TGFB1 and chronic obstructive pulmonary disease: Hence, these differences render the comparison of our results with the previous studies difficult.33, 34 Decreased expression of TGF-β1 in the small airways in COPD shown here and its critical role in regulating self-tolerance5 may explain the autoimmunity seen in some patients with COPD.6, 7 The complex signaling control points within the TGF-β activation pathway may enable targeted treatment of this complication.