Altered schistosome granuloma formation in nude mice.

Schistosome egg-induced lesions in congenitally athymic mice differed from those found in normal heterozygous controls. Heterozygote liver granulomas were chareacterized by poorly phagocytic epithelioid macrophages, and were rich in eosinophils and fibroblasts, with peripheral lymphocytes and plasma cells. Hepatic lesions in nude mice were much smaller and lacked epithelioid macrophages, with lesions about mature eggs, typically consisting of monocytes and macrophages filled with pigment, occasional neutrophils, and rarely one or more eosinophils or giant cells. While heterozygote granulomas damaged liver cells mainly by encroachment or by their vascular effects, in the nudes hepatocytes bordering the lesions showed microvesicular cytoplasmic damage and either hydropic degeneration or focal acidophilic necrosis of individual liver cells. In heterozygotes, immunofluorescent-stainable schistosome egg antigen (SEA) was concentrated in the granuloma center. In nude mice, SEA, was distributed throughout the infiltrates and in and around hepatocytes adjacent to egg lesions corresponding to the observed pattern of hepatocyte necrosis. We conclude that, in contrast to heterozygotes, nude mice lack hypersensitivity granulomas and fail to sequester toxic egg products, this resulting in zonal hepatocellular damage. Alternative explanations include the possibility of a latent hepatitis virus being activated by the schistosome infection; however, several cogent arguments are presented against that alternative.