Abstract
It is reported that lymphocytes work as a principal role in the cell-mediated immunity to the tumor. They are classified into some sub-populations and have respectively different radiosensitivities. It has been reported that low-dose whole-body irradiation to mice might bring about augmentation of immune responses. This experiment was studied on effect of dose and timing of whole-body irradiation on the growth of sarcoma 180 tumor, which was inoculated intracutaneously in the back of ICR mice. The effect on the tumor growth inoculated with different cell numbers was also investigated by a low dose whole-body irradiation. 1) Right after inoculation of 3×105 tumor cells, the mice were irradiated with 10, 20, 50 and 100 rad. The tumor growth in 20-rad group was inhibited, compareing with non-irradiated control group. The tumor growth in 10- and 50-rad groups were not inhibited, while in 100-rad group, it had conversely a tendency to be accelerated. 2) The 20-rad whole-body irradiation was administered on each group at the times varying from 2 days before to 5 days after tumor inoculation. The tumor growth was inhibited in the groups which were irradiated at the times from immediately to 2 days after tumor inoculation. The poor tumor growth which was most prominently inhibited was observed in the group irradiated right after tumor inoculation. 3) The mice inoculated with a small number (1×105) and with a large number (1×106) of tumor cells, were irradiated with 20 rad immediately after inoculation. The inhibition of the tumor growth was clearly found in a small number (1×105) cells group, buf not in a large number (1×106) cells group. These phenomena may be due to the fact that the radiosensitive suppressive lymphocytes are firstly impaired by low-dose radiation.
