MPO and chronic obstructive pulmonary disease: CD40 ligand (CD40L), epidermal growth factor (EGF), brain-derived neurotrophic factor (BDNF), Regulated upon Activation, Normally T-cell expressed, and Secreted (RANTES), and myeloperoxidase were the most highly overexpressed proteins in COPD, being on average 10-fold greater than the levels observed for the control cohorts.