Trypanosoma brucei: polyamine oxidase mediated trypanolytic activity in the serum of naturally resistant cattle

Trypanosoma brucei brucei are lysed when incubated in vitro in a mixture of bovine serum and polyamine. Normal bovine serum alone or polyamine alone does not show any trypanocidal activity. The bovine serum in the mixture can be replaced by purified polyamine oxidase, and addition of polyamine oxidase inhibitors blocks trypanolysis. Using this in vitro lysis test, it is shown that West African cattle which are resistant naturally to trypanosomiasis have a higher trypanolytic activity in their serum than do trypanosensitive cattle (P less than 10(-5]. Seric trypanolytic activity of individual animals remains stable when tested over a period of 18 months; moreover, it is not modified by trypanosome infection. Higher levels of seric polyamine oxidase in resistant cattle were demonstrated also by enzymatic analysis. The factors responsible for trypanolysis have been analyzed. Oxidation of spermidine by polyamine oxidase leads to the production of unstable aldehydes, acrolein, ammonia, O2-, HO, and H2O2. Acrolein and H2O2 show strong trypanolytic activity while the other products do not appear to be toxic for trypanosomes. The physiological importance of polyamine oxidase mediated trypanolysis is unclear; even at peak parasitemia in cattle (10(7) organisms/ml) it can be calculated that trypanosomes would not release enough spermidine for the generation of sufficient quantities of toxic degradation products. Additional polyamines could be released in serum from tissues damaged as a result of the infection.