Laboratory of Biochemistry and Molecular Biology, School of Marine Sciences, Ningbo University, Ningbo 315211, China; Key Laboratory of Applied Marine Biotechnology of Ministry of Education, Ningbo University, Ningbo 315211, China.
Laboratory of Biochemistry and Molecular Biology, School of Marine Sciences, Ningbo University, Ningbo 315211, China.
Fish Shellfish Immunol. 2018 May;76:58-67. doi: 10.1016/j.fsi.2018.02.038. Epub 2018 Feb 23.
The short-chain pentraxins (PTXs), including C-reactive protein (CRP) and serum amyloid P (SAP), are soluble pattern recognition molecules (PRMs) that exhibit calcium-dependent binding to bacterial surface molecules. They opsonize pathogens or other particles by phagocytic clearance. However, the detailed functions of short-chain PTXs in teleosts remained unclear. In this study, we identified a short-chain PTX gene from ayu, Plecoglossus altivelis, and tentatively named as PaCRP/SAP. Sequence analysis revealed that PaCRP/SAP has typical characteristics of fish CRP/SAP and is mostly closely related to rainbow smelt (Osmerus mordax) SAP. PaCRP/SAP transcripts were detected in all tested tissues, with the highest level in the liver, and its expression significantly upregulated following Vibrio anguillarum infection. The active recombinant mature PaCRP/SAP (rPaCRP/SAPm) agglutinated Gram-negative bacteria (Escherichia coli, V. anguillarum, Aeromonas hydrophila, and Vibrio parahaemolyticus) and Gram-positive bacteria (Staphylococcus aureus and Listeria monocytogenes) in a calcium-dependent manner in vitro, and it correspondingly bound peptidoglycan and lipopolysaccharide in a dose-dependent manner. The binding of rPaCRP/SAPm to E. coli and S. aureus resulted in a clear inhibition of the deposition of ayu complement 3 (PaC3) on the bacteria. Furthermore, rPaCRP/SAPm decreased phagocytosis of rPaCRP/SAPm-bound E. coli and S. aureus cells by ayu monocytes/macrophages (MO/MΦ) in a complement-dependent way. However, rPaCRP/SAPm alone had no significant influence on phagocytosis. These results provided the first evidence that PaCRP/SAP might function in ayu immune responses via agglutinating bacteria and inhibiting complement-mediated opsonophagocytosis by MO/MΦ.
短链五聚蛋白（PTXs），包括 C 反应蛋白（CRP）和血清淀粉样蛋白 P（SAP），是具有钙离子依赖性的可溶性模式识别分子（PRMs），可与细菌表面分子结合。它们通过吞噬清除作用来调理病原体或其他颗粒。然而，短链 PTX 在硬骨鱼中的详细功能仍不清楚。在本研究中，我们从日本牙鲆（Plecoglossus altivelis）中鉴定出一个短链 PTX 基因，并暂定名为 PaCRP/SAP。序列分析表明，PaCRP/SAP 具有鱼类 CRP/SAP 的典型特征，与虹鳟（Osmerus mordax）SAP 最为密切相关。PaCRP/SAP 转录本在所有检测组织中均有表达，在肝脏中表达水平最高，在感染鳗弧菌后其表达显著上调。体外实验中，重组成熟 PaCRP/SAP（rPaCRP/SAPm）以钙离子依赖的方式凝集革兰氏阴性菌（大肠杆菌、鳗弧菌、嗜水气单胞菌和副溶血弧菌）和革兰氏阳性菌（金黄色葡萄球菌和单核细胞增生李斯特菌），并以剂量依赖的方式结合肽聚糖和脂多糖。rPaCRP/SAPm 与大肠杆菌和金黄色葡萄球菌的结合导致 ayu 补体 3（PaC3）在细菌上的沉积明显减少。此外，rPaCRP/SAPm 以补体依赖的方式降低了 ayu 单核细胞/巨噬细胞（MO/MΦ）对 rPaCRP/SAPm 结合的大肠杆菌和金黄色葡萄球菌细胞的吞噬作用。然而，rPaCRP/SAPm 本身对吞噬作用没有显著影响。这些结果首次表明，PaCRP/SAP 可能通过凝集细菌和抑制 MO/MΦ 补体介导的调理吞噬作用来发挥作用，从而参与牙鲆的免疫反应。
