KLF4 and chronic obstructive pulmonary disease: Quantification of KLF4 and KLF2 staining data in these tissue sections suggest that in normal lung, the level of KLF2 is relatively lower than KLF4 (Supplementary Figure S2E), in contrast, in emphysema and COPD tissue sections, the levels of KLF2 is higher than KLF4 (Supplementary Figure S2E).