CASP4 and chronic obstructive pulmonary disease: Here, we found that caspase-4 mRNA levels were higher in COPD-derived PBMCs than smokers and non-smokers (data not shown; COPD: median = 14.12 ratio caspase-4/β-actin mRNA; Smokers: median = 4.971 ratio caspase-4/β-actin mRNA, Healthy non-smoker: median = 0.9059 ratio caspase-4/β-actin mRNA).