In vitro attachment of Pneumocystis carinii from mouse and rat origin.

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.