Trypanosoma brucei brucei, the causative agent of the bovine disease nagana, is non-infectious to humans because of its susceptibility to the cytolytic activity of normal human serum. Biochemical and genetic evidence indicates that the cytotoxic component of human serum is a minor subclass of high density lipoprotein (HDL) which we have termed Trypanosome Lytic Factor (TLF). Several possible mechanisms have been proposed for the killing of trypanosomes by TLF, however, there is now substantial evidence that receptor mediated binding, endocytosis and lysosomal localization might be required for lysis of T. b. brucei. Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense are resistant to the lytic effects of human HDL and result in the chronic and acute forms of human sleeping sickness respectively. The basis for the resistance of these parasites to TLF-mediated killing is unknown. In the proposed studies we will examine the biochemical and molecular properties of the apolipoprotein, haptoglobin-related protein, which has recently been shown to be involved in lysis. In addition we will examine the mechanisms involved in the resistance of T. b. rhodesiense and the insect developmental stages of T. b. brucei to lysis by human HDL. We will also initiate studies to explore the feasibility of developing animals lines resistant to T. b. brucei infection. The specific aims of the proposal are the following: 1) Biochemical characterization of TLF apolipoproteins. 2) Determination of the mechanism of TLF mediated lysis. 3) Investigation of the biochemical and molecular basis of TLF resistance. 4) Development of transgenic animals resistant to trypanosome infection. In previous studies we have shown that TLF killing of T. b. brucei is mediated by two unique apolipoproteins which upon internalization results in lysosomal disruption and ultimately cell lysis. The cloning and expression of the genes for these proteins in transgenic animals has obvious practical implications in animal infections with T. b. brucei. We further propose that modification of these apolipoproteins or changes in their targeting may lead to the identification of novel a roaches for the treatment of human trypanosomiasis.