SCGB1A1 and chronic obstructive pulmonary disease: In asymptomatic smokers and chronic obstructive pulmonary disease (COPD), the number of club cells and the expression of club cell marker SCGB1A1 in the human SAE are decreased [1, 7], and the SCGB1A1 levels in lung epithelial lining fluid is decreased in asthma [8, 9], together suggesting that COPD and asthma are the club cell deficiency disorders.