担頭蓋内腫瘍マウスの60Co局所照射によるnatural killer activityの変動について

CHANGES OF NATURAL KILLER ACTIVITY FOLLOWING LOCAL 60CO IRRADIATION IN INTRACRANIAL TUMOR-BEARING MICE

　抄録　担癌宿主の，腫瘍に対する免疫学的抵抗性におけるnatural killer cellの役割について検討するため，担頭蓋内腫瘍マウスを作製し，頭蓋内腫瘍に対して⁶⁰Co照射を行ない，放射線治療効果に伴う，マウスのspleen cellのYAC−1細胞に対するnatural killer activityの変化を，⁵¹Cr release assayを用いて測定した。C57 BLマウス4週齢雄の右前頭部に，同系マウスに20—methylcholanthreneを用いて誘発した203—Glioma cell 5x10⁵個を移植した。移植した腫瘍は100％生着し，マウスの50％生存期間は2.5週であった。腫瘍移植後10日目に1000radおよび1500radの1回⁶⁰Co全脳照射を行なうと，腫瘍は壊死をきたし増殖は抑制され，各々50％生存期間は4.5週，6.5週と延命した。これら⁶⁰Co照射により腫瘍が退縮し延命したマウスでは，spleen cellのnatural killer activityの上昇が認められた。このことは頭蓋内腫瘍に⁶⁰Co局所照射を行なうにとによって，宿主の抗腫瘍細胞性免疫が増強し，その中でnatural killer　cellが何らかの役割を果していると考えられ，natural killer activityを測定することにより，腫瘍に対する治療に伴う宿主の免疫学的抵抗性の変化を，ある程度推測することができると考えられる。

Changes of natural killer activity (NK activity, by local ⁶⁰Co irradiation in intracranial tumor bearing mice were studied by the method of ⁵¹Cr release assay. Local irradiation was administerec 10 days after intracranial transplantation of 203- Glioma which had been originally induced by 20- methylcholanthrene in C 57 BL mice. Irradiatior suppressed the growth of tumor and prolonged the mean survival time. The 50% survival time of untreated mice was about 2.5 weeks but that of mice treated by a single dose of 1000 rad and 150C rad of irradiation was about 4.5 weeks and 6. weeks respectively. NK activity of spleen cells. in these mice was serially examined. NK activity was gradually increased in mice treated by local irradiation, while it was gradually decreased in mice without treatment. On the other hand, NK activity remained unchanged in non-tumor-bearing control mice. Mice treated with 1000 rad and 1500 rad of irradiation showed 44.0% and 47.6% of % specific ⁵¹Cr release respectively 11 days after irra-diation while normal mice showed 18.0%. The increased NK activity after local irradiation sug-gested that local irradiation might have enhanced the immunological defence mechanism against the tumor in the tumor-bearing hosts. Some character-istics of effector cells in this assay system were examined. The cytotoxicity of spleen cells was removed by the treatment of anti-BAT serum and complement but was not removed by the treatment of anti-Thy-1.2 serum and complement. Since NK activity reflects the immunological resistance to tumors to some extent, it is felt important to clari-fy the significance of changes of NK activity in patients with brain tumors in relation to various treatments including surgery, radiotherapy, chemo-therapy and immunotherapy in the next step.