Comprehensive characterisation of pulmonary and serum surfactant protein D in COPD

Respir Res. 2011 Mar 11;12(1):29. doi: 10.1186/1465-9921-12-29.


Background: Pulmonary surfactant protein D (SP-D) is considered as a candidate biomarker for the functional integrity of the lung and for disease progression, which can be detected in serum. The origin of SP-D in serum and how serum concentrations are related to pulmonary concentrations under inflammatory conditions is still unclear.

Methods: In a cross-sectional study comprising non-smokers (n=10), young--(n=10), elderly smokers (n=20), and smokers with COPD (n=20) we simultaneously analysed pulmonary and serum SP-D levels with regard to pulmonary function, exercise, repeatability and its quaternary structure by native gel electrophoresis. Statistical comparisons were conducted by ANOVA and post-hoc testing for multiple comparisons; repeatability was assessed by Bland-Altman analysis.

Results: In COPD, median (IQR) pulmonary SP-D levels were lower (129(68) ng/ml) compared to smokers (young: 299(190), elderly: 296(158) ng/ml; p<0.01) and non-smokers (967(708) ng/ml; p<0.001). The opposite was observed in serum, with higher concentrations in COPD (140(89) ng/ml) as compared to non-smokers (76(47) ng/ml; p<0.01). SP-D levels were reproducible and correlated with the degree of airway obstruction in all smokers. In addition, smoking lead to disruption of the quaternary structure.

Conclusions: Pulmonary and serum SP-D levels are stable markers influenced by smoking and related to airflow obstruction and disease state. Smaller subunits of pulmonary SP-D and the rapid increase of serum SP-D levels in COPD due to exercise support the translocation hypothesis and its use as a COPD biomarker.

Trial registration: no interventional trial.

MeSH terms

  • Adult
  • Aged
  • Analysis of Variance
  • Biomarkers / blood
  • Bronchoalveolar Lavage Fluid / chemistry
  • Bronchoalveolar Lavage Fluid / cytology
  • Colorimetry
  • Cross-Sectional Studies
  • Exercise Test
  • Female
  • Forced Expiratory Volume
  • Germany
  • Humans
  • Lung / metabolism*
  • Lung / physiopathology
  • Male
  • Middle Aged
  • Oxidation-Reduction
  • Predictive Value of Tests
  • Protein Structure, Quaternary
  • Pulmonary Disease, Chronic Obstructive / blood*
  • Pulmonary Disease, Chronic Obstructive / etiology
  • Pulmonary Disease, Chronic Obstructive / physiopathology
  • Pulmonary Surfactant-Associated Protein D / blood*
  • Pulmonary Surfactant-Associated Protein D / chemistry
  • Reproducibility of Results
  • Severity of Illness Index
  • Smoking / adverse effects
  • Smoking / blood*
  • Vital Capacity
  • Young Adult


  • Biomarkers
  • Pulmonary Surfactant-Associated Protein D