Adaptation to Ionizing Radiation in Mammalian Cells

The concept of an ionizing radiation-induced increase in resistance against the effects of a subsequent exposure is an accepted and reasonably well-understood process in both prokaryotes (Walker, 1984, 1985) and nonmammalian eukaryotes (Calkins, 1967; Boreham et al., 1990, 1991; Boreham and Mitchel, 1991, 1993, 1994; Mitchel and Morrison, 1982, 1984, 1987; Koval, 1986, 1988). Such processes however, have been more difficult to demonstrate in mammalian cells, where their existence and/or significance have been very controversial (Olivieri et al., 1984; Olivieri and Bosi, 1990; Wiencke et al., 1987, Wilson, 1989; Wojcik et al., 1992a,b; Wolff, 1992 a,b). This lack of general acceptance, while reflecting the lack of volume of the data as well as the variability noted above and a lack of direct evidence of an influence on whole animal risk, also reflects the fact that the concept challenges long entrenched and widely held beliefs and practices, both scientific and public, on which all radiation protection programs and cancer risk estimates are based. Consequently, demonstration of the existence and quantification of the significance of adaptation to radiation in mammalian cells has, potentially, large social and economic implications.