Trypanosoma brucei brucei: differences in the trypanocidal activity of human plasma and its relationship to the level of high density lipoproteins.

Although high density lipoprotein (HDL) particles purified from human serum by ultracentrifugation are known to lyse Trypanosoma brucei brucei, it is unclear whether individual differences in the trypanocidal activity of human serum reflect changes in the concentration of HDL per se. In the present study, trypanolytic activity, whether assessed in vitro or in vivo, was greater with plasma from normal healthy individuals than with plasma from patients with various hepatic diseases and associated low levels of HDL. For all subjects taken as a single group there were highly significant positive correlations between the plasma concentration of apolipoprotein (apo) A-I, the major protein constituent of HDL and trypanolysis in vivo (r = 0.93, n = 10, P less than 0.001) or in vitro (r = 0.77, n = 36, P less than 0.001). Removal of plasma apoB-containing (i.e. non-HDL) lipoproteins by precipitation revealed that the trypanocidal activity was also significantly correlated with HDL-cholesterol and HDL-apoA-II, as well as with HDL-apoA-I, but not with HDL-apoE. Depletion of all or part of plasma apoA-I by non-ultracentrifugal methods abolished or decreased the trypanolytic effect of the plasma. The findings from these experiments, which were designed to avoid alteration in the composition of HDL by ultracentrifugal forces, provide additional support for the proposal that the trypanocidal action of human plasma resides with native HDL particles.