Regulation of Ctla4^−/− T cells does not absolutely require signaling through the IL-10 receptor. Rag1^−/− mice received a 1:1 mix of 4 × 10⁶ BM cells from WT and either Ctla4^−/− or Il10ra^−/−Ctla4^−/− mice. Mice were killed at 12 wk after reconstitution, and CD4⁺FoxP3⁻ (A) or CD8⁺ (B) splenic T cells were analyzed for the activation markers CD44 and CD62L in WT and KO T cell populations. FoxP3⁺ frequency was also assessed in the CD4⁺ T cell subset (A, bottom). Data shown are representative flow cytometric results from the spleen of reconstituted mice (three mice per group) in two independent experiments.