TABLE 1.

Expression of genes/proteins related to severe acute respiratory syndrome-coronavirus-2 infection in controls^# and COPD patients

First author [ref.]	Key findings			Sample type	Patient groups
	ACE2	Furin	TMPRSS2
Cai [40]	↑	↑	No difference	Bronchial epithelium	Current smoker versus never-smoker COPD versus ex-smoker
Leung [28]	↑	Not quantified	Not quantified	Bronchial epithelium	Current smoker versus never-smoker COPD versus controls Negative correlation with FEV1 %
Smith [41]	↑	Not quantified	No difference	Whole lung tissue	Current smoker versus never-smoker COPD versus current smoker
Brake [27]	↑	Not quantified	Not quantified	Bronchial epithelium	COPD versus controls¶
Zhang [29]	↑	No difference	↑	Bronchial epithelium	Current smoker versus never-smoker
Radzikowska [42]	↑	Not quantified	Not quantified	Bronchial biopsy	Current smoker versus never-smoker
Higham [43]	↑	No difference¶	No difference	Bronchial epithelium	Negative correlation with FEV1 % Overweight COPD versus not overweight COPD

↑: increase in cell number; FEV₁: forced expiratory volume in 1 s. ^#: controls were a mixture of never-, ex- and current smokers; ^¶: data not presented in manuscript.