A sequential ultrastructural study of rat lungs infected with Pneumocystis carinii to investigate the appearances of the organism, its relationships and its effects on pneumocytes.

A sequential study of the lungs of rats infected with Pneumocystis carinii is reported. The aim was to investigate variations in the appearance of the organism from the inception of infection until the death of the host and, during this period, the relationships of the organism with one another and changes occurring within pneumocytes. Trophozoites predominated at all stages of infection and were those first recognized but no clear role for the filopodia was evident. Organisms were related with both Type I and Type II pneumocytes but were not found within these cells. There was no obvious method of linkage to pneumocytes and the way in which lung damage is caused is unclear. However, from analogy with similar pulmonary disorders, lung damage probably involves a number of factors.