When Foxp3-deficient CD45.2+ naive T cells and Foxp3-wild-type CD45.1+ naive T cells were isolated and transferred into immunodeficient recipients, Foxp3-deficient cells were able to induce severe colitis in Il23a−/−Rag1−/− recipients (Figure 5A), whereas Foxp3-sufficient cells only induced colitis in IL-23-sufficient Rag1−/−, but not Il23a−/−Rag1−/−, mice. Here, RAG1 is linked to colitis.