Rhamnose-binding lectins (RBLs), a Ca²⁺-independent lectin family, are widely present in vertebrates and invertebrates, which involve in the innate immune response. However, the functional characterization and related regulation mechanisms of RBLs remain unclear in teleost fish. In this study, an l-rhamnose-binding lectin-like (OnRBL-L) was identified and functionally characterized from Nile tilapia (Oreochromis niloticus). The open reading frame of OnRBL-L is 678 bp encoding 225 aa. The sequence of OnRBL-L has relatively conservative characteristic peptide motifs, including YGR, DPC, and KYL-motif. Expression analysis showed that OnRBL-L was abundantly distributed in intestine tissue, and widely existed in all detected tissues. Meanwhile, the expression of OnRBL-L increased significantly in vivo (liver, spleen, head kidney, intestine, gills and peripheral blood) and in vitro (monocytes/macrophages) following challenges with two important tilapia pathogenic bacteria Streptococcus agalactiae and Aeromonas hydrophila. In addition, the recombinant OnRBL-L was found to bind and agglutinate S. agalactiae and A. hydrophila. Furthermore, OnRBL-L could participate in non-specific cellular immune defense, including reducing the expression of pro-inflammatory factors (IL-6、IL-8 and TNF-α), and enhancement of the phagocytosis and respiratory burst of MO/MФ. Overall, our results provide new insights into the understanding of RBL as an important pattern recognition molecule and regulator in non-specific cell immunity in an early vertebrate.

鼠李糖结合凝集素 (RBLs) 是一个不依赖 Ca ²⁺的凝集素家族，广泛存在于脊椎动物和无脊椎动物中，参与先天免疫反应。然而，RBLs 在硬骨鱼中的功能表征和相关调控机制仍不清楚。在这项研究中，从尼罗罗非鱼 ( Oreochromis niloticus ) 中鉴定出一种l-鼠李糖结合凝集素样 (OnRBL-L) 并对其进行功能表征。OnRBL-L的开放阅读框为 678 bp，编码 225 个氨基酸。OnRBL-L的序列具有相对保守的特征肽基序，包括YGR、DPC和KYL-基序。表达分析表明OnRBL-L大量分布于肠组织中，广泛存在于所有检测到的组织中。同时，在受到两种重要的罗非鱼病原菌无乳链球菌和嗜水气单胞菌的攻击后， OnRBL-L在体内（肝、脾、头肾、肠、鳃和外周血）和体外（单核细胞/巨噬细胞）的表达显着增加。此外，发现重组 OnRBL-L 与无乳链球菌和嗜水链球菌结合和凝集。此外，OnRBL-L 可参与非特异性细胞免疫防御，包括降低促炎因子（IL-6、IL-8和TNF-α），增强 MO/MФ 的吞噬和呼吸爆发。总体而言，我们的研究结果为理解 RBL 作为早期脊椎动物非特异性细胞免疫的重要模式识别分子和调节剂提供了新的见解。