RESUMO
The loosely associated lung mesenchymal cell found between the ducts of the 3-to 4-month fetus is considered to be the probable progenitor of lung fibroblast cultures and of alveolar interstitial cells. A possible stage- and tissue-specific property of this cell type, the reduction of cortisone to cortisol, is defined and its activity studied in a variety of cell lines. Fibroblast lines derived from both fetal and adult lung had about ten times the cortisone-reducing activity of corresponding skin fibroblast lines. This relatively high activity was also characteristic of cell lines established by cloning the initial fetal lung digest. Lines established from developmentally related esophagus and from trachea had less activity than corresponding lung fibroblasts. A high level of cortisone-reducing activity was maintained in four serially passaged lung fibroblast lines for at least 85% of the proliferative life span and a second cell property, the enhancement of this activity by pretreatment with cortisol, was also maintained in three of the four lines.