Alveolar pre-type II cells from the fetal rabbit lung. Isolation and characterization.

A method for preparing a homogeneous population of undifferentiated cells from the fetal rabbit lung is described. This method utilizes enzymatic digestion, differential adhesion to remove fibroblasts and centrifugation on a discontinuous metrizamide gradient. Cells isolated by this procedure replicate in vitro in medium supplemented with carbon-stripped fetal bovine serum. Mitosis can also be stimulated by heat-inactivated medium conditioned by fetal lung fibroblasts. After confluence, exposure of these cells to 0.55 or 55 nM dexamethasone significantly increased the incorporation of [14C]choline into phosphatidylcholine. Lower concentrations of the drug also increased incorporation, but not significantly so. Addition of heat-inactivated fibroblast-conditioned medium produced a 25% increase in choline incorporation, but this was not significant. Furthermore, the presence of conditioned medium tended to reduced the response of the cells to dexamethasone. After confluence, lamellar inclusion bodies were present in more than 90% of those cells exposed to dexamethasone. These organelles were not observed in cell monolayers not exposed to the steroid. These cells did contain a few small electron-dense bodies. The latter may be immature multivesicular bodies.