Immunocytochemical detection of chitin in Pneumocystis carinii

Polyclonal antisera against chitin and chitin oligomers were used to stain Pneumocystis carinii by the immunoperoxidase technique in Formalin-fixed, paraffin-embedded sections of four human lung biopsies and in alcohol-fixed, paraffin-embedded cell blocks of two bronchioloalveolar lavage specimens from infected human patients. In all cases, the antisera bound P. carinii but did not bind the host tissue elements. Moreover, the antisera bound not only to the cyst forms of P. carinii but also to the intracystic bodies and to the trophic forms. Preadsorption of the anti-chitin antiserum with purified chitin abolished all staining of P. carinii. Our results indicate that P. carinii produces chitin at more than one stage of its life cycle in the infected human host.