量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum and Radiological Science and Technology.
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Induction of adaptive response (AR) by combination of irradiations with different LET values was attempted in a series of investigations in young adult female mice of C57BL/6J strain using mainly thirty-day survival in vivo as the endpoint. For mouse total body irradiations, X-rays and high LET accelerated heavy ion irradiations were used. The heavy ion irradiations were from carbon, silicon, neon and iron beams. Existence of AR was demonstrated by delivering a priming low dose of X-rays (0.50 Gy) in combination with a challenge high dose of accelerated carbon, neon or silicon ion particles but not iron particle. AR was characterized by significantly decreased mortality in the 30-day survival test. On the other hand, when the priming dose was from heavy ion irradiations and the challenging dose was from X-rays, only the combination of carbon ion plus X-rays could induce AR. For the combination of irradiation from heavy ions, only two cases, namely, carbon ions plus carbon ions and carbon ions plus neon ions could induce AR. Results obtained so far showed that induction of AR by X-rays against high LET heavy ion irradiations is an event depending on the LET or/and species of the ions, it is hardly to induce AR by high LET heavy ion irradiations against X-rays, and it seems that high LET heavy ion irradiations hardly induce any AR against higher LET heavy ion irradiations. As this mouse AR model ( Yonezawa Effect ) was originally established by using X-rays as both the priming and challenge irradiations, and the mechanism underlying AR induced by X-rays as both the priming and the challenging doses was due to radioresistance occurring in hematopoietic tissues, to explore the mechanism involved in the AR induced by X-rays against heavy ion irradiations, we further investigated residual damage in the hematopoietic system in surviving animals. Results showed that the priming low dose of X-rays could relieve the detrimental effects on the hematopoietic system. We observed both an improvement in the blood platelet count and the ratio of polychromatic erythrocytes (PCEs) to the sum of PCEs and normochromatic erythrocytes (NCEs) and a marked reduction of the incidences of micronucleated PCEs and micronucleated NCEs. These findings suggest that the priming low-dose of low LET X-rays induced a protective effect on the hematopoietic system, which may play an important role in both rescue from acute lethal damage (mouse killing) and prevention of late detrimental consequences (residual anhematopoiesis and delayed genotoxic effects) caused by exposure to a high challenge dose from low-LET (X-ray) or high-LET (carbon and neon ion) irradiations. These findings bring new knowledge to the characterization of the Yonezawa Effect by providing new insight into the mechanistic study of AR in vivo.
Induction of adaptive response (Yonezawa Effect) by combination of irradiations with different LET values in mice.
