iTregs display a high activity of the p38 MAPK and MAPKAP-K2/3. Teffs (E) and iTregs (R) were induced and restimulated at day 5 as described in Figure 1. Immunoprecipitation of p38 and MAPKAP-K2/3 was performed with lysates prepared 0, 15, 60, and 240 minutes after restimulation. ATF-2 and HSP 25 served as specific substrates for p38 (panel A; top) and MAPKAP-K2/3 (panel B; top) in in vitro kinase assays. As a control, equivalent levels of the MAPK p38 and MAPKAP-K2/3 were measured in both iTregs and Teffs by Western blot (panels A and B; bottom). Similar results were obtained in 4 independent experiments.