Martin S, Bevan M J
Department of Immunology and Howard Hughes Medical Institute, University of Washington, Seattle 98195-7370, USA.
Eur J Immunol. 1997 Oct;27(10):2726-36. doi: 10.1002/eji.1830271037.
Analysis of antigen-induced negative selection of thymocytes in T cell receptor (TCR)-transgenic mice is complicated by the presence of an antigen-responsive peripheral T cell compartment. Our experiments address the question of whether and how peripheral T cell activation can affect immature thymocytes. Following three daily injections of peptide antigen into mice expressing a peptide-specific transgenic TCR and deficient for TAP1, we and others have found profound deletion of the CD4+CD8+ (DP) thymocyte subset. However, our work shows that even though mature CD8+ T cells are inefficiently selected in TAP1-deficient mice, there was a striking degree of peripheral expansion and activation of CD8+ peripheral T cells. Furthermore, when cells from TCR-transgenic mice were adoptively transferred, we found that deletion of nontransgenic DP thymocytes occurred in Thy-1-congenic and even more efficiently in TAP1-deficient recipients after repeated peptide injection resulting in peripheral T cell activation. In the adoptive transfer experiments the degree of deletion of immature bystander thymocytes was decreased upon blocking of TNF. These data show that deletion of DP thymocytes can result from excessive peripheral T cell activation and identify TNF as an important effector molecule for this process. When steps are taken to avoid peripheral T cell activation, peptide antigen can induce TCR-mediated thymocyte deletion, presumably in the thymus cortex, since injection of TAP1-deficient TCR-transgenic mice resulted in deletion of immature DP thymocytes prior to detectable peripheral T cell expansion and activation. This effect was not blocked by inhibiting tumor necrosis factor activity. In addition, DP depletion was seen in the absence of peripheral T cell activation when antibody-mediated depletion of CD8+ T cells was performed. Our work clearly shows that two mechanisms for deletion of DP thymocytes exist: deletion induced by antigen presentation in the thymus and deletion as a consequence of repeated stimulation of mature peripheral T cells.
在T细胞受体（TCR）转基因小鼠中，由于存在抗原反应性外周T细胞区室，对抗原诱导的胸腺细胞阴性选择的分析变得复杂。我们的实验探讨了外周T细胞激活是否以及如何影响未成熟胸腺细胞的问题。在每天向表达肽特异性转基因TCR且TAP1缺陷的小鼠注射三次肽抗原后，我们和其他人发现CD4 + CD8 +（双阳性，DP）胸腺细胞亚群出现了显著缺失。然而，我们的研究表明，尽管在TAP1缺陷小鼠中成熟CD8 + T细胞的选择效率低下，但CD8 +外周T细胞在外周有显著的扩增和激活。此外，当将TCR转基因小鼠的细胞进行过继转移时，我们发现在重复注射肽导致外周T细胞激活后，非转基因DP胸腺细胞在Thy-1同基因受体中出现缺失，在TAP1缺陷受体中缺失更为明显。在过继转移实验中，阻断TNF后未成熟旁观者胸腺细胞的缺失程度降低。这些数据表明，DP胸腺细胞的缺失可能是由于外周T细胞过度激活导致的，并确定TNF是这一过程中的重要效应分子。当采取措施避免外周T细胞激活时，肽抗原可诱导TCR介导的胸腺细胞缺失，推测发生在胸腺皮质，因为向TAP1缺陷的TCR转基因小鼠注射抗原后，在可检测到外周T细胞扩增和激活之前，未成熟DP胸腺细胞就出现了缺失。这种效应不受肿瘤坏死因子活性抑制的影响。此外，在进行抗体介导的CD8 + T细胞清除且不存在外周T细胞激活的情况下，也观察到了DP细胞的减少。我们的研究清楚地表明，存在两种导致DP胸腺细胞缺失的机制：胸腺中抗原呈递诱导的缺失以及成熟外周T细胞反复刺激导致的缺失。
