報告書番号

G03011

タイトル（和文）

低線量率放射線による腫瘍細胞排除能の変動 -メチルコラントレン誘発皮下がん細胞を用いて-

タイトル（英文）

Enhancement of tumor rejection in mice by low dose-rate gamma irradiation

概要 （図表や脚注は「報告書全文」に掲載しております）

これまでに、低線量率放射線を照射することによりICRマウスおよびC57BL/6マウスにおいて化学発がん剤（メチルコラントレン）による皮下がんの発生が抑制あるいは遅延されることを確認した。そもそも、発がんはいくつかの段階を経て進行する多段階であると考えられている。生体にはその進行を抑える機能があるが、最終的にがん化した細胞の増殖能力がこれを越えた場合にがんになる。そこで、がんを抑える能力の１つであると考えられる腫瘍細胞を排除する能力に及ぼす低線量放射線の影響を解析した。その結果、低線量率放射線に照射されたマウスにおける腫瘍細胞排除能は0.35, 0.7, 1.2 mGy/hrのいずれの線量率でも総線量250 mGy付近で亢進し、総線量1.2Gyの照射であっても腫瘍細胞排除能は低下しないことが示された。

概要 （英文）

We reported a suppression effect of low dose-rate gamma irradiation on the appearance of a Methylcholanthrene (MC) -induced tumor (fibrosarcoma) in C57BL/6N mice in Int. J. Low Radiat. To elucidate the mechanism of the suppression effect, we studied the effect of low dose-rate irradiation on the rejective response against taking tumor cells. In this study the rejective response was analyzed by applying methods of TD50 assay. TD50 is the abbreviation for tumor dose 50 and indicates the number of cells required for successful transplantation to one half of an injected site in the recipient animals. We transplanted the tumor cells prepared from an MC-induced tumor in C57BL/6 mice. The increase of the TD50 value suggests an enhancement of the rejective response against taking tumor cells. Irradiations were performed with Cs-137 gamma-rays at 1.2 mGy/hr or 0.35 mGy/hr for 1-8 weeks before tumor cell injection from six-week old mice, which were then injected with an appropriate number of single tumor cells. The value of TD50 in mice irradiated at 0.35 mGy/hr for 5 weeks was 5 times higher than in the non-irradiated control mice. The total dose at 0.35 mGy/hr for 5 weeks was about 250 mGy. At 1.2 mGy/hr or 0.7 mGy/hr, an increase in TD50 was observed when the total dose reached 250 mGy. These results suggest that low dose-rate radiation, under certain irradiation conditions, enhances immunological capacity against tumor cells in irradiated mice and thereby suppresses tumor incidence. For an estimation of risk of cancer incidence from low dose/dose-rate radiation, such protective effects as demonstrated in the present study should be taken into consideration.

報告者

キーワード