Similarly, a mouse immune-compromised model RAG2−/− (mice deficient in the recombination-activating gene (RAG)) colonized with Helicobacter hepaticus developed chronic colitis that resembled the inflammation features of human IBD [189], while colitis did not occur in the corresponding RAG immune-competent mice infected with Helicobacter hepaticus, implying that the host’s adaptive immunity actively controls the overgrowth of H. hepaticus, which is a cause of colitis [190]. Here, RAG2 is linked to colitis.