Influence of continuous, very low-dose gamma-irradiation on the mouse immune system

Purpose: To investigate whether continuous, very low-dose gamma -irradiation (10 cGy/year) modifies immune parameters in mice. Material and methods: C57BL/6 female mice, 4 weeks old, were irradiated for 24 months and compared with control mice living in the same room. B- and T-cell subsets were evaluated by flow cytometry before and after stimulation with lectins; subclasses of immunoglobulins were determined by ELISA 2, 4, 6, 8, 12, 18 and 24 months after the beginning of the irradiation. Results: No difference was found in the percentage of CD4(+) and CD8(+) cells in the thymus and the spleen, or in the reactivity of T-cells to lectins. While the number of B-cells in the spleen remained unchanged, a significant decrease of IgG1, IgG2b and IgG2a was observed after respectively 12, 18 and 24 months of irradiation. Conclusion: The parameters of cellular immunity studied were not affected by this chronic low-dose of irradiation, but this dose rate is probably too low to induce the hormetic effect previously described. Further investigations are necessary to assess whether the decline of immunoglobulin secretion is indicative of a lower rate of infectious diseases or a defect in B-cell function.