Because the glycerophospholipid metabolism pathway is essential for oxidative stress [45–47], the levels of five oxidative stress products (MPO, SOD, GSH, NE, and 8-iso-PGF2α) in induced sputum were measured by ELISA to evaluate the association between oxidative stress and COPD severity. The gene discussed is MPO; the disease is chronic obstructive pulmonary disease.