Identification of phagocytosed Pneumocystis carinii in human pulmonary alveolar macrophages.

Examination of Papanicolaou-stained bronchoalveolar lavage samples from cases with Pneumocystis carinii pneumonitis under ultra-violet light reveals alveolar macrophages packed with fluorescent inclusions. Immunoenzymatic staining of the alveolar macrophages with a monoclonal antibody specific for P. carinii (3F6) showed that these inclusions contain intact pneumocysts or their degradation products. Fluorescence microscopy of Papanicolaou-stained smears is advocated as a sensitive and specific method of diagnosing P. carinii infection.