Surfactant protein D (SP-D) counteracts the inhibitory effect of surfactant protein A (SP-A) on phospholipid secretion by alveolar type II cells. Interaction of native SP-D with SP-A.
Surfactant protein D (SP-D) counteracts the inhibitory effect of surfactant protein A (SP-A) on phospholipid secretion by alveolar type II cells. Interaction of native SP-D with SP-A.
复制标题
表面活性蛋白 D (SP-D) 抵消表面活性蛋白 A (SP-A) 对 II 型肺泡细胞磷脂分泌的抑制作用。
作者：
Y. Kuroki;M. Shiratori;Y. Murata;T. Akino
表面活性剂蛋白 SP-A 和 SP-D 是从给予二氧化硅气管内滴注的大鼠中获得的。从 33,000 g 大鼠支气管肺泡灌洗液上清液中分离出 SP-D，我们检测了 SP-D 是否影响肺泡 II 型细胞的表面活性剂分泌。天然SP-D既不影响II型细胞的基础分泌，也不影响刺激的分泌。然而，天然SP-D以浓度依赖性方式抵消了SP-A对表面活性剂分泌的抑制作用；然而，SP-D 未能抵消伴刀豆球蛋白 A 的抑制作用。SP-D 的活性不受过量甲基 α-甘露糖苷的影响。过量的天然 SP-D 与 125I-SP-A 竞争与 II 型细胞的高亲和力结合。 SP-D 的热处理和针对 SP-D 的抗体均降低了 SP-D 活性。天然 SP-D 的丁醇提取在破坏 SP-D 活性方面最有效，并削弱了蛋白质与标记的 SP-A 竞争结合 II 型细胞的能力。 SP-D 的丁醇可溶部分能够将 SP-A 的抑制作用改变到与天然 SP-D 相同的程度。 125I-SP-A 在硝化纤维素片上的直接结合表明 SP-A 可以结合天然 SP-D，但不能结合丁醇提取的 SP-D。我们得出结论，天然 SP-D 通过 SP-D 相关脂质与 II 型细胞中的 SP-A 相互作用而改变 SP-A 活性。
The surfactant proteins SP-A and SP-D were obtained from rats given intratracheal instillation of silica. SP-D was isolated from the 33,000 g supernatant of rat bronchoalveolar lavage fluids, and we examined whether SP-D affects surfactant secretion by alveolar type II cells. Native SP-D affected neither basal secretion nor stimulated secretion by type II cells. However, native SP-D counteracted the inhibitory effect of SP-A on surfactant secretion in a concentration-dependent manner; however, SP-D failed to counteract the inhibitory effect of concanavalin A. The activity of SP-D was unaffected by inclusion of excess methyl alpha-mannoside. Excess native SP-D competed with 125I-SP-A for high-affinity binding to type II cells. Heat treatment of SP-D and antibody against SP-D both decreased SP-D activity. Butanol extraction of native SP-D was most effective at destroying SP-D activity and attenuated the ability of the protein to compete with labelled SP-A for binding to type II cells. The butanol-soluble fraction of SP-D possessed the ability to alter the inhibitory effect of SP-A to the same extent as native SP-D. Direct binding of 125I-SP-A on nitrocellulose sheets demonstrated that SP-A could bind native SP-D, but not butanol-extracted SP-D. We conclude that native SP-D alters SP-A activity in type II cells through interaction with it via SP-D-associated lipids.