Abstract

Both fibronectin and vitronectin bind to Pneumocystis carinii (P. carinii) and mediate the attachment of the organisms to respiratory epithelial cells. Surfactant A and D play a role in the interaction between P. carinii and host cells. In this study we examined the expression of fibronectin, vitronectin, surfactant-A and D in the interaction between P. carinii and alveolar epithelial cells by immunohistochemistry and pre-embedding immunoelectron microscopy. The experimental rat model of P. carinii pneumonia was induced by administration of low protein diet (8%) and drinking water containing dexamethasone (2 mg/liter) for 6 to 8 weeks. The primary antibodies for light and electron microscopic immunohistochemistries were monoclonal antibodies including fibronectin (1:100) and vitronectin (1:100), and polyclonal antibodies including surfactant A (1:50) and D (1:50), respectively. Light microscopic immunohistochemistry for the fibronectin, vitronectin, surfactant-A and D showed strong expressions on the P. carinii and surface linings of type I alveolar epithelial cells. The electron microscopic immunohistochemistry of the fibronectin and vitronectin showed a strong immunoexpression along the surface pellicles and tubular extensions of P. carinii trophozoites, and surface membranes of the type I epithelial cells. The surfactant-A and D proteins showed a strong expression on the pellicles of P. carinii and surface membranes of the type I epithelial cells, but a weak expression on the free-floating surfactant materials. In conclusions, the trophozoites of P. carinii were mostly attached to type I epithelial cells. The fibronectin, vitronectin, surfactant-A and D were strongly expressed, and played an enhancing role in the binding between the P. carinii organisms and the type I alveolar epithelial cells.

• Keywords: Pneumocystis carinii;Type I epithelial cells;Fibronectin;Vitronectin;Surfactant-A and D