TNF and chronic obstructive pulmonary disease: Soluble TNF receptors (sTNFRI and sTNFRII) suppress TNF-α-driven chronic airway inflammation, and their serum and sputum levels positively correlate with lung function in COPD patients; therefore, sTNFRI and sTNFRII are considered important anti-inflammatory mediators responsible for lung repair and regeneration [53].