Properties of a factor in eland plasma that inhibits transformation of bloodstream-form Trypanosoma brucei brucei
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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.