IL4 and chronic bronchitis: The concentrations of eosinophil cationic protein (ECP) and interleukin-4 (IL-4) in blood during stable clinical conditions for 10 (n = 9 for ECP) healthy never-smokers (HNS), 10 current long-term smokers (LTS) and 26 (n = 25 for IL-4) current long-term smokers with exacerbations of COPD and chronic bronchitis (COPD-CB).