Zhang Nu, Zhang Xu-Jie, Chen Dan-Dan, Oriol Sunyer J, Zhang Yong-An
State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China; College of Fisheries and Life Science, Shanghai Ocean University, Shanghai 201306, China.
Dev Comp Immunol. 2017 May;70:94-105. doi: 10.1016/j.dci.2017.01.001. Epub 2017 Jan 3.
As the teleost specific immunoglobulin, IgT plays important roles in systemic and mucosal immunity. In the current study, in rainbow trout, we have cloned the heavy chain (Igτ) genes of a secretory form of IgT2 as well as the membrane and secretory forms of a third IgT subclass, termed IgT3. Conserved cysteine and tryptophan residues that are crucial for the folding of the immunoglobulin domain as well as hydrophobic and hydrophilic residues within CART motif were identified in all IgT subclasses. Through analysis of the rainbow trout genome assembly, Igτ3 gene was found localized upstream of Igτ1 gene, while Igτ2 gene situated on another scaffold. At the transcriptional level, Igτ1 was mainly expressed in both systemic and mucosal lymphoid tissues, while Igτ2 was largely expressed in systemic lymphoid organs. After LPS and poly (I:C) treatment, Igτ1 and Igτ2 genes exhibited different expression profiles. Interestingly the transcriptional level of Igτ3 was negligible, although its protein product could be identified in trout serum. Importantly, a previously reported monoclonal antibody directed against trout IgT1 was able to recognize IgT2 and IgT3. These data demonstrate that there exist three subclasses of IgT in rainbow trout, and that their heavy chain genes display different expression patterns during stimulation. Overall, our data reflect the diversity and complexity of immunoglobulin in trout, thus provide a better understanding of the IgT system in the immune response of teleost fish.
作为硬骨鱼特有的免疫球蛋白，IgT在全身免疫和黏膜免疫中发挥着重要作用。在本研究中，我们在虹鳟鱼中克隆了分泌型IgT2的重链（Igτ）基因以及第三种IgT亚类（称为IgT3）的膜型和分泌型重链基因。在所有IgT亚类中都鉴定出了对免疫球蛋白结构域折叠至关重要的保守半胱氨酸和色氨酸残基，以及CART基序内的疏水和亲水残基。通过对虹鳟鱼基因组组装的分析，发现Igτ3基因位于Igτ1基因的上游，而Igτ2基因位于另一个支架上。在转录水平上，Igτ1主要在全身和黏膜淋巴组织中表达，而Igτ2主要在全身淋巴器官中表达。经脂多糖（LPS）和聚肌苷酸-聚胞苷酸（poly (I:C)）处理后，Igτ1和Igτ2基因表现出不同的表达谱。有趣的是，尽管在鳟鱼血清中可以鉴定出Igτ3的蛋白产物，但其转录水平可忽略不计。重要的是，先前报道的一种针对鳟鱼IgT1的单克隆抗体能够识别IgT2和IgT3。这些数据表明虹鳟鱼中存在三种IgT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，我们的数据反映了鳟鱼免疫球蛋白的多样性和复杂性，从而为更好地理解硬骨鱼免疫反应中的IgT系统提供了依据。
