Differences in CD4⁺CD25⁺ regulatory T cell-depletion between Babesia microti and Babesia rodhaini infections in mice

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CD4⁺CD25⁺ regulatory T cells (T_reg cells) work as an immunoregulatory suppressor for the effector function of cell-mediated immunity. In the present study, we depleted a population of T_reg cells by hyper-treatment with an anti-mouse CD25 monoclonal antibody and evaluated the infectious development of two murine Babesia parasites,B. microti (non-lethal) and B. rodhaini (lethal), in mice. The T_reg cell-depleted mice were more resistant to the infection of B. microti than the control mice, as indicated by the lower development of parasitemia and faster recovery of anemia in the mice. On the other hand, in B. rodhaini infection, the depleted mice showed a severer clinical response than the control mice, as indicated by the parasitemia development and lethal rate dynamics. These findings indicated different effects of T_reg cell-depletion in Babesia infections, suggesting that cell-mediated immunity, which can be suppressed by T_reg cells, might be responsible for the control of B. microti infection but not for the B. rodhaini infection in mice.