Radiation response and cellular re-population kinetics of thymocytes in neonatal B6C3F1 mice.

Murine thymic lymphoma (TL) is a suitable model for studying the causative genes of human T-cell acute lymphoblastic leukemia (T-ALL) and radiation-lymphomagenesis. Risk of radiation-induced thymic lymphoma is dependent on the age at exposure. Incidence of thymic lymphoma after whole-body irradiation of neonate (one week-old) B6C3F1 mice is higher than that for adults (seven weeks of age). However, the mechanism(s) of susceptibility for neonates is unknown. In this study, we aimed to clarify age-dependent changes in thymocyte re-population kinetics and cellular responses to radiation, to shed light on the age effect for radiation carcinogenesis. After 4 Gy whole-body gamma-irradiation, the total number of thymocytes dramatically decreased and then increased in two waves. Cellular re-population especially CD4-CD8- cells was more immediate after neonate irradiation (day 4-10, day 14-25) than after adult irradiation (day 5-10, day 23-35). Apoptosis was delayed in neonates (6 h after irradiation) compared to adults (3 h), but cell proliferation persisted longer in neonates (6 h) than in adults (3 h). These differences in radiation response and recovery of thymocytes after irradiation may account for in part the higher susceptibility of the neonatal thymus to radiation carcinogenesis.6th International Workshop of Kyoto T Cell Conferenc