The aim of this work was to define the possible occurrence of hematological changes during the course of a chronic ingestion of (137)Cs. A mouse model was used, with ingestion through drinking water with a cesium concentration of 20 kBq l(-1). Ingestion started in parent animals before mating, and (137)Cs intake and its effect on the hematopoietic system was studied in offspring at various ages between birth and 20 weeks. (137)Cs content was measured in various organs, indicating that (137)Cs was distributed throughout the organism including lympho-hematopoietic organs, i.e., femurs, spleen and thymus. However, we did not observe any effect on the hematopoietic system, whatever the parameter used. In fact, blood cell counts, mononuclear cell counts and progenitor frequency in bone marrow and spleen, and Flt3-ligand, Erythropoietin, G-CSF and SDF-1 concentration in plasma remained unchanged when compared to control animals. Moreover, phenotypic analysis did not show any change in the proportions of bone marrow cell populations. These results indicate that, although (137)Cs was found in all organs implicated in the hematopoietic system, this did not induce any changes in bone marrow function.

The aim of this work was to determine the possible occurrence of damage to the immune system during the course of chronic ingestion of (137)Cs. BALB/C mice were used, with (137)Cs intake via drinking water at a concentration of 20 kBq l(-1). Adults received (137)Cs before mating and offspring were sacrificed at various ages between birth and 20 weeks. Phenotypic analysis of circulating blood cells and thymocytes did not show any significant modification of immune cell populations in animals ingesting (137)Cs as compared with control animals, with the exception of a slight increase in Treg percentage at the age of 12 weeks. Functional tests, including proliferative response to mitogens such as phytohaemagglutinin, response to alloantigens in mixed lymphocyte reaction and immunoglobulin response to vaccine antigens such as tetanus toxin and keyhole limpet haemocyanin did not show any significant functional modification of the immune system in (137)Cs-ingesting animals as compared with control animals. Overall, our results suggest that chronic ingestion of a low concentration of (137)Cs in drinking water in the long term does not have any biologically relevant effect on the immune system.

Twenty years after the Chernobyl accident, 137-Caesium (137-Cs) is the main residual radionuclide found in contaminated areas. 137-Cs progressively integrated food chains until man, inducing a chronic contamination of large populations through daily ingestion of small quantities of 137-Cs. Some studies indicated an accumulation of 137-Cs in the thyroid, the heart and muscles. It was then suggested that 137-Cs contamination could lead to some pathologies observed within populations living onto contaminated areas. In order to determine the possible influence of Cs137 onto the immune system, we developed a mouse model of chronic contamination through drinking water with a concentration of 20 KBq.l-1 of 137-Cs. This corresponds to a daily ingestion of 6 KBq.day-1.kg of body weight, ten times higher than the highest measurements made after the Chernobyl accident. Parent animals were contaminated before mating and during gestation. After weaning, contamination of offspring was continued through drinking water. Gamma counts indicated that 137-Cs was found in all tissue tested at a concentration between 2 and 20 Bq/g of tissue. However, a progressive accumulation of 137-Cs was observed in muscles and kidney, and to a lesser extend in the heart and in femurs, mainly until 9 weeks of age. The immune system was evaluated by several means, including phenotypic and functional analyses. Phenotypic analysis of blood cells did not showed significant changes in both CD4+ and CD8+ T lymphocytes, in CD4+CD25+ Tregs, or in B220+ B lymphocytes between control and 137-Cs contaminated animals. Intrathymic differentiation was evaluated by phenotypic analysis of thymocyte subpopulation and by T cell excision circle (Trec) detection. However, no significant changes in intra-thymic differentiation were observed whatever the age of animals. Three functional tests were also used to evaluate the immune system, response of splenocytes to a mitogenic stimulation, response of splenocytes in a mixed lymphocyte reaction test, and specific response to a vaccination against tetanus toxoid. However, no significant changes were observed in 137-Cs contaminated animals as compared to control animals, even in 35 weeks-old animals. Overall, these results suggest that 137-Cs may accumulate over time in some organs such as the heart, the kidney, the femurs and muscles. However, our results also demonstrate that 137-Cs ingestion does not induce a significant modification of the immune system. This suggests that the pathologies associated with the immune system observed within populations living onto contaminated territories might not be attributed solely to the 137-Cs internal contamination.