Recognition of Pneumocystis carinii antigen on its surface by immunohistochemistry and immunoelectron microscopy.

The aim of this study was to detect the surface antigens in different stages of experimental induced Pneumocystis carinii in Sprague-Dawley rats. Immunohistochemical staining with monoclonal (900, 902 and 904) and polyclonal (SP-D) antibodies demonstrated that the P. carinii organisms were mostly in the alveolar lumina. The binding sites of the monoclonal (900, 902 and 904) and polyclonal (SP-D) antibodies developed against P. carinii were examined at the ultrastructural level by using a post-embedding immunogold labeling. The gold particles were observed evenly on the surface of precyst and cyst stages of the P. carinii. In the trophozoite stage, scattered gold particles were seen on the pellicles and tubular expansions. The monoclonal antibodies reacted mainly with pellicles of P. carinii, whereas SP-D labeled pellicles, intracystic bodies, cytoplasms of alveolar macrophages, free floating surfactant material in the alveolar spaces, and adjacent type II epithelial cells. In the immunogold labeling, basically no significant differences were found in the precyst, cyst, and ruptured cyst stages. These results indicate that the gold particles were observed adhering to every stage of P. carinii, mostly concentrated on the pellicles, and more concentrated in the precyst or cyst stage than trophozoite stage which may be due to an increase in antigen accumulation during development from the trophozoite to the cyst.