Donnadieu E, Bismuth G, Trautmann A
Laboratoire de Neurobiologie, CNRS URA 1857, Ecole Normale Supérieure, Paris, France.
Curr Biol. 1994 Jul 1;4(7):584-95. doi: 10.1016/s0960-9822(00)00130-5.
Helper T-cell activation is initiated in vivo when the T-cell receptor complex recognizes an antigen fragment associated with MHC class II molecules on the surface of an antigen-presenting cell. In most previous studies of this phenomenon, T cells were stimulated not with antigen-presenting cells, but with CD3-specific antibodies. This approach provided considerable understanding of the cascade of molecular events triggered by T-cell receptor stimulation. However, the specific consequences of cell-cell interactions are still poorly understood. We therefore used a dual imaging system that provides simultaneous transmission and fluorescence images to study the morphological changes and variations of intracellular calcium concentration ([Ca2+]i) triggered in a human CD4+ antigen-specific T-cell clone in response to antigen presented by a class II-transfected murine fibroblast.
T cells loaded with the Ca(2+)-sensitive fluorescent dye Fura-2 were individually monitored for half an hour following their contact with a monolayer of antigen-pulsed antigen-presenting cells. The response was found to have three distinct phases. During the first few minutes after contact, the T cell moves over the antigen-presenting cells, as if 'scanning' them. After several minutes, an oscillating [Ca2+]i response begins, accompanied by the immobilization of the cell and the retraction of pseudopodia. This rounding-up was probably Ca(2+)-dependent, as it could also be triggered by ionomycin or thapsigargin. Later during the [Ca2+]i response, the T cell becomes flattened and further elongated, suggesting increased adhesion to antigen-presenting cells.
The physiological signal for T-cell activation, antigen recognition, is a three-step process reminiscent of the three steps previously observed in the interaction between neutrophils and endothelial cells. During these successive steps, a mobile, weakly interacting T cell is transformed into an immobile cell fully engaged in the activation pathway. Thus, antigenic recognition is not instantaneous, but evolves slowly by progressive amplification of the signal given by a few antigen molecules, eventually resulting in T-cell activation.
当T细胞受体复合物识别与抗原呈递细胞表面的II类主要组织相容性复合体分子相关的抗原片段时，辅助性T细胞激活在体内启动。在以往关于这一现象的大多数研究中，T细胞不是用抗原呈递细胞刺激，而是用CD3特异性抗体刺激。这种方法极大地增进了我们对T细胞受体刺激引发的分子事件级联反应的理解。然而，细胞间相互作用的具体后果仍知之甚少。因此，我们使用了一种能同时提供透射图像和荧光图像的双成像系统，来研究人类CD4 +抗原特异性T细胞克隆在响应II类转染鼠成纤维细胞呈递的抗原时所触发的形态变化和细胞内钙浓度（[Ca2 +]i）的变化。
加载了钙敏感荧光染料Fura-2的T细胞在与单层抗原脉冲抗原呈递细胞接触后，被单独监测了半小时。发现该反应有三个不同阶段。在接触后的最初几分钟内，T细胞在抗原呈递细胞上移动，就好像在“扫描”它们。几分钟后，开始出现振荡的[Ca2 +]i反应，同时细胞固定并伪足回缩。这种变圆可能依赖于Ca2 +，因为它也可由离子霉素或毒胡萝卜素触发。在[Ca2 +]i反应后期，T细胞变得扁平并进一步伸长，表明其与抗原呈递细胞的粘附增加。
T细胞激活的生理信号，即抗原识别，是一个三步过程，让人联想到先前在中性粒细胞与内皮细胞相互作用中观察到的三个步骤。在这些连续步骤中，一个可移动、弱相互作用的T细胞转变为一个完全参与激活途径的固定细胞。因此，抗原识别不是瞬间发生的，而是通过少数抗原分子发出的信号的逐步放大而缓慢演变，最终导致T细胞激活。
