Worth R G, Mayo-Bond L, van de Winkel J G, Todd R F, Petty H R
Department of Biological Sciences, Wayne State University, Detroit, MI 48202, USA.
J Immunol. 1996 Dec 15;157(12):5660-5.
Previous studies have suggested that complement receptors cooperate with Fc receptors to mediate Ab-dependent effector functions. In the present study, we tested the capacity of complement receptor type 3 (CR3; alphaM beta2; CD11b/CD18) to participate in Fc gammaRIIA (CD32)-mediated phagocytosis. To test this hypothesis, we transfected a phagocytosis-defective tail-minus mutant of Fc gammaRIIA into fibroblasts that did or did not express CR3. As controls, cells exposed to the transfection protocol but not expressing either CR3 or Fc gammaRIIA constructs were also selected. Expression of cell surface receptors was confirmed by both flow cytometry and fluorescence microscopy. Cells were tested for their ability to bind and internalize IgG-opsonized erythrocytes and for surface proximity of CR3 and Fc gammaRIIA using resonance energy transfer techniques. Resonance energy transfer studies showed a physical proximity between CR3 and Fc gammaRIIA on cell surfaces. Cells expressing only the tail-minus mutant of Fc gammaRIIA were unable to internalize erythrocytes but showed significant binding ability. In contrast, cells expressing both mutant Fc gammaRIIA and CR3 internalized opsonized erythrocytes. These results show that CR3 can complement the phagocytic function of defective Fc gammaRIIA. These data suggest that CR3 is capable of transducing a phagocytic signal generated by Fc gammaRIIA recognition events that mediates internalization of IgG-opsonized targets.
以往的研究表明，补体受体与Fc受体协同作用，介导抗体依赖的效应功能。在本研究中，我们测试了补体3型受体（CR3；αMβ2；CD11b/CD18）参与FcγRIIA（CD32）介导的吞噬作用的能力。为了验证这一假设，我们将FcγRIIA的吞噬缺陷型截尾突变体转染到表达或不表达CR3的成纤维细胞中。作为对照，还选择了接受转染方案但不表达CR3或FcγRIIA构建体的细胞。通过流式细胞术和荧光显微镜确认细胞表面受体的表达。使用共振能量转移技术测试细胞结合和内化IgG调理红细胞的能力以及CR3和FcγRIIA的表面接近度。共振能量转移研究表明细胞表面的CR3和FcγRIIA之间存在物理接近性。仅表达FcγRIIA截尾突变体的细胞无法内化红细胞，但显示出显著的结合能力。相比之下，同时表达突变型FcγRIIA和CR3的细胞内化了调理红细胞。这些结果表明CR3可以补充缺陷型FcγRIIA的吞噬功能。这些数据表明CR3能够转导由FcγRIIA识别事件产生的吞噬信号，该信号介导IgG调理靶标的内化。
