Effects of mesenchymal stem cells on thymus tissue injury induced by ionizing radiation in mice

Objective: To observe the migration,colonization and repairing effects of marrow mesenchymal stem cells (MSCs) on thymus tissue injury induced by ionizing radiation in mice. Methods: MSCs of C57BL/6 mice were isolated, purified and cultivated in vitro. Their migration and colorization were observed with laser confocal microscopy 1, 5 and 10 d after DAPI labeled. MSCs were injected into the thymus tissue of mice through tail vein. The model of thymus tissue injury induced by whole-body X-irradiation was established. The mice were divided into four groups: normal, irradiation, irradiation+saline, and irradiation+MSCs groups. The apoptosis was detected by flow cytometry and the repairing effect of MSCs on thymus tissue injury was observed by histological method 3 months later. Results: The occurrence of MSCs in the thymus was observed 1 d after MSCs injection, the diffusion of MSCs in the thymus appeared 5 d later, and widely dispersed 10 d later. The apoptotic rate of thymocytes in irradiation group was higher than that in normal (P<0.05) and was lower than that in MSCs group (P<0.05). The structures of cortex and medulla of thymus were clear in mice in normal group, there were a large number of lymphocytes in the cortex and small number of lymphocytes in the medulla. The structures of cortex and medulla of thymus were unclear in mice in both irradiation, irradiation and saline groups. The lymphocytes in thymus showed extensive coagulation necrosis. There were remnants or newborn lymphoid tissue in the cortex and medulla in mice in irradiation+MSCs groups. Conclusion: MSCs can be rapidly enriched in thymus tissue and promote regeneration and repair of damaged thymus. (authors)