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.
BACKGROUND Cell proliferation and apoptosis account for the major morphogenetic mechanisms during development of the central nervous system. We investigated these processes in developing human brains. METHODS We examined human embryonic and fetal brains. Cell proliferation was analysed by classical histology and MIB-1 immunohistochemistry; cell death was investigated by the TdT-mediated dUTP-biotin nick end labelling method. RESULTS Most proliferating cells were observed in the ventricular zone (VZ) in the 3rd-10th week of gestational age (GA), and in both the VZ and the subventricular zone (SV) in the 19-24th week of GA. The proliferation index of the VZ was highest in the 8th week of GA and then decreased as the GA advanced. Apoptotic cells were observed in the VZ as early as the 5th week of GA. They were also observed in the intermediate zone in the 19-24th week of GA, although they were significantly lower in amount compared to that in the VZ and SV. CONCLUSIONS These results suggest that apoptosis occurring early in the embryonic period is related to a cellular mechanism which selects and determines the cells that are committed to migration and differentiation during the development of the human brain.