Figure 3.

Transmission electron micrographs of cultured P. carinii. Before fixation, these organisms had been grown for 65 days with 7 subcultures. Trophozoites (T) with varying degrees of tubular extensions and crenations can be seen in A–C; D–F show cysts. Arrows point to membranous material that in some cases seem to be typical P. carinii cell membrane tubular extensions but in other cases may be similar material that has been shed from the organisms (B and D). D contains an immature cyst that has a typical thick cyst wall and multiple nuclei (N) but no developed intracystic bodies. The thickening of the cell membrane of the trophozoite in C may indicate an early stage in cyst formation. E and F show mature cysts with intracystic bodies (IB). A residual body (RB) can be seen in the cyst in E. (Bars = 1 μm.)