Kuan S F, Persson A, Parghi D, Crouch E
Department of Pathology, Jewish Hospital at Washington University Medical Center, St. Louis, Missouri 63110.
Am J Respir Cell Mol Biol. 1994 Apr;10(4):430-6. doi: 10.1165/ajrcmb.10.4.8136158.
Surfactant protein D (SP-D) is a calcium-dependent carbohydrate-binding protein that is secreted into the pulmonary airspaces by type II epithelial and Clara cells. Previous studies have shown that SP-D can bind to specific surfactant phospholipids and to glycoconjugates associated with the surface of various microorganisms, consistent with possible roles in surfactant metabolism and pulmonary host defense. We now describe specific saccharide-mediated interactions of SP-D with alveolar macrophages in lung tissue and in vitro. Biotinylated rat SP-D showed specific binding to alveolar macrophages in sections of rat lung; this labeling was inhibited by competing saccharides or EDTA. In addition, the binding of 125I-SP-D to isolated alveolar macrophages in the presence of calcium was time-dependent, saturable, and reversible and was preferentially inhibited by known monosaccharide and disaccharide ligands for SP-D. Scatchard analysis gave an apparent single class of binding sites with a Kd = 1.4 x 10(-6) M. We speculate that the multivalent structure of SP-D mediates bridging interactions between microbial glycoconjugates or surfactant phospholipids and specific glycosylated ligands expressed on the surface of phagocytic cells.
表面活性蛋白D（SP-D）是一种钙依赖性碳水化合物结合蛋白，由II型上皮细胞和克拉拉细胞分泌到肺腔中。先前的研究表明，SP-D可与特定的表面活性磷脂以及与各种微生物表面相关的糖缀合物结合，这与它在表面活性物质代谢和肺部宿主防御中可能发挥的作用一致。我们现在描述SP-D在肺组织和体外与肺泡巨噬细胞的特定糖介导相互作用。生物素化的大鼠SP-D在大鼠肺切片中显示出与肺泡巨噬细胞的特异性结合；这种标记被竞争性糖类或乙二胺四乙酸（EDTA）抑制。此外，在有钙存在的情况下，125I-SP-D与分离的肺泡巨噬细胞的结合具有时间依赖性、可饱和性和可逆性，并且优先被已知的SP-D单糖和二糖配体抑制。Scatchard分析得出一类明显的结合位点，解离常数（Kd）= 1.4×10^(-6) M。我们推测，SP-D的多价结构介导了微生物糖缀合物或表面活性磷脂与吞噬细胞表面表达的特定糖基化配体之间的桥连相互作用。
