Direct detection of p53-/- thymocyte appearing at an early stage of radiation-induced thymic lymphomagenesis in p53+/- heterozygous B10 mice

Purpose: The appearance of tumor suppressor protein 53 (p53) -/- thymocytes at an early stage of radiation-induced lymphomagenesis was investigated in the p53 heterozygous (+/-) B10 mice following a single dose of irradiation, since most thymic lymphomas manifested the loss of the wild-type p53 allele and the loss of heterozygosity was thought to be an early event critical for radiation-induced thymic lymphomagenesis in p53+/- mice. Materials and methods: The mice were exposed to a single dose (6 Gy) of irradiation to induce thymic lymphomas and, at various times after irradiation, treated with an extremely high dose (30 Gy) of whole-body irradiation to enrich p53-/thymocytes and, 24 h later, the remaining thymocytes were assayed for cell surface markers and p53 genotype. Results: In a significant fraction of the p53+/- mice 5 weeks after 6 Gy irradiation, there was a relative increase in the number of cluster of differentiation (CD) 4(+)CD(8+) thymocyte subpopulation among thymocytes remaining after 30 Gy irradiation. The CD4+CD8+ double-positive (DP) thymocytes were shown to contain p53-/- cells, and the number of p53-/- thymocytes was more than 10(5) in those individuals. Conclusions: The results clearly indicated that an extremely high dose (30 Gy) of whole-body irradiation enabled us to directly detect p53-/- thymocytes in an abundant p53+/- thymocyte population and that proliferative p53-/- thymocytes develop in a CD4+CD8+ DP thymocyte subpopulation within a few weeks after a single dose (6 Gy) of irradiation.