Histochemical and immunocytochemical identification of alveolar type II epithelial cells isolated from fetal rat lung

Primary cultures of epithelial cells isolated from organotypic cultures of fetal (Days 18 through 22) rat lung have been characterized by histochemical and immunocytochemical parameters. Immunocytologic analysis with monoclonal antibodies to cytokeratins and with those to adult type II cells (JBR-1) demonstrated that the cell cultures were composed almost entirely of epithelial type II cells. Additional evidence that the cultures had the type II phenotype was obtained by Maclura pomifera lectin binding studies and by positive immunocytochemical demonstration of surfactant apoproteins. Comparison of cell cultures established from fetal lung at the early canalicular and saccular stages of rat lung development revealed that early fetal type II cells (Day 19) contained much glycogen and few lamellar bodies. The reverse was observed in type II cells isolated from fetal lungs at 21 days of gestation. Immunohistochemically determined surfactant apoproteins showed a similar developmental pattern to lamellar bodies. The cell cultures exhibited alkaline phosphatase activity, but this did not increase with development. Administration of dexamethasone to pregnant rats at 19 days gestation resulted in a significant loss of glycogen from fetal type II cells isolated 24 h later. This decrease in glycogen content was accompanied by an increase in the number of cells containing lamellar bodies. These findings indicate that freshly isolated fetal type II cells retain the morphologic features of the type II cells in vivo and provide a good system for the study of biochemical events occurring in these cells during specific stages of lung development.