Immunoelectron microscopic and immunochemical demonstrations of serum proteins in the alveolar lining material of the rat lung.

By means of antibodies labeled with horseradish peroxidase, autologous albumin and IgG were visualized in electron microscopy on the alveolar epithelial surface of the rat lung, as a continuous cell coat, as free granular deposits, or associated with tubular myelin figures. These 2 proteins were detected by immunochemistry in alveolar washing. After ultracentrifugation of alveolar washing, they were still found in the phospholipid-rich precipitate fraction by immunization of rabbits and by immunoelectron microscopy. Thus, albumin and IgG appeared as normal alveolar components in the rat lung; fibrinogen was not found under normal conditions.