Temporal Lineage Tracing of Aire-Expressing Cells Reveals a Requirement for Aire in Their Maturation Program

Understanding the cellular dynamics of Aire-expressing lineage(s) among medullary thymic epithelial cells (AEL-mTECs) is essential for gaining insight into the roles of Aire in establishment of self-tolerance. In this study, we monitored the maturation program of AEL-mTECs by temporal lineage tracing, in which bacterial artificial chromosome transgenic mice expressing tamoxifen-inducible Cre recombinase under control of the Aire regulatory element were crossed with reporter strains. We estimated that the half-life of AEL-mTECs subsequent to Aire expression was similar to 7-8 d, which was much longer than that reported previously, owing to the existence of a post-Aire stage. We found that loss of Aire did not alter the overall lifespan of AEL-mTECs, inconsistent with the previous notion that Aire expression in medullary thymic epithelial cells (mTECs) might result in their apoptosis for efficient cross-presentation of self-antigens expressed by AEL-mTECs. In contrast, Aire was required for the full maturation program of AEL-mTECs, as exemplified by the lack of physiological downregulation of CD80 during the post-Aire stage in Aire-deficient mice, thus accounting for the abnormally increased CD80(high) mTECs seen in such mice. Of interest, increased CD80(high) mTECs in Aire-deficient mice were not mTEC autonomous and were dependent on cross-talk with thymocytes. These results further support the roles of Aire in the differentiation program of AEL-mTECs.

了解髓质胸腺上皮细胞（AEL - mTECs）中表达自身免疫调节因子（Aire）的细胞谱系的细胞动力学对于深入了解Aire在建立自身耐受中的作用至关重要。在这项研究中，我们通过时间谱系追踪来监测AEL - mTECs的成熟过程，即将在Aire调控元件控制下表达他莫昔芬诱导型Cre重组酶的细菌人工染色体转基因小鼠与报告基因小鼠品系进行杂交。我们估计Aire表达后AEL - mTECs的半衰期约为7 - 8天，由于存在Aire表达后的阶段，这比之前报道的要长得多。我们发现Aire的缺失并没有改变AEL - mTECs的总体寿命，这与之前认为髓质胸腺上皮细胞（mTECs）中Aire的表达可能导致其凋亡从而有效交叉呈递AEL - mTECs所表达的自身抗原的观点不一致。相反，Aire是AEL - mTECs完整成熟过程所必需的，例如在Aire缺陷小鼠中Aire表达后的阶段缺乏CD80的生理性下调，这就解释了在此类小鼠中观察到的CD80（高）mTECs异常增加的现象。有趣的是，Aire缺陷小鼠中增加的CD80（高）mTECs不是mTEC自主的，而是依赖于与胸腺细胞的相互作用。这些结果进一步支持了Aire在AEL - mTECs分化过程中的作用。