Lagoo A, Sell S
Department of Pathology and Laboratory Medicine, University of Texas Health Science Center, Houston 77025.
Cell Immunol. 1989 Jan;118(1):53-67. doi: 10.1016/0008-8749(89)90357-2.
Comparison of the effect of goat anti-rabbit Ig (GARIg) and its monovalent fragment (Fab-GARIg) demonstrates that surface Ig (sIg) crosslinking is not necessary to effect G0 to G1 transition in rabbit peripheral blood B cells but is required for induction of DNA synthesis. Five micrograms per milliliter or more of GARIg is sufficient to induce DNA synthesis but up to 50 micrograms/ml of Fab-GARIg is not. However, the monovalent reagent induces microscopically observable cytoplasmic and nuclear changes (blast transformation) in a dose-dependent manner. These differ qualitatively and quantitatively from the morphological changes seen with comparable doses of GARIg; Fab anti-Ig produces "small blasts" whereas complete GARIg induces large blasts. The monovalent reagent, in a wide range of concentrations, is as effective as the complete antibody in modulating sIg from rabbit B cells. Fab-GARIg treatment modulates sIg in a biphasic manner. It clears the high-density sIg within 5 min, whereas the remaining low-density receptors disappear after 4 hr. Cytosolic protein kinase C levels decline equally after treatment with either Fab-GARIg or whole anti-Ig. RNA synthesis, as measured by [3H]uridine incorporation, increases for the first 12 hr in cells activated with either reagent. It declines to basal levels in Fab-GARIg stimulated cells, but a continuous increase occurs in cells stimulated with 5 and 50 micrograms/ml of complete antibody. Simultaneous addition of 50 micrograms/ml Fab-GARIg with 5 microgram/ml of GARIg causes greater RNA synthesis for 12 hr after stimulation than is caused by GARIg alone. After 12 hr the monovalent reagent has an inhibitory effect on RNA synthesis. Fluorescence-activated cell sorter analysis of acridine orange-stained cells shows that Fab anti-Ig-stimulated cells have higher RNA content than resting cells, but lower than GARIg-activated cells. These findings suggest that rabbit B cells can be activated from the G0 stage of cell cycle to G1 by monovalent anti-Ig reagents but further cell cycle progression requires maintenance signals provided by receptor crosslinking. The implications of these results for B cell activation signalling are discussed in the context of the floating receptor model.
山羊抗兔Ig（GARIg）及其单价片段（Fab - GARIg）作用效果的比较表明，在兔外周血B细胞中，表面Ig（sIg）交联对于实现从G0期到G1期的转变并非必要，但对于诱导DNA合成却是必需的。每毫升5微克或更高浓度的GARIg足以诱导DNA合成，但高达50微克/毫升的Fab - GARIg却不能。然而，单价试剂能以剂量依赖的方式诱导在显微镜下可观察到的细胞质和细胞核变化（原始细胞转化）。这些变化在质和量上都与相同剂量的GARIg所引起的形态学变化不同；Fab抗Ig产生“小原始细胞”，而完整的GARIg诱导产生大原始细胞。在很宽的浓度范围内，单价试剂在调节兔B细胞的sIg方面与完整抗体一样有效。Fab - GARIg处理以双相方式调节sIg。它在5分钟内清除高密度sIg，而其余的低密度受体在4小时后消失。用Fab - GARIg或全抗Ig处理后，胞质蛋白激酶C水平均同等下降。用[3H]尿苷掺入法测定，在用任何一种试剂激活的细胞中，RNA合成在前12小时增加。在Fab - GARIg刺激的细胞中，它下降到基础水平，但在用5微克/毫升和50微克/毫升完整抗体刺激的细胞中则持续增加。同时添加50微克/毫升Fab - GARIg和5微克/毫升GARIg，刺激后12小时内引起的RNA合成比单独使用GARIg时更多。12小时后，单价试剂对RNA合成有抑制作用。对吖啶橙染色细胞进行荧光激活细胞分选分析表明，Fab抗Ig刺激的细胞比静止细胞具有更高的RNA含量，但低于GARIg激活的细胞。这些发现表明，兔B细胞可以被单价抗Ig试剂从细胞周期的G0期激活到G1期，但进一步的细胞周期进展需要受体交联提供的维持信号。在浮动受体模型的背景下讨论了这些结果对B细胞激活信号传导的意义。
