Abstract

Alveolar macrophages participate in the host defense against P. carinii, but the mechanisms in degradation and clearance of the organism from lung has not been well established. We observed the transmission and scanning electron microscopic features and evaluated the expression of TNF-alpha and Surfactant-D in the interaction of P. carinii with alveolar macrophages. Expression of TNF-alpha and Surfactant-D in the experimentally induced P. carinii pneumonia in rat was examined by immunohistochemistry and immunoelectron microscopy. Electron microscopically, the alveolar macrophages phagocytized trophozoites and cysts of P. carinii micro-organisms. Immunohistochemically TNF-alpha was strongly expressed in the cytoplasms of alveolar macrophages. Postembedding immunogold labeling for Surfactant-D protein was expressed on the pellicles of trophozoites and cysts, P. carinii micro-organisms in the cytoplasms of macrophages, free floating surfactant materials and multilamellar bodies of type II epithelial cells. We conclude that alveolar macrophages interacted with P. carinii micro-organisms respond with increased expression of TNF-alpha. TNF-alpha may bind to P. carinii and exert a direct toxic effect upon the micro-organisms. Surfactant-D protein may augment binding of P. carinii to the alveolar macrophages and enhance the clearance of the micro-organisms.

• Keywords: Pneumocystis carinii;Alveolar macrophages;TNF-alpha;Surfactant-D;Immunogold labeling