Edholm Eva-Stina, Bengtén Eva, Stafford James L, Sahoo Manoranjan, Taylor Erin B, Miller Norman W, Wilson Melanie
Department of Microbiology, University of Mississippi Medical Center, Jackson, MS 39216, USA.
J Immunol. 2010 Oct 1;185(7):4082-94. doi: 10.4049/jimmunol.1000631. Epub 2010 Sep 3.
Channel catfish Ictalurus punctatus express two Ig isotypes: IgM and IgD. Although catfish IgM has been extensively studied at the functional and structural levels, much less is known about IgD. In this study, IgM(+)/IgD(+) and IgM(-)/IgD(+) catfish B cell populations were identified through the use of anti-IgM and anti-IgD mAbs. Catfish IgM(+)/IgD(+) B cells are small and agranular. In contrast, IgM(-)/IgD(+) B cells are larger and exhibit a plasmablast morphology. The use of cell sorting, flow cytometry, and RT-PCR demonstrated that IgD(+) B cell expression varies among individuals. For example, some catfish have <5% IgM(-)/IgD(+) B cells in their PBLs, whereas in others the IgM(-)/IgD(+) B cell population can represent as much as 72%. Furthermore, IgD expressed by IgM(-)/IgD(+) B cells preferentially associates with IgL σ. Comparatively, IgM(+)/IgD(+) B cells can express any of the four catfish IgL isotypes. Also, transfection studies show that IgD functions as a typical BCR, because Igδ-chains associate with CD79a and CD79b molecules, and all membrane IgD transcripts from sorted IgM(-)/IgD(+) B cells contain viable VDJ rearrangements, with no bias in family member usage. Interestingly, all secreted IgD transcripts from IgM(+)/IgD(+) and IgM(-)/IgD(+) B cells were V-less and began with a leader spliced to Cδ1. Importantly, transfection of catfish clonal B cells demonstrated that this leader mediated IgD secretion. Together, these findings imply that catfish IgM(-)/IgD(+) B cells likely expand in response to certain pathogens and that the catfish IgD Fc-region, as has been suggested for human IgD, may function as a pattern recognition molecule.
斑点叉尾鮰（Ictalurus punctatus）表达两种免疫球蛋白（Ig）同种型：IgM和IgD。尽管对鮰鱼IgM在功能和结构层面已进行了广泛研究，但对IgD的了解却少得多。在本研究中，通过使用抗IgM和抗IgD单克隆抗体（mAbs）鉴定出IgM(+)/IgD(+)和IgM(-)/IgD(+)鮰鱼B细胞群体。鮰鱼IgM(+)/IgD(+) B细胞体积小且无颗粒。相比之下，IgM(-)/IgD(+) B细胞体积更大，呈现出成浆细胞形态。细胞分选、流式细胞术和逆转录聚合酶链反应（RT-PCR）的结果表明，IgD(+) B细胞的表达在个体间存在差异。例如，一些鮰鱼外周血淋巴细胞（PBLs）中IgM(-)/IgD(+) B细胞的比例低于5%，而在其他鮰鱼中，IgM(-)/IgD(+) B细胞群体的比例可高达72%。此外，IgM(-)/IgD(+) B细胞表达的IgD优先与IgL σ结合。相比之下，IgM(+)/IgD(+) B细胞可以表达四种鮰鱼IgL同种型中的任何一种。另外，转染研究表明IgD作为一种典型的B细胞受体（BCR）发挥作用，因为Igδ链与CD79a和CD79b分子相关联，并且从分选的IgM(-)/IgD(+) B细胞中获得的所有膜IgD转录本都包含有效的VDJ重排，在家族成员使用上没有偏向性。有趣的是，来自IgM(+)/IgD(+)和IgM(-)/IgD(+) B细胞的所有分泌型IgD转录本都没有V区，并且以与Cδ1剪接的前导序列开始。重要的是，鮰鱼克隆B细胞的转染表明该前导序列介导IgD的分泌。总之，这些发现表明鮰鱼IgM(-)/IgD(+) B细胞可能会因某些病原体而扩增，并且正如对人类IgD所提出的那样，鮰鱼IgD的Fc区域可能作为一种模式识别分子发挥作用。
