CD4 and chronic obstructive pulmonary disease: Another interesting finding emerging from our study was the demonstration that the percentages of Th17/Th1 cells among CD4 + T cells, as well as among Th17 cells, were significantly higher in current smoker COPD patients than in ex-smoker COPD patients, and positively correlated with pack-years of smoking, although there was no difference in the percentages of Th17 cells among COPD smokers and ex-smokers.