CD4⁺FoxP3⁺ regulatory T cells are selectively expanded in HIS-SGM3 mice. To determine the proportion of T_reg cells within the CD3⁺CD4⁺ T-cell population, human leukocytes from 6 HIS and 6 HIS-SGM3 mice were analyzed for expression of transcription factor FoxP3 by flow cytometry. Frequencies of human CD4⁺FoxP3⁺ T cells in blood, spleen, liver, and bone marrow (BM) of HIS and HIS-SGM3 mice are shown in (A), with representative fluorescence-activated cell sorter plots from blood, spleen, and liver shown in (B). To determine the frequency of T-helper subsets Th1, Th2, and Th17 within the CD4⁺ T-cell population, cells were stimulated ex vivo with phorbol-12-myristate-13-acetate/ionomycin for 5 hours at 37°C and subsequently stained for intracellular IFN-γ (Th1), IL-4 (Th2), and IL-17 (Th17). (C) Group data of a total of 6 HIS and 6 HIS-SGM3 mice. Unpaired Student t test: *P ≤ .05; **P ≤ .005; ***P ≤ .0001. Error bars indicate SEM.