KL-6 levels in induced sputum. KL-6 levels in induced sputum obtained from middle aged/elderly subjects (non-smokers; NS, smokers; S and COPD) in (A) both males and females, and in (B) males only. The box represents the 25th to 75th percentiles, the solid lines within the boxes show the median values, the whiskers are the 10th and 90th percentiles, and the points represent outliers. Horizontal bars indicate mean values. *p < 0.05; **p < 0.01; ***p < 0.001 (middle aged/elderly non-smokers vs middle aged/elderly smokers or COPD, Mann-Whitney U test).