Indications of repair of radon-induced chromosome damage in human lymphocytes: an adaptive response induced by low doses of X-rays.

Naturally occurring radon is a relatively ubiquitous environmental carcinogen to which large numbers of people can be exposed over their lifetimes. The accumulation of radon in homes, therefore, has led to a large program to determine the effects of the densely ionizing alpha particles that are produced when radon decays. In human lymphocytes, low doses of X-rays can decrease the number of chromatid deletions induced by subsequent high doses of clastogens. This has been attributed to the induction of a repair mechanism by the low-dose exposures. Historically, chromosome aberrations induced by radon have been considered to be relatively irreparable. The present experiments, however, show that if human peripheral blood lymphocytes are irradiated with low doses of X-rays (2 cGy) at 48 hr of culture, before being exposed to radon at 72 hr of culture, the yield of chromatid deletions induced by radon is decreased by a factor of two. Furthermore, the numbers of aberrations per cell do not follow a Poisson distribution but are overdispersed, as might be expected because high-linear energy transfer (high LET) alpha particles have a high relative biological effectiveness compared to low-LET radiations such as X-rays or gamma rays. Pretreatment with a low dose of X-rays decreases the overdispersion and leads to a greater proportion of the cells having no aberrations, or lower numbers of aberrations, than is the case in cells exposed to radon alone.(ABSTRACT TRUNCATED AT 250 WORDS)