Listman J A, Rimm I J, Wang Y, Geller M C, Tang J C, Ho S, Finn P W, Perkins D L
Laboratory of Immunogenetics and Transplantation, Brigham & Women's Hospital, Boston, MA 02115, USA.
Cell Immunol. 1996 Jan 10;167(1):44-55. doi: 10.1006/cimm.1996.0006.
The potential alpha beta T cell receptor (TCR) repertoire in normal mice is extremely large and estimated by M. M. Davis and P. J. Bjorkman (Nature 334, 395, 1988) to include 5.2 x 10(18) different receptor molecules. This tremendous diversity provides the basis for T cell recognition of the universe of antigens including bacterial, viral, and allogeneic epitopes. Expression of a single TCR beta-chain transgene should alter the repertoire by limiting the available diversity, therefore, creating holes in the repertoire or producing TCR with decreased affinity. To determine the effect of drastically decreasing the size of the repertoire, we investigated T cell responses in TCR beta-chain transgenic mice expressing the V beta 8.2 transgene. Previous results showed that > 98% of T cells in these mice express the transgene; thus, the TCR repertoire is reduced by orders of magnitude. We tested the T cell responses of the transgenic mice and nontransgenic littermates to nine different MHC haplotypes in mixed lymphocyte reactions, five protein antigens, and eight immunogenic peptides. Surprisingly, the transgenic mice responded to all antigenic stimuli tested indicating the lack of a hole in the TCR repertoire. Interestingly, however, the response in every case was quantitatively lower than the response by the nontransgenic littermates. In contrast, transgenic and nontransgenic T cells responded equivalently to stimulation with mitogens or to stimulation with immobilized alpha-TCR mAb indicating that the transgenic T cells had a normal capacity to respond. To differentiate between decreased TCR affinity and decreased precursor frequency, we performed a limiting dilution analysis to the peptide antigens CI:NP and OVA324-339. The results showed approximately a three-to eight-fold decrease in the frequency of transgenic T cells responding to the peptide compared to nontransgenic littermates. We previously showed that the response to cI84-98 and PLP could be blocked with anti-V beta 8 mAb indicating that V beta 8.2-bearing T cells are capable of responding to peptide antigen. Analysis of TCR V alpha chain expression by PCR and flow cytometry showed similar V alpha expression in both the transgenic and the nontransgenic mice. These results demonstrate tremendous plasticity in the TCR repertoire permitting T cell responses by the transgenic mice to all antigens tested. However, the decreased magnitude of the responses may impair the capacity to defend against natural pathogens. Therefore, although the large TCR repertoire of normal mice may not be necessary to produce in vitro responses to many experimental antigens, it may confer survival benefits in natural environments.
正常小鼠中潜在的αβT细胞受体（TCR）库极其庞大，据M.M.戴维斯和P.J.比约克曼（《自然》334, 395, 1988）估计，其中包含5.2×10¹⁸种不同的受体分子。这种巨大的多样性为T细胞识别包括细菌、病毒和同种异体表位在内的各种抗原提供了基础。单个TCRβ链转基因的表达应通过限制可用的多样性来改变TCR库，因此，会在TCR库中产生空缺或产生亲和力降低的TCR。为了确定大幅减小TCR库规模的影响，我们研究了表达Vβ8.2转基因的TCRβ链转基因小鼠的T细胞反应。先前的结果表明，这些小鼠中>98%的T细胞表达该转基因；因此，TCR库减少了几个数量级。我们在混合淋巴细胞反应中测试了转基因小鼠和非转基因同窝小鼠对九种不同MHC单倍型、五种蛋白质抗原和八种免疫原性肽的T细胞反应。令人惊讶的是，转基因小鼠对所有测试的抗原刺激都有反应，表明TCR库中不存在空缺。然而，有趣的是，在每种情况下，转基因小鼠的反应在数量上都低于非转基因同窝小鼠的反应。相比之下，转基因和非转基因T细胞对丝裂原刺激或固定化α-TCR单克隆抗体刺激的反应相当，这表明转基因T细胞具有正常的反应能力。为了区分TCR亲和力降低和前体细胞频率降低，我们对肽抗原CI:NP和OVA324 - 339进行了有限稀释分析。结果显示，与非转基因同窝小鼠相比，转基因T细胞对该肽的反应频率大约降低了三到八倍。我们先前表明，对cI84 - 98和PLP的反应可以被抗Vβ8单克隆抗体阻断，这表明携带Vβ8.2的T细胞能够对肽抗原作出反应。通过PCR和流式细胞术分析TCR Vα链表达，结果显示转基因小鼠和非转基因小鼠中的Vα表达相似。这些结果表明TCR库具有巨大的可塑性，使得转基因小鼠能够对所有测试抗原产生T细胞反应。然而，反应强度的降低可能会损害抵御天然病原体的能力。因此，尽管正常小鼠庞大的TCR库对于许多实验抗原的体外反应可能并非必需，但它可能在自然环境中赋予生存优势。
