sIL-2Rα facilitates the inhibition to CD8⁺ T cells mediated by IL-2–induced T_reg cells. (A) Representative histograms (n = 6) showing the proliferation of CFSE-labeled CD8⁺ T cells cocultured with CD4⁺ T cells pretreated with either IL-2 or sIL-2Rα alone or in combination. The proliferation of CD8⁺ T cells was measured based on CFSE^dim cells. (B) Representative dot plots (n = 5) showing the expression of perforin and granzyme B by CD8⁺ T cells measured by flow cytometry. The cells were treated and cocultured in the same way as above and then subjected to intracellular staining for perforin and granzyme B. The numbers of perforin- and granzyme B–expressing CD8⁺ T cells were calculated based on isotype control staining. (C) A graph showing induction of Stat5 phosphorylation in T cells treated with or without IL-2 in the presence of Stat5 inhibitor 573108. (D) Representative dot plots (n = 3) showing Foxp3 expression in CD4⁺ T cells treated with or without Stat5 inhibitor 573108. (E) Representative plots (n = 5) showing proliferation measured by CFSE staining of CD8⁺ T cells cocultured with IL-2/sIL-2Rα pretreated CD4⁺ T cells in the presence or absence of Stat5 inhibitor 573108. The graph on the right showing percentages of CD8⁺CFSE^dim (proliferated) T cells from 5 samples cocultured with IL-2/sIL-2Rα pretreated CD4⁺ T cells in the presence or absence of 573108.