Neutron-induced adaptive response studied in go human lymphocytes using the comet assay

This study demonstrates that cells adapted to ionizing radiation developed reduced initial DNA damage when compared to non-adapted cells. The results were obtained by subjecting in vitro irradiated whole blood from 10 healthy volunteers (including 2 A-bomb survivors carrying 1.5-2 Gy in vivo exposur e) in an unstimulated condition (G(0)) using the comet assay. The intensity of DNA damage was assessed by computing the 'tail moment'. Adaptive respon se (AR) was noticed in only donor 3, as indicated by reduced tail moment wh en the blood samples received priming + challenging doses over a 4 h interv al. The priming dose was either 0.01 Gy Cs-137 gamma -rays or 0.0025 Gy Cf- 252 neutrons. The delivered challenging dose was either 1 Gy Co-60 g-rays o r 0.25 Gy Cf-252 neutrons. The irradiation was conducted using the HIRRAC f acility. A prior exposure to 0.0025 Oy Cf-252 neutrons nullified the excess tail moment caused by 0.25 Gy neutrons given during a 4 h gap. In a simila r way, 0.01 Gy Cs-137 gamma -rays offered a cross-adaptive response to the neutron challenging dose. The tail moment of A-bomb survivors after in vitr o irradiation was less than that of the age-matched control and, at the sam e time, was not influenced by the priming dose. An altered subset and the i mmunological status of blood after A-bomb exposure were cited as possible f actors. Because AR can affect the outcome of RBE, its individual variabilit y only emphasizes the need to have individual biodosimetry for better risk assessment, especially in planning for a long space voyage.