School of Fisheries, Aquaculture, and Aquatic Sciences, Auburn University, Auburn, AL 36849, USA.
United States Department of Agriculture, Agricultural Research Service, Aquatic Animal Health Research Unit, Auburn, AL 36832, USA.
Fish Shellfish Immunol. 2018 Jan;72:426-435. doi: 10.1016/j.fsi.2017.11.015. Epub 2017 Nov 10.
Rhamnose-binding lectins (RBLs) are crucial elements associated with innate immune responses to infections and have been characterized from a variety of teleost fishes. Given the importance of RBL in teleost fishes, we sought to study the diversity and expression profiles of RBLs in an important cultured fish, Nile tilapia (Oreochromis niloticus) following experimental infection with Streptococcus agalactiae, a major cause of streptococcosis in farmed tilapia. In this study, four predicted RBL genes were identified from Nile tilapia and were designated as OnRBL3a, OnRBL3b, OnRBL3c, and OnRBL3d. These OnRBLs were composed of two tandem-repeated type five carbohydrate recognition domains (CRDs), classified as type IIIc, and all clustered together phylogenetically. OnRBL-CRDs shared conserved topology of eight cysteine residues, characteristic peptide motifs of -YGR- and -DPC- (or -FGR- and -DTC-), and similar exon/intron organization. OnRBLs had the highest expression in immune-related tissues, gills, intestine or liver. However, the changes of OnRBL expression in the gills and intestine at 2 h, 4 h and 24 h post S. agalactiae challenge were modest, suggesting that tilapia may not mediate the entry or confront the infection of S. agalactiae through induction of RBL genes. The observed expression pattern may be related to the RBL type and CRD composition, S. agalactiae pathogenesis, the accessibility of ligands on the bacterial surface, and/or the species of fish. OnRBLs characterized in this study were the first RBL members identified in Nile tilapia and their characterization will expand our knowledge of RBLs in immunity.
岩藻糖结合凝集素（RBLs）是与感染相关的先天免疫反应的关键组成部分，已从多种硬骨鱼类中得到鉴定。鉴于 RBL 在硬骨鱼类中的重要性，我们试图在一种重要的养殖鱼类——尼罗罗非鱼（Oreochromis niloticus）中研究其在受到无乳链球菌（Streptococcus agalactiae）感染后的多样性和表达谱，该菌是养殖罗非鱼链球菌病的主要病原体。在本研究中，我们从尼罗罗非鱼中鉴定出了 4 个预测的 RBL 基因，并将其命名为 OnRBL3a、OnRBL3b、OnRBL3c 和 OnRBL3d。这些 OnRBL 由两个串联重复的五型碳水化合物识别结构域（CRD）组成，归类为 IIIc 型，且在系统进化上聚为一簇。OnRBL-CRD 共享 8 个半胱氨酸残基的保守拓扑结构、-YGR-和-DPC-（或-FGR-和-DTC-）特征肽基序，以及相似的外显子/内含子组织。OnRBL 在免疫相关组织（鳃、肠或肝）中的表达水平最高。然而，在无乳链球菌攻毒后 2、4 和 24 小时，罗非鱼鳃和肠中的 OnRBL 表达变化不大，这表明罗非鱼可能不会通过诱导 RBL 基因来介导无乳链球菌的进入或对抗感染。观察到的表达模式可能与 RBL 类型和 CRD 组成、无乳链球菌的发病机制、细菌表面配体的可及性以及/或鱼类的种类有关。本研究中鉴定的 OnRBL 是尼罗罗非鱼中首次鉴定的 RBL 成员，它们的特征将扩展我们对免疫中 RBL 的认识。
