Adaptation-like response to the chemical induction of sister chromatid exchanges in human lymphocytes

Experiments have been performed to determine whether human lymphocytes in primary cultures can show an "adaptive" response to the induction of cellular lesions (manifested as a production of sister chromatid exchanges, SCEs) as previously found in bacteria and established human and mammalian cell lines. Human lymphocytes were pretreated with various subtoxic concentrations (5-50 ng/ml) of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) once every 6h for 72 h, and subsequently challenged by a high dose (4 micrograms/ml) of MNNG. The lymphocytes in MNNG-challenged cultures had the lowest frequency of SCEs when pretreated with 10 ng/ml MNNG. Further cross-resistance study revealed that repeated pretreatments of lymphocytes with 10 ng/ml MNNG for 72 h can render the cells resistant to the induction of SCEs by the following challenge with a high dose of MNNG, but not of mitomycin C or ethyl nitrosourea. The data also suggest variations in the degree of the adaptation-like response among individuals.