2-Gy whole-body irradiation significantly alters the balance of CD4 +CD25-T effector cells and CD4+CD25 +Foxp3+ T regulatory cells in mice

Abstract

CD4+CD25+T regulatory (Treg) cells are critical in inducing and maintaining immunological self-tolerance as well as transplant tolerance. The effect of low doses of whole-body irradiation (WBI) on CD4 +CD25+Foxp3+ Treg cells has not been determined. The proportion, phenotypes and function of CD4+CD25 +Treg cells were investigated 0.5, 5 and 15 days after euthymic, thymectomized or allogeneic bone marrow transplanted C57BL/6 mice received 2-Gy γ-rays of WBI. The 2-Gy WBI significantly enhanced the ratios of CD4 +CD25+Treg cells and CD4+CD25 +Foxp3+ Treg cells to CD4+T cells in peripheral blood, lymph nodes, spleens and thymi of mice. The CD4+CD25 +Treg cells of the WBI-treated mice showed immunosuppressive activities on the immune response of CD4+CD25-T effector cells to alloantigens or mitogens as efficiently as the control mice. Furthermore, 2-Gy γ-ray WBI significantly increased the percentage of CD4+CD25+Foxp3+ Treg cells in the periphery of either thymectomized mice or allogeneic bone marrow transplanted mice. The in vitro assay showed that ionizing irradiation induced less cell death in CD4 +CD25+Foxp3+ Treg cells than in CD4 +CD25-T cells. Thus, a low dose of WBI could significantly enhance the level of functional CD4+CD25+Foxp3 + Treg cells in the periphery of naive or immunized mice. The enhanced proportion of CD4+CD25+Foxp3+ Treg cells in the periphery by a low dose of WBI may make hosts more susceptible to immune tolerance induction. © 2010 CSI and USTC. All rights reserved.