An investigation into the mechanism of trypanosome lysis by human serum factors

African trypanosomes are the causative agents of sleeping sickness in human s and of Nagana in cattle. The infectivity of African trypanosome species f or humans appears to be defined by their susceptibility to two lytic factor s in human serum; trypanosome lytic factor (TLF)1, a subclass of human high density lipoprotein (HDL) and TLF2, a high molecular weight protein comple x. Available evidence indicates that following receptor mediated uptake, TL F is targeted to the lysosome where the low pH triggers a TLF-dependant per oxidase activity resulting in the formation of reactive oxygen radicals wit h consequent lipid peroxidation and destruction of the lysosomal membrane. Nearly all previous work on the mechanism of parasite lysis has been perfor med using TLF1. In this study, we directly test the hypothesis that TLF1 an d TLF2 kill Trypanosoma brucei by a mechanism involving oxidative stress. W e found no evidence for lipid peroxidation in trypanosomes exposed to high concentrations of trypanolytic HDL (impure TLF1), although lipid peroxidati on was detected in parasites exposed to low concentrations of low molecular weight peroxides. Neither HDL, TLF1 nor TLF2 generated detectable levels o f intracellular reactive oxygen intermediates. Various antioxidants also ha d no effect on TLF1 or TLF2-mediated lysis, although the antioxidants catal ase and superoxide dismutase were effective at inhibiting peroxide generati on and parasite lysis in control systems. Various metal chelating agents an d protease inhibitors were also rested without effect. These data provide s trong evidence against a peroxidative mechanism being involved in TLF-media ted lysis. (C) 2000 Elsevier Science B.V. All rights reserved.