treatment were used; 100 weed seeds were sown in each tray, and the number of remaining seeds was registered every 15 days. Pitfall traps were used to identify insects species occurring in the field and to estimate their abundance. The carabid Notiobia cupripennis was captured in pitfall traps, the higher population found during March (4.5 and 5.8 insect/trap in conventional tillage and 2.7 and 3.3 insect/trap in no-tillage). The highest predation rates was also registered in March (5.6% and 8% in conventional tillage and 2.7% and 3.8% in no-tillage) and both systems were significantly different as to abundance and predation. No significant differences were found from April to June, and the number of insects and predation rates decreased. There was a positive correlation between the predation rates and the values of insect abundance in both years