In this study, the functions of a recombinant propeptide (rProOn-Hep1) and the synthetic FITC-labelled mature peptides sMatOn-Hep1 and sMatOn-Hep2 were analyzed. Moreover, sMatOn-Hep1 and sMatOn-Hep2 were mildly detected in the lymphocytes of peripheral blood mononuclear cells (PBMCs) and strongly detected in head kidney macrophages. The in vitro binding and antibacterial activities of these peptides were slightly effective against several pathogenic bacteria. Immune regulation by sMatOn-Hep1 was also analyzed, and only sMatOn-Hep1 significantly enhanced the phagocytic index in vitro (p < 0.05). Interestingly, intraperitoneal injection of sMatOn-Hep1 (10 or 100 µg) significantly elevated the phagocytic activity, phagocytic index, and lysozyme activity and clearly decreased the iron ion levels in the livers of the treated fish (p < 0.05). Additionally, sMatOn-Hep1 enhanced the expression levels of CC and CXC chemokines, transferrin and both On-Hep genes in the liver, spleen and head kidney, for 1–96 h after injection, but did not properly protect the experimental fish from S. agalactiae infection after 7 days of treatment. However, the injection of S. agalactiae and On-Heps indicated that 100 μg of sMatOn-Hep1 was very effective, while 100 μg of rProOn-Hep1 and sMatOn-Hep2 demonstrated moderate protection. Therefore, On-Hep is a crucial iron-regulating molecule and a key immune regulator of disease resistance in Nile tilapia.

中文翻译：

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免疫调节而非抗细菌活性是铁调素在尼罗罗非鱼（Oreochromis niloticus Linn。）对病原细菌抵抗中的重要功能。

在这项研究中，分析了重组前肽（rPro On -Hep1）和合成的FITC标记的成熟肽sMat On -Hep1和sMat On -Hep2的功能。此外，在外周血单核细胞（PBMC）的淋巴细胞中轻度检测到sMat On -Hep1和sMat On -Hep2，在头肾巨噬细胞中强烈检测到sMat On -Hep1和sMat On -Hep2。这些肽的体外结合和抗菌活性对几种病原菌均有效。还分析了sMat On -Hep1的免疫调节作用，只有sMat On -Hep1显着增强了体外吞噬指数（p<0.05）。有趣的是，腹膜内注射sMat On -Hep1（10或100 µg）可显着提高吞噬活性，吞噬指数和溶菌酶活性，并明显降低了所治疗鱼肝中的铁离子水平（p <0.05）。此外，sMat On -Hep1在注射后1–96 h内可增强肝脏，脾脏和头部肾脏中CC和CXC趋化因子，转铁蛋白以及两个On -Hep基因的表达水平，但不能适当保护实验鱼免受S治疗7天后无乳杆菌感染。然而，注射无乳链球菌和论-Heps表示100μgsMat On -Hep1非常有效，而100μgrPro On -Hep1和sMat On -Hep2具有中等保护作用。因此，On- Hep是尼罗罗非鱼抗病的关键铁调节分子和关键免疫调节剂。