Histoplasma capsulatum infection in nude mice.

Congenitally athymic nude (nu/nu) mice, when injected intraperitoneally with Histoplasma capsulatum, developed a rapidly fatal disseminated infection characterized by heavy parasitization of reticuloendothelial tissues. In contrast, their heterozygous (nu/X) littermates, which possessed a functioning thymus, developed only a low-grade infection which was apparently self-limited and rarely fatal. Transplantation of thymic tissue into nu/nu mice diminished greatly the severity of infection and reduced mortality by about 50%. These studies emphasize the importance of cell-mediated immunity in host defense against histoplasmosis and suggest that the nude mouse may be a valuable model for the study of this chronic intracellular infection.