TMPRSS2 and chronic obstructive pulmonary disease: Compared to ACE2, the effect of current smoking on the expression of TMPRSS2 was modest (Additional file 3: Figure S7c), and as previously reported [10], expression levels of TMPRSS2 were higher in asthmatic than healthy controls, but not in COPD, and it decreased in association with steroid use (Additional file 3: Figure S7d).