IMMUNOHISTOCHEMISTRY OF NEW-TYPE-I ALVEOLAR EPITHELIAL-CELL MARKERS OF THE RAT

The presence of pan-cadherin and the MEP-1 antigen in normal and disea sed rat lung was established by employing immunoperoxidase and double label fluorescence techniques. The binding of a mouse monoclonal antib ody (MEP-1) reacting specifically with type I pneumocytes was assessed on paraffin sections of normal specimens as well as those with pulmon ary fibrosis induced by bleomycin or radiation treatment. In injured a lveolar 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 severe ly injured pulmonary parenchyma MEP-1-negative areas occurred, which w ere also negative with the type II pneumocyte marker Maclura pomifera lectin. Similarly, a polyclonal pan-cadherin antibody uniformly decora ted luminal surfaces of alveoli except the type II pneumocytes. Furthe rmore, pleural mesothelial cells, bronchiolar epithelial cells, endoth elial cells of large blood vessels and alveolar macrophage surfaces ex hibited pan-cadherin immunoreactivity. After injury, a remarkable loss of pan-cadherin immunoreactivity in the MEP-1-positive type I epithel ial 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.