Golgi complex and lysosomes in rabbit derived Pneumocystis carinii

Abstract

The ultrastructural morphology of Pneumocystis carinii obtained from nonimmunosuppressed rabbit is described in details. Golgi complex and primary lysosomes of P carinii are described here for the first time. They are easily revealed by the zinc iodide-osmium tetroxide cytochemical reagent. Thiamine pyrophosphatase and beta-glycerophosphatase activities are found in the parasite but cytidine 5' monophosphatase activity is not observed. A weak thiamine pyrophosphatase activity is detected in Golgi vesicles. An endomembranous saccular structure, present from the intracystic body stage to the precystic stage, apparently plays the role of secondary lysosome. A second type of endomembranous saccular structure, only present in the well developed trophozoitic and precystic forms is also described. The presence of carbohydrates in the cell wall of the parasite was demonstrated by periodic acid-thiosemicarbazide-silver proteinate staining and lectin concanavalin A labeling. The development of Golgi vesicles preceded the transition from double-layered to three-layered parasite stages.

Is Pneumocystis carinii a deep mycosis-like agent?

“…However, the presence of the parasite in other organs is occasionally reported in man (14,66) and, recently, we have found P. carinii in several extrapulmonary sites in deeply immunosuppressed laboratory animals (unpublished results). figure 1 shows the generally accepted life cycle of P. carinii (19,53,56). It includes the following parasite stages: an amoeboidal mononucleate trophozoite, a precyst and a mature cyst containing eight intracystic bodies that will evolve to trophozoite forms.…”

“…Surface structures also evolve through the life cycle: the trophozoite and the early precyst have a thin pellicle consisting of a plasma membrane and an electron-dense outer layer, whereas the other precystic stages and mature cyst have a thick pellicle (named "cyst wall" henceforth) consisting of a plasma membrane, an electron-lucent middle layer and an electron-dense outer layer ( Fig. 1) (19,47,53,56).…”

“…Thus, as in the fungal wall, carbohydrate was detected in P. carinii cyst wall at light microscopy level by periodic acid-Schiff (PAS) staining (91), and at the ultrastmctural level by Thi6ry staining (53,91). In the same way, the wall of P. carinii cystic organisms was reactive to the lectin Concanavalin A (ConA) (53,61,91).…”

“…Furthermore, the P. carinii cyst wall was about 5 to 10 times less reactive to ConA and Thi6ry reagent than the cell wall of Candida albicans (53,64) (Fig. 2).…”

“…Moreover, when reactivity ofP. carinii cyst wall to CortA is considered strong (16, 91) the authors overlook the fact that lectin concentration used to label the cell wall of C. albicans is about 20 times as low as the lectin concentration needed to label the P. carinii cyst wall (53,91). Comparative evaluation attempts should also take into account the fact that endogenous biotin could be present in the P. carinii cytoplasm and be directly labelled by streptavidin conjugates (53,59).…”