Cell Population Analysis of Radiation Leukemogenesis in Mice

Abstract

Young C57BL mice were irradiated with a leukemogenic dose of x-rays in four fractions with an interval of seven days. Differential cell count was carried out in the course of tumor development on the cellular suspension of the thymus or lymph nodes. The normal differentiation of large lymphocytes to small lympho-cytes was recognized always after each irradiation. The accumulation of blast cells due to maturation arrest was not seen in the whole period of regeneration. The population of neoplastic cells appeared among normal lymphocytes as early as 14 days after the fourth irradiation. The rate of tumor cell induction at the time of irradiation was 1×10-4 to 1_??_10-5/R in the blasts cells. The population of self-replicating cells increased exponentially with the doubling time of 7.3 days and constituted a large thymoma. In the lymph nodes, numerous foci of unusual proliferation of blast cells without differentiation were observed in the cortex, but further development of the foci was suppressed. The immunological in-sufficiency in the thymus may be responsible for the development of neoplastic cells in the organ. Extreme lymphopenia for a long period may also be associated with tumor cell development.