To evaluate stability of the ACE2 transcript between non-smoker, smoker, and COPD-derived HLFs, we treated these cells with actinomycin D (ActD 1 μg/mL), an inhibitor of RNA synthesis [28,37], for 3, 6, and 9 h, followed by an analysis of ACE2 mRNA. Here, ACE2 is linked to chronic obstructive pulmonary disease.