Department of Medicine, University of Colorado Denver, Aurora, CO 80045, USA.
Mol Immunol. 2011 Mar;48(6-7):883-94. doi: 10.1016/j.molimm.2010.12.019. Epub 2011 Jan 26.
We found that transgenic (tg) mice stably expressing a bacterial artificial chromosome (BAC)-derived human complement receptor type 2 (CR2/CD21) gene demonstrate B cell specific hCR2 protein expression, normal B cell development and no changes in B cell subpopulations. To determine whether this BAC-encoded human CR2 (hCR2) can replace mouse CR2/CR1 in Cr2(-/-) mice and restore humoral immune responses to model foreign antigens (Ags), we generated hCR2(+/-)Cr2(-/-) tg mice and immunized them with sheep red blood cells (SRBC). We found that hCR2(+/-)Cr2(-/-) mice demonstrated anti-SRBC antibody (Ab) levels that were initially comparable to Cr2(-/-) mice after a single injection of the Ag, but then showed marked increases in anti-SRBC IgM and IgG1 levels after a second immunization. Identical results were found with a second model Ag, NP-Ficoll. To further confirm that this improvement in Ag-specific Ab production over Cr2(-/-) mice was indeed due to hCR2 expression, as well as to examine the effects of treating hCR2(+/-)Cr2(-/-) mice with an inhibitory anti-hCR2 monoclonal Ab (mAb) in vivo, we used mAb 171, an anti-hCR2 mAb that we have shown directly recognizes the C3d ligand binding site on hCR2. We first found that mAb 171 completely blocked hCR2-dependent co-activation of hCR2-tg B cells by anti-BCR/C3d complexes as measured in vitro by intracellular calcium influx. The i.p. injection of 1mg of mAb 171 was then found to induce for at least three weeks only partial loss of hCR2 surface expression, without modifying B and T cell numbers or the apparent activation status of the cells. Treatment of hCR2(+/-)Cr2(-/-) mice with mAb 171 also substantially suppressed the development of anti-SRBC and anti-NP Abs following immunization with Ags. The development of this model system should allow the study of the effects of manipulating hCR2 function in vivo with potential therapeutic compounds.
我们发现，稳定表达细菌人工染色体（BAC）衍生的人类补体受体 2（CR2/CD21）基因的转基因（tg）小鼠表现出 B 细胞特异性 hCR2 蛋白表达、正常 B 细胞发育和 B 细胞亚群无变化。为了确定这种 BAC 编码的人类 CR2（hCR2）是否可以替代 Cr2(-/-) 小鼠中的鼠 CR2/CR1 并恢复对模型外来抗原（Ag）的体液免疫反应，我们生成了 hCR2(+/-)Cr2(-/-)tg 小鼠并对其进行了绵羊红细胞（SRBC）免疫。我们发现，hCR2(+/-)Cr2(-/-) 小鼠在单次注射 Ag 后最初表现出与 Cr2(-/-) 小鼠相当的抗 SRBC 抗体（Ab）水平，但在第二次免疫后显示出明显增加的抗 SRBC IgM 和 IgG1 水平。使用第二个模型 Ag，NP-Ficoll 得到了相同的结果。为了进一步确认这种改善的 Ag 特异性 Ab 产生超过 Cr2(-/-) 小鼠确实是由于 hCR2 的表达，以及检查用体内抑制性抗 hCR2 单克隆 Ab（mAb）治疗 hCR2(+/-)Cr2(-/-) 小鼠的效果，我们使用了 mAb 171，这是一种我们已经证明可以直接识别 hCR2 上 C3d 配体结合位点的抗 hCR2 mAb。我们首先发现，mAb 171 在体外通过细胞内钙流入完全阻断了抗 BCR/C3d 复合物介导的 hCR2-tg B 细胞的 hCR2 依赖性共激活。然后发现，腹腔注射 1mg mAb 171 至少在三周内仅导致 hCR2 表面表达的部分丧失，而不改变 B 和 T 细胞数量或细胞的明显激活状态。用 mAb 171 治疗 hCR2(+/-)Cr2(-/-) 小鼠也显著抑制了用 Ag 免疫后抗 SRBC 和抗 NP Ab 的发展。该模型系统的发展应允许研究在体内操纵 hCR2 功能的影响，使用潜在的治疗化合物。
