A, mesenchymal cells (ALI-MC) isolated from the lung of a patient with acute lung injury were cultured in 96-well cell culture plates in the presence of 10% FBS and grown to 80% confluence. Cells were then growth-arrested for 48 h and treated with/without TGF-β1 (2 ng/ml) in the presence or absence of serum for an additional 72 h. Apoptosis assays were performed as described under “Materials and Methods.” n = 4 for each group; *, p < 0.001 compared with serum/control; **, p < 0.001 compared with serum-deprived/control. B, normal fetal lung fibroblasts (IMR-90) were cultured, treated with/without TGF-β1, and assayed for apoptosis under identical conditions as described above. n = 4 for each group; *, p < 0.001 compared with serum/control; **, p < 0.01 compared with serum-deprived/control.