Acute cavitary histoplasmosis in Rhesus monkeys: influence of immunological status

Male rhesus monkeys were randomized into groups according to body weight, immunized with different Histoplasma capsulatum antigens, and two weeks later were infected intratracheally with 10(8)H. capsulatum yeast cells. Complement fixation antibody titers, skin tests, and chest X rays were performed at weekly intervals from immunization until autopsy, at which time the spleens were cultured and the lungs and other organs were dissected. Pulmonary cavities were found in 33% of the animals, and extrapulmonary dissemination was present in 85% of the animals. Delayed hypersensitivity and circulating antibody activity was detected in all animals at some time during the experimental period; however, animals which developed pulmonary cavities had a longer period before circulating antibodies were detected than animals which did not develop pulmonary cavities. Delayed hypersensitivity developed at approximately the same time in both cavitary and noncavitary animals. Early appearance of delayed hypersensitivity was associated with reduced amounts of extrapulmonary dissemination, in that animals with a later onset of skin test reactivity had more H. capsulatum cultured from the spleen. There was no correlation between the onset or titers of circulating antibodies and the spleen culture results.