We shall continue exploring the host- and parasite factors relevant to the pathogenesis of schistosomiasis and of granuloma formation, with special emphasis on: Direct cytotoxic effects of schistosome eggs on host liver cells, as manifested in mice with deficient T-lymphocyte function, and in mouse liver parenchymal cells in tissue culture monolayers. Comparative cellular and morphological characteristics and fibrous sequelae of schistosome granulomas in T-cell deficient, normal, and T-cell-adjuvant (lentinan) immunopotentiated mice, respectively; similar comparisons will be effected between two schistosome species of differing pathogenicity (S.mansoni and the Mekong schistosome). The immunopathogenesis of diffuse fibrous lesions in S. japonicum infection of hamsters and rabbits, such as portal fibrosis and bilharziomas. The modulatory influence of egg-directed antibody during the acute stage of schistosomiasis, and the in vivo effects of eosinophilic granulocytes on schistosome egg viability and on antigen metabolism. Our aim is to better define the factors which modulate the cell populations and morphological features of schistosome egg granulomas, and to better understand the pathogenic consequences of defective, normal, and excessive host immunological reactivity against schistosome eggs.