CD4 and colitis: 12 and Figs. 1–3). However, the reason for this remained unclear, especially as we found that Foxp3+ Tregs isolated from IL-10cKO mice exhibit impaired suppressive function ex vivo (Fig. 4). In this study, we characterized the CD4+Foxp3+ and CD4+Foxp3− compartments in IL-10cKO mice to better understand how IL-10cKO mice avoid severe colitis, and we identified a critical compensatory mechanism used by intestinal Tr1 cells to confer protection in the absence of Foxp3-specific IL-10.