Residual damage and discontinuity of recovery in the hematopoietic system of mice following gamma-irradiation.

Recovery of the hematopoietic system up to 35 days following whole body irradiation of mice was investigated by measuring the repopulation ability of femoral bone marrow in irradiated recipients. The assay was performed five days after transfusion by testing for incorporation of 125iodo-deoxyuridine (125IUdR) into DNA of femoral marrow and spleen. The DNA incorporating cells are progeny of transfused stem cells or early precursors. For non-irradiated donors 125IUdR incorporation in the recipient spleens was proportional to the number of transfused cells between 0.05-1.0 x 10(6)/mouse but decreased with larger grafts (5-30 x 10(6). Yet, in the femur 125IUdR incorporation remained proportional over the range of 0.5-30 x 10(6) transfused cells. Recovery was discontinuous and not complete 35 days after irradiation. A possible explanation is injury to stem cells that still permits these cells to produce progeny within a milieu of high proliferation stimulus.