To further reveal genes responsible for COPD in particular, we showed that the top COPD-associated DEGs among immune cells were from monocytes, including nuclear factor-kappa B (NF-κB) signaling genes such as REL, IL1B, KLF4 and FLNA; among non-immune cells, the top DEGs were from AT2s and club cells, including AZGP1, SNRPG, HNRNPM, EIF3E, TIE1, and IL7R (Fig. 2C). This evidence concerns the gene KLF4 and chronic obstructive pulmonary disease.