Tregs exacerbate ischemic brain damage in wild-type mice and Rag1^−/− mice lacking T cells independently of Treg immunologic function. (A) Purified CD4⁺CD25⁺ Tregs (750 000) were transferred into regular C57Bl/6 mice 24 hours before 30 minutes of tMCAO and infarct volumes were determined on day 1. (B) The stroke-protective effect observed in Rag1^−/− mice on day 1 after 60 minutes of tMCAO could be reversed by adoptive transfer of Tregs (CD4⁺CD25⁺ or CD4⁺CD25⁺FoxP3⁺) or non-Tregs (CD4⁺CD25⁻ or CD4⁺CD25⁻FoxP3⁻). (C) Adoptive transfer of “wannabe” Tregs (CD4⁺CD25⁺ or CD4⁺CD25⁺FoxP3⁺) from DEREG × scurfy mice into Rag1^−/− mice also induced infarctions of regular size on day 1 after 60 minutes of tMCAO, indicating that the immunologic function of Tregs is dispensable for stroke development. (D) CD4⁺CD25⁺ Tregs (750 000) were collected from Il-17^−/− mice, Ifnγ^−/− mice, and Ccr6^−/− mice and transferred into Rag1^−/− mice 24 hours before 60 minutes of tMCAO. Infarct volumes were determined on day 1. The detrimental effects of Tregs in ischemic stroke cannot be ascribed to one specific cytokine because infarct volumes after adoptive transfer were similar to those observed in Rag1^+/+ mice. *P < .05 and ***P < .0001 between the indicated groups; ns indicates not significant.