Mannose receptor (MR) as a member of the pattern recognition receptors (PRRs) plays an important role in the immune response. In mammals, the role of MR in the regulation of phagocytosis is clarified; however, its contribution to opsonize phagocytosis remains unclear in bony fish. In this study, the expression pattern of Nile tilapia mannose receptor gene (OnMR) was investigated and its regulation of the phagocytosis of monocytes/macrophages to pathogenic bacteria was identified. The full-length of OnMR open reading frame is 4314 bp, encoding a peptide containing 1437 amino acid residues. The deduced amino acid sequence revealed that OnMR contained a cysteine-rich domain, a fibronectin type II domain, multiple C-type lectin-like domains, a transmembrane domain and a short cytoplasmic domain. Tissue distribution analysis showed the OnMR transcripts was widely distribute in the ten detected tissues, and highly expressed in head kidney, hind kidney, intestine and spleen. After S. agalactiae and A. hydrophila infection, the expression of OnMR in head kidney and spleen increased significantly. Moreover, the expression of OnMR in MO/Mø were also upregulated post the infection of bacteria and mannose solutions in vitro. This suggested that MR, as a mannose receptor on macrophage surface, could respond strongly to the stimulation of pathogenic bacteria. In addition, the (r)OnMR protein could effectively bind and agglutinate S. agalactiae and A. hydrophila, and regulate the phagocytic ability of monocytes/macrophages to pathogenic bacteria. These results suggest that OnMR is involved in response against bacterial infection in Nile tilapia, and this study will help us better understand the function of MR in teleost fish.

甘露糖受体（MR）作为模式识别受体（PRRs）的一员，在免疫反应中发挥着重要作用。在哺乳动物中，阐明了 MR 在吞噬作用调节中的作用；然而，在硬骨鱼中，它对调理吞噬作用的作用仍不清楚。本研究对尼罗罗非鱼甘露糖受体基因( OnMR )的表达模式进行了研究，并确定了其对单核细胞/巨噬细胞对病原菌的吞噬作用的调控。OnMR全长开放阅读框为 4314 bp，编码一个含有 1437 个氨基酸残基的肽段。推导的氨基酸序列显示 OnMR 包含一个富含半胱氨酸的结构域、一个 II 型纤连蛋白结构域、多个 C 型凝集素样结构域、一个跨膜结构域和一个短胞质结构域。组织分布分析显示，OnMR转录本广泛分布于检测到的10个组织中，并在头肾、后肾、肠和脾中高表达。无乳链球菌和嗜水链球菌感染后，头肾和脾脏中OnMR的表达明显增加。此外，在细菌和甘露糖溶液感染后，MO/Mø 中 OnMR 的表达也上调。体外。这表明MR作为巨噬细胞表面的甘露糖受体，可以对病原菌的刺激产生强烈反应。此外，(r)OnMR蛋白能有效结合并凝集无乳链球菌和嗜水链球菌，调节单核/巨噬细胞对病原菌的吞噬能力。这些结果表明 OnMR 参与了对尼罗罗非鱼细菌感染的反应，这项研究将有助于我们更好地了解 MR 在硬骨鱼中的功能。