Fig. (1) Schematic of study flow design. Co-cultures were prepared with either fetal rat lung fibroblasts or type II cells cultured on the bottom of 6-well plates with BMSC cultured on the Transwell^®insert, or BMSC cultured on the bottom of the plates with either fetal rat lung fibroblasts or type II cells cultured on the Transwell^® insert. All cell studies were performed on the cells cultured on the plate bottoms after 48 hours of co-culture. Cell proliferation was measured by thymidine incorporation. Differentiated type II cell-like function was studied by choline incorporation into DSPC. Cell surface markers that help define BMSC were studied by flow cytometry in the BMSC only.