Postnatal thymic epithelial cell (TEC) homeostatic defect- or natural aging-induced thymic atrophy results in a decline in central T-cell tolerance establishment, which is constituted by thymocyte negative selection and cluster of differentiation (CD) 4⁺ thymic regulatory T (tTreg) cell generation. Emerging evidence shows this decline mainly results from defects in negative selection, but there is insufficient evidence regarding whether tTreg cell generation is also impaired. We mechanistically studied tTreg cell generation in the atrophied thymus by utilizing both postnatal TEC-defective (resulting from FoxN1-floxed conditional knockout [cKO]) and naturally aged mouse models. We found that the capacity of tTreg cell generation was not impaired compared to CD4⁺ thymic conventional T cells, suggesting thymic atrophy positively influences tTreg cell generation. This is potentially attributed to decreased T cell receptor (TCR) signaling strength due to inefficiency in promiscuous expression of self-antigens or presenting a neo-self-antigen by medullary TECs, displaying decreased negative selection-related marker genes (Nur77 and CD5^high) in CD4 single positive (SP) thymocytes. Our results provide evidence that the atrophied thymus attempts to balance the defective negative selection by enhancing tTreg cell generation to maintain central T-cell tolerance in the elderly. Once the balance is broken, age-related diseases could take place.

产后胸腺上皮细胞（TEC）稳态缺陷或自然衰老引起的胸腺萎缩导致中央T细胞耐受性建立下降，这是由胸腺细胞阴性选择和分化簇（CD）4 ⁺胸腺调节性T（tTreg ）细胞生成。越来越多的证据表明这种下降主要是由于阴性选择的缺陷造成的，但是关于tTreg细胞生成是否也受到损害的证据不足。我们通过利用产后TEC缺陷型（FoxN1缺陷条件基因敲除[cKO]产生的）和自然衰老的小鼠模型，对萎缩性胸腺中的tTreg细胞生成进行了机理研究。我们发现与CD4 ⁺相比，tTreg细胞的生成能力没有受到损害胸腺常规T细胞，提示胸腺萎缩对tTreg细胞生成有积极影响。这可能归因于由于自身抗原的混杂表达效率低下或髓质TEC呈递新的自身抗原而导致T细胞受体（TCR）信号强度降低，显示出与负选择相关的标记基因降低（Nur77和CD5^高）在CD4单阳性（SP）胸腺细胞中。我们的结果提供了证据，即萎缩性胸腺试图通过增强tTreg细胞的生成来维持老年人对中央T细胞的耐受性，从而平衡不良的阴性选择。一旦打破平衡，就可能发生与年龄有关的疾病。