Salivary gland (SG) hypofunction is a common post-radiotherapy complication. Besides the parenchymal damage after irradiation (IR), there are also effects on mesenchymal stem cells (MSCs) which were shown to contribute to regeneration and repair of damaged tissues by differentiating into stromal cell types or releasing vesicles and soluble factors supporting the healing processes. However, there are no adequate reports about their roles during SG damage and regeneration so far. Using an irradiated SG mouse model, we performed certain immunostainings on tissue sections of submandibular glands at different time points after IR. Immunostaining for CD31 revealed that already one day after IR, vascular impairment was induced at the level of capillaries. In addition, the expression of CD44—a marker of acinar cells—diminished gradually after IR and, by 20 weeks, almost disappeared. In contrast, the number of CD34-positive cells significantly increased 4 weeks after IR and some of the CD34-positive cells were found to reside within the adventitia of arteries and veins. Laser confocal microscopic analyses revealed an accumulation of CD34-positive cells within the area of damaged capillaries where they were in close contact to the CD31-positive endothelial cells. At 4 weeks after IR, a fraction of the CD34-positive cells underwent differentiation into α-SMA-positive cells, which suggests that they may contribute to regeneration of smooth muscle cells and/or pericytes covering the small vessels from the outside. In conclusion, SG-resident CD34-positive cells represent a population of progenitors that could contribute to new vessel formation and/or remodeling of the pre-existing vessels after IR and thus, might be an important player during SG tissue healing.

唾液腺 (SG) 机能减退是一种常见的放疗后并发症。除了辐照后的实质损伤 (IR) 外，间充质干细胞 (MSCs) 也有影响，MSCs 通过分化为基质细胞类型或释放支持愈合过程的囊泡和可溶性因子，有助于受损组织的再生和修复。然而，到目前为止，还没有关于它们在 SG 损伤和再生过程中的作用的充分报道。使用经照射的 SG 小鼠模型，我们在 IR 后的不同时间点对下颌下腺的组织切片进行了某些免疫染色。CD31 的免疫染色显示，在 IR 后一天，毛细血管水平已诱导血管损伤。此外，CD44（一种腺泡细胞标志物）的表达在 IR 后逐渐减少，并且，到20周，几乎消失了。相比之下，IR 后 4 周 CD34 阳性细胞的数量显着增加，并且发现一些 CD34 阳性细胞位于动脉和静脉的外膜内。激光共聚焦显微分析显示，CD34 阳性细胞在与 CD31 阳性内皮细胞密切接触的受损毛细血管区域内积聚。在 IR 后 4 周，一部分 CD34 阳性细胞分化为 α-SMA 阳性细胞，这表明它们可能有助于平滑肌细胞和/或从外部覆盖小血管的周细胞的再生。综上所述，