CD4 and chronic obstructive pulmonary disease: McKendry et al. (2016) discovered that the expression of PD-1 on lung CD8+T cells was elevated in individuals with COPD compared to controls. Similarly, our study revealed a higher level of PD-1 expression on CD4+ T cells and Tregs, but not on CD8+ T cells, in GOLD stage I/II and stage III/IV COPD patients compared to controls.