However, there is as yet no research exploring the possibility of TGF-β receptors constitutive phosphorylating SMAD2/3 in the absence of TGF-β1, and previous research in large airways demonstrated immunohistochemically detectible increases in TGF-β1 expression in COPD patient utilising the same methodology (26). Here, TGFB1 is linked to chronic obstructive pulmonary disease.