Departments of Biochemistry, Sapporo Medical University School of Medicine, Sapporo 060-8556, Japan.
J Biol Chem. 2010 Mar 12;285(11):8434-43. doi: 10.1074/jbc.M109.074765. Epub 2010 Jan 7.
Pulmonary collectins, surfactant proteins A (SP-A) and D (SP-D), play important roles in innate immunity of the lung. Legionella pneumophila is a bacterial respiratory pathogen that can replicate within macrophages and causes opportunistic infections. L. pneumophila possesses cytolytic activity, resulting from insertion of pores in the macrophage membrane upon contact. We examined whether pulmonary collectins play protective roles against L. pneumophila infection. SP-A and SP-D bound to L. pneumophila and its lipopolysaccharide (LPS) and inhibited the bacterial growth in a Ca(2+)-dependent manner. The addition of LPS in the culture blocked the inhibitory effects on L. pneumophila growth by the collectins, indicating the importance of LPS-collectin interaction. When differentiated THP-1 cells were infected with L. pneumophila in the presence of SP-A and SP-D, the number of permeable cells was significantly decreased, indicating that pulmonary collectins inhibit pore-forming activity of L. pneumophila. The number of live bacteria within the macrophages on days 1-4 after infection was significantly decreased when infection was performed in the presence of pulmonary collectins. The phagocytosis experiments with the pH-sensitive dye-labeled bacteria revealed that pulmonary collectins promoted bacterial localization to an acidic compartment. In addition, SP-A and SP-D significantly increased the number of L. pneumophila co-localized with LAMP-1. These results indicate that pulmonary collectins protect macrophages against contact-dependent cytolytic activity of L. pneumophila and suppress intracellular growth of the phagocytosed bacteria. The promotion of lysosomal fusion with Legionella-containing phagosomes constitutes a likely mechanism of L. pneumophila growth suppression by the collectins.
肺表面活性物质蛋白 A（SP-A）和 D（SP-D）是肺固有免疫的重要组成部分。嗜肺军团菌是一种呼吸道细菌病原体，能够在巨噬细胞内复制，并引起机会性感染。嗜肺军团菌具有细胞溶解活性，这是由于与巨噬细胞接触时在细胞膜中插入孔所致。我们研究了肺表面活性物质蛋白是否对嗜肺军团菌感染起到保护作用。SP-A 和 SP-D 与嗜肺军团菌及其脂多糖（LPS）结合，并以 Ca2+依赖性方式抑制细菌生长。在培养物中添加 LPS 可阻断肺表面活性物质蛋白对嗜肺军团菌生长的抑制作用，表明 LPS-肺表面活性物质蛋白相互作用的重要性。当分化的 THP-1 细胞在 SP-A 和 SP-D 的存在下感染嗜肺军团菌时，通透性细胞的数量显著减少，表明肺表面活性物质蛋白抑制了嗜肺军团菌的孔形成活性。当感染存在肺表面活性物质蛋白时，感染后第 1-4 天巨噬细胞内活细菌的数量显著减少。用 pH 敏感染料标记的细菌进行吞噬实验表明，肺表面活性物质蛋白促进细菌定位到酸性隔室。此外，SP-A 和 SP-D 显著增加了与 LAMP-1 共定位的嗜肺军团菌的数量。这些结果表明，肺表面活性物质蛋白可保护巨噬细胞免受嗜肺军团菌接触依赖性细胞溶解活性的侵害，并抑制吞噬细菌的体内生长。溶酶体与含有军团菌的吞噬体融合的促进可能是肺表面活性物质蛋白抑制嗜肺军团菌生长的机制之一。
