NGF and chronic obstructive pulmonary disease: This study examined 11 serum growth factors representing four pathobiological axes relevant to COPD: epithelial repair and mesenchymal remodeling (EGF, FGF-2, LIF); angiogenesis and tissue perfusion (VEGF, PDGF); neuro-immune signaling (NGF, BDNF); and hematopoietic/progenitor and tissue repair signalling (SCF, HGF).