Yao Yuan-Yuan, Pan Chen-Xi, Hao Yu-Dong, Liu Xun, Chen Dan-Dan, Cui Zheng-Wei, Zhang Xiang-Yang, Ye Jian-Min, Zhang Yong-An, Zhang Xu-Jie
Natioanl Key Laboratory of Agricultural Microbiology, Hubei Hongshan Laboratory, Engineering Research Center of Green Development for Conventional Aquatic Biological Industry in the Yangtze River Economic Belt, Ministry of Education, College of Fisheries, Huazhong Agricultural University, Wuhan, China; Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China.
Natioanl Key Laboratory of Agricultural Microbiology, Hubei Hongshan Laboratory, Engineering Research Center of Green Development for Conventional Aquatic Biological Industry in the Yangtze River Economic Belt, Ministry of Education, College of Fisheries, Huazhong Agricultural University, Wuhan, China.
Fish Shellfish Immunol. 2025 Nov;166:110614. doi: 10.1016/j.fsi.2025.110614. Epub 2025 Aug 5.
Immunoglobulin M (IgM) is considered the most ancient and prevalent Ig in fish, which plays important roles in systemic and mucosal immunity. In the current study, two heavy chain genes of IgM (named Ighμ1 and Ighμ2) were cloned in Nile tilapia (Oreochromis niloticus), and the amino acid identity between the constant regions of the two IgM heavy chains were 82.58 %. Cysteine and tryptophan residues that are crucial for forming disulfide bonds and the folding of the Ig domains were conserved. Genomic localization showed that the two Ighμs were adjacent within the same IgM locus. By mass spectrum detection in the native IgM purified from tilapia serum, the specific peptides in the heavy chains of each IgM could be detected. At the transcriptional level, Ighμ1 and Ighμ2 had similar expression patterns, and both were constitutively expressed in both systemic and mucosal lymphoid tissues. Detection of the expression of Ighμ1 and Ighμ2 in single IgM B cells sorted by flow cytometry revealed that Ighμ1 and Ighμ2 are mainly co-expressed by single IgM B cells. After Poly I:C, Aeromonas hydrophila or Streptococcus agalactiae treatment, Ighμ1 and Ighμ2 exhibited different expression profiles, the transcriptional level of Ighμ1 mainly involved in bacterial infection while Ighμ2 was more related to Poly I:C stimulation. These data from the genome, transcription, and protein levels have demonstrated that there exist two subclasses of IgM in tilapia, and that their heavy chain genes display different expression patterns during stimulation. Overall, our data reflect the diversity and complexity of IgM in tilapia, thus provide a better understanding of the IgM evolution in teleost fish.
免疫球蛋白M（IgM）被认为是鱼类中最古老且最普遍的免疫球蛋白，在全身免疫和黏膜免疫中发挥着重要作用。在本研究中，尼罗罗非鱼（Oreochromis niloticus）的两个IgM重链基因（命名为Ighμ1和Ighμ2）被克隆出来，两条IgM重链恒定区之间的氨基酸同一性为82.58%。对于形成二硫键和Ig结构域折叠至关重要的半胱氨酸和色氨酸残基是保守的。基因组定位显示，两个Ighμ在同一IgM基因座内相邻。通过对从罗非鱼血清中纯化的天然IgM进行质谱检测，可检测到每个IgM重链中的特定肽段。在转录水平上，Ighμ1和Ighμ2具有相似的表达模式，并且在全身和黏膜淋巴组织中均组成性表达。通过流式细胞术分选的单个IgM B细胞中Ighμ1和Ighμ2表达的检测表明，Ighμ1和Ighμ2主要由单个IgM B细胞共表达。在用聚肌胞苷酸（Poly I:C）、嗜水气单胞菌或无乳链球菌处理后，Ighμ1和Ighμ2表现出不同的表达谱，Ighμ1的转录水平主要参与细菌感染，而Ighμ2则与Poly I:C刺激更相关。这些来自基因组、转录和蛋白质水平的数据表明，罗非鱼中存在两种IgM亚类，并且它们的重链基因在刺激过程中表现出不同的表达模式。总体而言，我们的数据反映了罗非鱼中IgM的多样性和复杂性，从而有助于更好地理解硬骨鱼中IgM的进化。
