Nashar Toufic O, Betteridge Zoe E, Mitchell Richard N
Department of Pathology and Microbiology, School of Medical Sciences, University of Bristol, Bristol, UK.
Immunology. 2002 May;106(1):60-70. doi: 10.1046/j.1365-2567.2002.01397.x.
Plasma membrane rafts are sphingolipid- and cholesterol-rich patches that function as membrane trafficking and surface signalling regions. Ganglioside GM1 is an integral component of these microdomains, and Escherichia coli enterotoxin B subunit (EtxB) is a pentamer that binds with high affinity to GM1 resulting in GM1 cross-linking. We previously demonstrated that antigen coupled directly to EtxB resulted in enhanced presentation relative to antigen taken up by fluid-phase endocytosis. Here we demonstrate a new role for GM1 in antigen presentation by examining the effects of cross-linking GM1 on the kinetics of presentation and processing of antigen by the B-cell receptor (BCR), fluid-phase endocytosis and GM1-targeted antigen. EtxB bound to B cells does not augment the subsequent kinetics or magnitude of presentation of either BCR-internalized antigen or soluble antigen. Moreover, presentation of GM1-bound antigen is significantly slower than antigen presentation following BCR-mediated uptake. In contrast to the rapid internalization of BCR-bound antigen (which has a half life of 60 min), the majority of EtxB-bound antigen forms a plasma membrane depot detectable for many hours after initial incubation (and with a half life of 12 hr). We conclude that cross-linking of GM1 by EtxB minimally affects the processing and presentation of antigens internalized via other pathways. Nevertheless, binding of antigens to GM1 results in delayed presentation that has important implications for in vivo immunization using GM1-targeted adjuvants.
质膜筏是富含鞘脂和胆固醇的斑块，作为膜运输和表面信号区域发挥作用。神经节苷脂GM1是这些微结构域的一个组成部分，大肠杆菌肠毒素B亚基（EtxB）是一种五聚体，它与GM1具有高亲和力结合，导致GM1交联。我们之前证明，与直接与EtxB偶联的抗原相比，通过液相内吞作用摄取的抗原的呈递增强。在这里，我们通过研究GM1交联对B细胞受体（BCR）、液相内吞作用和GM1靶向抗原呈递和加工动力学的影响，证明了GM1在抗原呈递中的新作用。与B细胞结合的EtxB不会增强随后BCR内化抗原或可溶性抗原呈递的动力学或幅度。此外，GM1结合抗原的呈递明显慢于BCR介导摄取后的抗原呈递。与BCR结合抗原的快速内化（半衰期为60分钟）相反，大多数EtxB结合抗原在初始孵育后数小时内形成可检测的质膜储存库（半衰期为12小时）。我们得出结论，EtxB对GM1的交联对通过其他途径内化的抗原的加工和呈递影响最小。然而，抗原与GM1的结合导致呈递延迟，这对使用GM1靶向佐剂的体内免疫具有重要意义。
