Kinetics of lymphohematopoietic progenitor cell populations in chronically irradiated RF/J mice.

Continuous protracted gamma irradiation (17.5 rad/22 h day for 28 days) resulted in significant life-shortening in RF/J mice due to lymphohematopoietic malignancies. The latency period of these neoplasms was decreased in irradiated RF/J versus unirradiated RF/J mice. No effect on leukemia incidence was observed in either irradiated or unirradiated CAF1 mice that served as control animals representing a strain with normal baseline lymphohematopoiesis. Lymphohematopoietic progenitor cell populations (CFU-GM and CFU-BL) were quantitated in unirradiated and chronically irradiated mice of both strains. The most remarkable differences in these parameters were seen with respect to CFU-BL. Unirradiated and irradiated RF/J mice produced over three times as many CFU-BL as CAF1 mice. Tremendously expanded lymphoid progenitor cell compartments in the RF/J mice may reflect the presence of numerically increased sensitive targets subject to radiation-induced damage and transformation. During a 12-week recovery period, CFU-BL and CFU-GM in the RF/J mice exhibited enhanced regenerative capabilities and overcompensatory responses that surpassed homeostatic baseline levels. Despite strain and strain X dose differences in CFU-BL and CFU-GM, no significant strain X dose relationships were seen in circulating leukocyte counts. This heightened proliferative activity and temporary overstimulation of radiation-damaged lymphohematopoietic tissues may allow sufficient promotional effect for leukemogenesis.