HUMAN HIGH-DENSITY-LIPOPROTEIN KILLING OF AFRICAN TRYPANOSOMES

Trypanosoma brucei brucei is noninfectious to humans because of its se nsitivity to the cytolytic activity of normal human serum. Biochemical evidence indicates that the active component of human serum is high-d ensity lipoprotein (HDL). Several possible mechanisms have been propos ed for the killing of trypanosomes by human HDL, and while a unified m odel that accounts for all experimental information is lacking, there is substantial evidence that receptor-mediated binding and endocytosis might be required for lysis. Trypanosomes resistant to the lyric effe cts of human HDL cause human sleeping sickness. The basis for the resi stance of these parasites to HDL-mediated killing is unknown. The sens itivity of T. brucei brucei to the cytolytic action of human HDL is de velopmentally regulated and resistance correlates with life-cycle spec ific changes in macromolecular uptake by the organism.