As expected, HDAC2 expression was observed to be reduced markedly in PBMCs of COPD patients compared with smokers (0.43±0.05 vs. 0.93±0.06, P < .0001) and nonsmokers (0.43±0.05 vs. 1.07±0.05, P < .0001) (Fig 1A and 1B). Here, HDAC2 is linked to chronic obstructive pulmonary disease.