The clastogenic effect of irradiated human plasma.

Normal unirradiated human lymphocytes were cultured in medium containing 20 per cent homologous or autologous plasma collected from samples of blood exposed in vitro to various doses of X-irradiation. Metaphases were stained by the BrdU/FPG method. The yields of chromatid-type aberrations in cells at first mitosis (M1 cells) were similar for cultures containing plasma irradiated at 0, 0.05 or 0.25 Gy but were significantly increased at 0.5, 5.0 and 10.0 Gy. The response was dose dependent but the data were insufficient to propose a particular model of dose response. The absence of chromosome-type aberrations confirmed the suggestion that earlier workers' observations of dicentrics and rings were artefacts of long culture times. The level of chromosomal damage was unaffected by omitting folic acid from the medium. Irradiated plasma did not alter the frequency of sister chromatid exchange observed in M2 cells. The ratios of M1, M2 and M3 cells were markedly affected by the presence of irradiated plasma which caused a dose-dependent speeding up of the cell cycle.