報告書番号

T43

タイトル（和文）

免疫脾細胞における低線量Ｘ線照射の影響に関する研究

タイトル（英文）

EFFECT OF LOW-DOSE X-RAY IRRADIATION ON IMMUNE SYSTEM

概要 （図表や脚注は「報告書全文」に掲載しております）

免疫に対する低線量放射線の影響を調べるために，健常なラットとマウスにＸ線を全身照射し，脾細胞の応答を検討した。その結果，ラットに５ｃＧｙ照射すると，脾細胞のマイトジェン誘導幼若化反応は照射４時間後に一過性に亢進し，ＬＴＢ４産生も増加した。マウスに２．５ｃＧｙ照射しても，脾細胞の若化反応は亢進し，ＩＬ－１の産生も増加した。また，低線量照射によって誘導される腫瘍免疫の抗ガン作用の確認を行った。ＡＫＲマウスを低線量照射しながら生涯飼育すると，胸腺リンパ腫の発生が減り，マウスの寿命が延びた。担ガンマウスに１５ｃＧｙ照射を行うと，ガン細胞の肺転移は５７％にまで抑制され，このとき脾細胞のＩＬ－６とＴＮＦ－アルファの産生は増加した。これらの事実は，低線量Ｘ線照射による抗ガン作用の誘導には，低線量Ｘ線照射による免疫機能の活性化が関与していることを示すものである。

概要 （英文）

TO CLARITY THE HORMETIC EFFECT ON THE IMMUNESYSTEM,WE STUDIED MITOGEN-INDUCED PROLIFERATION OF SPLENOCYTES IN F344/NSLC RATS AND BALB/C MICE AFTER LOW-DOSE X-RAY IRRADIATION.CON A,PHA OR LPS-INDUCED PROLIFERATION OF RAT SPLENOCYTES PREPARED 4 H AFTER IRRADIATION WAS AUGMENTED BY IRRADIATION AT 5 CGY.THIS AUGMENTATION WAS OBSERVED WITHIN A FEW HOURS AFTER IRRADIATION,AND WAS TEMPORARY.IN MICE,PROLIFERATION OF SPLENOCYTES INDUCED BY CON A,PHA OR LPS WAS AUGMENTED BY IRRADIATION AT 2.5 CGY.THUS,SOME HORMETIC EFFECT ON THE IMMUNE SYSTEM WAS OBSERVED.HOWEVER,THE MECHANISM IS UNCERTAIN.THEREFORE,WE EXAMINED CHANGES IN PRODUCTION OF LTB4 AND IL-1 INFLAMMATORY MEDIATORS.AFTER 5 CGYIRRADIATION,LTB4 PRODUCTION OF RAT SPLENOCYTES SHOWED A SIGNIFICANT INCREASE.FUTHERMORE,2.5 CGY IRRADIATION ALSO ENHANCED THE BIOLOGICAL ACTIVITY OF INTRACELLULAR IL-1 OF LPS-STIMULATED MOUSE SPLENOCYTES. TO CLARITY THE STIMULATION OF ANTITUMOR IMMUNITY BY LOW-DOSE X-RAY IRRADIATION,WE STUDIED CHANGES IN THE INCIDENCE OF THYMIC LYMPHOMA USING AKR MICE,AND OF SPONTANEOUS METASTASIS IN THE LUNG USING TUMOR-BEARING MICE.THE INCIDENCE OF THYMIC LYMPHOMA WAS SIGNIFICANTLY DECREASED AND THE LIFE SPAN WAS SIGNIFICANTLY PROLONGED BY PERIODIC LOW-DOSE X-RAY IRRADIATION.IRRADIATION WITH 15 CGY DECREASED THE NUMBERS OF LUNG-TUMOR BEARING MICE BY 57% RELATIVE TO SHAM-IRRADIATED CONTROLS.THE IL-6 AND TNF-ALPHA PRODUCTION OF TUMOR-BEARING MICE SPLENOCYTES WAS ENHANCED. THESE FINDINGSSUGGEST THAT LOW-DOSE X-RAY IRRADIATION MIGHT CAUSE LIGHT INFLAMMATIONAND MIGHT INDUCE AUGMENTATION OF IMMUNE SPLENOCYTES.FUTHERMORE,THESE RESULTS INDICATE THAT AUGMENTATION OF ANTITUMOR IMMUNITY IS INDUCED BY LOW-DOSE X-RAY IRRADIATION.

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