Resistance and cross-resistance to chromosome damage in human blood lymphocytes adapted to bleomycin

Human peripheral blood lymphocytes cultured in the presence of low concentrations of bleomycin (BLM), 0.01-0.1 microgram/ml, for 48 h and then treated with a high concentration (1.5 microgram/ml) of the same agent or with 1.5 Gy X-rays, became significantly less sensitive to the induction of chromosomal damage than those which did not receive the pre-treatment with BLM. They responded with lower frequencies of chromatid and isochromatid breaks. These results lend further support to the operation of an adaptive repair system in lymphocytes which offers resistance and cross-resistance to the induction of chromosomal damage by the same or similar DNA-damaging agents.