The bystander effect has been widely described in vertebrates, and to a lesser extent in other Metazoa and unicellular organisms. In the present study, we have demonstrated the ability of unicellulates to generate this effect in bystander cells of mulicellular organisms. Human peripheral blood lymphocytes were cultivated in medium RPMI-1640 at 37• C for 48 h. At the beginning of the incubation procedure, set of cultures were irradiated by X-ray in dose 1 Gy, than nonexposed and irradiated cultures was experimentally contaminated with nonirradiated or X-ray irradiated yeast Saccharomyces cerevisiae (haploid strain, the dose of irradiation was 10 Gy). The preparation of slides for chromosome analysis was performed according to standard procedure. Well spread metaphases were scored for chromosomal aberrations (CA). It was found that the level of CA was significantly increased in nonirradiated human lymphocytes incubated with irradiated S. cerevisiae as compared with control (7.67±1.76% and 2.33±0.88% respectively, p<0,01). Analysis of the spectrum of CA indicated chromatide type aberrations as the main chromosomal lesions for these experiments. We found no influence of incubation with irradiated yeast cells on the average level of chromosomal instability in X-ray exposed lymphocytes. The chromosome type aberrations were the main chromosomal lesions for noncontaminated and contaminated irradiated lymphocyte cultures, but shift to chromatide type aberrations was observed for CA spectrum of irradiated lymphocytes incubated with irradiated S. cerevisiae. The incubation with nonirradiated yeast cells had no effect on lymphocytes chromosomal stability. Thus, our findings show the evident bystander effect in human lymphocytes incubated with irradiated S. cerevisiae. Possible implications of these results will be discussed.
Abstract. The comparison of strength of bystander effect induction in human lymphocytes by rho 0 (complete loss of mitochondrial DNA) and rho + (with fully functional mtDNA) strains of Saccharomyces cerevisiae was carried out. The cultures of human peripheral blood were experimentally contaminated with nonirradiated or X-ray irradiated yeast cells (haploid rho 0 and rho + strains of S. cerevisiae). The doses of irradiation were 1 and 10 Gy. Well spread human metaphases were scored for chromosomal aberrations (CA). It was found that nonirradiated yeast cells (no matter rho 0 or rho + ) had no effect on lymphocytes chromosomal stability. Statistically significant increased level of CA was observed in lymphocytes incubated with irradiated rho + yeast cells. The increasing of the CA was dose independent. However, after cocultivation with irradiated rho 0 cells the bystander effect was revealed for dose 10 Gy only and his manifestation was mild in comparison with rho + data. Thus, our findings suggest that strength of bystander effect depends on existence of mitochondrial DNA and normally functioning mitochondria.
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