ABSTRACT
BACKGROUND: Pneumocystis carinii (P. carinii) attaches to alveolar cells and causes injury to the epithelial cells by direct toxic effects or inhibition of epithelial growth and replication. Although respiratory cell damage or death is a common feature in P. carinii pneumonia, there has been little reports about expression of apoptosis of the lung tissue in the literatures. METHODS: We examined expression of fibronectin and vitronectin in the interaction between P. carinii and alveolar cells, and in situ terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end-labeling (TUNEL) expression of apoptosis in the respiratory cells by immunohistochemistry and pre-embedding immunoelectron microscopy. RESULTS: Light microscopic (LM) and electron microscopic (EM) immunohistochemical stains for the fibronectin and vitronectin showed strong expressions on the pellicles and tubular extensions of P. carinii and weak expression along the surfaces of type I alveolar cells. LM and EM TUNEL stains showed positive expression in the nuclei of alveolar cells, apoptotic bodies in the cytoplasm of alveolar macrophages and cellular debris in alveolar spaces. CONCLUSIONS: P. carinii induces injury and apoptosis of alveolar cells after attachment of the organisms to host cells, and alveolar macrophages enhance the clearance of apoptotic bodies of alveolar cells as well as phagocytosis and degradation of P. carinii.