Reconstitution of the trypanolytic factor from components of a subspecies of human high-density lipoproteins.

Trypanosoma brucei brucei is non-infectious to man due to the sensitivity of these parasites to the lytic activity of normal human serum. Apolipoproteins (apo) have been purified, under non-denaturing conditions, from the subclass of human high-density lipoprotein (HDL), termed trypanosome lytic factor (TLF), which is responsible for the cytotoxicity of human serum to T. b. brucei. The TLF apolipoproteins were purified by anion exchange chromatography in the presence of the nonionic detergent octylglucoside and a reconstitution method was developed which allowed the role of the individual apolipoproteins and different lipids to be assessed. The results suggest that the TLF lipids do not have a direct role in lysis but are necessary for the correct assembly of the lytic HDL particle. Apo A-I, apo L-III and apo L-I contribute to lysis in reconstituted particles but individually they are not cytotoxic. Apo A-II was not required in the reconstituted TLF particle for trypanosome lysis. Formation of a lytic HDL particle required apo L-III suggesting its potential role as a toxin. Thermal inactivation of TLF activity correlated with the amount of denatured apo L-I, indicating that apo L-I was involved in lysis of T. b. brucei by native TLF.