Studies carried out on populations exposed to the fall-out of the Chernobyl accident have found numerous modifications in the immune system such as a change in the physiology of the thymus in a population of liquidators1 (Yarilin et al., 1993), a decrease in the level of circulating immunoglobulins in children living in the contaminated areas (Titov et al., 1995) or a change in the percentages of the various subsets of circulating lymphocytes, again in children (Vykhovanets et al., 2000). A review of studies published in Russian on this subject was recently published (Yablokov, 2009), and highlights significant changes in the full blood count and an increase in the incidence of myelodisplastic diseases amongst populations living in contaminated areas. These changes in the immuno-haematopoietic system are mostly associated with caesium 137 contamination as well as external radiation received during clean-up operations, as in the liquidators.
We have therefore used the murine model of chronic caesium 137 ingestion previously described to analyse the haematopoietic system. Monitoring of the blood cell count, measurement of blood levels of cytokines implicated in the hematopoietic regulation, phenotyping of medullary cells and determination of the frequency of haematopoietic progenitors in the spleen and bone marrow were carried out in mice from birth up to the age of 20 weeks. The monitoring of these parameters is allows to follow the homeostasis of the haematopoietic system. However, no change in these parameters was observed in the contaminated animals, regardless of age or gender (Bertho et al., 2010).
Similarly, different functional, phenotypic parameters of the immune system were assessed.. Once again, no changes in the immune system were detected in the contaminated animals. As well the use of a vaccination model as an immune system function test did not highlight any significant change in the response to two antigens, the tetanus toxin (TT) and Keyhole lymphet haemocyanin (KLH). This response was measured by determining the blood concentration of IgG and IgM specific to the antigens used. This type of test, which represents an integrated response by the immune system, strongly suggests that the chronic ingestion of caesium 137 by mice, under our experimental conditions, does not have a major effect on either of these two physiological systems, namely the haematopoietic system and the immune system.
This lack of effect of caesium 137 in our murine model for chronic ingestion is in contradiction with the studies of human populations living in contaminated regions, which have highlighted numerous phenotypic and functional changes in both physiological systems (Titov et al., 1995, Vykhovanets et al., 2000, Yablokov, 2009, Yarilin et al., 1993). However, the health status of the population prior to the Chernobyl accident is unknown which may induce some bias in theses results. However, although our murine model is representative of the chronic ingestion observed in contaminated areas (as shown in the biokinetic studies), other factors were not taken into account in our studies. In fact, this murine model presents a certain number of limitations.