Molecular evidence of radiation hormesis at occupational exposure

Abstract

The idea of favourable effects of low dose ionising radiation in biological systems has existed for many years and is the basis of radiation hormesis hypothesis. New evidence at subcellular levels might contribute to further clarify this problem. We used molecular epidemiological biomarkers (DNA/protein changes in peripheral blood; immunological changes in lymphocytes) in occupationally-exposed individuals (400 Nuclear Power Plant (NPP) workers). Two levels of investigations were studied: molecular (spontaneous and induced DNA repair by unscheduled DNA synthesis, induced protein synthesis, DNA damage) and cellular (lymphocyte subsets, immunofluorescent-stained mouse monoclonal antibodies). Potentially lethal damage is decreased in persons with mean annual dose ≤5 mSv. The highest repair capacity (after 2 Gy γ-rays) was also evaluated. Significant decreases of CD3+4+, CD4+25+, CD4+62L+ lymphocytes and CD4/CD8 ratio were observed at <200 mSv. Simultaneously, increased natural killer cells, CD57+8+, CD8+28+ and CD8+38 were recorded. Our study showed DNA repair capacity elevation following high dose irradiation and increased cellular resistance at annual doses twice lower than natural radiation background. We postulated that the positive dose correlation with CD4+25+ and CD57+8+ as well as the negative one with CD4+62L+, CD8+28+ and CD8+38+ could reflect adaptive processes and compensatory activated immune system due to the low dose irradiation.