No abstract

The attachment of Pneumocystis carinii to lung cells could play a role in the pathophysiology of P carinii pneumonia. The trophozoite attaches to type I alveolar epithelial cells. Physical, chemical, and extracellular matrix factors, involved in the mouse-or rat-derived P carinii attachment to fibroblastic cells in culture, were examined using a new model of in vitro adherence. The development of parasite filopodia penetrating deeply the host cell cytoplasm was observed using transmission electronic microscopy. Killed P carinii organisms were unable to attach to cultured cells. Also, parasites were unable to attach to killed target cells. The P carinii in vitro attachment was partially inhibited by cytochalasin B. In contrast, the parasite attachment was not affected when the target cell cytoskeleton was altered. In our work conditions, sialic acids were not involved in the attachment process. Present results showed that fibronectin (Fn) plays a role in the parasite attachment, and suggest that a specific Fn-binding receptor is present at the surface of mouse-derived P carinii organisms.

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.

No abstract

Changes in Pneumocystis carinii induced by the extraction of the parasite from rabbit lung have been investigated. Samples obtained using 4 extraction methods were evaluated by light and transmission electron microscopy. Light microscopic evaluation was insufficient to give a measure of the P. carinii viability or to detect parasitic cellular alterations. In contrast, ultrastructural evaluation provided information on host and P. carinii cell integrity, which is a critical condition for viability. None of the tested methods was ideal. How thoroughly and in what shape P. carinii need to be extracted from tissues will determine which extraction technique is of best use.