Isolation and immortalization of rat pre-type II cell lines.

The fetal respiratory distress syndrome is due, in part, to the presence of abundant pre-type II alveolar epithelial cells that have not yet differentiated into mature type II cells. Studies of this syndrome have been limited somewhat by the lack of an adequate in vitro model. In the present study we immortalized pre-type II cells by infecting primary isolates obtained from fetal rat lung with a retroviral construct expressing the adenoviral 12S E1A gene product. The immortalized pre-type II cells retained many of the ultrastructural features typical of pre-type II cells in primary culture, most notably lamellar bodies were not detected and the cells contained abundant stores of glycogen, expressed cytokeratin filaments, and bound the lectin Maclura pomifera. Karyotyping revealed that the cells are diploid. Growth studies demonstrate log phase growth in the presence of serum with a markedly decreased growth rate shortly after the cells reach confluence. Exposure of the immortalized pre-type II cells to hydrocortisone and dibutyryl cAMP resulted in the induction of lamellar bodylike organelles; however, these cells did not secrete surfactant or express surfactant protein A. These cells may serve as useful models for some in vitro studies of fetal type II cell maturation or the fetal respiratory distress syndrome, or both.