Surfactant Protein D
Biological or Clinical Significance:
Human surfactant protein D (SP-D) is a member of the collageneous subfamily of glycoproteins and calcium-dependent lectins (collectins).
SP-D is a homotrimeric protein consisting of three 43kDa units that are bonded at their N-termini. Most preparations of SP-D contain predominantly dodecamers (four trimeric subunits), but higher multimers also have been observed. Each unit consists of at least four discrete structural domains: a short N-terminal domain, a relatively long collageneous domain, a short amphipatic connecting peptide, and a C-terminal, C-type lectin carbohydrate recognition domain (CRD). Maintenance of the multimeric structure of SP-D requires two cysteine residues in N-terminal domain. SP-D is synthesized and secreted by two types of non-ciliated epithelial cells in the peripheral airway, alveolar type II cells and Clara cells. It is also expressed by various other epithelial cells. In the lungs, SP-D is part of the innate response to inhaled microorganisms and organic antigens. SP-D binds to surface glycoconjugates of various microorganisms and to oligosaccharides associated with the surface of numerous organic antigens. However, the structural integrity of SP-D is compromised by MPO, and the resulting oxidation renders the collectin inactive. Studies have shown that SP-D expression may be related to a number of human diseases, including cystic fibrosis, acute interstitial pneumonias (ARDS), asthma, bronchopulmonary dysplasia, and alveolar proteinosis Animal studies have shown increased levels of SP-D expression in cases of silicosis and hyperoxia, as well as in IL-4 over expression during invasion of infectious agents.
Principle of Test Method:
The Surfactant Protein D ELISA is a sandwich enzyme immunoassay for the quantitative measurement of human surfactant protein D in serum, plasma (citrate, heparin), bronchoalveolar lavage fluid and amniotic fluid.
*Please contact nexelis for stability information.
**Note: Due to instability of the specimen upon thawing, it is recommended that two aliquots be submitted in the event repeat anlysis is required.