TNF and chronic obstructive pulmonary disease: Though these were unexpected findings in the context of COPD exacerbations, pro-inflammatory cytokines, including the individual components of the cocktail (IL-1β, IL-6, IL-8 and TNF-α) were previously suggested to stimulate epithelial proliferation and/or survival in injury models (25–29), whereas chronic inflammation is associated with airway remodeling and alterations in the composition of the epithelium (30).