PRF1 and chronic obstructive pulmonary disease: There were significantly more CD56dimCD16+ NK cells and NKT-like (CD56+CD3+) cells expressing only perforin and no granzyme B in COPD subjects (63.5% and 28.4%, respectively) compared to smokers (27.3%; p < 0.01 and 10.1%; p < 0.01) and HNS (32.2%; p < 0.01 and 7.0%; p < 0.01).