Meydan D, Lambert B, Hellgren D
Karolinska Institute, Department of Biosciences, Huddinge, Sweden.
Environ Mol Mutagen. 1997;30(3):245-53. doi: 10.1002/(sici)1098-2280(1997)30:3<245::aid-em1>3.0.co;2-k.
Immunoglobulin and T-cell receptor (TCR) genes are assembled by a site-specific rearrangement known as V(D)J [variable-(diversity)-joining] recombination. These rearrangements occur normally in pre-B- and pre-T-cells using signal sequences adjacent to coding exons for immunoglobulin and TCR genes, respectively. However, aberrant recombination may result in the generation of hybrid TCR genes by joining of TCR-beta with TCR-gamma specific sequences. Such hybrid TCR genes occur at a low frequency in peripheral blood lymphocytes (PBL) of healthy individuals, and can be detected by PCR amplification. We have determined the in vivo frequency of hybrid V gamma-J beta 1 TCR (hybrid TCR) genes in lymphocyte DNA from 12 healthy individuals. The average frequency was found to be 5.83 in 0.75 x 10(6) PBL, with a threefold difference between the highest and lowest individual value. The presence of similar TCR gene rearrangements in individual samples suggests that T-cells with a hybrid TCR gene are capable of clonal expansion in vivo. The individual hybrid TCR gene frequency remained relatively constant during 72 hours of in vitro cultivation. In long-term culture, the frequency gradually decreased, and after 28 days no hybrid TCR genes were detectable in lymphocyte DNA. These results show that T-cells with a hybrid TCR gene are able to respond to mitogen stimulation in vitro, and may have a proliferative disadvantage or are selected against during prolonged in vitro cultivation. No hybrid TCR genes were detected in ten proliferating T-cell clones, indicating that the rate of hybrid TCR gene formation is < 2.0 x 10(-8) per cell per cell division. No hybrid TCR genes were detected in DNA from B-lymphocytes, sperm, granulocytes, fibroblasts, keratinocytes, and three B-lymphoblastoid ataxia telangiectasia cell lines. In agreement with previous reports, the frequency of hybrid TCR genes in peripheral blood DNA from two ataxia telangiectasia patients was found to be more than 15-fold higher than in lymphocytes from normal individuals. These data show that formation of hybrid TCR genes is restricted to T-cells in vivo, and occurs at a very low frequency, if at all, in proliferating T-cells in vitro, and with an increased frequency in patients with ataxia telangiectasia.
免疫球蛋白和T细胞受体（TCR）基因通过一种称为V（D）J[可变区-（多样性区）-连接区]重组的位点特异性重排进行组装。这些重排分别利用免疫球蛋白和TCR基因编码外显子相邻的信号序列，正常发生于前B细胞和前T细胞中。然而，异常重组可能通过TCR-β与TCR-γ特异性序列的连接导致杂交TCR基因的产生。这种杂交TCR基因在健康个体外周血淋巴细胞（PBL）中出现频率较低，可通过PCR扩增检测到。我们测定了12名健康个体淋巴细胞DNA中杂交Vγ-Jβ1 TCR（杂交TCR）基因的体内频率。发现在0.75×10⁶个PBL中平均频率为5.83，个体最高值与最低值之间相差三倍。单个样本中存在相似的TCR基因重排表明，带有杂交TCR基因的T细胞能够在体内进行克隆扩增。在体外培养72小时期间，个体杂交TCR基因频率保持相对恒定。在长期培养中，频率逐渐降低，28天后淋巴细胞DNA中未检测到杂交TCR基因。这些结果表明，带有杂交TCR基因的T细胞能够在体外对有丝分裂原刺激作出反应，并且在长时间体外培养期间可能具有增殖劣势或被选择淘汰。在10个增殖性T细胞克隆中未检测到杂交TCR基因，表明杂交TCR基因形成率低于每细胞每细胞分裂2.0×10⁻⁸。在B淋巴细胞、精子、粒细胞、成纤维细胞、角质形成细胞以及三个B淋巴母细胞性共济失调毛细血管扩张症细胞系的DNA中未检测到杂交TCR基因。与先前报道一致，发现两名共济失调毛细血管扩张症患者外周血DNA中杂交TCR基因频率比正常个体淋巴细胞中的频率高15倍以上。这些数据表明，杂交TCR基因的形成在体内仅限于T细胞，在体外增殖性T细胞中即使发生频率也非常低，而在共济失调毛细血管扩张症患者中频率增加。
