NCAM1 and chronic obstructive pulmonary disease: Using the same number of effector cells (effector to target ratio of 5:1) the CD56+ cells from COPD subjects were significantly more cytotoxic (36.8% specific lysis) than those from smokers (22.4%; p < 0.01) and HNS (16.1%; p < 0.001) (Figure 4A).