3.3.3. The adaptive response (AR) phenomenon
The term radio adaptive response is generally used for describing increased radio resistance and/or reduced carcinogenicity after a priming dose followed by a challenging high-dose. However,behind the same term, very different protocols of irradiation are applied. The most frequently used AR protocol is a challengingexposure to high-dose of more than 1 Gy due to a conditioning exposure to low-dose (0.001–200 mGy) generally delivered at dose-rate higher than 100 mGy min−1and with an interval period (4–6 h) between the priming dose and the challengingdose (Calabrese, 2009). Very few research groups have focused on human cells. Furthermore, some genetic statuses, some cell cycledistributions appear to be more prone to AR revealing that it is not necessarily the most radio resistant cells that show AR, but to the contrary, a minimal radio sensitivity is required to observe its reduction by AR. However, care must be taken with regard to the potential biases linked to the different cellular models. Hence,dose and time interval between doses condition both DSB repair and chromatin condensation/decondensation that appear there-fore two essential causes and consequences of AR phenomenon.Interestingly, it is noteworthy that, like for HRS phenomenon,the method of anomalous viscosity time dependence contributed to establish quantitative relationship between AR and chromatin response . Again, the development of research in this field is required, inasmuch as AR phenomenon is at the crossroads of the debates about low-dose effects and the LNT/NLTmodels controversy .