[The rabbit, experimental host of Pneumocystis carinii]

Pneumocystis carinii can be collected from experimentally immunodepressed rats. However, development of experimental pneumocystosis in this host requires corticoid-treatment during 8 to 12 weeks while P. carinii can be obtained from immunodepressed rabbits after 2 to 4 weeks. In 400 to 650 g body weight-white rabbits normally fed, two immunodepression protocols were used: (a) daily subcutaneous injections of hydrocortisone acetate (10 mg/kg body weight) and G penicillin (25,000 IU)-streptomycin (3 mg); (b) continuous oral administration of prednisolone (20 mg/l/day) and amoxicillin (25 mg/l/day) both diluted in drinking water. Between 55 and 78% of rabbits treated by any immunodepression protocol died within 5-20 days after a terminal important diarrhoea. Seventy and seventy-seven per cent of the young rabbits respectively treated by protocols (a) or (b), showed the presence of Pneumocystis by the direct microscopic examination, but all of them were found positive after lung concentration. Fifty-five per cent of the older rabbits (950-1,400 g) were positive by pulmonary smear examination when treated with protocol (a). Pneumocystis obtained were good antigens for indirect immunofluorescence and immunoblot assays using human and rabbit sera.