Immunodeficient and immunosuppressed mice as models to test anti-Pneumocystis carinii drugs

Congenitally immunodeficient and immunosuppressed normal mice with naturally acquired Pneumocystis carinii infection were compared as models for testing anti-P. carinii drugs. Among the immunodeficient mice, mice with severe combined immunodeficiency disease (scid), which lack B and T cells, had higher levels of P. carinii pneumonia than did microMT mice, which lack K cells. Normal mice administered dexamethasone in the drinking water had more extensive pneumocystosis than mice administered parenteral methylprednisolone or hybridoma cells making a monoclonal antibody to CD4 cells. The standard anti-P. carinii drugs trimethoprim (TMP)-sulfamethoxazole (SMX), pentamidine, and atovaquone, which work well in rats and humans, worked well in the mice. Clindamycin and primaquine were effective in the scid and microMT mice but not in the immunosuppressed normal mice. High doses of epiroprim, an analog of TMP, appeared to enhance the activities of low doses of SMX and dapsone, while high doses of TMP did not; however, further studies are needed before definitive conclusions about the actions of these drugs can be drawn. Taken together, the data obtained in this study support the growing body of literature suggesting that the mouse is a valid alternative to the rat as a model for testing anti-P. carinii drugs. Additional differences involving the activities of individual drugs in these models will probably emerge as more experience is gained.