Transformation of alveolar type 2 cells to type 1 cells following exposure to NO2.

This research was undertaken to study the fate of Type 2 cells after they have divided. To accomplish this, male rats were exposed to NO₂ to increase the number of dividing Type 2 cells. Dividing cells were labeled with ³H-TdR and studied with autoradiographic techniques in the electron microscope for up to 14 days after labeling. The results show that initially most of the ³H-TdR labeled cells were Type 2. However, by 2 days there was a decrease in frequency of labeled Type 2 cells and a large increase in labeled Type 1 cells. The new frequencies of labeled alveolar epithelial cells were stable from 2 through 14 days. This evidence supports the interpretation that Type 2 cells may transform into Type 1 cells. In addition, it was shown that under the conditions of this experiment: (1) the time for transformation was about 2 days, and (2) during this process an intermediate cell type was present.