Since cell proliferation was inhibited by CSE at 48 h (Figure 5), we investigated the protein levels of the different stress pathways (ATF6, IRE1, PERK, and CHOP) at a preceding timepoint (8 h) after exposure to different concentrations of CSE in lung fibroblasts from healthy and COPD subjects (Figure 6). This evidence concerns the gene EIF2AK3 and chronic obstructive pulmonary disease.