Increased serum SP-D in identification of high-risk smokers at high risk of COPD
Pulmonary surfactant protein D (SP-D) is an important component of the pulmonary innate immune system with the ability to dampen cigarette smoke-induced lung inflammation. However, cigarette smoking mediates translocation of SP-D from the lung to the blood, and serum SP-D (sSP-D) has therefore previously been suggested as marker for smoke-induced lung injury. In support of this notion, associations between high sSP-D and low lung function measurements have previously been demonstrated in smokers and in COPD. The present investigations employ a 12-year longitudinal Danish twin study to test the hypothesis that baseline sSP-D variation has the capacity to identify smokers with normal baseline lung function who are in high risk of significant future smoke-induced lung function decline. We find that sSP-D is significantly increased in those with normal lung function at baseline that develop lung function decline during follow up compared to those who stay lung healthy. Moreover, we demonstrate that it is the smoke-induced baseline sSP-D level, and not the constitutional level, which has capacity as biomarker, and which is linearly increased with the decline in lung function during follow up. In conclusion, we here present first observation of increased sSP-D for identification of high-risk smokers.