Loss of immunoreactivity for RT140, a type I cell-specific protein in the alveolar epithelium of rat lungs with bleomycin-induced fibrosis

After lung injury, the epithelial cells lining the alveolar surface in rat lung show an altered distribution of several membrane proteins, Pulmonary fibrosis was induced by intratracheal administration of bleomycin into the lung of rats and the distribution of RTI40, a recently detected a lveolar epithelial type I cell antigen, was examined, as well as the relati onship between RTI40 and a type I cell-specific antigen recognized by the m onoclonal antibody MEP-1 and the type I cell-binding lectin Bauhinia purpur ea in serial sections and double stainings, Loss of RTI40 protein was observed in fibrotic lungs, particularly in areas with obliteration of alveoli. Pre-embedding immunoelectron microscopy conf irmed this observation by detection of RTI40 protein in the alveolar lumen, Western blot analysis revealed elevated levels of RTI40 in the bronchoalve olar fluid of bleomycin-treated rats with a maximum at day 7 after treatmen t. Twenty-eight days after bleomycin application, the bronchoalveolar fluid contained three times the amount of RTI40 mg protein(-1) of control lungs, as determined by semiquantitative dot blot. These results suggest RTI40 as a tool for the evaluation of alveolar epithe lial type I cell behaviour during re-epithelialization processes.