Dráberová L, Dráber P
Institute of Molecular Genetics, Academy of Sciences of Czech Republic, Praha.
Immunology. 1993 Sep;80(1):103-9.
Rat peritoneal and pleural mast cells and rat basophilic leukemia cells, RBL-2H3, have been previously shown to be activated by Thy-1-specific monoclonal antibodies (mAb). In the present study we investigated the mechanism of Thy-1-mediated activation and compared it with activation induced by cross-linking of the high-affinity IgE receptor. Binding of an IgG Thy-1 x 1-specific mAb, MRCOX7 (OX7), to RBL-2H3 cells and mast cells, and activation of RBL-2H3 by the OX7 were abrogated by pretreatment of the cells with phosphatidyl inositol-specific phospholipase C (PI-PLC). The F(ab')2 fragment of OX7, in contrast to the Fab' fragment, induced cell activation as well as intact OX7 mAb. Cells sensitized with IgE exhibited an increased responsiveness to anti-Thy-1 antibodies suggesting formation of functional complexes of IgE receptor/IgE/Thy-1/anti-Thy-1. Pretreatment of RBL-2H3 cells with cholera toxin potentiated activation induced by IgE+antigen (Ag) and IgE+OX7, but had no effect on activation induced by OX7 antibody alone. Similarly, dexamethasone had no effect on OX7-induced activation but inhibited IgE+Ag- and IgE+OX7-induced activation. Analysis of phosphotyrosine-containing proteins in RBL-2H3 cell lysates revealed that IgE+Ag and IgE+OX7 induced a marked increase in tyrosine phosphorylation of several proteins that were not tyrosine phosphorylated in cells exposed to OX7 mAb alone. Similar results were obtained when RBL-2H3-derived cells, expressing transfected mouse Thy-1.2, were activated with Thy-1.2-specific IgM antibody. The combined data suggest that Thy-1-specific antibodies activate cells by a mechanism that is different from activation induced by cross-linking of high-affinity IgE receptor.
先前已证明，大鼠腹膜和胸膜肥大细胞以及大鼠嗜碱性白血病细胞RBL-2H3可被Thy-1特异性单克隆抗体（mAb）激活。在本研究中，我们研究了Thy-1介导的激活机制，并将其与高亲和力IgE受体交联诱导的激活进行了比较。用磷脂酰肌醇特异性磷脂酶C（PI-PLC）预处理细胞后，IgG Thy-1 x 1特异性mAb MRCOX7（OX7）与RBL-2H3细胞和肥大细胞的结合以及OX7对RBL-2H3的激活作用均被消除。与Fab'片段相比，OX7的F(ab')2片段诱导细胞激活的效果与完整的OX7 mAb相同。用IgE致敏的细胞对抗Thy-1抗体的反应性增强，提示形成了IgE受体/IgE/Thy-1/抗Thy-1功能复合物。用霍乱毒素预处理RBL-2H3细胞可增强由IgE +抗原（Ag）和IgE + OX7诱导的激活，但对单独由OX7抗体诱导的激活没有影响。同样，地塞米松对OX7诱导的激活没有影响，但抑制了IgE + Ag和IgE + OX7诱导的激活。对RBL-2H3细胞裂解物中含磷酸酪氨酸的蛋白质进行分析发现，IgE + Ag和IgE + OX7诱导几种蛋白质的酪氨酸磷酸化显著增加，而单独暴露于OX7 mAb的细胞中这些蛋白质未发生酪氨酸磷酸化。当用Thy-1.2特异性IgM抗体激活表达转染小鼠Thy-1.2的RBL-2H3衍生细胞时，也得到了类似的结果。综合数据表明，Thy-1特异性抗体通过一种不同于高亲和力IgE受体交联诱导激活的机制激活细胞。
