Immunohistochemistry of new type I alveolar epithelial cell markers of the rat.

The presence of pan-cadherin and the MEP-I antigen in normal and diseased rat lung was established by employing immunoperoxidase and double label fluorescence techniques. The binding of a mouse monoclonal antibody (MEP-1) reacting specifically with type I pneumocytes was assessed on paraffin sections of normal specimens as well as those with pulmonary fibrosis induced by bleomycin or radiation treatment. In injured alveolar epithelium, a diminished type I cell and a focal type II cell immunoreactivity was found. Electron microscopy of immunogold-labelled lung tissue confirmed the type I cell specificity of MEP-1. In severely injured pulmonary parenchyma MEP-1-negative areas occurred, which were also negative with the type II pneumocyte marker Maclura pomifera lectin. Similarly, a polyclonal pan-cadherin antibody uniformly decorated luminal surfaces of alveoli except the type II pneumocytes. Furthermore, pleural mesothelial cells, bronchiolar epithelial cells, endothelial cells of large blood vessels and alveolar macrophage surfaces exhibited pan-cadherin immunoreactivity. After injury, a remarkable loss of pan-cadherin immunoreactivity in the MEP-1-positive type I epithelial cells was detectable. These findings suggest that characterization of normal alveolar epithelial cells and monitoring of the epithelial remodelling in pulmonary pathohistology are sufficiently described by the antibodies MEP-1 anti pancadherin.