CD4 and colitis: To further investigate the contribution of lymphoid cells to the exacerbated colitis phenotype seen in Rasal3−/− and Arhgef2−/− mice, we tested the ability of B6, Rasal3−/− and Arhgef2−/− naïve CD4+ CD25−CD45RBHi T cells to induce colitis upon adaptive transfer into lymphopenic Rag1−/− mice.