Activation of immunological network by chronic low-dose-rate irradiation in wild-type mouse strains: Analysis of immune cell populations and surface molecules

Purpose: To analyse the effects of chronic whole body low-dose-rate irradiation on the immune system in various wild-type mouse strains in comparison with the effects from acute high-dose-rate irradiation.Materials and methods: Wild-type mouse strains (C57BL/6, BALB/c, C3H/He, DBA/1, DBA/2 and CBA) were observed after chronic low-dose-rate γ irradiation at 1.2 mGy hour−1 by intensive analysis of immune cell populations and their various surface molecules, together with antibody-producing activity both with and without immunization by sheep red blood cells (SRBC). The cell surface functional molecules [cluster of differentiation (CD) 3, CD4, CD8, CD19, CD45R/B220, intercellular adhesion molecule (ICAM)-1, Fas, natural killer (NK)-1.1, chemokine {C-X-C motif } receptor 4 (CXCR4) and chemokine {C-C motif } receptor 5 (CCR5)] and activation molecules [thymocyte-activating molecule (THAM), CD28, CD40, CD44H, CD70, B7-1, B7-2, OX-40 antigen, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), CD30 ligand and CD40 ligand] were studied in the bone marrow, thymus, spleen, lymph nodes and peripheral blood by flow cytometry.Results: By chronic low-dose-rate irradiation alone, CD4+ T cells and CD8 molecule expression increased significantly by a maximum of 30%, while CD40+ B cells decreased significantly. Increases of CD4+ T cells, CD40+ B cells and anti-SRBC antibody-producing cells by immunization were significantly enhanced by continuous low-dose-rate irradiation at 1.2 mGy hour−1. CD3− CD4+ T cells, representative of abnormal immune cells, were absent in the chronically low-dose-rate-irradiated mice, while a dose-dependent increase of these cells was found in acutely high-dose-rate-irradiated mice given the same total doses.Conclusion: Chronic low-dose-rate radiation activated the immune system of the whole body.