In this model, Rag1−/− mice transferred with naive CD4+CD25−CD45RBhi T cells develop wasting disease and colitis (Powrie et al., 1994) with splenomegaly, mesenteric lymph node (MLN) enlargement, and severe leukocytic infiltration of the colon (Figure 1A). Here, RAG1 is linked to Splenomegaly.