1965 年 77 巻 1 号 p. 71-86
In the series of studies being conducted on radiation leukemogenesis, observations lasting for one year were carried out to see the changes in the hematopoietic organs with lapse of time, using 30-50 days old mice of the Cb, D103, StA, and Zb strians after a single whole body X-irradiation of 350 r. The findings of the study are presented in the following.
1. In the observations lasting for one year, there was no development of leukemia in 18 mice of the D103 strain, in 19 mice of the StA strain, and in 13 mice of the Zb strain. In one out of 20 mice of the Cb strain, however, leukemia did develop, and it was confirmed to be myelogenous leukemia from its peripheral blood picture and tissue culture. Cell transplantations from this mouse to other mice of the same strain were not successful.
The changes in hematopoietic organs occurring with lapse of time after X-irradiation in aech strain of mice that did not develop leukemia are as described as follows.
2. Lymph nodes, spleen and thymus after the irradiation showed degeneration, necrosis and lymphoctyopenia, with a decrease in their weight.
3. Two weeks after the irradiation the spleen was transiently enlarged, showing an acceleration of splenic function. This was striking in mice of the D103 strain.
4. After the decrease in the weight of lymph nodes, spleen and thymus, the proliferation of reticuloendothelial cells and lymphocytes was accelerated, but this tendency in any organs was limited to the proliferatioan of mature cells only. There could also be recognized distortion of thymus in some.
5. The changes in the bone marrow were slight and the peripheral blcod showed a relative neutrophilia.
6. These changes were similar in each strain of mice, especially those changes in the initial stage were exactly identical with those observed in RF strain mice. In the RF strain mice, however, young cells proliferated at a relatively early stage whereas in the resistant strains such as the Cb, D103, StA and Zb strains the reactive proliferation of only mature cells could be observed.
7. Liver cells were greatly affected by X-ray, showing degeneration, necrosis, and vacuolization even 16 weeks after the irradiation, but no specific infiltration of leukemic cells as in the case of mice of the RF strain could be demonstrated.
From these findings it is assumed that mice of the RF strain possess leukemogenic factor in the form of provirus and this is activated by X-irradiation, while mice of the Cb, D103, StA or Zb strains do not have provirus or has provirus in a state in which it is difficult to be activated by X-irradiation.