CLCA1 and chronic obstructive pulmonary disease: The average area of CLCA1-expressing epithelium per millimeter of basal lamina was significantly greater for smokers (5232 ± 1126 μm2, p = 0.02) and COPD patients (6954 ± 1504 μm2, p = 0.002) than for non-smokers (1524 ± 326 μm2) (Figure 3).