Shivnan E, Biffen M, Shiroo M, Pratt E, Glennie M, Alexander D
Department of Immunology, Institute of Animal Physiology and Genetics Research, Babraham, Cambridge, Great Britain.
Eur J Immunol. 1992 Apr;22(4):1055-62. doi: 10.1002/eji.1830220427.
The binding of agonistic monoclonal antibodies (mAb) to the CD3 antigen in T cells induces a rapid increase in tyrosine phosphorylation, inositive phosphate (IP) production, a rise in intracellular calcium and protein kinase C (PKC) activation. These intracellular signals have been implicated in the control of interleukin-2 and interleukin-2R receptor gene expression, thereby regulating T cell proliferation. Previous studies have shown that co-ligation of the CD45 and CD3 antigens inhibits CD3-induced tyrosine phosphorylation, IP production, calcium signals and T cell proliferation. It has therefore been suggested that the CD45 antigen uncouples the T cell receptor (TcR) from mitogenic signal pathways. In this study co-ligation of the CD3 and CD45 antigens with precisely constructed bispecific mAb did not inhibit CD3-induced T cell proliferation, IP production, calcium signals, diacylglycerol production or PKC activation. Furthermore, co-ligation of CD3 and CD45 antigens already cross-linked with IgM mAb did not lead to inhibition of CD3-induced calcium signals. Inhibitions of CD3-induced intracellular signals were observed following co-ligation of IgG CD45 and CD3 mAb with anti-IgG (F(ab')2 fragments. However, comparable inhibitions were also noted following co-ligation of CD3 with other abundant cell-surface antigens such as CD5 and LFA-1, and inhibitions were only observed when the CD3 mAb used required cross-linking to induce signals. These results suggested that the inhibitory effects of CD45 IgG mAb were not specific and were caused by the prevention of CD3-CD3 cross-linking following CD3 antigen co-ligation with other cell surface molecules. These findings are inconsistent with a specific inhibitory role for the CD45 phosphotyrosine phosphatase in uncoupling the TcR from mitogenic signal pathways.
激动性单克隆抗体（mAb）与T细胞中的CD3抗原结合会导致酪氨酸磷酸化迅速增加、肌醇磷酸（IP）生成、细胞内钙水平升高以及蛋白激酶C（PKC）激活。这些细胞内信号与白细胞介素-2和白细胞介素-2R受体基因表达的调控有关，从而调节T细胞增殖。先前的研究表明，CD45和CD3抗原的共同连接会抑制CD3诱导的酪氨酸磷酸化、IP生成、钙信号和T细胞增殖。因此，有人提出CD45抗原会使T细胞受体（TcR）与促有丝分裂信号通路解偶联。在本研究中，用精确构建的双特异性mAb将CD3和CD45抗原共同连接，并未抑制CD3诱导的T细胞增殖、IP生成、钙信号、二酰基甘油生成或PKC激活。此外，将已经与IgM mAb交联的CD3和CD45抗原共同连接，并不会导致对CD3诱导的钙信号的抑制。在用抗IgG（F(ab')2片段）将IgG CD45和CD3 mAb共同连接后，观察到了对CD3诱导的细胞内信号的抑制。然而，在将CD3与其他丰富的细胞表面抗原（如CD5和淋巴细胞功能相关抗原-1（LFA-1））共同连接后，也观察到了类似的抑制作用，并且只有当所用的CD3 mAb需要交联才能诱导信号时，才会观察到抑制作用。这些结果表明，CD45 IgG mAb的抑制作用并非特异性的，而是由CD3抗原与其他细胞表面分子共同连接后阻止CD3-CD3交联所导致的。这些发现与CD45磷酸酪氨酸磷酸酶在使TcR与促有丝分裂信号通路解偶联方面的特异性抑制作用不一致。
