Expression of Antigenic Surface Molecules of Pneumocystis Carinii by Immunoelectron Microscopic Examination

ABSTRACT

This study was carried out to investigate the morphologic characteristics and localization of antigenic molecules of Pneumocystis carinii in experimentally induced P. carinii pneumonia in rats. After six weeks of administration of low protein diet and dexamethasone, Sprague-Dawley rats were sacrificed to submit lungs or bronchoalveolar lavage for the study. Monoclonal (092, 900, 902, and 904) and polyclonal (SP-D) antibodies were used for immunohistochemistry and immunoelectron microscopy (ITEM and ISEM). Immunohistochemically P. carinii organisms were well identified as clusters or separated forms in the alveolar spaces being frequently attached to the alveolar walls. Immunoelectron microscopically the adherences of gold particles were observed on the surface of all stages of the P. carinii. Occasionally positive immunogold labeling was observed in the cytoplasm of the trophozoites and on the pellicle of the intracystic bodies within the cysts. The monoclonal antibodies 092, 900, 902, and 904 reacted mainly with pellicles of P. carinii, whereas SP-D labeled on the pellicles, intracystic bodies, cytoplasms of the alveolar macrophages, and free floated surfactant material in the alveolar spaces. The immunogold particles were observed more diffusely and intensely in the cysts than in the trophozoites. These results indicate that antigen is mainly localized on the pellicles, and accumulated during development from the trophozoite to the cyst stages.