Ultrastructural Study of Pneumocystis carinii in Explant Cultures of Rabbit Lung and in Cultures with and without Feeder Cells

Pneumocystis carimV‐parasitized lung explains were obtained from corticoid‐lrealed rabbits and maintained in vitro. Twenty‐one days after the beginning of explant cultures, the ultrastructural morphology of trophozoite, precyst and cyst forms was normal as compared to the in vivo ul‐trastructure of P. carinii from infected rabbit. However, after the 36th day, only altered forms of P. carinii were observed. Lung tissue showed only minor alterations. Intracyloplasmic lamellar inclusions were observed in type 2 alveolar cells from which they were released. While the total number of parasites increased approximately 4‐fold from day 0 to day 41, trophozoite counts increased approximately 6 times. Pneumocystis cells from inocula and supemaies of cultures with and without Vero cells showed important ultrastructural alterations.