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Properties of a factor in eland plasma that inhibits transformation of bloodstream-form Trypanosoma brucei brucei
Published online by Cambridge University Press: 19 September 2011
Abstract
Fresh plasma from the African eland, Taurotragus oryx, contains a factor that inhibits the transformation of bloodstream-form Trypanosma brucei brucei into procyclic (midgut) forms. Heating of the plasma at 42, 50 and 60 °C for 30 min resulted in a 20, 38 and 40% loss of inhibitor activity respectively, whereas only negligible loss occurred below 42 °C. Similarly, one and four freeze-thawing cycles resulted in 32 and 60% loss of activity respectively. Inactivation of the inhibitor activity, which occurred rapidly during storage (for example, 80% loss after 7 days at -20 °C) could not be stopped by the addition of various protease inhibitors or lyophilisation of the plasma. Treatment of plasma with pronase (1 mg/ml for 2 h) completely abrogated the inhibitor activity, whereas trypsinisation had only a partial effect. Ammonium sulphate fractionation of fresh plasma showed that the inhibitor was insoluble above 50% salt. When the plasma was fractionated by anion-exchange chromatography, the inhibitory activity was recovered in the bound fractions. Efforts to purify the inhibitor were unsuccessful due to the rapid loss of activity under all conditions tested. It is concluded that the low capacity of eland blood to support transformation of bloodstream trypanosomes is due to an inhibitor present in the plasma fraction.
Résumé
Le plasma frais de l'élan africain, Taurotragus oryx, contient un facteur qui inhibe la transformation des formes sanguines de Trypanosoma brucei brucei en formes procycliques (intestinales). Le chauffage du plasma à 42, 50 et 60 °C pendant 30 min provoque 20, 38 et 40% de perte de l'activité inhibitrice respectivement, alors que la perte est négligeable en dessous de 42 °C. De même, un et quatre cycles de congélation-décongélation provoquent respectivement 32 et 60% de perte d'activité. L'inactivation de l'activité inhibitrice, qui intervient rapidement pendant le stockage (par exemple, 80% de perte après 7 jours à -20 °C) ne peut pas être arrêtée par l'addition de différents inhibiteurs de protéases ou la lyophilisation du plasma. Le traitement du plasma avec de la pronase (lmg/ml pendant 2 heures) supprime complètement l'activité inhibitrice, alors que la trypsinisation a seulement une effet partiel. Le fractionnement par le sulphate d'ammonium du plasma frais indique que l'inhibiteur est insoluble au dessus de 50% de sel. Quand le plasma est fractionné en Chromatographie par échange d'anions, l'activité inhibitrice est retrouvée dans les fractions liées. Les tentatives de purification de l'inhibiteur ont échoué à cause de la perte rapide d'activité pour toutes les conditions testées. On en conclut que la faible capacité du sang d'élan à favoriser la transformation des formes sanguines du trypanosome est dû à un inhibiteur présent dans la fraction plasmique.
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