Turka L A, Kanner S B, Schieven G L, Thompson C B, Ledbetter J A
Department of Medicine, University of Michigan, Ann Arbor 48109.
Eur J Immunol. 1992 Feb;22(2):551-7. doi: 10.1002/eji.1830220238.
Stimulation of thymocytes or mature T cells via the T cell receptor (TcR)/CD3 complex activates a cascade of processes inducing cells to enter the cell cycle. A key step is the activation of phosphatidylinositol-specific phospholipase C (PI-PLC) within seconds following TcR/CD3 stimulation, an event which is strongly enhanced by co-ligation of the CD4 (or CD8) accessory molecule with TcR/CD3. In contrast, co-ligation of CD45 inhibits the same TcR/CD3 responses. The machinery which couples the TcR/CD3 complex, CD4, and CD45 to PI-PLC appears to involve regulation of tyrosine phosphorylation, as the TcR/CD3 and CD4 receptors are associated with the tyrosine kinases p59fyn and p56lck, respectively, and CD45 has intrinsic tyrosine phosphatase activity. Here, we have examined the ability of CD45 to regulate signal transduction via TcR/CD3 in human thymocytes. Co-cross-linking CD45 to the TcR/CD3 complex strongly suppressed the tyrosine phosphorylation of several intracellular substrates normally seen following TcR/CD3 stimulation. This effect of CD45 was associated with inhibition of a rise in intracellular calcium following TcR/CD3 ligation. Since TcR/CD3 stimulation of mature T cells induces tyrosine phosphorylation of PLC gamma 1, we investigated this phenomenon in thymocytes, and asked whether ligation of CD45 might regulate this process. By immunoprecipitation we found that TcR/CD3 stimulation induced tyrosine phosphorylation of PLC gamma 1, an effect which was enhanced by co-cross-linking CD4 to TcR/CD3. In contrast, co-ligation of CD45 strongly blocked PLC gamma 1 phosphorylation induced by either stimulus. Consistent with previous findings in mature T cells, CD45 cross-linking was able to partially inhibit TcR/CD3-induced thymocyte proliferation when interleukin 2 was used as a second signal, but almost completely (80%-90%) blocked proliferation when anti-CD28 mAb was used as the second signal, suggesting that CD45 cross-linking may be able to block interleukin 2 production via the CD28 pathway. These effects of CD45 on TcR/CD3 signaling and proliferation in thymocytes point towards a potential role for this pathway in thymic selection.
通过T细胞受体（TcR）/CD3复合物刺激胸腺细胞或成熟T细胞会激活一系列过程，诱导细胞进入细胞周期。关键步骤是在TcR/CD3刺激后数秒内激活磷脂酰肌醇特异性磷脂酶C（PI-PLC），CD4（或CD8）辅助分子与TcR/CD3的共连接会强烈增强这一事件。相反，CD45的共连接会抑制相同的TcR/CD3反应。将TcR/CD3复合物、CD4和CD45与PI-PLC偶联的机制似乎涉及酪氨酸磷酸化的调节，因为TcR/CD3和CD4受体分别与酪氨酸激酶p59fyn和p56lck相关联，且CD45具有内在的酪氨酸磷酸酶活性。在此，我们研究了CD45调节人胸腺细胞中通过TcR/CD3进行信号转导的能力。将CD45与TcR/CD3复合物共交联会强烈抑制通常在TcR/CD3刺激后出现的几种细胞内底物的酪氨酸磷酸化。CD45的这种作用与抑制TcR/CD3连接后细胞内钙的升高有关。由于成熟T细胞的TcR/CD3刺激会诱导PLCγ1的酪氨酸磷酸化，我们在胸腺细胞中研究了这一现象，并询问CD45的连接是否可能调节这一过程。通过免疫沉淀我们发现，TcR/CD3刺激会诱导PLCγ1的酪氨酸磷酸化，CD4与TcR/CD3的共交联会增强这一效应。相反，CD45的共连接会强烈阻断由任何一种刺激诱导的PLCγ1磷酸化。与先前在成熟T细胞中的发现一致，当使用白细胞介素2作为第二信号时，CD45交联能够部分抑制TcR/CD3诱导的胸腺细胞增殖，但当使用抗CD28单克隆抗体作为第二信号时，几乎完全（80%-90%）阻断增殖，这表明CD45交联可能能够通过CD28途径阻断白细胞介素2的产生。CD45对胸腺细胞中TcR/CD3信号传导和增殖的这些作用表明该途径在胸腺选择中可能具有潜在作用。
