Human age-related thymus involution is characterized by loss of developing thymocytes and the thymic epithelial network that supports them, with replacement by adipose tissue. The mechanisms that drive these changes are difficult to study in vivo due to constant trafficking to and from the thymus. We hypothesized that the loss of thymocytes that occurs during human thymic organ cultures could model some aspects of thymus involution and begin to identify mechanisms that drive age-related changes in the thymic microenvironment. Potential mechanistically important candidate molecules were initially identified by screening conditioned media from human thymus organ cultures using antibody microarrays. These candidates were further validated using cultured tissue extracts and conditioned media. Results were compared with gene expression studies from a panel of well-characterized (non-cultured) human thymus tissues from human donors aged 5 days to 78 years. L-selectin released into conditioned media was identified as a biomarker for the content of viable thymocytes within the cultured thymus. Levels of the chemokines CCL21 and CXCL12, likely produced by surviving thymic epithelial cells, increased markedly in conditioned media as thymocytes were lost during culture. Native non-cultured thymus from adults older than 18 years also showed a strong trend toward increased CCL21 expression, in conjunction with significant decreases in thymocyte-related mRNAs compared with thymus from subjects younger than 18 years. Together, these findings demonstrate that use of postnatal human thymus organ cultures can model some aspects of human age-related thymic involution.

人类与年龄相关的胸腺退化的特征是发育中的胸腺细胞和支持它们的胸腺上皮网络的丧失，被脂肪组织替代。由于进出胸腺的不断运输，驱动这些变化的机制很难在体内研究。我们假设在人类胸腺器官培养过程中发生的胸腺细胞丢失可以模拟胸腺退化的某些方面，并开始确定驱动胸腺微环境中与年龄相关的变化的机制。最初通过使用抗体微阵列从人类胸腺器官培养物中筛选条件培养基来鉴定潜在的机械上重要的候选分子。使用培养的组织提取物和条件培养基进一步验证了这些候选物。结果与来自 5 天至 78 岁人类供体的一组充分表征（非培养）人类胸腺组织的基因表达研究进行了比较。释放到条件培养基中的 L-选择素被鉴定为培养的胸腺内活胸腺细胞含量的生物标志物。由于胸腺细胞在培养过程中丢失，趋化因子 CCL21 和 CXCL12 的水平可能由幸存的胸腺上皮细胞产生，在条件培养基中显着增加。与来自 18 岁以下受试者的胸腺相比，来自 18 岁以上成年人的天然非培养胸腺也显示出 CCL21 表达增加的强烈趋势，同时胸腺细胞相关的 mRNA 显着减少。一起，