Lack of synergistic effect between X-ray and UV irradiation on the frequency of chromosome aberrations in PHA-stimulated human lymphocytes in the G1 stage

PHA-stimulated human lymphocytes in the G1 stage were irradiated with UV radiation and X-rays, and the cells were analysed for chromosomal aberrations in the first mitotic division. The frequency of dicentric chromosomes after single X radiation in the G1 stage was about twice the yield in the G0 stage. No increase in the yield of dicentrics was observed after combined irradiation with UV and X-rays. This is contrary to the finding for G0 lymphocytes, where a 2-fold increase of chromosome aberrations was observed. UV irradiation of G1 lymphocytes induced chromatid-type aberrations whereas no significant yield of dicentric chromosomes was observed. This in agreement with previous findings in Chinese hamster cells in the G1 stage. Irradiation of G0 lymphocytes with UV radiation induce a low frequency of dicentric chromosomes. Thus, the present data indicate that the ratio between chromosome-type and chromatid-type aberrations is different in the G1 and G0 stages in human lymphocytes irradiated with UV radiation