Pulmonary surfactant-associated protein D (SP-D) is a 43 kDa member of the collectin family of innate immune modulators. Mouse SP-D cDNA encodes a 19 aa signal sequence and a 355 aa mature region with a 25 aa N-terminal linking-region, a 177 aa hydroxyproline and hydroxylysine collagen-like domain, a 46 aa coiled-coil segment, and a 106 aa, C-terminal collectin-like C-type lectin domain . SP-D is found in serum, plasma, broncho-alveolar lavage (BAL) fluid, and amniotic fluid. It also binds SIRP alpha and the calreticulin/CD91 complex on macrophages. SP-D contributes to the lung's defense against inhaled microorganisms, organic antigens and toxins. It Interacts with compounds such as bacterial lipopolysaccharides, oligosaccharides and fatty acids and modulates leukocyte action in immune response. It may participate in the extracellular reorganization or turnover of pulmonary surfactant. It binds strongly maltose residues and to a lesser extent other alpha-glucosyl moieties.
