Elevation of surfactant protein A in plasma and sputum in cigarette smokers

Serum surfactant protein (SP)-A has been postulated to associate with pulmonary fibrosis, but its role in cigarette smoking-related lung diseases is undefined. SP-A levels in plasma and induced sputum in nonsmokers, smokers with respiratory symptoms (cough and/or phlegm) and symptom-free smokers were assessed using a validated EIA method. A total of 474 current smokers without any diseases or medications were enrolled and followed for 2 yrs with 111 of them succeeding in stopping. Plasma SP-A level was detectable in all subjects and elevated in smokers independently of the symptoms compared to nonsmokers (p=0.001). After 2 yrs of follow-up, the SP-A level was higher in those who continued smoking compared to the quitters (p < 0.001). Plasma SP-A levels were associated with age, smoking history and lung function. Sputum (n=109) SP-A was nondetectable in most nonsmokers, whereas smoking and symptoms increased sputum SP-A highly significantly (p=0.001). In conclusion, SP-A may be involved in pathogenesis of cigarette smoking-related lung diseases. Further studies are needed to elucidate the role of SP-A in chronic obstructive pulmonary disease.