PRF1 and pulmonary emphysema: A potential role for T-lymphocytes in the development of pulmonary emphysema in human smokers has been suggested, since cytotoxic CD8+ T-cells are increased in the lungs of smokers and have the capacity to cause (perforin- or granzym B-mediated) cytolysis and apoptosis (by Fas-Fas ligand interaction or by caspase activation) of alveolar epithelial cells [6,7,9,10,19-21].