DEFB1 and chronic obstructive pulmonary disease: Finally, as disruption of the balance between apoptosis and regeneration of structural lung cells in the lung is reported to be important in the progressive destruction of healthy lung tissue during COPD [32], we speculate that DEFB1, the cytotoxic peptide abundantly produced by the airway epithelial cells of patients with COPD, may contribute to the apoptotic cell death within the conducting airway epithelium, an important upstream event in the pathogenesis of COPD.