Abstract
Hematopoietic cells of mice have been examined for the evidence of in vivo delayed effects long time after radiation exposure. Ten-week male C3H/HeN mice were exposed to 3 Gy x-rays and kept for up to one year. Parts of them were sacrificed periodically, and bone marrow cells were collected. The cells were spread onto clean slides followoing the hypotonic treatment and fixation, and foci of phosphorylated histone H2AX were detected by the immunofluorescence microscopy. Another batch of mice were also exposed to x-rays, and bone marrow cells of them were served for the CFC assay and the CAFC assay to analyze the cellular composition of the hematopoietic system. The number of phosphorylated histone H2AX rapidly decreased after irradiation, and became comparable to those of the control mice after two months. At 6 months post irradiation, however, the foci were about one and half times as many as the unexposed, and the high level was retained even one year after irradiation. The assays of hematopoietic cells showed that CFU-C (myeloid progenitors) had reached to the almost normal level within a month while CAFC-d14 (multipotent progenitors) and CAFC-d28 (very primitive progenitors) had not recovered even at 5 months post irradiation. These phenomena could be manifestations of delayed radiation effects in murine hematopoietic system. The relevance to radiation leukemogenesis is also discussed.
