PRF1 and chronic obstructive pulmonary disease: The proportions of CD8+ T lymphocytes, CD56dimCD16+ NK cells and NKT-like (CD56+CD3+) cells that expressed both perforin and granzyme B were significantly lower in COPD subjects (6.4%, 5.2% and 33.4%, respectively) than in smokers (33.0%; p < 0.01, 58.9%; p < 0.01 and 58.6%; p < 0.01) and HNS (33.2%; p < 0.01, 67.7%; p < 0.01 and 60.7%; p < 0.01) (Figure 3B).