Isersky C, Rivera J, Segal D M, Triche T
J Immunol. 1983 Jul;131(1):388-96.
We have assessed the internalization of variously sized oligomers of IgE bound to rat basophilic leukemia (RBL) cells by measuring their accessibility to the extracellular environment, and by direct visualization of the radiolabeled ligands. We also followed the fate of the internalized ligands and their receptors, as well as the fate of the free receptor on cells internalizing oligomers. In contrast to monomeric IgE, surface-bound oligomeric IgE was internalized. Notably, dimers provided an effective signal for internalization, although larger oligomers seem to be internalized more efficiently. In our experiments, 48% of the cell-bound dimers and 67% of the trimers were eliminated from the cell surface in 180 min. One-half of the maximal internalization observed with dimers and trimers occurred in 25 and 11 min, respectively. Release of radioactivity into the supernatant followed internalization; the released radioactivity did not bind to fresh cells and was only partially TCA-precipitable. Radioactive ligands remaining associated with the cells were unchanged as judged by m.w; they also were shown to remain receptor-bound. During either internalization or release of substantial amounts of the originally cell-bound oligomers, there was no increase in IgE-binding activity. In contrast, there was a transient drop (25%) in the number of free surface receptors suggesting internalization of the free receptors together with the oligomer-occupied receptor. Cells that failed to release histamine (RBL-I) processed dimeric and trimeric IgE similarly to histamine-releasing (RBL-2H3) cells. We conclude that dimeric and trimeric IgE are internalized by RBL cells and later are released to the medium in a partially degraded form. The ligand-bound receptor seems to be internalized with the ligand, along with some free receptor, and does not appear to be reusable or to recycle rapidly to the cell surface.
我们通过测量与大鼠嗜碱性白血病（RBL）细胞结合的不同大小的IgE寡聚体对细胞外环境的可及性，并通过直接观察放射性标记配体，评估了这些寡聚体的内化情况。我们还追踪了内化配体及其受体的命运，以及内化寡聚体的细胞上游离受体的命运。与单体IgE不同，表面结合的寡聚体IgE会被内化。值得注意的是，二聚体为内化提供了有效的信号，尽管更大的寡聚体似乎内化效率更高。在我们的实验中，180分钟内，48%的细胞结合二聚体和67%的三聚体从细胞表面消失。二聚体和三聚体观察到的最大内化量的一半分别在25分钟和11分钟时出现。放射性物质释放到上清液中是在内化之后；释放的放射性物质不与新鲜细胞结合，且只有部分可被三氯乙酸沉淀。通过分子量判断，与细胞保持结合的放射性配体没有变化；它们也被证明仍与受体结合。在大量最初细胞结合的寡聚体内化或释放过程中，IgE结合活性没有增加。相反，游离表面受体的数量有短暂下降（25%），表明游离受体与被寡聚体占据的受体一起被内化。未能释放组胺的细胞（RBL-I）处理二聚体和三聚体IgE的方式与释放组胺的细胞（RBL-2H3）相似。我们得出结论，二聚体和三聚体IgE被RBL细胞内化，随后以部分降解的形式释放到培养基中。与配体结合的受体似乎与配体一起被内化，同时还有一些游离受体，并且似乎不可重复使用或快速循环到细胞表面。
