The AUC for MUC5AC was down-regulated upon CS exposure in ALI cultures from COPD patients (from −1.1 ± 0.9 ∆Ct to –1.5 ± 0.5 ∆Ct, p = 0.3252) and healthy controls (from −1.3 ± 0.6 ∆Ct to −2.0 ± 0.5 ∆Ct, p = 0.2080). Here, MUC5AC is linked to chronic obstructive pulmonary disease.