c) Blunted Treg response (Figure 6): Treg cells, the immunosuppressive subset of CD4+ T cells, play an indispensable role in the maintenance of peripheral immune tolerance150,151 Studies have reported lower Tregs in COPD patients when compared to healthy controls and blunted Treg cell response in COPD patients with a history of tobacco smoking. This evidence concerns the gene CD4 and chronic obstructive pulmonary disease.