Franco M D, Nunès J, Boursier J P, Imbert J, Mawas C, Acuto O, Olive D
Unité de Cancérologie et Thérapeutique Expérimentales U 119 de L'INSERM 27, Marseille, France.
Cell Immunol. 1994 Sep;157(2):341-52. doi: 10.1006/cimm.1994.1232.
The CD8 molecule regulates T cell activation mediated via the CD3 T cell receptor and the adhesion molecule CD2. CD8 mAbs have been found to inhibit early (Ca2+ rise) as well as late events (cytotoxicity, proliferation, and lymphokine secretion) mediated via the CD2 pathway. A panel of eight anti-human CD8 mAbs was tested for inhibition of CD2-mediated Ca2+ rise in a cytotoxic T cell clone. The inhibition ranged from 5 to 53% independently of mAb isotype and affinity measured by half saturation binding. We then characterized these mAbs for their reactivity toward three mutants of the human CD8 alpha carrying amino acid sequence changes in the surface-exposed loops homologous to the immunoglobulin CDR1, 2, and 3. The mutations included replacement of the human CD8 alpha CDR1- and CDR2-like loops by the homologous mouse sequences and the insertion of a glycine in the middle of the CDR3-like loop. Thus, five mAbs were found to be affected by the mutation in the CDR2-like loop but not by alterations in the other CDR-like loops. Conversely, the other two mAbs (8E1.7 and B9.8) were affected only by mutations in the CDR1- and CDR3-like loops, respectively. Cross-inhibition experiments were essentially in agreement with these results. Interestingly, all the mAbs directed against the CDR2-like loop were potent inhibitors of CD2-mediated Ca2+ rise, with one exception probably due to poor affinity. Thus, in addition to being a site of interaction with major histocompatibility complex Class I as recent data have indicated, this region of the CD8 alpha subunit may play a role in regulating T cell activation.
CD8分子调节经由CD3 T细胞受体和黏附分子CD2介导的T细胞活化。已发现CD8单克隆抗体可抑制经由CD2途径介导的早期事件（Ca2+升高）以及晚期事件（细胞毒性、增殖和淋巴因子分泌）。检测了一组八种抗人CD8单克隆抗体对细胞毒性T细胞克隆中CD2介导的Ca2+升高的抑制作用。抑制率范围为5%至53%，与单克隆抗体的亚型和通过半饱和结合测量的亲和力无关。然后，我们对这些单克隆抗体针对人CD8α的三个突变体的反应性进行了表征，这些突变体在与免疫球蛋白CDR1、2和3同源的表面暴露环中携带氨基酸序列变化。这些突变包括用人CD8α CDR1和CDR2样环的同源小鼠序列替换，以及在CDR3样环中间插入一个甘氨酸。因此，发现五种单克隆抗体受CDR2样环突变的影响，但不受其他CDR样环改变的影响。相反，另外两种单克隆抗体（8E1.7和B9.8）分别仅受CDR1样环和CDR3样环突变的影响。交叉抑制实验基本与这些结果一致。有趣的是，所有针对CDR2样环的单克隆抗体都是CD2介导的Ca2+升高的有效抑制剂，但有一个例外可能是由于亲和力差。因此，正如最近的数据所表明的，除了是与主要组织相容性复合体I类相互作用的位点外，CD8α亚基的这个区域可能在调节T细胞活化中起作用。
