Surfactant Protein D (SP-D)

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 also higher multimers have been observed. Each unit consists of at least four discrete structural domains: a short N-terminal domain; a relatively long collagenous domain, a short amphipathic connecting peptide, and a C-terminal, C- type lectin carbohydrate recognition domain (CRD). In the lungs, SP-D participates in 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. Studies have shown that SP-D expression may be related to a number of human diseases: cystic fibrosis, acute interstitial pneumonias (ARDS), asthma, bronchopulmonary dysplasia, alveolar proteinosis etc.