Localization of markers of apoptosis in lung tissue sections from patients. (Left) Lung tissue sections from a patient who died with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS). (Right) Lung tissue sections from a patient who died without pulmonary disease. (a–f ) Tissue sections that are counterstained with hematoxylin. ( g–j) Tissue sections that were imaged using differential interference contrast optics, without counterstain, because the epithelial cell immunostain reaction product was subtle. The rows of pictures are matched for one marker of apoptosis: (a,b) TUNEL, (c,d ) caspase-3, (e, f ) Bax, ( g, h) Bcl-2, and (i, j) p53. Cells lining, and in, the alveolar walls demonstrate more TUNEL-labeled nuclei, caspase-3-labeled cytoplasm (arrow), Bax-labeled cytoplasm (arrow), and p53-labeled cytoplasm (arrow) in the tissue sections from the patient who died with ALI or ARDS compared with the patient who died without pulmonary disease. However, Bcl-2-labeled cells lining, and in, the alveolar walls are more prominent in the tissue sections from the patient who died without pulmonary disease compared with the patient who died with ALI or ARDS, as expected. All of the panels are of the same magnification. Reprinted with permission from the American Society of Pathology.