MAPK p38 induces G₁ cell-cycle arrest via high expression of the cdk inhibitor p27^Kip1. iTregs (R) and Teffs (E) CD4⁺ T cells were generated by coculture of IL-10DCs or mature DCs with CD4⁺ T cells. The p38-specific inhibitor SB203580 was added during priming of the T-cell population as indicated. Distribution of DNA content was measured 24 hours after restimulation in iTregs and Teffs. The percentage of T cells in G₀/G₁, S, and G₂ phases is indicated (A). Results represent 2 independent experiments. After restimulation (24 and 48 hours), lysates of T-cell populations were prepared and proteins were separated on SDS-PAGE, blotted, and probed for the cdk inhibitor p27^Kip1 (B). The blot was stripped and reprobed for actin as a control for equal loading. Similar results were obtained in 4 independent experiments.