Smoking reduces surfactant protein D and phospholipids in patients with and without chronic obstructive pulmonary disease

Background: Pulmonary surfactant D (SP-D) has important regulatory functions for innate immunity and has been implicated as a biomarker for chronic obstructive pulmonary disease (COPD). We hypothesized that COPD patients would have reduced bronchoalveolar lavage (BAL) fluid SP-D levels compared to healthy smoking and non-smoking controls. Methods: BAL SP-D and phospholipids were quantified and corrected for dilution in 110 subjects (65 healthy never smokers, 23 smokers with normal spirometry, and 22 smokers with COPD). Results: BAL SP-D was highest in never smokers (mean 51.9 mu g/mL +/- 7.1 mu g/mL standard error) compared to both smokers with normal spirometry (16.0 mu g/mL +/- 11.8 mu g/mL) and subjects with COPD (19.1 mu g/mL +/- 12.9 mu g/mL; P < 0.0001). Among smokers with COPD, BAL SP-D correlated significantly with FEV1% predicted (R = 0.43; P < 0.05); however, the strongest predictor of BAL SP-D was smoking status. BAL SP-D levels were lowest in current smokers (12.8 mu g/mL +/- 11.0 mu g/mL), intermediate in former smokers (25.2 mu g/mL +/- 14.2 mu g/mL; P < 0.008), and highest in never smokers. BAL phospholipids were also lowest in current smokers (6.5 nmol +/- 1.5 nmol), intermediate in former smokers (13.1 nmol +/- 2.1 nmol), and highest in never smokers (14.8 nmol +/- 1.1 nmol; P < 0.0001). Conclusions: These data suggest that smokers, and especially current smokers, exhibit significantly reduced BAL SP-D and phospholipids compared to nonsmokers. Our findings may help better explain the mechanism that leads to the rapid progression of disease and increased incidence of infection in smokers.