Department of Pathobiology, Ontario Veterinary College, University of Guelph, Ontario, Canada.
Dev Comp Immunol. 2012 Dec;38(4):487-94. doi: 10.1016/j.dci.2012.08.003. Epub 2012 Sep 16.
C3d is a sub-fragment of the C3 component of the complement system. Covalent binding of multiple C3ds to antigen reduces the activation threshold of cognate B lymphocytes by one thousand fold through co-ligation of the B cell antigen receptor (BCR) and complement receptor 2 (CR2/CD21). Reverse transcriptase polymerase chain reaction (RT-PCR) revealed that, in cattle, four distinct complement receptors are produced from the Cr2 gene by alternative splicing. Cattle express two major variants of the Cr2 gene representing homologues of murine CR1 and CR2, each of which is expressed in both a long and a short form. Expression of CR1 and CR2 was detected in IgM(+) cells from both the spleen and peripheral blood. Additionally, the coding sequence of CD19, the CR2 co-signaling molecule, was determined. CD19 was confirmed to be expressed by IgM(+) cells from the spleen and peripheral blood.
C3d 是补体系统 C3 成分的一个亚片段。通过 B 细胞抗原受体 (BCR) 和补体受体 2 (CR2/CD21) 的共交联，多个 C3d 与抗原的共价结合将同源 B 淋巴细胞的激活阈值降低了一千倍。逆转录聚合酶链反应 (RT-PCR) 显示，在牛中，通过替代剪接，Cr2 基因产生了四个不同的补体受体。牛表达两种主要的 Cr2 基因变体，代表鼠 CR1 和 CR2 的同源物，每种变体都以长和短两种形式表达。在来自脾脏和外周血的 IgM(+)细胞中检测到 CR1 和 CR2 的表达。此外，还确定了 CD19 的编码序列，即 CR2 的共信号分子。通过脾脏和外周血的 IgM(+)细胞证实 CD19 的表达。
