Lastly, administration of 5% DSS in the drinking water resulted in accelerated weight loss at day 2 and 3 and increased colon mass in Rag2−/−x Ctla4−/− mice in comparison with Rag2−/− mice, consistent with more severe colitis in the absence of CTLA-4, but there was no change in spleen mass or colon length (Supplementary Figs. 15a–d). The gene discussed is CTLA4; the disease is colitis.