Department of Oral Microbiology and Immunology, Showa University School of Dentistry, Tokyo, Japan.
Mol Oral Microbiol. 2013 Oct;28(5):379-91. doi: 10.1111/omi.12031. Epub 2013 Jun 4.
Streptococcus gordonii is a commensal gram-positive bacterium that resides in the human oral cavity, and is one of the most common causes of infective endocarditis (IE). Bacterial surface molecules play an important role in establishing IE, and several S. gordonii proteins have been implicated in binding to host cells during the establishment of IE. In this study, we identified a putative lipoprotein, peptidyl-prolyl cis/trans isomerase (PpiA), and clarified its role in evasion of phagocytosis by macrophages. Attenuation of the gene encoding prolipoprotein diacylglyceryl transferase (Lgt) altered the localization of PpiA from the cell surface to the culture supernatant, indicating that PpiA is lipid-anchored in the cell membrane by Lgt. Both human and murine macrophages showed higher phagocytic activity towards ppiA and lgt mutants than the wild-type, indicating that the presence of PpiA suppresses phagocytosis of S. gordonii. Human macrophages treated with dextran sulfate had significantly impaired phagocytosis of S. gordonii, suggesting that class A scavenger receptors in human macrophages are involved in the phagocytosis of S. gordonii. These results provide evidence that S. gordonii lipoprotein PpiA plays an important role in inhibiting phagocytic engulfment and in evasion of the host immune response.
戈登链球菌是一种定居于人类口腔的共生革兰氏阳性菌，也是感染性心内膜炎（IE）最常见的病因之一。细菌表面分子在建立 IE 中起着重要作用，已有几种 S. gordonii 蛋白被牵连在建立 IE 过程中与宿主细胞结合。在本研究中，我们鉴定了一种假定的脂蛋白、肽基脯氨酰顺/反异构酶（PpiA），并阐明了其在逃避巨噬细胞吞噬作用中的作用。编码前脂蛋白二酰基甘油转移酶（Lgt）的基因衰减改变了 PpiA 从细胞表面到培养上清液的定位，表明 PpiA 通过 Lgt 脂锚定在细胞膜上。人和鼠巨噬细胞对 ppiA 和 lgt 突变体的吞噬活性均高于野生型，表明 PpiA 的存在抑制了 S. gordonii 的吞噬作用。用葡聚糖硫酸盐处理的人巨噬细胞对 S. gordonii 的吞噬作用明显受损，表明人巨噬细胞中的 A 类清道夫受体参与了 S. gordonii 的吞噬作用。这些结果提供了证据表明 S. gordonii 脂蛋白 PpiA 在抑制吞噬作用和逃避宿主免疫反应中起着重要作用。
