Experimental Pneumocystis carinii infection in nude rats.

The role of cell-mediated and humoral immunities to Pneumocystis carinii infection was studied on athymic nude rats and their heterozygous euthymic littermates inoculated intranasally with 10(6) cysts. Some of both groups were injected subcutaneously with cortisone (25 mg) twice a week. At 30 and 60 days postinoculation a large number of cysts were detected in the lung of cortisone treated euthymic rats as well as athymic rats with or without cortisone treatment. IgG antibody appeared in all groups of rats at 60 days post-inoculation while IgM antibody was not detectable. Delayed type footpad reaction to P. carinii antigen was recognized in euthymic rats without cortisone at 4 and 5 weeks postinfection but not in those rats with cortisone or without infection. These results suggest that cell-mediated immunity is important for protection of P. carinii infection in rat.