The qualitative and quantitative features of the host-parasite immunologic interactions in vitro and in vivo of Trypanosoma cruzi and its mammal are to be studied. Normal, non-specifically and specifically immune macrophages, as well as non-specifically immune macrophages in the presence of specific T. cruzi antibody will be studied with regard to how they cope with T. cruzi of each morphogenetic form. The manner by which macrophages deal with these intracellular parasites will be studied by electron microscopy and the role of lysosomal fusion assessed. The isolation, purification and infectivity of each form of T. cruzi will be evaluated, while further attempts at defining its culture requirements are continued. In vivo studies are to be done in order to determine the effect of cell transfer, antibody, antibody with activated macrophages, and sensitized lymphocytes on experimental infection. Finally, non-living antigens will be prepared using procedures such as acetoacetylation, periodation and solubilization in order to assess their practical protective value. BIBLIOGRAPHIC REFERENCES: Y. Kress, B. Bloom, M. Wittner, A. Rowen, H. Tanowitz, Resistance of Trypanosoma cruzi to killing by macrophages. Nature, 257:394-396, 1975. H. Tanowitz, M. Wittner, M. Sveda, and R. Soeiro, Studies On Ribosomal RNA of Trypanosoma Cruzi. Journal of Parasitology 61:1065-1069, 1975.