SP-D levels in BAL and Serum. SP-D levels in BAL (A) serum (B) and the ratio of BAL/serum SP-D levels (C) of healthy, non-smoking subjects (H, open squares n = 10), young smokers (S1, black squares, n = 10), elderly smokers (S2, open triangles, n = 20) and smokers with COPD (C, black triangles n = 20). Log-transformed individual data points are provided together with the respective mean of the log transformed data. Values are displayed on a logarithmic scale. *p < 0.05, **p < 0.01, ***p < 0.001 compared to H, #p < 0.05, ##p < 0.01 compared to C.