Plasma Surfactant Protein D Levels and the Relation to Body Mass Index in a Chinese Population

Surfactant protein D (SP‐D) is a member of the collectin family and is an important component of the pulmonary innate host defence. The protein has a widespread distribution in the human body and is present in multiple epithelia, in endothelium and in blood. Various studies have looked at the relationship between serum SP‐D levels and pulmonary inflammatory diseases. The SP‐D distribution has been most thoroughly described in European populations and appears with a broad range of serum values highly influenced by genetic factors. In the present study, we investigated the plasma SP‐D distribution in a Chinese population from the Tai An region comprising 268 individuals. We found that (i) plasma SP‐D in the Chinese population was distributed with a median value of 380.2 ng/ml (324.9; 418.7) and a range from 79.4 to 3965.3 ng/ml, (ii) significantly higher plasma SP‐D in men than in women, and no significant effect of age, and (iii) a significant inverse association between serum SP‐D and body mass index (BMI) (P = 0.012). The data indicate that racial differences in SP‐D expression exist as the median plasma SP‐D in the Chinese population was approximately two times lower than the median serum SP‐D previously measured in a Danish population using the same immuno‐assay. The inverse association between serum SP‐D and BMI found in the Chinese population indicates that serum SP‐D is related to obesity in similar ways in Chinese and Danes.